High-resolution Auger Electron Spectroscopy Research Articles

High resolution Auger electron spectroscopy and microscopy of a supported metal catalyst

High spatial resolution Auger electron spectra and scanning Auger microscope (SAM) images of supported metal catalysts have been obtained in a UHV scanning transmission electron microscope. Ag/α-Al 2O 3 was used as a model catalyst system, where silver was evaporated, in situ, onto polycrystalline alumina carriers. Silver particles, as small as 2 nm in diameter, were clearly revealed in SAM images with high contrast. On large islands, an edge resolution < 3 nm was achieved. Information about surface and bulk properties of supported catalysts can be extracted from images formed with different signals generated from the same area which are obtained simultaneously.

Electronic properties of highly saturated caesium-graphite intercalation compounds studied by high resolution Auger electron spectroscopy

For the first time C KVV Auger spectra of highly saturated caesium-graphite intercalation compounds (Cs-GICs) are obtained. The possible nature of the spectrum transformation as well as the character of electron transfer in the range from the ‘equilibrium’ C 8Cs-GIC to the highly saturated C 4Cs-GIC are discussed.

High-resolution Auger Electron Microscopy and spectroscopy of supported metal particles

A detailed understanding of catalytic processes requires structural knowledge of the catalyst system. The surface properties of small metal particles which are highly dispersed on insulating supports must play a dominant role in determining this system's catalytic behavior. Therefore characterization of surface topography and composition of heterogeneous catalysts is important. Surface topography of the carrier materials can be obtained by high resolution secondary electron imaging (SEI) in a STEM. The small metal particles can also be located and their topographic relationship with the support morphology determined. However, an elementally specific signal such as the Auger electrons must be used to extract chemical information about the surface species. High resolution Auger electron spectroscopy (AES) and scanning Auger microscopy (SAM) have recently been incorporated into a UHV STEM. In this paper we report some results from the application of this instrumentation to the study of supported metal clusters.

Effect of electron-electron interaction on projectile K-shell ionization in energetic ion-atom collisions studied by 0° Auger electron spectroscopy

Cross sections for 1s ionization of the ground state of O 4(1s 22s 2) were obtained in 10–30 MeV collisions of O 4+ with H 2 and He targets. High resolution Auger electron spectroscopy was used to detect at 0° with respect to the beam direction, the electrons emitted from the Auger decay of O 5+ (1s2s 2) → O 6+ (1s 2) + e − following 1s ionization of the O 4+ ions. The electron-nucleus ( σ enI) and electron-electron ( σ eeI) ionization cross sections, due to ionization of the projectile electron either by the target nucleus or the target electrons, respectively, were independently computed. σ enI was calculated within a PWBA treatment, while σ eeI was computed within an impulse approximation (IA) treatment of electron impact ionization of O 4+. The incoherent sum σ enI + σ eei was found to be in good agreement with the data. K-shell ionization of the metastable O 4+(1s 22s2p 3P) component of the beam was also observed.

Hydrogen induced structure changes of GaAs(1 0 0) surfaces

The interaction of hydrogen with GaAs(1 0 0) surfaces has been studied at room temperature by means of high-resolution electron energy-loss spectroscopy (HREELS), low-energy electron-diffraction (LEED), and Auger electron spectroscopy (AES). Sample cleaning by Ne+ ion bombardment (500 eV) and annealing resulted (with increasing temperatures) in “1 × 1”, 1 × 6, 4 × 1, 4 × 6 and c(8 × 2) LEED structures. As a function of hydrogen exposure, the intensity ratio of the stretching vibrations (As-H/Ga-H) is shown to be characteristic for the specific reconstructed surface. In particular the arsenic hydride concentration gradually decreased in all cases. In addition, an initial weakening of the fractional order LEED spots occurred with increasing hydrogen exposures. Finally, a strong 1 × 2 structure was observed independent of the reconstruction we started with. Simultaneously, a shift of the energetic position of the Ga-H stretching vibration occurred.

Microanalytical investigations of the intermediate sintering state of silicon carbide

The intermediate state of sintering of boron- and carbon-doped pressureless sinterable silicon carbide was analyzed in situ using analytical transmission electron microscopy (including electron energy loss spectroscopy and energy dispersive analysis of X-rays) as well as high resolution Auger electron spectroscopy. From the results obtained it became evident that any type of liquid phase—even a transient liquid phase—can be excluded. The segregation of boron on the SiC grain boundaries has not been confirmed. The investigations have shown the reduction of SiO 2 layers present on the SiC grains and the development of secondary SiC. The microanalytical in-situ results concerning the intermediate and also the final state of sintering as well as the specific roles of the sintering additives boron and carbon are discussed in detail.

