DOCSLIB.ORG

Cohesive Mechanism and Structure of Cluster-Assembled Solid Al12c

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Cohesive Mechanism and Structure of Cluster-Assembled Solid Al12c CBPF-NF-030/96 CohesiveMechanism and Structure of Cluster-Assembled Solid Al C 12 X.G. Gong Centro Brasileiro de Pesquisas Fisicas, Rua Dr. Xavier Sigaud, 150-Urca RJ, Brazil Institute of Solid State Physics, Academia Sinica, 230031-Hefei, China Abstract Wehave prop osed a p ossible crystal structure for the cluster-assembled solid Al C, 12 and its electronic structures and stabilityhave b een studied in the framework of the density functional theory and ab-initio molecular-dynamics. We nd that Al C clusters are con- 12 densed byvan der Waals force, with a very small cohesive energy of 1.1 eV. A signi cant energy gap exists in solid, which suggests that it can b e a novel semiconductor. The com- bined steep est descent calculations show that up on the formation of solid, the relaxation of atomic distances of the Al C cluster is very small. The stability of the Al C solid is 12 12 also con rmed by a dynamical simulation at low temp erature. Key-words: Cluster-assembled Al C. 12 PACS. No. 36.40; 61.50Lt; 71.15Mb+Pd -2 - CBPF-NF-030/96 In the past decades, a great deal of e orts have b een devoted to the synthesizing and the fundamental understanding of new materials in atomic dimension[1]. With the discovery of C molecule and its solid phase[2], an enormous interest in the study of cluster 60 and cluster-assembled materials has b een aroused. Since the prop erties of clusters are quite di erent from that of atoms, it is reasonable to exp ect that the cluster-assembled materials haveunusual prop erties, whichwould b e quite di erent from that in atomic solid phase, like what observed in solid C [3]. To obtain the cluster-assembled materials, a high stability 60 of the clusters is usually essential, otherwise the clusters would coalesce when bringing them together, and the merits for synthesizing the cluster-assembled materials would b e lost, it is also necessary to have smaller interaction b etween clusters as compared to the interaction in the cluster itself. Recently, from the total energy and electronic structure calculations[4], it had b een found that the stabilityofAl cluster can b e signi cantly enhanced by doping with a 13 tetravalent carb on atom. Since there exists ab out 2 eV gap b etween the highest o ccupied molecular orbitals(HOMO) and the lowest uno ccupied molecular orbitals(LUMO), the in- teraction b etween Al C cluster can b e exp ected to b e small. Therefor the Al C cluster 12 12 is suggested to b e a go o d candidate to form a cluster-assembled solid. In fact, the high stabilityofAl C cluster was con rmed by a few recent studies[5,6]. Seitsonen et al.[6] 12 studied the dynamical stabilityofAl C cluster by Car-Parrinello metho d, and they found 12 that, even ab ove 900 K, the structure of Al C cluster remains icosahedral-like, which 12 indicates that the Al C cluster is indeed stable. Moreover, Kawai et al.[5] have studied 12 the interaction b etween twoAl C clusters byCar-Parrinello metho d, they found that 12 the structure of Al C clusters remains unchanged. However no successful studies for the 12 cluster-assembled Al C solid have b een made. Seitsonen et al.[6] studied the prop erties 12 of Al C solid with fcc-like structure, but they found that the total energies increased 12 monotonically with the decreasing of the lattice constant, and there is no lo cal minimum which is necessary for the formation of a meta-stable phase. In this letter, based on the recentsimulation on the cluster dimer and cluster- as- sembled solid[7], we prop ose a crystal structure for the Al C solid. In the total energy 12 calculations, wehave obtained a minimum at lattice constant of 30.8 a.u., and wedo nd that the interaction b etween the clusters in Al C solid is very weak, and the cohesive en- 12 ergy is very small. By p erforming the combined steep est descent on the ions and electrons, and dynamical simulation at low temp erature, weshow that Al C solid is a stable van 12 -3 - CBPF-NF-030/96 der Waals solid. As discussed by Khannan and Jena, the geometric e ects are imp ortant in the cluster- assembled materials[8]. In the icosahedral Al C cluster, although 12 aluminum atoms are 12 homogeneously distributed on a spherical surface, it can not b e rotational invariantlike a rare-gas atom. It is well known that, even in the icosahedral fullerene of C , which 60 has a smo other surface since it contains 60 carb on atoms on the surface, various phases with di erent rotational order have b een observed at low temp erature[9]. Obviously, the relative orientation of clusters mayplay an imp ortant role in the formation of a solid from the icosahedral Al C clusters. 