The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG)
Small Metallic ParticlesProduced by
Evaporation in lnert Gas at Low Pressure
Size distributions, crystal morphologyand crystal structures
KazuoKimoto physiosLaboratory, Department of General Educatien, Nago)ra University
Various experimental results ef the studies on fine 1. Introduction particles produced by evaperation and subsequent
conden$ation in inert gas at low pressure are reviewed. Small particles of metals and semi-metals can A brief historical survey is given and experimental be produced by evaporation and subsequent arrangements for the production of the particles are condensation in the free space of an inert gas at described. The structure of the stnoke, the qualitative low pressure, a very simple technique, recently particle size clistributions, small particle statistios and "gas often referred to as evaporation technique"i) the crystallographic aspccts ofthe particles are consid-
ered in some detail. Emphasis is laid on the crystal (GET). When the pressure of an inert is in the inorphology and the related crystal structures ef the gas range from about one to several tens of Torr, the particles efsome 24 elements. size of the particles produced by GET is in thc
range from several to several thousand nm, de-
pending on the materials evaporated, the naturc
of the inert gas and various other evaporation
conditions. One of the most characteristic fea-
tures of the particles thus produced is that the
particles have, generally speaking, very well-
defined crystal habits when the particle size is in
the range from about ten to several hundred nm.
The crystal morphology and the relevant crystal
structures of these particles greatly interested
sDme invcstigators in Japan, 4nd encouraged
them to study these propenies by means of elec-
tron microscopy and electron difliraction.
Apart from the crystallographic interest, there
has recently been a considerable number of
studies ofsmall metal particles, from the point ef
view of solid state physios, many of which may be
traced back to the work of Kubo. In 1962 Kubo
published a paper2) on thc electronic properties Physics Laboratory, Department ef General Education, of small mctallic His approach to the Nagoya Univcrsity particles. Fure-cho, Chilcusaku, Nagoya 464, Japan problem was quite diflbrent from the classical 88 (122> Hlgkeftdift7kts
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to several Torr was a traditional one where the smal1 particles were at low pressures of a tenth
usually regarded as a system having larger sur- very good absorber of infrared radiation.
"black" face-to-volume ratio compared with the bulk Pfund5-'} first applied bismuth evapo-
materials. His theory is based on the simple fact rated from a hot tungsten spiral in covering the
that the numbers of free electrons in a metal delicate receiving area of his bolometer for use
in a bell at a particle becomc fewer when the particle size in infrared spectroscopy placed jar O.25Torr air. Gradually becomes srnaller. Kubo pointed out clearly for pressure of about
relatcd to infrared spectros- the first time that many physical properties of studies, not always
the ef these metal blacks small metal particles at helium temperature copy, on properties investigators. difler radically from those of the bulk matcrials (or smokes) were begun by various
SiegelB) studied smoke when the diameter of the particlc is less than Harris,JeflViesand gold rang- about 10 nm where the numbers of atoms con- deposits prepared in nitrogen at a pressure
ing from O.3 to 3 Torr by electron microscopy stituting a particle are of the order of 104. found that the mean size of the individual Metal particles produced by GET have been and
extensively used as materials suitable for testing colloidal geld particles increascd with the in-
crease of the of nitrogen. The increase the predictions by Kubo and for other purposes pressure
also had the same of solid state physics and, recently, evcn for of the rate of evaporation
size distributions. industrial purposesS'4). Unfbrtunately, howcver, eflbct resulting in the broader They also confirmed that the smoke deposits thc particles produced by GET have a greater gold showed no evidenee of orientation and that they range of size distributions than those of islands in spacing of bulk Uyeda the discontinuous films produced by means of gave only the lattice gold.
zinc black evaporated in vacuum deposition. Although this does not and Kimoto9) studied
air at 1 rv 80 Torr by electron neccssarily imply that the particles by GET are pressuresbetween and found that the zinc black cen- inferior to those made by vacuum deposition, it diffVaction
not only metallic zinc and zinc oxide ZnO is important to know the accurate size distribu- tained
tungsten trioxide WO, due to the tung- tions and the expcrimenta1 conditions which but also filament used for the evaporation source. govern the distributions in order to obtain a stcn replaced air by nitrogen and confirmed correct understanding of the experimental re- Kimoto*
that the zinc black in nitrogen sults on the propcrties of small particles prepared prepared gave electron Debye rings consistent with by GET. diffiraction
zinc and that the size of the zinc The particle size distributions and the crystal pure grain decreased with the decrease of the morphology and the relevant crystal structures black pressure the nitrogen. The diameter of the ef these particles (mainly metals) will be the of particles was less than 10nm when the of thc main subjects of this review paper. However, pressure was about 1 Torr; howevcr thesc results before considering the individual items a very nitrogen not been MamiyaiO) also brief historical survey will be given. have published. pre- pared metal blacks of nickel, zinc, silver, lead, 2. BriefHistoricalSurvey tin and bismuth in air at reduced pressures and
that their lattice were censis- It was already known in the early 1930's that found pararneters
"metal of the corresponding bulk metals the soot-like substance called black" or tent with those
"metal accuracy of O.5% by smoke" produced by evaporating metals within the er[perimental
- -- .- * such as bismuth, zmc etc. in air or in nitrogcn K. Kimoto: unpublished data. 89 VoL 6 No. 3&4 (J23)
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means of X-ray Debye rings. Fritsche, Wolf A conical basket or a boat made of tungsten and Schaberii} first demonstrated the fact, by (or molybdenum) wire or foil is generally used
means of Tyndall scattering, that thc particles as an evaporation source into which scveral to are formed in the free space of an ambient gas sevcral tens of mg of the evaporant is placed. before they deposit en the wall of the evaporation For the purpose of obtaining a Iarge amount of chambcr. Based upon their own experiments on particles, of the order of grams, oven made of bismuth particles and on the results of other incrt refractory material (sintered aluminai`})
investigators so far obtained, thcy made clear is used at a controlled temperature. Wadai5} the relations between the particle size and thc dcveloped the method by means of a plasma jet pressure of the gas and the evaporation tempera- flame in helium containing hydrogen and this
ture. They also made clear the influenoeon the method has been used for industrial purposes of the distance between particle the evaporation to obtain a large number of particles having high source and the places where the particles were melting temperature. Laser light is also used to
caught. Although their results were of a rather cvaporate particular substances such as silicatei6) nature, it is qualitative seen that they have ar- for geophysical study or olivine* for cosmogonic
rived at a correct understanding, in outline, of study. To collect the particles, for elcctron mi-
the important of phenomenon particlegrowth in eroscopic studies, grid meshes covered with a
GET. In l963 Kimoto et al.i2) published results suitable substrate arc placed anywhere in the
on finc of some fifteen metals particles produced evaporation chamber; when a Iarge number is
by GET in argon. In this study they first paid needed the particles are often deposited on a
attention te the shapes, crystal i.e.the morphol- largc metal block, the inside of which is cooled
ogy, of the small thus particles produced by by running water or liquid nitrogen, which is taking fu11advantage ef the modern techniques placed around or above the evaporation sourcei4).
of electron microscopy. Fig. 1 shows, for example, the evaporation Before closing this brief historical survey, the units which are being used by the prcscnt author. author would like to cite the review papers by They consist of three main parts: an ultrahigh Comsa and Henseli3), by Granqvist and vacuum evaporation chamber with oil-free
Buhrmani4) and by UyedaBi). The former two pumping systerns, high purity inert gas reservoir deal with the results on the small metallic par- and a quadrupole mass anal)rzer. The mass ana- ticles produced by GET which appeared up to lyzer is provided with a small, interchangeable l975 and the last one deals with the crystal orifice and is installed vertically at the top ofthe
morpho]ogical aspects of the particles. evaporation chamber. It is used for the examina-
tion of residual gas or for the detection of very 3. Production ofParticles small clusters. The experimental procedures arc 3.1 Experimentalarrangement as follows : after carefu1 outgassing ofthc evapora-
The techniques and the equipment necessary tion source and then the evaporant by melting,
for producing the particles by GET have been the evaporation chamber is further evacuated
simple since the time of Pfund5-') when he first to a pressure of 10'9'Torr. Immediately after evaporated bismuth in air at reducod pressure the ion pump is switched ofl; the inert gas is
in a an glassbellljar.When inertgas is used a introduced into the evaporation chamber through
gas inlet system becomes necessary besides the * B. K, Kothari and J. R. Stcphens: Presented at the vacuum evaporation units and the manometer. 39th Annual Meeting ofthe Mcteoritical Society, 1976.
90 (]24) HJzlCre&dift\kes
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tic sketch ofthe experimental arrangements.
E: Evaporation source. I: Ion pump. G: Glass rcservoir ofinert gas, L: Ultrahigh vacuum-tight leak valve. O: OrMce of QMA. P: Vacuum gauge. Q: Quadrupolc rnass analyser. R: Rotary pump. S: Sorption pump. T: Turbo-molecular pump, g :r U: Ultrahigh vacuum evaporation chamber, fib."lt X-Y: Recorder (er oscMoscope).
Fig. 2
Schematic diagram illustrating the structurc of a typical smoke (lcft). (Fig. 21 in re £ 18) l
the leak valve and the evaporation is carried out. video tape recerder. Fig. 2 represents their sche-
The time needed for the entire process from the matic sketch of the srnokeiS}. Accordmg to their
instant of switching off the ion pump to the nomenclature, the part of the figure termed
"inner completion of the evaporation is about one mi- front"is seen as smoke*; the inner zone by nutes in most cases. The total partial pressure which appears dark is the space surrounded
of thc of residual gases at the timc Df evaporation is the wall of the srnoke and the outer space
estimated to be of the order of 10'"A. 10-S Torr. smoke is called th ¢ outer zone.
at difl The pressure of the inert gas is usually estirnated They examined the particles collected
approximately from the whole volume of the ferent parts of the smoke and found the gcneral interme evaporation unit and the fact that the inert gas trcnd that the particles collccted in the
at a pressure of one atmosphcre is contained in diate zone were 1arge and had a greater range
were small and a glass flask of ve1ume 1 litre. When a more of size distributions,while they
accurate value of the pressure is required, it uniform in size in the imer and outer zoneiS). can be measured by Pirani gauge connected to Thev `the also found that there were cases in which
were accord- the evaporation chamber. shapes of the particles diflerent ing to the places where they were collectediD). "smoke" 3.2 Structure ofthe metal and its 4. ParticleSize relation to particle size and shape
As soon as the evaporation begins the sudden 4.1 Particlesizeclistributions appearance of the smoke around the evaporation Although very qualitative in nature, it has
source and the subsoquent ascent of the smoke becn known empirically that there is a general
can be observed, provided that the evaporation tendency for the size of the particles produced rate is suMcient and the pressure of the inert gas by GET to bccome more unifbrm when the mean
exceeds a certain value, for example, about 1 size becomes smaller, say, less than about 10 nm.
Terr in the case of argon. Wadai7) first paid In general, however, there is a considerable
attention to this smoke and Uyeda and his * This part of the smoke is now referred to as the inter- studied the dynamical behaviour "intermediate groupiS-2i) mediate zone (ref; 19). The terminolog)r and the structure of the smoke in detail with a zone" will be used throughout this paper.
Vol. 6 No.3&4 (l25) 91
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kT}ige:,g,･.･asl'/tt'l"11"1'i/tL/','l'////･il/liew,xttecl,,;,/fiilil/11,/ililllllill/:,,/2i//11ee,-ii
Fig.3 Feparticlesproduce d at S different pressures ofargon. (a) O.8 Torr. (b) 6 Torr. (c) 30 Torr. Mg.d ' Aluminum smokes formed (a) m 200 Torr He, (b) 10 Torr Ar and (c) 1 Torr Xe. (Fig. 2 in ref 20)
scatter of the particle size among the particles
produced by a single cvaporation. He:2001brr Ar:10 Xe:1 It ha$ long been known also that the pressure
of the inert gas has a predominant eflect on the argon and 1 Torr xenon (see Fig. 4). particle size. Fig. 3 shows typical micrographs As was stated in Section 3.2, Uyoda and his
of iron particles produced at three different group found the general correlation between
pressures of argon. The particles were prepared the mean particle sizc and the zones of the smoke ' by evaporation ata temperature Just above the in which the particles had grown. They (Yatsuya
melting point of iron and were collected 10 cm et aLi8) further carried out systematic measure-
above the evaporation source. The eflect of the ments of the size distributions of the aluminium ' pressure of argon on the particle size is evident; particles grown in helium under various condi- the higher the pressure of the gas, the larger the tions, i.e. the pressure ofhclium (P), the evapora- particle size. However, the eflbct ef pressure on tion temperature (T) and the distance (D)
the size reaches a Iimit at particle , approximately between the collecting Ievel of the particles and Torr in the 30 case of argon. the evaporation source. The particles were de-
Wadai7,22) influence studied the of the nature posited on some fifty EM-grids juxstaposed on the inert of gas on the mean particle sizc of a straight line at a given distance from the level
various metals and found that in order to obtain of the evaporation source so that the relative
the same mean size th e particle pressure ofhelium pesition of each grid to each zone of the smoke
had to be about 1O timos as high as that of argon could be known; a specially designed shutter
and that in the case of xenon the mean particle was used to collect only the particles which were
size was about three or four times larger than evaperated at a constant temperature Z Table
that for those prepared in argon at the same 1 shows the data from their experiments at a
pressure. Ohno et al.2e) also observed the effbct of constant D in the inner zone.
"mean the nature of thc inert gas on the shape of the Here the word diarneter" was conven-
aluminium smoke; its visible appearance was tionally used for the most frequently occurring
roughly the same at 2oo Torr helium, IOTorr diameter. In general, the mean diameter becomes
92 (I26) HJ4screfiJiSeft\kts
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Table 1 Pressure Torr When the evaporatien tempcrature is fixed, T(OC) 10 50 230 Mean diameter (nm) of Al the rnean particle size increases as the pressure in He at a 1500130011OO45 65 230 particlesproduoed P and/or the distance D increases. Figs. 7 and 8 collecting in given position 25 45 90 show the size of the the inner zone: D =8 cm. distributions panicles pro- 10 25 45 18) (refi duced at P=IOTorr and 50Torr respectively,
collected at various distances in the inner zone,
larger as T increases at a constant P and also as the evaporation temperature being fixed at
P increases at a censtant TL Fig. 5 shows the 13ooOc.
size distributions of the particles from the same In Fig. 9 the mean diameters are plotted
data used for Table 1. It is worth noting that against D for P== 10, 50 and 250 Torr; in Fig.
the distributions are nearly Gaussian at a first !O they are plotted against D for T= 1 1oo, 1300
glance and that at higher evaporation tempera-
tures the distribution becomes broader. Fig. 6 Al-He T,=!3ooec He:lo fo.
shows the case where the size as a whole is particle loo oA-Oe Distonae:D {crn) the mean approximately small, i.e, diameter is o--2
8nm. The distribution is comparatively sharp A-.4
1--･..6 despite the fact that the particles were collected gttease e---8 without the use of the shutter and a very has Am -e . ---.-16 slight inclination towards thc smaller particle . size. . I - × . D He-5crTbrr / i o twoX' 100 Oe100/ 2eo 3eo 4oe Dlameler (X} Fig. 7 s7ytgts Size clistributions of Al particles produced in Hc and collected at various clistances D's. P== 10 Torr, T=1300eC. Peak values normalized to 1oo (Fig. 50tsnE=z 15 in refl 18).
Al-He n=13ooec He:soforr
leo * D tcm) O soo loeo --e--.-4--- Diameter (A) Fig. 5Size
== clistributions ofAl particles produced in Hc at pres$ure P 50 -lEe 2---1 Torr arid evaporation temperatures T t= 1100, 1300 and 1500eC.
