Title a New Polytype of Zinc Selenide Crystal (Commemoration Issue Dedicated to Professor Keinosuke Kobayashi on the Occasion Of

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A New Polytype of Zinc Selenide Crystal (Commemoration Title Issue Dedicated to Professor Keinosuke Kobayashi on the Occasion of His Retirement)

Author(s) Mannami, Michi-hiko

Bulletin of the Institute for Chemical Research, Kyoto Citation University (1977), 55(2): 163-167

Issue Date 1977-08-31

URL http://hdl.handle.net/2433/76732

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Type Departmental Bulletin Paper

Textversion publisher

Kyoto University Bull. Inst. Chem. Res., Kyoto Univ., Vol. 55, No. 2, 1977

A New Polytype of Zinc Selenide Crystal

Michi-hiko MANNAMI*

ReceivedMarch 9, 1977

A new polytype structure of zinc selenide crystal was found in crystals grown from vapor. The crystal structure was found to be eight layered ZnSe lattice having Z(11 21 121, i.e. the packing Aa Bfl Aa Bp Cy Bp Cy BP.

INTRODUCTION

Zinc selenide has been known to have zincblende- and wurtzite-structure,1) although considerable polytype structures are known about similar compounds, e.g. zinc sulphide and silicon carbide. In the course of the electron microscopic study of the growth of zinc selenide crystals from vapor, a new polytype structure was found. The crystal structure of the new polytype and the irregularities in the structure were studied by electron microscopy and diffraction.**

CRYSTAL STRUCTURE OF POLYTYPE OF EIGHT ZN-SE DOUBLE LAYERS

The crystals of zinc selenide were grown from their vapor at 1000°C. Most of the crystals were either zincblende- or wurtzite-structure as has been reported. 2,3) In some of the crystals it was found that there are regions where the crystal structure is different from their surrounding regions of wurtzite structure. This region is a long band parallel to the [1010] direction of the wurtzite structure. Periodic fringes parallel to the (00, 1) planes of the wurtzite structure, i.e. parallel to the close-packed planes, were observed in this band as shown in Fig. 1. The spacing of the regular fringes was 25.0±1.0 A, which is equal to four times as large as the lattice constant co of the wurtzite structure. Figure 2 shows the electron diffraction pattern of the region shown in Fig. 1. The extra spots other than those due to the wurtzite structure are observed and correspond to the spacing of the fringes observed in the micrograph. Thus zinc selenide in this band has the structure having eight Zn-Se double layers in the unit cell. Based on this long periodicity in the direction perpendicular to the close-packed plane, the diffraction spots are indexed as shown in Fig. 2. It was difficult to obtain the diffracted intensities reliable to use for the structure analysis, because of the multiple scattering of the Bragg diffraction. However, the fact that the diffracted intensities are zero at 10,4n+2 spots (n; integer) can be used for the analysis. It is easy to find that there are six possible ways of packing of eight close-packed double * T711 : Department of Physics, Faculty of Science, Kyoto University and Polymer Crystal Labo- ratory, Institute for Chemical Research, Kyoto University. ** A part of the present work was carried out at Surface Physics, Cavendish Laboratory, University of Cambridge.

(163) I\2. MANNAMI

1fiit~ts'* [flE1,,int.fwwli;9E'i1''ii.1'{~l~:Triit;4111,1~(I ti....'1z11i1fisrf0it1111,11H1~',t`ttit°fl~ll.Ill 1~~iiii1i_tirt 1. .?~, r.s{I,fi~l1 1i'rt1pi~ii-i.'r,^1iii :01iH1jI°,r ,'..!,.Ili"'i',11if~rrti(~~~'~~' ~F~'l^t'3tiF~'IlitiIirf1r}flii~r`Icii('r'q('/.11,.1#ijitEIliti}ifii ~: I~~11,i,`i~i~~r~]]((itti}}!i)1Ii' I1jt.S 401i1lrid111fi11I0)fi.r'l'IIlltdifi§{frlt"1r}}rr((fff:~~1li~~(jII{^di~jJill(I(

i1[ I3ffitj-IiI • r~~_li.fl;~I tifEi•~~ i` f~~1 1'i.rf ~r iiI :r,. f11(i'ii`lil.I.l!~~ 1a 1~~il,l } 1(i~IIItl~EI~~~l~l~fIi~~~I ~~~,'1 Ep^1'=~~,iI~(,t~IJ~ I1t'4 ~~~1iflillIiOliit;ill(l(ii^r1j~{'i'~}i~',1if(r'lirjifiliI'E~r it I irItit}~1ff~Iillif,.{I1~yl)iI(lI~{i~1i1~~rIf1ill~~~;ll~1,1,'it~'.,I.1,',l~Ii,!IMO 1=pl1,'1l1i1'f':.1,,1fli: i11~ir~,l11$ ,11/i11;;ifi'lC•iiiiI 11.i1±gi' Ii;ill!III'1111"1I111l1111•ili°i.~1lIi~,III;(!I`I'i1u1.1iail^((iiliiIib~i'1liitI111^i' r,''4 i}}iilIl~i,Y1!i11lSI'~; E,' : Ii's 111,'1f~a ,'4;1,ifItj `

• 10 ,4 10,3 10,2 '*10 ,1 *10,0

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Fig. 2. The electron diffraction pattern from the crystal shown in Fig . 1.

