bluuebunny/crossref_metadata_2025 huggingface dataset:
CHEMISORPTION OF O2 AND CO ON COPPER CLUSTERS
Authors: GRÖNBECK HENRIK , ROSÉN ARNE
Published: October 2004

The initial chemisorption of O 2 and CO on small copper clusters in the range from six to nine atoms has been investigated using a self-consistent jellium description of the clusters. The calculations were performed within the local-density approximation expanding the wave functions in a linear combination of atomic and spherical jellium orbitals. The results indicate a strong size dependence in the chemisorption energies. O 2 was found to be most strongly bound to the Cu 9 cluster while COCu 6 was the most stable product in the case of CO chemisorption. The observations are consistent with experiments and the underlying reasons were traced to differences in cluster-adsorbate hybridization and charge-transfer mechanisms.
IRON CLUSTERS AND OXYGEN-CHEMISORBED IRON CLUSTERS
Authors: WANG LAI-SHENG , FAN JIAWEN , LOU LIANG
Published: October 2004

The photoelectron spectroscopy of size-selected [Formula: see text](n=3–24) clusters and oxygen-chemisorbed clusters Fe n O −(n=1–16), has been studied at 3.49-eV photon energy with a magnetic-bottle time-of-flight photoelectron spectrometer. While the spectra of the pure iron clusters show rather sharp features in the whole size range, those of the oxygen-chemisorbed species are considerably different, with extensive sharp structures observed for n only up to 6. The electron affinities (EAs) of both the bare and chemisorbed clusters exhibit strong size variations. However, the first oxygenation of the iron clusters induces a systematic lowering of EA in the size range n=9–15. Towards a complete molecular picture of these interesting clusters, density-functional calculations are being performed to determine the equilibrium cluster structures, oxygen chemisorption sites, and their electronic structures. The equilibrium structures obtained for Fe n O with n=2–6 are reported.
FERROMAGNETISM OF ALKALI-METAL CLUSTERS INCORPORATED IN THE PERIODIC SPACE OF ZEOLITE LTA
Authors: NOZUE Y. , KODAIRA T. , OHWASHI S. , TOGASHI N. , TERASAKI O.
Published: October 2004

Magnetic properties are reported for rubidium and potassium clusters arrayed in a simple-cubic structure in zeolite LTA crystal. A ferromagnetism is observed, although no magnetic element is contained there. The result clearly indicates the intercluster interaction. The ferromagnetic properties vary depending on the average number of ns electrons of cluster. Optical properties reveal quantum electronic levels of cluster. The ferromagnetism is interpreted qualitatively in terms of the itinerant electron model based on the quantum levels of cluster. The magnetic properties of various clusters observed in zeolites are discussed from the microscopic point of view.
OPTICAL PROPERTIES OF CdS AND Se CLUSTERS IN ZEOLITES
Authors: ARAI T. , MURAI M. , OHMORI J. , MATSUISHI K. , ONARI S.
Published: October 2004

We have studied the electronic and vibrational properties of CdS and Se clusters in zeolites by Raman scattering and photoluminescence measurements. CdS clusters were formed photochemically through the dissociation of S 8 molecules in A and X types of Cd 2+-exchanged zeolites by laser irradiation, while CdSe clusters were not successfully produced in the same manner. The 1LO mode of CdS at 300 cm −1 shifts to lower frequencies in the zeolites in comparison with that of bulk CdS , indicating the effect of phonon confinement. Se clusters incorporated into zeolites with different pore sizes (3A, 4A, 5A, and 13X) exhibit strong dependence of the structural phase stability and the structural unit on the geometrical constraints of zeolites.
PHOTOINDUCED PHENOMENA OF CHALCOGEN MICROCLUSTERS CONFINED IN THE ZEOLITE CAGES
Authors: MARUYAMA K. , TSUZUKI T. , YAO M. , ENDO H.
Published: October 2004

Photoacoustic spectroscopy measurements have been carried out on the Se-ring microclusters confined in the cages of zeolite 4A. The shift of photoabsorption edge and the new absorption bands around 1.5 and 1.9 eV appeared by illumination of the light having the band-gap energy at low temperature. These phenomena may be associated with the distortion of Se ring and the formation of dangling bonds. Mixing of S or Te to the Se microclusters causes appreciable change in the photoinduced phenomena.
MAGNETIC AND OPTICAL PROPERTIES OF SODIUM CLUSTERS IN ZEOLITE LTA
Authors: KODAIRA TETSUYA , NOZUE YASUO , OHWASHI SATOSHI , TOGASHI NOZOMU , TERASAKI OSAMU
Published: October 2004

Cationic Na clusters are formed in the α and β cages of Na-form LTA by incorporating Na atoms from vapor. The maximum number of Na atoms incorporated is 4.9 per unit cell. Ac magnetic susceptibilities and optical reflection spectra are measured as a function of Na loading density. Na clusters show diamagnetism independent of Na loading density while K clusters in K-LTA and Rb clusters in Rb-LTA show ferromagnetism at certain loading densities. All Na clusters contain therefore an even number of the electrons, which are supplied from 3s-electrons of the guest Na atoms, irrespective of the cages they are formed. The electron-phonon interaction plays an important role in stabilizing the singlet state. In the reflection spectra of highly loaded sample, a strong band is observed at 1.95 eV. An oscillator strength of this band exceeds unity per cluster by a great deal. This band is assigned to surface-plasmon-like excitation of Na cluster formed in α cage.
ELECTRONIC STRUCTURE OF C60 SIMPLE CUBIC PHASE BY FULL-POTENTIAL MIXED-BASIS BAND CALCULATION
Authors: OHNO KAORU , MARUYAMA YUTAKA , TAKAHASHI MANABU , YU JING-ZHI , GU BING-LIN , KAWAZOE YOSHIYUKI
Published: October 2004

