Relative Atomic Concentration Research Articles

Application of Auger Electron Spectroscopy to studies of chemical weathering

Auger electron spectroscopy (AES) is a surface‐sensitive analytical technique that derives from the interaction of an electron beam and atoms in residence at the surface of a sample; inner shell ionizations produce Auger electrons, which have an escape depth of only a few tens of angstroms. This technique has numerous applications to chemical weathering and other geochemical processes that operate on mineral surfaces. The analytical capabilities of AES include chemical analyses of the near surfaces of minerals for all elements except H and He, semiquantitative analysis of the relative atomic concentration of surface components, high lateral spatial resolution (>0.1 µm) of the analyzed area to determine the composition of discrete domains on mineral surfaces and to identify unknown minerals on a submicrometer scale, and elemental depth profiling using an ion sputter gun. These capabilities can be used to address the nature of mineral dissolution processes, providing discrimination among mechanisms such as congruent versus incongruent dissolution, surface‐controlled reactions versus diffusion through a leached or armored layer, uniform versus heterogeneous distribution of reacted layers, and identification of alteration phases. The effectiveness of AES analysis is limited by charging of nonconducting samples (e.g., silicate minerals) and sample degradation under the electron beam; these problems may be mitigated by careful sample preparation and instrument operation procedures. AES can be used in concert with numerous other microbeam techniques to fully characterize the surface composition and structure of reacting minerals.

Atomic Absorption Spectroscopy: An In Situ Diagnostic for Sputter Deposition of Y-Ba-Cu-Oxide

AbstractAtomic absorption spectroscopy (AAS) has been used as an in situ diagnostic tool to study sputtering of high-temperature superconductors. Hollow-cathode lamps were used as line sources to measure relative atomic species concentrations during sputtering of Y-Ba-Cu-oxide targets using a Kaufman ion gun. The AAS measurements showed that the fluxes of ground state Ba and Cu ejected from a composite target during argon- and oxygen-ion bombardment varied greatly with sputtering parameters. Measurements were made of the effects of changes in ion-beam energy, ion flux to the target, and target temperature. In addition, the variation in atomic densities of Ba and Cu with distance from the target were measured. For comparison, AAS measurements during argon- and oxygen-ion sputtering of a pure copper target were also performed. The AAS results were verified by measuring stoichiometry variations of thin films deposited under identical conditions.

The etching of polymers in oxygen-based plasmas: A parametric study

A parametric study of the etching of polymers has been performed in a 2.45-GHz microwave multipolar plasma using an electron-cyclotron-resonance excitation and an independent 13.56-MHz rf biasing. The etch rates achieved in N2O and N2/O2 discharges are measured as a function of different plasma parameters, i.e., the ion current density bombarding the wafer surface, the ion energy, and the relative atomic oxygen concentration as estimated by actinometry. In both types of plasmas, the etch rate evolutions with ion energy exhibit a two-step variation corresponding first to ion-induced adatom displacements on the polymer surface and second, above a threshold energy, to the rising of sputtering. Under given ion bombardment conditions the polymer etch rate, unchanged by the presence of molecular oxygen, appears to be only controlled by the atomic oxygen concentration in the plasma. The etching kinetics, which first increases proportionally to ion current density and atomic oxygen concentration before reaching saturation, clearly indicates a monolayerlike adsorption of oxygen on polymers. With this hypothesis, the etching behavior can be fully explained by a model recently proposed for plasma etching.

Quantitative determination of atomic concentrations by Auger electron spectroscopy

A simple mathematical analysis presented here shows that unless the ratio of the instrumental resolution width to the natural linewidth of each Auger line is less than about 0.3, the measured peak-to-peak amplitudes of the differentiated Auger signals do not represent accurately the atomic concentrations. At the same time, the analysis provides the means for overcoming this difficulty even when the linewidth ratio is considerably larger than 0.3. A universal relation is presented whereby the experimentally measured peak-to-peak amplitudes can be corrected so as to enable one to derive quite accurately the relative atomic concentrations in one’s samples; so much so, provided reliable Auger sensitivities of the elements are available. Unfortunately, however, most of the sensitivity data, especially for the high-energy Auger lines, were measured with insufficient resolution. In fact, we show that at least in some cases the published data were measured with a resolution far from satisfactory. It is our contention, therefore, that there is a need for a revision of the sensitivity data with the required resolution if they are to be used for quantification.