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i * i A New Polytype of Zinc Selenide Crystal layers of Zn and Se atoms to form 4coperiodicity of hexagonal symmetry (co is the lattice constant of wurtzite structure of ZnSe). They are, following Zhdanov symbol4); Z(11 11 22) Aa B/3 Aa B/3 Aa B/3 Cy B/3 Z(11 21 12) Aa B/3 Aa B/3 Cy B/3 Cy B/3 Z(11 33)Aa B/3 Aa B/3 Aa Cy B/3 Cy Z(12 32)Aa B/3 Aa B/3 Cy B/ Aa Cy Z(17)Aa BP Aa BP Cy Aa B/3 Cy Z(44)Aa BP Aa Cy BP Aa B/3 Cy, where Aa, B/3,Cy show the packing positions of Zn-Se double layer. The crystal structure factors for the diffraction of electrons of these possible structures were calculated for (10, 1). The atomic scattering amplitudes for electrons tabulated in the International Tables for X-ray Crystallography were used in the calculated.5) The results are shown in the Table I. In order to compare the observed intensity distribution and the calculated ones, it was assumed that the IFkkrI2-law'isa good approximation. The structure which has zero or negligible values of IF1.o,r12for 1=4n+2 was searched. Fortunately it was only Z(11 21 12) structure that satisfies the condition. The most probable structure is, therefore, Z(11 21 12). The unit cell of this polytype is hexagonal and the lattice constants are; ao=4.00+0.04 A, co=26.1+0.3 A. This polytype structure is different from the corresponding eight layered polytype Z(44) found in SiC and ZnS crystals.

Table I. !Flo,z12 of Six PossibleStructures (A2)

ructure 10 indices10, 7 St , 0 10,1 10,2 10,3 10,4 10,5 10,6 10,7 10,8 Z (11 11 22) 626 266 258 247 3015 215 197 179 348 Z (11 21 12) 358 531 0 493 2784 430 0 358 199 Z (11 33)89 421 258 1088 1624 949 197 284 50 Z (12 32)89 669 69 970 2088 319 736 12 50 Z (17)89 177 965 3617 232 86 53 45 50 Z (44)89 46 775 1439 696 1255 591 31 50

50A I ~

61A Fig. 3. An exampleof microdensitometer traces of the fringes. (165) M. NIANNAMI

0,3 10,2 i 10, 1 +10,0

Fig. 4. The electrondiffraction pattern from the crystalshowing irregular fringe periodicity. As the structure factors F00,1is zero for any of the possible packings of eight Zn-Se double layers, it is supposed that the periodic fringes in the electron micrographs are formed by the interference of the transmitted beam and 00,1 diffracted beam, which is formed by the effect of multiple Bragg diffraction.

IRREGULARITIES IN Z (11 21 12) STRUCTURE

The electron micrograph shown in Fig. 1 has irregularities in the fringe periodicity. Figure 3 shows an example of microdensitometer traces of the fringes. Most of the irregularities had the width 5/4 of the spacing of the regular fringes, which are equal to ten double layers. This suggests the possibility that the new polytype of ten double layered Zn-Se could be formed under this condition of crystal growth. There were other types of irregularities in the fringe spacing which were wider than ten double layers. The electron diffraction patterns from less regular fringed region gave some anomalies as shown in Fig. 4. The broad and sometimes weak intensity distribution were observed at h0,4n+2, and h0,4n+1 spots became broad and appeared closer to the neighboring h0,4n spots. These anomalies depended on the irregularity of the fringes. These diffraction patterns can be interpreted due to the irregular packing of the close-packed planes.

ACKNOWLEDGMENTS

The author thanks Dr. A. D. Yoffe for his interest in this work. His thanks are due (166)

4• • A New Polytype of Zinc Selenide Crystal to Mrs. E. H. Pogson for her assistance in preparation of crystals and due also to Prof. Kakinoki for his critical comment on the structure determination of polytype.

REFERENCES

(1) E. Crucianu and Y. D. Chistyakov, Kristallografia, 5, 354 (1960). (2) A. G. Fitzgerald, M. Mannami, E. H. Pogson, and A. D. Yoffe, Phil. Mag., 13, 197 (1966). (3) A. G. Fitzgerald, M. Mannami, E. H. Pogson, and A, D. Yoffe, J. Appl. Phys., 38, 3303 (1967). (4) F. C. Frank, Phil. Mag. 42, 1014 (1951). (5) J. A. Ibers and W. C. Hamilton, Ed., "International Tables for X-Ray Crystallography," Vol. 4, The Kynoch Press, Birmingham, 1974.

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