Epitaxial Ge films (< 3 ML) have been grown at elevated temperatures on Si (001) grating substrates (repeat spacing of 2.0 μm) and imaged using room temperature scanning tunneling Microscopy (STM). The Ge films exhibit the 2×n reconstruction associated with missing dimer rows. The value of n and the growth morphology are influenced by the deposition rate and by annealing. At substrate temperatures of 600° C and deposition rates >0.5 ML/Min., islands elongated along the the dimer row direction nucleate at steps and on terraces. With sufficient annealing at 800° C, the islands coarsen and are eventually eliminated. The roughness of the A-type step becomes greater than that of the B-type step, which is the reverse of the situation with pure Si (001). The separation between missing dimer rows and hence the value of n are increased by annealing. Differences in substrate terrace widths due to the periodically varying step density of thegratings affect the growth Modes: two-dimensional islands occur near the extrema of the gratings whereas step flow occurs when steps are separated by ∼150 Å or less.

We identify the binding sites for adsorption of a single Ge atom on the Si (100) surface using ab initio total energy calculations. The calculated diffusion barriers are in excellent agreement with experimental estimates. Using a large supercell we resolve the controversy regarding the binding geometry and migration path for the adatom, and investigate the influence of the adatom on the buckling of Si dimers. The adatom induces a buckling defect that is frequently observed using scanning tunneling Microscopy (STM); therefore the study of single adatoms may be experimentally accessible.

We have used the tunneling microscope to measure the lattice relaxation of Ge islands on Si (111) as a function of their height. Lattice constants on the top surfaces of individual Ge islands can be measured with an uncertainty of approximately one percent. The lattice constant is a continuous, Monotonically increasing function of island height up to 20 bilayers. At heights around 5O bilayers, the island-top lattice parameter may exceed that of bulk Ge. Defects can be observed penetrating the top surface of islands which have heights around 90 bilayers.

Surface diffusion of In and Sb on Ge (111) has been measured by optical second harmonic Microscopy. This technique employs surface second harmonic generation to directly image submonolayer surface concentration profiles. At low coverage, the activation energy Ediff and pre-exponential factor D0 are extraordinarily large for both systems and cannot be explained by theories based on simple site-to-site hopping.

Molecular dynamics simulations of a Lennard-Jones (111) surface has revealed a new mechanism for high-temperature diffusion which is probably operative on Ge (111). At low coverages and high temperatures, adatoms sink into the top layer of Ge, and diffusion is dominated by thermal formation of adatom-vacancy pairs. This process is characterized by a high enthalpy of pair formation and a high entropy of activation due to lattice relaxation near the vacancy.

At high coverages, the behaviour of Sb and In are quite different. As the In coverage increases, a larger fraction of In resides in the adlayer, so the diffusion parameters slowly approach those for site-to-site hopping. For Sb there is evidence for immobile islands at higher coverages. This does not affect Ediff, but decreases D0 due to the smaller number of diffusion paths around the islands. The gradual change of In diffusion parameters with coverage is interrupted by an apparent phase transition at θ=0.16, where both Ediff and D0 peak sharply.

We have elucidated the atomic structure of the γ-phase, which appears at 1ML coverage of Al on the Si (111) surface, using scanning tunneling Microscopy (STM). The structure is based on the 9×9 dimer-adatom-stacking fault (DAS) structure. Al atoms replace Si atoms in the second layer of the DAS Model. As a result, excess silicon atoms are produced during the formation of the γ-phase and migrate on the surface to form Monatomic-height islands. The area ratio of the upper and lower terraces is in good agreement with the proposed formation Mechanism.

The development of surface morphology during homoepitaxial growth on one-dimensionally periodic, patterned Si substrates and subsequent annealing has been investigated using transmission electron Microscopy. Si layers grown by MBE are characterized in terms of facets which develop at a trench edge. 1000 Å thick films deposited at ∼ 600°C on Si substrates develop large (311) facets at the bottom and top of the sidewall. After annealing at high temperatures for short times (∼ 1 hour), the amplitude of corrugation decreases but the surface profile is facetted along its length. The “annealed shape” at the trench edge is shown to consist of several surfaces including: (211), (311), (511), and (711). This evidence suggests that (311) facets develop as a result of the growth kinetics.

We describe periodic arrangements of Ge islands grown on Si (111) using Ge deposition at room temperature and post-deposit annealing. A Mesh pattern of relaxed Ge islands is obtained under conditions of a Ge thickness of 10 Å and an annealing temperature of 400°C. The Mesh pattern is due to the preferential crystallization of α-Ge films at steps and at out-of-phase boundaries of 7×7 reconstructions. We also demonstrate that the Ge island pattern is modified when Ge is grown on a substrate changed by Si homoepitaxy or In adsorption.