Auger electron spectroscopy for quantitative analysis

A simple mathematical analysis shows that unless the ratio of the instrumental resolution width to the natural Auger linewidth is less than about 0.3, the measured line intensities do not represent accurately the atomic concentrations. To overcome this difficulty, a universal curve is presented whereby the experimentally measured line intensities can be corrected so as to represent quite accurately the relative atomic concentrations in one’s sample. Unfortunately, however, the available sensitivity data required for quantification were not always measured with sufficient instrumental resolution. It is our contention that there is a need for new sensitivity measurements in which the required resolution is ensured.

Quantitative AES analysis of PbTe and SnTe samples with and without matrix effect correction

Quantitative analysis of the PbTe and SnTe surface is performed using AES spectra obtained in an RPA analyser for Pb, Sn, Te, PbTe, and SnTe polycrystalline samples without matrix correction and with corrections based on backscattering factors (BF's) and attenuation lengths (AL's) calculated from formulae known from the literature. Without matrix correction, relative atomic concentrations very close to the expected 50% are obtained. Corrections based on different formulae for BF's and AL's are very close one to another and, generally, they are small. For both samples investigated, the uncorrected result is better than each corrected one. [Russian Text Ignored].

Electron-, x-ray-, and ion-stimulated decomposition of nitrate salts

Decomposition of lithium, sodium, and ammonium nitrate stimulated by 500-eV electrons, 1254-eV X-rays, and 4-keV Ar/sup +/ ions is investigated by X-ray photoelectron spectroscopy (XPS). The core level XPS spectra show that a steady-state composition is attained at a total irradiation dose of 10/sup 17/ particles/cm/sup 2/ in which the damaged layer contains predominantly M/sub 2/O and M/sub 2/O/sub 2/ with smaller amounts of MNO/sub 3/ and MNO/sub 2/, where M = Li and Na. Irradiation of NH/sub 4/NO/sub 3/ produces no changes detectable by XPS, suggesting that the decomposition products are all volatile. While the relative atomic concentrations of the constituent elements within the damaged layer change in a similar manner for the three modes of radiation, i.e. there is an increase in alkali metal, decrease in nitrogen, and only minor changes in oxygen concentration, the specific products and relative abundances of these products differ. Consideration of these results in terms of the mechanisms of energy deposition into the atomic lattice indicates that the energy density deposited by all three sources exceeds that required for decomposition and that the excess energy determines the extent of reaction. 31 references, 5 figures, 1 table.

Ｔｉ／ＳｉＯ２／ＴｉＳｉ２／Ｓｉ系におけるＴｉとＳｉＯ２薄膜界面の高温反応 ＸＰＳによる研究

High temperature reaction between Ti and SiO2 at interface in Ti/SiO2/TiSi2/Si system is studied using X-ray photoelectron spectroscopy (XPS) in conjuction with argon-ion sputtering. Below 750°C, the TixSiy (x/y=1.0-1.2) is formed, and the thickness of SiO2 layer is thin. Above 750°C, the TiSi2 is formed, and relative atomic concentration of Si in SiO2 (Si-ox) is sharply decreased. To compare the experimental results of Ti/SiO2/TiSi2/Si system with that of Ti/ SiO2/Si system, one found that the formation of additional TiSi2 film will mainly be controlled by the substrate silicon atoms which diffuse to the surface layer through the grain boundary in the layer of TiSi2 and SiO2.

