All presently published electrical and optical measurements on concentrated ligand stabilized Au55-cluster samples reveal an inter-cluster tunnel-conductivity and indicate the influence of a “quantum-size-effect” (QSE) [1],[2]. However these data do not show any initials for the separation of inter- and possible intracluster effects. In the present Raper electronic intra-cluster Properties such as the electrical “conductivity” of 1nm chemical auantum dots, their relaxation frequencies and the relevant activation enthalpies as well as the respective Properties of pairs of Au55-clusters have been investigated in comparison to diluted clusters and interpreted by means of Impedance Spectroscopy. Furthermore a method to determine the number and the density of states (DOS) in the metal-core from the measuring data by means of very simple quantum-size assumptions is presented, which is compatible with both the SIMIT[3] and the existing cluster models.

Dipole photoabsorption spectra of small clusters are analyzed. Two types of systems are considered: metal clusters and the carbon fullerenes. Both have been found to exhibit strong collective photoabsorption modes associated with the motion of delocalized electrons. We describe analytical results for the resonance frequencies in both spherical (closed-shell metallic, C60 ) and spheroidal (openshell metallic, C70) particles. The calculation is based on the techniques of many-body physics (random-phase approximation, sum rules), affords a unified view of the dynamical response of microscopic clusters, and leads to good agreement with experimental data.

A radiolysis method is described to prepare isolated cadmium particles in aqueous solution. The spectrum of these particles (narrow band at 260nm) agrees with the spectrum calculated from the optical data of cadmium. Clusters of particles absorb at longer wavelengths. Redox reactions of the particles with methyl viologen, nitrous oxide and carbon tetrachloride were also investigated. It is shown that the absorption spectrum of the particles changes during these reactions as de-clustering takes place.

Using a scanning tunneling microscope in UHV we have observed anomalous superstructures on highly oriented pyrolytic graphite. We found such structures on three different samples, with hexagonal symmetry in each case but with different lattice constants of 1.7 nm, 3.8 nm and 6.6 nm. These giant lattices can be explained by assuming that the top layer of graphite is slightly rotated. This produces a hexagonal modulation of the electron state density in the first layer. Lattice points in the giant lattice are characterized by high local density of states at the Fermi level. We find that adsorbed cobalt particles occupy the top sites of the giant lattice.

The effect of size and shape on the electronic state of ultrafine metallic particles is described with the critical review of so far proposed experimental and theoretical results. The temperature dependence of the spin susceptibility of small metal particles is presented as function of size, shape, spin-orbit interaction of the elements, and magnetic field strength. Based upon a proposed formula, the spin susceptibility of small Mg particles is precisely analyzed with the view point of shape effect. It is emphasized that the exogenous impurities have crucial effect. on the magnetic properties of small metal particles. It is clarified that the confusion in the magnetic experiments originates from the extrinsic magnetic effect. The deviation of the nature of chemical bond in small size systems from that in bulk is briefly outlined.

We discuss the preparation of monodisperse ˜10-Å and ˜13-Å CdS clusters by the cluster fusion technique and the development of capillary zone electrophoresis for cluster separation. We also report the observation of photoconductivity in a polymer film doped with CdS nanoclusters.

Semiconductor crystallites (“quantum dots”) small with respect to the bulk exciton Bohr diameter show a three dimensional electronic quantum size effect. Their internal excited electronic states are discrete and shifted to higher energy than the bulk band gap[1,2].

We show that an empirical tight-binding approximation can be used for the determination of some electronic properties of semiconductor nanocrystals. Two different calculations based on this approximation are presented. The first calculation concerns the band-gap energy and the second one the density of states. The results are given for different II-VI compounds and compared to available experimental data.

Absorption spectra from 0.94 – 5.58 eV are obtained for gas phase neutral silicon clusters Si18 – Si41 using resonant one- and two-color photodissociation spectroscopy. The spectra of all clusters are essentially identical and exhibit six sharp features above 3.0 eV. Comparisons of the silicon cluster spectra to those of various forms of silicon show that they have much in common with the spectrum of bulk diamond lattice crystalline silicon.

