Quantitative Auger electron spectroscopy of PtSi and Pd2Si

Summary Quantitative AES analysis has been carried out on PtSi and Pd₂Si using dN(E)/dE spectra. The concentration ratios are determined by elemental sensitivity factors after correcting for matrix and sputter effects. In the case of matrix correction an improved correction procedure has been developed which considers effects created by different atomic densities, electron backscattering, electron attenuation and peak shapes. The concentration ratios X_metal/X_Si deduced from measurements of mechanically cleaned sample surfaces agree very well with the nominal bulk values of the silicides. Ion bombardment creates strong intensity and line shape changes of the Auger signals. Therefore, in case of sputtered silicide surfaces, both matrix and sputter effects must be corrected.     

High-resolution emission spectroscopy of CO2 collisionally excited by N2. Rotational distribution

We obtained, for the first time, high-resolution rotational distribution of CO₂ collisionally excited by N₂. The rotational distribution is non-Boltzmann, and the initial results suggest that surprisingly large impact parameter collisions contribute substantially to the collisional excitation, even though small impact parameter collisions are more effective, as expected.     

High-resolution electron microscopic study of V6O13

High-resolution structure images of V₆O₁₃ were taken with a 1-MV electron microscope with a cutoff resolution of 0.14 nm. Individual V atom rows, as well as tunnels in the structure, were resolved. The effect of the electronic state on the structure image was investigated by comparing the observed image with the simulated images calculated by assuming various ionized states to the constituent atoms. The neutral-state model interpreted the observed image more satisfactorily than the ionized-state models. A modification of V₆O₁₃ was displayed as an image. In order to interpret the image, a structure model was proposed, which is orthorhombic with lattice parameters a = 1.1922, b = 1.19912, and c = 0.3680 nm and belongs to the space group Cmma. This structure is derived from the V₂O₅ structure by removing all the atoms on every third (001) oxygen atom plane and then introducing crystallographic shear $\text{1}\text{2}\text{[0}\text{1}\text{1}\text{]}$, instead of $\text{1}\text{6}\text{[10}\text{3}\text{]}$ in the case of normal V₆O₁₃.     

X-ray and electron induced Auger processes for I2 adsorption on uranium

The accurate determination of the kinetic energy of X-ray induced Auger electrons, which is necessary in XPS experiments, e.g. for calculating the Auger parameter, is sometimes hampered by peak interferences or by the high secondary electron background. The latter is of special importance for low kinetic energy electrons like e.g. the U(OPV) and U(OVV) Auger electrons. These problems can be circumvented by using electron induced Auger transitions (AES). However, since XPS and AES use different reference points for the energy scales, both scales have to be matched. This can be done by measuring the kinetic energy of an appropriate Auger transition in XPS and relating this value to the maximum of the second derivative of the same peak in AES.     

Site-selected Auger electron spectroscopy of N2O

The N 1s Auger spectra for the two nonequivalent N atoms in N2O have been measured via Auger electron-photoelectron coincidence spectroscopy. The site-selected Auger spectra are compared with the normal Auger spectrum and with accurate theoretical calculations accounting for the effects of the dynamics of the nuclei on the energy and linewidth of the Auger bands. Such effects are found to be crucial factors in determining the different band shapes in the site-selected spectra.     

High-resolution electron microscopy of defects in W4Nb26O77

Several different kinds of planar defects have been observed by means of high-resolution electron microscopy in W₄Nb₂₆O₇₇, such as disordered intergrowth of WNb₁₂O₃₃ and W₃Nb₁₄O₄₄ structural slabs, locally ordered intergrowth with a sequence of AABAAB, two separate microdomains of WNb₁₂O₃₃ and W₃Nb₁₄O₄₄ coexisting with W₄Nb₂₆O₇₇ and a complicated intergrowth of W₄Nb₂₆O₇₇, NNb₂O₅, W₃Nb₁₄O₄₄, and Nb₃₁O₇₇F types of structure.     