We study the crystallization of a thin film of amorphous Ge deposited at room temperature on Si (111). Features of the silicon surface buried beneath the Ge film are shown to affect the rate of crystallization. In particular, solid phase epitaxy is observed to be enhanced at surface steps and defects in the surface reconstruction. It is further shown that one-dimensional crystallization patterns can be caused by impurity-Mediated crystallization. Precipitates of an impurity rich phase migrate in the plane of the film, leaving behind a crystalline trail. The Migration path of these precipitates is also dependent on the buried surface structure.

We have studied the development of a microscopically ridged [110] Morphology during (001) GaAs Molecular beam epitaxy, as a function of layer thickness and growth temperature. The ridge slopes are consistent with the [110] separation required to incorporate a majority of adatoms by step-flow growth. Thus step-flow can be a dominant growth mode even on nominally on-axis (singular) substrates. With increasing epilayer thickness, the ridge slopes, and surface step density, remain approximately constant, while the ridge spacings, and therefore roughness amplitude, increase steadily.

In this work, MBE growth of GaAs on CaF2/Si (111) substrates has been studied with both Rutherford backscattering spectrometry, transmission electron microscopy and atomic force Microscopy. It has been observed that, under certain conditions, a chemical reaction between As adatoms and the CaF2 layers can be induced, by which a more stable As layer on the CaF2 surface is formed. The existence of the As layer modifies the CaF2 surface free energy, which, if properly controlled, leads to two-dimensional (2D) nucleation of GaAs on the CaF2/Si (111) surface as opposed to the more commonly observed three-dimensional (3D) growth. Artificial Modification of the CaF2 (111) surface by introducing Ca prior to GaAs growth is also discussed as a promising way to achieve 2D nucleation. In subsequent growth, two kinds of twins have been observed. All samples were observed to have Micro-twins near the GaAs/CaF2 interface. These twins can be suppressed during the first 1000Å, if the layer is grown in a narrow optimal growth window. Otherwise, the growth will be in a 3D Mode at lower temperatures, or it will suffer from the formation of large rotational twins at higher temperatures. It has been observed that growth on vicinal substrates tilted toward [112] azimuth is helpful in suppressing the development of rotational twins so that growth on these substrates have a wider optimal growth window. Surface Morphology of CaF2 epitaxial layers grown on Si (111) substrates with different vicinal angles has also been investigated. It May have significant impact on the twin development during subsequent GaAs growth.

The phenomenon of graphoepitaxy, whereby island nucleation occurs preferentially at steps, is a prime example of a manner in which the substrate morphology (and notably surface steps) can affect the microstructure of as-deposited thin-films. This paper provides a further illustration of the fundamental importance of the substrate morphology to the development of the thin-film microstructure, employing the example of TiO2 deposited by pulsed-laser deposition (PLD) directly onto specially prepared (100) MgO TEM foils. The same areas of these foils are imaged both before and after deposition.

We present the results of a detailed Molecular-dynamics study of single-atom diffusion on the surfaces Ag (100) and (111), and Au (111), using the embedded-atom method to describe the interactions between the atoms. We find that diffusion is Arrhenius-like up to temperatures corresponding to a large fraction of the activation energy. We demonstrate, in addition, that an excellent description of the rate of diffusion is provided by a simple transition-state theory, together with parameters that derive directly from the static potential-energy surface. The Model predicts very accurately the activation energies, while the prefactor for diffusion is obtained within a factor of 2, a discrepancy we attribute to the neglect, in the Model, of the details of the structure of the surface. At higher temperatures, diffusion becomes clearly non-Arrhenius, and the model fails.

Interfacial properties of thin Si/Ge heterostructures are discussed. It is shown that (SimGen) p superlattices with well defined periodicity can be synthesized on both (100) Si and Ge using low temperature (350 °C) Molecular beam epitaxy. Multilayer structures are however intermixed over one or two monolayers and exhibit a roughness with lateral scale > 100 nm and an amplitude of the order of two Monolayers. On Si the roughness is strongly correlated from interface to interface, possibly due to small surface mobility during growth. Segregation of Ge during growth has also been evidenced by x-ray photoelectron spectroscopy and may explain some of the interface Mixing. The strong composition dependence of Ge diffusion in Si1−xGex alloys causes anisotropie diffusion upon annealing whereby a large composition gradient can be preserved at the heterointerfaces due to the very slow diffusion rate of Ge atoms in pure Si. This effect is important in structures which alternate thin Ge and thick Si layers and is thus more prominent in superlattices grown on Si substrates.

