The energies of various two-dimensional GaAs on Si films have been calculated using the first principles pseudopotential method and density functional formalism. For GaAs on Si(111), the structures formed by adding a bilayer of GaAs to Si(111)1×1:As are shown to have positive formation energies, even after exchange reactions which eliminate the interface dipole are allowed. For GaAs on Si(100), the dependence of the formation energy of the films on the chemical potentials of the atomic constituents has been calculated. In the limit where μAs=μAs(bulk), and assuming the films have equilibrated with a bulk GaAs reservoir (μGa + μAs = μGaAs (bulk)), the lowest energy film is found to be the Si(100)2×1:As surface. In the opposite limit, μGa=μGa(bulk), the lowest energy film is the Si(100)2×1:(GaAs) surface. A new metastable structure obtained by adding 1/2 monolayer of Ga to Si(100)2×l:As has been studied.

GaAs samples deposited on Si by molecular beam epitaxy (MBE) with a graded thickness of 0–3 nm initially show the presence of a metastable two dimensional (2D) layer containing Ga and As. In the thicker regions of the wedge samples, islands (3D topography) form in the presence of the 2D sea, i.e., Stranski – Krastanov growth. Compositional profiles of these wedges were made with in situ Auger electron spectroscopy (AES) which has allowed the identification of at least four regimes of growth. Lattice images from cross – sectional transmission electron microscopy (XTEM) are consistent with the AES profiles. Substrate temperature during deposition of the films has a strong effect on film topography, as does the beam – flux ratio on film stoichiometry.

We present scanning tunneling microscopy images and atomic models for a variety of GaAs(100) reconstructed surfaces. For homoepitaxial material we show the sequence of phases from c(4×4) through c(8×2) as the As surface concentration is reduced. For the heteroepitaxial GaAs/Si(100) growth we show the first two stages of film development, namely, Si(100):As-(1×2) monolayer coverage followed by adsorption of a submonolayer of Ga dimers. The next stages of film development are discussed.

An ultra high vacuum scanning electron microscope equipped to an MBE system is utilized to study a transient of a surface atomic structure during MBE growth of GaAs and AlGaAs by the alternate supply method. Lateral growth of a Ga-monolayer over microns is realized utilizing Ga droplets. This is confirmed by discriminating the Ga and As top layer by using the secondary electron intensity difference between the Ga and As top layer. The growth mechanism of the Ga monolayer is discussed based on the results.

LEED and Auger electron spectroscopy have been used to studied the interface formation of bismuth on InSb(110). For the first time, well defined superstructures were observed at room temperature on metal/semimetal-III-V semiconductors. A (1×2) phase, at 0.5 ML bismuth coverage, and a (1×3) phase, at 0.4 ML bismuth coverage, appear with different thermal heat cycling. The dynamical origin of these phases is thought to be a repulsive interaction between overlayer chains due to the detailed geometry of the overlayer chain structure and to the overlayer induced strain field within the substrate.

The temperature and coverage dependent ordering of bismuth overlayers on GaAs(110) is examined using low energy electron diffraction (LEED). Sixth order electron diffraction profiles associated with overlayer ordering are observed at coverages of 0.7, 1.0, and 1.5 monolayers (ML) and for temperatures ranging from -110 C to 200 C. The full-width at half-maxima (FWHM) of the sixth-order spots are examined. Profile analysis reveals narrowing widths with increasing annealing temperature, indicating an improvement of the long-range ordering of the overlayers. Differences in inter- and intrachain ordering are observed, analyzed, and discussed.

Synchrotron radiation photoemission was used to characterize Sm and Mn thin film nucleation and growth on solid Xe substrates, in the 3×1014 - 2×1016 atoms/cm2 coverage range. Film growth is well approximated by a model in which the nucleation site density remains constant and hemi-ellipsoidal particles increase in size until coalescence is achieved. Site density and average cluster size are determined from the coverage-dependence of metal and Xe photoemission intensities. Size estimates are confirmed by experimental fingerprints of coalescence.

