Auger electron spectroscopy for thin film analysis

Auger Electron Spectroscopy (AES) for thin film analysis reviewed with emphasis on state-of-the-art technical capabilities and applications. The physical phenomena are reviewed and the qualitative and quantitative aspects of AES are discussed. The procedures used to study metals, semiconductors, and insulators are described, and the technique for obtaining in-depth profiles on thin films is presented. Several applications of AES to the study of thin films are included.     

On the backscattering factor in quantitative Auger electron spectroscopy of binary alloys

The matrix dependent relative sensitivity factor S_rel(c) is considered for use in quantitative Auger analysis. It is affected by matrix dependent factors like the backscattering factor, the escape depth of Auger electrons and the number of atoms per unit volume. The backscattering factor, especially, is evaluated and possibilities of its determination are shown. Measurements of Auger intensities and of the energy distribution of backscattered electrons were carried out for this purpose on a series of CuPd and CuSb alloys, respectively. The backscattering factor thus obtained is compared with values resulting from a formula of JABLONSKI and by experimental data of SMITH and GALLON .     

Polarity identification of GaN bulk single crystals (0001) surface by Auger electron spectroscopy

An attempt to identify the polarity of (0001) polar surface of GaN bulk single crystals grown by high nitrogen pressure solution method has been made using Auger electron spectroscopy (AES). AES concentration depth profiles of the top layer in (0001) direction starting from both (0001) faces of the sample have been measured. Distinct difference in the Ga concentration at the sample surface of both faces has been observed. The dependence of Ga eoncentration on depth is also different for both faces of the sample.     

Surface oxidation of basalt glass/liquid

To evaluate surface oxidation of Fe²⁺-rich multi-component silicate glass, powder and pieces of natural basalt glass are heat-treated in Ar and subsequently investigated by Mössbauer spectroscopy to monitor the increase of Fe³⁺. Glass pieces show no increase in oxidation with time or temperature, suggesting that the oxygen potential between glass and Ar is insufficient to cause volume oxidation. In contrast, glass powder oxidizes readily to a degree comparable with that of powder oxidation in air, suggesting that surface oxidation does not depend on the oxygen potential. No cation diffusion to the glass surface is detected in Ar, though it is observed upon heat treatment in air; cation diffusion is therefore unlikely to be involved in oxidation. We suggest the following mechanism for surface oxidation: (1) adsorption of water on the glass surface as OH⁻, by exposure to air and (2), a concomitant reaction, i.e., oxidation with the glass, upon heating (chemisorption). Hereby, either oxygen of air or residual oxygen in Ar would react with the hydrogen of the -OH, liberating the oxygen for oxidation of iron. Heat treatment in vacuum of 10⁻⁸ mbar does not result in any oxidation, and we assume that the adsorbed OH is exhausted from the glass surface.     

Auger electron spectroscopy studies of impurity effects on the hot deformability of AISI M2 high speed steel

The effects of various materials parameters on hot deformability f of AISI M2 high speed steel are studied in a complex way. These studies revealed beside other parameters (e.g. carbides) a strong correlation between some impurities (S, Sn) and f, determined by hot deformability tests. The correlation between f and the P content prooved to be weaker. The paper is devoted to impurity effects. The composition and impurities of the samples and their isolated carbide phases have been determined by chemical analysis. In situ AES fractography and SEM were applied to study the fracture surfaces. The main results are: The S concentration of the fracture surfaces exhibits a correlation with the bulk content. Strong enrichment of S and P within a thin (1–3 nm) surface layer was revealed by AES in-depth profiling, showing also carbide phases. In the temperature range -150°C — +250°C no grain boundary fracture was observed, fracture was ductile and void type. The fracture path is determined by carbides, being the sites of S and P enrichment.     

Magnetic properties of a basalt glass and glass-ceramics

Mössbauer, ESR and magnetization measurements have been carried out on a basalt glass heat-treated at different temperatures (600, 650, 700, 800 and 900°C for 8 h). The as-annealed glass and the above five samples showed two-doublet Mössbauer spectra, while the last two samples also showed a six line magnetic hyperfine pattern at 300 K. At 4 K, the last four samples showed magnetic hyperfine patterns, while the as-annealed glass showed that there was already short range magnetic ordering present. High field Mössbauer data at 4 K showed that the surface spins are canted. The minimum quadrupole splitting and the maximum isomer shift around 700°C are related to the improved symmetry of the magnetite lattice. ESR spectra showed paramagnetic resonances at g = 4.3 and g = 2.0 for the first two samples, while the last four samples showed superparamagnetic resonance centred around g = 2.0 at 300 K. At lower temperatures, the 650 and 700°C samples showed ferrimagnetic resonance. Magnetization curves against H/T superpose well both at 300 and 77 K, showing the typical superparamagnetic behaviour of the small magnetite particles. The saturation magnetization (at 270 K) showed a sharp change around 700°C, showing the formation of magnetite. The magnetic structure of the small magnetite particles are discussed in terms of the above results.     

