Surface and Interface Structures

We assume in the following discussion that the solid surface under consideration is of the same chemical identity as the bulk, that is, free of any oxide film or passivation layer. Crystallization proceeds at the interfaces between a growing crystal and the surrounding phase(s), which may be solid, liquid, or vapor. Even what we normally refer to as a crystal surface is really an interface between the crystal and its surroundings (e.g., vapor, vacuum, solution). An ideal surface is one that is the perfect termination of the bulk crystal. Ideal crystal surfaces are, of course, highly ordered since the surface and bulk atoms are in coincident positions. In a similar fashion, a coincidence site lattice (CSL), defined as the number of coincident lattice sites, is used to describe the goodness of fit for the crystal-crystal interface between grains in a polycrystal. We ll return to that topic later in this section. 

we assume that the solid surface in question is untarnished. Even so, most surfaces are not ideal. They undergo energy-lowering processes known as relaxation or reconstruction. The former process does not alter the symmetry, or structural periodicity, of the surface. By contrast, surface reconstruction is a surface symmetry-lowering process. With reconstruction, the surface unit cell dimensions differ from those of the projected crystal unit cell. It will be recalled that a crystal surface must possess one of 17 two-dimensional space group symmetries. The bulk crystal, on the other hand, must possess one of 230 space group symmetries. 

The terrace-ledge-kink (TLK) model (Kossel, 1927 Stranski, 1928) is commonly used to describe equilibrium solid surfaces. This model was proposed by the German physicist Walther Kossel (1888-1956), who had contributed to the theory of ionic bonding earlier in the century, and by the Bulgarian physical chemist Iwan Nichola Stranski (1897-1979). It categorizes ideal surfaces or 

Solid-Vapor and Solid-Liquid Interfacial Structures 

We can specify the thickness of the crystal interface as that depth over which the structural order of the crystal transitions to that of the surrounding phase(s). On the solid side of the interface, the depth can vary from one lattice spacing for ordered interfaces to several lattice spacings for disordered surfaces 

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Information about the surface and interface structures in hexadecylamine-capped CdSe NC of 2 nm size has been obtained by a variety of 1H, 13C, 113Cd, and 77Se NMR techniques [342]. The 77Se CP-MAS-NMR spectrum showed five partially resolved peaks from surface or near-surface Se environments. It was possible to obtain 2D heteronuclear correlation (HETCOR) spectra between 1H and the other three nuclei despite the inherent sensitivity limitations (the 77Se- 3I-I HETCOR experiment required 504 h ). The latter experiment indicated that the methylene protons of the hexadecylamine chain interact with the surface Se atoms via a tilt of the chain toward the surface. The surface Se atoms were not seen to interact with thiophenol present, and it was suggested that thiophenol binds to a selenium vacancy at the surface. 

Persello, J., Surface and interface structure of silicas, in Adsorption on Silica Surfaces, Papirer, E., ed., Marcel Dekker, New York, 2000, p. 297. 

With TER-XSW, we measure the Fourier transform of an atom distribution over a continuous range in Q = 1 ID, with variable period D ranging from roughly 100 A to 1 pm. Therefore, TER-XSW is ideally suited to measure surface and interface structures of length scales in the range of 10 to 2000 A. 

Surfaces modified with functionalized SAMs are finding use in the study of cell and molecular biology, materials science, chemical and biosensing, heterogeneous catalysis and nonlinear optical phenomena. The science and technology of SAMs will undoubtedly continue to develop in parallel with the trends and needs for miniaturized devices displaying control of surface and interface structure at the molecular level. 

Ellipsometry is very sensitive to sample surface and interface structures. Hence, to incorporate these structures into an optical model for the investigated sample is necessary in ellipsometry data analysis. The effective medium approximation (EMA) [66] has been applied to calculating the complex refractive indices and dielectric constants of surface roughness and interface layers. In addition, the volume fractions in composite materials can be got from ellipsometry analysis using EMA. 

Rare-Earth Silicides Surface and Interface Structure... 

A system of interest may be macroscopically homogeneous or inliomogeneous. The inliomogeneity may arise on account of interfaces between coexisting phases in a system or due to the system s finite size and proximity to its external surface. Near the surfaces and interfaces, the system s translational synnnetry is broken this has important consequences. The spatial structure of an inliomogeneous system is its average equilibrium property and has to be incorporated in the overall theoretical stnicture, in order to study spatio-temporal correlations due to themial fluctuations around an inliomogeneous spatial profile. This is also illustrated in section A3.3.2. 