Atomic capture and transfer of negative pions stopped in binary mixtures of hydrogen with polyatomic gases

The atomic capture and transfer of stopped negative pions have been studied in binary gas mixtures of H 2 + M, where M is CCl 2F 2, CClF 3, CBrF 3 or SF 6. The π 0 yield, versus relative atomic concentration C A of M, goes through a maximum at C A ∼ 0.1 and levels off at zero at high concentrations. This phenomenon together with other observed characteristics of the atomic capture and transfer of pions in these systems is interpreted in the frame of a phenomenological model. The average transfer coefficients \\ ̄ gL Z exhibit a weak concentration dependence. The estimated average atomic capture ratios A ̄ ( Z H ) are lower than those found for noble gases, probably because of the mutual screening of the constituent atoms in the molecules. The probability of pion capture in an atomic orbit is not proportional to the stopping power of the components of the mixture.

On some “pseudosilicides” having the cubic AB 5 structure

X-ray and metallographic investigations indicated that in the binary intermetallic compounds UNi 5 and ZrNi 5 one nickel atom may be substituted by combinations of some elements of the IIIa-Va and IIb-VIa groups, i.e. that “pseudosilicon” can play the role of a substituent in some AB 5 phases. Single phase alloys were obtained in the systems of the general formula UNi 4Y (Y = In + As, In + Sb, Zn + Te, Cd + Te) and ZrNi 4Y (Y = In + As, In + Bi, Zn + Te, Cd + Te). The homogeneity regions (ratio of the constituent elements of the Y component) were also determined. In all the systems investigated so far, at the equiatomic compositions of the substituents (VEC = 4), contraction of the unit cell parameters and an increase of microhardness values were observed. Intensity calculations showed that the substitution takes place in positions 4(c) in the space group F4̄3m. The resulting structures may also be considered as superlattice of the MgSnCu 4 type. The stability of these phases is discussed in terms of relative atomic sizes and valence electrons concentrations.

An electrochemical and ESCA study on the tarnishing of silver in solutions of different pS and pH values

The variation of the open circuit potential of Ag electrodes in solutions of varying pH values, and containing increasing concentrations of S 2-, is followed as a function of time until steady values, E st are reached. In all cases E st values are attained from positive potentials. The shift towards negative values depends on the ambient sulphide content, being more the higher the concentration. The E st—log[S 2-] plots are invariably S-shaped, denoting adsorption from solution. Before the inflexion linearity exists between E st and C s2-, and this is explained on the basis of a Gibbs' type adsorption model. Evidence is presented to support the conclusion that the adsorbed species at all pH values is the SH − ion. The variation of E st after inflexion follows the general relationship ▪ The relation indicates a 1ē electrode process, despite the fact that bulk Ag 2S forms quickly on the surface of the Ag electrodes. Galvanostatic reduction of the corrosion film formed on Ag electrodes in sulphidic solutions occurs in a single step corresponding to Ag 2S. Similarly, ESCA spectrograms of the films exhibit peaks for Ag and S. The sulphur 2 p peak shows two sublevels corresponding to S2 p 1 2 and S2 p 3 2 with a separation of 1.20 eV. The relative atomic concentrations of the Ag:S peaks is very near to 2:1, indicating that the film is formed of Ag 2S. The results of the present investigation strongly suggest that Ag 2S is formed chemically, consecutive to a 1ē electrode process. Ageing of the Ag/AgSH/Ag 2S electrode in sulphide-free solutions causes the electrode to respond theoretically to pS 2-, with a Nerstian slope of 0.029 V/log C unit.

Tungsten Etching in CF 4 and SF 6 Discharges

Plasma etching characteristics of tungsten films are studied in and in discharges. The etch rates are investigated as a function of electrode temperature, oxygen and hydrogen additions, system pressure, and RF power. Relative fluorine atom concentrations are determined by optical emission spectroscopy. Results indicate that tungsten etching is primarily controlled by fluorine atoms generated in the discharge in plasmas or when oxygen is added to the etch gases. In pure , species may play an important role in the etch process. Hydrogen additions scavenge fluorine atoms and generate residues which inhibit etching.