An organic molecular beam epitaxy (OMBE) system has been designed and constructed with in situ reflection high-energy electron diffraction (RHEED) specifically for the deposition of organic molefelar layers under ultrahigh vacuum (UHV), the order of 10–10 torr. The system is equipped with a portable UHV chamber which allows easy transfer of the OMBE film samples to a separate UHV scanning tunneling microscopy (STM) system. A structural investigation of heteroepitaxially grown organic ultrathin layers of copper phthalocyanine (CuPc) on inorganic substrates was carried out by the combined UHV system from less than a monolayer of CuPc.

The initial stages of heteroepitaxy of InSb on GaAs(100) grown by MBE have been studied by transmission electron microscopy. Three dimensional InSb island growth occurs in which the majority of the 14.6% misfit strain is accommodated by a square array of a/2<011= edge-type misfit dislocations. The implications of each island having a well defined defect array before coalescence into a continuous epilayer are discussed. Some 600-type a/2<101= interfacial defects and associated threading dislocations are also observed in coalesced films and possible reasons for their existence are explained. A strong asymmetrical distribution of planar defects in the InSb islands is observed and the origin of the asymmetry is discussed. Finally some evidence for local intermixing in the vicinity of the interface is presented.

Surface extended x-ray absorption fine structure (SEXAFS) measurements on the nanometer level were made for AI/M interfaces where M was Cu or Ni. The samples were studied immediately after deposition and after heat treatments. Significant differences in interface reactions were observed depending on deposition direction (Cu on Al or Al on Cu) and the amount of mixing was also related to whether M was Cu or Ni. The SEXAFS measurements revealed that there were no detectable amounts of C or O present. One percent Zn was observed to be in the Al layers. The results obtained from the as-deposited interfaces correlate well with data obtained from buried interfaces of like element combinations.

Various techniques using transmission electron microscopy for determining the relative position of two crystals separated by an interface are reviewed briefly. Measurements obtained by these means can be used to identify unrelaxed interfacial configurations. The modelling of relaxed configurations based on these unrelaxed candidate structures requires additional information from experimental techniques such as electron diffraction and high resolution microscopy, or theoretical investigation by computer simulation. This procedure is illustrated for a selection of grain and interphase boundaries. {211} grain boundaries between twin related crystals of Al and Ge, and interfaces in NiSi2:Si, CoSi2:Si and AI:GaAs epitaxial systems, are discussed.

CoGa/GaAs and ErAs/GaAs grown by molecular-beam epitaxy have been studied using high-resolution transmission electron microscopy (HRTEM). The epitactic interfaces have been shown to be abrupt on the atomic scale. Computer simulations of the HRTEM images have been obtained for different interface structures under various specimen and image conditions. Practical problems in the comparison between the simulated and experimental images are discussed.

Low energy lamellar interfaces in the directionally solidified eutectic (DSE) NiO-ZrO2(CaO) have been investigated using transmission electron diffraction and imaging. The symmetry of this bicrystal and an aspect of interfacial relaxations in the form of symmetry lowering in-plane rigid body translation (RBT) have been explored by performing convergent beam electron diffraction (CBED) experiments of plan-view bicrystals. Edge-on interfaces have also been studied by conventional and high resolution transmission electron microscopy (CTEM and HRTEM respectively), and electron diffraction fine structure analysis. Despite certain experimental difficulties due to interfacial defects and strain, plan-view CBED patterns offered valuable information concerning bicrystal symmetry and indicated no symmetry lowering RBT in this bicrystal. The suitability of plan-view CBED is briefly discussed in view of its potential as a technique to determine bicrystal symmetry and RBT.

Corrections are required for double crystal X-ray diffraction characterization of epitaxial AlxGa1-xAs layers grown on offcut GaAs (100) substrates. Double crystal X-ray diffraction measurements show that the cubic film unit cell defined by Vegard's law is triclinicly distorted and tilted with respect to the substrate unit cell. The distortion and tilt angles oppose each other defining a crystal geometry where the substrate and film <100= axes remain approximately coplanar with the surface normal. This film/substrate crystal geometry leads to formulation of a model describing heteroepitaxy on offcut (100) substrates. When film atoms are bonded to an offcut substrate, the already tetragonaly distorted film unit cell is subjected to additional cell distortions. The magnitude of this additional strain depends on where the film atoms are positioned on a substrate terrace. The first few layers of film atoms establish swain grades across individual substrate terraces. Constrained by the geometry of this interface region and driven by strain relaxation in the net growth direction, subsequent heteroepitaxy forms the measured film/substrate crystal geometry.