An electronic structure calculation with full-potential and all-electron ab initio formalism is performed for hypothetical low-temperature simple cubic phases ([Formula: see text] and [Formula: see text] space groups) of C 60 molecular crystal, in which every molecule is orientationally freezed. The degeneracies at special k-points, the magnitudes of energy gaps, and the widths of bands have been found to be sensitive to the orientation of the fullerenes in the crystal. Our result suggests that the structure with [Formula: see text] space group with –22° rotation around [111] directions, which David et al. proposed, is more stable compared to the structure with [Formula: see text] space group with the same rotation angle.
ELECTRONIC PROPERTIES OF C58BN HETEROFULLERENES
Authors: ESFARJANI KEIVAN , OHNO KAORU , KAWAZOE YOSHIYUKI
Published: October 2004

Recent studies of electronic structure of solid fullerenes have revealed many interesting properties of these systems. Here, we are interested in the effects of substitution of two carbon atoms by nitrogen and boron. We calculate the electronic structure of the C 58 BN cluster as well as its dispersion relation in the fcc crystalline phase. We consider the two cases where the nitrogen and the boron are neighbors and the case where they are situated far apart. In our all-electron calculation, we adopt the mixed basis approach in which we include the 1s and 2p orbitals in addition to plane waves. We investigate the existence of the donor and acceptor levels in both cases where N and B are neighbors and where they are apart. Furthermore, the electronic density in their neighborhood will be largely affected. The double bond which existed in the C 60 case is now replaced by a single bond. The consequences of substitutional doping, which is to create donor and acceptor levels and to broaden the valence and conduction bands; the anisotropy in the band dispersion; and the eventual relaxation of the nitrogen and boron atoms to a new position are also discussed.
NOVEL STRUCTURES FROM ARC-VAPORIZED CARBON AND METALS: SINGLE-LAYER CARBON NANOTUBES AND METALLOFULLERENES
Authors: KIANG C.-H. , VAN LOOSDRECHT P.H.M. , BEYERS R. , SALEM J.R. , BETHUNE D.S. , GODDARD III W.A. , DORN H.C. , BURBANK P. , STEVENSON S.
Published: October 2004

By covaporizing metals with carbon in a fullerene generator, diverse fullerene-related structures can be produced. Adding cobalt to the graphite anode leads to the production of single-layer carbon nanotubes. We find that the relative abundance of tubes with different diameters can be successfully altered by the presence of various catalyst promoters such as sulfur, bismuth, or lead. If Sc is covaporized in the arc, many Sc-containing metallofullerenes form abundantly. Purified Sc 3@ C 82 has been obtained by HPLC techniques, and its dynamics have been investigated using electron paramagnetic resonance spectroscopy. The unusually large, strongly temperature-dependent linewidths and the temperature-dependent hyperfine coupling suggest that the Sc atoms form a trimer which rapidly reorients within the C 82 cage.
POSITIVE AND NEGATIVE IONIZATION PROBABILITIES OF ATOMS SPUTTERED FROM C60
Authors: JOYES P. , TARENTO R.J. , WALLE J. VAN DE
Published: October 2004

We study the positive and negative ionization probabilities P+ and P− of atoms sputtered from C 60 at energy Ec. As the atom leaves the target molecule, its atomic level progressively decouples from the target levels; this can be described by means of the Anderson Hamiltonian with time-dependent parameters. In a first part we neglect the repulsion between electrons and study the positive ionization. We present an exact numerical solution of the Schrödinger equation. We obtain for P+(Ec) a power-law dependence with an exponent slightly varying with Ec. This dependence is different from the exponential law given by another commonly used model. In a second part we introduce an intra-atomic repulsion between electrons which allows us to calculate negative ionization probabilities.
PHOTODISSOCIATION OF ${\rm{C}}_n^+$ CLUSTERS
Authors: BOUYER R. , MONCHICOURT P. , PERDRIX M. , PRADEL P. , ROUSSEL F.
Published: October 2004

Photodissociation of jet-cooled, mass-selected [Formula: see text] clusters with 16≤n≤36 has been analyzed as a function of the dissociation laser fluence. From the dependence of the [Formula: see text] depletion, the number of absorbed photons and the absorption cross section have been determined. The dissociation energy is deduced from the internal energy before fragmentation. A decreasing stability is observed from [Formula: see text] to [Formula: see text]. Above [Formula: see text], two isomeric forms are found, with one having a higher stability.
SYNTHESIS OF La@C2n BY DIRECT La-FULLERENE REACTIONS IN THE LASER-ABLATION PLASMA OF A La2O3/FULLERENE MIXTURE
Authors: YANG SHIHE , HUANG RONGBIN , LU WENYUN
Published: October 2004

Reaction of excimer laser (XeCl, 308 nm) vaporized and excited fullerenes with La was carried out in a mixture of fullerenes and La 2 O 3. The reaction products La@C 60, La @60−2n, and La@C 60+2m were identified by a reflectron-type time-of-flight mass spectrometer (RTOFMS). The endohedral nature of these metallofullerenes is discussed in terms of a “window” mechanism. As an initial effort, a macroscopic amount of La@C 2n was also collected by this method and confirmed by laser-desorption time-of-flight mass analysis.
LASER-DRIVEN SYNTHESIS OF CARBON AND SILICON CLUSTERS FROM GAS-PHASE REACTANTS
Authors: EHBRECHT M. , FERKEL H. , SMIRNOV V.V. , STELMAKH O. , ZHANG W. , HUISKEN F.
Published: October 2004

A newly developed technique is employed for the production of carbon and silicon cluster beams starting from gaseous compounds. It is based on the CO 2-laser-induced decomposition of molecular gases containing carbon and silicon, such as CO 2H2 and SiH 4, in a flow reactor. In order to decompose acetylene, SF 6 is used as a sensitizer. By introducing a skimmer into the reaction zone, the generated silicon and carbon clusters are transferred to free molecular flow and analyzed with a time-of-flight mass spectrometer. It is shown that the technique can be efficiently employed to produce fullerenes C 60 and C 70 and, in the case of silicon, ultrapure nanosized particles of up to 3-nm diameter.
GROWTH AND SCANNING PROBE MICROSCOPY OF BUCKYTUBES AND BUCKYCONES
Authors: SATTLER KLAUS
Published: October 2004

