We have investigated the structural properties of sputter deposited granular AU-Al2O3 films. The films exhibit an abrupt percolation transition from insulating to metallic behavior at the composition of xc-40 vol.% Au. STM measurements yield images of individual grains and clusters of grains consistent with the TEM images. The surface roughness increases abruptly from 30Å to 50Å as the Au concentration increases from 35 to 45 vol.%. The roughening of the films in the metallic regime is consistent with behavior of the X-ray reflectivity.

The width of the single-phase stability field of nickel titanate spinel (Ni2(1+x)Ti1−xO4) has been determined in order to resolve an ambiguity in the analysis of the microstructure of equilibrated and quenched spinel-containing specimens. Bulk polycrystalline diffusion couples of the constituent oxides, NiO and NiTiO3, have been prepared at several reaction temperatures between 1400°C and 1550°C. The microstructure of the reaction layers of slow-cooled specimens has been examined by SEM and the composition has been mapped using x-ray microanalysis. It is concluded that the nickel titanate spinel phase has a narrow range of stability, and that the stoichiometry of the spinel is temperature dependent. The microstructure of equilibrated and quenched specimens is discussed in light of these findings.

Residual monomer and other low molecular weight volatile components are removed from polymer melts in a devolatilization step involving bubble formation and growth. Polymer strands containing residual volatiles were extruded into a heated and evacuated devolatilization tank and were then frozen by the flow of cooling water. They were subsequently fractured in liquid nitrogen to reveal their cross-sections and examined in a scanning electron microscope (SEM).

SEM observations revealed a previously unknown growth phenomenon in which devolatilization was seen to proceed through a ‘blistering’ mechanism. We discovered that volatile bubbles growing in the melt are fed by the formation of blisters on their inner surfaces. These blisters are formed by the coalescence of a growing bubble and the many satellite micro-bubbles formed around it as it expands. We propose a general mechanism for bubble growth in which we have shown that heterogeneous bubble nucleation in the core, which is governed by the degree of superheat, plays a major role in determining the overall rate of devolatilization. Tensile stresses accompanying bubble growth may result in a local increase in superheat by reducing the local pressure in the melt. This additional superheat combined with the possible accumulation of impurities on the macrobubble surface may be sufficient to increase the nucleation rate of microbubbles in the melt adjacent to the growing bubble, resulting in the large number of blisters formed on the bubble surface.

Most detailed studies of morphological evolution during epitaxial growth and recovery make use of computer-based simulation techniques. In this paper, we discuss an alternative, analytic approach to this problem which takes explicit account of the atomistically random processes of deposition and surface diffusion. Beginning with a master equation representation of the dynamics of a solid-on-solid model of epitaxial growth, we derive a discrete, stochastic equation of motion for the surface profile. This Langevin equation is appropriate for growth studies. In particular, we are able to provide a microscopic justification for a non-linear continuum equation of motion proposed for this problem by others on the basis of heuristic arguments. During recovery, the deposition flux and its associated shot noise are absent. We analyze this process with a completely deterministic equation of motion obtained by performing a statistical average of the original stochastic equation. Results using the latter compare favorably with full Monte Carlo simulations of the original model for the case of the decay of sinusoidally modulated initial surfaces.

We consider a non-linear version of Edwards-Wilkinson interface model for the growth in the presence of a collimated partjcie flux. We include both surface tension and surface diffusion relaxation. In a range of positive small values of the surface tension, the interface develops a state which fulfills standard criteria for spinodal decomposition. This suggests the existence of a phase transition from the ordinary state with the interface perpendicular to the incoming flux to a novel, noue.induced state with the interface apontaneously tilted with respect to the direction of the flux.