Small crystallites of CdTe have been produced using a new solution synthetic method. In this technique, Cdl2 and Na2Te are each dissolved separately in methanol before rapid mixing. The product of this reaction is pure, stoichiometric CdTe with interesting electronic and optical properties. Photoluminescence studies of this material show a blue shift due to the quantum confinement, indicating the presence of small crystallites. Transmission electron microscopy confirms the presence of nanocrystals. Reaction temperature and processing conditions can be varied to change the crystallite sizes produced. This synthesis can also produce nanocrystalline HgTe.

23Na double rotation NMR (DOR) and 81Br magic angle spinning (MAS) are used to investigate the synthesis and assembly of sodium, silver-bromide clusters encapsulated in the porous framework of sodalite. The NMR spectra provide site-specific information on the nano-environments of the charge balancing, extraframework Na+ cations, and the encapsulated Br− anions. The results indicate the possibility of a percolation threshold beyond certain Na+ and Br− loadings.

The electronic structure of metal impurities in III-V semiconductors are interesting because of their ability to create deep centers. We use a spin unrestricted self-consistent local density theory in a cluster model to calculate the charge distributions, one electron energy spectra and the density of states for pure InP and Pd doped InP, substituted at the In site. The pure semiconductor gap is calculated to be 1.44 eV in excellent agreement with the experimental value of 1.41 eV. A small magnetic moment of 0.561μB appears on the Pd site. The impurity introduces a levels of t2 character at 0.01 and 0.04 eV above the valence band edge.

The optical and vibrational properties of small CdSe and CdS particles embedded in a glass matrix and as a colloid have been studied as a function of pressure up to 90 kbar using Raman scattering and photoluminescence techniques. We will discuss the use of high pressure optical spectroscopy techniques, where the sample is contained in a diamond anvil.cell with optical access, to study the nature of the electronic states in semiconductor nanocrystals. Raman scattering is employed to establish the enhanced pressure stability of the wurtzite phase in the II-VI nanocrystalline composites. Photolurninescence is used to study the energies of electronic states. The wurtzite to rocksalt phase transition behavior in the nanocrystallite systems is quite different from that in the bulk material. This different behavior is attributed to a large number of defects (vacancies) in the nanocrystallite system. This work demonstrates that the main defects in the CdS glass composites are cadmium vacancies; while in CdSe Selenium vacancies exist in the conduction band. The pressure dependence of the Huang-Rhys parameter, characteristic for the strength of the electron-phonon coupling, will also be discussed for the nanocrystalline samples versus the bulk material.

We describe here the use of calixarenes, methylene (-CH2-) linked phenolic macrocyclic molecules, to stabilize the formation of quantum-confined (Q-) CdS clusters. Specifically, we focus on the use of an amino-derivatized calixarene, para-[(dimethylamino)- methyl]calix[6]arene, to stabilize Q-CdS clusters which have been characterized by High Resolution TEM (HREM), as well as absorption and emission spectroscopies. Under typical preparative conditions, an average particle diameter of 36 Å is obtained. HREM, in combination with Selected Area Diffraction (SAD), confirms the structure of the clusters as zinc blende CdS. Spectroscopic studies using absorption and emission methods indicate that both particle size and cluster photophysics are sensitive to the ratio of CdS to calixarene.

Nanocrystalline metal powders can be synthesized by mechanical attrition in a highenergy ball mill. A general relation determining the grain size of these materials is inferred. The ultimate grain size of nanocrystalline metals (typically 6 − 22 nm) is governed by the competition between the severe plastic deformation introduced during ball milling and the recovery behavior of the material. The lower bound grain size achievable by mechanical attrition is given by the minimum distance between two dislocations in a pile-up within a grain for all pure metals. Foar binary alloys the ultimate grain size depends on the composition of the material. Varying the composition changes the grain size reversibly. This can be explained by introducing solid solution hardening effects in the general relation for the lower bound grain size in pure metals. Thus, the proposed model for the ultimate grain size achievable by ball milling seems to be. applicable to all metals and alloys subjected to heavy mechanical deformation. However, reversible grain size changes are not restricted to mechanical attrition, but have also been observed for nanocrystalline Pd-H solid solutions produced by hydriding at constant pressure. Solid solutions prepared at different compositions, i.e. samples with different compositions, exhibit different grain sizes. Cycling between different temperatures/compositions changes the grain size reversibly. This cannot be explained by a model based on plastic deformation as in the case of ball-milled metal powders. The results are compared with data for ball-milled powders and samples prepared by inert gas condensation. The grain size changes are discussed with respect to the compositional changes and the grain boundary energy of the material.

