A partitioned system of fermions is mathematically equivalent to an assembly of two-level atoms described by spin operators. A number-phase uncertainty relation can therefore be derived to describe the noise properties of divided electrons. We examine both the number (or electron flux) and phase (or electron wave phase) decorrelation introduced by electron branching in mesoscopic circuits. Initially Poissonian, this electron number partition noise is increasingly suppressed by inelastic scattering in the transition from ballistic to dissipative electron division. Graphical results from our model show a trend from a coherent spin state in the ballistic regime toward a number-squeezed spin state in the dissipative regime, even when detrimental elastic scattering is present.

In the effective-mass approximation, the validity of the boundary conditions for an envelope function F acoss an interface between two different materials is predicated on the similarity of the nearest band-edge Bloch functions. Such approximations break down when the two materials are very dissimilar, e.g., a metal and a semiconductor. By studying one-dimensional model potentials we derive more accurate functional relations between the total wave function and its envelope. From these the usual boundary conditions are restored (continuity of F and F’/${\mathit{m}}^{\mathrm{*}}$) when similiar band edges are aligned at abrupt interfaces in semiconductor heterostructures. More importantly, we also derive appropriate boundary conditions for the case when band edges with qualitatively different Bloch functions are aligned. In particular, we find unique boundary conditions for interfaces between regions with and without periodic potentials. These boundary conditions are shown to apply to semiconductor heterostructures described within the nested effective-mass approximation and are arguably reasonable approximations for metal-semiconductor interfaces.

We study the effects on the scaling properties of self-affine fractal surfaces due to domains where a distribution of domain sizes and shapes is simulated through a Gaussian function. Approximate expressions for the roughness spectrum and surface width are confirmed with comparison to surface-width data acquired by means of scanning tunneling microscopy.

First-principles local-density-functional (FP-LDF) and embedded-atom-method (EAM) total energies, for a single Pt atom adsorbed on Pt(111), are compared to each other and to field-ion-microscope (FIM) observations. Our EAM calculations predict a small barrier to diffusion and only a slight energy difference between adsorption in the fcc and hcp threefold hollows (both smaller than 1 meV). They correspond poorly to the results of the FP-LDF calculations, which imply a diffusion barrier of 0.38 eV for passage over a bridge, and a preference of 0.18 eV for the fcc against the hcp site. FIM measurements yield a diffusion barrier of (0.25±0.02) eV, and imply that binding in the fcc site is preferred.

Angular-resolved autoionization spectra after core-to-bound excitation of CO absorbed on Ni(110) in the (2×1)p2mg structure are presented. The experimental autoionization spectra are compared with calculated spectra for the model system Ni-CO by application of the many-body Green’s-function technique using self-consistent-field results–molecular orbital–complete neglect of differential overlap one-particle wave functions. In order to supplement the semiempirical approach we furthermore carried out ab initio calculations of the autoionization rates. The angular dependences of the autoionization lines are explicitly calculated. The core-valence-valence Auger spectrum of Ni-CO after ${\mathrm{C}}_{1\mathit{s}}$ and ${\mathrm{O}}_{1\mathit{s}}$ excitation has been calculated by the particle-particle Green’s-function method with subsequent calculation of the radiationless Auger rates. The combination of the theoretical approaches and the information gained from the angular electron distribution allows one to assign the spectra obtained after core-to-bound and core-to-continuum excitation within the framework of molecular-orbital theory.

The intrinsic dynamics of photoexcited carriers in an oxygen-free ${\mathrm{C}}_{60}$ film and their remarkable evolution as the film is exposed to oxygen are revealed by transient and steady-state photoconductivity (PC) measurements at various temperatures, light intensities, and photon energies. Exposure of ${\mathrm{C}}_{60}$ film to oxygen creates deep traps that reduce drastically the carrier lifetime and, consequently, the room-temperature steady-state photoconductivity by three to six orders of magnitude. Oxygen affects the steady-state photoconductivity excitation spectrum in a qualitatively similar way, as does decreasing the ambient temperature; in both cases, the photoconductivity decreases faster when carriers are photoexcited into the band edges. The transient and steady-state PC of a ${\mathrm{C}}_{60}$ film fully exposed to oxygen becomes temperature independent.