An electron microscopy study of crystallography and phase relationships in the Be3N2BeSiN2 system

Transmission electron microscopy and diffraction have been used to examine structural aspects of phases along the BeSiN₂Be₃N₂ tie line of the BeSiON system. Electron diffraction experiments are found to substantiate previous X-ray evidence for the derived structures of BeSiN₂, β-Be₃N₂, and α-Be₃N₂ and the presence of a number of long-period superstructures at intermediate compositions. Real space observations using direct fringe and structure imaging techniques have been made and are in agreement with the 15R polytype structure derived from X-ray diffraction data. This structure is composed of coherent intergrowths of BeSiN₂ and β-Be₃N₂. Further observations made on a nonstoichiometric BeSiN₂ sample suggest that the polytypes may be described in terms of a regularly faulted BeSiN₂ structure. Each fault changes the coordination of tetrahedral sites from base sharing to edge sharing in the fault, allowing excess beryllium atoms to be accommodated in the close-packed nitrogen lattice. For larger deviations from the BeSiN₂ stoichiometric composition, a higher density of faults occur which interact to form ordered arrangements and the observed polytype structures. The present observations establish that polytypism in the BeSiN system is related to the general phenomenon of crystallographic shear as observed in other complex oxide and ceramic systems. It is suggested that similar faulting may account for the polytype structures in other sialon systems.     

High-resolution UV photoelectron spectrum of CO2

The highly-resolved HeI photoelectron spectrum of CO₂ is presented and its vibrational structure studied in detail. In the X? ²Π_g ionic state the v₃ antisymmetric mode is found to be excited in double quanta (v_1-v_2-v₃ = 0. 0. 2) with energy hv₃ = 181 meV. In the C? ²Σ_g⁺ state a single quantum of the same mode is found to be excited (hv₃ = 189 meV) in combination with a v₁ excitation. Vibronic interaction with vibrational levels in the B? ²Σ_u⁺ state of the ion is suggested to promote this (1, 0, 1) excitation. It is established that inelastic scattering processes contribute to the vibrational structure in the C? ²Σ_g⁺ band. The spin-orbit splitting in the X? ²Π_g is determined to be 19±1 meV and 10±2 eV in the ā²Π_u state. Vibronic structure is resolved in the X? ²Π_g band where the Renner-Teller coupling constant is determined to be ? = 0.21±0.02 and the vibrational energy of the v₂ mode as 60±7 meV. In the ā²Π_u state the v₂ energy is found to be hv₂ = 60 meV from the observed hot-band structure.     

Electron deformation density in titanium diboride chemical bonding in TiB2

Titanium diboride, TiB₂, crystallizes in the AlB₂-type structure, hexagonal P6/mmm. The conventional, free atom crystal structure refinement led to R=2.23%, and including extinction corrections to R=1.58%. Multipole refinements with multipoles up to order four (hexadecapole) reduced the R value to 1.21%. Difference density maps revealed charge deficiencies on the boron sites and broadbands of charge accumulations between the boron atoms indicating a graphitic B-delocalization of the boron sp² hybrid orbitals.     

High-resolution electron microscopy of microsyntactic intergrowth in VnO2n−1

Structural features of the Magnéli phases V_nO_2n?1 were studied by means of high-resolution transmission electron microscopy. Microsyntactic intergrowth on a unit cell scale of several phases with neighboring n were frequently observed in arc-melted specimens, and this was ascribed to the structural compensation of the local composition fluctuation. Also observed were periodic microsyntaxy, where two neighboring phases intergrow periodically, and the crystallographic shear (CS) structure with laterally displaced CS planes. The origin of this microsyntactic intergrowth is discussed from the standpoint of the CS plane interaction.     

Gas phase electron diffraction study of SiH3N3 and (SiH3)2 NCN

The molecular structures of SiH₃N₃ and (SiH₃)₂ NCN have been determined by electron diffraction : SiH₃N₃ has a non-linear SiN₃ skeleton, and (SiH₃)₂ NCN is a carbodiimide with SiNCN Si probably linear. A new model is proposed which rationalises the observed geometry of a number of molecular pseudohalides.     

Structural studies by electron microscopy: High-resolution observations on β-ZrO2·12Nb2O5

Reliable idealized structures for the β and γ forms of ZrO₂·12Nb₂O₅ have been deduced following the observation of lattice images, recorded at a resolution of about 0.3 nm, from crystals oriented with their short b axes parallel to the incident electron beam. The structure of the β form is confirmed by preliminary results from single crystal X-ray studies. The present observations are compared with previous work on these phases.     