Peak values normalized to 100. 13 in ref, 18) so (Fig,
Al-He He-1.31brr s
Fig.6 sioO Sizedistribution ofN g o o PHaJt;:i;S..ef8d.".C.Od.:: O 1000 tsCse Dii:t:,.O (x) Fig. S 0C, { T= 1100 collected Size distributions of Al particles produced in He Z at D=8 cm. Peak value and collected at various distances D's. P==50 Torr,
normalized to lOO T..,13000C. Peak va!ues norrnalized to 100 o so ioo iso (Fig. (Fig. 16 in re £ !8). Diameter {X) 14 in refl 18)+
VoL6 No. S&4 (127) 93
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and 15000C. It can be seen that the mean di- looe ameter increases with increase of the distance
D and saturates at a value which is smaller e temperature. Eseo,pos Comsa and Henseli3) studied the influenee of asE the evaporation temperature (wattage supplied to the source), the pressure and the nature of the o O 4 8 16 inertgas, helium,argon and xenon, on the size Distente : D Ccm) Fig. 9 of the vanadium particles and found that the Mean diameters of Al particles produced in He trends were in accord general good with those plotted against distance D. T=1300"C and P=== 1O, 50 and 250 Torr 17 in refl 18). of previous workers. (Fig. The mean size and sizc distribution of the particles produced by GET depend upon the various conditions, including the preparation 1ooOAe nature and the amount of the evaporant material. However, the main factors which determine the ¢ size distribution of the particles are, for the given E.g sooos{ instrumental conditions, the pressure and nature of the inert gas, the evaporation temperature and the position, relative to the evaporation 4 8 16 source, where the particles are collected. The Distcr}ce : D(cm) Fig. 10 results are summarized as follows: i) the mean Mean diameters ofAl particles produced in He and collected at various distances D's. P=50 Torr and particle size becomes larger in the sequcnce T=1100, 1300 and 1500eC (Fig. 20 in refi 18). helium, argon and xenon provided that the other evaporation conditions are kept the same; ii) it becomes larger as the pressure andlor the evap- variate whose Iogarithm obcys the nermal law oration temperature increases; iii) it becomes ofprebability2S). larger as the distance of the collecting position Granqvist and Buhrmani4,24,25) preparcd a from the evaporation source increases, even large amount, of the order of 1 gram, of alumin- though the efllects of the conditions ii) and iii) ium and tin particles by efllision from a tempera- on the particle size become saturated at certain ture-controlled oven placed in argon at a pressure limits. of a few Torr and by subesquent deposition on to a large, water-cooled copper plate placed 4.2 Small-particle statistics, Lognormal above the oven. They measured the size of these distribution particles by random sampling method and con- It has been well that the established size dis- cluded that the ]ograithm of the particle vo]ume tributions of small particles occurring either in obeys a norrnal distribution. In the casc of nature or in industrial products tend to incline spherical particles a diameter of a particle, x, markedly towards larger particle sizes and the has also a lognormal distribution of which a statistics of these smal1 particles obeys the log- normalized distribution function, jL(x), can be normal distribution, i.e. the distribution of a expressed by sc (128) NJiPredintft#ftts NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) produced by GET ab always gives the value !L(X) == exp(-(ln2Xin2lna,jg)21 vlz lnlo, a,=1.48 ± O.12 (6) kind mean (1) irrespectiveef the of metals, particle size or the of evaporation conditions, where 6e is the geometric standard deviatien details defined as provided that the particle diameters werc below approximately 20 nm and were without noticca- ln ag = ni (ln xt-ln r,)2]ii2 (2) [Iie4 ble crystal habits. They cenclude that the of GET occurs and rg is the geornctric mean diameter defined as particle growth in the case pre- ... Xg =:= (Xlni'x2n,. x.ns)liN (3) dominantly by coalesccnce which results in the having a Here N is the total number of thc particles and lognormal distribution; i.e. the one ni denotes the number of particlcs in an interval tail towards larger particle size. out the ofsize histograrn centrcd around xi, On the otlier hand, Comsa2`)pointed -･i inadequacy of neglecting completely the effect N= ni+n2+ +n. (4) of by absorbing single atoms on By integrating eq. (1> with respect to ln x, one Partic]egrowth obtains the cumttlative form of.fL(x) in terms of the particle size distributions in Granqvist and an error function, Buhrman's treatment where the growth due to is to be the only X.fl(x') coalescence of particles assumed i.e K(x) = d (In x') inevitably li" mechanism ef particle growth which results in lognormal distributions. Comsa et al.27} =--IY+-;-erf[V'6X,ki"2,] (s) produced vanadium particles in helium at a reduced and deposited thern onto a where IJL(x) is the fraction of the total number pressurc cooled collector surfacc. Fig. 13(a) 1 in refi of thc particles that have diameters smaller than (Fig. 26 and 27) shows their size distribution in a a given value x. The function FL(x) yields a histogram; Fig. 13(b) shows the same distribu- straight 1ine vs. x when plotted on logarithmic tion plotted in the cumulative marmer on linear prebability paper. Fig. 11 (Fig. 1 in refl 14 and and in Fig. 13(c) it is 24) shows the result of mcasurements by probabilitypaper plotted in the same way on log-probability If Granqvist and Buhrman, a size histogram for paper. the original distribution is normal, such cumula- oxide-coated aluminium particles produced by tive should form a straight line in Fig. 13 evaporation from the oven at a pressure of 3.5 p]ots Torr argon containing a small amount of air. The inclination of the distribution towards en ]arger size is conspicuous. Fig. 12 also : particle Ytoo shows their results for various metals depicted t E in cumulative form on log-probability paper. 6 ec From the log-probability plots the two con- : 50 s z stants x and a, which characterize the distribu- tion may be determined; j is found at FL(x)= o O S tO dS 50% mark by its dcfinition and o. is equal to PARTeCLE DtAMETER nm the size corresponding te FL=84.13% divided Hg. 11 Size histogram of oxide-coated N par- tiales by oven evaporation at that from pr(KIllced by S. Granqvist and Buhrman claim ' P (argon)=3.5Torr with deliberate the slopcs of the straight lines obtalped by exten- additien of a small amount of air (Fig. 1 sive investgations on the small metallic particles in refs. 14 and 24). VoL 6 No. 3&4 (1pa) 95 NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth{JACG)Growth (JACG) 2e Fig. 12Log-probability toEEsxeV plots for various ultrafine metal particles. Ordinates indicate the particle diameters in nm; the abscissae the fraction ofthe total number of particles that have diameters smaller than those cor- to 2gSle:!Er(-i responding the ordinates. (a) Oxideooated Al particles prepared by filament evaperation at P (Ar) = 15 Torr together with some O,, (b) Al particles as described in Fig. 11. (c) Sn particles by oven evaporation at P (Ar) =O.5 Torr, (d) =4 and (e) are Fe and Co particles by filament evaporation at P (He) Torr. The shaded area indicates an excess amount of small particles (Fig. 2 in ref, 24). i[i 1 that, neglecting thc eflbct of the substrate, the particle size distributions of the intermediate d e ""sfe type, which, she considers, are often encountered by GET, are the i[to a among the particles produced result of the superposition ef the size distributions due to the absorption growth and to the coa- lescence growth. The conditions which favour the coalescence growth are the higher pressure of the inert gas, PERCENTAGE between the evaporatiori source and the collect- (b); if it is lognormal, they should forrn a ing posltions, and collection of large ameunt of linein Fig. 13(c). in straight As seen the figures, particles, especially on the non-coeled collector hewever, both plots deviate from the straight surface. The epposites of the above statements 1ines; in Fig. 13(b) (normal distribution) the are the conditions unfavourable for the coales- deviations occur at larger diameters, while in cence growth, even though the cealescence can Fig. 13(c) (lognormal distribution) the deviations never be ru]ed out. Comsa26) considers that the are on the smaller diameter side. size distributions depicted in Figs. 6 and 7 may This means that the size distribution in Fig. 13 servc as good examples of the distributions is in-between the normal and the lognormal brought about by the superposition of two kinds "intermediate" distributions, i.e. of the type. of distributions where the role of the absorption Comsa cencluded that, from the analysis ofa large grQwth is clealy recognized. In these special cases number of measurements of experimental size the histograms give normal-like appearances or distributions, the distribution of the intermediate even the very faint inclination towards smaller in Fig. the ex- type is the typical size distribution for the par- particle size as seen 6. In usual ticles produced by GET. Chakraverty2B･29) has perimental conditions, where coalescence growth shown that in the case of the particle growth on is more important, the superposition may result a substrate by interface reaction controlled atom in either an intermediate or a lognorrnal distri- transport, which belongs to the category of bution. A typical example of the lattcr case is growth by absorption of single atoms, thc size Fig. 1 1 having a very distinct inclination towards distribution is a skew bell type having a tail larger particle size. Comsa recommends to use a "modified" towards smaller diameters. Comsa comsiders lognormal distribution function 96 (l30) H zFkeftrkft\ftts NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) g.gs% 99 95 eo so so 40 l 20 te o.ta02 Fig. 13 (a) Size distribution histogram of the vanadium particles prodaced in He at a reduced pressure. Full line: experimental size distribution. Dashcd which ranges a xmid, from minimum diameter, line: calculated number dcnsities ofthe normal size to a maximum diameter, x..., instead of using distribution having the same arithnetic mean diameter, d., and standard doviation, a., as the the true lognormal distribution function, Eq. experimental distribution. Dash-dotted line: cal- in which x ranges frem x==O to x=oo. (]), culated number densities of the lognormal size the same According to Iranisp.Bi), the modified lognormal clistribution having geometricdiameter, 4, and standard dedation, ag, as the expcrimental distribution functionf(x) is given by the fol- distribution. N: total number of the counted par- lowing expression, ticles. (Fig. 1 in reL 26). Linear ofthe size distribution 1 (b) probability plot f(x) - shown by the fUll line in Fig. 13 (a). The ordinate VTn ln o, indicate$ the percentage of the particles with dia- (X-X.'M.ti.).(.X.Mt!-.r)XMi")12 meters smaller than d. (Fig. 2 in refl 26) Iln Logarithmic plet of the size dis- ..p[ (7) (c) probability ln2 av 2 1 tribution shown by the fu11 line in Fig. 13 The L 1 (a). ordinate indicates thc percentage of the particles where rg and ag are the geometric mean dia- with diamcters smaller than d. (Fig. 3 in re £ 26) meter the deviation and geometric standard , respectively. meters were in the rangc from 10nm to 1 ptm approximately, very small and very large par- 5. Characterization of Small Particles 'the ticles bcing excluded. In fo11owing brief Produced by GET; Their Colours, comments on Table 2 will be given. External Shapes, Crystal Structures and Oxide Films Coating Them 5.1 Colours WilkinsonS2) reported that the gold srnokes flowing Up to the present time the small particles of prepared at a pressure of 1 Torr of m- some twenty-four elements produced in inert trogen, with great care being taken to insure the gas by GET have been studied by electron mi- purity of gas and gold, were not black but pos- croscopy and electron diffraction. Colours, sessed high reflectivity of yellowish colour. On shapes and the corresponding crystal structures the contrary, the gold particles prepared using a of these particles and the relevant references are tungsten fiIament in the presence of more than summarized in Table 2. It was based upon the about O.1 Torr of o)rygen were black in visual to observations on the particles whose lincar dia- appearance because of contamination due VoL 6 No. 3&4 (l31) 97 NII-Electronic Library Service The JapaneseAssociationJapanese Association forforCrystalGrowth Crystal Growth (JACG){JACG) tungsten oxides. No other systematic observa- triangular plate and the ftc.c. (7-Fe), etc. The tions are known conccrning the colours of the exact shapes of the particles whose shapes are "cemplex "long particles in connection with thc impurities pre- designated as polyhedron" or sent in the inert gas prepared by GET. Most of rod" etc. are not yet elucidated or they do not the colours 1isted in Table 2 are based upon the show regular polyhedral shapes. A]though the ebservations by Kimoto and Nishida of the crystal structures are simply designated likc particles and the smokes produced in argon at h.c.p. er £ c.c., it has becn confirmed by electron a pressure of about 10 Torr in an ordinary diffraction that the lattice parameters are iden- vacuum chamber in which a vacuum of about tical with thosc of the bulk within the experi- 1 × IO-6 Torr was attainable. The colour of the mental accuracy of 1%. More accurate, reliable 'smoke was the same as that of the particles de- measurements of the lattice parameters of small posited on the EM-grids. The names of the metal particles have not yet been reported. colours were referred to refi 33. Many high temperature phases known in the bulk states are found at room temperature in the 5.2 External shapes and crysta1 structures particles produced by GET; they are considercd Particles having crystalline structure show a to be due to the rapid quenching by the ambient morc or 1ess polyhedral character; the names of gas because their size is small. The only crystal the polyhedra and the corresponding crystal structure so far known whSch had not been re- structures are listed in the 3rd and the 4th col- ported in the literature and has been found umns of Table 2 ; for example, in the case ofiron, recently in the particles produced by GET is rhombic dodecahedron and the b.c.c. Table 2 ElementsCelours Shapes LatticesOxidesReferences Be dark greyThin hexagonal plate (hexagonal bi- h.c.p･ BeO 19, 42 pyramid of lst order truncatcd parallcl to the c-plane) tt-t-tt----+-t-r------L-erH------reTT-+------r------tTrr-rr------r-rr--L----++L------F""'i"ljl"h'h'"H""'-'""""' Rhombic dodecahedron b.c.c. h.c.p. Mggreyishwhite Thin hexagonal plate (hexagonal prism ef h.c.p. MgO 12, 19, 42 lst order, thin in the ""'i'ill"h".'l'll'"g'6'};2i'i'"b'il･k'lll'`."ii'gl`'6'iak'l'1}-.']ll:"""'directionofc-axis) 19, 42 cated by 6 {IO.1} planes, and other complcx polyhedra Alblack Cubo-octahedron fic.c･ 12, 21, 41, 42 si yellow Combination of trisoctahedron and octa- diamond 68, 69 hedron bounded' by 24 {31l}planes and 8 {111} planes, respectively V Truncated rhombicdodecahedron b.c.c. V!03 13, see foot- note" of p. 113 Crblack Rectangular or cube b.c.c. 12, 42, 46, 49 --"------H-]-----]--+L------L--"rF------r-----T------t----parallelepiped -":,'i';'4i]'"4'6"""-'`"' Icositctrahedron bounded by 24 {211} A-l5 type planes (i-Cr) 47, 49, 53 Rhombic dodecahedron Mnblack Tristetrahedron T-tt-ttT----T------r------T----t61oc-Mn Rhombic doclecahedron ''"-l'ot'fig"'-l"o-d'"-""'`-"H"'`"""'"'-"'"'""'"'-"'-"'""'""'""Hn'E;;i"i5-h"5k'U"""""""-""""'"'-fi-Mn . (structure unknown) 98 (132) H Jzis re&liseft\ftts NII-Electronic Library Service The JapaneseAssociationJapanese Association forforCrystal Crystal Growth (JACG){JACG) ElementsColours Shapes LatticesOxidesRefbrences Fe black Rhombic dodecahedron b.c.c.(a-Fe) Fe304 12, 21, 42 Multiply-twinned particle (pentagonal £ c.c.