Temperature modification of oxidized multiwall carbon nanotubes studied by electron spectroscopy methods

First stages of the InP(1 0 0) surfaces nitridation studied by AES, EELS and EPES

Electron inelastic mean free path (IMFP) is an important parameter for surface chemical quantification by surface electron spectroscopy techniques. It can be obtained from analysis of elastic peak electron spectroscopy (EPES) spectra measured on samples and a Monte Carlo simulation method. To obtain IMFP parameters with high accuracy, the surface excitation effect on the measured EPES spectra has to be quantified as a surface excitation parameter (SEP), which can be calculated via a dielectric response theory. However, such calculated SEP does not include influence of elastic scattering of electrons inside samples during their incidence and emission processes, which should not be neglected simply in determining IMFP by an EPES method. In this work a Monte Carlo simulation method is employed to determine surface excitation parameter by taking account of the elastic scattering effect. The simulated SEPs for different primary energies are found to be in good agreement with the experiments particularly for larger incident or emission angles above 60° where the elastic scattering effect plays a more important role than those in smaller incident or emission angles. Based on these new SEPs, the IMFP measurement by EPES technique can provide more accurate data.

The inelastic mean free path (IMFP) of electrons is a fundamental material parameter needed for surface analysis. The IMFP data of semiconducting III–V compounds have been calculated by Tanuma et al., Kwei et al. and Gries. The present paper completes previous research and reports experimental studies on the IMFPs of GaP and InAs. Elastic peak electron spectroscopy (EPES) was used with Ni, Au and Ag reference samples. Both InAs(100) and GaP(100) have been studied in three laboratories, using different types of electron spectrometer analysers and energy ranges: HSA (0.2–5 keV), DCMA (0.2–2 keV), DESA 100 (0.5–2 keV). The surface of the samples was cleaned and amorphized by Ar+ ion bombardment with controlled parameters (energy, dose, etc.) to eliminate crystallinity effects. The surface composition of the ion-bombarded samples was determined in situ by XPS and Auger electron spectroscopy. Their crystallinity and incoherent elastic scattering were tested with Renninger plots of the elastic peak intensity, rotating the sample around its axis perpendicular to the surface. The IMFPs were calculated by a Monte Carlo algorithm using the NIST database of elastic scattering cross-sections. A reasonable agreement was found with theoretical IMFP values calculated by other authors. Copyright © 2000 John Wiley & Sons, Ltd.

Optical characterization of MBE grown cubic and hexagonal SiC films on Si(111)

The growth and decomposition kinetics of very thin oxides on Si(001) surfaces were investigated by reflection high-energy electron diffraction combined with Auger electron spectroscopy (RHEED–AES) to monitor the reaction rates of oxide growth and decomposition in real time, and changes in surface structure and interface morphology simultaneously. The oxides prepared by stopping the second oxide layer growth at various coverages following the first oxide layer growth by Langmuir-type adsorption at 500 °C under an O2 pressure of 2.6×10-4 Pa were isothermally annealed by increasing temperature from 500 to 666 °C at the same time that O2 gas was quickly evacuated. It was observed that (1) oxide thickness continued to decrease significantly as measured on the basis of changes in O KLL Auger electron intensity ΔIO-KLL before voids appeared at a nucleation time tN as recognized by the appearance of half-order spots in RHEED patterns, (2) the SiO2/Si interface morphology was considerably roughened corresponding to ΔIO-KLL during void nucleation as observed by the evolution of the RHEED intensity of bulk diffraction spots ΔIbulk, (3) the ratio of ΔIbulk to ΔIO-KLL was almost constant, and (4) oxide decomposition rate during void nucleation, which was approximately given by ΔIO-KLL/tN, showed a good linear correlation with the second oxide layer growth rate α immediately before starting the decomposition reaction. The good correlation between ΔIO-KLL/tN and α clearly indicates that the rate-limiting reaction of the second oxide layer growth is closely related to that of the oxide decomposition during void nucleation. All the above-mentioned observations can be comprehensively interpreted using a reaction model proposed for the rate-limiting reactions of oxide growth and decomposition, in which the point defect generation (emitted Si atoms + vacancies) caused by the strain due to the volume expansion of oxidation plays a crucial role because of the high reactivity of the emitted Si atoms and vacancies with dangling bonds. Under an O2 atmosphere, both emitted Si atoms and vacancies are the preferential adsorption sites of O2 molecules in the oxide and at the SiO2/Si interface, respectively. The oxide can be decomposed by the emitted Si atoms to produce SiO molecules, which desorb from the surface, leading to oxide removal in vacuum with SiO2/Si interface morphology roughening, but may be oxidized within the oxide under an O2 atmosphere.

Study of the adsorption of hydrogen and oxygen on Si(100) using positron-annihilation induced Auger electron spectroscopy (PAES)

A summary is given of the workshop entitled ‘Electron Scattering in Solids: from fundamental concepts to practical applications,’ which was held in Debrecen, Hungary, on July 4–8, 2004, under the sponsorship of the International Union of Vacuum Science, Technique, and Applications (IUVSTA). This workshop was held to review the present status and level of understanding of electron‐scattering processes in solids, to identify issues of key importance (hot topics) in the light of the most recent scientific results, and to stimulate discussions leading to a deeper understanding and new solutions of current problems. This report contains summaries of presentations and discussions in sessions on elastic scattering of electrons by atoms and solids, inelastic scattering of electrons in solids, modeling of electron transport in solids and applications, and software. The principal areas of application include Auger‐electron spectroscopy (AES), X‐ray photoelectron spectroscopy, elastic‐peak electron spectroscopy (EPES), reflection electron energy‐loss spectroscopy (REELS), secondary‐electron microscopy, electron‐probe microanalysis (EPMA), and the use of coincidence techniques in electron‐scattering experiments. A major focus of the workshop was determination of the inelastic mean free path of electrons for various surface spectroscopies, particularly corrections for surface and core‐hole effects. Published in 2005 by John Wiley & Sons, Ltd.