Determination of structural parameters of surfaces and interfaces very high resolution depth profiling... 

EXAFS is a nondestructive, element-specific spectroscopic technique with application to all elements from lithium to uranium. It is employed as a direct probe of the atomic environment of an X-ray absorbing element and provides chemical bonding information. Although EXAFS is primarily used to determine the local structure of bulk solids (e.g., crystalline and amorphous materials), solid surfaces, and interfaces, its use is not limited to the solid state. As a structural tool, EXAFS complements the familiar X-ray diffraction technique, which is applicable only to crystalline solids. EXAFS provides an atomic-scale perspective about the X-ray absorbing element in terms of the numbers, types, and interatomic distances of neighboring atoms. 

Structure of Surfaces and Interfaces as Studied Using Synchrotron Radiation. Faraday Discussions Chem. Soc. 89, 1990. A lively and recent account of studies in EXAFS, NEXAFS, SEXAFS, etc. 

This article has been devoted to understanding the structural order at surfaces and interfaces through XPD and AED. However, these techniques are not limited to... 

Solid state NMR is a relatively recent spectroscopic technique that can be used to uniquely identify and quantitate crystalline phases in bulk materials and at surfaces and interfaces. While NMR resembles X-ray diffraction in this capacity, it has the additional advantage of being element-selective and inherently quantitative. Since the signal observed is a direct reflection of the local environment of the element under smdy, NMR can also provide structural insights on a molecularlevel. Thus, information about coordination numbers, local symmetry, and internuclear bond distances is readily available. This feature is particularly usefrd in the structural analysis of highly disordered, amorphous, and compositionally complex systems, where diffraction techniques and other spectroscopies (IR, Raman, EXAFS) often fail. 

MEIS has proven to be a powerful and intuitive tool for the study of the composition and geometrical structure of surfaces and interfaces several layers below a surface. The fact that the technique is truly quantitative is all but unique in surface science. The use of very high resolution depth profiling, made possible by the high-resolution energy detectors in MEIS, will find increased applicability in many areas of materials science. With continued technical development, resulting in less costly instrumentation, the technique should become of even wider importance in the years to come. 

Other topics recently studied by XPS include the effects of thermal treatment on the morphology and adhesion of the interface between Au and the polymer trimethylcy-clohexane-polycarbonate [2.72] the composition of the surfaces and interfaces of plasma-modified Cu-PTFE and Au-PTFE, and the surface structure and the improvement of adhesion [2.73] the influence of excimer laser irradiation of the polymer on the adhesion of metallic overlayers [2.74] and the behavior of the Co-rich binder phase of WC-Co hard metal and diamond deposition on it [2.75]. 

Recent developments in Raman equipment has led to a considerable increase in sensitivity. This has enabled the monitoring of reactions of organic monolayers on glassy carbon [4.292] and diamond surfaces and analysis of the structure of Lang-muir-Blodgett monolayers without any enhancement effects. Although this unenhanced surface-Raman spectroscopy is expected to be applicable to a variety of technically or scientifically important surfaces and interfaces, it nevertheless requires careful optimization of the apparatus, data treatment, and sample preparation. 

Surface SHG [4.307] produces frequency-doubled radiation from a single pulsed laser beam. Intensity, polarization dependence, and rotational anisotropy of the SHG provide information about the surface concentration and orientation of adsorbed molecules and on the symmetry of surface structures. SHG has been successfully used for analysis of adsorption kinetics and ordering effects at surfaces and interfaces, reconstruction of solid surfaces and other surface phase transitions, and potential-induced phenomena at electrode surfaces. For example, orientation measurements were used to probe the intermolecular structure at air-methanol, air-water, and alkane-water interfaces and within mono- and multilayer molecular films. Time-resolved investigations have revealed the orientational dynamics at liquid-liquid, liquid-solid, liquid-air, and air-solid interfaces [4.307]. 

SFG [4.309, 4.310] uses visible and infrared lasers for generation of their sum frequency. Tuning the infrared laser in a certain spectral range enables monitoring of molecular vibrations of adsorbed molecules with surface selectivity. SFG includes the capabilities of SHG and can, in addition, be used to identify molecules and their structure on the surface by analyzing the vibration modes. It has been used to observe surfactants at liquid surfaces and interfaces and the ordering of interfacial... 

Electronic Structure of Surfaces and Interfaces in Conjugated Polymers... 

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