(7-Fc) 65, 66 decahedron>, triangular plate Coblack Multiply-twinned particle (pentagonal f:c.c. 12, 21, 42 decahedron, icosahedron) Hexagonal and triangular plate Polyhedron with hexagonal profiIe Niblack Multiply-twinned particle (pentagonal f:c.c. NiO 12, 21, 42 decahedron, icosahedron) Hexagonal and triangular plate Polyhedron with hexagonal profile CuPale redMultiply-twinned particle (mainly pen- fic.c. cuto 12, 21, 42 tagonal clecahedron) Hexagonal and triangular platc Octahedron Zngrcyishwhite Polyhedron with hexagonal profile h.c.p. zno 12, 42 Hexagonal and triangular plate * Plate with two-fold symmetry; others Gagreyishwhite Sphere arnorphous 42 Gebrown Trapezohedron boundcd by 24 {311} planesdiamDnd 68, 69 new modi- 'H'Mriil]t'fp1'Y':l'v'v'i'n"i'e"d'HP'a""Vic'l'E"(P'e'H{a'"g'6'h'"a'i-`'-'"""'Hfa"'th'o-n"d'""-fioation 70 decahedron) Se deepcarmlne Sphere amorphous 42 Aglight greyMultiply-twinned particle (peritagonal flc,c. 12, 21, 41 decahedron and icosahedron) 42, 78, 79 Hexagonal and triangular plate see fbotnotes Octahedron, cubo-octaheciron ofp. 124 Truncated triangular bipyramid Mo Rhombic dodecahedrom b.c.c. see fbotnotes Cube A-15 type ofp. 113 Icosi tetrahedron bounded by 24 {2 l 1 } planes Cdlight greyPolyhedron with hexagonal profile h.c-P- CdO 12, 42 In black Polyhedron fic.c. 42 Sn grey Rectangular parallelepiped with reunded tetragonal 42 edges and corners Teblack Rod-like hexagonal prism of lst order hexagonal 19, 42, 80 (often with 3 prongs along the c-axix in trigonal symmetry) Egg-shape Aumaroon Multiply-twinned particle (pentagonal flc,c. 12, 21, 42 decahedron and icosahedron) 7S ,-...H..g.T.e.g..o.-n..4-L?p.rl..t!l-.a..n..g..u.l.ar...Et!ntfi...... "...... -.." Cubo-octahedron, octahedron Pb black Polyhedron with hcxagonal profile £ c.c. PbO(massicot)12, 42 Bi black Polyhedron rhomb"hedral 42 * T. Okazaki, Y. Ando and R. Uyeda: Read at the autumn meeting of The Phys, Sec. ofJapan, Oct. 1976. Abstract II. p. 89. VoL6 No.3&4 (l33) 99 NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) among the particles of chromium and molyb- denum. Some of the rnanganese and germanium 6.1 Beryllium particles also show new crystal structures which, The particles of bery11ium are, in general, thin however, have not yet been analysed. flat hexagona1 plates. Fig. 14 gives a general view of the electron micrograph of beryllium 5.3 Oxides particles prepared in the ordinary vacuum evap- Usually the metal particles are oxidized by oration chamber containing argon at a pressure being exposed to air before examination in the of 8 Terr; all the particles are hexagonal plates, electron microscope. The oxidcs listed in the 5th the partiale having a rod-like appearancc is also column of Table 2 are those which have been a hexagonal plate standing parallel te the elec- identified by means of electron diffiraction. No tron beam. Fig. 15(a) is an example of a well- reilerence to the oxide in the column does not grown beryllium plate; thc striations are extinc- mean that the corresponding particles arc not tion contours. Fig. 15(b) is a selected area dif:- oxidized. The electron diffiraction Debye rings fraction pattern from a beryllium plate lying due to oxide, if any, are rather weak and diffuse parallel to the supperting base. These photo- whereas the rings due to metals are spotty. This graphs revealed that the beryllium particle is a implies that the oxide films coating the particles thin, flat hexagonal bipyramid of the lst order, are very thin. Kimoto et at.t2) estimated the oxide cut parallel to the (OO.1) plane. Fig. 15(c) shows layer of each particle to be thinner than about a clinographic projection of the beryllium 5 nm from the diffuseness of diffi;action rings. crystallite. When beryllium particles were pre- Granqvist and Buhrmani4) took electron pared in the ultrahigh vacuum evaporation micrographs of aluminium particles by bright chamber which had been evacuated to about field and dark field electron microscopy and 3 × 10-g Torr, the crystal growth of the particles compared the particlc size distributions obtained was enhanccd and the ratio of the thickness-to- by the two methods. The slopes of the straight width of the crystal plate was fbund to increase lines, plotted on a log-probability paper, repre- considerably. senting the relations between thc diameters of Beryllium particles were covercd, when the particles and the percentages of the numbers examined by the electron microscope, with the epitaxially thin exide layer, of the particles in cumulative form were smaller grown BeO. The in the bright field images than in the dark field orientations of the oxide on the c-plane relative images. By taking advantage of the fact that the to the base metal were amorphous oxide layers of aluminium particles (OO･1)Befl(oo･1)Beo, [10･O]Bell[10･O]Bce･ the do not contribute te the dark ficld images, they When inert gas was not pure, for example, concluded that the thickness of the amorphous O.OOI ewO.Ol Torr of air was added in argon at oxide layer was constant irrespective of the par- 6 Torr, the profiles of the particles became ir- ticle diameter and was about 1,O nm thick. regular and the surfaces were rough (Fig. 15 (d)), and the average size of the particles was 6. Results fbr Individual Elements much smaller than that of those prepared in pure In the following, brief characterization of the argon at the same pressure. particles from some of the elements will be given, The particles having the profile shown in the emphasis being laid on the crystal morphol- Fig, 15(e) were fbund in company with the plate- ogy of the particles. like particles, although the frequencies of occur- 100 (134) HptMabntft\ftes NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) rences were lowig,22)*. The parallel striations allotropic form of bery11ium which is reported to seen in the particles are equal thickness fringes. be stable from just below the melting point The shape in Fig. 15(e) was easily identified as (about 12900C) to about 12500Ca`-3`). Some of a rhombic dodecahedron (sec Fig. 50) ; however, the diffiraction patterns could not be indexed. the crystal structure of thc beryllium particles As wil1 be described Iater, the rhombic dodecahe- having this polyhedral shape was not uniquely clron is a Wulff polyhedron of a b.c.c. Iattice if determincd. The electron difliaction patterns only the first nearest neighbour interactions are frem some particles having this form were con- takcn into account in calculating the anisotropy sistent with ordinary hexagonal beryllium; and of surface encrgies of the crystalliteS7,62,63). some of them were consistent with the b.c.c. Therefore, it may be reasonablc to infer that the particles under discussion had been formed as *) K. Kimoto and I. Nishida: Read at the autunm meet- b.c,c. crystallites having rhombic dodecahedral ing ofThe Phys. Soc. ofJapan, Oct. 1968, Abstract V, p, 36. shape. Sorne ef the particles were quenched by mx waasee vaes whee x ･ ,, ew, .ew ee, lg.. ee,eeww Fig. 14 {c) eAN Be. view ofelectron micro- General /lt "Ntit "N graph. Thin, flat hexagonal platesl tll "N rod-1ike particle is also a hexagonal plate standing parallel to the inci- dent electron beam. Ar 8 Torr, ';t'zak, {e} Fig. 15{a) Be. Hexagona1 plate. Striations are extinction contours. Xe 20 Torr. (b) Be. Selected area difl?action pattern from a hexagonal plate. The incident beam is normal to the plate, The spots are due to Be metal and the aros, to BeO, (c) Clinographic prejection ofa Be crystallite. Hexagonal bipyramid of lst order, cut parallel to the (OO.1) plane. (d) Particlcs ofBe fbrmed in 6 Torr ofAr containing O.1 Torr ofair. . (e) Be particle ef rhombic dodecahedral shape. .lgll,iiz;.# . Ar 20 Terr. Parallel striations are equal thickness fringes. VoL6 No. 3&4 (J35) 101 NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) the ambient gas keeping their shape and crystal similar to those of beryllium in many aspects. structure; however, some particles had undergone The shape of magneslum particles, prepared in the allotropic transformation from the b.c.c. to argon at from a few to a few tcns of Torr in the the h.c.p. Iattice. The remaining unlndcxed difi pre-evacuated ordinary vacuum evaporation fraction patterns might represent the transitional chamber with evaporation temperature just stages from the b.c.c. to h.c.p. structure. The above the melting point of the metal, is a thin, exact conditions at which the rhombic dodeca- flat hexagonal plate. Fig. 17(a) is an electron hedral particles of bcryllium occur are not clear micrograph of a single magnesium particle seen but experience indicates that heavier inert gases from above the fiat plate and Fig. 17(b) is an and seem to the higher pressures favour occur- edge-view. Fig. 17(c) shows the selected area rence of the particles. We often use xenon at a difltaction pattern when the incident electron rv Torv fbr pressure 20 30 the purpese ofob'taining beam was normal to the plate. From these data the particles. it is concluded that the shapes of magnesium Sometimes beryllium plate-like crystals are so crystals such as shewn in Fig. I7 are thin hexa- thin that, together with their low atomic weight, gonal prisms of lst order, i.c. the crystals are they may be overlooked during observation of bounded by {OO.1} and {Ol.O} planes (Fig. 17 electron microscope imagcs on the fluorcscent (d)). screen. The structure of these beryllium single Magnesium crystallites, like beryllium, werc crystal flakes is very uniform and they do not observed to bc covered with an epitaxially grown show noticeable granular structures of the kind thin oxide layer, MgO, when exarnined by the associated with thin amorphous films used as electron microscope. The orientations of the supporting films on electron microscope grids. oxide on the c-plane relative to the base metal Carbon films or any other plastic films always were show granular structure when the magnification (oo･1)Msll(111)Mso, [10･O]Mg//[ITO]Mso- of the microscope excceds more than about The oxidation is considered to be due to the × 500,OOO. Fig. 16(a) shows a part of the peri- particles being taken out into the air. The influ- phery of a hole of the plastic film; Fig. 16(b) ence of oxygen included in the argon on the shows the periphery of a beryllium single crystal shapc, the size and the surface condition of the which is deposited, without background sup- magnesium particles (Fig. 17(e)) were exact]y port, on the peripheries of the holes of a perfo- the same as in the case of beryllium particles. In rated plastic film prepared by the technique the case of magnesium, howevcr, when the par- reported by Fukami and Adachi3S), Granular tial pressure ef air was O.1 Torr in argon at 6 structures are evident in Fig. 16(a), while in Torr, all the Debye rings were consistent with Fig. 16(b) they are far less evident. Figure 16(c) MgO. No other metals apart from magnesium shows evaporated gold particles en beryllium; were oxidized so perfectly in argon with O.I Torr the gold particles of approximately O.7 nm can of air. be observed clearlv i without the eflect of the Uyeda and his co-workersi9) carried out de- background structure3g). tailed investigations on the crystal habits of magnesium particles formed under various con- 6.2 Magnesium ditions in helium. Figs. 18 (a) and (b) show the Magnesium has the h.c.p. structure like projections of the shapes of their magnesium beryllium and the particles of magnesium are particles, collected at the inner and outer zones 102 (136) HA[reftrkft#kss NII-Electronic Library Service The JapaneseAssociationJapanese Association forforCrystal Crystal Growth (JACG){JACG) Fig. 16(a) Peripher)r ofa hole of a perforated plastic film.(b) Periphery of a Be single crystal flake. (c) Evaporated gold particles on Be single crystal. Fig. 17 (a) Mg. A thin, flat hexa- gonal plate. 6 Torr Ar. {b) Mg. An edge-view of a Mg crystallite such as that shown in (a). (c) Mg.Selectedarcadiffrac- tion from a Mg cry- pattern / /''v'. t tttt {b} tttt stallite. The incident beam is 'i/t ..I,sc/tt.ttt:"t normal to the plate. The slightly elongated spots are due to MgO. t/ t/tt't '1'' ex5･ tttt ttt# 't ':'tt,/ltt-l (d) Clinographic projection ge Mg crysta11ite. Thin hexa- ofa (d) c-axes,1 gonal prisin oflst order, (e) Particles ofMg formed at ,4 6Torr of Ar containing O.1 .L-.--- ''' s s- Torr of air. The particles are (10.0} actually MgO. structures of thc which respcctively, onto the planes parallel to the c- dimensional particles, axis of the crystal ; they are compiled so that the may not be clearly reproduced in the print, can dependency of the crystal shapes on the pressure be seen. This kind of magnesium particlc was ' of helium and the evaporatlon temperature can frequently obscrved when the pressure of argon be recognized. In Fig. 18 there can be secn many was high, say, 250 Torr; and these particles havc shapes which had not been observed among the fairly isometric shapes in contrast te the plate- particlcs prepared at relatively low pressuresi2.42). 1ike particles formed in argon at relatively low Fig. 19(a) shows the profile of a magnesium pressure. The shape of these particles is the hex- particle, prepared in argon at 250 Terr in the agonal prism of lst order truncated by {Ol.1} ordinary vacuum chamber, viewed along the planes, i.e. the crystals are bounded by {oo.1}, <10.0> direction of the particle; in Fig. 19(b) a {Ol.O} and {Ol.1} planes. The solid bounded by 'mlcrogviewed raph of a particle of the same kind when {oo.1}, {Ol.O} and {Ol.1} planes is a Wulff along the 103 VoL 6 No. 3&4 (137) NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) though the dimensions of the body vary prccise ,l accordmg to the axial ratie c/a of the hexagonal lattice and to the variation of the bond energy "aspect with bond length The quantity R, called ratio" and defined as the ratio of the length from the centre of the body m the <10 O> direction to that m the dron for the ideal hcp crystallite (c/a==1633) is calculated to be 106 on the assumption that the 12 nearest neighbour bonds have the same energv Accordmg to Miller et al40' R of the Wulff polyhcdron for a magnestum crystalhte (a) v,tw (ela=16235) is 1Ol, taking mto account the "yaspm vanation of the bond energy with the bend Iength Fig 19(c) shows the chnographic prqec- tion of a Wulff polyhedron of the h c p crystal Fig. 18 (a) Typical shapes found in electron micrographs of Mg crystallites collected in the inner zone Prejections of the shapes ofthe particles on a plane parallel to the c-axus are compiled Abscissa evaporation temperature Ordinate pressure of the He gas Segment below each picture indicates O5"m (black) or O2ptm (white) (Fig 11 m ref 19) (b) Typical shapes found in electron mrcregraphs of Mg crystalhtes collected in the outer zone Preqections on a plane parallel to the c-axis are compiled Abscissa evaporation temperature Ordinate pressure of the gas Segment belo" each picture indicates O5pm (Fig l2 m ref 19) ajdi)tt es" {ts} : Fig. 19(a) Mg particle -ewed along the <100> <[10TO]) direction Ar 250Torr Collected at the mtermediate zone Aspect ratio R is 1 Ol (see text) (b) Mg particle viewed along thc termediate zone O 5pt - -es (c> Clrnographic prqection of Wulff poly- hedron for the hcp crystal when only the Cd) tc) (OOI) 12 nearest neighbour bends are considered 8x-- " considcred, assuming them to be the same The length of each y is proportional to the eL I O) specific surface energy of the corresponding crystallographic plane calculated according to the formula given by Miller et al (ref mo) F--- 1os - [ a=1s2e04' R=1 06 104 (l38) H ?S re&fSlft\kst NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) Bg. eeScanning electron micrographs of Mg crystallitcs. (Fig. 14 in ref. 19). #ttt"pt,""tl '. tt ･,,i ttt; t/.tt l, ,1 ir,,Ill ,,.'tt t=tttttt.tt/ tttt/ /rmt/., .:t/z,/.... , (a) (b) (c) t. t. t/t 'kIY;.･:･ /･ './'' .n..tpt. /th4p. .//' . ,. .. ,tmu..t,, ,.t . . ,L.,t.tt t.t su.ttmt.ta+t/t .nte.vatitt.,.'tt t" ' when only the 12 nearest neighbour bends are "'ttue-igei/;,'/' Fig.21 Zn. ,ee･iji?･･/k'ii･,/12,il･"sh'ee" considered and Fig. I9(d) thc cross section of thc Ar 6 Torr. the ideal Wulff polyhedron of h.c.p. crystal at '･tt li'L'/..,. v L/'/:. ,t･.･ --,t."lth' ./ -}a/.et:,t OK the The by {11.0}plane. aspect ratio R of l/,'tT.ly,1･,,-''･et/ttt t ,' .mtt -Il''･' .t f/,･{ll{'-,,,.c,1･X-,/ikk,,1/L,.1,/ftlZ.l:it/-:.1t,,,, t ,,. .. t... ,f"tt tr,?= .. :t ttttt ttt ttwt/ .t. ttt,t ,. tt tt tttttt t ., . ,/ ;.ur ... . wil il the reproduced in Fig. 19(a) was meas- particle /, :･',t.l･g,"s/el,Zl,://.t.i'i "'/･1: /;:,ilgf't/ ured to be 1.01*.The measured vaLues ofR's for ..,,,.,.,.,,,, /iX･TS'il･S･E va which ge.w the several of lengths in the llll/･,/lss,ma.t･i",k,g`,ltXli･itr/'"f'"' particles, i:ig diagonal direction in the basal happened to g.x.tst" plane .x.