In deposited on UHV cleaved p-WSe2 (0001) is investigated by photoelectron spectroscopy (XPS, UPS), low energy electron diffraction (LEED), scanning electron microscopy (SEM), and surface photovoltage (SPV) experiments. In forms an atomically abrupt, non-reactive metallic overlayer on the substrate. It grows in threedimensional clusters (Volmer-Weber growth mode). The experimentally observed band bending induced by In at RT is smaller than expected by the Schottky limit. Photoemission source induced SPV values at 100 K are saturated and different for the substrate and In overlayer emission lines. The results are explained by laterally inhomogeneous electric potential distributions due to the In clustering on the semiconductor surface.

The geometric and electronic structure of ultrathin oxide films grown by oxidation of NiAI(110) was studied by LEED (low energy electron diffraction), EELS (electron energy loss spectroscopy), XPS (X-ray photoelectron spectroscopy) and ARUPS (angle resolved ultraviolet photoelectron spectroscopy). Two diffcrent ultrathin aluminum oxide films have been observed which are characterized by a hexagonal arrangement of oxygen atoms. The films are approximately 5 Å thick, most likely consisting of two alternating oxygen - aluminum layers and are oxygen terminated. The second oxide phase shows close similarities with the (111) face of γ − A12O3 and the (0001) face of α – A12O3 respectively.

We studied interfacial behavior of coherent NiAl intermetallic layers on compound semiconductor heterostructures qualitatively via computer simulations using the embedded atom method. From the static simulations, a tentative model structure at the interface between the NiAl (CsCl type) and zincblende structure is proposed. The real time epitaxial growth simulations using the molecular dynamics technique show the effects of various parameters on the growth sequence along with other interesting results like surface diffusion and melting.

The initial stage of epitaxial growth of GaP on Si by low pressure metalorganic chemical vapor deposition was studied. The surface changes from heavily islanded morphology to more planar morphology with increasing V/III flux ratio. GaP on Si grown at low V/III flux ratio contains a high concentration of defects, however, a significant reduction in the density of these defects is observed in GaP grown using a high V/III flux ratio. The antiphase domains generated at the GaP/Si interface are annihilated during the growth. The critical V/III ratio where the growth changes from island-type growth to planar-type growth reduces with increasing growth pressure.

The codeposition of Co and Si by molecular beam epitaxy on Si substrates in a highly Si rich flux ratio results in the growth of epitaxial CoSi2 columns surrounded by high quality single crystal Si. The formation of such columnar layers is indicative of selectivity in the growth of CoSi2 and Si. The nature of this selectivity was explored by examining the effects of depositing Si, CoSi2 and Co respectively, on ‘template’ layers containing CoSi2 columns grown on (111) oriented Si substrates at 800°C.

Increased selectivity was observed with increasing growth temperature in the range of 650 - 800°C. The overgrown Si and CoSi2 appear to grow preferentially on exposed Si and CoSi2 areas respectively, of the template layer. The selectivity could be reduced by either a decrease in the growth temperature or an increase in the Co:Si flux ratio. Surface diffusion of the growth species coupled with a high rate of bulk diffusion of Co in Si appears to promote the selective growth behavior, resulting in changes in the sub-surface dimensions of the CoSi2 columns in the template layer as well. The deposition of Co alone results in the growth of large islands of CoSi2, seeded on the exposed surfaces of CoSi2 columns in the template layer. These islands are probably a consequence of the formation, migration and coalescence of CoxSiy clusters on the substrate surface.

Self nucleation layers, nominally 50 nm in thickness, have been predeposited at temperatures in the range 600–1100°C and shown to markedly and uniformly improve the surface morphology of epitaxial layers of GaN on highly oriented (0001) sapphire substrates. However, the epitaxial relationship between the GaN film and the sapphire substrate and the electrical and optical properties of these films depend strongly on the temperature at which the nucleation layer is deposited. For example, growth on a nucleation layer deposited at 1100°C yields a film little changed In carrier concentration or mobility and exhibiting the epitaxial relationship [(O0 0 1)GaN// (O001)sapphire and (1010)GaN //(1120)sapphire] characteristic of films grown directly onto (0001) sapphire. In contrasT, film growth onto a nucleation layer deposited at 600°C results in a typically oriented but semi-insulating layer. Of particular interest, an intermediate growth temperature (850°C) yields GaN films that are unconventionally twinned and semiinsulating. The twinning is distinguished by GaN sublattices that are rotated ±10.9° with respect to the sapphire lattice, such that (3030)GaN //(4150)sapphire. While all films in this regime are twinned and highly resistive, examples of scattering from twins with unequal volumes and non-ideal rotation angle have been occasionally encountered. The results clearly demonstrate that the orientation of the nucleation layer governs the orientation and properties of the final film.