Effect of electron irradiation on Na-K silicate glass investigated using X-ray photoelectron spectroscopy and pattern recognition method

Alkali silicate glasses and melts play an important role in material science. Electron interaction with glasses is important for radioactive waste deposition, where electrons of various energies lead to irreversible changes. These changes are caused mainly by ionization and ballistic interaction of electrons with atoms, introducing structural disorder, changes in atomic composition and chemical state, accompanied by alkali ions diffusion. The Na-K silicate glass (5Na₂O · 10K₂O · 85SiO₂), pristine and electron irradiated (doses from 25 C m⁻² to 20 236 C m⁻²) are investigated using X-ray photoelectron spectroscopy (XPS) and the pattern recognition (PR) and fitting procedures. Changes of composition and chemical state of atoms dependent on electron dose are analyzed. At low doses (100-300 C m⁻²), decrease followed by increase of O and Si concentrations was observed. Surface segregation, probable desorption, and in-bulk diffusion of K and Na ions (doses of about 50 C m⁻² and 2000 C m⁻², respectively) were observed. This was accompanied by changes in the chemical state of K atom, where with an electron dose increasing content of elemental K form accompanied by decreasing potassium peroxide form were observed. No difference in chemical state of Si and O atoms was visible under electron irradiation dose to 20 236 C m⁻², within the sensitivity of the applied method.     

An easy and economic method for preparing completely reduced basalt glass

Four basalt glass samples were prepared by fusing basalt rock (powder) with different amounts of sulfur in a platinum crucible at 1550 °C for 30 min. Each melt was quenched in air. Sulfur addition to the basalt powder was changed from 0 to 5, 10 and 15 wt%. The prepared glass samples were pulverized for measuring the Mössbauer spectra by the constant acceleration method. The basalt rock spectrum can be analyzed into four peaks; two sites due to Fe³⁺ with octahedral (Oh) and tetrahedral (Td) symmetry, and the other two due to Fe²⁺ with Oh and Td symmetry. Pure basalt glass (sulfur-free) consists of four doublets; two of them represent Fe²⁺(Oh) sites and the third represents Fe²⁺(Td); while the fourth doublet belongs to Fe³⁺(Td). The sample containing 5 wt% sulfur has four iron sites also, although there is a slight difference in the relative absorption area when compared with sulfur-free sample. The fraction of Fe³⁺ in the 5% sulfur sample was estimated to be only 7.1%; i.e., the fraction of Fe²⁺ was 92.9%. Three iron sites present in the 10% sulfur sample, two of them represent Fe²⁺ with (Oh) symmetry, while the third one represents Fe²⁺(Td) site. Mössbauer spectrum of 15 wt% sulfur sample is essentially the same as that of the sample which contains 10 wt%. It is noteworthy that the sulfur content shows a linear relationship with the Fe²⁺ fraction which is calculated from the Mössbauer spectra of basalt glasses. 7.5 wt% of sulfur is large enough to completely reduce the iron in basalt glass. The reduction of glasses could occur easily and economically using sulfur as a reducing agent. This method is a very easy and economic method for the preparation of completely reduced oxide glass.     

Optical spectroscopy of silver ion-exchanged As-doped glass

Soda-lime-silicate glass containing arsenic oxide and undoped soda-lime-silicate glass (blank) are prepared by melting from pure sand (iron concentration lower than 0.01 wt%). The effect of arsenic on the optical properties of the glass with and without silver ion exchange at 325 °C for various times is investigated by optical absorption and photoluminescence spectroscopy. Emission/excitation spectra of silver ion exchanged glass allow differentiation of three stages in the silver incorporation into the glass network. First and second stages are only observed in the undoped glass ion exchanged for short times. Such stages are associated with the presence of isolated Ag⁺-ions and Ag⁺-Ag⁺ pairs, respectively. The third stage appears in the undoped glass ion exchanged for times longer than 10 min and in the arsenic-doped glass even for exchange times as short as 1 min. Then, this stage is characterised by molecular mixed species formed with Ag⁺ and Ag⁰, which coexist with nanoparticles of metallic silver. The presence of those Ag⁰-aggregates gives a yellow colour to the glasses, which show the well-know absorption band at about 400 nm due to surface plasmon resonance.     

Broadband dielectric spectroscopy and aging of glass formers

We present the results of aging experiments on a variety of glass formers, including xylitol, glycerol, propylene carbonate, and [Ca(NO₃)₂]_0.4[KNO₃]_0.6 (CKN). In addition, broadband dielectric spectra of xylitol and CKN are provided. We demonstrate that, irrespective of which dielectric quantities (real and imaginary part of dielectric permittivity and modulus) are analyzed, and irrespective of the spectral region where they have been measured, the aging-time dependence always is governed by the structural rearrangements constituting the α-relaxation. If the time dependence of the structural relaxation time during aging is taken into account, relaxation times and stretching parameters, fully consistent with equilibrium data, are obtained. In CKN, both the structural relaxation time and the strongly decoupled conductivity relaxation time are deduced from the same dielectric aging experiment.     

