On the information depth of auger electron appearance potential spectroscopy

The information depth of AEAPS in comparison with AES was estimated using the overlayer technique. The strengths of the AES and AEAPS L₃ and L₁ signals of Cr and Ti were measured as a function of the Cr overlayer thickness on a Ti substrate. No significant differences between the information depths of both methods have been found. It follows that the information depth of AEAPS is basically limited by the mean free path of the primary electrons. Slight disagreement between the results obtained for the L₃ and L₁ subshells of Ti and Cr may indicate that the information depth of AEAPS could be modified by the kind of relaxation mechanism and the subsequent transport process.     

A study of the nitridation of silicon surfaces by low-energy electron diffraction and auger electron spectroscopy

Low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES) have been used to study the initial stages of the nitridation of silicon. Most of the experiments involved pressures of 10^?5?10^?7 torr of ammonia and silicon temperatures in the range 800–1100°C. An earlier study of the nitridation of the Si (111) surface, has been extended to allow comparison between the (111), (311) and (100) faces of silicon. These surfaces provide a series of unit meshes with different shapes and symmetries while retaining some common geometrical features. Of particular interest for epitaxial theory is the growth of an impurity induced nitride structure, which is common to both Si(111) and Si (311). This may be explained if the nucleation and orientation of the niti ide are determined by the geometry of localised sites, common to both substrates. Subsequent growth of the nitride layer is then dominated by intra-layer bonding, so that the difference in substrate symmetries has little effect.     

A study of the oxidation of tantalum nitride by ellipsometry and auger electron spectroscopy

Ellipsometry and Auger electron spectroscopy in conjunction with in-situ ion sputtering have been used to study the thermal and anodic oxidation of thin tantalum nitride (Ta₂N) resistor films which are used in microelectronic circuits. In addition, the effects of thermal oxidation on the resistor-conductor contact resistance and conductor adhesion have been investigated.Thermal oxide thickness and stoichometry were estimated by Auger electron spectroscopy. A more accurate determination of oxide thickness was obtained by using multiple angle-of incidence ellipsometry. The thermal oxide was found to demonstrate a parabolic growth rate, in agreement with other workers. It was determined that the contact resistance should not be adversely affected by oxidation of the tantalum nitride at room temperature for storage times of several months; no significant decrease in the conductor adhesion was observed for oxide thicknesses up to 8 nm.A significant difference in the stoichiometry and refractive index of the thermally and anodically oxidized films was found, however. Depletion of the nitrogen from the surface of the anodically oxidized Ta₂N films resulted in an increase in the refractive index of the anodic oxide layer to a value close to that of pure Ta₂O₅.     

Absolute atomic densities determined by auger electron spectroscopy

The secondary electron distributionN(E) obtained with a spherical grid retarding field analyser is stored in a multichannel analyser. The experimental intensities of Auger lines are accurately determined by numerically substracting the background in theN(E) distribution and taking the area under the resulting peaks. Broadening of the lines due to several experimental factors, the multiple structure of the lines and the characteristics energy losses are taken into account. The absolute atomic densities on the surface are deducted from the Auger line intensities by a simple theoretical model. A comparison is made with atomic densities on the surface which are known either from the crystal structure (cleaved muscovite) or from Rutherford backscattering experiments (thin layer of Ag) or simply from the specific weight in the case of bulk materials (C, Cu, Ag). The maximum deviation is smaller than a factor of 2. Generally, the values differ by about 30%, which shows that AES, performed in this way, can give reliable quantitative results for densities ranging from a fraction of a monolayer to the bulk material.     

Elastic and inelastic contributions to the auger electron appearance potential spectrum of titanium

The energy distribution of electrons contributing to the L-shell Auger electron appearance potential spectrum of a polycrystalline titanium surface has been measured. The Auger electron appearance potential spectrum is obtained by differentiating the total secondary electron yield of an electron bombarded sample as a function of incident electron energy. At the threshold for scattering from a core level the secondary yield increases. Most of the electrons contributing to this increase have energies below 30 eV, and result from secondary processes following Auger recombination of the core hole. The elastic yield decreases at the threshold, however, due to opening a new channel for inelastic scattering. A comparison of the elastic yield spectrum (DAPS), the total yield spectrum (AEAPS) and the soft X-ray yield spectrum (SXAPS), shows very similar line shapes, but differences in the relative strengths of the lines.     

A comparative study of single crystal magnesium oxide and oxidised magnesium by auger electron spectroscopy

In a study by AES of the surfaces of single crystal magnesium oxide and magnesium after various stages of oxidation, it has been shown that Auger energy shifts are produced by surface charging. Recognition of the charging effects has enabled the peak in the low energy spectrum of magnesium oxide crystal to be assigned. The low energy secondary electron spectra of both MgO crystal and oxidised magnesium are complicated by the presence of extra features which arise from diffraction of true secondary electrons, and in particular for oxidised magnesium a cross-transition occurring at the metal-oxide interface. Oxidation studies of sodium also reveal transitions arising from a similar process.     

