Surface morphological and compositional evolution during the initial stages of Si growth on Ge(001)2×1 by cyclic gas-source molecular-beam epitaxy (GSMBE) from Si2H6 has been investigated using in-situ reflection high-energy electron diffraction (RHEED), Auger electron spectroscopy (AES), electron energy-loss spectroscopy (EELS), and scanning tunneling microscopy (STM). At 550 °C, single-step-height island growth was observed for nominal Si deposition thicknesses tsi up to ≃ 1.5 ML. The islands were essentially pure Ge which segregated to the surface as H was desorbed. At higher tsi, the Ge coverage decreased, the surface roughened, and two-dimensional multi-layer island growth was observed for tSi up to ≃8 ML above which three-dimensional island growth was obtained. For thick layers (t S: 75 ML), no Ge was detected at the surface.

A quantitative approach for characterizing the interface roughness between two materials by cross sectional transmission electron microscopy (XTEM) is proposed. This approach is based on obtaining an interface height distribution curve (IHDC). The interface roughness can be characterized quantitatively by extracting from IHDC three parameters: the mean, median and maximum interface height. This new method has been applied in the characterization of the interface between thermally grown silicon dioxide and polycrystalline silicon thin films deposited by low pressure chemical vapor deposition. It is shown that high temperature processing yields an interface that has higher roughness.

The evolution of surface roughness in kinetic growth with diffusion is studied by computer simulation of ballistic deposition with an activated hopping algorithm, in which the deposited particles diffuse on the surface via random walks. The results demonstrate that the KPZ-type scaling dictates the asympototic statistical properties of surface roughness at elevated temperatures, which are consistent with earlier studies. As surface diffusion is crucially dependent on substrate temperature and deposition rate, we show that they play essential roles in determining the morphology of the film.

Growth kinetics on non-singular surfaces were studied by Monte Carlo simulations. In contrast to the growth on singular and vicinal surfaces, the sticking coefficient on the non-singular surfaces was found to decrease with increase of the surface roughness. Simulations of annealing processes showed that surface diffusion of atoms leads to a stationary surface roughness, which is explained by multiple configurations having the lowest energy in the non-singular surface.

A Monte Carlo model has been used to study growth morphologies of steps on vicinal surfaces in molecular-beam epitaxy. The model accounts for molecule attachment, detachment, and surface diffusion. Through variation of surface temperature, impingement rate of source molecules, and the orientation of vicinal surface, we have explored the surface diffusion and the conditions under which two dimensional nucleation (2DN) growth and step flow (SF) growth occur. We have found optimum growth windows for 2DN growth and SF growth. For SF growth we have found that morphological stabilitity of steps are closely dependent on their step height. Steps with multi-molecular-layers are seen to be less stable than single-layer steps in a surface diffusion field, due to a decrease in the attachment of growth units from the upper terrace.

When a continuous film is deposited on a planar, single crystal substrate, there is usually a single set of relative film-substrate orientations for which the free energy of the film-substrate interface is minimized. It is often assumed that epitaxial films have adopted the orientation which minimizes this energy. However, this is not necessarily the case. Orientation selection is also constrained by minimization of the energy of the/ree surface of a film, as well as by minimization of the strain energy. In systems in which films grow by an island mechanism, epitaxial orientations can be established during or after nucleation, and can change before or after formation of a continuous film. Interfacial and surface energy minimization is constrained differently for islands and films. Epitaxial grain growth is a process which occurs in continuous films, in which epitaxially-aligned, energy-minimizing grains grow at the expense of other grains. Recent experiments on epitaxial grain growth in polycrystalline Ag films on single crystal Ni is discussed to illustrate, the affects of surface, interface, and strain energy minimization on epitaxial orientation selection.

The equilibrium phase diagrams of monolayers of many substances adsorbed on graphite have long been studied as examples of 2-dimensional (2D) matter. One typically observes 2D gas and liquid phases, and solid phases that may be commensurate or incommensurate with the substrate lattice. Many experimental techniques have been used, but thermodynamic measurements are generally the most useful for tracing out phase boundaries.

Recent advances in technique have made it possible to use thermodynamic measurements to study the phase diagrams of the second and higher layers, up to the fifth or sixth. These advances include ultra high resolution scanning calorimetry, and a detailed understanding of the role of capillary condensation in corners and pores of the graphite foam substrate. We find a rich array of phases and phase transitions in multilayer methane, argon and krypton. The second and third layers typically have distinct 2D gas, liquid and solid phases evidenced by 2D triple points and critical points. We observe phase transitions between solid phases that are commensurate and incommensurate with the layer below. We also observe melting of the first layer at higher temperatures, even when one to five additional layers are adsorbed on top of it.