Nucleation and growth of fullerenes and other carbon nanostructures are little understood. We show that there is an alternative to the arc-source generator. Spherical, tubular, and conical carbon-shell structures can be synthesized in the vapor phase. Very hot carbon vapor, deposited onto highly oriented pyrolytic graphite (HOPG), forms small carbon clusters, single-shell tubes, multishell tubes, bundles of tubes, and cones. The structures were analyzed by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). High-resolution images show the surface atomic structures of the tubes and their helicities. A growth pathway is proposed for fullerenes, tubes, and cones.
CARBON CAGES WITH NANOSPACE INSIDE: FULLERENES TO NANOCAPSULES
Authors: SAITO YAHACHI
Published: October 2004

The arc-vaporization method is now widely used for the formation of fullerenes and related materials. One of the remarkable properties of fullerenes and related materials is that they have hollow structures with a cavity of nanometer-scale diameter; outer cages are made up of single or concentric multilayers of graphene sheets. When foreign materials, such as metal atom(s) or nanocrystallite, are trapped in the inner cavity, unusual physical and chemical properties are expected to be brought about. Attempts to place atoms, clusters, and nanocrystals are reviewed.
MOLECULAR DYNAMICS STUDY OF TOROIDAL AND HELICALLY COILED FORMS OF GRAPHITIC CARBON
Authors: IHARA SIGEO , ITOH SATOSHI
Published: October 2004

The rotational symmetry, cohesive energies, and thermal stabilities of the toroidal forms, as well as helically coiled forms derived from C 240, C 360, and C 540, are studied by molecular dynamics. For various rotational symmetric helically coiled forms, the dependence of the polygon patterns in the inner ridge line on the coil length is studied. For the short-coil-length limit, the surface consists of pentagons, hexagons, and heptagons. For C 240 and C 360 helices the surface patterns are changed with increasing coil length. By stretching the helically coils along the fiber axis, we found that the surface of C 384 helix, eightfold rotational symmetric form derived from torus C 240, consisting of pentagons and heptagons without heptagons becomes stable as the coil length becomes longer.
ELECTRONIC STATES OF NANOSTRUCTURES OF CURVED GRAPHITIC CARBON CAGES
Authors: TSUKADA M. , AKAGI K. , TAMURA R. , IHARA S.
Published: October 2004

Electronic structure of carbon nanotubes with cap and that of the helically coiled nanotubes are studied by the simple tight-binding models. The method of the development map is used for a systematic study of the electronic states. Several remarkable features of these cage structures are found and the relation to the topological disorders due to the disclination centers is discussed, which are inherent to the curved graphitic layer.
ON THE COULOMB INTERACTION IN CARBON ONIONS AND THEIR ABSORPTION SPECTRA
Authors: ÖSTLING D. , ROSÉN A. , APELL S.P. , MUKHOPADHYAY G.
Published: October 2004

We have previously demonstrated the existence of a rich spectrum of collective resonances for both carbon tubes and carbon onions using a classical electrodynamic model. Collective resonances in these systems are predicted to dominate their respective UV spectra. In this study we present results which demonstrate how the coupling between the shells via the Coulomb interaction completely determines the absorption cross section. The outermost shells are strongly screened for low frequencies and frequencies close to the effective plasma frequency of the shells.
CARBON NANOCAPSULES AND SINGLE-WALL NANOTUBES FORMED BY ARC EVAPORATION
Authors: SAITO Y. , OKUDA M. , KOYAMA T.
Published: October 2004

Iron nanocrystals wrapped in graphitic carbon were produced by arc evaporation of iron-carbon composites, and an excellent protective nature of the outer graphitic carbon against oxidation of the core crystallites was revealed by an environmental test (80°C, 85% R.H., 7 days). Single-wall (SW) tubes were also produced by the arc method with various catalysts, Fe, Co, Ni, F/Ni, La, and Ce. Growth patterns and morphology of SW tubes were classified into three groups: (i) tubes tangled with each other to form “highway junction” pattern for Co and Fe/Ni, (ii) long and thin tubes radially growing from Ni particles, and (iii) short and thick tubes growing from lanthanide compound particles.
LOW-DAMAGE SURFACE TREATMENT BY GAS CLUSTER-ION BEAMS
Authors: AKIZUKI M. , HARADA M. , MIYAI Y. , DOI A. , YAMAGUCHI T. , MATSUO J. , TAKAOKA G.H. , ASCHERON C.E. , YAMADA I.
Published: October 2004

Low-damage irradiation effects of gas cluster-ion beams have been studied at acceleration voltages below 20 kV. The surfaces of targets have been smoothened significantly by CO 2-cluster-ion irradiation at normal incidence. Si substrate surfaces have been cleaned and exhibited low damage after CO 2- and Ar-cluster-ion irradiation at low doses. In the case of CO 2-cluster-ion irradiation, SiO 2 film of about 5.5-nm thickness have grown on Si substrate at room temperature. A damaged layer of less than 2.5-nm thickness has been formed underneath the SiO 2 film.
REACTIVE ACCELERATED CLUSTER EROSION (RACE)
Authors: GSPANN JÜRGEN
Published: October 2004

Beams of ionized clusters of some thousand atoms are accelerated to about 100-keV kinetic energy to be used for area selective surface erosion. Mask projective cluster-impact lithography allows surface structuring in the submicron regime. Chemical reactions between the cluster and the target material may provide volatile reaction products facilitating ejecta removal. The reactive accelerated cluster erosion (RACE) process is applied to metals like copper and gold, to semiconductors such as silicon, and to insulators like glass, quartz, or sapphire, giving very smooth eroded surface and steep sidewalls.
FULLERENES ADSORPTION ON Cu(111) AND Ag(111) SURFACES
Authors: HASHIZUME T. , SAKURAI T.
Published: October 2004

