Initial condensations of Cu, Ag and Au on Si(lll)-7x7 surface are seen continuously by video tape recording and intermittently by photographic films using an UHV electron microscope in reflection electron microscopy (REM). The growths of initial superlattice structures are found to relate with the steps of the 7x7 surface and the superlattice structures of a for Cu, for Ag and 5x2 for Au are nucleated at the upper side of the stepsand grow over the lower side terrace accompanied by the step movement. The growth of Au on Si(lll)-7x7 surface is seen in transmission electron microscopy (TEM) to supplement geometric information. It is found that the 5x2 domain of Au grows in the <llO>Si direction preferentially. The superlattice structures formed at submonolayer range are seen for the first time in TED pattern, which is useful to judge the previously proposed models from intensity distribution. REM-RHEED and TEM-TED allow us to study dynamic process of the initial growth stages of metals on Si(lll)-7x7 in real space and to analyse the geometrical structures of the superlattice structures at submonolayer.

Although epitaxial growth of single crystal metal films was reported at least five decades ago, the availability of modern ultra high vacuum technology and sensitive characterization of thin film properties has opened many new directions in this area of materials research. Of considerable interest is the utilization of the interfacial forces associated with epitaxial growth to stabilize structures which may exist in a metastable minimumenergy configuration. The problem of metastable structural phases of elemental metals will be discussed with particular emphasis upon the 3-d transition metals. In these materials the magnetic properties both depend dramatically upon the structural phase and contribute toward determining the stable minimum energy configuration.

The use of convergent beam electron diffraction patterns (CBPs) for investigating metal—semiconductor interfaces in plan—view samples is considered. It is shown that a wide—angle diffraction technique provides a sensitive method of measuring tetragonal distortions in NiSi 2/(001)Si bicrystals. A study of CBP symmetry and the detailec branch structure in higher order Laue zone rings has enabled the interfacial rigid body displacement in NiSi 2/(001)Si and Al/(001)GaAs films to be determined.

Thin (<200Å), epitaxial CoSi2 films have been grown on (111) Siwafers in a UHV system using a variety of growth techniques including solid phase epitaxy (SPE), reactive deposition epitaxy (RDE), and molecular beam epitaxy (MBE). SEN and TEN studies reveal significant variations in the epitaxial silicide surface morphology as a function of the sillciqd formation method. Pinhole densities are generally greater than 107 cm-2, although some reduction can be achieved by utilizing proper growth techniques. Si epilayers were deposited over the CoSi2 films inthe temperature range from 550ºC to 800ºC, and the reesuulttinng structures have been characterized using SEM, cross—sectional TEN, and ion channeling measurements. These measurements show that the Si epitaxial quality increases with growth temperature, although the average Si surface roughness and the CoSi2 pinhole density also increase as the growth temperature is raised.

Strains in both type-A and type-B NiSi2 epitaxial films grown on Si(lll) substrates were measured by means of MeV 4He+ ion channeling. The results show the critical thickness to maintain pseudomorphic growth strongly depends on theepitaxial orientation of the NiSi2 film. The difference in critical thicknesses between type-A and type-B NiSi2 can be explained by considering the different type of misfit dislocations introduced at the interface. Namely, at the type-B interface, 1/<112> partial dislocations associated with interface steps are allowed while they are prohibited at the type-A interface. Dislocation densities measured by TEM also support these results.

We discuss the use of electron beam induced current measurements in a scanning electron microscope to deduce local Schottky barrier height with high spatial resolution. For theNiSi2/Si system, using UHV-prepared thin “templates”, wedemonstrate the uniformity of barrier heights for A or B single crystal films. In comparison, there is evidence for local variation of barrier height in mixed A+B films. Quantitative models for EBIC dependence on barrier height are discussed. Local variations in barrier height can be overlooked by other techniques and may be much more common than previously suspected.