Alternate layers of GaAs and Ca0.5Sr0.5F2 are grown by molecular beam epitaxy. The morphology, orientation, composition and crystallinity of the layers are analyzed as a function of growth temperature and sequence. The fluoride layers show a high degree of crystallinity and a smooth surface morphology. The structural and morphological quality of the GaAs overlayer is improved by electron irradiation of the fluoride surface prior to GaAs growth, and by a two-step growth procedure for the GaAs over-growth.

A four-circle diffractometry technique is used to determine the heteroepitaxial relations of VO2 and TiO2 thin films grown by an MOCVD technique on sapphire (0001) and (1120) surfaces. The use of a reflective geometry eliminates special sample preparation of the sample for the x-ray diffraction measurements. The distribution of epitaxial domains is found to depend strongly on the symmetry of the underlying substrate.

Epitaxial α-Fe films have been grown on Si(111) substrates at 30 and 320°C by electron beam evaporation in an ultra high vacuum environment to a thickness between a few hundred and several thousand Angstroms. Conventional θ – 2θ x-ray diffraction and transmission electron microscopy show that the α-Fe films are oriented with the Fe(1ll) plane parallel to the Si(111) plane and with the Fe[110] direction parallel to the Si[110] direction in the plane of the substrate.

A bilayer of CoSi2 covered with TiN on (100)Si has been processed in a nonvacuum environment using a (100)Si wafer deposited with a thin film bilayer of Ti under Co. The Si/CoSi2/TiN stack has been studied using transmission electron microscopy, Rutherfor Backscattering Spectrometry and Auger Electron Spectroscopy. Cross section TEM and RBS studies showed that CoSi2 film is a single crystal and epitaxial with (100)Si. Ledges parallel to (111)Si were also observed at the (100)Si/CoSi2 interface, which was mostly planar. The orientation relationship at Si/CoSi2 interiace, microstructural characteristics of CoSi2 and TiN and the mechanism of 2the reaction are presented.

Planar strain in CaF2 and Ge/CaF2 films grown on (111) Si substrate has been measured by an x-ray double crystal diffraction technique using rocking curves. The films grown by a solid phase epitaxial approach using in situ rapid isothermal processing are found to have small tensile planar strain.

FeIr superlattices with short periodicities are realised by Molecular Beam Epitaxy. Ir on (1120) sapphire and Fe on (111) Ir growths are studied in situ by electron diffraction. Like FeRu superlattices, a new Fe state is stabilized with in-plane interatomic distances expanded. FeIr superlattices are analysed by X-Ray θ-2θ diffraction. It is shown that this technique allows precise calibration of Fe and Ir thicknesses and a direct determination of distances between Fe (and Ir) planes in the axis of growth. Diffraction study of FeIr superlattices reduced in powder shows that the stacking sequence in the multilayer is ABC.

Silver-nickel multilayers have been prepared by cathodic sputtering on glass, silicon and carbon-covered mica substrates kept at 100 K. X-ray diffraction experiments show that highly textured, polycrystalline superlattices are formed. There exists a critical number of atomic planes nc = 3, below which non-crystalline samples are obtained. This critical number can even be lowered in samples with non-equal numbers of Ag and Ni atomic planes. The simulation of the X-ray spectra assuming sharp interfaces and Ag and Ni (111) distances slightly larger than the bulk values leads to a good agreement with the experimental spectra. Transmission x-ray and electron diffraction experiments show that equivalent crystallographic directions are aligned in the Ag and Ni (111) planes, with a noticeable relaxation of the in-plane distances at the interfaces. Preliminary high-resolution electron microscopy results are also presented.

The structures of e-beam evaporated Pd/V multilayer thin films have been studied under various film growth conditions. Both the deposition rate and the substrate temperature were varied in an e-beam source UHV deposition system, and the films were subsequently characterized by xray scattering and cross-sectional TEM.

We report the comprehensive investigation and characterization of the band structure and interband transitions for the strained InxGa1−xAs/GaAs heterostructures and QW by use of a combination of- different spectroscopic techniques, that is photocurrent, photoreflectance and photoabsorption spectroscopies under low temperatures and high pressures.