Initial stage adsorption and film growth of C 60, C 70, C 60(x) C 70(1−x), and Sc 2@ C 84 fullerene molecules on Cu (111) and Ag (111) surfaces have been investigated by field-ion scanning tunneling microscopy. Fullerene molecules are mobile on the terrace and initially segregate to the step edges. A well-ordered monolayer films form with a close-packed arrangement upon annealing the fullerence-covered surfaces. The (4×4) phases form in the case of the C 60, C 70, and C 60(x) C 70(1−x) adsorption on the Cu (111)-(1×1) surface, indicating a strong interaction between the Cu substrate and fullerenes. Intramolecular structures of the C 60 and C 70 molecules are observed and interpreted as the mappings of the local electron density of states. On the Ag (111) surface, C 60 and Sc 2@ C 84 monolayer films show several phases that have almost identical nearest neighbor distance but are rotated from each other, indicating weaker interaction between the Ag substrate and fullerenes compared with the case of Cu .
ELECTRONIC STATES OF C60 AND C70 MOLECULES ON Si(111)-(7×7) SURFACE
Authors: YAMAGUCHI T. , FUJIMA N.
Published: October 2004

Electronic states are calculated by the DV-Xα-LCAO method for two model clusters C 60 Si 101 H 60 and C 70 Si 101 H 60 of the C 60/Si(111) and C 70/Si(111) surfaces where fullerene molecules reside at the center of the unfaulted half of the 7×7 unit cell. For the C 60 molecule, occupied (unocupied) orbitals near the Fermi level have high charge density around double bonds between two hexagons (around single bonds on pentagons). For the C 70 molecule, both occupied and unoccupied orbitals have high charge density around single bonds. The charge density of an individual occupied (unoccupied) orbital has a shape like a trigonal doughnut (clover leaves) over the C 60 molecule, and it is high in three (four) regions over the C 70 molecule which is nearly C s(D2) symmetry. These should be compared with the scanning tunneling microscopy images.
ELECTRONIC STRUCTURE AND STM IMAGE OF C60–C70 ADSORBED ON THE Cu(111) SURFACE
Authors: MARUYAMA YUTAKA , OHNO KAORU , KAWAZOE YOSHIYUKI
Published: October 2004

A recent scanning tunneling microscopy (STM) experiment has revealed that C 60–C70 mixture on the Cu (111)–(1×1) substrate shows specific bias-voltage-dependent images which reflect intramolecular structure. In order to understand this observation, we perform a band-structure calculation. In this study, we adopt a simple model assuming a two-dimensional (2D) molecular crystal and a proper adsorption geometry. By comparing the calculated charge distributions of the lowest unoccupied molecular orbital (LUMO)-induced bands and the highest occupied molecular orbital (HOMO)-induced bands with the observed STM images, we find that the shapes of the intramolecular structures which change with the bias voltage strongly reflect the positions of pentagonal and hexagonal rings.
ADSORPTION AND REACTION OF C60 ON Si(111) SURFACE: A COMBINED STUDY BY HREELS AND STM
Authors: HU C.-W. , KASUYA A , SUTO S. , WAWRO A. , NISHINA Y.
Published: October 2004

A combined system of STM and HREELS has been demonstrated to be a powerful technique for studying the adsorption and reaction of C 60 molecules on Si(111) surface, and has bridged the gap between adsorbate bonding states and STM topographic images. We find that the ordered close-packed C 60 islands can be grown at room temperature. A brief annealing at 800°C gives rise to the aggregation of C 60 molecules into three-dimensional islands. In this case, the nearest neighbor distance among C60 molecules has decreased from 10.0 to 9.4 Å as displayed in STM images, and the icosahedral symmetry of C 60 has been reduced as showed in the HREELS spectrum. It indicates that the intermolecular covalent bond exists and a new structure has been stimulated by annealing C 60 film on Si(111) surface. Further annealing results in the formation of SiC film on Si(111) substrate.
DEPOSITION OF MASS-SELECTED Ag7 ON Pd(100): FRAGMENTATION AND IMPLANTATION
Authors: VANDONI G. , FÉLIX C. , MONOT R. , BUTTET J. , MASSOBRIO C. , HARBICH W.
Published: October 2004

Mass-selected silver-cluster ions [Formula: see text] with an incident energy of 2.86 eV/atom and of 13.6 eV/atom are directed on a well-prepared Pd(100) surface, which is probed with thermal-energy atom (helium) scattering (TEAS), before, during, and after the deposition, yielding information on the collision process. We find that part of the cluster atoms are implanted into the surface layer, the fraction depending on the impact energy. Considerable fragmentation is present at both impact energies. Molecular dynamics calculations based on embedded atom method (EAM) potentials are used to model the collision process. These calculations confirm qualitatively the experimental results.
FORMATION AND MODIFICATION OF MESOSCOPIC STRUCTURES ON GRAPHITE (HOPG) AND SILICON SURFACES BY MEANS OF SCANNING TUNNELING MICROSCOPY
Authors: CZAJKA R. , KASUYA A. , WAWRO A. , HORIGUCHI N. , NISHINA Y.
Published: October 2004

This paper presents results of our experimental investigations of the adsorption and interaction of microclusters on some crystalline surfaces to form regular arrangements. Microclusters were produced and deposited up to a monolayer coverage on the c-plane of graphite (HOPG) or Si(111) substrates by thermal evaporation, laser ablation, or deposition from STM tip. A rectangular lattice arrangement of Se n(n=5–8) ring cluster has been fabricated for the first time on the HOPG. Also, arrays of Au clusters with a well-controlled diameter, desired periodicity, and size have been obtained by applying a sequence of voltage pulses between the STM tip and the substrate. A variety of carbon clusters have been produced by laser modification of C 60 fullerenes, and observed by means of scanning tunneling microscope (STM). Finally, various nanometer-scale structures have been modified by applying different bias voltages (between tip probe and sample) or induced by thermal treatment.
INFLUENCE OF THE METALLIC CLUSTER BAND DEGENERACY ON THE CHARGE TRANSFER BETWEEN METALLIC CLUSTER AND SEMICONDUCTOR SUBSTRATE
Authors: TARENTO R.J. , JOYES P. , WALLE J. VAN DE
Published: October 2004

