Optical anisotropy induced by ion bombardment of Ag(001)

Grazing incidence ion bombardment results in the formation of nanoripples that induce an anisotropic optical reflection The evolution of the reflectance anisotropy has been monitored in situ with reflectance anisotropy spectroscopy. The Rayleigh-Rice theory (RRT) has been used to analyze the optical spectra quantitatively and provides the evolution of the average ripple period and root-mean-squared surface roughness. After an incipient phase, both the increase in the periodicity and the roughness vary roughly with the square root of the sputter time. Additional high-resolution low-energy electron diffraction (HR-LEED) measurements have been performed to characterize details of the average structure created by ion bombardment

Kinetics of the adsorption of atomic oxygen (N2O) on the Si(001)2x1 surface as revealed by the change in the surface conductance

The adsorption behaviour of N2O on the Si(001)2 × 1 surface at 300 K substrate temperature has been investigated by measuring in situ the surface conductance during the reaction process. For comparison we monitored in the same way the adsorption of O2 on the same surface which ultimately leads to the flat band situation. The adsorption of atomic oxygen as released by decomposition of the N2O molecule, in contrast with molecular oxygen, was found to result in an increase of the band bending. The difference in behaviour of the change of the surface conductance between the two solid-gas reactions can be explained by considering that the adsorption of O2 will also remove deep-lying backbond states in addition to the dangling bond (DB) and dimer bond (DM) related surface states. It is well known that only the DB and DM surface states are affected by N2O. The surface conductance measurements (SCM) presented in this paper complement our previous spectroscopic differential reflectivity measurements and Auger electron spectroscopic results for the system Si(001)2 × 1 + N2O; we have found evidence that the second step of the proposed three-stage adsorption process of atomic oxygen can be divided into two substages. From our SCM data we could derive that the distance between the valence band edge and the Fermi energy of the clean Si(001)2 × 1 surface is 0.32 ± 0.02 eV, which is in agreement with previous photoemission results

The influence of inter-atomic transitions in Auger valence band spectroscopy: oxygen on Si(001)2x1

In this paper we will show that the description of an Auger process in terms of a process confined to one atom is in general not adequate and the Mulliken population is only in very specific cases a good alternative in evaluating the strength of inter-atomic transitions. The ionicity of the chemical bond cannot be used as a direct measure of the contribution of inter-atomic Auger transitions, as will be demonstrated in the case of the oxygen KVV Auger transitions in gaseous molecular oxygen and oxygen chemisorbed on the Si(001) surface. A full evaluation of inter-atomic transition rates shows that their strength depends on the inter-atomic distance as well as on the screening of the initial core hole

Optical anisotropy of Ge(001)

The surface induced optical anisotropy in the electronic structure of clean Ge(001) 2×1 was studied with an ellipsometer at normal incidence. The change in the reflection difference between light polarized parallel and perpendicular to the dimer bond at this surface upon either absorption of molecular oxygen or Ar+ ion bombardment was recorded. Both procedures were found to give the same results. It was possible to obtain a qualitative agreement of the optical spectrum recorded and the position and parity of the occupied and unoccupied surface states known on the clean surface

In-situ growth studies of sputtered ybco thin films by spectroscopic ellipsometry

Using spectroscopic ellipsometry we studied in-situ the growth of off-axis sputtered YBa2Cu3O6+x thin films on (001) SrTiO3 as a function of the deposition parameters. Especially in the very first growth stage (<5 nm) we observed that the optical properties of the grown layer differs from the "bulk" optical properties of YBCO and strongly depends on, both, the deposition temperature and the oxygen partial pressure. Both properties are well established as influencing the superconducting properties of thin YBCO films. YBCO thin film growth under optimal deposition conditions (Tcnot, vert, similar90 K; jc>106A cm¿2 @ 77 K) is smooth and homogeneous, except for the first unit cell layer (initial stage regime). The smoothness of the response is indicative for a step-mode like growth mechanism. In contrast, the initial stage regime is governed by a 2D nucleation mechanism. This behaviour changes when the deposition temperature is lowered. Due to increased disorder, the initial stage regime is extended to larger thicknesses and a true 2D growth mode is no longer apparent. Similar behaviour is observed with increasing oxygen partial pressure, where the optical response is shifted from a step-flow mode like mechanism to an island-growth mode

The influence of the (2 × 1) reconstruction of the Si(1 0 0) surface on the Si---L2,3 VV Auger lineshape

The extreme surface sensitiveness of the Si---L2,3 VV Auger process and its ability to probe the atomic electron distribution in the direct neighbourhood of the L2,3-core-hold makes this electron spectroscopic technique a candidate for investigations of the local changes in the electron distribution due to surface reconstruction. In this paper we show, explicitly, the influence of the (2 × 1) reconstruction of the Si(1 0 0) surface on the Si---L2,3 VV Auger lineshape. Furthermore, the calculated Auger lineshape will be compared with an experimentally obtained line profile

Effect of quantum confinement on the dielectric function of PbSe

Monolayers of lead selenide nanocrystals of a few nanometers in height have been made by electrodeposition on a Au(111) substrate. These layers show a thickness-dependent dielectric function, which was determined using spectroscopic ellipsometry. The experimental results are compared with electronic structure calculations of the imaginary part of the dielectric function of PbSe nanocrystals. We demonstrate that the size-dependent variation of the dielectric function is affected by quantum confinement at well-identifiable points in the Brillouin zone, different from the position of the band-gap transition

Deconvolution, differentiation and Fourier transformation algorithms for noise-containing data based on splines and global approximation

One of the main problems in the analysis of measured spectra is how to reduce the influence of noise in data processing. We show a deconvolution, a differentiation and a Fourier Transform algorithm that can be run on a small computer (64 K RAM) and suffer less from noise than commonly used routines. This objective is achieved by implementing spline based functions in mathematical operations to obtain global approximation properties in our routines. The convenient behaviour and the pleasant mathematical character of splines makes it possible to perform these mathematical operations on large data input in a limited computing time on a small computer system. Comparison is made with widely used routines

Calculated and measured Auger lineshapes in clean Si(100)2×1, SiOx and Si-NO

The measurements were performed on the clean 2*1 reconstructed Si(100) surface and this surface exposed to molecular oxygen (O2) or nitric oxide (NO) at room temperature. The data were corrected for electron loss and spectrometer distortions using the authors' newly developed deconvolution method. This method which uses global approximation and spline functions can overcome several difficulties with respect to deconvolution and allows them to derive high-quality auger lineshapes from the SiL2.3 VV Auger electron spectra. The authors experimentally obtained Auger lineshapes were compared with theoretical lineshapes utilising quantum chemical cluster calculations. They used this type of calculation for the interpretation of the Auger lineshape in the actual p-like and s-like partial local density of states for different types of silicon atom. The observed intensities of the major features are in reasonable agreement with the authors' calculations

New approach for correction of distortions in spectral line profiles in Auger electron spectroscopy

A new deconvolution method for Auger electron spectroscopy is presented. This method is based on a non-linear least squares minimizing routine (Levenberg-Marquardt) and global approximation using splines, solving many of the drawbacks inherent to the Van Cittert and Fourier transform based deconvolution methods. The deconvolution routine can be run on a personal computer. The application of this method goes beyond the electron spectroscopies and can be considered as a general deconvolution method