In argon and krypton, but not in methane, a strange new phenomenon is observed at temperatures above the gas-liquid critical point of the nth layer for n> 3. Below that temperature, nthlayer gas coexists with a condensed nth layer. At some temperature above it, a new coexistence region is observed in which a partial nth layer coexists with a partial n + 1st layer. This behavior is thought to be evidence for a theoretically predicted phase transition of the bulk interface, called the preroughening transition.

Epitaxial Cu thin films have been grown on H-terminated Si(OOl) substrates at room temperature by D.C. ion-beam sputter deposition in ultrahigh vacuum. The development of orientation and microstructure during epitaxial growth from the initial stages of Cu growth up to Cu thicknesses of few hundred nm has been investigated. Analysis by in-situ reflection high energy electron diffraction, thin film x-ray diffraction, and plan-view and cross-sectional transmission electron microscopy indicates that the films are well textured with Cu(001)∥ Si(001) and Cu[100]∥ Si[110]. Interestingly, it is found that a distribution of orientations occurs at the early stages of Cu epitaxy on Si(001) surface, and that a (001) texture emerges gradually with increasing Cu thickness. The effect of silicide formation and deposition conditions on the crystalline quality of Cu epitaxy is also discussed.

Many of the fundamentals of epitaxial growth, long predicted by theories of crystal growth, have been seen during the molecular beam epitaxial growth of monolayer films. In general, high temperatures and low deposition flux favor nucleation at atomic steps. The opposite extreme of low temperature and high flux favors island nucleation in terraces, and steps play little role. For intermediate conditions a wide variety of growth morphology is seen. High temperatures and high flux have been seen to produce two-dimensional dendritic growth. Atomic steps on substrates have been observed to migrate during sublimation. Pinning of steps during migration gives rise to complex atomic step and terrace structures and a distribution of terrace widths. For terraces wider than the diffusion length of adsorbed atoms, nucleation of islands is favored in the terraces, whereas narrow terraces favor nucleation at the atomic steps. For a constant substrate temperature and deposition flux, morphology can vary profoundly depending upon local terrace width. Complex structures in monolayer films are produced during sublimation. These include lockeime or hole nuclei which are one atomic step deep. Steps are seen to oscillate during step flow apparently due to considerable mass transport between steps and terraces.

The microstructure of epitaxial thin films grown on sapphire substrates using the metal organic chemical vapor deposition (MOCVD) technique were found to depend on the substrates surface structure. The epitaxial Ti02 films grown on the sapphire (0001) substrates were highly-oriented poly-crystal and the films on the (1120) substrates were single crystal. First-principles total energy calculations were carried out to gain atomistic understandings of sapphire surface structures and their effects on microstructure of epitaxial films. The surface terminating atom planes were found to be Al atoms for the (0001) surface and O atoms for the (1120). The minimum step heights were found to be one sixth of the lattice constant c for the (0001) and one half of the lattice constant α for the (1120). The steps of the minimum height or its odd multiples on sapphire (0001) surface were shown to double the number of variants in the deposited films. The symmetry and step of the substrate surface and the symmetry of the epitaxial growth plane were found to control the microstructure of the epitaxial films.

The evolution of the surface microstructure of sputtered c-axis oriented epitaxial YBa2Cu3O7-δ films has been monitored by scanning tunneling microscopy (STM). The results indicate that growth is dominated by the incorporation of depositing species at defect sites. These defect sites, which provide energetically favorable positions for accommodating the arriving species, are at ledges—either along growth spirals emanating from screw dislocations, or due to the closely spaced surface steps arising from the macroscopic tilt of the substrate. If the substrate is misoriented sufficiently, the depositing species may diffuse to and be accommodated by these surface steps, without the supersaturation on the terraces attaining a high enough level for two-dimensional nucleation to occur. Under these conditions, growth occurs by step propagation. Otherwise, a high density of screw dislocations (≈109 cm-2) is nucleated during the initial stages of growth, which provides a continual supply of ledge incorporation sites in the vicinity of the depositing species. The surface evolution reported appears to be an intrinsic feature of c-axis oriented YBa2Cu3O7-δ films for a wide range of growth conditions, irrespective of the substrate material or vapor phase deposition method.

The textured oriented overgrowth (epitaxy) of certain metals evaporated onto substrates consisting of highly oriented ultra thin polymer films of polyethylene (PE), polypropylene (PP) and polybutene-1 (PB-1) has been well known since a few years. However, the origin of the observed epitaxy is not clear at all: graphoepitaxy (i. e. orientation induced by nucleation onto oriented topographic features of the substrate), the formation of a chemical layer (i. e. of metal-methyl groups building up the polymer-metal interface, or simply classic epitaxy (i.e. lattice matching) seem all to be possible explanations for the observed orientations. Here, we used Transmission Electron Microscopy (TEM) and Scanning Force Microscopy (SFM) to investigate the possibility of graphoepitaxial growth on polymeric surfaces. Our investigations show that the morphology of polymeric bulk material determine the topographic properties observed at the polymer surface. The semicrystalline nature of the polymer films leads to polymeric surface steps which are suitable as locations for graphoepitaxial growth. Artificial epitaxy (graphoepitaxy) seems to be the most likely orientation mechanism.