A self-consistent analysis of the charge transallographie semiconductor has been investigated with respect to the cluster size, the metal-band degeneracy, and the semiconductor doping concentration. The calculation has been carried out with the Tersoff idea on the pinning of the Fermi level.
FORMATION OF SURFACE DIPOLES FOR SMALL PALLADIUM CLUSTERS DEPOSITED ON α-(0001)Al2O3
Authors: OGAWA S. , ICHIKAWA S.
Published: October 2004

The Kelvin-probe method is utilized to measure the work function of a single-crystal aluminum covered with palladium clusters. It is found that formation of interface dipoles occurs by charge transfer from Al 2 O 3 to Pd clusters, particularly for those less than 2 nm in diameter. These results provide valuable clue to the understanding of metal-support electronic interactions, which is important in catalysis.
TUNNELING SPECTROSCOPY OF NANOMETER-SIZE CLUSTERS DEPOSITED ON GRAPHITE
Authors: WAWRO A. , KASUYA A. , CZAJKA R. , NISHINA Y.
Published: October 2004

The electronic structures of Sb, Ni, and Au clusters of nanometer size are discussed. Clusters were deposited on a graphite substrate and analyzed with a scanning tunneling microscope in an ultrahigh-vacuum system. Scanning at constant-current mode at different bias voltages was used as a method of spectroscopic measurements. Disappearing of the clusters images at certain range of voltage biases is attributed to occurrence of the energy gap in electronic structure of clusters, suggesting their nonmetallic behavior.
SCANNING TUNNELING MICROSCOPY OF CLUSTERS ADSORBED ON SUPERPERIODIC LATTICE OF HIGHLY ORIENTED PYROLYTIC GRAPHITE
Authors: HORIGUCHI N. , KASUYA A. , NISHINA Y.
Published: October 2004

We observed superperiodic lattices in clusters deposited on HOPG surfaces by STM. Furthermore, we clearly identified two types of bias-voltage dependences in the corrugation of superperiodic lattices. Cluster adsorption sites are strongly influenced by the superperiodic lattices. On the superperiodic lattices, clusters are found to form arrays. This suggests that one can control the surface electronic structure as well as the cluster array by preparing graphitic sheets with various stacking arrangements.
LOW-ENERGY CLUSTER BEAM DEPOSITION: NUCLEATION AND GROWTH OF ANTIMONY PARTICLES ON GRAPHITE: EXPERIMENTS AND MODEL
Authors: BARDOTTI L. , JENSEN P. , MELINON P. , HOAREAU A. , CABAUD B. , TREILLEUX M.
Published: October 2004

We present in this work the TEM results on the nucleation and growth process of antimony particles on graphite produced by low-energy cluster beam deposition. In order to acquire more details about the first stages of film growth, we compare the experimental results with a new theoretical model named “Deposition-Diffusion-Aggregation”. Moreover this comparison allows an estimate of the diffusion coefficient D for antimony clusters of 5-nm diameter on graphite; we find D≈10−8 cm2/s.
DESIGNING CLUSTERS AS SUPERELEMENTS
Authors: JENA P. , KHANNA S.N. , RAO B.K.
Published: October 2004

Atomic clusters formed by agglomeration of atoms constitute a new state of matter with novel properties which depend uniquely on their size, shape, dimensionality, and composition. If clusters could be designed in such a way that they can retain their structure when assembled into a material form, it is possible to envision a new class of solids with clusters as building blocks. These cluster-assembled materials would exhibit rather uncommon properties, thus enlarging the frontiers of material science. Self-consistent calculations have been carried out to study the effect of composition and geometry on the stability and reactivity of clusters. An understanding of the role that atomic and electronic structure play on cluster-cluster interaction would enable us to design cluster materials. This paper deals with the design guidelines, as well as properties of cluster-assembled crystals. It is shown that clusters designed to mimic the properties of known atoms can be viewed as superelements and thus help extend the limits of the current periodic table.
ELECTRONIC STRUCTURE OF ASSEMBLED CLUSTERS WITHIN THE STABILIZED JELLIUM MODEL
Authors: GRÖNBECK HENRIK , ROSÉN ARNE
Published: October 2004

The electronic structure of assembled closed shell clusters have been analyzed using a spherical, stabilized jellium description of the clusters. The effects of including stabilization terms to the jellium model were investigated by calculating the properties of cluster dimers, (Na20)2 and ( Cu 20)2. In addition, the electronic properties of a material consisting of closed shell Al 12X clusters, where X is C or Si, were investigated using a model of six clusters. The large gap at the Fermi level present for the building blocks was also found to appear for the cluster-assembled material. The binding energy of the clusters in the cluster-assembled material was compared with that of an atomic Al lattice.
CORRELATION BETWEEN FREE-CLUSTER PROPERTIES AND THIN FILMS ELABORATED BY LOW-ENERGY CLUSTER-BEAM DEPOSITION
Authors: MÉLINON P. , PAILLARD V. , DUPUIS V. , PEREZ J.P. , TUAILLON J. , PEREZ A. , BARBARA B. , THOMAS L. , BOUDEULLE M.
Published: October 2004

The properties of thin films obtained by low-energy cluster-beam deposition are reviewed. The main characteristics are the nanoscale granular structure and the memory effect of the free-cluster properties. The first point is evidenced by the specific magnetic properties of transition-metal films, which are intermediate between amorphous and bulk phases, while the second point is illustrated from carbon films exhibiting the electronic structure of the free carbon cluster.
SPUTTERING WITH GAS CLUSTER-ION BEAMS
Authors: MATSUO J. , AKIZUKI M. , NORTHBY J. , TAKAOKA G.H. , YAMADA I.
Published: October 2004