Positron-annihilation-induced Auger-electron spectroscopy (PAES) employs positrons trapped at the surface to create core-holes and to initiate the Auger process in atoms in the topmost layer of the surface. The results of experimental and theoretical investigations of the attenuation of the positron-annihilation-induced Cu ${\mathit{M}}_{2,3}$VV Auger signal with Cs coverage on the Cu(100) surface at low and high temperatures are discussed. They reveal that at 163 K the normalized intensity of the positron-annihilation-induced Cu ${\mathit{M}}_{2,3}$VV Auger signal remains nearly constant at the clean-surface value until the Cs coverage reaches approximately 0.7 physical monolayer, at which point the signal intensity drops precipitously. We present an analysis of this unusual behavior using a model that treats the positron as trapped in a double-well potential in the direction perpendicular to the surface: one well is associated with the Cu substrate and the other with the Cs adsorbate. The sharp drop in the Cu PAES intensity which occurs over a small change in the Cs coverage is attributed to a migration of positrons trapped at low Cs coverages at the Cs/Cu interface to the positron surface state on the vacuum side of the alkali-metal overlayer at high Cs coverages. This migration can be accounted for in terms of a structural phase transition in the Cs overlayer from a disordered distribution of adsorbate atoms to adsorbate metallic islands with an ordered hexagonal close-packed structure.

The photoelectron spectrum of (CeS${)}_{1.16}$${\mathrm{NbS}}_2$ shows a strong resonance enhancement at a photon energy of 120 eV for states with a binding energy of 2.4 eV. The resonance is due to Ce 4${\mathit{d}}^{10}$4${\mathit{f}}^1$→4${\mathit{d}}^9$4${\mathit{f}}^2$ transitions, and is evidence that the Ce atoms in this compound have the valency ${\mathrm{Ce}}^{3+}$ (4${\mathit{f}}^1$). The 3d x-ray-absorption spectrum of (LaS${)}_{1.14}$${\mathrm{NbS}}_2$, (CeS${)}_{1.16}$${\mathrm{NbS}}_2$, and (SmS${)}_{1.19}$${\mathrm{NbS}}_2$ exhibit a multiplet structure which is characteristic for ${\mathrm{La}}^{3+}$ (4${\mathit{f}}^0$), ${\mathrm{Ce}}^{3+}$ (4${\mathit{f}}^1$), and ${\mathrm{Sm}}^{3+}$ (4${\mathit{f}}^5$). We conclude that in the misfit-layer compounds (RS${)}_{1+\mathrm{\delta }}$${\mathrm{NbS}}_2$ (R= La,Ce,Sm) the rare-earth atoms are trivalent.

Experimental evidence is presented for the atomic origin of quasimelting of small Au clusters. Real-time high-resolution transmission electron microscopy, an in situ evaporation facility, and the choice of a controlled substrate clearly shows atomic motion adjacent to and on nanoclusters in the <20 Å size range. We have been able to observe partial melting, atom sharing, absorption of small clusters, and shape adjustment. These phenomena are consistent with low-energy surface sputtering, energy minimization, and diffusive surface migration. Related to the transformation from icosahedral multiply twinned to single crystal observed under low voltage conditions, we propose a geometric model of the transformation which produces a continuum of low-energetic intermediate structures.

Film growth by molecular-beam epitaxy is modeled by a simple solid-on-solid model using Monte Carlo simulations. L×L substrates are used and both deposition and surface diffusion are allowed to occur simultaneously. Surface roughness is studied by measuring different surface characteristics: interface width, reflection high-energy electron-diffraction intensity, and kink density are calculated from configurations generated by simulation. We find a region of temperature and flux for which apparent layer-by-layer growth occurs. For long times, the interface width grows logarithmically with time, and its saturated value diverges logarithmically with substrate size. This unusual result suggests that within the context of this model all growing surfaces are asymptotically rough for infinite lateral extent. Because of the logarithmic behavior of the interface width, our model falls into the Edwards-Wilkinson universality class. The growth is intermediate between two-dimensional and three-dimensional nucleation and is experimentally observed in many epitaxial systems.