High-resolution auger electron spectroscopy of grain boundary phosphorus segregation in NiCrMoV and NiCr steels

This communication presents some AES data which compare average measurements of grain boundary phosphorus segregation to those from specific microstructural features such as the prior austenite grain boundary carbide/ferrite interface

Investigations of PbO-modified Bi-Sr-Ca-Cu-O superconductors by Auger electron spectroscopy

High-temperature superconducting ceramic with the nominal composition Bi2Pb0.5Sr2Ca2.5Cu3.5Ox was prepared by firing at different temperatures and investigated by high-resolution Auger electron spectroscopy (AES). The ceramic material was inhomogeneous with a higher concentration of calcium at the grain boundaries. Generally, the differences in concentration of calcium are less pronounced for ceramics fired at higher temperatures. In PbO-modified Bi-Sr-Ca-Cu-O superconducting material lead was observed mainly at the grain boundaries. Depth profiling through the grain boundaries of Bi-Sr-Ca-Cu-O material fired at higher temperatures reversed the concentration variation of bismuth and oxygen.

Interfacial Characterization of Silicon Carbide Fiber/Lithia‐Alumina‐Silica Glass Matrix Composites

The development of the carbon‐rich interphase in Nicalon SiC fiber/Li2O‐Al2O3–SiO2 glass matrix composites was examined as a function of processing parameters with the use of high‐resolution scanning electron microscopy and Auger electron spetroscopy. Specifically, hot‐pressing temperatures (1000°, 1100°, and 1200°C) and times (15, 30, 60, and 240 min) were systematically varied in such a manner so as to fabricate dense composites suitable for evaluation of reaction kinetics. Carbon‐rich interphase thickness, which ranged from 1400 to 5400 Å (140 to 540 nm), was observed to increase with either increasing times at constant temperature or increasing temperatures at constant time. The kinetics of formation of the carbon‐rich interphase followed a diffusion‐controlled model, with an activation energy of 25.4 kcal/mol.

Mikroanalytische untersuchungen Faserverstärkter keramischer Werkstoffe

AbstractMicroanalytical investigations have been made on samples of ceramic fibers (SiC‐fibres (Nicalon), C‐fibre coated with TiN) and fibre‐reinforced ceramics (SiC‐ and glass‐matrices). High resolution Auger electron spectroscopy (HRAES), electron probe microanalysis (EPMA) and scanning electron microscopy were employed for these examinations. Analysis was best performed with HRAES on account of its lateral and depth resolution. AES depth profiles of ceramic fibres are reported and compared with the surface analysis of fibers in the composites after being broken in situ.

Effect of Cs and Ba adsorption on the electronic properties of carbon films adsorbed on metals (Ir, Re)

The effect of adsorption of cesium, barium and oxygen on the electronic properties of mono- and multilayer carbon films on the surface of metals (Ir, Re) has been studied by high resolution (Δ E E ≈0.1%) Auger electron spectroscopy. The shape of the high-energy part of the carbon Auger spectrum has been found to change dramatically after the adsorption of Cs and Ba atoms on a monolayer of graphite film on metals. This change is similar to the effect observed on single crystal intercalated by donor atoms. The reason for the close electronic properties between a graphite layer adsorbed on a metal surface and that representing a part of a macroscopic graphite crystal is that the graphite film is separated from the metal surface at a distance characteristic of the van der Waals forces. This effect was not observed in the adsorption of Cs and Ba atoms on a film of chemisorbed carbon on metals, which does not exhibit a graphite structure. Oxidation of the Cs or Ba adsorbed on a graphite layer on a metal has been shown to affect the direction of the electron exchange by restoring the electrons from the graphite valence band to the adparticles.

Characterization of SiC-platelets

Three fractions of SiC platelets were characterized using polarizing microscopy, X-ray diffraction, high resolution Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA) and scanning electron microscopy with energy dispersive analysis (SEM/EDX). The chemical analysis of the three fractions is given. The determination of the SiC polytypes (4H, 6H, 15R, 3C) was done and has been correlated with the chemical analysis. The results of the X-ray diffraction investigations confirm the polarizing microscopy observations. Using microanalytical techniques important conclusions about the impurity elements (e.g. B, Al, Fe) and their local distribution could be drawn. Most of them were found to be present on the outermost surfaces of the platelets. Some conclusions concerning the processing of the platelets are suggested.

Investigations of superconducting YBa 2Cu 3O 7 ceramic by Auger electron spectroscopy

High temperature superconducting ceramics, based on YBa 2Cu 3O 7, were prepared from oxides and carbonates, from the pre-reacted binary compounds BaCuO 2 and Cu 2Y 2O 5, or by partial substitution of Y 2O 3 and BaO by Bi 2O 3 and PbO, respectively. Fractured and polished samples were investigated by high resolution Auger electron spectroscopy. Sputter depth profiles were obtained by the AES method and Ar + ion sputtering. The analysis revealed a nonhomogeneous composition of ceramic material with a higher concentration of barium on grain boundaries. In the case of modified YBa 2Cu 3O 7, Bi 2O 3 and PbO were found mostly on grain boundaries.