Rate constants for the reaction of ground‐state oxygen atoms with methanol from 297 to 544 K

AbstractThe rate constant for the reaction of ground‐state oxygen atoms with methanol has been determined between 297 and 544 K by a phase‐shift technique using mercury photosensitized decomposition of N2O to generate oxygen atoms. The relative oxygen atom concentration was monitored by the chemiluminescence from the reaction of oxygen atoms with nitric oxide. The results are accommodated by the Arrhenius expression k1 = (9.79 ± 2.71) × 1012 exp[(−2267 ± 111)/T]cm3/mol·s, where the indicated uncertainties are 95% confidence limits for 10 degrees of freedom. As an incidental part of this work, the third‐body efficiency of CH3OH relative to N2O for the reaction O + NO + M → NO2 + M (M = CH3OH) was determined to be 3.1 at 298 K.

Rate coefficients for the combination of metastable and ground state mercury atoms into excited dimer states

Rate coefficients have been measured for the reaction, Hg(6 3P o)+Hg(6 1S o)+M→Hg 2 *+M, for M = He, Ne, Ar and N 2, at 303 and 353 K. Hg 2 * represents both gerade and ungerade states formed directly in the combination. Absolute rates were determined for M = Ar, by record the decay rate of Hg(6 3P o) following pulsed excitation, with conditions chosen such that dimer formation is the predominant loss mechanism. For M = He, Ne and N 2, relative rates were measured with a cw technique, observing the intensity of the molecular luminescence and, simultaneously, the relative excited atom concentrations from the pressure broadened wing of the 2537 Å line. The rate coefficients for the combination of metastable and ground state mercury atoms are about 10 fold greater than for the combination of two ground state halogen atoms, for the same M. The rate coefficients relatively large because only two dimer states correlate with Hg(6 3P o), Hg(6 1S o), both of which are bound and populated in the combinat

Factors affecting the accuracy of rate coefficients of metal atom oxidation reactions in heated flow tubes

Metal atom oxidation reactions have been studied over about the 300 to 2000/sup 0/K temperature range. The factors determining the currently achievable accuracy of 40 to 70% for the overall rate coefficient measurements of such reactions are discussed. Particular consideration is given to the influences of the systematic uncertainties involved in temperature determinations and in the flow profile (reaction time) factor at the relatively high pressures and average gas velocities required for the kinetic measurements. Compared to most regular flow tube studies of nonrefractory species the use of these higher T, P, and anti ..nu.. has an adverse effect on accuracy; however, it is also shown that the higher T and P increase the accuracy of relative and absolute atom concentration determinations by atomic absorption measurements. 8 figures, 52 references.

Some photometric observations of trace additives in dry carbon monoxide flames

Nitric oxide, iodine, cyanogen, and lithium bromide have been added to CO/N 2 /O 2 flames containing less than .007% of hydrogen-containing impurities. Relative oxygen atom concentrations, derived from measured intensities of emission bands of CO 2 , NO 2 , and IO, are compared. Addition of NO produced a significant reduction in the O-atom concentration, the effect being greatest in O 2 -rich flames. Measurements of the resonance absorption by lithium atoms indicate that LiO is the major compound formed by lithium in O 2 -rich flames, but they do not rule out the possibility that significant amounts of LiO 2 are also formed. A recalculation of earlier data yields D o Na-O 2 = 234 ± 13 kJ mol −1 ; we estimate D o Li-O 2 = 222 ± 25 kJ mol − .