-g･pug':,'ig."ue''li s lie in the range O.6psmrv1.1"m, in produced ma .. li..it/,irml///･th･･.il-'Sll,i':i:'"'':;･g-"i･''i,/''･.;il'f･/1',/xi,'1//lil'":l}'i'l//ill,lag..ee argon at 250 Torr were in the range O.99N 1.04. i ,'･ Fig. 22 Cd. ,: ,t,tt , ldi/t R.i,k7t'･;lilliiii･,･ ', 'i'," ･K}.ff,,., The magnesium bounded by 1. 'i particles {OO.1}, Ar 6 Torr. ewt//x'l,. .' s ,,, ,s,･i,4,//ee {Ol.O} and {Ol.1} planes were also often found among the particles produced in argon at about graphs of magnesium particles obtained by 10Torr and at elevatod temperatureco) (ev120 Kasukabe et aLi9) The crystals were prepared in OC). In these particles, however, the {Ol.O} helium at about 250 Torr ; they have grown large planes were prominent compared with the and have isometric shapes with complicated {Ol.1} planes and the aspect ratio R was in 2AJ surfacc structures. The particle shown in Fig. 20 3. The particles prepared in argon at about 10 (c) appears as if it were cemposed of severar Torr but in the ultrahigh vacuum chamber crystallites of diffbrent orientations; however, showed the trend that the thickness in the conditions in the ordinary vacuum chamber as was case of beryllium. However, they were 6.3 Zincandcadmium bounded by only the basal and prismatic plancs Selected area difltaction patterns showed that and were still plate-like and their aspect ratio the crystallite with hexagonal profile were con- R's were much larger than unity. sistent with the h.c.p. Iattice of zinc and cadmium, Fig. 20 shows the scanning electron micro- respectively (Figs. 21 and 22). The e-axis was nermal to the hexagonal plane and the sides of * The profile ofthc particle in Fig, 19 (a) gives the lcngth the hcxagon were parallel to {10.0} plaiies. The of the diagonal (<11.0> direction) in the basal plane bacause it is viewed along the <10,O> direction ef the shape of the zinc and cadmium particles having particle; however, by multiplying by VS/2 one can hexagonal profi1es is probably an hexagonal immediately obtain the lcngth of the partic]e along thc R. of order 17(d)). Besides Vol.6 No.3&4 (l39) I05 NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) Fig. 23Zn particles formed in 6orr Torr of Ar with O.1 T of air. Fig. 24 Cd particles formed in 7 Torr ofAr with O.Ol Torr ofair. Fig. 25Al particles formed in an ordinary vacuum charnber in Ar at about 1O Torr. Fig. as Al particles formed in a clean atmosphere of Ar at 20 Torr in an ultrahigh vacuum chamber. hexagons, truncated square and rectangles and The aluminium particles are nearly spherical also reels were observed. These profiles, except even when the argon is pure if they are produced reels, suggest that these particles are hexagonal in the ordinary vacuum chamber where the best prisms of the lst order truncated by {Ol.1} vacuum attainable is of the order of 10-6 Torr. In any cvent all of the planes. particleswerc not Fig. 25 shows an example where the particles so thin as the crystals which were very often found tend to be spherical in shape rather than poly- in the cases of beryllium and magnesium and hedral and, also, the shapes of the individual were nearly equally thick in three dimensions, particles are clearly observed even though many although they were produced in argon at rela- particles have come into contact with one an- tively low pressures. other. A tendency to exhibit a polyhedral charac- The particles become remarkably irregular ter was perceived when the evaporatiDn was car- and rough when the argon contained a slight ried out with the utmost care bcing takcn to amount of oxygen 23 and (Figs. 24). keep the argon pure in the ordinary vacuum evaporation chamberiS.42}. 6.4 Aluminium On the contrary, Fig. 26 shows a typical elec- The crystal habit of aluminium was particles tron micrograph of aturninium particles forrned first revealed when they were in a produced in a very clean atmosphere of argon at about 20 very clean atmospher ¢ of argon in an ultrahigh Torr in the ultrahigh vacuum evaporation cham- vacuum evaporation charnber4i)*. ber. Two kinds of particles are observed; iso- * Yatsuya et at.iS) first the electron micrographs published lated, single particles having well-defined profiles of a]uminium particles having the pelyhedral charac- and coalesced particles of irregular shape. These tcr but without mentioning their shape. The particles wer ¢ found among thosc collected at the intermediate two kinds of particles coercisted always indepen- zone which can be considered to be the place where dent of the places where the particles were col- the density of the smoke is greatest and, beca use of that, lack of oxygen is most li1[ely to occur locally. lected but the average size of the particles 106 (l40) HAckenntft\ftes NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) (a (b) e . e020 2oe. Fig. 29(a) Schematic illustration of a cubo-octahedron secn above along the [oo1] direction. (b) Electron diffraction pattern corresponding Fig. 27 to Fig. 29 (a) when the particle has the flc.c. (a) Al particle. Cubo-octahedron with smoothly Iattice. curved edges and corners. The [OOI] direction is normal to the plane of the figure. e) (b) (b) Electron difliaction pattern from Fig. 27 (a). e Fig. 3030(a) Schematic illustration of a cub"octahedron scen from above along the [fiO] direction. (b) Electron difftaction pattern corresponding to Fig. 30 (a) when the partiale has the £ c.c. Iattice. Fig. 28 (a) Al particle. Cubo-octahedron, The [!10] direction is normal to the plane ofthe figure. A A (b) Electron diffiraction pattcrn from Fig. 28 (a). Figs. 27 and 28 are from the same particle. Fig. 31 A Clinographic prejections il1ustrating thc combinations of an octahedron and a cube. (a) Octahedron. (b) Cubo-octahedron with reqular hexagonal {111} faces. (c) Cubo-octahedron with equilateral triangular {111} faces. A cubo-octahedron is a combination of a cube and an octahedron. The octahedral cornponent can be recognized by its 8 equivalent planes (orplanes), each ef which is of {111} type. Six faces of thc cube-component truncate symmetrically the 6 corners of the octahedron. Suppose one of the 6 equivalent {OOI} plancs cuts one of the lines GA at a point P in Fig. 31 (a). When G-A > d7p > % (;7A, the o-faces are truncated equilateral triangles with decreasingarea as thc point P moves from A towards G along AG; when aTp = % C7A, the o-faces are regular hexagons (Fig. 31 (b)). When % G-A > (;TP>Jt6 li TA, the o-faces are again truncated equilateral triangles, When d7t=>6 crt, the o-faces are equilateral triangles (Fig. 31 (c)). For simplicity, unless otherwise stated, the word cubo-octahedron in this section (6.4) refers to the selid shown in Fig. 31 (b) where the {111}faces arc regular hexagons. the interme- depended on the location of the place where they observed in the samples co11ected at were co11ected. Generally speaking, however, a diate zone of the smoke, while in the inner and isolated largc numbcr of isolated, single panicles were the outer zone the number of particles VoL 6 No. 3&4 (l41) 107 NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) was less and the longer chains of the coalesced particles predominated. Fig. 27(a) and (b) show an electron micro- graph of an aluminium particle in a given orien- tation and its selected area diflfactien pattern, respectively. Fig. 27(b) is consistent with an aluminium single crystal when the ineident elec- tron beam is parallel to the [OOT] direction of the crystallite. These photographs suggest that the Fig. 32Al aluminium has the shape of a cubo- particle particles formed in a clean atmosphere of argon octahedron (see Fig. 31) with smoothly curved at 20Torr in an ultrahigh vacuum evaporation chamber. The particles arrange themselves in edges and corners. Fig. 28(a) and (b) were ob- irregular chains due to incornplete coalescence. tained from thc same particle which gave Fig. 27; they are consistent with a cubo-octahedral aluminium particle with the incident electron shapes of the aluminium particles produced in beam parallel to the [l10] direction of the par- an ultrahigh vacuum evaporation unit and those ticle. Figs. 29(a) and 30(a) show illustrations of produced in an ordinary vacuum cvaporation a cubo-octahedron secn from above the plane of unit. These facts suggest the importance of the the drawing along the [OOT] and [rTO] direc- eflect of residual impurities in an inert gas on tions respectively and Figs, 29(b) and 30(b) are the crystal growth of metallic particles. It is respectively the corresponding electron diflTaction coniectured that even in a vacuum of 1O'-e rv 1O-5 patterns from the particle when it has the £ c.c. Torr aluminium particles are oxidized to some crystal structure. From th ¢ se obscrvations and extent or adsorb oxygen during their growth though no tracc models, together with others not described here processes, of oxide could be in order to save space, it is concluded that the detected by electron diMactien cvcn after the aluminium particles have the shape of a cubo- particles had been taken out into the air. Judging octahedren with smoothly curved edges and from the nearly spherical shape of the aluminium formed in an ordinary vacuum chamber, corners. The much smaller particles whose size particles was about 10um or less werc observed to be oxygen atoms worked to smear out the anisotropy spherical. All the isolated particles whose poly- of the surface layer rather than sticking to par- hedral character could be recognized were of ticular low index planes of the particles so as to cubo-octahedral shape and no other crystal habits deepen the corresponding cttsps in the r-plot. were observed. The contaminated surface layers also hinder the Fig. 32 shows another aspect of aluminium particles from coalescing if each particle has particles formed in a very clean atmosphere of attained a certain size. This explains why the argon at about 20 Torr pressure. The particles aluminium particles formed in the ordinary tend to arrange themselves into irregular arrays vacuum chamber retain their separate nearly like tang!ed chains or ropes where the shapes of spherical shapes. On the other hand, fn the clcan the component particles forming chains are also atmosphere of argon the metallic surfaces rcmain irregular and definite boundaries between the uncontaminated so that when two particles col- particles are seldom observed. lide they fuse into each ether and the boundary Marked diffbrences can be seen between the between them disappears irrespcctive of their 108 (l42) HpNtwitrkft\kts NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) size. However, if the size of each particle exceeds or air, for example, air at about O.1 Torr, must a certain limit, say a few tens of nm, transforma- be added to the argon at 10Torr. Fig. 33(a) tion into a single particle having a well-defined shows an electron micrograph of chromiurn par- crystal habit, i.e. the shape with minimum surface ticles thus prepared and Fig. 33(b) the corre- free energy, may not occur, for the energy neces- sponding Debye pattcrn in which all the rings sary for the transportation of a huge number of are consistent with the b.c.c. structure having a atoms cannot be covered by thc gain due to the lattice parameter 2.88 A which is vcry close to decrease of surface free energy43). This rcsults in 2.8847A found in the literature for ct-chro- the irregular shapes in Fig. 32. miumS4). The shape of the particles is a cube or A cubo-octahedron is a Wulff polyhedron of a rectanglar parallelepiped bounded by six a £ c.c. Iattice when only the first nearest neigh- {100} planes, always with very sharp edges and bour interaction is taken into account in calculat- corners. Such sharp edges and corners can rarely ing thc spccific surface encrgies ef a solid37,6S.64). be seen in metal particles except for the casc of When the second neighbour interactions are a-chromium; the parti¢ 1es of other metals have added, the Wulff polyhedron becomes a cubo- morc or less smoothly ¢ urved edges and corners. octahedron truncated by {110} planes at the Although the reasons are unknown at the cdges between two {lll} planesS7,6S). As de- momcnt, it is an empirically established fact that scribed already, these edges were rounded and oxygen is indispensable to stabilize the b.c.c. the existencc of {110} planes could not be ob- Iattice of chromium particles produced by GET. served despite the carefu1 inspections of the On the other hand, chromium particles pre- electren micrographs. The aluminium particles pared in any kind of pure inert gas, have shapes belong to the type (c) of Herring's classifica- and crystal structure that difller from those of tion43,44). ct-chromium particles. When prepared in a very clean atmosphere in the ultrahigh vacuum 6.5 Chromium evaporation chamber, no trace of a-chromium the Chromium particles prepared by GET show particles was observed. Fig. 34(a), (b) show very peculiar natures from the crystallographic electron micrographs of chromium particles difltrent vicwpoint. When chromium is evaporated in a produced in pure argon at pressures; diffraction from pure inert gas of any kind from helium to xenon, Fig. 34(c) the electron pattern most of the particles are not the ordinary b.c.c. Fig. 34(b); Fig. 34(d) the schematic sketch of The Debye rings shown in Fig. 34(c) are not a-chromium. In order to obtain the particles of (c). ct-chromium eMciently, a small amount ofoxygen consistent with any of thc crystal structures of , -,f:e/;ll-.,1..::i:･:-I?:erllli･l-{:1/t ..,nes, /tt#tt1･ll;tt,IY, "i:1''"i' t t/tt ttt Fig. 33(a) Particles of Cr produced l'i in Ar at 6 Torr containing air at O,1 Torr. Particles are b.c.c, 'ettttiii'"kL'l'ii'ttt a-Cr.(b) ,,.,t Electron diflVaction pat- tttt tern from the particles shown t//t/t/t pa' ; :i' t t tttt,'tt''r'l::;,i-ii',i in (a), consistent with the b.c.c. tttttil.il/{tttttt/.ttttttt!t///;tttttwrYffl/':aE･il/ts#.ntwtit":Veellleeeel ct-Cr. iltltt :i.-･ ,,, i'/1"ft:11"11': ''i'1,/'Ii'1/1.:''as./,wt,t/-:w,lhtt.'f 109 VeL 6 No. 3&4 (143) NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) Fig. 34(a) Partieles of Cr produced in pure Ar at 20 Torr. A new medification of Cr (6-Cr) . (b) Particles ef Cr produced in pure Ar at 1.5 Torr. A new 1;" modification of Cr (6-Cr). (c) Electron difltaction pat- gastern from the particles shown in Fig. 34 (b). (d) tt Left half:schcmatic sketch of Fig. 34 ttt.,-.l/l-I-'-i,l-,L.:.l/. (d) Right half: schematically drawn Debye -.-.. "..-.c...')･'ts"X.. (c). .x';/,,,e,i,1･･iS,i.t --N'.' consistent with the erctinction rules of I'i't 1･"･,1) '/// pattern }/,,, ,1,, the A-15 type structure. The inserted numbcrs Z.J ' ttt1,t'/"tus･ "/)ix refer to IV=h2+kt+l2. The of each /1111/11t/tttt width -/1/･,{/.!,i ring is very roughly preportional to its ' lntenslty. Z-,g.t. t ' ssfug.g..i-.tt..tr.g ttt zbe chromium which have been given in the litera- ture. It was dedueed from the electron diffYaction data that the crystal structure was of the A-15 type* (Fig. 35; P-tungsten structure, Cr,Si-type) and the accurate determination of the lattice Y parameter by means of the X-ray back reflection technique yielded the value ao - 4.588± O.oo1 A a4 -4,sssA Fig. 35 where a. is the length of the unit cube. Kimoto CIinographic projection of the unit cell of the A-15 and Nishida4e) confirmed by means of a type structure. 