Coordination and optical attenuation of TiO2-SiO2 glass by electron energy loss spectroscopy

Electron energy loss spectroscopy (EELS) techniques have been applied to investigate both the coordination and optical attenuation of TiO₂-SiO₂ glass. The coordination was determined from the electron energy loss near edge fine structure (ELNES) of Ti L_2,3-edges, and the results show that Ti ions substitute for Si ions in the tetrahedral coordinated sites. The optical attenuation of the glass was obtained from low energy loss of EELS data through Kramers-Kronig analysis, and the results show that Ti-doped silica has an absorption edge near 4.0 eV.     

Micro-Raman studies on 50 keV electron irradiated silicate glass

A potassium–lime-silicate glass was irradiated with a 50 keV electron beam. The impact of irradiation conditions on the glass structure (beam diameter, current, and irradiation time) was studied by Micro-Raman spectroscopy. For irradiation time less than the incubation time (around 360 s), structural evolutions are attributed to a glass densification. Irradiations longer than the incubation period led to a precipitation of supposed calcium enriched phase and formation of a more depolymerized silicate phase. A non-homogeneous irradiated glass structure was observed with the existence of an area (along the electron beam border) composed by a mixture of a concentrated Ca phase diluted into the amorphous silicate phase.     

Use of FTIR reflectance spectroscopy to monitor corrosion mechanisms on glass surfaces

Fourier transform infrared (FTIR) reflectance spectroscopy was used to monitor corrosion mechanisms on the surface of lithium disilicate (Li₂O-2SiO₂) glass samples exposed to an aqueous solution for short times. The traditional mechanisms of glass corrosion were observed but a spectral feature was resolved that was previously unreported. This feature consisted of a peak suspected to result partially from a silanol (Si-OH) vibration in the region 800-1050 cm⁻¹ that shifted and reappeared in a cyclic fashion throughout the corrosion process. The behavior of this peak tends to suggest that the creation and condensation of Si-OH groups is the reaction responsible for causing the shift of the main Si-O-Si and Si-O⁻ peaks, a phenomenon which has previously lacked a detailed explanation.     

Auger electron spectroscopic studies of the water vapour adsorption on the (100) surface of austenitic chromium-nickel steel

The water vapour adsorption on the (100) surface of chromium-nickel steel was studied by Auger electron spectroscopy (AES) in the temperature range of 300 K to 700 K at water vapour pressures of 13.3 μPa to 133 mPa. The water vapour adsorption goes on more slowly than the oxygen adsorption under the same conditions. The measured kinetic isotherms may be described by logarithmic time laws as they are typical of the adsorption on inhomogeneous surfaces. With rising temperature of the samples the rate of adsorption as well as the quantity of fragments of the water molecule adsorbed during saturation state increases, i.e. the adsorption is activated. By means of the measured adsorption isotherms it may be concluded that a dissociative adsorption takes place.     

XPS and nuclear analysis of compositional changes occurring in glass on electron beam irradiation

X-ray photoelectron spectrometry and nuclear microanalysis have been utilized to study the compositional changes occurring in a commercial soda-lime-silica glass after electron beam irradiation. Samples were irradiated with electron energies between 2.5 and 4.5 keV and current densities of 1.2 and 4.0 μA/cm².After electron bombardment a reduction in the Na and O surface concentration appears. Na has been observed to migrate towards the inside of the sample. It accumulates at depths comparable to the maximum electron ranges. The accumulation rate has been observed to depend on the beam power.For a beam energy of 4.5 keV the amount of Na accumulated at depth is nearly twice its surface depletion, supporting the hypothesis that the irradiation influences the glass composition at depths greater than the maximum electron ranges.     

Fabrication, spectroscopy and laser performance of Nd-doped lead-silicate glass fibers

The fabrication of a highly efficient Nd³⁺-doped single-mode fiber laser operating at 1.06 μm is described. The Nd₃₊ is introduced by doping Nd₂O₃ into a multicomponent (flint) lead-silicate glass host, Schott commercial optical glass F7. A fabrication technique for doping rare-earth evenly into commercial optical glasses is demostrated. Spectroscopic properties relevant to laser operation in the Nd³⁺-doped lead-silicate glass fibers were measured and the influence of Pb₂₊ ions on the spectral properties was analyzed. Owing to the long lifetime and large absorption and emission cross-sections of Nd₃₊ in this lead-silicate glass host, a high-performance Nd³⁺-doped lead-silicate fibre laser device operating at 1.06 μm has been successfully demonstrated.