12 The recent simulations on the cluster dimer (two icosahedral 13-atom clusters) and cluster-assembled solid with the Leonard-Jones p otential show that[7], the relative cluster orientation is very imp ortant for the stability of the cluster dimer. If we put 12 surface atoms of a b o dy-center icosahedron on the six faces of a cubic b ox, the most stable struc- ture for a cluster dimer is with two cubic b oxes in alternated orientation of 90 degrees, as shown in Fig. 1. In fact, only in this con guration, the mass centers of two icosahedron can approach more closely than any other isomers whichhave higher energies, as con rmed by the charge densityshown b elow. This suggests that, when the clusters are brought together, they should b e prop erly arranged according to their geometric shap e. In fact, the intuitive fcc-like structure, whichisthelowest energy structure for the atomic van der Waals solid, was proved to b e unstable for cluster-assembled Al C solid. So, wehave 12 tried to design a structure for Al C solid, in whicheachAl C cluster is alternated 90 12 12 degrees with all its nearest neighb ours. This turns out to b e a cubic-like structure, each unit cell contains eightAl C clusters. Actually, similar structure has b een observed in 12 AB system[10], where B has icosahedral structure, the large atom A is b elieved to b e 13 13 an electron donor to close the electronic shell of B whichmakes B stable[11]. To show 13 13 whether this structure is stable for Al C solid, wehave p erformed rst principles calcula- 12 tion and ab-initio molecular-dynamics simulation, and its stability is con rmed. With the same crystal structure, wehave studied the prop erties of the cluster-assembled Al Si solid 12 whichwas proved to b e unstable for fcc-like structure[12], and also the cluster-assembled solid Al K, whichwas suggested to have CsCl structure[13] but recent calculation showed 13 that icosahedral Al K cluster would not b e stable in CsCl structure[14]. The results on 13 Al Si and Al K solid will b e published elsewhere[15]. 12 13 All our calculations are based on the density functional theory with the lo cal density -4 - CBPF-NF-030/96 approximation[16] and Car-Parrinello metho d[17]. The electronic density is expressed in terms of Kohn-Sham orbitals[18], which are expanded into plane waves with energy cuto of 35Ry. Only the valence electrons are treated explicitly and their interactions with the ionic cores are describ ed by the Bachelet-Hamann-Schluter typ e pseudop otentials[19] with sp non-lo cality for Al and also for C. The minimization of the energy functional is p erformed with conjugate gradient for the xed atomic distances, also with combined the steep est descent for electrons and ions in Al C solid at a lattice constant of 30.8 a.u. 12 Wehave used time step of 4.0 a.u. and ctitious mass of 300 a.u for electrons in all the calculations. At rst, wehave studied the isolated icosahedral Al C cluster. Due to the plane wave 12 expansion, one is forced to use p erio dical b oundary condition. We use only the p ointof Brilliouin zone in the k-summation. To erase the interaction b etween the cluster and its images, it is necessary to haveavery large cell. As it was observed by Seitsonen et al.[6], wehave found that a fcc-cell with the lattice constantupto30a.u.isenoughtomake the interaction b etween the cluster and its images negligible. This can also b e con rmed by the total charge densityofAl C cluster, as shown in Fig. 2. By calculating the total 12 energies at di erent Al-C distances, wehave got the equilibrium Al-C distance of 4.69 a.u. which is equal to what was obtained in Ref.[6]. The obtained binding energy value of 45.9 eV is also comparable to 45.3 eV obtained by Seitsonen et al., and the small di erence may come from di erent psudop otentials used for carb on. These results are also in agreement with the results of other previous ab-initio metho ds[20]. To calculate the cohesive energy of Al Csolid,wehave used a primitive cell with two 12 Al C clusters. By changing the lattice constant with rigid cluster, the di erentcohesive 12 energies can b e obtained, and its values, relative to the isolated clusters, are shown in Fig.