8 atoms per unit cell. Two atoms in stoichiometric study using the particles which position (a); OOO, SSS. 6 atoms in position (c); 4e) * Kimoto and Nishida45 first reported that the crystal oli･ ol2･ structure of this new modification ef chrernium had a iol･Sio･ Soi･l2o･ disordered structure derivable frem the A-15 type structure, its space group being Pms. Ferssell and Pcrsson47i4e} condensed chromium onto thc cleavage had not been exposed to air that these A-15 type surfaces of NaCl and KCI crystals by evaportion in vacuum and found chromium in ultrahigh particles particles were pure metallic chromium. They the carly stages of cendensation whose crystal structure namecl this new modification O-chromium. Two could be regarded as being tlte same as the new crystal structure found by Kimoto and Nishida4e). However crystal habits, i.e. icosltetrahedron and rhombic they proposed the genuine A-l5 type belonging to the dodecahedron, were found among the 6-chre- space group Pm:n for the crystal structure of these chromium particles and explained in terms of double mium particles; most of them had the former diffiraction all those electron diflYaction spots which and very few of them the latter. were inconsistent with the A-i5 type structure. Nishida and Kimoto4S) recxamined the crystal structure ofthese Icositetrahedral particles. Fig. 34(a) shewsa chromium particles using fine single crystals prepared typical electron micrograph of an assemblage by GET; this proved that tht proposal of Forssell and A. Persson was correct. of the icositetrahedral particles. In Figs. 36 40 110 (1") H7Swt&dift\kts NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) various profiles of single particles having this group Pm3n to which the A-15 type structure shape ancl exhibiting good symmetry and the belongs can be explained by the double reflec- corresponding selccted arca diffVaction patterns tions occurring in the individual particles as are shown. These photographs led te the conclu- Forssell and Persson47'4S) first suggested. sion that the shape of the 6-chromium particles Rhombic dodecahedral particles. The occa- was an icositetrahedron bounded by 24 {211} sions on which the majority of the chromium Fig. 41(a) shows a clinographic planes. prejec- particles formed in a single evaporation had tion of an icositetrahedron,and Figs.41(b), (c) rhombic dodecahedral shape were rare. Fig. and (d) show its profile when viewed along the 42 shows an example of such a rare case. The [100], [110] and [111] directions, respectively. Debye pattern from these particles was exactly These profiles correspond to those of the particles the same with that from the icositetrahedral in the electron micrographs shown in Figs. 39(a), particles despite the diflerence of shape; the 37(a) and 40, respectively. Equal thickness selected area diffiraction pattern and the corrc- fringes are recognized clearly in the original sponding profi1es from a single particle also micrographs and congruent with the suggested showed that the particle was a rhombic dodec- shape of the particle. The many difftaction spots ahedron bounded by 12 {110} planes. inconsistent with the extinction rules of the space Thc e-chremium particles thus obtained l･i･ll,lIII'1･il･;1･,llllli･illilll･i,likisilI2,,,'"1'' /'li':// ･,･ f,･:･l:Ir:/ ,, t/,.,., t/'t -..,'"'t'tt-' g/.Iiftmpwa.,Tkma//ss,,,t/.f,r･;･i';;･l/･wwwtIie:u-.:i"tfi::inE .::: ,/1/1,w,･/1･1:'l:":'i･･-:･:'1/il',7.l,';'!,'L' 1 ,Xf l-il;ll':tt!}fri:･l'Si:/{/t/'lis:i:/1.l.li/i'l'i,. i'I}t :ttllww t:i/' /t . ttt ., .. . .tt.t..ttt Fig. 36 Fig. 37 (a) Electron micrograph of an icositetrahedral (a) Profile of an icositetrahedral particle. The particle when the incident electron beam was incident beam was parallel to the [ITO] clirection parallel to the [I20] direction of the particle, The ofthe particle. Compare with Fig. 41 (c). short rod drawn in (a) shows the [OOI] direction (b)tttSelected area difllraction pattern from (a). tttt tttttttt ofthe particle. ,e,,･i･xi･ eeli't//･gll",;ig;,;I'l"t'S/','' Selected area diffl'action from paI (b) pattern (a). l,:1li･l'g/ ,//.tt "'//''iiilL/･'i,Iiii'l'it;ii/k#L･v,n -/ttt T-ttt';･ ･:,:,,-i-, . ./,.,,:1;l, l/.lb:-III i･ ..t, :L･1.,-. ,F, ..l,1 , t-tttttt i.,:Iitht2pt Fig.39 T---,･･. Ca) Octagonal profile of an icositetrahedral The incident beam was to the (a) Profilc of an icositctrahedral particle. The particle. parallel the with Fig. beam was parallel to the [130] direction of the [TOO] direction of crystal. Compare crystal.(b) 41 (b). from Difll;action pattern from (a). (b) Diffraction pattern (a). VoL 6 No. 3&4 (145) 111 NII-Electronic Library Service The JapaneseAssociationJapanese Association forforCrystalGrowth Crystal Growth (JACG){JACG) Flg. roHexagonal profile of an icositetrahedral particle. The incident beam was parallel to the [M] di- rection of the crystal, Compare with Fig, 41 (d). Fig. 42 , {b} rtool] Electron micrograph showing rhombic dodecahe- dral particles, a-Cr. The arrows indicate typical profiles ef a rhombic dodecahedron. .[tDO] to1ot- Table 3 The results of X-ray tests on the trans- formation from 6-Cr into or-Cr after heating at various temperatures for varlous tlmes. (c} 1[oot] (d) Temperature Time /[iOi] Diffraction pattern (ec) (hours) soo 7 i-Cr+b.c.c.Cr [ilO]- [lton- (no change) .Vloj .[tll] 40040045050060017111 weaker fi-Cr+b.c.c.Cr trace efO-Cr+b.c.c.Cr trace of 6-Cr+b,c.c.Cr entirely b.c.c.Cr Flg. 41 Icositetrahedron. (a) Clinographic pro- entirely b.c,c.Cr jection. (b), (c) and (d) show its various profi1es when viewed along various zone axes. The black dot and the nearby the film thickness exceeded a certain value, from index mean the direction of the particle about a few to 10 nm, depending on the experi- upwards normal to the plane of the mental conditions the normal b.c.c. chromium paper. being observed. Granqvist et al.53) also dcmen- transform into the b.c.c.or-chromium at about strated that the thickness rangc where the 6- This 4500C, was confirmed as fo11ows; about 700 chromium may be found can be increased ap- mg of the in argon were particlesproduced pure preciably if the films are made by evaporation in collected without being exposed to air in a small argon at a pressure of the order of 10-2 Torr. transparent silica ampoule. The silica ampoule, The results are summarieod in Table 4. together with its content, was heated in an clec- Yukawa et al.54,55) demonstrated also that the tric furnace. The results of X-ray tests after heat- A-15 type structure occurred when chrornium- ing is in Table 34") given (see also rei 53), rich alloy particles, Cr-Ni, Cr-Fe, Cr-Co and Subsequent works47.48'50-52) have demon- Cr-Ni-Fe, were produced in pure argon by GET. strated that the same structure occurs when Based on this fact they inferred that the 6-chro- chromium is vacuum-deposited onto various mium was a high temperature phasc in pure bulk substrates under various conditions. One thing chromium (see also ref 53); however, therc has which is common to all these studies isthat the been no experimental evidence to prove this and 6-chromium was found only in the early stages they seem to have withdrawn, implicitly, this of condensation and that it ceased to exist when notion in a later publication56). 112 (J46) Hlgre&JStft\kts NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) Table 4 GasPressure (Torr) Structurc Crystal structure of Cr films with thickness of about 10 nm. ArArhrair 2 × lo-s only b.c.c. Normal incidence onto amorphous carbon substrates located 8 2 × 10-4 b.c.c,+traceA15 cm from the seurce (W-spiral). (Table 1 in re £ 53) 4 × 10-2 A15+trace b,c.c. 4xlO--2 b.c.c.+A15 (a) (b) Recently Hayashi et al.2i) published the idea loX /ox that the b.c.c. a-chromium is stable only at high temperatures and the 6-form is more stable at room temperaturc. They inferred that the Fig. 43 icositetrahedra formed in the 6-phase, and the (a) 13-atom icosahedron. A surface atom has 5 nearest neighbours and the numbers of nearest rhombic dodecahedra formed in the ec-phase and neighbour bonds as a whole are 42. transformed to the 6-phase, bascd upon an ex- {b) 13-atom cubo-octahedron. A surface atom pectation that rhombic dodecahedra are charac- has 4 nearest neighbours and the numbers ofnearest neighbour bonds are 36. teristic of the b.c.c. Iattice. They inferred further that ct-phase is easily quenched and the trans- formation from ct to 6 can occur only when the unit cell are taken away to make its shape ap- readjustment is particles are small and their surfaces are clean. proximately spherica1 and slight In this way thcy tried to explain the facts that made on the remaining atoms on the sides of the the or-phase is usually found at room temperature the original unit cell, 13-atom icosahedron However, the that and that the 6-phase, only as small particles in immediately follows. possibility clean vacuum. the natural occurrence of large numbers of atorns might be arranged in the icosahedral way is With regard to the origin or the nature of 6- unlikely as Mackay5S) has out. It may be chromium, thc present author is inclined to pointed coajectured case ofchromium that think that the 6-chromium particles are the in the particles atoms in the cluster increases, vestiges of the small clusters of icosahedral con- as the number of then the long range order which results figuration which are considered to have been gradually A-l5 type latticc becomes formed at the very beginning of thc particle in the predominant the small ef 6-chromium whose unit growth. Fripiat et al.57) have shown by Selfi and particlos Consistent-Field Xct Scatterecl Wave Method cell is very akin to the icosahedral configuration appear. As well as chromium, very that the 13-atom lithium cluster (lithium is b.c.c. begin te in bulk) with the icosahedral configuration is small particles of molybdenum*'**,***, most stable of all the lithium clusters they ex- niobium*** and ironS") also take A-15 typc amined. Apart from such sophisticated quantum- structure or the amorphous structure60) which mechanical calculations, thc 13-atom icosahe- is also very similar to the A-15 type. wnen the dron has the structure where the number of * Y. Saito, S. Yatsuya, K. Mihama and R. Uyeda: nearest neighbour is a maximum compared with Read at thc autumn meeting of The Phys. Soc. of 1976. Abstract II, 88. 13-atom clusters of other ,cenfigurations (see Japan,Oct. p. ** Y. Saito, S. Yatsuya, K, Mihama and R. Uyedat Fig. 43). Read at the S2nd anriual meeting of The Phys. Soc. Abstract II, 267. On the other hand, there are 21 atems in a efJapan, Oct. 1977. p. *** T. Aoyama, S. Ino and S. Ogawa: Read at the 30th single unit cell unit cell) of the A-15 type (notper annual meeting of The Phys. Soc. ofJapan, April structure and if the 8 atoms at the corners of the 1975. Abstract II, p, 19. 113 VoL 6 No. 3&4 (147) NII-Electronic Library Service The JapaneseAssociationJapanese Association for CrystalGrowth{JACG)Crystal Growth (JACG) particle size exceeds a certain limit the crystal second, B, has a hexagonal profile and the third, structure changcs into the ordinary b.c.c. Iattice, C, is a long rod-like crystal. The manganese altheugh the explanation fbr this transformation particles as a whole consisted mainly of A and B ls not yet glven. particles and C particles were rather rare. Electron as well as X-ray Debye patterns from 6,6 Manganese the particles were consistent with a mixture of Fig. " shows typical electron micrographs of a- and fi-mariganese. manganese particles producod in argon, collected A particles. Fig. 45(a), (b) and (c) show a without any precautions to avoid the eflbcts of single A particle, the selected area difliraction turbulence in argon, which ]eads to a mixing of pattern from it and a schematic diagram which particles produced at various locations of the shows the relationship between the crystal shape smoke, during and after evaporation. Three and the diMaction pattern, respectivcly. The A kinds of particle shape marked A, B and C are particle has a profile of a regular or slightly found. The first, A, looks like a tetrahedron, the truncated triangle, often with one side or two ...- .. Fig. 44 Manganese particles. #S$.:lin,X.k£ h,S,:s ntmr (a) Argon,6Torr. (b) Argon, 12 Torr. The A's look like tetrahe- dra. The B's have hexa- gonal profiles. The C:s are needle-like rods, (Fig. 3 in re £ 61}. ww lei (c) Fig. t5ct-Mn. The A particle. . (a) Micrograph. (b) DiMac- tion pattern from (a). (c> . -e211 Iol shows the relation between (a) and (b). The indices are con- 6.3oA 110. sistent with cr-im. Thc thin . straight lincs in the triangle are traces of {llO} planes by . the paper. (Fig. 5 in ref, 61) O.1" (a) Cc) ab Fig. 46ct-Mn. . e. . The A 222 231 particle. (a) Micrograph. (b) Diflfac- tion pattern from (a). (c) shows the relation between (a) and (b). The broken line and the --T--Oll thin straight line in the particle in (c) are the traces of the (Ill) and thc (OIT) plane, O.1" respectively. (Fig. 6 in rei 61) 114 (148) H7SMftrkft\kts NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) (b) (c) (d) G! 2r' a2 apGl t t2rf Fig. 47 a4 A tristetrahedron. triangle. The parallel lines indicate (d) Profile of (b) when (b)is rota- (a) Clinographicprojection, equal thickness fringes. ted in the reverse direction of the (b) ProfiIe of (a) secn along the (c) Profile of (b) when (b) is rota- circular arTows about XX'. [111] axis indicated by the arrow in ted in the direction ofthe circular (Fig. 7 {n refi 61) (a) , The profile forms an equilateral arrows about XX'. sides of it bulged. The diffraction pattern in (b) has never been observed among the A particles. is consistent with or-manganese (for the details Parallel Iines drawn in the particle in Fig. 47(b) of the analysis, see refl 61). Fig. 46(a), (b) and indicate, schematically, equal thickness fringes (c) gives another example of an A particle. One which may be expected in electron micrographs. side of the triangle is bulged in (a). The electron They forrn a distorted hexagon, the angle ct being 147". diflbaction pattern and its relatien to the particle 93O and the angle fi= If the solid is rotated in Fig. 46 can be explained without contradiction around the line XX' through a small angle in the direction indicated by the circular arrows in to the case of Fig. 45. The different profiles in Fig. 47(b), the becomes that showri in Figs, 45 (a) and 46 (a) are due to a diflbrent profile orientation with respect to the supporting sub- Fig. 47(c). Ifit is rotated in the reverse direction the becomes that shown in Fig. 47(d). strate of a particle of the same shape. The direc- profile tion of the incident electron beam is in the [Irr] All these characteristics of a tristetrahedren direction of the particle in Fig. 45 and in the can actually be found in the electron micrographs. [?TT] direction of the particle in Fig. 46. Based Fig. 48(a) shows an example of a particle which upon these observations, it is concluded that the corresponds te Fig. 47(b), standing on one of Fig. The measured A particles of manganese have the shape of a the apices labelled G in 47(a). tristetrahedron bounded by 12 {211} planes. values of ct of various particles lay between 89O lt16e and 1500. In Fig. 47(a) shows a clinographic projection of a and 96e; those of fibetween tristetrahedron. If the origin of the crystal axes Fig. 48(c) the solid is supported by one of the is chosen at O, the centre of mass of the solid, the edgcs (i7a lying on the substrate. In Fig. 48(b) rests the supporting vectors drawn from O towards the eight apexes one of the {211}planes on is the most stable. This fact (four C's and four a's in Fig. 47(a)) are int he film. This position explains why the shown in Fig. <1l1> directions. If one looks at the tristetrahe- probably profile appeared most frequently in the electron dron along one of the <11l> directions the pro- 48(b) file of the solid is an equilateral triangle as shewn micrographs when no tilting was applied to the .speclmen. in Fig. 47(b). This profile is due to the fact that B Fig. 49(a) shows an electron the solid is bounded by the {21l} planes. Ifthe particles. solid were bounded, for instance, by {311} micrograph of a particle which is of the same Fig. The of planes, the profile would become a hexagon which kind as those marked B in 44. profile VoL6 No. 3&4 (149) 115 NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) thc particle and the geometrical arrangement of have the shape of a rhombic dodecahedron. equal thickness fringes in the electron micro- All thcse features of a tristetrahedron and a graphs suggest that the shape of the B particle rhDmbic dodecahedron were demonstrated is a rhombic dodecahedron bounded by 12 {11O} firstly by Nishida6') by rotating a single man- planes. Fig. 50(a) is a clinographic prQjection of ganese particle and by observing its profile in the a rhombic dodecahedron bounded by l2 {110} electron microscope. Figure 50(b) a view ofa rhom- planes. gives plan Fig. 50(b'), (c') and (d') give schematic dia- its with one bic dodecahedron in stable position grams of electron difTraction pattern which may of the {110} planes supported by the plane of be produced by a singre crystal having a cubic the drawing. If the solid is rotated about the YL lattice. The diflVaction spots are drawn from the axis through 35e, the profile becomes a regular lowest order upwards without any consideration hexagon as in Fig. 50(c) and ifit is rotated about to the extinction rules of the space group to which the Z-axis through 450 the profile becomes a the crystal may belong. The orientations of the square as in Fig. 50{d). The parallel lines drawn crystal corresponding to the electron difltaction in the figures indicate the equal thickness fringes pattcrns arc represented in the figures adjacent which may appear in the electron micrographs. to the patterns respectively. The crystal is viewed The agreement between the calculated values along the direction of the electron beam and it of the angles ct (109028') and B (125016') in is assumed that the crystal has the shape of a Fig. 50(b) and the measured values of ct (108Otv rhembic dodecahedron bounded by {110} 1100) and fi (123e"v127e) is satisfactory if one planes. If the lattice parameter of fi-manganese takes into account various arnbiguities of the is given to the patterns, these spots agree per- experimental conditions; this is also thc case for fectly with the electron difliaction patterns the ratio ZIY (-V2) in Fig. 50(b) and the actually obtained. Only one example is cited; measured values (1.29rvl.43). These observa- Fig. 51(a) and (b) correspond to Fig. 50(d) and tions lead to the cenclusion that the B particles (d') respectively. The results of the analyses t:/ttt/t/t/.tt..'''' .ttt.t ttttt.ttt.. 