Electronic structure of pyrolytic graphite by auger electron spectroscopy

We have used Auger electron spectroscopy to study the effect of defects on the surface electronic states of graphite. We modeled the effects of outer layer inclusions composed of carbon and cesium atoms. The experimental Auger spectra are compared with theoretical calculations of the density of states in the valence band of graphite. An increase in defect density deforms the energy bands. Chelyabinsk State Teachers University. Translated from Izvestiya Vysshikh Uchebnykh, Zavedenii, Fizika, No. 10, pp 84–88, October, 1997.     

A review of electronics design for auger electron spectroscopy

The technique of modulation phase-sensitive detection for Auger electron spectroscopy has changed little in principle since its inception in the late 1960's. However the 1970's have seen significant improvements with the introduction of highly-tuned preamplifiers, high performance oscillators, the use of integral rather than derivative spectra, and dynamical background substraction. These Improvements have largely been brought about by the availability of inexpensive integrated circuits (IC's) and by computer control. The authors have considered new modulation coupling approaches and the up-dating of high voltage ramp windowing circuits.     

Thickness measurements of adsorbed layers by auger electron spectroscopy

Thicknesses of various oxygen layers, adsorbed on a clean Ge (111) surface, were obtained by monitoring the amplitude-changes of the Ge-89 eV and the oxygen 510 eV Auger transitions during overlayer growth. For thicknesses not larger than the electron escape lengths the results were in excellent agreement with published values.     

In-depth information from auger electron spectroscopy

In-depth information on impurity concentrations in the surface region of a solid can be obtained in a non-destructive way from Auger electron spectroscopy by varying the energy of the primary electrons. Examples are given for a silicon crystal covered by monolayers and multilayers of several types of impurity atoms.     

Sputtered metal-silicon thin films studied by auger electron spectroscopy

The silicon KLL Auger spectrum from a range of stainless steel-silicon thin films was studied to provide information on changes in the silicon-silicon to silicon-metal bond ratio. This work complements earlier Auger spectroscopic studies of stainless steel-carbon films. Unlike the carbon KLL spectrum, the silicon KLL spectrum contains little chemical information. Changes in the principal plasmon loss peak associated with the silicon KLL spectrum may however prove useful in identifying the silicon phases.     

A study of atomic iodine and molecular thallium iodide by X-ray photoelectron and auger electron spectroscopy

The I3d5/2 binding energy has been measured in atomic iodine, thallium iodide and cesium iodide by high temperature gas-phase photoelectron spectrscopy using Al K (1486.6 eV) X-rays. The iodine M₅N_4,5N_4,5 (¹G₄) Auger energies for TlI and CsI have also been measured and combined with binding energies to yield extra-atomic relaxation energies of 0.5 and O.3 eV, respectively, after corrections are applied to the Auger parameter. Charges were calculated using the simple potential model, which was also used to obtain an estimate of the atomic T14f binding energy. Two other estimates of the atomic T14f7/2 binding energy have also been calculated, both based on Dirac-Fock ΔSCF binding energies. The results of the three methods suggest a value of 125.3 ± 0.2 eV for T14f7/2.     

The secondary-electron background problem in electron excited auger electron spectroscopy

Dynamic background subtraction is used to demonstrate that the recently suggested spline-polynomial scheme for characterizing the secondary electron background neglects an important aspect of the Auger feature. As a consequence of this neglect, area measurements using the spline approximation are difficult to relate to the true Auger current.     

The surface composition of platinum-palladium alloys determined by auger electron spectroscopy

Pt-Pd alloys were prepared as powders by a chemical reduction method and as films by evaporating the specpure metals onto a quartz substrate. Results were evaluated by means of the Gallon equation; the parameters of this equation — the signal intensity of a monolayer and of the bulk material — were determined experimentally for all relevant Auger peaks. The backscattering factor for the alloy system was evaluated from experiments in which a layer of one metal was evaporated on top of the other. The value determined in this way was compared with results obtained in the literature on similar systems. The theoretical surface compositions are calculated for several models and compared with the experimental results. Experimental results reveal surface enrichment in Pd, in good agreement with the theoretical calculations. Interactions of alloys with carbon monoxide and propane are discussed and a possible explanation of the effects observed is suggested.     

Investigation of grain-boundary diffusion of nickel in molybdenum by auger electron spectroscopy

The dependence of the grain-boundary diffusion coefficient of nickel in molybdenum on annealing temperature was investigated. Possible causes are analyzed for differences in the values of the grain-boundary diffusion coefficients and the activation energies for this process from those obtained by earlier researchers.Institute of the Physics of Strength and Materials Science, Siberian Branch, Russian Academy of Sciences (SO RAN). Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 28–31, July, 1992.     

Segregation of sulphur on a molybdenum surface studied by auger electron spectroscopy

The kinetic behaviour of sulphur segregation was studied during heat treatment of a molybdenum ribbon between 750°C and 1350°C by using an Auger electron spectroscopic technique. When the specimen is heated to high temperatures, the sulphur present as an impurity in the polycrystalline molybdenum diffuses on to the surface along grain boundaries. The intensity changes of Auger electron signals of sulphur and molybdenum showed that the rate of the diffusion remained constant until the surface was covered with a first sulphide layer in the temperature range studied. The activation energy in the initial stage of the diffusion was 26kcal/mol. High resolution Auger spectra of the sulphur were measured and explained from the density of states of MoS₂.