A microscopic study of the system Ga/GaAs(001) is presented to explain the origin for different Ga cluster shapes on a single surface. The model is based on the finding that a significant fraction of the Ga clusters reaches below the GaAs surface plane and the shape of these depressions represents a minimum energy configuration if low-index planes are formed. Other metal/compound semiconductor systems may display similar shape modifications.

Nucleation layers of GaN have been deposited in an MOCVD reactor on (0001) sapphire, over a range of temperatures and layer thicknesses, using either N2 or H2 carrier gas. The layers have been found to be continuous, textured films as deposited at low temperatures (600°C), but to reorder upon annealing, segregating into nucleation sites which exhibit the normal heteroepitaxial relationship with the sapphire substrate.

The conducting oxysalt Ag(Ag3O4)2NO3 has been electrodeposited onto highly oriented conducting oxides of Tl2 03 and Pb0.8Tl0.2O1.9. T12O3 was grown in a [100] texture while the Pb0.8Tl0.2O1.9 was grown with two different thickness-dependent textures of [110] and [210]. The orientation of the Ag(Ag3O4)2NO3 crystals with respect to the substrate surface was determined by x-ray diffraction. The face-centered-cubic Ag(Ag3O4)2N03 crystals deposited on body-centered-cubic T12 03 and face-centered-cubic Pb0.8Tl0.2O1.9 followed the orientation of these prelayers. However, Ag(Ag3O4)2N03 which was electrodeposited onto polycrystalline 430 stainless steel had a nearly random orientation. The lattice mismatch is 6.6% between T12 03 and Ag(Ag3O4)2N03, and it is 7.8% between Ag(Ag3O4)2N03 and the doubled unit cell of Pb0.8Tl0.2Ol.9.

We present precise simulation results for a simplified model of irreversible nucleation and growth of islands during deposition. We characterize the scaling of the island and adatom densities, the complete island size distribution, and the adatom-island and island-island separation distributions, with the ratio of diffusion to deposition rates (for fixed coverages,θ<1). We also make some comparisons with rate equation predictions.

We present general results demonstrating the existence of thermodynamic driving forces that effect the shape of small equilibrium regions (“droplets”), such as islands in epitaxial growth. These effects are due to critical fluctuations. They occur when the droplet, if it were infinite, would be at or near a second-order phase transition. Depending on the droplet geometry, they can lead to elongation, sharpening of “points”, or healing of “dents”. It is important to consider such effects, since in many surface preparation and modification techniques the shape of small islands can have a significant influence on the ultimate surface morphology.

Microstructure development in thin films of Ba2YCu3O7-x (BYC) synthesized on (001) LaA1O3 using an ex situ process was characterized by TEM and STEM examination of specimens quenched from different points in the growth heat treatment. The microchemistry of the growing oxide films was characterized by EDS in STEM. Phase development was also studied by X-ray diffraction. Several investigators have suggested that growth of BYC during ex situ processing occurs by nucleation and growth of BYC into an amorphous precursor film. Our observations indicate that this process involves growth into a substantially crystalline matrix. X-ray diffraction was used to identify three phases, BaF2, BaCuO2, and CuO, which are present prior to BYC nucleation. Nucleation of both c-axis normal and a-axis normal BYC occurred at approximately 760°C during rapid heating to 830°C in the growth heat treatment. Rapid growth of the c-axis normal material parallel to the substrate surface caused this orientation to become dominant in the fully converted films. Chemical microanalysis of the quenched films suggests that the BYC grows into an overlying layer that, after quenching, is composed of relatively large (25–100 nm diameter) yttrium- and copper-rich particles in a nanocrystalline barium-rich matrix.

We have calculated the equilibrium shape of a silicon crystal at orientations near (001), both at T=0 and at elevated temperature [1], using methods developed previously to study stepped surfaces [2,3,4]. Comparison with recent experiments shows that several topographic features observed on Si direcdy reflect the equilibrium shape. In particular, our results resolve an apparent discrepancy between theory and experiment, regarding facetting between regions of single-layer and double-layer steps. In addition, the calculated crystal shape suggests an explanation for observed low-angle facetting on very flat (001) surfaces.

We study a reversible phase transition of one monolayer of Pb on a Ge(l11) surface over a range of temperature from below to above the transition temperature (∼175°C) with the tunneling microscope. The high temperature l×1 phase is a ordered monolayer l×l 2D solid. Below the transition temperature, Pb atoms are displaced from their ideal T1 positions to form trimers with periodicity.