'Eewi'/11i/1,l･･･,-･ ･･a･ , .;:/.g't,/.."l" ,1 ill.:/./, s.,a}･ (bre ic)' tttttttE/,t/...iSl,I,',/i//11,i/i,ll･i;llii:.:/'/s'.;lll:,tS"l#ljlk. V V.,?,//,//l,"'lii-/ ttt ,/tt /tt' 1/; ,/l･{･r/i･;{l･l-i･l'k'llil:tla/t. -l/l./.r/:l:/:r.', ./.t-,,1:il ttttttt , .,t/a/tttt.t"/t/-t/tttnn/."tt"'t tt :t/t/s=/t'ttttiltt"" ,. .g ,,,/tSxil.t,. l..ill' lf/t.t/t///=t ttt ' , , ,1 ,ltt meOth1 l-::,'Si,il.'l･:･/S.ll･I,''1･ t.t.tt-tv.tttttttt tl::t{',l./-. .tttttt. ./.ttt . tt ttt ',･'--1-tt ･- o,2"･ S,&E-ma.+2pt buSlva, tt L,4a., tt - Fig. es Typical profiles ofMn particles oftype A. (a), (b) and (c) correspond to Figs. 47 (b), and (d) re- spectively If the electron beam is normal to supporting film (a) stands on an apex, (c) lies on an edge and (b) rests on one of the {211} planes, (Fig. 8 in ref. 61) Fig. -9 fi-Mn. The B particlc. (a) Micrograph. (b) Selected area difftaction pattern fromCa). As far as the spacings only of the diffiraction spots are concerned, the spots can be indexed as either ct-Mn or fi-Mn. (Fig. 10 in ref. 61) 116 (J50) HiSme&ntft\ftts NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) z {b') (b) ¢ T le] ll ey Fig. 50 p Rhombic dodeca- a hedron bounded l by 12{110}planes. F-- y ---- {c) {cl .Odt121 spots corresponding to and respectivelywhen the (b),(c) (d) oto incident beam is normal to the The indices and paper. . . spacings are consistent with fi-Mn, provided that the extinc- tion rules are disregarded. (Fig. 11 in reft 61) . .1// t. proved that the B particle is consistent with /////// tttt/t l/ ilii･ fi-manganese6i). C particles. The C particles have the shape ofa needle-like rod;, there were very few of these when compared with the A or the B particles 11/111 ･ 111i'11'''''11'11/'1'111"1'111/"1'111'/' manganese evaporated argon or xenon at ''1iiii'11i''1i''''illlilllll''1'iillll{1111i'f is in pressures from a few to some 20 Torr6i). Neither 1i･･i',llj.･g･' Fig. 51 exact shape nor their crystal structure are yet (a) Electron micrograph of the B particle. (b) known. The selected area electron difl}raction Selected area difftaction pattern from (a). Compare with Figs, 50 (d) and (d'). (Fig. 13 in reft 61) pattern from the C particles is not consistent with any crystal structure of manganese reported in the surrounding atmosphcre in the literature. This form is probably a new perature (fi- manganese is known to be very easily allotropic form of manganese. quenched to room temperature). The A are con- One of the characteristic features ofmanganese particles sidered to form in the temperature range below particles prepared by GET is that thcre always eC exists one-to-one correspondence between the about 800 as ct-rnanganese with the shape of a clear-cut external shape of the and its partiale * There are four allotropic forms ef bulk rnanganesc 34, crystal structure. NishidaSi) infers that the B (refl p. 191). 727 ℃ 1co5 ℃ 11ss℃ Z244℃ liquid i particles are considered to form as fi-manganese in a-fi-7-j- a: b.c.c., space group I43m-Td3, 58 atems in the unit the temperature range between approximately cell. 8000C and 1100OC* and to retain their shape of fi: cubic, space group P4s32-Oe and enantimorphous P4,32-O', 20 atoms in the unit cell. rhombic dodecahedron and the crystaI structure 7: fc,c, as fi-manganese when quenched to room tem- j: b,c.c. 117 Vo!. 6 No. 3&4 (l51) NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) tristetrahedron, symmetry and also on an expectation that the Uyeda et al.ie} studied spatial distributions of rhombic dodecahedron is characteristic of the the three kinds of manganese particle relative to b.c.c. Iattice. They think that Nishida's con- each zone of the smoke. According to their clusion on the origin of the A particles is correct the the the results, B, A and C particles were since ct-manganese has tetrahedral symmetry. thc inner, intermediate found in and euter zones However, fi-, 7- and 6-rnanganese have octahe- when the respectively evaporation was carried dral symmetry and his conclusion fbr the B par- out in helium at a pressure of about 250Torr ticles is not correct because of the syrnmetry from the evaporation boat at about 14000C, relations. This way ef thinking means, however, When the of helium was lowered to 50 pressure that the A particles were formed and grew in Torr, each particle was not so distinctly distrib- the temperature range below 7000C and the B uted as in the case of 250 Torr. When the Pres- particles were formed and grew at least to an sure was further lowercd to IO Torr, the particie extent where the particles had the b.c.c. Iattice shapc was small nm) irregular in (AJ20 and the and the rhombic dedecahedral shape in the inner zone, larger B particles ( A. 100 nm) being temperature range above 11300C. If so, therc found in the intermediate zone and the C par- remains one question for the present author as ticles in the outer zone. When the evaporation to what shape the particles which are formed in temperature was to the lowered 1200eC, C par- the temperature range between 730eC and 1I30 eC ticles were observed all over the cross section ef take, It seems most unlikely that no particles the smoke at a of 50 Torr. These results pressure grow in the above-mentioned temperature range. suggest that the C particles grow in the lowest temperature range compared with those whcre 6.7 Iron the A and the B particlesgrow. Fig. 3 shows typical electran micrographs of Further Uyeda et al.2i) concluded that the B the iron particles as a whole. As seen in the figure, particles are formed originally as 6-manganese the particles of ferromagnetic metals which have (see footnote), which is b.c.c., with the shape ofa grown more than about 1O nm in size stick to one rhombic dodecahedron and only the crystal another resulting in long chains. Micrographs of structure transformed to that of 6-manganese, iron and cobalt particles deposited onto the EM- the conclusion being based upon the crystal grids placed in magnetic field of about 1OOO gauss (a) {b) (c) Cd) Fig. 52 .. Projections of rhombic dodccahedra truncated by {1OO} and the corresponding difflraction from [110] planes, patterns b.c.c. Top, middle and bottom rows show .1. Iatticc. projections along [110], [10e] and [111] directions, respectively, and columns, (a), (b) and (c) correspond to .al. various of shows .. degrees truncation. Column (d) their [1oo] diffraction patterns (schematic). The thin parallel lines indicate schematically equal thickness fringes. R defines the degree of truncation. R=O for a non-truncated == polygon. When a corner is truncated, for instance, R 20 if a new plane produced by truncatien intersects [111] -iXii'i edges coming to the corner at the points which are distant 209'. ofthe original length ofthe edges from the R=O R=25 R=SO cerner. (Fig. 4 in ref. 21) 118 (l52) H?Sre&fikft#kss NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) by 12 {110} planes by means of the study on the splitting of the electron difTtaction spots due to double refraction of the electren beam by the shape of the iron particles. Hayashi et al.2i) observed the iron particles having shapes of rhombic dodecahedra truncated to various ex- tents by {100} planes as well as non-truncated ones. Fig. 52 shows models of truncated rhombic dodecahedra and Fig. 53 shows thc iron particles actually observed. They infer that these trun- Fig. 53 Electron micrographs of non-truncated catcd rhombic dodecahedra** of iron particles and truncated rhombic dodecahedra of are not formed in the or-phase but in the 6- Fe particles correspending to Fig. 52. The reason, however, is not (Fig. 5 in refi 21) phase***. given. Fukano65.66) evaporated iron by using a straight tt,., /, , ,. t., 'l'it'1/t;: e- ' '' 1': :' "''' fts''t/"' 1/l1/ tungsten filarnent in xenon or argon at a pres- t ttt whose / tttt sure IOtv20Torr and found particles tt ttt tt ' '1 thin ttdit tt shapes were pentagonal decahedron and / t ' triangular as shown in Fig. 54. Both of these : plate ---- 1--sstw o,espt shapes are characteristic of £ c.c. metal particles ttt t ' tt t k,'','i'--,11I..,･ d such as gold and silver. Some pentagonal par- ,/:/,/ i1'l'l. /tt /, .,.. ticles were pcrfect 54(a)), while some were /. , ., (Fig. ,/t ,/,1 tttt ttt; tt ttt l/,. : with dislocations 54(b)). / internallydistorted (Fig. tttt:t/ t the t Their difllraction patterns indicate that per- tt/ t.- -1･ ･ -wt--ful ･･ a fc.c. ]attice and fect ones belong to (7-iron) lgmlpt "eg}c Fig. 5- distorted ones to a b.c.c. Iattice (ct-iron). Trian- Electron micrographs of Fe particles formed in Xe gular plates were equilateral perfect crystals at 20 Torr, (a) and (c) are 7-Fe; (b) and (d) are when they were smaller than about 30 nm, while a-Fe. (a) and (b) are pentagonal decahedra; (c) are equilateral and isosceles triangle$, and (d) thcy were isosceles and striated when they were respectively. (Fig. 1 in refi 65) larger than about 30nm (Fig. 54(c) and (d), respectively). Their diffraction patterns indicate and showing arrangement * pronounced parallel K. Fuiita and M, Kogiso: rcad at the joint meeting of The SQc. Appl. Phys. and Thc Phys. Soc. of chains are shown in Figs. 19 and 20 in refl .12. Japan Japan, April, 1964, Abstract p, 206. In the absence of a magnetic field, however, # The rhornbic dodecahedron beunded by {110} Wulff of a b.c.c.crystal if these long chains arrange themselves into irreg- planes is a polyhedren only the first-nearest neighbour interactions of ular arrays like tangled spider's web because of atorns are takcn inte acceunt in calculating the the turbulence due to the convection in the specific surface energies, When the second neighbour interactiens are added, the Wu]ff polyhedron be- evaporation chamber. cornes a rhembic dodecahedron truncated by { 1OO} 37, 62-64); the degree of truncation The shape of the individual iron particles was planes (refs. depending on the ratio of the energy of a second- Kogiso and Fuiita" the firstto be determined by ncarest neighbour bond to that of a first-nearcst neighbour bond. among all the particles produced by GET. They *** There arc four allotropic forms in iron, the shape of the must showed that iron particle 910 ℃ l390 ℃ l535℃ a-7-i-]iquid bc a rhombic dodecahedron (Fig. 50) bounded b.c,c. Lc.c. b,c.c. 119 VoL 6 No. 3&4 (1ss) NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) that the equilateral ones belong to 7-iren and intermediate zone were found to have grewn as the isosceles ones to ct-iron, A triangular plate of large as 50nm in diameter and showed the ct-iron particle (Fig. 54(d)) is parallel to (OIT) distinct crystal habit (Fig. 55) at al1 values of T plane and the base of the isosceles triangle is and P used. The solid is a combination of a tra- parallel te [111] direction. The parallel stria- pezohedron bounded 24 {311} planes and an tiens are twins; the twinning plane and the octahedron, i.e. the former is truncated by 8 twinning direction are (21T) plane and [111] {111} planes. The edges and corners of the direction, respectively. The lattice constant of actual particles, however, were slightly rounded, the 7-iron particles was measured to be "gs\lg,Ii z 3.58± O.Ol A, in agreement with the ue,..me,.tt,.iieeew..wak"Vtk'I"tl.ii,re-tetil.IMIIillS$i.ii'tS'i･i'/1//1･\/l good va.-ts ( .,e'illrl,,/ys'esafi/tvl:lif,?,,zantw,'I.#tiwwstntveiluigll/.,:'scl/.F!'/Lt/t.sa/ttthk,,wplk'i,/l･･ll･i.il:;2,i i,',11l:;.:-/:s't,lv':/Y,1ltE extrapolated value to room temperature 3.59 A6'). Since iron in bulk takes the £ c.c. ' '.ni',II{".11./,;,il,:l･:1{x ,. Iattice in the temperature range 910A. I390 Y aC, it is reasonable to infer that the 7-iron ,,.-t,..:1 x-;:1･{11 ll..1,l'.IL,,IS:,'i'r;1 particles have grown in this range and some small have been particles quenched extre- ..l ttt/ttttttt/ mely rapidly retaining their internal struc- '":i ture and shape because of the very steep Fig.55 S{ particles. (a) graph. Ar 10Torr. (b) Clinographic of A temperature gradient around the particular prqection (a). polyhedron beunded by 24 {311}planes and 8 {111} planes. evaporation source used. The larger partic- (Figs. 3 and 4 in ref. 69) Ies are cooled more slowly and they have }{:eza-£cai:･:-ll,ll::'lt;:･li/･/sc,,,:';r,'/･igeil;'il':11/';;g;l:, sl':l･lxiesIS,t:l･Il;ll.:/:i,,r1;g,･t"/t;t/･ltt･::,:::..-i:･:･'l;S./v't'..:,/:/-1 transformed to the stable b.c.c. Iattice. ''i .t,EIilm s,:;il'/t/1'lll.l/111/,'l:':'/ili;iii'?ili'1'/--ll'li'1'l'Li,l[1t/Iri/.t Fukano considered the tranformation to be martensitic and discussed its mechanism based upon his detailed observations on ct- Y x iron with £ c.c, crystal habits66). particles 1/ ttttt The ratio of the numbers of 7-iron tttttttt.tt' tt=ttttt tttttt t,il', particles to those of a-iron particles in a 'qg,pt.,l･,li t/ singlc evaporation was, in the most favo- t tt urable cases, about l%66). (c} Cd) 7.sO 6.8 Siliconandgermanium Silicon and germanium particles were studied by Uyeda and his group6S-'O). The particles were prepared in argon in the "30 (it3) ordinary vacuum system unless otherwise {t specifically stated. The evaporation tempe- ig. 56 Ge Particles. rature T and the argon pressure P used (a) Micrograph. Ar 30 Torr. were l800A･2000eC and 4N15Torr re- (b) Clinographicprojectionof(a).Trapezohedronbound- spectively for silicon, and 1500.vl9000C ed by 24 {311} planes. (Figs. 6 and 7 in re £ 69) (c> Schematic sketch ofpentagonal decahedral particle of and 1OAJ 40 Torr for germanium. germanium (Fig. 2 (a) in ref. 70). Silicon68t69}. The particlescollected at the (d) Geometrical assembly effive regular tetrahedra. 