Load more

Recommended publications
  • 1. INTRODUCTION Geometric Structure
    1. INTRODUCTION Clusters, in general, are aggregates of atoms that are too large compared to atoms and molecules and too small compared to small pieces of crystals (bulk materials). Generally, clusters does not have the same structure or atomic arrangements as a bulk solid and can change its structure with the addition of just one or few atoms. As the number of atoms in the cluster increase, the bulk structure is established and the addition of atoms has no more effect on the structure. Of course there will be some rearrangement of the atoms on the surface of this bulk structure, but since the surface to volume ratio is very low in bulk material it can be neglected with a good approximation. However, in case of clusters, most of the atoms lie on the surface (extremely high surface to volume ratio) and such rearrangement produce a drastic effect. Owning to their high surface to volume ratio, the surface science from both chemical and physical point of view has become crucial in order to collect data and information about such systems. The ways to study such small cluster is nearly the same as the way they have been fabricated. With Bottom-up approach (chemical point of view) these clusters are formed from atoms and/or molecules by assembling it together to form the cluster, and there were many calculation based on this view point. Also these clusters can be fabricated, starting from the bulk material by reducing its dimension somehow, which is the Top-down approach. Geometric structure Usually the crystal structure of a large nanocluster is the same as the bulk structure of the material, with somewhat different lattice parameters (in general clusters are slightly contracted as compared to bulk).
    [Show full text]
  • Transformation of Doped Graphite Into Cluster- Encapsulated Fullerene Cages
    ARTICLE DOI: 10.1038/s41467-017-01295-9 OPEN Transformation of doped graphite into cluster- encapsulated fullerene cages Marc Mulet-Gas1, Laura Abella2, Maira R. Cerón 3, Edison Castro 3, Alan G. Marshall1,4, Antonio Rodríguez-Fortea 2, Luis Echegoyen3, Josep M. Poblet 2 & Paul W. Dunk 1 An ultimate goal in carbon nanoscience is to decipher formation mechanisms of highly ordered systems. Here, we disclose chemical processes that result in formation of high- 1234567890 symmetry clusterfullerenes, which attract interest for use in applications that span biome- dicine to molecular electronics. The conversion of doped graphite into a C80 cage is shown to occur through bottom-up self-assembly reactions. Unlike conventional forms of fullerene, the iconic Buckminsterfullerene cage, Ih-C60, is entirely avoided in the bottom-up formation mechanism to afford synthesis of group 3-based metallic nitride clusterfullerenes. The effects of structural motifs and cluster–cage interactions on formation of compounds in the solvent- extractable C70–C100 region are determined by in situ studies of defined clusterfullerenes under typical synthetic conditions. This work establishes the molecular origin and mechanism that underlie formation of unique carbon cage materials, which may be used as a benchmark to guide future nanocarbon explorations. 1 National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA. 2 Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Tarragona 43007, Spain. 3 Department of Chemistry, University of Texas at El Paso, El Paso, TX 79968, USA. 4 Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA. Marc Mulet-Gas and Laura Abella contributed equally to this work.