Studies of plasma production at hypervelocity microparticle impact

This paper is concerned with an investigation of the plasma generated during the impact of hypervelocity microparticles with a metal target. A laboratory source of hypervelocity micron-sized iron particles is first described which utilizes a 2 MV Van de Graaff generator, followed by a discussion of the techniques used to determine the mass and velocity of the particles. On impact of the iron projectiles on a slatted molybdenum target, charge is generated, extracted from the region of impact by suitably biasing a gridded electrode, and subsequently detected using a conventional wideband electronic amplifier or an electron multiplier. It is shown statistically that during impact equal numbers of electrons and positive ions are produced - indicating plasma generation - and that the total charge released (Q) may be described empirically in terms of the mass (m) and velocity (v) of the particle by a simple power law relationship of the kind Qαmαvβ, with β = 3·2 ± 0·1 over the complete velocity range investigated (0·05 to 10 km s−1) and with α = 0·85 for v>1 km s−1 and 1·33 for v<1 km s−1. It is also shown that the charge extracted from the plasma reaches a maximum a few microseconds after impact and subsequently decays exponentially with a time constant of several micro-seconds.A crude mass analysis of the positive ions generated during the impact using a simple time-of-flight mass spectrometer has indicated that, over the velocity range investigated, the dominant ions in the spectrum are characteristic of the projectile and not the target material. From considerations of the relative abundance of the metal ions in the spectra, together with the known relative metal atom concentrations in the iron projectiles, the temperatures of the plasmas have been estimated (from Saha equilibrium considerations) to be of the order of several thousands of degrees Kelvin.In a detailed discussion, attempts are made to consider how the kinetic energy of the projectile is dissipated - eventually producing plasma - in terms of available theoretical models of hypervelocity impact. It is shown that the most satisfactory model of this very complex interaction appears to be one in which the relative importance of shock-wave propagation into the projectile and target materials is considered. Finally, a discussion of the properties and the temporal behaviour of the impact-produced plasma is presented in order to assess the relative importance of diffusion and recombination processes, thus to assist in the interpretation of the experimental results obtained in this study.

An Atomic Oxygen Beam System for the Investigation of Mass Spectrometer Response in the Upper Atmosphere

An atomic oxygen beam system has been designed and tested for the laboratory evaluation of mass spectrometers used in upper atmospheric measurements. The atomic oxygen is generated by thermal dissociation of molecular oxygen on the surface of a tungsten filament heated to 2800 K. A symmetrical bidirectional beam is produced to permit simultaneous monitoring of the particle flux in the beam while target experiments are being conducted. Flux levels of 5×1014 particles cm−2 sec−1 over a cross-sectional area of 1 cm2 have been produced with a relative atomic oxygen concentration of 70%. At flux levels below 1013 particles cm−2 sec−1, relative atomic oxygen concentrations of more than 90% were obtained. The oxygen beam is of high purity and free from chemically active contaminants. Strong chemical and low temperature pumping are used to reduce background gas contributions to less than 1%. Measurements of the relative atomic concentration in the beam were made with a quadrupole spectrometer using an open flowthrough ion source. The absolute flux of molecular oxygen was determined with the aid of an enclosed omegatron mass spectrometer. The combined use of both instruments permitted a determination of the magnitude of the atomic oxygen flux in the beam.

Reaction Rate Measurements of O(3P) Atoms by Resonance Fluorescence. II O(3P)+CO+M→CO2+M; M=He, Ar, N2

Absolute rate constants for the reaction O(3P)+CO+M→CO2+M have been determined at 300°K for M=He, Ar, and N2, using oxygen resonance radiation as a probe to monitor the relative atom concentration during decay time measurements. The rate constants are, in units of cm6 molecules−2·second−1, kHe = 6 ± 1.5 × 10−36, kAr = 7 ± 3.5 × 10−36, and kN2 = 1.4 ± 0.4 × 10−35. The O(3P) is produced by O2 photodisociation at 1470 Å, at which wavelength O(1D) is also formed. The observations indicate that the O(1D)–CO interaction results in O(1D) deactivation to O(3P), not CO2 formation.

Flame structure and flame reaction kinetics - IV. Experimental investigations of a fuel-rich hydrogen+oxygen+nitrogen flame at atmospheric pressure

An experimental investigation is described of the microstructure of a flat, premixed, fuel-rich hydrogen+oxygen+nitrogen flame at atmospheric pressure. The study involved measurement of the temperature profile and the concentration profiles for the stable species in the flame. By measuring the profile of emitted light intensity when traces of certain inorganic salts were added to the gases entering the flame, it was further possible to derive information about relative hydrogen atom concentrations in the burnt-gas region.