120 (154) H]t:reiftrkft\kts NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) at a from 10 to 20 Particles twinned on (111) plane following the ticlcs were prepared pressure tcmperature from 1700 spinel law were also found. On the other hand, Torr with evaporation to 19000C. The shape of the is a the particles collected in the inner and outer particles pen- zones showed no crystal habit and thcir diame- tagonal decahedron truncated by {311} planes 56(c)). Besides the with ters werc about 20 nm at all values of T and p' (Fig. particles perfect symmetry, those containing the used. The coleur of the particles were yellow five-fold planer cleft were found. Two kinds of clefts w ¢ re ob- irrespective of their size. served. One was nearly parallel to plane, Germanium6S-70). The particles collected in (lle) thus one of the tetrahedra constituting the inner zonc were about 20nm in diameter dividing halves and another was and showed no distinct crystal habit at all values the solid into parallcl to onc of the twin boundaries bctween tetrahedra. of T and P used. The electron diflVaction Debye The former type was found more frequently. pattern from these particles showed many extra et at.7") explained this faet by assuming rings in addition to those which were consistent Saito that the elastic tension unit area due to the with the ordinary diamond structure of germa- per distortion inside the tetrahedra is larger in the nium. The same Debye pattern was also obtained because its area is O.82 times smal- from the particles prepared in helium under {110}plane twin boundary The apprepriate conditions. Saito et al.69) suggested ler than that of the plane. diffractionspots were the existence of a new modification of germa- corresponding electron two about 70 in accord with 7.5e nium; however, the crystal structure is yet split into by space deficit when five regular unknown. On the other hand, the size of the expected from the togethcr 56(d)). particles collected in the outer part of thc smoke tetrahedra were packed (Fig. was increased with the increase of T and P used. The diameter of these pentagonal particles much larger than the Moreover the distinct crystal shape, a trape- between 100AJ400nm, 72.5nm calculated by Ino7i) zohedron bounded by 24 {311} planes, was maximum value found among the particles prepared at about T=1700eC and p==30Torr (Fig. 56(a), (b)). Besides this shape, the particles twinned on (111) plane as in silicon and the triangular plate-like crystals having rounded corners were also found, though the latter crystals were observed rarely. The colour of the particles was brown irrespeg- - Fig. 57Se.Ar tive ef their size. The behaviour of germamum smoke was quite different from that of silicon 7 Torr. and of other metal smokes69). It lacked the inter- "ge. i '' .. nl l' .. mediate zone which rose from the edgc of the me tungsten boat; however, the reason is not clcar. e in When gerrnanium particles were prepared e in very clean atmosphere of argon (99.999%) e . e ultrahigh vacuum evaporation chamber pre- wktt.'r . .b t/ nr.,s#gb tt'' evacuated to about 3 × 10-8Torr, multiply- *eemes lll" /･ s Fig. 58Ga.Ar twinned particles (see g6.10) were found besides 7 Torr. trapezohedra7e). This occurred when the par- k'l,//wa.xtttt""eltw'- 121 VoL6 No. 3&4 (155) NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) Fig. 59Pentagonal .4a)･ -tt (c) MT particle. A silver of (a) particle pen- ' tagonal shape prepared in Ar at 12 Torr at 3000C. , t.---- The b (b) electron diffraction a' ts ' s t N pattern from the shewn i particle 1 ' N in (a).(c) ' t Clinographic projection of a pentagonal decahedron. sooA tt tt tttttt t tt tt tttttttt.: tt.ditttttt.t ttt tt t tt/.t.tt ewt,:::II･,I l･:'. /tttttttt Fig. 60MT ...t../#. ttt t /tt..,nt''t'l,'::,'l･ {c} ,kt,/+"ttt,,S,l, T,.t/..t.t,..,t ofhexagenal ., particle pro- t,11::/..:'11- ,1.l 1.11. /. .t =,.t hlt/.t /I file, an icosahedron boundcd tt by 20 //:,tttttt.. {111}planes. l,' I:li',l' (a) Micrograph. Ag particle prepared in Ar, 4 Torr, 400OC. (b) Electron diffraction pat- tern from (a). tt1 (c) Clinographic prejection 1/ / , l･;u/ ,. //1,･ :5ooA- of icosahedron. :,l.,,'',y/ 1:. MT /tt tt tt /: for quasi-stable,pentagonal decahedral ger- distorted cubic close-packed five or twenty manium particle. tetrahedra bounded by {111} planes are packed together, forming pentagonal decahedra and 6,9 Galliumandselenium hexagonal icosahodra respectively, thereby The colour of the se]enium smoke was deep maintaining the twin relations to one another. carmine, The shape of these particles are gen- Later these two kinds of MT configurations were uinely spherical 57 (Figs. and 58). Electron as also found very frequently in the particles of well as X-ray difl}Taction from these patterns various £ c.c. metals produced by GET. showed diflUse halos. These are the particles Fig. 59(a) shows a particle of silver with the only elements for which the were not particles pentagonal profile prepared in argon of 12 Torr crystalline. at 300eC and (b) the electron diMaction pat- tcrn from it7S). The results of the analyses of 6.10 Silver and other flc.c. metals except Fig. 59(b) together with the dark field elcctron aluminium microscopy revealed that the structure of the The of [c.c. metals such particles as silver, particle is in complete agreement with that which nickel, copper and gold, palladium, produced was discussed in detail by Ino78) and called the by GET, show various external shapes. Therefore, model B by him (Fig. 59(c)). It was fbund'S' the shapes which have becn commonly observed that the frequency of occurrence of MT panicles in these metal particieswill be describedfirst. in argon increases and, at the same time, the Multiply-twinnedparticles(MTP), TheMT size of the particles increases by raising the configuratiens were first found in the gold par- temperature of the argon. In the case of silver ticlesat the initial stage of vacuum depesitien on the pentagonal MT particles were observed in NaCl and KC172-'6) and also mica77) substrates. the range between room temperature and 400OC They are the structures where the slightly and it was between room temperature and 500eC 122 (156) H ZS/di&ntft\ftes NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) MT for gold. Above 4ooeC such silver crystals were gold. Arnong observed maximum sizes ef seldom observed and this was also the case for particles of silver and gold 300 nm of pentagonal by gold crystals above 5000C. A very sharp boun- silver particle agrees with that calculated dary of the argon temperature seems to exist Ino7i). near 400eC for silver and 5000C for gold, cven MT particles of pentagema1 and hexagonal though the tcmperature of particles themselves profiles were also observed in particles of palla- is unknown. If the pcntagonal crystal consisted dium, nickel and cobalt prepared in argon78). of perfect tetrahedra, a misfit angle of several Wada22} found pentagonal MT particles of degrces would be observed (Fig. 56(d)). Contrary copper prepared in xenon. to thc case of germanium (g6.8), the fact that no Finally, it is worth noting that when the silver such cleft has been reported indicates that the particles were prcpared in argon in the ultrahigh misfit angle is shared between tetrahcdra. No vacuum charnber the most frequently eccurring was the array of misht disIocations along the interfaces shape of the isolated single particles MT ef tetrahedra could be observed; however, icosahedron and that the MT particles of pen- fringes which were parallel to and seemed to tagonal decahedral shape were scarecely observed originatc from the interfaces were observed in in contrast to the fact that they were most frc- many particles. These fringes are probabry due quently found arnong the silver particles prepared to twins. The maximum size of the pentagonal in the ordinary vacuum chamber"ii). the the cr}stal measured along ab (Fig. 59(c)) was about Plate-like crystals. In second place, 340 nm for silver and it was about 120 nm for plate-like crystals are alse commonly observed gold. among flc.c. metals, particularly in silver and rlhe The MT particles of hexagonal profile werc gold and also in cobalt and palladium. also observed both for gold and silver. Fig. 60 (a) shows ari example; (b) a difli7action pattern from (a). These particles were found to be con- sistent with the icosahedral MT structure (Fig. 60(c)) which was referred to as model C by Ino72). The average size of the icosahedral crys- tals was smaller than that of the pentagonal crystais prepared in the same conditions; the rnaximum size observed for icosahedral par- Fig. 61Plate-1ike crystals showing various degrees ticles was about 150 nm for silvcr and 40 nm for of truncatien. Cr)rsta!s in (a) and (b) are cobalt and that in (c) is palladium. R indicates thc degree of tnmcation t--.-,,retttt,/..t,t..,-, -l{e)･w IMrc"ge-w.--i,/1:Jf.IIL･:, /, . Itil-,llL';::1,:..,.,,. which varies ffom R=O (equilateral triangle) to R=(J6)xloo (regular hexagon). (Fig. 15 in refl 21) Fig. 62(a) Typical electron micrograph ot containing plate-1ike crystals of silver. Ar 12 Torr. (b) Electrondiffractionpatternfrom /M/l･ a platelike crystal when the bearn is mai,k'Il,ix'i'I,i/k,ijili,l:il.I,i.,,ge,.,ma...,ige,.lr/,,2,1111ii.i･ig,l{'l,iiill,i･ilig･･i#･･,k-tiI'';'normal to the surface of the plate. 123 VoL 6 No. 3&4 (l57) NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) "･. x･･･ Fig. 63Ag. gg "ili",vi,. Electron micrographs of a ,; plate- IXr, ".･ 1ike crystaL ･ Side view when the beam is ･ (a) pt parallel to the surface of the plate. (b) The same crystal when the beam . e/ tlt. is nearly normal to the plate. 1.1. -･ i'' ･ ･',lf,lill, X,s." a e･ profiles of these plate-like crystals vary from equilateral triangles to regular hexagons and between these two extremes there are triangular plates truncated in various degrees. Fig. 61 shows crystals of cebalt and palladium demon- Fig.64 Ag, strating various degrces of truncation. They Selected area electron diflVaction pattern from a exhibit distinct extinction contours. Fig. 62(a) plate-like crystal and small silver particles. The spots indicated by asterisk (*) can not be indexcd shows a typical electron micrograph containing with intergers. plate-like crystals in the case of silver; (b) is the sclected area diffraction from pattern a crystal Debye rings are (1l1), (200), (220),･･･from the when the incident electron beam was normal to innermost to the outside in the usual scquence. the The surfaces of the are plate. plate {111} It can be secn that 6 strong {220} spots coincide and the directions along the side are planes faces exactly with the (220) ring and that the weak directions. <11O> spots indicated by the asterisk (*) in Figs. 62(b) thickncss The of the plate can be determined and 64 can not be indexed with integers. By directly from the electron micrographs. Fig. 63 tilting the specimen in order to see the intensity shows an example. The particle shown in (b) distributions of these spots in the reciprocal was tilted until it came into the position shown lattice space, it was found that they appeared at of the in (a).The thickness platewas uniform in any angle ef tilt indicating that all the corre- all the cases observed and it was in the range sponcling reciprocal lattice points wcre connected between 23 and 30 nm for the observed l4 silver by thin elongated streaks which were normal to in particles prepared argon at 12 Torr and most the (111) plane, though the intensity of these of them were cencentrated in 25 and 27 nm. The streaks was weak. The specimen tilting experi- ratio of the measured length of the diagQnal in ments also revealed that all the plate-like crystals the plate to that of thickness was between 20 and of silver examined had twins parallel to and 22*. throughout the plate witheut exception*,**. Fig. 64 shows a selected area diflfaction pat- Hayashi et al.20 explained the appearance of tern from a plate-like crystal and from small i I. Nishitia and K. Kimoto : Read at the autumn meet- silver particles which coexisted within the same ing of The Phys. Soc. efJapan, Oct. 1975. Abstract irradiated area, the incidcnt electron beam being II, p. 73. ** T. Hayashi, Y, Saito, S. Yatsuya and R. Uyeda : Read normal to the plate. The indices of the spotty at the autumn meeting ef The Phys, Soc. ofJapan, * I. Nishida: Unpublished data, Oct, i975. Abstract II, p. 50. 124 (!58) H7Xtsft!ikft\kts NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) these extra spots by making the spacing between reported2i). Fig. 65 shows illustrations of the neighbouring twin boundaries small enough, i.e. profi1es of an octahedron projected along the 4 by assuming the existence of repeated twins main directions, Fig. 66(a) and (b) show mi- parallel to the plate. No other experimental crographs of octahedral silver particles and Fig. evidence, however, for thc existence of repeated 66(c) shows that ofa carbon replica. The replica twins was shown. was prepared by carbon evaporation onto silver These plate-like crystals of silver were most particles and subsequent dissolving away the frequently collected at the intermediate zone in silver by streng acid. Fig. 67 shows the micro- the ordinary vacuum evaporation chamber. grapks of copper particles of octahedral shape, However, they havc not becn observed in the almost non-truncated and truncated. Various silver particles prepared in the ultrahigh vacuum degrees of truncation are also shown in Fig. 68. evaporation chamber. Hayashi et al.2i) emphasize that ainong all the Octahedron. Ueda7e} observed the silver fic.c. metal particles produced by GET only the particles of standard octahedral shape prepared particles having an octahcdral shape, either in argon. Subsequently other varieties due to truncated or non-truncated, are single crystals c.c. with shapes the various degrees of truncatien were also and all the other £ particles Fig. 65 Illustration of an octahedron projected aleng (a)[OOI] (b)llM] {c)[110] (d)[112]vX the 4 main directions and the corresponding electron diMaction patterns of a £ c.c. Iattice (schematic). Thin parallel lines illustrate the sstlN equal thickness flinges. 3 in re £ 79). , (Fig. " @ [iool a tei C2o7} - xC020)x {oo2) + xXx x +"TT) -----+ {2eo)x C21o) c"e)x [l}1] , ie x,, + l x (111) nywa kesge eqgegeny,x# eeeewht.ISiliiewew El123 e e N ee ew 'Se [llel e e - pt pt Fig. 67Cu eswatff,,,s･r,,:,･/l'tl'tl.･ili particles, Micrographs of slightly truncated column) and extensively Fig. 66 Silver particles ofoctahedral shape. (left truncated octahedra column) of (a) [OOI] direction. Compare with Fig. 65 (right (a) and (b), respectively, (c) Three dimensional carbon replica copper. [hkq directions (left column) indicate the axes of the crystals nortnal to for (b) orientation. (Fig. 2 in reL 79). the planes ofthe figure. (Fig. 9 in re £ 21) Fig. 68Micrograpbs of octahedral particles in [OOI] projoction, showing various degrces oftruncation. (Fig. 10 in reft 21) (a) and (b) are Pd particles, (c) Cu particles. R indicates the degree ef truncation (see also the figure caption ofFig. 52), 125 VoL 6 No. 3&4 (159) NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) (b)[il1I Cc}[1111 (d}[olT] (e)[1121 tWlnpiane{111) f) ' x x Fig.69 eetCuaptA/v 2ie)):iAISI'meiAAA Truncated triangular bipyramid. i71-i,, a2oxtlTl) tttttttil.-int.t Flg. 70 Silver particles ef truncated triangular bipyramidal shape. (a) [Oll] direction. (b) [11I] direc- tion, (c) Three dimensional carbon replica for (b) orientation. (Fig. 4 in refl 79) Fig. 71Particles of Te. Ar 6 Torr. Four kinds ofprofiles (A, A', A" and B) are alrpar- ently observed. ･S -ww' ' N!k . ･(,, 1 {a)V 4 x Fig.72 Transformation of the profile of A t particle. Figure 72 (b) was obtained " from Fig. 72 (a) by tilting the specirnen s :,.. about 30e around the direction ofthe ' /i.'./ ･1･1 length ofthe rod-like specimen. 31{tlEfL". ･-, L- ," Fig. 69(d) and respectively. described in this section are twinned. (b), Ueda'9} observed truncated triangular bipyra- 6.11 Tellurium mids of silver particles. Fig. 69 shows the clinographic projectien of a truncated triangular Fig. 71(a) and (b) show typical micrographs bipyramid having a (111) twin plane and the of tellurium particles collected 10 cm above the prejections of its profiles along various axes and vapour source, no precautions having been taken the corresponding electron difltaction patterns to avoid the effects of the turbulence which occurs for the £ c.c. Iattice. Fig. 70 shows the micrographs in the argon during and after the cvaporationSe). of silver particles of truncated triangular bipyra- Nthough the observed profiles are subject to midal shape; Fig. 70 (a) and (b) correspond to variations, the crystal habit of the tellurium 126 (160) NJzprenntft\ftts NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) particles ¢ onsists of two main types, i.e. rod-like diffraction pattern, is shown clinographically in crystals (A, A', A" in Fig. 71) and smoothly Fig. 73. The crysta1 structure of the rod-like curved, nearly spherical or egg-shaped crystals particle is consistent with ordinary hexagonal (B in Fig. 71(b)). a-tellurium and the particle has its c-axis parallel The profiles A and A' transform into each to the Iength of the rod. The rod has a hexagonal other when the particles are rotated by about 30e cross-section and is bounded by 6 { IO.O} planes. around their long axes as shown in Fig. 72(a) In addition to this basic shape both ends of a and (b). Therefore the difllerence in the profiles given rod often have a set of three prongs which A and A' is due to the different orientations of extcnd along the c-axis in trigonal symmetry. the particles relative te thc substrate. The par- The particle profiles labelled A and A' correspond ticles A and A' have three prongs cxtending to the model when viewed along the <11.0> and from both ends along the axis of the rod, the <10.0> directions, respectively. Frequently there symmetry being trigonal. A" particlcs do not have are indcntations at the centre of each end of a these prongs; however, the crystal habit of these given rod rather like tunnel entrance; howevcr, particles is considered to be fundamentally the in no case has a hollow partiele been observed same as that for thc A and A'particles. Theshape for tellurium. of a rod-like tellurium particle, as deduced frem Fig. 74(a) shows a micrograph of smooth thc observations described abeve and also from round tellurium particles and Fig. 74(b) shows those made in a 1 MeV electron microscope to a selected area diffraction pattern from the par- see the inner structure and the equal thickness ticlc indicated by the arrow in (a). Despite the fringes together with the selected area electron marked difference in shape, the rounded particles have the samc crystal structure as the rod-shaped Fig. 73 particles. The rounded particles, particularly thc Clinegraphic of projection larger ones, are deformed in a certain direction the shape ef a rod-like so as to become egg-shaped instead ef sphericaL particle of Te. 