Total energy minimization calculations show that the interface bonds are strained in nominally lattice matched In0.53 Ga0.47As/InP (001) heterostructures, in agreement with recent X-ray measurements. Anion intermixing relieves the interface strain. The calculated valence band offset varies with the interface bond lengths so the minimum energy structure must be used for a given composition. Then the calculated offset is independent of composition and is in good agreement with experiment. A simple model exhibits the qualitative features revealed by these calculations.

The CaSi2/Si interface is studied with state-of-the-art first-principles calculations. Various models for the interfacial structure are examined, in which the Ca atoms at the interface exhibit 5-, 6-, 7-, or 8-fold coordination. The structures with sevenfold coordination (as in bulk CaSi2) have the lowest energy. However, the sixfold- and eightfold-coordinated structures are only ∼0.1 eV higher in energy. Schottky barrier heights are briefly discussed.

We have studied and analyzed critical thickness required for the formation of misfit dislocations in semiconductor heterostructures. The present analysis has been carried out assuming that the nucleation of a misfit dislocation is controlled by the activation energy. The energy of the cohernt interface and the misfit dislocation configuration has been evaluated using a discrete dislocation analysis. Further, atomic structures of coherent and semicoherent interfaces containing misfit dislocations of the type a/2<110={111} ↑ <110= (600 dislocation), a/2<110={001} ↑ <110= (90° dislocation) and a/6<112={111} ↑ <110= (90° partial dislocation) in Ge/Si system were simulated. The total energy, consisting of both core and elastic energy components, was calculated using Stillinger-Weber interatomic potentials. The results show that the energy is a strong function of the nature of dislocations. A 60° dislocation is found to exist in undissociated form in shuffle configuration, but the core contains a dangling bond at the interface. The core of a 90° dislocation reconstructs at the Ge/Si interface with no dangling bonds. The calculated atomic configurations of dislocations and interfaces are found to be in good agreement with high resolution transmission electron microscopy observations.

The growth mode of Ge on the (1102) surface of sapphire is explored with X-ray photoelectron spectroscopy. Ge exists in two bonding states at the interface, Ge-Ge and Ge-sapphire. Ge forms islands at submonolayer coverage for deposition temperatures of 25°C and 625°C. The formation of the islands is revealed by the rapid increase in the relative fraction of the Ge-Ge bonding state for Ge coverage less than 1 ML. The shift in the Ge-Ge peak binding energy to the bulk Ge value at less than i ML suggests that the islands are three dimensional for deposition at 625°C.

The growth, ordering, and energetics of Hg overlayers on Cu(O01) have been studied using atom beam scattering, LEED and angle-resolved photoemission. Two stable ordered phases have been identified: one phase is a c(2↑2) and the other phase is a higher density square lattice which has a coincidence c(4↑4) structure. A phase diagram has been determined using LEED and atom beam diffraction data for surface temperatures between 180 and 330 K. ABS data suggest out that there is a narrow coexistance region between these two phases. The isosteric heat of adsorption has been determined as a function of coverage.

A new type of phase transformation at the interface is described in CoSi2/Si(111) B (i.e. twinned) epilayers. Thin (25Å) CoSi2 films are codeposited at room temperature on Si (111) with a Si-rich surface layer, and subsequently annealed. Plan-view transmission electron microscopy (TEM) shows that these films have low symmetry, the interface being characterised by a shift “R” between (220) planes in CoSi2 and Si. X-ray diffraction from “R” films differs from otherwise identical films either grown without Si-rich surface layer, or not annealed, which have the conventional cubic structure (“C”); R-CoSi2 cannot be indexed on a single reciprocal lattice. Cross-section high-resolution TEM suggests the presence of a separate (non-cubic) layer ≈9Å thick at the interface in these films. Annealing of R-CoSi2in-situ in the TEM shows a reversible transformation R⇔C occuring at temperatures varying from 180°C to 150K, depending on layer stoichiometry. Rt⇔C is thus a quasi-equilibrium, diffusionless transformation. We propose that R-CoSi2 lowers interfacial free energy for certain stoichiometries, but that bulk constraints stop the entire layer from transforming.