Combined ellipsometric and reflectometric measurements of surface processes on noble metal electrodes

Linear approximation expressions for the optical effects due to the growth of very thin films on metal electrodes are discussed. It is concluded that the combined results of electromodulated reflectometric and ellipsometric measurements may provide better diagnostic criteria in the analysis of this type of surface processes. Transient measurements of the small changes in Δ may be performed with an off-null ellipsometric technique. Results of such experiments are discussed for three different surface processes: the early stage in the surface electro-oxidation of gold in acid solution, anionic electrosorption on platinum and hydrogen ad- and absorption on platinum and palladium. Variation of the modulation frequency allows to resolve surface processes which occur simultaneously, according to their characteristic relaxation times.     

Relaxation processes on A ZnO surface irradiated by electrons

The dependence of effective charge carrier lifetime and the surface conductivity relaxation constant of polycrystalline zinc oxide as functions of electron irradiation dosage at constant residual gas pressure, partial oxygen pressure at constant irradiation dosage, and partial water vapor pressure at constant irradiation dosage are studied. Surface state types and the charge carrier relaxation mechanism are determined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 81–85, June, 1985.     

Ion-enhanced processes on a solid surface

The results of studies performed by the authors in the field of ion enhancement of various processes on the solid surface were generalized. The effect of ion irradiation on the kinetics of elementary processes during thin film formation was analyzed. Systematic features of ion enhancement of film formation on a metal and ionic crystal surface were studied. The effect of ion enhancement of epitaxy on the ionic crystal surface was revealed and the observed features were explained. An important role of inelastic ion-atom interactions in the effect of ion enhancement of surface processes was shown, and their features were investigated. It was found that the efficiency of ion enhancement on the ionic crystal surface under conditions of inelastic interactions can be increased by one or two orders of magnitude in comparison with the yield of elastic processes. Inelastic ion-atom interactions at low ion energies occur in selective energy ranges, nonmonotonically depend on the current density, and require a selective approach to the choice of the ion type and ion irradiation parameters.     

Concerning experiments on coherent transition radiation by relativistic electrons

It is shown that the macroscopic transverse dimensions of the target can strongly influence the spectrum of transition radiation emitted by relativistic electrons in thin layers of matter and that the effect is extremely important in experiments on coherent transition radiation in the infrared. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 581–584 (25 April 1997)     

Angular and energy dependences of the surface excitation parameter for electrons crossing a solid surface

When fast electrons cross a solid surface, surface plasmons may be generated. Surface plasmon excitations induced by electrons moving in the vacuum are generally characterized by the surface excitation parameter. This parameter was calculated for 200-1000 eV electrons crossing the surfaces of Au, Cu, Ag, Fe, Si, Ni, Pd, MgO and SiO₂ with various crossing angles. Such calculations were performed based on the dielectric response theory for both incident (from vacuum to solid) and escaping (from solid to vacuum) electrons. Calculated results showed that the surface excitation parameter increased with crossing angle but decreased with electron energy. This was due to the longer time for electron-surface interaction by glancing incident or escaping electrons and by slow moving electrons. The results were fitted very well to a simple formula, i.e. , where P_s is the surface excitation parameter, E is the electron energy, α is the angle between the electron trajectory and the surface normal, and a, b and c are material dependent constants.     

Sputtering of solid argon by keV electrons

Thermochemical maskless etching of compound semiconductors (GaAs, InP, InSb, and GaP) has been performed by focused Ar-laser irradiation in chloride gas atmospheres. A controlled minimum linewidth of down to 0.6 m with a maximum etching rate of up to 13 m/s has been obtained. Minimum laser powers necessary for thermochemical etching in each of compound semiconductors were found to be 0.24, 0.56, and 0.06 W, corresponding to minimum local temperature rises of 190, 515, and 110°C for GaAs, InP, and InSb, respectively. Etching rates exhibited Arrhenius behavior with activation energies of 3.6–3.9 kcal/mole. Etching at excessively higher laser powers than those minimum powers was found, by microprobe photoluminescence measurements, to degrade the optical quality of the etched substrate.     

Angular distributions of electrons and light ions elastically reflected from a solid surface

The angular distributions of elastically reflected electrons are described on the basis of the transfer equation for a radiation particle. The exact solution of the problem is obtained. This solution is compared with experimental spectra of elastically reflected electrons and with the approximate solutions.     

Analysis of inelastic scattering processes of electrons by localized electrons in quantum dots

The inelastic Coulomb scattering rate 1/τ_in of conduction electrons has been theoretically evaluated in the presence of localized states such as quantum dots. By a diagrammatical method, we have formulated 1/τ_in and its relation to the conductivity σ_loc(ω) through localized states. The dependence of τ_in on temperature T is examined in the case that σ_loc(ω) follows the Mott's model. It is found that 1/τ_in varies as T²(ln Δ/T)^d+1 where d is the dimensionality and Δ is tunneling energy between the localized states in the asymptonic T = 0 limit, in agreement with Imry's calculation. It is also found that calculated 1/τ_in deviates from T²(ln Δ/T)^d+1 as T increases, suggesting the importance of correction term at high temperature.     