    [Show full text]
  • Clusters: Structure, Energetics, and Dynamics of Intermediate States of Matter A
    Subscriber access provided by Johns Hopkins Libraries Article Clusters: Structure, Energetics, and Dynamics of Intermediate States of Matter A. W. Castleman, and K. H. Bowen J. Phys. Chem., 1996, 100 (31), 12911-12944• DOI: 10.1021/jp961030k • Publication Date (Web): 01 August 1996 Downloaded from http://pubs.acs.org on May 8, 2009 More About This Article Additional resources and features associated with this article are available within the HTML version: • Supporting Information • Links to the 42 articles that cite this article, as of the time of this article download • Access to high resolution figures • Links to articles and content related to this article • Copyright permission to reproduce figures and/or text from this article The Journal of Physical Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 J. Phys. Chem. 1996, 100, 12911-12944 12911 Clusters: Structure, Energetics, and Dynamics of Intermediate States of Matter A. W. Castleman, Jr.* Department of Chemistry, PennsylVania State UniVersity, 152 DaVey Laboratory, UniVersity Park, PennsylVania 16802 K. H. Bowen, Jr. Department of Chemistry, The Johns Hopkins UniVersity, 3400 N. Charles Street, Baltimore, Maryland 21218 ReceiVed: April 4, 1996; In Final Form: June 20, 1996X The field of cluster research can trace its origins back to the mid-nineteenth century when early studies of colloids, aerosols, and nucleation phenomena were reported. The field underwent a resurgence of interest several decades ago when well-defined clusters were observed in supersonic expansions that could be investigated using mass spectrometers. The advent of the laser provided a new dimension, enabling detailed spectroscopic observations through the probing of systems of varying size and degree of solvation.
    [Show full text]
  • Transformation of Doped Graphite Into Cluster- Encapsulated Fullerene Cages
    ARTICLE DOI: 10.1038/s41467-017-01295-9 OPEN Transformation of doped graphite into cluster- encapsulated fullerene cages Marc Mulet-Gas1, Laura Abella2, Maira R. Cerón 3, Edison Castro 3, Alan G. Marshall1,4, Antonio Rodríguez-Fortea 2, Luis Echegoyen3, Josep M. Poblet 2 & Paul W. Dunk 1 An ultimate goal in carbon nanoscience is to decipher formation mechanisms of highly ordered systems. Here, we disclose chemical processes that result in formation of high- 1234567890 symmetry clusterfullerenes, which attract interest for use in applications that span biome- dicine to molecular electronics. The conversion of doped graphite into a C80 cage is shown to occur through bottom-up self-assembly reactions. Unlike conventional forms of fullerene, the iconic Buckminsterfullerene cage, Ih-C60, is entirely avoided in the bottom-up formation mechanism to afford synthesis of group 3-based metallic nitride clusterfullerenes. The effects of structural motifs and cluster–cage interactions on formation of compounds in the solvent- extractable C70–C100 region are determined by in situ studies of defined clusterfullerenes under typical synthetic conditions. This work establishes the molecular origin and mechanism that underlie formation of unique carbon cage materials, which may be used as a benchmark to guide future nanocarbon explorations. 1 National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA. 2 Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Tarragona 43007, Spain. 3 Department of Chemistry, University of Texas at El Paso, El Paso, TX 79968, USA. 4 Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA. Marc Mulet-Gas and Laura Abella contributed equally to this work.