The experimental technique and the physical principles of the fundamental electron spectroscopic methods are examined:X-ray electron spectroscopy (XES), Auger electron spectroscopy (AES), and ultraviolet photoelectron spectroscopy (UPES).Their advantages and disadvantages are compared. The application of electron spectroscopic methods in the study ofchemical reactions on the surfaces of metals is considered in relation to the investigation of the oxidation of metals andalloys in both the vapour-gas phase and in aqueous electrolytes. In addition, studies on the application of XES and AES tothe investigation of corrosion processes at the metal–electrolyte interface are discussed. The bibliography includes 76 references.

Vacuum-annealing induced band bending in phosphorus-doped (111) diamond

Abstract— Wet chemical treatments have been performed on phosphor particles. ZnO: Zn phosphor was reductively etched with a basic aqueous solution of sodium borohydride. The etch resulted in a two‐fold increase in the cathodoluminescent efficiency without any detected change in particle size or surface composition as detected by Auger electron spectroscopy. The low‐voltage cathodoluminescent characteristics are particularly enhanced. The enhanced efficiency of the phosphor particles may be attributable to a change in surface structure or an increase in the surface coverage of luminescent centers induced by the reductive etch.

We have investigated and characterized changes in film morphology and surface structure that occur when ultrathin multilayered polyelectrolyte films fabricated from linear poly(ethylene imine) (LPEI), sodium poly(styrene sulfonate) (SPS), and two hydrolytically degradable polyamines (polymers 1 and 2) are incubated in physiologically relevant environments. Characterization of the physical erosion profiles of films having the structure (LPEI/SPS)10(1/SPS)4(2/SPS)4 (approximately 80 nm thick) by atomic force microscopy (AFM), reflective optical microscopy, and scanning electron microscopy (SEM) demonstrated that these materials undergo large-scale changes in surface structure and morphology upon incubation in phosphate-buffered saline (PBS) at 37 degrees C. The patterns and structures generated during this transformation (e.g., nucleation and growth of holes, coalescence of holes, formation of cell-type structures, and the subsequent breakup of these features into droplets) are similar in many ways to those observed for the dewetting of thin films of conventional polymers, such as polystyrene, on nonwetting surfaces. The processes reported here are sufficiently slow (they occur over approximately 100 h) and occur under sufficiently mild conditions (e.g., incubation in PBS at 37 degrees C) to permit characterization and quantification of the structures and features that arise during the course of these transformations. The apparent dewetting of these ultrathin films upon exposure to aqueous environments creates future opportunities to investigate and characterize processes of mass transport in this class of ionically cross-linked assemblies.

UHV aluminium oxide on silicon substrates: electron spectroscopies analysis and electrical measurements

The inelastic mean free path (IMFP) of electrons was determined experimentally for selected polyaniline and polyacetylene samples with Ag and Ni references using elastic peak electron spectroscopy (EPES). The surface composition was determined by XPS and density by helium pycnometry. The high resolution hemispherical ESA-31 and ADES-400 spectrometers were used for measurements in the energy range E = 0.5–3.0 keV and E =0.4 − 1.6 keV, respectively. The integrated elastic peak intensity ratios for sample and reference were calculated using the Monte Carlo (MC) algorithm based on the electron elastic scattering cross-sections database NIST SRD64 version 3.1 and applying TPP-2M IMFPs for polymers. Surface excitation parameters (SEP) and material parameters (ach) for polymers were determined, using the model of Chen, from comparison of measured and MC calculated elastic peak intensity ratios. These corrections proved to be efficient in decreasing the percentage deviations between the obtained IMFPs and the TPP-2M formula IMFPs. The elastic peak of hydrogen was observed in the EPES spectra of polymers. The experimental contribution of the hydrogen to the total elastic peak was 0.58%, while this value obtained from the MC simulations was 1.98%.

Positron-annihilation-induced Auger electron spectroscopy (PAES), electron-induced Auger electron spectroscopy, and low-energy electron diffraction have been used to study the composition and structure of vapor-deposited Pd films on Cu(100). Our results show that the PAES intensity from Pd saturates while that from Cu attenuates to near zero by one monolayer of Pd deposition at 173 K. This is confirmation of the top-layer selectivity of PAES in metal-on-metal systems. Changes in the PAES intensities provide a direct indication of the intermixing of Cu and Pd in the topmost layer as a Pd film deposited at 173 K is warmed to 303 K, and of the formation of a Cu overlayer upon further warming to 423 K. Lack of agreement between model calculations which assume delocalized positron states and measured PAES intensities at 173 K suggests that positrons are localized at sites containing Pd atoms.

Oxygen vacancy induced structure change and interface reaction in HfO2 films on native SiO2/Si substrate