Periodic step arrays on Si(001) surfaces have been produced using photolithography, reactive ion etching and vacuum annealing. These have been studied by optical diffraction, low energy electron diffraction(LEED), and scanning tunneling microscopy (STM). The periodically varying step density on these arrays has been examined by STM. For small deviations from (100) along the [110] zone, single atomic steps dominate, while at larger angles biatomic steps are the most common; at intermediate angles the steps are of mixed character and there is some evidence for a range of unstable orientations. Interesting differences in the ratio of the areas of the two types of terrace (2×1) reconstructions are observed for the minima and maxima of the quasi- sinusoidal surfaces; these differences may be due to stresses produced by the step arrays or to differences in the line tensions associated with the two different types of steps on reconstructed Si(001) surfaces. The observations will be compared to the predictions of capillarity theory for isotropie materials. At high temperatures surface diffusion leads to a decay in amplitude of these surface gratings probably by mutual annihilation of atomic steps at the extrema. The overall rate of this process has been followed by monitoring the change in the distribution of intensity in the diffraction pattern from the grating using a He-Ne laser while the sample is annealed in UHV. With some simplifying assumptions, the intensity distribution can be directly related to the grating amplitude. The experiments are being performed for a range of grating spacings (to allow identification of the dominant transport process from scaling laws) and for a range of temperatures. The relationship between the ‘macroscopic’ observations of the shape development and the STM results will be explored.

We have mapped out the energy surfaces seen by a single silicon adatom over the Si(100) surface and Si(100) steps, using Molecular Dynamics methods. This identifies the most likely binding sites as well as the activation energies for diffusion over the terraces and steps. We find that only the 5e step with no rebonded atoms is a good sink for adatoms - the SA, rebonded Sb and Db steps are weak sinks. Because of a higher density of binding sites and lower activation energies for surface diffusion along die step edge, we expect mat growth at the Sb and Db steps take place much more readily man at the SA step.

The ability to make highly doped δ-layers in semiconductors depends on the rate of interchange of atoms between layers at the crystal surface. We have simulated molecular beam epitaxy on a silicon (100) surface covered with a monolayer of impurity atoms. The kinetics of impurity segregation to the surface was examined for various growth conditions and segregation energies. We find that segregation is facilitated by appreciable inter-layer diffusion of atoms in the top several layers. The amount of diffusion is much greater during deposition than it is when the beam is off.

The segregation behavior of model dopants during liquid phase epitaxy of A/A1−xBx heterostructures is studied using Non-equilibrium Molecular Dynamics computer simulation. Interatomic interactions are modelled using the Lennard-Jones potential and the dopant “B” atoms are assigned to have a different diameter than the host “A” atoms. The extent of segregation as a function of regrowth velocity is found to be well represented by the Continuous Growth Model of Aziz for solidification on the (111) orientation. The mechanism of segregation, however, more closely resembles the physical picture due to Jackson, Gilmer and Leamy.

Vapor deposition of smooth, microstructurally uniform amorphous films on dissimilar substrates requires coalescence of clusters that form during initial nucleation. We have developed techniques that provide sub-monolayer sensitivity to this phenomenon, relying on real time spectroscopie ellipsometry observations during ultrathin film growth (thicknesses < 50 Å). An investigation of tetrahedrally-bonded amorphous semiconductors lends insights into the role of nucleation density and adatom surface diffusion in determining the ultimate atomic-scale roughness on the film.

The formation and evolution of chemisorbed digermane layers in context with germanium thin film growth was investigated by time-resolved surface reflectometry. Modulation of the source gas supply made possible the separation and independent study of the temperature dependence of the adsorption and desorption processes. The regeneration of active sites by molecular hydrogen desorption was identified as the rate-limiting step at low substrate temperatures. A dynamic method of thin film growth was demonstrated by repetitively replenishing the active film growth sites regenerated between two successive source gas pulses. The film growth rate was shown to be related to the substrate temperature and the delay time between successive source gas pulses.

The surface morphology of MBE - grown GaAs(001) has been investigated using scanning tunnelling microscopy (STM) and reflection high - energy electron diffraction (RHEED). STM shows that the missing - dimer - row structure of the (2 × 4)/c(2 × 8) reconstruction consists of rows of clusters of two As dimers separated by rows of two missing dimers, in agreement with previous reports. Layers grown on nominally flat substrates display a multi - level system of terraces elongated along [110] suggesting that growth occurs primarily by sticking at B - type steps. For films grown under certain growth conditions, B - type steps on vicinal substrates exhibit a dendritic step morphology, which may be an example of a step flow growth instability consistent with limited Ga diffusion over steps.