Matrix-isolation spectroscopy of Pb2

Fluorescence and Raman scattering were observed from Pb₂ isolated in neon and argon matrices. Two new excited states were observed by two-photon stepwise excitations, which involve low-lying electronic states of Pb₂. Most spectroscopic constants of the states observed could be given and complement previous results. Two resonance Raman progressions with ω_c = 112.5 and 123.1 cm⁻¹ and a single Raman signal at 80 cm⁻¹ were observed in argon matrices. The ω_c = 123.1 cm⁻¹ Raman signal which had recently been assigned to a larger Pb cluster was shown to arise from Raman scattering within the electronically excited A state of Pb₂ at 5500 cm⁻¹.     

Gas phase electron diffraction study of tetravinyltin Sn(CHCH2)4

The tetravinyltin molecule has been studied by gas phase electron diffraction. The r_a structure analysis is based on the assumptions that a single conformer occurs in Sn(CHCH₂)₄ and that tin has a tetrahedral bond configuration. The preferred model (S₄ symmetry) predicts all four vinyl groups to be intermediate between staggered and eclipsed conformations. The structure refinement gives the following parameters (bond lengths, r_a, in nm, valence angles in degrees):

, SnCC = 121.9(0.6), CC = 0.1349(8), SnCH = 116.8(4.5),<C—H?_av. = 0.1098(14). The uncertainties given in parentheses represent three times the standard deviation values.The observed shortening of the

bond in Sn(CHCH₂)₄ from

in SnMe₄ (by 0.0027 nm) is equal to the shortening that occurs on going from

in ethane to

in propylene. With the corresponding Si and Ge derivatives, this effect is less pronounced.     

Ab initio prediction of MnOH2/MnOH2 electron transfer reactivity at electron correlation level

An ab initio calculation of electron transfer reactivity of Mn²⁺OH₂/Mn³⁺OH₂ redox system, in gas and in solution, has been made in this paper. The detailed geometry optimization and the scanning of the potential energy surfaces have been carried out at UMP2 (full)/6-311+G^* level. The relevant energy quantities (such as the activation energy and the binding energy) are calculated at different levels of theory (HF, MP2, MP3, MP4 and QCISD and corresponding spin-projection PUHF, PMP2 and PMP3) with the same basis set (6-311+G^*). Both all-electrons and valence electrons have been correlated in energy calculations. The electronic transmission coefficient is calculated using the ab initio potential energy surface slopes and the coupling matrix element determined from the two-state model and the Slater-type d-electron wave functions. The pair distribution function is obtained using both a classical sphere approximation scheme and a novel scheme. The relevant kinetic parameters are obtained at different ab initio levels in terms of the new model. The contact-distance dependence of these parameters and the applicability of the presented models are also discussed.     

Depth profiles of Ta2O5/SiO2/Si structures: a combined X-ray photoemission, Auger electron, and secondary ion mass spectroscopic study

Summary We prepared thin films of tantalum oxide on SiO₂/Si substrates by thermal oxidation of tantalum. The different oxide layers and their interfaces were characterized by SIMS, AES, and XPS. Characteristic structures were obtained after different oxidation procedures. The comparative discussion of AES and SIMS depth profiles makes possible an unequivocal characterization of the reactive interfaces between the oxides of Ta and Si. The Ta₂O₅/SiO₂ interface in particular shows non-stoichiometries which depend on the oxidation procedures and which determine the performance characteristics of pH-sensitive Ta₂O₅ field-effect transistors.

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Tiefenprofile von Ta₂O₃/SiO₂/Si-Strukturen: Eine kombinierte Untersuchung mit Röntgen-Photoemissions-, Auger-Elektronen- und Sekundär-Ionen-Massen-Spektrometrie

     

Measurement of the Compton profiles of CH4 and C2H4 by high energy electron impact spectroscopy

We present a new experimental determination of the Compton profiles of CH₄ and C₂H₄ molecules using high energy electron impact. The observable q range has been extended up to 10 au (6 au for C₂H₄). Good agreement is found with an earlier X-ray scattering experiment and with new theoretical calculations.