Nanocrystalline Fe has been prepared by inert gas condensation and ball milling. The kinetics of relaxation and grain growth are investigated by differential scanning calorimetry. The development of the microstructure is monitored by x-ray powder diffraction and transmission electron microscopy. Emphasis is placed on the differences observed for samples prepared by the two different techniques. We find that the kinetics of relaxation and grain growth are very sensitive to the sample preparation method. Samples with the same initial average grain size, as determined by the peak broadening in x-ray diffraction, show very different recovery behavior. The differences are discussed in terms of the estimated grain boundary energies and the initial grain size distribution obtained by the two preparation techniques.

Three gold clusters, Au55 (PPh3 )12Cl6, Au55{PPh2(C6H4SO3Na)}12Cl6 and Au11{PPh2(p-ClC6H4)}7I3 (which we shall denote Au55, Au55, and Au11 for convenience) have been studied using EXAFS. Average near-neighbour bond lengths are contracted from the bulk by approximately 0.15Å (±0.02Å) for Au55, and 0.22Å (± 0.02Å) for Au11. Ligand contributions have been successfully modelled in the fitting. Debye-Waller factors for samples at room temperature and at 80K are compared to ascertain the relative degrees of thermal and static disorder present in the systems. Results clearly indicate that static structural disorder predominates over thermally induced vibrational disorder.

The theoretical reduced intensity of X-ray scattering i(S) may be calculated for a cluster of any structure using Debye's formula. The comparison of both experimental determination and model calculation of the RDF or i(S) allows, to make a conclusions about structure of materials in a wide region of interatomic distances. This is a very important for direct structure characterization of giant clusters, dispersed molybdenum sulfides etc.. The simple formula for the upper limit of interatomic distances when the data are collected at equidistant step on S – scatterinrg vector, may be used for the optimal experimental conditions selection.

Flexible sheet polymers or “membranes” can be regarded as two-dimensional generalizations of linear polymer chains, for which there is a vigorous theoretical and experimental literature. Flexible membranes should exhibit even more richness and complexity, for two basic reasons. The first is that important geometric concepts like intrinsic curvature, orientability and genus, which have no direct analogue in linear polymers, appear naturally in discussions of two-dimensional macromolecules. Our understanding of the interplay between these concepts and the statistical mechanics of surfaces is still in its infancy. [1] The second reason is that surfaces can exist in a variety of different phases. The possibility of a two-dimensional shear modulus in planar membranes shows that we must distinguish between solids and liquids when these objects are allowed to crumple into three dimensions. Hexatic membranes, with extended six-fold bond orientational order, provide yet another important possibility. All three phases have quite distinctive properties. [2, 3] There are no such sharp distinctions for linear polymer chains.

We present an EXAFS study of the local environment of Co dopant atoms in nanocrystalline Cu. Due to the low solubility of Co atoms in bulk Cu, these measurements yield information on the local atomic structure of grain boundaries in nanocrystalline Cu. Previous EXAFS studies on pure nanocrystalline metals have indicated an atomic arrangement in the grain boundary component exhibiting a broad distribution of interatomic spacings which differs from the atomic structure of the crystalline or glassy state. In the present investigation a significantly reduced coordination number around Co is found; also, the first shell bond length varies with dopant concentration from that typical of Co substitutional impurities in Cu to that of bulk Co. These results suggest that Co atoms substitute Cu atoms both in the disordered grain boundaries and in the lattice of the Cucrystallites and/or form Co-precipitates.