Energy distributions of electrons emitted from alkali-metal surfaces by impact of metastable He atoms reveal that there is a high probability for transformation of singlet atoms (excitation energy ${\mathit{E}}^{\mathrm{*}}$=20.6 eV) into triplet atoms (${\mathit{E}}^{\mathrm{*}}$=19.8 eV) prior to deexcitation into the ground state. The conversion probability (as expressed by the ratio R of the intensities of valence-band emission due to triplet and singlet ${\mathrm{He}}^{\mathrm{*}}$ deexcitation, respectively) increases with increasing alkali-metal coverage on a Ru(0001) substrate, and in turn decreases with increasing oxygen exposure at a fixed alkali coverage. These findings indicate that R is a qualitative measure for the degree of ‘‘metallization’’ of the adlayer. R also increases with temperature due to broadening of the nearest-neighbor distribution whereby, on the average, a larger part of the adlayer becomes metalliclike. For Cs overlayers exhibiting work functions <2 eV the mechanism of deexcitation changes and may proceed via ${\mathrm{He}}^{\mathrm{*}\mathrm{-}}$ (1${\mathit{s}}^1$2${\mathit{s}}^2$) formation as reflected by the R data as well as by the widths of the electron spectra.

We have calculated the physical and electronic properties of rubidium polybenzide ${\mathrm{Rb}}_2$${\mathrm{C}}_{24}$. It is a metal whose five lowest conduction bands have their minima at the (1/21/21/2) corner of the cubic Brillouin zone. Its bulk modulus is 5.3% greater than that of polybenzene while its positive formation enthalpy (with respect to Rb intercalated graphite) is appreciably smaller than that of polybenzene (with respect to graphite).

We present a theoretical study of photoemission from the Al(001) surface. The purpose of this work is to examine the validity of the nearly-free-electron-gas model for Al, and to study the importance of many-body and surface effects in its photoemission spectra. This is an extension of our earlier study on the Na spectra, but the band structure of Al is much more complicated and requires a detailed band calculation. A slab model is employed to self-consistently determine its band—with the inclusion of the self-energy correction. The band states are then used to calculate the photoemission spectra, which are compared with measurements. Reasonable agreement has been found for the Al bandwidth, and also for the spectral profiles at various photon energies. This result strongly supports the view that, once the many-body and surface effects are properly taken into account, the spectra can be well described with the nearly-free-electron bands—as in the case of Na. Special attention has been paid to surface-state emissions. A resonant enhancement in its spectral intensities has been found both in the calculation and in the measurement. However, there still exist some discrepancies which call for further studies.

We study the combined effects of local anharmonicity and transverse layer rigidity on the nonlinear gallery expansion in ternary intercalated systems. Numerical simulations are performed using both Lennard-Jones potentials and cubic anharmonic potentials between the intercalant atoms and the host-layer atoms. The harmonic approximation is used for the host-layer deformation energy. Simulation results are compared with analytic calculations within an effective-medium approximation. We find that the gallery expansion is determined by a competition between the compressibilities of the intercalants and the transverse rigidity of the host layer. A single small impurity limit clearly brings out the role of anharmonicity. The effective-medium solution reduces to exact results in three limiting cases; for perfectly floppy and perfectly rigid host layers, and for the harmonic potential with arbitrary host-layer rigidity. While it is well known that Vegard’s law (linear expansion of the gallery spacing) is observed in the harmonic limit when the two intercalants have the same compressibility, we find that the inclusion of anharmonicity gives rise to deviations from Vegard’s law which increases with the increase in host-layer rigidity and the degree of anharmonicity.

The ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ nuclear magnetic resonance (NMR) of thin diamond films deposited from naturally abundant (1.1 at. %) as well as 50% and 100% ${}_{}{}^{13}{}_{}{}^{}\mathrm{enriched}$ ${\mathrm{CH}}_4$ heavily diluted in ${\mathrm{H}}_2$ is described and discussed. Less than 0.6 at. % of hydrogen is found in the films which contain crystallites up to ∼15 μm across. The ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ NMR consists of a broad 50–65-kHz-wide Gaussian line attributed to H atoms bonded to carbon and covering the crystallite surfaces. A narrow Lorentzian line was only occasionally observed and is found not to be intrinsic to the diamond structure. The ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ NMR demonstrates that >99.5% of the C atoms reside in a quaternary diamondlike configuration. ${}_{}{}^1{}_{}{}^{}\mathrm{-}_{}^{13}{}_{}{}^{}$C cross-polarization measurement indicates that, at the very least, the majority of ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ nuclei cross polarized by ${}_{}{}^1{}_{}{}^{}\mathrm{H}$, i.e., within three bond distances from a ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ at a crystallite surface, reside in ${\mathit{sp}}^3$ diamondlike coordinated sites. The ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ relaxation rates of the films are four orders of magnitude faster than that of natural diamond and believed to be due to ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ spin diffusion to paramagnetic centers, presumably carbon dangling bonds. Analysis of the measured relaxation rates indicates that within the ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ spin-diffusion length of √${\mathit{DT}}_1^{\mathit{c}}$ ∼0.05 μm, these centers are uniformly distributed in the diamond crystallites. The possibility that the dangling bonds are located at internal nanovoid surfaces is discussed.