    [Show full text]
  • A Unified View of Ligand-Protected Gold Clusters As Superatom Complexes
    A unified view of ligand-protected gold clusters as superatom complexes Michael Walter†, Jaakko Akola†‡, Olga Lopez-Acevedo†, Pablo D. Jadzinsky§¶, Guillermo Calero§, Christopher J. Ackerson§ʈ, Robert L. Whetten††, Henrik Gro¨ nbeck‡‡, and Hannu Ha¨ kkinen†§§¶¶ Departments of †Physics and §§Chemistry, Nanoscience Center, University of Jyva¨skyla¨, FI-40014 Jyva¨skyla¨, Finland; ‡Institut fu¨r Festko¨rperforschung, Forschungszentrum Ju¨lich, D-52425 Ju¨lich, Germany; §Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305; ¶Department of Applied Physics, Stanford University, Stanford, CA 94305; ††School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332; and ‡‡Competence Centre for Catalysis and Department of Applied Physics, Chalmers University of Technology, SE-41296, Go¨teborg, Sweden Edited by Royce W. Murray, University of North Carolina, Chapel Hill, NC, and approved April 10, 2008 (received for review January 31, 2008) Synthesis, characterization, and functionalization of self-assembled, 6s orbitals (10, 11), representing a finite-system analogy to the ligand-stabilized gold nanoparticles are long-standing issues in the bulk conduction electron states, which have 6s-character close to chemistry of nanomaterials. Factors driving the thermodynamic the Fermi surface. Exceptional stability is associated with a total stability of well documented discrete sizes are largely unknown. count of Herein, we provide a unified view of principles that underlie the stability of
    [Show full text]
  • Experimental Evidence for Interatomic Coulombic Decay in Ne Clusters
    PHYSICAL REVIEW LETTERS week ending VOLUME 90, NUMBER 20 23 MAY 2003 Experimental Evidence for Interatomic Coulombic Decay in Ne Clusters S. Marburger, O. Kugeler, and U. Hergenhahn* Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany and Max-Planck-Institute for Plasma Physics, Boltzmannstrasse 2, 85748 Garching, Germany T. Mo¨ller Hamburger Synchrotronstrahlungslabor HASYLAB, Notkestrasse 85, 22603 Hamburg, Germany (Received 11 November 2002; published 23 May 2003) Electron spectra of photoexcited Ne clusters are shown to display a signal at low kinetic energies that is neither present in the Ne monomer nor at photon energies below the inner-valence 2s threshold. These findings are strong evidence for the existence of interatomic Coulombic decays (ICD), a mechanism that was recently predicted theoretically [Phys. Rev. Lett. 79, 4778 (1997)]. In ICD, an inner-valence hole state in a weakly bonded system can undergo ultrafast relaxation due to energy transfer to a neighboring atom, followed by electron emission from this neighboring site. DOI: 10.1103/PhysRevLett.90.203401 PACS numbers: 36.40.Mr, 33.80.Eh, 34.30.+h, 82.33.Fg The nonradiative decay of a core hole vacancy in an ICD make a relatively higher contribution to the signal excited atom by electron emission is a well known process close to zero kinetic energy. in spectroscopy, commonly denoted as Auger decay. In this Letter we present direct experimental evidence Traditionally, it is assumed that in extended aggre- for ICD in the photoexcited electron spectra of small Ne gates—molecules or bulk matter—electrons only at the clusters.
    [Show full text]
  • Nanoparticles and Nanotechnology Research
    Journal of Nanoparticle Research 1: 1–6, 1999. © 1999 Kluwer Academic Publishers. Printed in the Netherlands. Editorial Nanoparticles and nanotechnology research M.C. Roco (Editor-in-Chief) McLean, Virginia, USA; Address for correspondence: National Science Foundation, Directorate of Engineering, 4201 Wilson Blvd, Suite 525, Arlington, VA 22230, USA (Tel.: 703 306 1371; Fax: 703 306 0319; E-mail: [email protected]) We would like to welcome you to this new journal discoveries in this field will require matching via a short (JNR) that has its origin in the significant and grow- publication cycle, particularly of the letters to the edi- ing interest in nanoscale science, engineering and tech- tor and brief technical communications. nology. The focus of the journal is on the specific Nanoparticles are seen either as agents of change properties, phenomena, and processes that are realized of various phenomena and processes, or as building because of the nano size. Experimental and theoretical blocks of materials and devices with tailored charac- tools of investigation at nanoscale, as well as synthe- teristics. Use of nanoparticles aims to take advantage sis, processing and utilization of particles and related of properties that are caused by the confinement nanostructures are integral parts of this publication. effects, larger surface area, interactions at length scales The overall objective is to disseminate knowledge where wave phenomena have comparable features to of the physical, chemical and biological phenomena the structural features, and the possibility of gen- and processes in structures that have at least one erating new atomic and macromolecular structures. length scale ranging from molecular to approximately Important applications of nanoparticles are in disper- 100 nm (or submicron in some situations), and exhibit sions and coatings, functional nanostructures, consol- novel properties because of size.