In this paper we discuss results for the clustering of Ga on GaAs(001). The dominant dynamic process which drives this system toward this three dimensional equilibrium changes from Ostwald ripening at low deposition rates to coalescence at higher deposition rates. The experimental data allow us to test several theoretical predictions for cluster size distributions based on a detailed study of the microscopic processes. These include, at higher deposition rates, the observation of local ripening effects and diffusion limited growth.

A variety of recent measurements has shown that the phase diagrams of Langmuir monolayers of relatively simple amphiphiles such as fatty acids and their methyl and ethyl esters are remarkably complex. Nine condensed phases have been identified; their structures can be related to those of known smectic phases. A key distinction between phases is the orientation of the molecular tilt azimuth with respect to the local hexagonal order of the head groups. When monolayers are examined by fluorescence microscopy, regions of uniform tilt can be observed if the exciting radiation is polarized with respect to the surface normal. The tilt regions form patterns similar to those observed in freely suspended films of smectic liquid crystals. The patterns can be changed by compressing the film and by changing the temperature. Transitions between different phases can be observed.

Molecular dynamics calculations were carried out for a Langmuir monolayer at high density. A model was employed in which the motions of both the amphiphiles and the water are allowed, enabling investigation of the details of the water-monolayer interaction and the structure of the interface. Results are presented for the density profiles of the water and the amphiphiles and for the distribution of gauche defects.

Grazing incidence X-ray reflectometry has been used to characterize Langmuir-Blodgett films of cadmium arachidate deposited on silicon substrates. The agreement between layer parameters deduced from the interference fringe period and low angle Bragg peak positions was excellent. Good agreement was found between experimental and simulated reflectivity profiles only when interface roughness and a varying molecular layer thickness was included. Inclusion of interface roughness alone results in a substantial enhancement in the intensity of the Bragg peaks. This effect is identified as being equivalent to the reduction in extinction found in classical X-ray diffraction due to crystal imperfections.

In performing compression-expansion-recompression process during preparation of diacetylene (DA) monolayer, the change in colour of polydiacetylene (PDA) LB films was observed and more ordered structure of the films was achieved. The effect on optical properties could be ascribed to better arrangement of DA monomer which favoured the formation of PDA films in blue-form in polymerization.

We describe the two dimensional structure of n-Alkyl Thiols, CH3(CH217SH(C18, self-assembled on the surfaces of Au(111) and Ag(111). By using Grazing Incidence X-ray Diffraction (GIXD), we show that C18 forms ordered and dense monolayers. Although the properties of Au and Ag are very similar (for instance, the lattice constants of Au an Ag are nearly identical), the structure of C18on these two substrates is very different.

The adsorption kinetics of self-assembling n-alkyl thiol films on poly cry stalline gold substrates was studied in situ by optical second harmonic generation (SHG). The relation between the SHG signal change and the thiol coverage was established by comparison with ex situ X-ray photoelectron spectroscopy measurements. We find that the temporal dependence of the adsorption is well described by Langmuir adsorption kinetics. The source of the SHG signal is found to be linearly related to the nonlinear susceptibility of the adsorbate-substrate interaction. Experiments with chain lengths ranging from 1 to 22 showed, that the saturation coverage for thiols longer than hexanethiol is equal.

Recently developed methods of fabricating layers of long-chain molecules with functional tailgroups have provided new possibilities in the design and modification of surface properties.fi] An ui.derstanding of the relationship between the detailed molecu.'.ar structure and macroscopic properties, such as wetting and adhesion, is needed to facilitate the design of surface characteristics for specific applications such as coatings, adhesives, optical devices and substrates for binding biomolecules. [1, 2]