Background subtraction in electron spectroscopy by use of reflection electron energy loss spectra

The use of reflected electron energy loss spectra (REELS) in deconvoluting the inelastic background signal from XPS and AES spectra from homogeneous samples is studied. It is demonstrated that under certain assumptions, the cross section for inelastic electron scattering can be extracted from a REELS spectrum. This cross section is applied to deconvolute an experimental XPS spectrum of aluminium. The method, its limitations and its relation to other methods are discussed.     

Direct numerical reconstruction of inelastic cross sections from REELS and ISS spectra

The reconstruction of inelastic scattering cross sections faces two problems: the measured signal (energy spectrum) is a multiple scattering signal; the inelastic energy loss is nonuniform over the target depth. In this paper, we present a method for numerical reconstruction of cross sections from characteristic energy loss spectra, which efficiently solves both problems within a multilayer model. It is shown that the inverse problem of cross section extraction in the three-layer model is ill-conditioned, and the method is practically inapplicable to the three-layer model. The direct numerical reconstruction method yields a strongly “noised” result and can be applied only to obtain a priori information on the inelastic cross section form for further fitting. Using a combination of two methods, inelastic scattering cross sections were reconstructed for aluminum from characteristic energy loss spectra at probe beam energies of 5 and 40 keV. It is shown that ionization in solids should be described as a local process and as a collective one using the dispersion formula similarly to the case of excitation plasmons.     

Comparative analysis of characteristic electron energy loss spectra and inelastic scattering cross-section spectra of Fe

The inelastic electron scattering cross section spectra of Fe have been calculated based on experimental spectra of characteristic reflection electron energy loss as dependences of the product of the inelastic mean free path by the differential inelastic electron scattering cross section on the electron energy loss. It has been shown that the inelastic electron scattering cross-section spectra have certain advantages over the electron energy loss spectra in the analysis of the interaction of electrons with substance. The peaks of energy loss in the spectra of characteristic electron energy loss and inelastic electron scattering cross sections have been determined from the integral and differential spectra. It has been shown that the energy of the bulk plasmon is practically independent of the energy of primary electrons in the characteristic electron energy loss spectra and monotonically increases with increasing energy of primary electrons in the inelastic electron scattering cross-section spectra. The variation in the maximum energy of the inelastic electron scattering cross-section spectra is caused by the redistribution of intensities over the peaks of losses due to various excitations. The inelastic electron scattering cross-section spectra have been analyzed using the decomposition of the spectra into peaks of the energy loss. This method has been used for the quantitative estimation of the contributions from different energy loss processes to the inelastic electron scattering cross-section spectra of Fe and for the determination of the nature of the energy loss peaks.     

Accuracy of the Tougaard method for quantitative surface analysis. Comparison of the Universal and REELS inelastic cross sections

Three tests have been performed to investigate whether cross sections determined experimentally from reflection electron energy loss spectroscopy (REELS) are more accurate than the Universal cross section for background correction of electron spectra. In the first test, the shape of background corrected spectra from a thin layer and from an infinitely thick layer of the same element were compared for the Ag3d, Au4d, and Yb4d peaks. It was found that the Universal cross section is more accurate than the experimentally determined REELS cross sections to determine consistently the peak shape of background corrected spectra. In the second test, the intensity ratio of the two components in the Au4d, Cu2p, Zn2p, and Yb4d doublets were compared to theoretical photoionization cross sections. For both the Universal and the REELS inelastic cross sections, the obtained intensity ratios agree well with theory. In the third test, we compare with theory the peak intensity ratios to Au4d of major peaks from Si, Cu, Ag, Yb, and Au obtained by using the Universal and the REELS cross sections for background correction. For the metals, the two cross sections give peak intensity ratios that are equally close to theory to within the expected uncertainties in the theoretical peak intensity ratios. However, for Ag with application of the Universal cross section the deviation from theory is slightly larger. For Si the REELS cross section is clearly most accurate.     

Inelastic electron scattering observation using energy filtered transmission electron microscopy for silicon -- germanium nanostructures imaging

This paper presents a new technique using energy filtered TEM (EFTEM) for inelastic electron scattering contrast imaging of Germanium distribution in Si-SiGe nanostructures. Comparing electron energy loss spectra (EELS) obtained in both SiGe and Si single crystals, we found a spectrum area strongly sensitive to the presence of Ge in the range [50-100 eV]. In this energy loss window, EELS spectrum shows a smooth steeply shaped background strongly depending on Ge concentration. Germanium mapping inside SiGe can thus be performed through imaging of the EELS background slope variation, obtained by processing the ratio of two energy filtered TEM images, respectively, acquired at 90 and 60 eV. This technique gives contrasted images strongly similar to those obtained using STEM Z-contrast, but presenting some advantages: elastic interaction (diffraction) is eliminated, and contrast is insensitive to polycrystalline grains orientation or specimen thickness. Moreover, since the extracted signal is a spectral signature (inelastic energy loss) we demonstrate that it can be used for observation and quantification of Ge concentration depth profile of SiGe buried layers.     

