We show that low area density Ge/Si(100) island ensembles comprised solely of hut and pyramid clusters do not undergo Ostwald ripening during days-long growth temperature anneals. In contrast, a very low density of large, low chemical potential Ge islands reduce the supersaturation causing the huts and pyramids to ripen. By assuming that huts lengthen by adding single {105} planes that grow from apex-to-base, we use a mean-field facet nucleation model to interpret these experimental observations. We find that each newly completed plane replenishes the nucleation site at the hut apex and depletes the Ge supersaturation by a fixed amount. This provides a feedback mechanism that reduces the island growth rate. As long as the supersaturation remains high enough to support nucleation of additional planes on the narrowest hut cluster, Ostwald ripening is suppressed on an experimental time scale.

Low area density Ge/Si(100) hut cluster ensembles are stable during days-long growth temperature anneals. Real-time scanning tunneling microscopy shows that all islands grow slowly at a decreasing rate throughout the anneal. Island growth depletes the Ge supersaturation that, in turn, reduces the island growth rate. A mean-field facet nucleation and growth model quantitatively predicts the observed growth rate. It shows that Ostwald ripening is kinetically suppressed for Ge supersaturations high enough to support a critical nucleus size less than the smallest facet.

This review describes progress in the field of physisorption. Significant advances in the knowledge of microscopic structures and interactions of weakly bound adsorbates are reviewed, including the first studies for the adsorption sites of rare gases on flat metal surfaces and at surface steps, the structures of higher-order commensurate solids, collective excitations in rare-gas monolayers, molecular orientations and growth processes in alkane films, and adsorbate diffusion. The development and improvement of experimental techniques are reviewed, including high-resolution thermal desorption spectroscopy and ellipsometry for studying thermodynamics; low-temperature scanning tunneling microscopy, very low current electron diffraction, and surface x-ray diffraction for studying structures; inelastic atom scattering for studying collective excitations; quasielastic helium atom and neutron scattering and laser techniques for studying diffusion; and the quartz crystal microbalance for studying interfacial friction. The present state of knowledge of the physical adsorption potentials and the role of the van der Waals interaction are discussed in the context of the widespread use of density-functional theory. Experimental and theoretical results for many adsorption systems are described and tabulated; a few case studies are presented in which a unified picture has (nearly) been achieved by the synthesis of many contributions. Some new applications of physisorption are also presented.

Mean-field nucleation and growth modeling is important for understanding various adsorbate-substrate systems, particularly in the context of epitaxial growth. Conventional mean-field theory does not take into account nonlocal interactions, but adparticles may interact with strained islands via long range elastic interactions mediated by the substrate. We show that recent extensions of mean-field theory to deal with nonlocal interactions do not describe such processes faithfully. Here, we derive a generally applicable mean-field theory of adparticle dynamics on strained surfaces, when interdiffusion is neglected. This approach enables us to determine the transport coefficients from the microscopic physics; in particular, we find explicit expressions for the diffusion coefficient and drift velocity at all positions relative to an arbitrarily strained island. We demonstrate the role of strain on island growth, using island strain fields that are dynamically updated, for Ge/Si(001) parameters. This approach has important applications in the modeling of nucleation and growth of many nanostructures, such as metal nanoclusters, semiconductor hut clusters, and silicide nanowires.

It is well established that nucleation of metal clusters on oxide and halide surfaces is typically dominated by defect sites. Rate equation models of defect nucleation have been developed and applied to these systems. By comparing the models with nucleation density experiments, energies for defect trapping, adsorption, surface diffusion and pair binding have been deduced in favourable cases, notably for Pd deposited on Ar-cleaved MgO(001). However, the defects responsible remain largely unknown. More recently, several types of ab initio calculation have been presented of these energies for Pd and related metals on MgO(001) containing several types of surface defect; these calculated values are surveyed, and some are widely divergent. New rate equation nucleation density predictions are presented using the calculated values. Some calculations, for some defect types, are much closer to experiment than others; the singly charged F(s)(+) centre and the neutral divacancy emerge as candidate defects. In these two cases, the Pd/MgO(001) nucleation density predictions agree well with experiment, and the corresponding surface defects deserve to be taken seriously. Energy and entropy values are discussed in the light of differences in calculated charge redistribution between the metal atoms, clusters and (charged) surface defects, and (assumed or calculated) cluster geometries.