Surface diffusion has been studied in the Ag/Ge (111) and Cs/Si (100) systems using UHV-SEM based techniques, biassed secondary electron imaging (b-SEI), Micro-AES and RHEED. Ag and Cs were deposited through a mask of holes held close to the substrate at room temperature, and annealed at higher temperatures Ta. Under certain conditions, the Ag and Cs patches split into two distinct regions with different sub-Monolayer (ML) coverages θ, observable using b-SEI; the sensitivity for Cs/Si (100) is below 0.5% ML. These patch widths were measured as f(ø,Ta,t), and effective diffusion coefficients extracted. Both systems were modelled using coupled diffusion equations, involving adatoms in two different surface phases. Comparison with experiment yields activation energies for adsorption (Ea) and diffusion (Ed).

We have measured the kinetics of roughness evolution during low energy ion sputtering of SiO2 surfaces using in situ X-ray reflectivity. Sputtering with heavy ions (Xe) leads to rapid roughening of the surface that can not be explained by a simple random removal process. Subsequent bombardment with light ions (He, H) leads to an exponential decrease in the surface roughness. These kinetics are explained quantitatively by a linear model that contains a balance between smoothing by surface diffusion and viscous flow and roughening by sputter removal of Material. A curvature dependent sputter yield leads to amplification of a limited range of spatial frequencies on the surface and the formation of a ripple topography.

We present in situ scanning tunneling Microscopy (STM) results which show the morphological aspects of Ag electrodeposition on Au (111). The experimental conditions enabled us to follow, in real time, with monolayer resolution, the morphological details of Stranski-Krastanov (SK) growth under a fixed electrochemical potential (constant supersaturation). Two epitaxial layers of Ag were sequentially formed prior to the heterogeneous nucleation of three-dimensional Ag crystallites. STM images are presented showing that the second silver monolayer has a coarsened (surface) diffusion-limited-aggregation growth front. IMMediately after the completion of the second silver monolayer which took approximately five Minutes, we observed the formation of 3D clusters preferentially at step edges. Our analysis of the SK growth process indicates that it is not well described by heterogeneous-nucleation thermodynamics owing to the almost identical lattice parameters of Ag and Au. Instead, we argue that the wetting-nonwetting transition we observed was kinetically stabilized by the relatively high activation energy involved with the motion of Ag adatoms over a descending Ag step.

We investigated the scaling behaviour of vapor-deposited silver films at room temperature by means of scanning tunneling Microscopy. The film-thickness range was ≈ 10 – 1000 nm. The roughness exponent H is observed to be H = 0.82 ± 0.05. The growth and dynamic scaling exponents are respectively observed to be β = 0.29 ± 0.06, and z = 2.53 ±0.50.

A continuum equation for epitaxial and thin-film growth in which diffusion along the surface is the dominant relaxation process and the full diffusion along the surface is taken into account, is studied. The interface width is found to grow linearly with time (height) in agreement with recent experiments. At late times dynamic scaling breaks down and the surface develops a characteristic morphology which is similar to that found in experiments.

Two regimes of growth are observed for epitaxial films of InP prepared by metalorganic molecular beam epitaxy. Below a minimum growth temperature, kinetic roughening is observed. At temperatures higher than smooth morphologies are obtained. From the dependence of on the substrate Misorientation, we estimate a value of ∼0.4–0.5eV for the Schwoebel barrier. At growth temperatures higher than we observe two types of defects: large oval defects related only to the initial conditions of the substrate surface and small defects with the density strongly dependent on the growth condition. Increasing temperature above or decreasing V/III ratio, results in increased density of these defects. In addition, their density increases with an activation energy that depends on the substrate Misorientation. The origin of the oval defects is attributed to non-stoichiometric, P-defficient, clusters on the growing surface, formed either by enhanced cracking of metalorganic s on the substrate due to the presence of contaminants or by a low V/III ratio used for growth.

We study the elastic strain relaxation in highly strained layers deposited on a [001] substrate induced by coherent 3D islanding. We first calculate the elastic strain distribution within several pyramidal 3D islands with different faces (the observed ones being usually [114] or [014]). For this, we use a valence force field (VFF) description. Our calculation includes interactions between islands, which appear to be a key parameter. We study how the shape of the island modifies the strain relaxation which is proved to vary within the island. Very simple considerations on surface tension indicate why pyramidal islands are the most stable.