Extraction of cross-sections of inelastic scattering from energy spectra of reflected atomic particles

REELS spectra of the electrons reflected off niobium are measured with energy resolution <0.5 eV within the 5–40 eV energy range of the probing beam. The measurements were performed for the scattering angles θ = 45° and θ = 120° by means of two electron guns. The process of energy losses is described within the framework of a model with three different energy loss laws: surface, intermediate, and bulk layers are considered. Differential cross-sections of inelastic scattering are represented in the form of simple equations.     

Resonant electron exchange scattering in late transition metal monoxides

Intra-atomic d-d transitions in NiO(100) and CoO(100) have been investigated with angle-resolved electron energy loss spectroscopy (EELS) at primary energies close to the metal 3s excitation threshold. Electron exchange scattering was found to be resonantly enhanced at the 3s threshold due to the temporary formation of a negative ion core state and its subsequent decay via Auger-like transitions. In both oxides the threshold is lowered several eV due to a strong electron- core hole interaction. Angle-dependent studies reveal a different dependency of exchange processes on the scattering angle as compared with nonresonant measurements and reveal a different angle dependence for each specific d-d transition. It is suggested that in these oxides large-angle single-step inelastic scattering contributes significantly to the EELS measurements in reflection mode.     

Electronic and optical properties of Cu, CuO and Cu2O studied by electron spectroscopy

The electronic and optical properties of Cu, CuO and Cu(2)O were studied by x-ray photoelectron spectroscopy (XPS) and reflection electron energy-loss spectroscopy (REELS). We report detailed Cu 2p, Cu LVV, O 1s and O KLL spectra which are in good agreement with previous results. REELS spectra, recorded for primary energies in the range from 150 to 2000 eV, were corrected for multiple inelastically scattered electrons to determine the effective inelastic scattering cross section. The dielectric functions and optical properties were determined by comparing the experimental inelastic electron scattering cross section with a simulated cross section calculated within the semi-classical dielectric response model in which the only input is Im(-1/ε) by using the QUEELS-ε(k,ω)-REELS software package. By Kramers-Kronig transformation of the determined Im(-1/ε), the real and imaginary parts (ε(1) and ε(2)) of the dielectric function, and the refractive index n and extinction coefficient k were determined for Cu, CuO, and Cu(2)O in the 0-100 eV energy range. Observed differences between Cu, CuO and Cu(2)O are mainly due to modifications of the 3d and O 2p electron configurations.     

Elastic and inelastic scattering of nucleons from 16O

Measurements of differential elastic and inelastic cross sections for neutron scattering from ¹⁶O at incident energies 18 to 26 MeV are presented. In addition to cross sections for neutron scattering differential cross sections for proton scattering up to 66 MeV are described in terms of phenomenological optical model potentials. At 24.5 MeV incident energy inelastic scattering up to 11.5 MeV excitation was measured. The elastic and inelastic compound nucleus contributions were examined. Direct inelastic scattering from the normal parity states was calculated using the DWBA and coupled-channel formalisms. The inelastic scattering cross section from non-normal parity state 2⁻ was calculated using the coupled-channel formalism via multi-step processes. Cross sections due to inelastic scattering from some of the states, which are thought to be members of an excited state rotational band were calculated using both vibrational and rotational approaches and were compared.     

Electron energy loss spectroscopy of Pd and Pd–Au catalysts supported on multiwall carbon nanotubes

The X-ray PhotoElectron Energy Loss Spectroscopy (XP-EELS) and Reflection Electron Energy Loss Spectroscopy (REELS) were used for analysing surface layers of “as-received” and functionalised multiwall carbon nanotubes (MWCNT), and MWCNT decorated with Pd and Pd–Au particles after calcination/reduction. The decorated MWCNT were previously applied as catalysts in a reaction of formic acid electrooxidation. These spectroscopies, used as complementary methods of structural surface analysis, provide information on the energy position, intensity and full width at half maximum of the quasi-elastic peak and inelastic π and π + σ energy loss peaks. Analysing the π + σ energy loss peak, the bulk and surface C sp²/sp³ components can be separated. Functionalisation of MWCNT, catalyst reduction and Ar⁺ ion sputtering increase the C sp³ content in comparison to the “as-received” MWCNT and calcined catalysts. The intensity ratios of surface and bulk C sp³ and sp² components evaluated from the REELS π + σ energy loss peak indicate: (i) functionalisation leads to attachment of functional groups to the MWCNT surface, (ii) calcined catalysts show an amorphous carbon overlayer at the surface and (iii) reduction of calcined catalysts leads to increasing C sp³ hybridisations.     

Scattering of excitons by excitons in semiconducting quantum well structures

We have theoretically investigated the scattering of excitons by excitons in a two-dimensional semiconducting quantum well system. The scattering cross sections have been calculated using the Born approximation for both the elastic and inelastic scattering of the excitons by excitons. The threshold for inelastic scattering is increased over the value in a bulk semiconductor because of the enhancement of the exciton binding energy by its confinement. The behavior of the scattering cross section as a function of the energy of relative motion of the excitons is different than in the bulk and the cross section is a more sensitive function of the ratio of the electron and hole masses than in the bulk.     