    [Show full text]
  • And Deuterium D(0) and Their Relation to Ordinary Rydberg Matter: a Review
    Physica Scripta PAPER • OPEN ACCESS Ultradense protium p(0) and deuterium D(0) and their relation to ordinary Rydberg matter: a review To cite this article: Leif Holmlid and Sindre Zeiner-Gundersen 2019 Phys. Scr. 94 075005 View the article online for updates and enhancements. This content was downloaded from IP address 131.169.5.251 on 06/05/2019 at 14:09 Physica Scripta Phys. Scr. 94 (2019) 075005 (26pp) https://doi.org/10.1088/1402-4896/ab1276 Ultradense protium p(0) and deuterium D(0) and their relation to ordinary Rydberg matter: a review Leif Holmlid1 and Sindre Zeiner-Gundersen2 1 Atmospheric Science, Department of Chemistry and Molecular Biology, University of Gothenburg, SE-412 96, Göteborg, Sweden 2 Norrønt AS, Vaterlandsveien 19, 3470 Slemmestad, Norway and Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavik, Iceland E-mail: [email protected] Received 5 November 2018, revised 22 February 2019 Accepted for publication 22 March 2019 Published 24 April 2019 Abstract The extremely large density of ultra-dense hydrogen H(0) has been proved in numerous experiments by three laser-induced methods, namely Coulomb explosions observed by particle time-of-flight (TOF) and TOF mass spectrometry, rotational emission spectroscopy in the visible, and annihilation-like meson ejecting nuclear reaction processes. The density of H(0) at the quite common spin level s = 2 is of the order of 100 kg cm−3. The theory of ultra-dense hydrogen H(0) is described briefly, especially the ‘mixed’ spin quantum number s and its relation to the internuclear distances. The orbital angular momentum of the bonding electrons in H(0) is l=0, which gives the H(0) designation.
    [Show full text]
  • Nanotechnology: the New Features
    Nanotechnology: The New Features Gang Wang Dept. of Computer Science and Engineering University of Connecticut Email: [email protected] or [email protected] Abstract—Nanotechnologies are attracting increasing invest- of bulk materials and single atoms or molecules [3]. Using ments from both governments and industries around the world, structures designed at this extremely small scale, there exist which offers great opportunities to explore the new emerging opportunities to build materials, devices, and systems with nanodevices, such as the Carbon Nanotube and Nanosensors. This nano-properties that can not only enhance existing technolo- technique exploits the specific properties which arise from struc- gies but also offer novel features with potentially far-reaching ture at a scale characterized by the interplay of classical physics technical, economic, and societal implications [4]. and quantum mechanics. It is difficult to predict these properties a priori according to traditional technologies. Nanotechnologies Nanotechnology products can be used for the design and will be one of the next promising trends after MOS technologies. processes in various areas. It has been demonstrated that nan- However, there has been much hype around nanotechnology, both otechnology has many unique characteristics, and can signifi- by those who want to promote it and those who have fears about its potentials. This paper gives a deep survey regarding different cantly fix the current problems which the non-nanotechnology aspects of the new nanotechnologies, such as materials, physics, faced, and may change the requirement and organization of and semiconductors respectively, followed by an introduction of design processes with its unique features [5].
    [Show full text]
  • Cluster in Helium-Tropfen Fortgeschrittenen-Praktikum 3
    Cluster in Helium-Tropfen Fortgeschrittenen-Praktikum 3 Introduction into Cluster physics [1] Clusters have been experimentally produced the first time in the middle of last century. Since 1980 the interest in cluster physics have grown rapidly because clusters are of special interest for catalysis, photography, physics and chemistry of aerosols and the growing of such complexes in space, and the structure of amorphous substances. As a general definition the expression cluster means an ensemble of particles (atoms or molecules) which are linked by certain kind of bond. Homogeneous clusters consist only of the same kind of atoms or molecules whereas mixed clusters consisting of different atoms are denoted as heterogeneous clusters. At this point the question arises which number of atoms or molecules is necessary to speak of clusters. Märk [2] defines as the minimum size 2 for a cluster, i.e. the dimer. Type of cluster Example Binding forces Mean binding energy Van-der Waals (rare gas)n, (H2)n Van der Waals forces 0.01-0.3 eV clusters (induced dipole interaction) Valence clusters Cn, S8,As4 Chemical forces (covalent 1-4 eV bond) Ionic clusters (NaCl)n Ionic bond (Coloumb force) 2-4 eV Hydrogen-bonded (H2O)n, (HF)n, Dipole-dipole 0.15-0.5 eV clusters (HNO3)n interaction Molecular clusters (I2)n, (organic molecules)n Like Van der Waals 0.3-1 eV with additionial covalent contribution Metallic clusters (alkali metal)n, Aln, Cun, Dispersion covalent metallic 0.5-3 eV Fen, Ptn Table 1. Classification of clusters by their binding properties and mean binding energies.