In models of nucleation and growth of crystals on surfaces, it is often assumed that the energy surface of the substrate is flat, that diffusion is isotropic, and that capture numbers can be calculated in the diffusion-controlled limit. We lift these restrictions and formulate the general time-dependent problem in a two-dimensional (2D) potential field. We utilize the master equation discretization (MED) method to solve the 2D time-dependent diffusion field of adparticles on general nonuniform (rectangular grid) substrates, and compare it against competing algorithms, including the fast Fourier transform (FFT) and hybrid-FFT methods previously introduced, for periodic boundary conditions. The physical context is set by the importance of repulsive interactions in the nucleation and growth of many nanostructures, e.g., metal nanoclusters, hut clusters, and nanowires. The programs, realized in MATLAB((R))6.5, are used to obtain quantitative capture numbers, aspect and direct impingement ratios, and other island growth quantities in the presence of potential fields, when particular surface processes are included. The case of no corner rounding is studied in detail. Strongly anisotropic potentials favor wire growth, which can be considerably influenced by alternate deposition and annealing, and the location of neighboring islands. Physical examples are given based on Ge/Si(001) material parameters. Essentially similar programs, differing only in outputs, are used to visualize the diffusion field and to produce realistic movies of crystal growth. Examples given here are linear deterministic calculations, but the framework allows for inclusion of nonlinear and statistical effects for particular applications.

An overview of the conception and development of the MIDAS system at Arizona State University is given: a Microscope for Imaging, Diffraction and Analysis of Surfaces. John Cowley's vision in the early 1980s was ambitious and far-reaching, and it was because of him the authors came to ASU. We were centrally involved in the design and implementation of MIDAS from the mid 1980s onwards; the novel design features are briefly reviewed. Practical results obtained using this instrument are listed, and the scope for future development and applications are indicated. While it is clear that many new results have been demonstrated, even more possibilities still remain to be explored. Some comments are made about the feasibility of such developments in the light of competing instrumentation.

A brief review is given of studies of surfaces and small particles using electron beam techniques. The principal tools are secondary, Auger and backscattered electrons, either energy-filtered using various types of analyzers, or as a stronger signal with coarser energy filtering. These tools have been deployed in wide-beam surface science instruments, but also increasingly in scanning electron and scanning transmission electron microscopes, especially in ultra-high vacuum instruments capable of analyzing clean surfaces. The different choices that need to be made are illustrated with examples of clean surfaces, thin films and catalyst particles at high spatial resolution.

We report a low-energy electron microscopy study of novel bamboo-like (quasi-one-dimensional) growth during deposition of Ag on Si(001) surfaces at elevated temperatures. The bamboo crystals, with typical dimensions of 10 μm in length and varied height and width (tens to hundred of nanometers), align primarily along Si[110] or Si[1−10] orientation. Low-energy electron microscopy imaging further demonstrates that the Ag bamboo crystals are initially stable against annealing, but break into segments upon prolonged annealing at 843 K. Possible growth mechanisms of the bamboo-like crystals are discussed.

Recent experiments and calculations have shown that weak repulsive interactions between adsorbate atoms may shift nucleation kinetics from the well-known diffusion limit towards the attachment-limited case. The distinctions between diffusion- and attachment-limited kinetics are clarified, and the increased importance of the transient nucleation regime in the latter case is shown to be due to a combination of delayed nucleation and reduced capture. A time-dependent interpolation scheme between attachment- and diffusion-limited capture numbers is proposed, and tested against KMC simulations. Using this scheme to interpret recent STM results on Cu/Cu(l 11), bounds on the maximum adatom-adatom potential repulsive energy of 12+/-2 meV are deduced. Time-dependent effects also occur in the growth and ripening of strained Ge islands on Si(001), and the similarities and differences between these two systems are discussed.