Matrix effective potential for electronic response in electron scattering with application to He at 30–400 eV impact energy

A new method is presented for modelling the virtual and real charge polarization of a target in an electron scattering event. Preliminary results are presented for inelastic and total scattering cross sections.     

正电子被分子散射总截面的计算

将光学势方法与可加性规则（ａｄｄｉｔｉｖｉｔｙｒｕｌｅ）相结合，我们计算了能量在１０－１０００ｅＶ范围内正电子被分子（Ｈ２，Ｎ２，ＨＣｌ，ＮＨ３，ＣＨ４，ＳＦ６）散射的总截面，计算结果与已有的实验结果进行了比较。     

Simple algorithm for quantitative analysis of reflection electron energy loss spectra (REELS)

A detailed comparison of two different physical approaches for quantitative analysis of reflection electron energy loss spectra (REELS) is presented. The Tougaard–Chorkendorff (TC) algorithm [S. Tougaard, I. Chorkendorff, Phys. Rev. B35 (1987) 6570] is analyzed theoretically and applied to experimental spectra of four elemental solids (Si, Cu, Ag, and Au). A closed expression is derived for the quantity retrieved by the TC-algorithm, the so-called “effective” cross section, which was originally only given as a recursive procedure. Single scattering loss distributions are derived from the experimental spectra using the bivariate reversal method [W.S.M. Werner, Phys. Rev. B74 (2006) 075421]. The latter agree satisfactorily with density functional theory (DFT) calculations and other data found in the literature. Using these single scattering loss distributions, the TC “effective” cross section can be perfectly reproduced if the fact is taken into account that the effective cross section is not a single scattering loss distribution and is governed to a significant extent by elastic scattering. On the basis of the above results, a dramatically simplified deconvolution scheme for quantitative analysis of REELS is developed.     

He-HF（DF，TF）碰撞体系分波截面的理论计算

运用质心变换-拟合方法,使用Murrell-Sorbie势能函数拟合在对称性匹配微扰理论下精确计算He-HF体系的相互作用能数据,得到了He原子与同位素分子HF（DF,TF）复合物的相互作用势的解析形式.完成了入射He原子能量从30 meV至120 meV时,He-HF（DF,TF）碰撞体系分波截面的密耦计算,获得了分波截面等信息,进一步讨论了分波截面的变化趋势及特征,并确定了He-HF（DF,TF）碰撞体系开始产生弹性和非弹性散射的有效相互作用范围. 关键词： He-HF（DF TF）复合物 密耦近似 分波截面 质心偏移     

Inelastic interactions of fast nucleons with nuclei and fission of nuclei

The cross section for the fission of actinide nuclei that is induced by fast neutrons is considered as a fraction of the cross section for inelastic nucleon interaction with nuclei. In turn, inelastic nucleon interaction with a nucleus is treated as scattering on intranuclear nucleons. It is shown that this interaction model describes satisfactorily the cross section for the inelastic interaction of 60- to 2200-MeV nucleons for a broad set of nuclei and that the energy dependence of the cross section for the fission of actinide nuclei that is induced by 400- to 1000–MeV protons replicates the energy dependence of the cross section for inelastic interactions with respective nuclei. From the model used, it follows that the cross sections for proton-nucleus interactions exceed cross sections for respective neutron-nucleus interactions in the energy range extending up to 550 MeV; at higher energies neutron cross sections are larger than proton cross sections.     

Quark Energy Loss and Shadowing in Nuclear Drell-Yan Process

The energy loss effect in nuclear matter is another nuclear effect apart from the nuclear effects on the parton distribution as in deep inelastic scattering process. The quark energy loss can be measured best by the nuclear dependence of the high energy nuclear Dre11-Yan process. By means of three kinds of quark energy loss parameterizations given in literature and the nuclear parton distribution extracted only with lepton-nucleus deep inelastic scattering experimental data, measured Dre11-Yan production cross sections are analyzed for 800 GeV proton incident on a variety of nuclear targets from FNAL E866. It is shown that our results with considering the energy loss effect are much different from those of the FNAL E866, who analyzes the experimental data with the nuclear parton distribution functions obtained by using the deep inelastic IA collisions and pA nuclear Drell-Yan data. Considering the existence of energy loss effect in Drell-Yan lepton pairs production, we suggest that the extraction of nuclear parton distribution functions shoul““““d not include Dre11-Yan experimental data.     

Influence of quark energy loss on extracting nuclear sea quark distribution from nuclear Drell-Yan experimental data

By means of two typical kinds of quark energy loss parametrization and the nuclear parton distributions determined only with lepton-nuclear deep inelastic scattering experimental data, a leading order analysis is performed on the proton-induced Drell-Yan differential cross section ratios of tungsten versus deuterium as a function of the quark momentum fraction in the beam proton and target nuclei. It is found that the theoretical results with quark energy loss are in good agreement with the experimental data. The quark energy loss effect produces approximately 3% to 11% suppression on the Drell-Yan differential cross section ratios R_W/D in the range 0.05≤x₂≤0.3. The application of nuclear Drell-Yan data with heavy targets is remarkably subject to difficulty in the constraint of the nuclear sea quark distribution.