The C 1s photoelectron angular emission from a disordered CO layer on Ni(110) at 300 K (coverage approximately 0.7 monolayer) was studied for polar angles up to 80° and several azimuths. The experimental intensity distributions are compared to multiple-scattering cluster calculations which include the possibility of anisotropic bending vibrations of the adsorbed molecule based on a new formalism for thermal averaging in the diffraction theory. From the azimuth-dependent width of the forward scattering peak we have determined bending vibraional amplitudes of 12° and 17° for the [11¯0] and [001] azimuths, respectively. The optimum agreement between experiment and theory over the whole range of polar angles is obtained for a CO layer with short-range order domains and equal occupation of on-top and short-bridge sites.

We examine atom transfer resulting from coherent multiple excitation of the adsorbate-substrate bond caused by inelastic tunneling of a single electron (or hole) via a negative- (or positive-) ion resonance. At low biases and in particular for the transitions resulting in atom transfer, the rates of coherent multiple excitation are nonlinear and also highly asymmetrical with respect to the polarity of the bias. We establish a simple criterion for the regime in which this mechanism dominates over earlier proposed mechanisms for atom transfer resulting from vibrational heating by sequential (incoherent) inelastic resonance tunneling. In the case of the atomic switch, where a Xe atom is transferred between a Ni surface and a tip, the vibrational heating mechanism is found to dominate over the coherent mechanism. For other systems, such as Na adsorption on Cu or ${\mathrm{O}}_2$ adsorbed on Pt, the coherent mechanism is argued to play a role in bond breaking.

A semi-infinite spatially dispersive dielectric medium is re-examined. The analytical properties of the dielectric response similar to the Kramers-Kronig relations are proved in a q variable. This analysis permits one to introduce the surface energy-loss function, which generalizes the well-known expression Im{-1/[ε(ω)+1]} to the spatially dispersive case. The theory is illustrated by application to the hydrodynamical model of a semi-infinite medium with aluminum parameters. The reflected-electron surface energy-loss spectrum is obtained. The results are discussed.

X-ray reflection from periodical multilayers with randomly rough interfaces has been described within the distorted-wave Born approximation. The method is suitable for calculating both specular x-ray reflection and nonspecular (diffuse) scattering. In this paper, both in-plane and vertical correlations of the roughness profiles have been considered and it has been demonstrated that the vertical roughness correlation substantially affects the nonspecular scattering. The theory can explain resonant effects observed in the beam scattered nonspecularly from a periodical multilayer. The theoretical approach has been used for the study of interfacial roughness in a long-periodic AlAs/GaAs multilayer and good agreement has been achieved between the experimental results and the theory.

Fluctuation and morphology of steps growing in a surface diffusion field are studied theoretically and by the Monte Carlo simulation. Owing to the asymmetry in step kinetics (Schwoebel effect), a morphological instability takes place for advancing steps at a critical impingement rate ${\mathit{f}}_{\mathit{c}}$ of gas atoms. The fluctuation of a step is reduced for receding steps with f<${\mathit{f}}_{\mathrm{eq}}$, and enhanced for advancing steps with f>${\mathit{f}}_{\mathrm{eq}}$. The width of a single step shows critical divergence at ${\mathit{f}}_{\mathit{c}}$. Above the instability f>${\mathit{f}}_{\mathit{c}}$, the step motion exhibits spatiotemporal chaos, in which the crystal anisotropy influences the morphology. For a vicinal face, when the step advancement rate increases, the motion of consecutive steps is strongly correlated and the terrace width becomes stable although the fluctuation of each step is enhanced. When steps recede in sublimation, bunching of the steps is observed, which is analyzed as an instability of antiphase oscillation.