Electrostatic properties of mercaptoundecanoic-acid-coated-gold surfaces interacting with TiO2 surfaces

We studied electrostatic properties of the MUA-coated-gold surface and the TiO₂ surface for design of gold–TiO₂ distribution, which may be controlled with electrostatic interactions. The forces between the surfaces were measured as a function of the salt concentration and pH value using the AFM. By applying the DLVO theory to the forces, the potential and charge density of the surfaces were quantitatively acquired for each salt concentration and each pH value. The potential and charge density dependences on the salt concentrations and the pH values were explained with the law of mass action and the ionizable groups on the surface.     

Semiconductor surfaces

This article reviews current evidence about the atom arrangements on clean low index faces of most elemental and compound semiconductors that have been studied. Knowledge of surface states and energy levels is also summarized for the better-studied cases.     

Magnetic surfaces

The magnetic ground state, magnetic anisotropies and spin excitations of surfaces, interfaces and ultra-thin films of ferromagnetic 3d-metals are discussed. Enhanced magnetic ground state moments and altered hyperfine fields as predicted by ab initio band calculations have not been conclusively verified by experiments up to now. Future calculations should take into account dipolar fields and the role of interface roughness. Very large magnetic anisotropies are observed at magnetic surfaces and interfaces. In Ni/Cu multilayered films, the superposition of surface and stress-induced anisotropies was used to switch the easy axis of magnetization from the film plane to a perpendicular orientation by a proper choice of the Ni layer thickness. This could be an attractive possibility to develop new magnetic materials for technical applications. The temperature dependence of the spontaneous magnetization at surfaces and in ultra-thin films deviates from the behaviour of bulk material. Size effects as well as surface effects of spin wave excitations are discussed, comparing theoretical and experimental results. The need for more complete theories including surface exchange, surface anisotropy and realistic surface structures is emphasized.     

Diffraction from stepped surfaces: I. Reversible surfaces

In electron or atom diffraction experiments on surfaces, the angular shapes of the diffracted beams depend upon the distribution of steps over the surface. In this paper we analyze diffracted beam profiles from stepped surfaces that are reversible. A reversible surface is one in which the pair correlation function over the surface is symmetric with respect to positive and negative directions. We show that the intensity profile across a diffracted beam can be separated into a sharp central spike due to the limit of the correlation function at large separation plus wings or shoulders due to the finite extent of the step disorder. Simple functional expressions for these angular profiles are obtained by a Markov method of treating a one-dimensional geometric distribution of steps. The result explicitly displays the deep structure found for the general case. The method reduces the calculation to a simple eigenvalue problem so that even the continuously changing step distributions that occur in epitaxial growth can be treated easily. As in the general case, the resulting intensity profile is a sharp central spike plus a step-broadened term which now is a sum of Lorentzians. The widths of the Lorentzians are the logarithms of the eigenvalues of the matrix of probabilities which describe the step distribution over the surface. This matrix method, which treats the surface as a Markov chain, also points the correct way to account for correlations between surface atoms for two-dimensional distributions of steps. For a two-dimensional surface one must consider a Markov Random Field as opposed to a simple multiplication of two one-dimensional results. We compare the results of the general calculation to the Si epitaxy experiments of Gronwald and Henzler. The coverage and momentum transfer dependencies of the shapes of the calculated profiles agree with their measurements. The calculation is also applied to the RHEED measurements of Van Hove et al. during GaAs MBE. The measured intensity oscillations can be accounted for by a cyclically changing one-dimensional geometric distribution of steps among three layers in which the third-layer scattering increases with time.     

Fabrication of superhydrophobic surfaces on engineering material surfaces with stearic acid

Via a simple wet chemical etching followed by stearic acid modification, the presence of synergistic binary structures at micro- and nanometer scales and stearic acid bestows superhydrophobic property on steel and aluminum alloy surfaces. The as-prepared surfaces show superhydrophobic not only for pure water but also for corrosive liquids such as acid, basic and salt solutions. The stable superhydrophobicity of steel and aluminum alloy surfaces will extend their applications as engineering materials.     

Hyperfine-interaction studies of surfaces

Applications of hyperfine-interaction techniques, like NMR, PAC and Mößbauer spectroscopy, to well-characterized surfaces are discussed and the present knowledge of surface hyperfine fields is reviewed. Measurements of nuclear spin relaxation permit to extract the local density of electron states at the Fermi level of adsorbed alkali atoms. From the observed electric-field-gradient properties surface probe sites and diffusion processes can be inferred; the experimentally determined magnetic hyperfine fields give access to the electron-spin behaviour at magnetic surfaces.     

