Angular effects in Auger electron emission from Cu (110)

Angular variations in the emission intensities of M_{2, 3}VV (62 eV) Auger electrons from a Cu (110) surface have been measured. Large changes are observed as a function of both polar and azimuthal angles. Effects of the incident beam energy and angle of incidence have been determined, and interpretations of the the data are proposed.     

Angular resolved L3VV Auger emission spectra from Cu(100)

The angular intensity distribution of electron induced L₃VV Auger electron emission from a Cu(100) crystal has been measured. Angular positions of relative maxima in the distribution are aligned with prominent crystallographic directions suggesting strong diffraction effects.     

Angular resolved Auger emission from clean and sulfur covered Ni(110) surface

The angular dependence of the nickel M₂₃VV and of the sulfur L₂₃VV Auger transitions are studied in detail, on clean and sulfur covered Ni(110) surfaces. New experimental data are presented for the anisotropy of both transitions as a function of polar and azimuthai angles of emission. Our model, which incorporates at the same time the multiple scattering effects in the final state wave function and the intrinsic anisotropy of the Auger emitter, is found to give a satisfactory account of the observed auger anisotropy. We find a large sensitivity to the position of the sulfur adsorbed atoms. The best agreement is obtained for the hollow site. slightly less than 0.9 Å above the top nickel layer. This conclusion is consistent with previous LEED and MEIS studies, but does not agree with the long bridge site obtained from quantum chemistry calculations. Moreover the sulfur emitter on this particular Ni(110) face appears to have an intrinsic anisotropy.     

A preliminary study of pure metal surfaces using Auger Electron Spectroscopy (AES), X-ray Photoelectron Spectroscopy (XPS) and Secondary Ion Mass Spectroscopy (SIMS)

A system is described which incorporates Auger spectroscopy (AES), x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) in one UHV chamber. The system has been used to determine sensitivity factors for XPS for a number of pure metals. These factors are then compared with ion yields from surfaces using SIMS. By performing similar XPS measurements in another, more conventional, system, comparison has been made of the electron transmissions of the double-pass cylindrical analyser in the XPS (retarding) mode and of the hemispherical analyser.     

Characterization of silicon compounds using the Auger parameter in X-ray Photoelectron Spectroscopy (XPS)

The Auger parameter is demonstrated to be valid for determining the change in the extra-atomic relaxation energy and is applied to the characterization of silicon dielectric thin layers. The changes in extra-atomic relaxation energy on going from Si to SiN_1.3 and to SiO₂ derived from the Auger parameter are -1.1 and -2.0 eV, respectively. These values are in good agreement with those derived from the polarization energy by Mott et al. The relationship between the polarizability and the Auger parameter is linear. Using the Auger parameter in XPS is a powerful and excellent method to determine the dielectric constant of very thin (⪅100 Å) silicon insulators since the electron escape depth is very small (⪅20 Å).     

Angular anisotropy and dichroism in molecular Auger spectroscopy following photo-absorption

This paper shows that angular distribution of spin-unresolved Auger electrons emitted in the decay of a vacancy created by the absorption of a photon in a certain class of free, unpolarized and gaseous non-linear molecules is completely characterized by three, rather than by two well-known parameters. The presence of this additional third parameter gives rise to circular dichroic effect which varies as cosine of the angle made by the departing Auger electron with the direction of incidence of the circularly polarized radiation. Linear dichroic effect varies as the square of sine of the angle made by the direction of emission of Auger electron and the polar axis of the space frame. Linear and circular dichroism in the angular correlation between theE ₁ photoelectron and Auger electron emitted sequentially from a molecule belonging to one of the 32 point groups has also been investigated.     

Study of a Nonequilibrium Auger-Transition Using Emission Auger Spectroscopy

Journal of Applied Spectroscopy - A nonequilibrium Auger transition consisting of a vacancy in the valence layer being filled within ~10–14 s by a probe electron that receives the energy...     

Metal-Enhanced Fluorescence from Gold Surfaces: Angular Dependent Emission

The first observation of Metal-Enhanced Fluorescence (MEF) from large gold colloids is presented. Gold colloids, 40 and 200 nm diameter, were deposited onto glass substrates in a homogeneous fashion. The angular-dependent fluorescence emission of FITC-HSA, adsorbed onto gold colloids, was measured on a rotating stage which was used to evaluate MEF at all spatial angles. The emission intensity of FITC-HSA was found to be up to 2.5-fold brighter than the emission on bare glass substrates at an angle of 270 degrees. This is explained by the Radiating Plasmon Model, whereby the combined system, composed of the fluorophore and the metal colloids, emits with the photophysical characteristics of the fluorophore, after the excitation and the partial radiationless energy transfer between the excited states of the fluorophore and the surface plasmons of the gold colloids. The fluorescence enhancement was found to be higher with 200 nm gold colloids as compared to 40 nm colloids due to the increased contribution of the scattering portion of the 200 nm gold colloid extinction spectrum. These observations suggest that gold colloids could be used in MEF applications, offering more stable surfaces than the commonly used silvered surfaces, for applications requiring longer term storage and use.     

Angular distributions of sulphur Auger emission from H2S and S adsorbed on NI(100) surfaces

We have studied at 300 K and under low pressures the adsorption and reactivity of gaseous carbon monoxide on platinum with preadsorbed oxygen. The reaction is first order dependent and evidently proceeds through strongly adsorbed oxygen and weakly bond carbon monoxide species interactions. Three tentative interpretations are given in order to explain the independence of the reaction rate on the oxygen coverage in a large domain. One of them, purely geometrical, is of course inadequate at low coverages: the two others attribute the main reactivity to the α or β states, observed when using temperature programmed desorption.     