AES analysis of pits and passive films formed on FeCr FeMo and FeCrMo alloys

A single pit was produced on binary iron-chromium (Fe17Cr), iron-molybdenum (Fe1Mo, Fe3Mo, and Fe5Mo) and ternary iron-chromium-molybdenum alloys (Fe17CrxMo, x = 1, 3, 7 w%) in 1 N H 2SO 4 with Cl − additions (0.02 to 0.08 molar) at room temperature. Compositional changes at the bottom of the pit and in the surrounding passive film were determined using high resolution Auger-Electron Spectroscopy. The chromium and molybdenum content of the passive layers are not changed in the presence of Cl − and there is no incorporation of chlorine in the passive film as long as the films were formed in a chlorine free electrolyte and Cl − was added later. At the bottom of the pits precipitated salt films could be determined after removing the electrolyte with filter paper. These salt films are strongly enriched in chromium, molybdenum and chlorine. The salt film was not detectable for FeCr after rinsing the samples with destilled water, whereas in the case of molybdenum additions the salt film could not be washed away with water. At the salt free bottom of pits in Fe17Cr we found an enrichment of chromium which is less than that in the passive film but similar to that determined for active corrosion.

Formation of Stacking Faults and Misfit Dislocations During Zn Diffusion-Enhanced Intermixing of a GaInAsP/InP Heterostructure

ABSTRACTThe microstructural degradation of a lattice-matched Ga0.28 In0.72As0.61P0.39/InP heterointerface during atomic intermixing induced by Zn diffusion has been investigated using high-resolution transmission electron microscopy and Auger electron spectroscopy. The localized interfacial stress caused by intermixing appears to create stacking faults in the Ga-mixed InP substrate, and dislocation tangles in the In-mixed GalnAsP layer. The results are attributed to the contrasted effect of tensile and compressive stresses upon the nucleation of partial dislocations from both sides of the intermixed interface. A qualitative model is proposed for the homogeneous nucleation of misfit dislocations from the locally stressed interface.

Effect of Cs and Ba adsorption on the electronic properties of carbon films adsorbed on metals (Ir, Re)

A study has been made of the effect of the Cs and Ba intercalation on the electronic properties of ultrathin, monolayer (n=1) and multilayer (n=10), graphite films on the surface of transition metals (Ir, Re), as well as of the effect of oxygen on the electronic properties of these intercalated films, by means of high resolution (Δ E/E ∼ 0.1%) Auger electron spectroscopy. The role in this effect of remarkable electronic properties of the graphite layer, a natural two-dimensional crystal, is established by comparing the influence of Cs adsorption on the electronic properties of two structurally different carbon films on the metal surface, namely a graphite monolayer and a monolayer of chemisorbed carbon.

Carbon Inclusions in Sintered Silicon Carbide

The carbon additions in the pressureless sintering of SiC are commonly used for the removal of SiO2 layers on the starting powders. In practice, it is common to add more C than is necessary for stoichiometric removal to ensure a complete deoxidation. As a result, inclusions of excess free C are a general feature of the microstructure of sintered SiC. This phenomenon was studied by high‐resolution Auger electron spectroscopy on ultra‐high‐vacuum‐exposed fracture surfaces as well as by high‐resolution transmission electron microscopy of B‐ and C‐doped materials.

Microanalytical investigation of fibre-reinforced ceramic materials

Microanalytical investigations have been made on samples of ceramic fibres (SiC fibres, (Nicalon) C fibre coated with TiN) and fibre-reinforced ceramics (SiC- and glass-matrices). High resolution Auger electron spectroscopy (HRAES), electron probe microanalysis (EPMA) and scanning electron microscopy were employed for these examinations. Analysis was best performed with HRAES on account of its lateral and depth resolution. Some of the problems involved in this technique are discussed e.g. electron beam effects. AES depth profiles of ceramic fibres are reported and compared with the surface analysis of fibres in the composites after being broken in situ.

High-resolution Auger electron spectroscopy of phase boundaries in TiC/TiB2 materials

Multi-phase hard materials free from binder metals are used to meet the requirements of high wear resistance and high temperature stability. Investigations of properties and wear behavior showed extremely high values in carbide/boride combinations, particularly a TiC/TiB2 mixture of a 1∶1 molar ratio. The pseudobinary phase diagram shows low intersolubilities. High-resolution Auger Electron Spectroscopy was used to examine mixed two-phase TiC/ TiB2 hard materials and compare them to pure TiC and TiB2. The AES analyses were carried out on cross sections and fresh fracture surfaces. At the grain boundaries in pure TiC as well as in pure TiB2, some amounts of Fe, Cr, Co and P can be detected. These elements are already in the powders as received. In addition, an O-rich phase has been identified in hot pressed TiB2. The same impurity elements as in the pure materials can be found at a few phase boundaries and triple points in two-phase TiC/TiB2 with a thickness of a few monolayers. However, large areas of the fracture surface were found to carry a TiBxCy phase on the grains. The considerable increase in wear resistance and fracture toughness of TiC/TiB2 compared to pure TiC and pure TiB2 can be explained by the presence of this TiBxCy phase.

Summary Abstract: High energy resolution Auger electron spectroscopy of Ti and TiN

Summary Abstract: High energy resolution Auger electron spectroscopy of Ti and TiN