Theory of semiconductor surfaces

Three kinds of recent theories of the atomic and electronic structure of semiconductor surfaces are relevant to experiment. Self-consistent calculations have provided a firm basis for understanding covalent bonding at the surface. Realistic tight-binding models can study larger unit cells which commonly occur on reconstructed surfaces. Thermochernical analysis explains the atomic arrangements obtained by annealing clean covalent surfaces.     

Manipulation of oxide surfaces

Metal oxides have considerable potential as insulating supports for nanoscale electronic devices. One of the key attributes of metal oxide surfaces is their capacity to be modified by electron beams and scanning probe tips. Such modifications can involve the creation of O vacancies or an area of a different reconstruction, which in principle can act as anchoring points or templates for molecules or metal interconnects. In this Prospective we describe previous attempts at well-defined modification in order to illustrate this potential.     

Thermodynamics of solid surfaces

In contrast to the thermodynamics of fluid surfaces, the thermodynamics of solid surfaces was not elaborated in detail by Gibbs and other founders of surface thermodynamics. During recent decades, significant progress in this field has been achieved in both the understanding of old notions, like chemical potentials, and in formulating new areas. Applying to solid surfaces, basic relationships of classical theory of capillarity, such as the Laplace equation, the Young equation, the Gibbs adsorption equation, the Gibbs-Curie principle, the Wulff theorem and the Dupré rule, were reformulated and generalized. The thermodynamics of self-dispersion of solids and the thermodynamics of contact line phenomena were developed as well. This review provides a fresh insight into the modern state of the thermodynamics of solid surfaces. Not only a solid surface itself, both in a macroscopic body and in the system of fine particles, but also the interaction of solid surfaces with fluid phases, such as wetting phenomenon, will be analyzed. As the development of surface thermodynamics has given a powerful impetus to the creation of new experimental methods, some of these will be described as examples.     

Growth of rough surfaces

The growth of objects with rough surfaces is a common phenomenon. We describe several models used in the study of the temporal evolution of fluctuating interfaces and then we explain the dynamical scaling in this class of growth models with self-affine surfaces. The recent progress in this field is reviewed. Much emphasis is put on roughness properties and in particular on a possible kinetic roughening transition — a nonequilibrium analog of the thermal roughening transition. Both analytical and numerical results for scaling exponents are summarized and indications of a phase transition in some models are discussed.     

Symmetries of sub-Riemannian surfaces

We obtain some results on symmetries of sub-Riemannian surfaces. In case of a contact sub-Riemannian surface we base on invariants found by Hughen [15]. Using these invariants, we find conditions under which a sub-Riemannian surface does not admit symmetries. If a surface admits symmetries, we show how invariants help to find them. It is worth noting, that the obtained conditions can be explicitly checked for a given contact sub-Riemannian surface. Also, we consider sub-Riemannian surfaces which are not contact and find their invariants along the surface where the distribution fails to be contact.     

Raman spectroscopy of surfaces

Raman scattering has usually a very low efficiency. Therefore, during the first five decades after its discovery, Raman spectroscopic investigations of adsorbate-covered surfaces (except surfaces of highly porous samples) were out of reach. This changed in 1970s, when for molecules adsorbed on some surfaces, very large increase of the intensity of Raman spectrum (denoted as surface-enhanced Raman spectroscopy – SERS) was reported. In the past decade, two other very important achievements in surface Raman spectroscopy have been made: observation of SER spectrum of a single molecule and coupling of Raman spectroscope with the scanning probe microscope (STM or AFM) allowing a significant increase in the spatial resolution of Raman measurements in so-called tip-enhanced Raman spectroscopy (TERS). In the latter approach, fine tip made of a metal that supports surface plasmon resonances (such tip may be treated as a very local electromagnetic resonator) is brought at the nanometer distance above the surface, which induces large increase of the Raman scattering from molecules adsorbed at a surface located underneath the tip. This short review presents an overview of the state of the art and further possible applications of Raman spectroscopy in surface analysis. We mainly focus on SERS and TERS. Future prospects in these fields are also discussed.     

Singular sets of surfaces

Sets of values of the metric projection for an approximatively compact subset of Hilbert space are studied. The results obtained in this way are used to study the geometry of hypersurfaces in ? ⁿ and their singular sets.     

Diffusion on surfaces

A commentary is presented on current progress towards understanding diffusion on surfaces. Recent work by field ion microscopy shows that interactions between diffusing adatoms lead to correlated motions and add unexpected complexity to the elementary diffusion mechanisms. Work on high temperature surface self-diffusion also suggests the importance of interactions between diffusing atoms. Mass transport, catalysed surface diffusion, giant diffusivities, impurity, tracer and adsorbed layer diffusion, diffusion in sintering and other applications, are briefly discussed.