The Study of Zeolite ZSM-5 by Auger Electron Spectroscopy

The dependence of the surface Si/Al ratio in function of the volume Si/Al ratio was studied, for zeolite of type: A, X, clinoptilolite, mordenite and three samples of ZSM-5. Surface measurements were made by Auger electron spectroscopy (AES), and volume (bulk) measurements by atomic absorption spectrophotometry. It was found that the surface Si/Al ratio is identical with the volume Si/Al ratio. The dependence of the surface Si/Al ratio on the crystallization degree for zeolite ZSM-5 was also studied. We obtained some informations about the kinetics and mechanism of the crystallization process.     

An Interference Approach to Perturbed Angular Correlation Spectroscopy

This paper recalls the formalism of H. J. Leisi, which shows an alternative way to understand Perturbed Angular Correlation Spectroscopy: as a quantum interference effect. This revised version was published online in July 2006 with corrections to the Cover Date.     

Experimentally derived Auger transition probabilities in X-ray excited Auger electron spectroscopy (XAES)

The capability of Auger transition probabilities experimentally derived from X-ray excited Auger electron spectra in XPS were tested. The relative sensitivity factor (RSF) method has been employed in the quantification by AES (Electron excited Auger electron spectroscopy). However, the difference between experimentally derived RSF and theoretically calculated ones has been found in some reports. One of the great reason of the difference may be caused by the calculated values of the Auger transition yield which has been commonly employed without the consideration of the allotment of coupling scheme in the transition selected in the quantification, for instance, the allotment of each six coupling KL₁L₁, KL₁L₂, KL₁L₃, KL₂L₂, KL₂L₃, and KL₃L₃ in KLL transition. The employment of derived Auger transition probabilities reduce the difference between theoretically calculated RSF and experimentally derived one.     

时间分辨偏振红外光谱及其应用

时间分辨偏振红外光谱已被广泛应用于研究光化学过程中的分子结构动力学. 通过测定瞬态物质跃迁偶极矩之间的角度等结构信息,可以提供光化学过程中伴随的电荷分布、分子结构和构象变化等动态信息. 包括简要介绍时间分辨偏振红外光谱技术的原理和应用：(i) 时间分辨偏振红外光谱概述;(ii) 时间分辨偏振红外光谱的原理及其优势;(iii) 利用时间分辨偏振红外光谱探测多种化学动力学过程,例如蛋白质构象动力学、激发态的电子局域化和光致异构化等;(iv) 时间分辨偏振红外光谱的局限和发展前景.     

Angular Momentum and Euler Angle Conventions in Molecular Spectroscopy

Abstract

Although the theory of angular momentum is treated in almost every textbook on quantum mechanics and molecular spectroscopy, problems are always experienced-especially by the beginner-when formulas from various books and papers are compared. During a survey of all the available relevant textbooks and papers which deal with angular momentum, it was realized that the majority of them can be ordered into two main groups of conventions with two sub classifications each. It is the object of this paper to present these conventions in an unambiguous fashion and to display the relevant formulas in order to facilitate comparisons between various textbooks. However, almost no attention is given to describing the theory of angular momentum, and the textbooks cited below should be consulted for the theoretical background.     

Auger analysis of etched (100) GaAs surfaces

The Auger depth profiling technique has been used to study the surface oxygen coverage and stoichiometry of (100) GaAs surfaces etched in various etching solutions. The quality of the surface varies with the etching solution, the etching time and the relative concentrations of the agents in each solution. The electrical behaviour of Schottky contacts deposited on the etched surfaces, was clearly affected by the characteristics of the surface.     

Resonant Auger spectroscopy of poly(4-hydroxystyrene)

The electronic structure of poly(4-hydroxystyrene) (PHS), which presents strong similarities with that of phenol, has been studied via resonant Auger spectroscopy. Spectator shifts and relative intensities of participator channels are extracted from our data. Symmetry considerations on the occupied and unoccupied molecular orbitals (MO) are helpful in the assignment of the resonating valence band structures of PHS. However they are clearly not sufficient to explain the MO intensities when close-lying intermediate electronic states are involved, as interference effects may play an important role.     

Spin polarized Auger spectroscopy from Fe(100)

The spin polarization of the M₂₃M₄₅M₄₅ Auger line of Fe(100) is shown to reveal two gain satellites at 4 and 17 eV, respectively, above the M₂₃ threshold. The lower one was previously identified as autoionization emission, whereas the higher one is a newly observed feature with a strikingly large positive spin polarization of > 80%. The spin polarization of the M₁M₄₅M₄₅ line is also reported.     

LEED and Auger investigations of Cu (111) surface

After ultrahigh vacuum bake-out, electropolished Cu (111) surfaces were shown by Auger analysis to be contaminated by C, N, O, S and Cl. Other than C and S, which were contained in the bulk, the impurities were introduced by surface preparation; but all were easily removed by light Ar ion bombardment. Heating to ≈ 750°C caused diffusion of C and S from the bulk to the extent that a clear diffraction pattern corresponding to a √7 × √7 structure was produced by S on the surface. At ≈ b 900°C evaporation of Cu occurred to an observable degree, and S and C could no longer be detected on the surface. Auger analysis of clean Cu surfaces showed many details of the LMM and MMM types of transitions. Kinetic energies of all observed Auger electrons were in excellent agreement with calculated values. Also, the ≈ 62 eV MMM peak was resolved into two components related to the small differences in the M₂ and M₃ energy levels. The LMM transitions were classified according to their intensities, which could be rationalized on the basis of Coster-Kronig transitions and transition probabilities, as L₃MM > L₂MM > L₁MM.