Use of surface acoustic waves for analysis of gases and surface processes induced by them

An analytical expression for the magnitude of the “response” of surface acoustic waves (SAWs) to gases is obtained. It is tested experimentally. The main features of the detection of gases by means of SAWs are predicted theoretically and confirmed experimentally. The SAWs in coated and uncoated gas sensors are compared. A technique for using SAWs to determine the relative changes in the density (Δρ/ρ) and the elastic moduli (ΔC ₁₁/C ₁₁ and ΔC ₄₄/C ₄₄) of films upon the adsorption (desorption) of gases is proposed. The possibility of using this technique to analyze adsorption and desorption processes is demonstrated. The adsorption properties of polycrystalline, thermally deposited palladium films before and after low-temperature vacuum annealing, as well as unannealed Pd and Pd:Ni films, are compared. The prospects of using SAWs to detect gases and to study surface processes induced by them are discussed. Zh. Tekh. Fiz. 68, 73–81 (February 1998)     

The polarization of electrons by tunneling through a spin-dependent surface potential

A model calculation is discussed which demonstrates that the spin-dependence of the surface potential can be an important factor in determining the field-emitted electron spin polarization (FEESP) from ferromagnetic metals. The significance of this model calculation for the interpretation of FEESP from Ni and Fe is discussed.     

The effect of a surface layer on determination of the dielectric functions of ZnTe films by the ellipsometric technique

By means of spectroellipsometric technique, the dielectric functions of zinc telluride films, 0.1–1.7 μm thick, grown by molecular beam epitaxy (MBE) are studied. The presence of a thin layer on the surface of the films, noticeably affecting the results of measurements, is established. The analysis of spectra of the ZnTe dielectric functions available in the literature shows that the surface layer was present in all samples studied, regardless of the method of preparation. It is shown that studying the interference oscillations of the pseudodielectric function makes it possible to detect this layer and to correct properly the measured spectra of the dielectric functions. __________ Translated from Optika i Spektroskopiya, Vol. 92, No. 5, 2002, pp. 847–850. Original Russian Text Copyright ? 2002 by Shvets, Yakushev.     

Methods of ellipsometric analysis of polarization optical properties of inhomogeneous surface layers of optoelectronics elements

The basic regularities of changes in the main ellipsometric parameters of a light beam reflected from inhomogeneous surface layers of silicate glasses have been described on the basis of the Drude-Born theories of polarized light reflection. A method of physicomathematical modeling of the refractive index profile in an inhomogeneous surface layer of silicate glasses is reported, which makes it possible to determine, with the lowest second-kind error probability, a model of an inhomogeneous reflecting system that is adequate to the object of study.     

Mobility and surface recombination processes of primary electrons in dielectric systems during Auger electron spectroscopy

The time evolution of the surface electric field in a dielectric system during Auger electron spectroscopy is calculated. It is shown that steady electric fields are very quickly attained. Their steady value is connected to primary electron mobility.     

Evaluation of surface kinetic data by the transform analysis of modulated molecular beam measurements

The merits of different modulated molecular beam detection systems are discussed and the application of modern data handling methods described. It is shown that by using time domain analysis together with fourier transform techniques, information on the kinetics of surface processes is obtained. Data at a number of excitation frequencies is obtained in a single experiment. A means of detecting non-linear surface processes, and an accurate method for the determination of reaction orders is given. The origin of spurious coherent signals is considered, and finally the application of the techniques is illustrated with data obtained from an investigation of the interaction of modulated As₄ beams with GaAs surfaces.     

Adatom self-organization induced by quantum confinement of surface electrons

We present a novel mechanism of nanostructure growth based on quantum confinement of surface-state electrons. Ab initio calculations and the kinetic Monte Carlo simulations reveal the phenomenon of confinement-induced adatom self-organization in quantum corrals. Our studies indicate that new atomic-scale nanostructures can be engineered exploiting the quantum confinement of surface electrons.     

Polarization properties of surface plasma radiation excited by electrons

Some interesting features of the radiation associated with non-radiative surface plasmons, excited by electrons have not been explained previously. We give here an explanation of the origins of these features, based on recent work by Elson and Ritchie.     

On the possible influence of surface roughening on ellipsometric data in electrochemical studies

A model is suggested which shows that, if anodic dissolution is heterogeneous, it may give, in time of minutes, surface irregularities which cause changes of the ellipsometric parameters, Δ and ψ, as large as that caused by passive film formation.