    [Show full text]
  • Structure of a Thiol Monolayer-Protected Gold Nanoparticle at 1.1 Å Resolution
    Science Highlight – December 2007 Structure of a Thiol Monolayer-Protected Gold Nanoparticle at 1.1 Å Resolution Nanometer-size metal particles are of fundamental interest for their chemical and quantum electronic properties, and of practical interest for many potential applications [1, 2]. Historically gold nanoparticles are the best studied, dating back to ancient Rome where colloidal gold was thought to have medicinal properties due to its blood red color. Gold has proven to have applications in medicine with some modern arthritis drugs using gold compounds. With all this interest in gold parti- cles the structure of a thiol-protected gold nanoparticle had yet to be unambiguously determined. Electron microscopy [3,4], powder x-ray diffraction [5] and theoretical studies [6] had led to the idea that gold nanoparticles would adopt closed geometric shells with crys- talline packing. This would lead to defined core sizes such that the gold clusters would have a discrete number of atoms representing closed geometric shells [7]. For example icosahedrally packed gold clusters were predicated to have "magic number" sizes corresponding to 55, 147, 309. An alternative to the closed geometric model was the jellium model, which predicted closed electronic shells instead of geometric shells (reviewed in Rev. Mod. Phys 65, 611- 676). Testing of these theories requires the unambiguous structural determination of a Fig. 1. X-ray crystal structure determination series of gold nanoparticles. of Au102(p-MBA)44 nanoparticle. Electron density map (red mesh) and atomic Structural determination of thiol protected gold structure (gold atoms depicted as yellow spheres, p-MBA shown as framework and nanoparticles has been complicated by the small spheres sulfur in cyan, carbon in gray problem that particles are typically heteroge- and oxygen in red).
    [Show full text]
  • The Recent State of Endohedral Fullerene Research
    a Sc2C2 carbide cluster is included in a D2d-C84 cage (Fig. 2a). Meanwhile, dimetallofullerenes of scandium often reduce the larger cage size by forming a 6 Sc2C2 cluster. As the existence of such a carbide cluster fullerene was also proved 7,8 for a diyttrium structure with Y2C2, one asks whether only scandium and yttrium metals can form such carbides. Nevertheless the structures isolated so far show that metal carbide endohedral fullerenes represent a type of endohedral fullerenes with a cluster inside. Cages other than C82 demonstrably also encase the metal carbide inside. Among the multimetallofullerenes, the Sc3@C82 structure was important as the three metal ions were shown by electron spin resonance (ESR) spectroscopy to be completely equivalent in the position and redox The Recent State of state of each of the scandium ions.9 Furthermore the position of the Endohedral Fullerene Research scandium ions inside the cage can be changed at lower temperatures as by Lothar Dunsch and Shangfeng Yang detected by ESR spectroscopy.10 As the equivalence of the three scandium ions inside the cage seemed ince the last general reviews in cages have been isolated. This group to point to a balanced ordering of them, the field of endohedral fullerenes of multimetallofullerenes considerably it was surprising that in a recent study by Shinohara in 20001 and by extended the scope of the field by S a carbide endohedral fullerene was Akasaka and Nagase in 2002,2 the giving rise to completely new types of proposed by the group of Akasaka.11 variety of endohedral structures has endohedral fullerenes.
    [Show full text]