A high-current (~100 nA) cluster-ion-beam equipment with a new mass filter has been developed to study the energetic cluster-bombardment effects on solid surfaces. A dramatic reduction of Cu concentration on silicon surfaces has been achieved by 20-keV Ar cluster (N~3000) ion bombardment. The removal rate of Cu with cluster ions is two orders of magnitude higher than that with monomer ions. A significantly higher sputtering yield is expected for cluster-ion irradiation. An energetic cluster-ion beam is quite suitable for removal of metal.
MOLECULAR-DYNAMICS SIMULATION OF SURFACE SPUTTERING BY ENERGETIC RARE-GAS CLUSTER IMPACT
Authors: INSEPOV Z. , YAMADA I.
Published: October 2004

The molecular-dynamics simulation is used for simulation of sputtering of gold and silicon surfaces by accelerated [Formula: see text] cluster ions with n~55–200 and energies of 10–100 eV per cluster atom. The sputtering yield Y can be described by a power dependency Y ∝E2.35 on the total cluster energy. The result of the calculation agrees with the experimental data point at the energy of 29 keV and cluster size of 300 Ar atoms. The simulation shows that the sputtered flux has a significant lateral-momentum component and the sputtered surface materials contain not only atoms but also small clusters.
STUDY OF METALLIC CLUSTERS IN ORGANIC THIN FILMS
Authors: XUE Z.Q. , GAO H.J. , LIU W.M. , LIU Y.W. , WU Q.D. , PANG S.J.
Published: October 2004

The polyethylene (PE) and the metallic materials are deposited alternatively on substrates in the chamber of the ICB-TOFMS deposition system. The metallic-cluster-polyethylene thin films are formed. The film thickness is about 30 nm. The structures of these samples including Au-PE, Ag-PE, In-PE, and Sn-PE thin films are studied. These special thin films with suspension metal clusters display many special properties.
CLUSTER ION BOMBARDMENT-INDUCED SURFACE DAMAGE OF Si
Authors: ASCHERON C.E. , AKIZUKI M. , MATSUO J. , INSEPOV Z. , TAKAOKA G.H. , YAMADA I.
Published: October 2004

Surface damage of single-crystalline Si caused by irradiation with Ar-ion cluster beams of different energies has been studied in comparison with that caused by Ar-monomer ion beams. The defected layers have been characterized by RBS channeling, XTEM, and ellipsometry. The experimental results are interpreted on the basis of TRIM and molecular dynamics simulations of the interaction processes with the target. It is found that cluster irradiation damages only a very thin near-surface layer which has a smooth interface to the undamaged substrate. Cluster-ion bombardment forms an oxide layer on the surface by the activation of adsorbed O atoms and substrate atoms.
HOPPING CONDUCTION IN SiO2 FILMS CONTAINING CLUSTERS OF GROUP-IV ELEMENTS
Authors: INOUE Y. , HAYASHI S. , YAMAMOTO K.
Published: October 2004

SiO 2 films doped with C, Si, and Ge atoms were prepared by an rf cosputtering method and their electrical transport properties were measured. The films show nonohmic conduction with a conductivity increasing drastically with increasing the dopant concentration in the films. The observed temperature dependence of the conductivity obeys the ln σ∝ T −1/4 law, where σ and T are the conductivity and temperature, respectively. This behavior of the conductivity is indicative of the conduction by the variable-range hopping mechanism. Since the previous optical data for the same films indicate the existence of clusters in the films, it is very likely that the hopping is mediated by localized states associated with the clusters.
GIANT MAGNETORESISTANCE AND CLUSTER-SIZE DISTRIBUTION IN Co/Ag GRANULAR MONOLAYERS
Authors: MOREL R. , STEREN L.B. , BARTHÉLÉMY A. , PARENT F. , FERT A. , MASSON A. , BELLAMY B.
Published: October 2004

In this paper, we report on granular Co/Ag monolayers grown by MBE on MgO(100). The clusters sizes and distribution are governed by nucleation and growth processes onto the surface. By a careful fitting of the giant magnetoresistance, using a Langevin formalism that relies solely on the number of Bohr’s magnetons in the superparamagnetic clusters, we infer their size distribution and its dependence on cobalt content. In Co 20 Ag 80, clusters sizes found range from 13 to 206 atoms, while in Co 60 Ag 40 they range from 40 to 3200, with the bigger clusters having sizes comparable to the total thickness of the samples. Also, by measuring the size of the effective clusters as function of temperature, we can estimate their blocking temperature and anisotropy constant.
CHARACTERIZATION AND OPTICAL PROPERTIES OF Au/SiO2 COMPOSITE THIN FILMS
Authors: TANAHASHI I. , YOSHIDA M. , MANABE Y. , TOHDA T.
Published: October 2004

Au/SiO 2 composite thin films were prepared by a multitarget sputtering method. The multilayer structure where the Au-particle layer was sandwiched between SiO 2 layer was clearly observed in the as-deposited film by the cross-sectional TEM. The diameter of the Au particles in the film was estimated to be 2–3 nm and it began to increase when the film was heat-treated above 700° C. The diameter was proportional to the cube root of the heat-treatment time, suggesting that the Au particles grew in the supersaturated solid solution. In the optical absorption spectra of the films, the absorption peak due to the surface-plasmon resonance of Au particles was observed at the wavelength of 528–544 nm. With increasing mean diameter of Au particles, the peak intensity became large and the full-width-at-half-maximum of the absorption band was decreased from 130 nm to 80 nm.
FORMATION AND ATOMIC STRUCTURE OF NANOSCALE SILVER IN GLASS
Authors: DUBIEL M. , HOFMEISTER H. , THIEL S.
Published: October 2004