We have performed low-temperature photoluminescence (PL) to characterize the properties of heteroepitaxial ZnTe grown by MBE as a function of Zn/Te flux ratio, growth temperature, ZnTe layer thickness, and type of IIl-V substrate. In contrast to most previous studies, we consider the effects of the residual thermal strain in the material and re-assign the shallow exciton peaks. The main features of the PL spectrum of ZnTe/GaAs for Te-rich growth conditions are double acceptor-bound exciton and oxygen isoelectronic center bound exciton peaks. Zn-rich conditions result in a strong shallow acceptor bound exciton peak, excitons bound to closely spaced acceptor pairs, and donor-acceptor pair peaks due to As and possibly other shallow acceptors. High growth temperature reduces the strength of peaks due to excitons bound to closely spaced acceptor pairs, oxygen related structures and a deep level peak. Thick layers are needed to avoid deep levels (possibly Ga related) which appear in the thin layers. The PL spectra for ∼1.3 µm thick ZnTe layers on GaAs and GaSb are almost identical. ZnTe/InP yields strong deep levels, which are possibly In related. Our results show that high quality ZnTe epilayers can be obtained at moderately high growth temperature under Zn-rich conditions, if the thickness is sufficiently large.

Magnetic superlattices are of great current interest due to the improvement of crystal growth techniques for their preparation and their potential for practical applications in high density magnetic recording. It is apparent that a strong correlation exists between structural and magnetic properties of these supcrlattices. Careful sample preparation and structural characterization arc necessary in order to tailor their magnetic properties. Molecular Beam Epitaxy (MBE) provides the capability for controlled crystal growth and in-situ strtuctoral, chemical and physical characterization. Ex-situ techniques such as X-ray diffraction and high-resolution TEM, also provide insight into interfaces in these structures. Co layers sandwiched with Au, Cu and Pt layers of various thickness are discussed in this paper.

New phenomenon in epitaxial systems - the formation of strain controlled modulated domain and heterophase structures in epitaxial layers - is under theoretical investigation. These structures should form due to the elastic interaction of an epitaxial layer with a substrate (or another epitaxial layer). Modulated structures consist of periodically alternating layers of differently oriented domains of one phase (e.g. twins) or layers of different stable and metastable phases. It can also include stabilized virtual phases i.e. metastable phases which cannot be formed in bulk systems.

The phase, orientation, defect structure, and surface morphology of an epitaxial thin film grown on a structurally dissimilar substrate can depend critically on the first few monolayers of growth. Using examples from metal/III-V semiconductor epitaxy, we illustrate how the overlayer structure and properties depend on the substrate surface reconstruction, the substrate temperature, and the order of deposition. For example, the orientation of a NiAI film grown on the {100}AIAs surface is determined by the composition of the first deposited monolayer. In another example, the nucleation of the bulk metastable phase, τMnAl is favored over the nucleation of the high temperature ∊ phase when the nucleation step occurs at the interface between a thin amorphous Mn-Al template and the AlAs/GaAs substrate. Furthermore, the orientation of the easy magnetic axis of ferromagnetic τMnAl can be controlled by a single monolayer of Mn.

We have investigated the relationship between interface chemistry, overlayer structure, and band bending when thin epitaxial overlayers of Ni, Al, and NiAI are grown by molecular beam epitaxy on anion-stabilized GaSexAsl−x/GaAs(001)-(2×l) surfaces. The substrates were prepared by passivating GaAs(001) with H2Se in a metal-organic chemical vapor deposition reactor. This treatment is now known to result in Se-As anion exchange in the top several anion layers, as well as a significant reduction in surface-state density. Chemistry of interface formation and band bending were monitored by x-ray photoemission. Overlayer structures were characterized by low-energy electron diffraction and x-ray photoelectron diffraction. Al, Ni, and NiAI overlayers assume fcc-R45°, metastable-bcc, and CsCl structures respectively. The free surfaces as prepared were nearly flat-band, exhibiting only ∼0.180 meV of band bending. The growth of Al, Ni, and NiAI epitaxial films at a substrate temperature of 100°C increased the band bending, resulting in Schottky barrier heights of 0.48, 0.89, and 0.90 eV, respectively. The smaller increase in band bending when Al is depositied is correlated with a lack of disruption of the anion sublattice. Ga and As 3d core-level spectra for the growth of 25 monolayers of epitaxial NiAI on GaAs(001)-c(2×8) at 100C are virtually identical to those measured for NiAI growth under the same conditions on GaSex Asl×x/GaAs(001)-(2×l). Moreover, the band bending is the same, leading to a Schottky barrier height of 0.90 eV, and establishing that the rather high Schottky barrier height at the NiAI/GaAs(001) interface is a result of Fermi-level pinning deep in the forbidden gap.