'l.1l',,l 11//1 Fig. 74(a) 1,-eei'}･l:l,' l,1'i･ i･1 i, ll' i-i11･ I,i, ,l･,,l', E 1, ,et" /iE// #=ttt.-t... ,, .,, /':,t/.., ./,' egg- , /. ,l,, ; , . , ., ,/ Te with /{-1il/l'tttttttttttt/t;:l,11.'/:/ tttttttttt / 1:. particles ttt.ttttttt t. . t ":",' tr"':;za't'ltl/':'I,ttaElt/,/t..t/ t/' 1ike shape. ttttttttt t tt :.,/'1/'''1':'/tw ttt tt (b) Selccted area diffraction : pattern from the particlc in- dicated by the arrow in (a). t tttttttt ttt tt ttli'''/rt tt ?rfl tttttt ' ' ' ttttt t t lt tt tttttt tt 1 t,.ttttt Illil,･l･li･ll:f,llV,:-,,,,,.,....,tttt, t , ,.. ttttt t.t// t. tt II,,1:,li:}:,l,1:･:,::.. ' ',:1.e.x t/tttt ....t/"tsut/vt'''.' tt ttt tt Flg. 75 Sketch ofthe tellurium smoke in argon at 4 Torr. The numbers are expressed in terms ofmm. (a) shews a section through the smoke by a vertical plane including the evaporation source at the instant when the smoke first became visible. (b) shows the same vertical section ofthe smoke in its stationary state 10 seconds after thc appearance of (a). Zones A, B and C are referred to as inner, intermediate and outer zones, respectively. P127 Vol.6 No. 3&4 (l61) NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) Fig. 76Micrograpks of the tellu- rium partiales collected at various places in the smoke. Argon 10 Torr. .l me tt ge#ll'th tt w Tt/ ' The direction of the deformation was found to of the source rises and the evaporation centinues, coincide with the [OO,I] direction of the particle. the point P moves downwards and the sheet of Nearly spherical particlesare sometimes observed smoke as a whole swells, the upper part of the among the smaller particles smoke beginning to ascend due to the convection Tellurium is easy to evaporate at relativcly in the argon. When the filament temperature low temperature thc and stable and reproducible reaches the stationary value of about 9000C, as smokc can be obtained easily. The fo11owing are measured by an optical pyrometer, thc shape ef the results of the ebservations on the behaviours the sheet attains its final form which is shown of the smoke of tellurium and some conclusions schematically in Fig. 75(b), the distance t being concerning the growth processes of telluriurn about 15 mm. This sheet of smoke is the interme- particles in the smoke. diate zone. The time which elapses between the Immediately after the tellurium in the vapeur initial appearance of the smoke and the devel- source begins to melt, a sheet ofgrcy smoke about opment of its final form is about 10 seconds. The 1 mm in thickness suddenly appears round the initial and final value of l were approximately Fig. source. 75(a) shows schematically the shape 3 mm and IO mm respectively when the pressure of the sheet of the smoke at the instance of its of the argon was 1O Torr. appearance, The distance l between the tip of Thc final form remained stable until the evap- the vapour source and the point P, bottem of the orant in the source had become exhausted and smoke, was approximately 6 rnm when the pres- was fairly reproducible in different runs providcd sure of the argon was 4 Torr. As the tcmperature the conditions of evaporation were kept constant. 128 (162) H?Sffftntft\kes NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) of 2 mm above er below Thus it was possible to obtain samples from difi placed within a distance This region close to source is ferent locations in diflerent runs yet at the same the vapour source. tirne these samples were characteristic of par- called the vapour zone by Kasukabe et al.i9) inferredthat the ternpera- ticular lecations in a given run. A sample was It has been generally zone is higher obtained by introducing into the smoke an clec- ture of the particles in the inner at the intermediateand tron microscope grid attached to a slender stecl than that of the particles rod. outer zone at thc same level from the vapour source. In fact, it was confirmed by measuring The photographs in Fig. 76 show the cor- the time lapse of the temperatures of thermor rcspondence between the places where the par- locationsin thc smoke ticles were cel]ected and the sizes and shapes of couples placed at various that the temperature of the in the inner the particles. The particles collected at the places particles zone is highcr than the temperature of the g and h indicated in the sketch of Fig. 76 are parti- cles the zoneSO). The small and of the same order of magnitude in in intermediate particles collected in the imer zone arc not size, i.e. 10± 5 nm. They do not show a definite polyhodral but are smoothly rounded 76(a)). crystal habit. The distribution of particles en (Fig. The marked diflbrence between the final shape the substrate is much more dense in h than in g. of tellurium colJected inside and outside The grid placed at h was crossed by the expand- particles the zone suggests that there is a diflbrenee ing intermediate zone before this zone reached inner in the state of the during the its final position whereas the positibn g was in particles growth in these regions. The fact that the shape the outer zone and thc grid placed there was processes of collected in the inner zone is never crossed by the intermediate zone. Thc the particles suggests that thc are photos. g e, d and b in Fig. 76 show particles smoothly rounded particles to a considerable extent in the liquid collected at varying p}aces in the intermediate grown that thermal zone as indicated in the figure. It is apparent that state or at least at temperatures such has destroyod al1 cusps in the a remarkable growth in the size and shape of the agitation r-plot where is the specific surface free energy. It is particles has occurred at location f in the in- 7 that by the time these had termediate zone compared with the particles coniectured particles cooled to thc temperature range where cusps in collected at g and h. The increase in size and the began to appear the had appreach to the final crysta1 form becomc con- the 7-plot particles too massive to undergo the appreciable spicuous along the intermediate zone above e become shape a smoothly rounded which is at the same level as the bottom of the change of from par- ticle to a As Herring`S) has pointcd vapour source. (Note thc diffbrence in magnifica- polyhedron. the energy required for the transport tion between the photos. e, d and b.) The par- out, proc- is too large when ticles collected at b are in their final stage of csses which have to occur compared with the of the total surfacc growth both with respect to size and shape and lowering the On the other hand, the background of the photograph is clear of freeenergies of particles. the tellurium are cooled srnall particles which are always seen in the the majority of particles to the temperature where the sharp cusps in the photos. g e, d and c. The particles collected in at the intermediate the outer zone are small, even though they have 7-plot exist when they arrive they become wel1-defined crystal habits as shown in photo, c, zone. They are small initially but Photographs characteristic of vacuum- polyhedra at a comparatively early stage of fand c deposited thin films were obtained from grids their growth, as indicated by the photos. VoL 6 No. 3&4 (163) 129 NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) in Fig. 76. The particles in the photo. fgrow in (References) the solid state while they are carried up by con- 1) S. Kashu, M. Nagase, C. Hayashi, R. Uyeda, vection in the intermediate zone. The fact that N. Wada and A. Tasaki: Japan. J. appl. Phys. Suppl.2.Part1 no particles of smoothly curved or irregular (19n) 491. 2) R, Kubo: J. Phys. Soc. Japan 17 (1962) 975. shape are observed among those ¢ ollected at a 3) A. Tasaki : Shizen (Nature, in Japanese) No. 4 high level in the intermediate zone indicates that (1972) 50. 4) C. Hayashi:Japan. J. appl. Phys. a given particle continues to grow retaining its Suppl. 2. Part 1 (1974) 241. crystal habit. This mode of growth is considered 5) A. H. Pfund; Phys. Rev. 35 (1930) 1434. to take place by absorbing, through coalescence, 6) A. H. Pfimd: Rev. Sci. Instt 1 (l930) 397. mainly small particles which arc always seen in 7) A, H. Pfund: J.O.S.A. 23 (19S3) 375. 8) L. Harris, D. JeM'ies and B. M. Siegel: J, the background of the photos. g e, d and c in Appl, Phys. 19 (1948) 791. Fig. 76. The contribution to the particlegrowth 9) R. Uyeda and K. Kimoto: Oy6-Butsuri due to direct condensation from the vapour (Japan. J. Appl, Phys,, in Japanese) 18 (1949) 76. phase is probably of negligible importance, for lO) S. Mamiya: HthanLno-Khgatu (Seience of the main growth of the particles occurs in the Light, in Japanese) 1 (1951) 42. region far above the vapour zone. 11) L. Fritsche, F. Wolf and A. Schaber: Z. Naturforschg. 16a 31. The crystal structure of a-tellurium is trigQnal ; (1961) 12) K. Kimoto, Y. Kamiya, M. Nonoyama and it consists of infinitely extended helical chains R. Uyeda: Japan. J. appl. Phys.2 (1963) 702. parallel to the c-axis with three atoms per turn 13) G.-H. Comsa and F. Hensel: Vakuum- Technik 24 169. of a helix. The Te-Te atom distance in a chain (1975) 14) C. G. Granqvist and R. A. Buhrman: J. is 2.83A and each tellurium atom has four Appl. Phys. 47 (1976) 2200. neighbeurs in adjacent chains at 3.49 A3`). 15)16) N. Wada:Japan. J. appl. Phys.8(1969) 551. R. Uyeda, M. Kurnazawa, M, Kato, N. Although the surface energies of tellurium are Wada and M. Matsumoto: Technical Report of not known it is anticipated that there will bc a TOYOTA RD center TD-26 (1973), p. 66 (in large anisotropy in the 7-plot. This anisotropy Japanese). 17>18)N, Wada: Japan, J. appl. Phys.6(1967) 55S. is reflected in the sharp edges and corners of the S. Yatsuya, S. Kasukabe and R. Uyeda: particles and in the extension of the particles Japan. J. appl. Phys. 12 (1973) 1675. along the c-axis. The observed rod-shape of the 19) S. Kasulvabe, S. Yatsuya and R. Uyeda: Japan. J. appL Phys. 13 (1974) 1714. particles corresponds well to their crystal struc- 20) T. Ohno, S. Yatsuya and R. Uyeda: Japan. ture. The at the ends of the rods and protrusions J. appl. Phys. 15 (i976) 1213. the indentations which are sometimes observed 21) T. Hayashi, T. Ohne, S. Yatsuya and R. Uyeda: Japan. J. appl. Phys. 16 (1977) 705. at the ends of the rods may be attributed to the 22)23) N. Wada: Japan. J, appl. Phys. 7 (1968) 1287. kinetics during the of growth growth the particles. J. aitchison and J. A. C. Brown: The Lognormal Distribution (Cambridge University Press, England, 1963). Aclmowledgements The author would 24) C. G. Granqvist and R. A. Buhrman: Solid like to thank Dr. I. NishSda for his help over rnany State Communications 18 (1976) 123. 25) C. G. Granqvist: J. Physique years concerning the study of small particles Colloq. 38 (1977) C2-147. produced by GET. The various investigators 26) G.-H. Comsa: J, Physique Colloq. 38 (1977) who generously permitted the reproduction of C2-185. their figures and electron micrographs arc also 27) G.-H. Comsa, D. Heitkamp and H. S, Rade: Solid State Communications 20 (1976) 877. acknowledged with gratitude. 28) B. K. Chakraverty: J. Phys. Chem. Solids 28 (1967) 2401. 130 (164) H1ptreitetft\kts NII-Electronic Library Service The JapaneseAssociationJapanese Association for Crystal Growth (JACG){JACG) 29) B. K. Chakraverty: J. Phys. Chem. Solids 55) N. Yulcawa, M. Hida, T. Imura, M. 28 (lg67) 2413. Kawamura and Y. Mizuno: Met. Trans. 3 30) R, R. Irani: J. Phys. Chem. 63 (1959) 1603. (1972) 887. 31) R. R. Irani and C. F. Callis: Particle stze 56) N. Yukawa, K. Hattori, N. Okarnoto and lldeasttrement, lateipretation and 4aPtisation (Wiley, T. Tono: Ropurt ofthe 123rd Convnittee en Hlrat- York, 1963) New p, 44, Resisting 2Vtletats and AUojs, Japan Society for the 32) P. G. Wilkinson: J. AppL Phys. 22 (1951) 226. ?romotion of Science. 15 (1974) 309 (in 33) fro ne 1ij,ojttn (Guide to Color Standard, in Japanese). Japanese) ed. by Sanzo Wada (Tokyo, 1954) 57) J. G. Fripiat, K. T. Chow, M. Boudart, J. B. 5th ed. Diamond and K. H Johnson : J. Mole. Cata1ysis 34) J. Donohue: 7;be structures ofthe etements (Jehn 1 (1975176) 59. Wiley & Sons, 1974). 58) A. L. Mackay: Acta Cryst. 15 (1962) 916. 35) A. J, Martin and A. J, Moore: J. Less- 59) K. Kimoto and I. Nishida: Thin Solid Films Common Metals 1 (1959) 85J 17 (1973) 49. 36) V. M. Amonenko, V. E. Ivanov, G. F. 60) T. Ichikawa: Phys. Stat, Sol. (a) 19 (1973) Tikhinski, V. A. Finkel ancl I. V. Spagin: Phys. 707. Metals Metallogr. 12 (1961) 77. 61) I.Nishida:J.Phys.Soc.Japan26(1969)1225. 37) G.A.WolffandJ.G.Gualtieri:Am.Mineral. 62) J. K. Mackenzie, A. J. W. Moore and J. F. 47 (1962) 562. Nicholas:J. Phys. Chem. Solids 23 (1962) 185. 38) A. Fukami and K. Adachi: J. Electron Micro- 63) B. E. Sundquist: Acta Metallurgica 12 (196tl) scopy 14 (1965) 112. 67.64) 39) T. Komoda, I. Nishida and K. KiTnoto: W. Romanowslci:Surfacc Sci. 18 (1969) 373. Japan, J. appl. Phys. 8 (1969) 1164. 65) Y. Fukano: Japan. J. appl. Phys. 13 (1974) 40) W. A. Millcr, G. J. C. Carpenter and G. A. 1001. Chadwick; PhiL Mag. 19 (1969) 305. 66) Y.Fukario:NipponKinzokuGaldcai-h6(Bul1. and I. Japan. J. appl. 41) K. Kimoto Nishida: Japan Inst. Metals; in Japanese) 15 (1976) 639. Phys. 16 (1977) 941. 67) R. W. G. Wyckoff: bystal stnecture (John 42) K. Kimoto and I, Nishida: Japan, J. appl- Wiley and Sons, New Yark, London and 1047. Phys. 6 (1967) Sydncy, 1963) 2nd ed., Vol. I, p. 10. 43) C. Herring: Strttctare and properties of solid 6S) T, Hayashi, Y. Saito, S. Yatsuya, K. Mihama sutt?ices, eds. R. Gomer and C. S. Smith (Univer- and R. Uyeda: J. Ph)rsique Colloq. 38 (1977) sity of Chicago Press, 1953) p. 28, C2-191. 44) C. Herring: Phys. Rev. 82 (1951) 73. 69) Y. Saito, S. Yatsuya, K. Mim and R. K. Kimoto, I. Nishida and R. Uyeda: J. 45) Uyeda: Japan. J. appl. Phys. 17 (1978) 291. Phys. Soc. Japan pa (1965) 1963. 70) Y. Saito, S. Yatsuya, K. Mihama and R. 46) K.KimotoandI.Nishida:J.Phys.Soc.Japan Uyeda: Japan. J. appl. Phys. 17 (1978) 1149. 22 (1967) 744. 71) S. Ino: J. Phys. Soc. Japan 27 (1969) 941. 47) J. Forssell and B. Persson:J. Plrys, Soc. Japan 72) S. Ino: J. Phys. Soc. Japan 21 (1966) 346. 27 (1967) 1368. 73) S. Ogatva, S. Ino, T. Kato and H. Ota: J. 1963. 48) J. Forssell and B. Persson: J. Phys, Soc. Japan Phys. Soc. Japan 21 (1966) 74) K. Mihama and Y. Yasuda: J. ?hys. Soc. 29 (1970) 1532. 49) I. Nishida and K. Kimoto: Thin Solid Films Japan 21 (1966) 1166. 23 (1974) 179. 75) S. Ino and S. Ogawa:J. Phys. Soc. Japan 22 50) M. I. Birjega, F. Gledeanu, N, Popescu- (1967) 1365, Pogrion, I. A. Teodorescu and V. Tepa: Rev. 76) T. Komoda: Japan. J. appl. Phys. 7 (1968) Roum. Phys. 18 (1973) 211. 27.77) 51) V. Topa, M. I. Biniega, C. Sarbu and N J. G. Allpress and J. V. Sanders: Surface Sci. Popescu-Pogrion: Rev. Roum. Phys. 18 (!973) 7 (1967) l. 219. 78) K.KimotoandI.Nishida:J.Phys.Soc.Japan 52) I. Nishida, T. Sahashi and K. Kimoto: Thin 22 (1967) 940. Solid Films 17 (1973) 49. 79) K. Ueda: Oy6-Butsuri (Japan J. appl. Phys., 53) C. G. Granqvist, G, J. Milanowski and R. A. in Japanese) " (1975) 611. and appl. Buhrman: Physics Letters 54A (1975) 245. 80) I. Nishida K. Kimoto: Japan J. 54) N. Yukawa, Y. Fulcano, M. Kawamura and Phys. 14 (1975) 1425. T. Imura: Trans, Japan. Inst. Metals 9 (1968) 81) R. Uyeda: J Cryst, Growth 24125 (1974) 69. 372. 131 VoL 6 No. 3&4 (165) NII-Electronic Library Service