Epitaxial NiSi2 layers have been grown onto (100) and (111) Si substrates by multiple scan electron beam annealing. The formation and the composition of the silicides have been analyzed by Rutherford backscattering techniques and by electron diffractionobservation. The phase and the composition of the silicides depend on the power density of the electron beam. Under the optimum conditions, epitaxial NiSi2 layers with a high surface morphology can be grown. An attempt has been made to form crystalline Si—NiSi2—Si heterostructures and the preliminary data are also presented.

A systematic study of superconducting Te, Hc and also the behavior of resistivity of Nb/Si mfltiiayers is reported. Nb and Si layers with different thicknesses were deposited alternatively in an LUIV two electron—beam evaporating installation and controlled automatically by a microcomputerquartz—monitor system. Well reproduciole results were achieved. Structural analyses show very good modulated structure with (110)textured polycrystallino Nb and] amorphous Si layers. Superconducting Tc of Nb/Simultilayers are significantly higher than that of the sputtered Nb/Ge system. Thevariation of Hc(T) in parallel field manifests a 2D–3D crossover with transformation temperature of 0.7– 0.8 Tc. The possible mechanism and implication of these phenomena were discussed.

The crystallographic and electronic structure of iron films epitaxially grown on Cu single crystals was investigated by LEED, AS, EELS and UPS. The Cu(l00), Cu(ll0) and Cu(lll)faces were used as substrates for the growth of the iron films. In our study emphasis was placed on the modification of surface properties due to the Fe/Cu interface. Significant variation with respect to α—Fe was observed in the electronic structure of fcc iron formed on the various crystal faces.

Computer simulations of the Ni/Ag-(001) interphase boundary have been performed with the Embedded Atom Method. The relaxed atomic configurations, the periodic interaction potential, the shear modulus of the interface, and the interaction of an Au impurity with the interface have been evaluated. In addition, experimental studies have been conducted on the same system; and the structure and composition of the interface have been simultaneously examined.

He ion channeling experiments indicate that molecular beam grown epitaxial multilayers of EuS/SrS on (111) Si are under strain. Angular scans of the normalized He backscattering yields showed that inclined [100] directions vary by 0.28 ± 0.05º between the first two 30 nm thick layers due to tetragonal distortion of the EuS and SrS lattices. Comparison of theoretical estimated kink angles and experimental results indicated cormplete elastic accommodation of the 0.9 % lattice mismatch between EuS and SrS in the superlattice. In contrast, thin EuS layers on (111) Si are epitaxial but incommensurate because of the large 10 % lattice mismatch.

Superlattices of Au-Cr, with Au:Cr=2:l have been prepared. Their electrical resistivities have been measured between 0.3-300 K. Whereas simple ρ-T behavior was found forλ = 30, 51, 90 and 150 Å, complicated behavior, similar to magnetic ordering is found for λ = 45 Å. No correlation is observed with the extremum wavelength for phonon velocities - a maximum occurs at 75 Å - unlike that found for most metallic superlattics.

The stacking structure and epitaxial ordering are studied in MBE-grown Ru-Ir superlattices of wavelengths λ = 41\ and 62\. These samples span the fcc-hcp crossover previously found to occur when the Ir component is thinner than about 10 monolayers. Evidence for a new stacking sequence of period 3λ is found in the λ=41\ sample, possibly resulting from stacking faults in the Ir layers. The superconducting transition temperature is significantly higher in the 41\ sample (Tc=0.19K) than in the 62\ sample (Tc=0.15K).

High quality single crystal rare earth Gd-Y superlattices with wavelength varying from 8to 42 atomic layers were grown by the recently developed metal molecular beam epitaxy technique. The crystallinity and coherence of the superlattices were examined by X-ray diffraction, and the profiles of composition modulation and strain modulation were determined from a quantitative analysis based on a simple diffusion model for the Gd-Y interfaces. The sharp boundaries achieved in these metallic superlattices are approaching those in semiconductor superlattices. The various in-plane magnetization behavior at low fieldsamong superlattices of different wavelengths suggests the possible presence of new magnetic ordering structures as caused by the artificial modulation.