Nucleation and growth models are well developed for nucleation on homogeneous substrates, and they can typically be described in terms of three energy parameters. Nucleation on substrates containing point-defect traps has been investigated, at the cost of introducing more energy parameters. This paper outlines the quantitative description of such growth models, using rate and rate-diffusion equations, in terms of energies for individual surface processes, with examples taken from metal-metal, metal-insulator and semiconductor growth. The challenge to modelling is to describe the large range of length and time-scales in thin-film fabrication and degradation, without relying on too many (unknown) material parameters, which often occur in combination. Separating them into elementary processes often proves to be a challenge. One typically requires selective nucleation using patterned substrates, in combination with controlled, self-organized, growth for reliable nanotechnology. Reconstructed semiconductor surfaces offer both a further challenge to modelling and an opportunity for future technology; these paradoxes are discussed briefly.

A review is given of nucleation and growth models as applied to the earliest stages of thin film growth. Rate equations, kinetic Monte Carlo, and level set simulations are described in some detail, with discussion of remaining uncertainties, in particular the functional form of the so-called capture numbers in rate equations. Recent examples are given of sub-monolayer nucleation at surface defects, attachment-limited capture, and Ostwald ripening. The experimental literature is cited, and experiment–theory comparisons are made where possible. Emphasis is given to fast computational models that can span a large range of length and time scales, which might be further developed in the direction of on-line process control.

Capture numbers are used in models of nucleation and growth on surfaces, and have been widely applied to predict nucleation densities and other quantities via rate equations. In conventional nucleation theory, much effort has historically been expended on obtaining good expressions for capture numbers in the diffusion-limited case. However, recent experiments and calculations have shown that weak repulsive interactions between adsorbate atoms on relatively smooth (e.g., close-packed metal) surfaces may shift nucleation kinetics towards the attachment-limited case. This paper clarifies the distinctions between diffusion- and attachment-limited kinetics, and emphasizes the increased importance of the transient nucleation regime in the latter case, which is due to a combination of delayed nucleation and reduced capture. The consequences of long-range repulsive adsorbate interactions for the form and values of the capture numbers are explored, and the effects of attachment-limited kinetics in relation to low-temperature deposition and annealing experiments are demonstrated. An approximate interpolation scheme between attachment- and diffusion-limited kinetics is proposed, and tested against kinetic Monte Carlo simulations. Using this scheme to interpret recent scanning-tunneling microscopy results on Cu/Cu(111), lower and upper bounds on the maximum adatom-adatom potential repulsive energy of 10 and 14 meV are deduced.

The flux and temperature dependence of titanium silicide islands formed by reactive deposition near 500 degrees C indicate a critical nucleus containing 2 Ti atoms and a single activation energy of E(d) + 1/2E(2) = 1.4 +/- 0.2 eV, where E(d) and E(2) are the surface diffusion and cluster binding energies, respectively. These values are not consistent with STM observations of Ti dimer-vacancy hopping at lower temperatures and show that silicide island nucleation involves a different, highly mobile Ti species.

This chapter gives, in section 6.1, some generally accessible models of metallic behavior, and tabulates the values of work function and surface energies of selected metals. In section 6.2 we discuss electron emission properties of metals, concentrating on the role of low work function, high surface energy materials as electron sources; we also show that electron emission and secondary electron microscopy can be used to study diffusion of adsorbates. An introduction to magnetism in the context of surfaces and thin films is given in section 6.3.

Nucleation and growth of Pd on cleaved MgO(001) surfaces were studied by variable-temperature atomic force microscopy in the temperature range 200-800 K. Constant island densities (similar to 3x10(12)cm(-2)) were observed over a wide temperature range, indicating nucleation kinetics governed by point defects with a high trapping energy. These results are compared to a rate equation model that describes the principal atomistic nucleation and growth processes, including nucleation at attractive point defects. Energies for defect trapping, adsorption, surface diffusion, and pair binding are deduced, and compared with recent nb initio calculations.

This book presumes that the reader is interested in experimental techniques for examining surface and thin film processes; however, there are many books devoted to surface physics and chemistry techniques, some of which are given as further reading at the end of the chapter. There are even several books which are just about one technique, such as Pendry (1974) or Clarke (1985), both on low energy electron diffraction (LEED) in relation to surface crystallography. By the mid-1980s it was already stretching the limits of the review article format to compare the capabilities of the available surface and thin film techniques (Werner & Garten 1984).