Silver particles of sizes ranging from about 2 to 100 nm embedded in a glass matrix were formed by silver-sodium ion exchange in sodium silicate glasses. By high-resolution electron microscopy examination, lattice contractions depending on the particle size were found that are comparable to or larger than those reported for nonembedded silver particles. From these lattice contractions values of the interface stress acting on the particles at room temperature as an effective compressive stress are determined. By deformation of the glasses at elevated temperatures, an elongation of spherical particles results that allows us to determine the interface stress at the deformation temperature. The large discrepancy of the resulting values points to an essential role of the cooling procedure taking place after the particle formation.
NONLINEAR AND ELECTRO-OPTIC PROPERTIES OF II-VI SEMICONDUCTOR NANOCRYSTALS IN POLYMER AND GLASS MATRICES
Authors: WOGGON U. , WIND O. , SPERLING V. , PORTUNÉ M. , KLINGSHIRN C.
Published: October 2004

In the present contribution a short overview will be given on the influence of growth parameters, matrix, and interface properties on the nonlinear and electro-optical behavior of II–VI quantum dots. The experimental techniques comprise standard experiments as pump-and-probe spectroscopy and degenerate four-wave-mixing as well as electric-field-induced absorption modulation.
PHOTODARKENING ENERGY STATE IN NANOCRYSTALLINE CdSxSe1−x-DOPED GLASS PROBED BY TIME-RESOLVED RAMAN SPECTROSCOPY
Authors: ZHANG XIAOJIE , HAMAGUCHI HIRO-O
Published: October 2004

We studied the photodarkening effect in nanocrystalline CdS x Se1−x-doped glasses by pump-probe time-resolved Raman spectroscopy. A marked decrease in the phonon Raman intensities was observed when the photodarkened samples (commercial glass color filters) were pre-excited by the pump pulse. Such an intensity change was not observed for the fresh (unphotodarkened) samples. These findings have been interpreted in terms of a new photodarkening-induced state that traps the photoexcited electrons efficiently. The magnitude of the decrease in Raman intensities increased linearly with increasing selenium fraction, suggesting that the photodarkening energy state is related to the Se anion or corresponding vacancy on the surface of CdS x Se 1−x microcrystallites.
PHOTOINDUCED FORMATION OF AGGREGATED SILVER PARTICLES FROM SILVER SALT OF POLYSACCHARIDE
Authors: YONEZAWA Y. , SATO T. , MIYAMA T. , TAKAMI A. , UMEMURA J. , TAKENAKA T.
Published: October 2004

The thin film of silver salt of alginic acid is available for synthesis of small silver particles and aggregates embedded in the polymer matrix. Variations in the Raman spectrum of the silver alginate film with UV irradiation have been examined. A Raman signal at 1398–1405 cm−1 corresponding to symmetric COO− stretching vibration of silver alginate has been increased, manifesting the contribution of surface-enhanced Raman scattering (SERS).
SIZE AND SHAPE MANIPULATION OF SILVER AND INDIUM SMALL PARTICLES BY ELECTRON-BEAM IRRADIATION
Authors: HEILMANN A. , MÜLLER A.-D. , WERNER J.
Published: October 2004

Small particles of indium or silver were encapsulated in a thin polymer film matrix by simultaneous plasma polymerization and metal evaporation. Electron-beam irradiation inside transmission electron microscopes and with a microfocus electron source was used to induce changes of the encapsulated particle size and shape. At encapsulated indium particles, substantial microstructural changes were observed during the electron-beam irradiation in the electron microscope. Selected area diffraction demonstrates that indium oxide was formed during the electron irradiation. Additional in situ annealing demonstrates that the indium melting point was not reached during electron-beam-induced local heating of the indium particles. At electron-beam irradiation of plasma polymer films with encapsulated silver particles by using a microfocus electron source, the coalescence of the silver particles can be limited to the irradiated areas of the films.
MAGNETIC PROPERTIES OF COBALT-CLUSTER DISPERSIONS GENERATED IN AN ELECTROCHEMICAL CELL
Authors: BECKER J.A. , SCHÄFER R. , FESTAG J.R. , WENDORFF J.H. , HENSEL F. , PEBLER J. , QUAISER S.A. , HELBIG W. , REETZ M.T.
Published: October 2004

Magnetization curves of stabilized cobalt-cluster dispersions in tetrahydrofuran with a narrow size distribution have been studied by SQUID and Gouy balance measurements. The cobalt colloids are generated by a newly developed electrochemical method which allows one to generate clusters with mean cluster sizes of about 1000 atoms. The final size distribution of the clusters is examined by small-angle x-ray scattering (SAXS) and high-resolution transmission electron microscopy (HRTEM) measurements. The magnetization curves have been measured with special emphasis on changes at the freezing point of the solution. The liquid phase shows typical superparamagnetism whereas strong deviations from Langevin behavior occur in the solid dispersion which can be understood in terms of magnetic anisotropy effects. These observations are discussed with regard to recent Stern-Gerlach experiments on isolated ferromagnetic clusters in molecular beams. It is shown that cluster size and susceptibility of the dispersions are related. This permits the control of the growth of the clusters during the electrolysis by measuring the susceptibility as a function of the charge that is converted in the cell.
SIZE EFFECTS OF EXCITONS OF BiI3 IN LAYERED MATRICES
Authors: KOMATSU T. , KIM D. , KOBAYASHI T. , WATANABE K. , AGUEKIAN V.F. , KARASAWA T. , AKAI I. , IIDA T.
Published: October 2004

The size effects on the exciton absorption and luminescence spectra are studied in nanostructure of BiI 3 embedded in the matrices of bulk BiI 3 and CdI 2 crystals. The quantum-confined exciton states are observed as the absorption lines of the series W J (J=I, II, III, …). The results are compared with a model calculation of the confined excitons in the disks with thickness L z and radius R. The disk-size distribution is directly observed with a high-resolution electron microscope. The relaxed luminescence from the BiI 3 disks in CdI 2 matrix is analyzed by the model of the confined excition interacting with acoustic phonons by taking into account the size-dependent Stokes shift and the distribution of the disk size.
ELECTRON TRANSPORT PROPERTIES IN FINE-PARTICLE FILMS OF Au EVAPORATED ONTO Si NATIVE OXIDE: THERMAL ANNEALING EFFECTS
Authors: KASAHARA H. , SHIKATA T. , YAMAMOTO K.
Published: October 2004