The conduction band energy levels and wavefunctions in a number of superlattices with more than two layers per unit cell have been calculated using an effective mass model. Many of these structures exhibit energy levels which can be modeled as resulting from a conventional superlattice with a modified bulk conduction band minimum in the effective wells. These structures should be useful for extending the size of the superlattice periodsallowed in strained—layer superlattices.

Photoluminescence and photoluminescence excitation spectroscopy have been used to identify excited state energy levels in ZnSe/ZnMnSe strained-layer superlattices. Several ZnSe/ZnMnSe superlattices have been grown by MBE with different concentrationsof Mn in the barrier material and consequently with different degrees of lattice mismatch between the ZnSe well and ZnMnSe barrier materials. A strain-induced decrease of the band gap is observed in these structures. Photoluminescence excitation spectra reveal a strain dependent splitting of the heavy and light hole n=1 subbands. The magnitude of this splitting, as well as the observed photoluminescence red-shift, are compatible with expectations based on calculated strains and the deformation potentials of ZnSe.

We have developed a convenient photoluminescence microimaging technique to probe misfit dislocations in epitaxially grown semiconductor alloys and multilayers. Using this technique, we have examined the microscopic optical quality of thick (~ 1 μm ) III-V semiconductor epitaxial layers, mismatched to their substrates. The layers includeseveral kinds of [100] strained-layer superlattices (GaP/GaAsxP1-x on GaP and GaAs/GaAs. P on GaAs grown by MOCVD, and GaAs/In Ga1-x As on GaAs grown by MBE) and associated alloys. For each type of superlalti e, we have studied a large number of samples corresponding to different compositions and layer thicknesses. The results show that misfit dislocations can be completely eliminated in the uppermost layers of the strained-layer superlattices if these structures have thin layers, less than the critical thickness for elastic accommodation, and sufficient numbers of interfaces to block threading dislocations.

Structures of CdTe-Cd0.6Mn0.4Te superlattices which are caused by the lattice mismatch between suterlattice layers have been studied by high resolution electron microscopy (HREM). In thin-layer superlattices, the crystal lattice in each layeris elastically distorted, resulting in the change of the crystal symmetry from cubic to rhombohedral. The presence of the small rhombohedral distrotion has been confirmed through a phase contrast effect in HREM images. In a thick-layer superlattice, the lattice mismatch is accommodated by dissociated misfit dislocations. Burgers vectors of partial misfit dislocations have been identified from the shift of lattice fringes in HREM images.

Magneto—optic studies on InGaAs/GaAs and GaAs/GaPAs strained—layer superlattices are used to determine the in—plane light—hole valence—band effective masses. Also, hydrostatic pressure—dependent magneto—optic studies have been performed on these samples for magnetic fields up to 65 kG andpressures to 4 kbar in the temperature range of 1.6 - 4 K. The experimental pressure coefficients of the band—gap energy and the effective mass in the InGaAs/GaAsSLS structures were determined.

Strains in CaF2 films, grown by molecular beam epitaxy at 700ºC on Si(lll) subsrates, have been measured by MeV 4He+ ion channeling. For CaF2 films thinner than 200nm, the strain parallel to the (111) plane is found to be tensile. No strain is observed for films thicker than 200nm. The observed tensile strain cannot be explained by a simple pseudomorphic growth model because the larger lattice constant of CaF2 relative to Si should result in a compressive misfit strain. The tensile strain is an indication of the relaxation of the compressive misfit strain at the growth temperature due to nucleation of interfacial defects. If these defects are not annealed out as the substrate temperature is lowered after growth, the tensile strain can result because of the larger thermal contraction of CaF2 compared to Si. The final film quality near the interface improves as the film thickness is increased. This indicates that reordering of interfacial disorder is caused by the strain energy accumulated during the cooling process.