We investigated electron transport in fine-particle films of Au prepared onto Si native oxide. Electron transport measurements and TEM observations were carried out for as-deposited and after thermal treatment of the films in air. We observed the anomalous resistance increases in as-deposited fine-particle films of Au and obtained α T =4.5. After 150°C thermal treatment in air, however, these anomalous resistance increases in the Au films disappeared and its topography appeared on the TEM images drastically changed into percolative structure. We found that the size of the Au fine particles causes anomalous resistance increase at low temperature.
OBSERVATION OF CYTOCHROME b-562 ADSORPTION ON GOLD-PARTICLE SURFACE BY OPTICAL ABSORPTION MEASUREMENT
Authors: AOKI S. , ZHOU H.S. , HONMA I. , NAGAMUNE T. , KOMIYAMA H.
Published: October 2004

The plasmon absorption peak of 31-nm gold particles in aqueous solution was redshifted and broadened by the adsorption of protein. This effect is more striking in the acidic solution than in the alkaline solution. The adsorption is irreversible. When a small amount of protein was added to the colloidal solution, this effect was weak, but a small shoulder emerged at about 680 nm. With increasing quantity of the protein, the effect of the interaction became very strong. The small shoulder became larger and shifted to about 720 nm. But further addition of protein reduced the effect and finally the absorption spectrum became identical with the original colloidal solution. A model is presented which considers two adsorption manners of the protein on gold. Cytochrome b-562 is of cylindrical shape (height is 5.0 nm and diameter is 2.5 nm.) and has the chromophore at the position of about 3.5 nm from the bottom. Consequently, the “side-on” adsorption manner of the protein on gold which dominates at low concentrations and the “tail-on” adsorption fashion which dominates at high concentrations cause difference in the interaction distance between the surface plasmon and chromophore. The interaction between gold particles and the protein depends largely on the distance between the gold-particle surface and protoheme IX in the protein. The redshift and broadening of absorption peaks occurred at the side-on adsorption manner. We disclose an initial effort for developing a novel method to determine the configuration of protein adsorbed on colloidal particles.
PLASMON ABSORPTION OF GOLD NANOPARTICLES AND THEIR MORPHOLOGIES OBSERVED BY AFM
Authors: ISHIKAWA H. , IDA T. , KIMURA K.
Published: October 2004

We have studied the effect of heat treatment on Au-island film prepared by a sputtering method, atomic force microscopy (AFM), and UV-VIS spectrophotometry. The structure and absorption spectrum of Au-island film are significantly changed by heat treatment, which corresponds to the visible color change from blue to red. In order to elucidate the relation between the structural and optical changes, we have simulated the change of spectrum using the Maxwell-Garnett theory. The calculated spectra are qualitatively in agreement with the experimental spectra.
A QUANTUM-SPONGE MODEL FOR POROUS SILICON
Authors: SAWADA S. , OOKUBO N.
Published: October 2004

We propose a “quantum-sponge” model for porous silicon. This model exhibits energy-gap widening and nonexponential decay of photoluminescence describable by the stretched exponential function. These properties are in good agreement with those observed for porous silicon. We suggest that the fractal character of its wave functions is the origin of the nonexponential decay of photoluminescence.
NONEXPONENTIAL DECAY OF VISIBLE LUMINESCENCE FROM POROUS SILICON: EXCITON LOCALIZATION AND HOPPING
Authors: KANEMITSU Y. , OGAWA T.
Published: October 2004

We have studied the decay dynamics of visible photoluminescence (PL) from nanometer-sized Si crystallites. The slow decay behavior of red PL in 10 −6−10−2- s time regions is characterized by a stretched exponential function. The temperature dependence of the effective PL decay rate coincides with that of variable-range hopping of carriers in two-dimensional systems. Thus, it is naturally considered that the slow decay PL is caused by the hopping-limited recombination of excitons in surface localized states.
SPONTANEOUS ALLOYING IN NANOMETER-SIZED AMORPHOUS ANTIMONY CLUSTERS
Authors: YASUDA H. , MORI H.
Published: October 2004

Alloying behavior of gold atoms into namometer-sized amorphous antimony (a-Sb) clusters has been studied by TEM. Gold atoms which came in contact with a-Sb clusters quickly dissolved into the clusters, and clusters of either an a-(Sb-Au) alloy or the compound AuSb 2 were formed, depending on the gold concentration in clusters. The ease with which such rapid spontaneous alloying takes place decreased with increasing size of original a-Sb clusters. It is suggested that the origin and mechanism of rapid spontaneous alloying are common to both amorphous and crystalline atom clusters.
PREPARATION OF BIMETALLIC PtnPdm SUPPORTED CLUSTERS WITH WELL-DEFINED STOICHIOMETRY
Authors: ROUSSET J.L. , CADROT A.M. , AIRES F. SANTOS , RENOUPREZ A. , MÉLINON P. , PEREZ A. , PELLARIN M. , VIALLE J.L. , BROYER M.
Published: October 2004

Supported bimetallic Pd-Pt clusters with a well-defined stoichiometry are produced using a laser-vaporization source. Free clusters are also studied by time-of-flight mass spectrometry and photofragmentation. The supported clusters are characterized by energy dispersive x-ray analysis. The low binding energy of palladium atoms compared to that of platinum is clearly demonstrated in both free and supported clusters. The reactivity is briefly discussed.
FORMATION OF AgI CLUSTERS BY SPONTANEOUS ALLOYING OF IODINE INTO SILVER CLUSTERS
Authors: MORI H. , YASUDA H. , FUJII K.
Published: October 2004

Alloying behavior of iodine atoms into nm-sized silver clusters has been examined by transmission electron microscopy (TEM). It is confirmed that even at such reduced temperatures as ambient temperature, vapor-deposited iodine atoms quickly dissolve into silver clusters, and clusters of either an Ag-I solid solution or the β-AgI compound are formed depending on the iodine concentration in the cluster.