X射线光电子能谱

X射线光电子能谱（X-ray photoelectron spectroscopy, XPS）技术也被称作用于化学分析的电子能谱（electron spectroscopy for chemical analysis,ESCA）.XPS属表面分析法,它可以给出固体样品表面所含的元素种类、化学组成以及有关的电子结构重要信息,在各种固体材料的基础研究和实际应用中起着重要的作用.文章简要介绍了XPS仪器的工作原理和分析方法,并给出了XPS在科学研究工作中的应用实例.     

X-ray photoelectron spectroscopy characterization of stain-etched luminescent porous silicon films

The surface and in-depth chemical nature of the photoluminescent stained Si layer obtained with a novel procedure based on HF/HNO₃ is presented. Oxide-free porous Si surfaces result from controlled preparation, storing and handling of samples, as revealed by parallel X-ray photoelectron spectroscopy and X-ray-induced Auger electron spectroscopy measurements, coupled with Ar⁺ ion sputtering. The present findings support the model for the porous layer of oxidized samples of Si grains embedded in a silica gel matrix.     

X射线光电子能谱

X射线光电子能谱（X-ray photoelectron spectroscopy，XPS）技术也被称作用于化学分析的电子能谱（electron spectroscopy for chemical analysis，ESCA）．XPS属表面分析法，它可以给出固体样品表面所含的元素种类、化学组成以及有关的电子结构重要信息，在各种固体材料的基础研究和实际应用中起着重要的作用．文章简要介绍了XPS仪器的工作原理和分析方法，并给出了XPS在科学研究工作中的应用实例．     

X-ray and neutron reflectivity analysis of thin films and superlattices

X-ray and neutron reflectivity measurements provide a wealth of information on thickness and interfacial properties on the nanometer scale. This method is therefore well suited for the study of nano-structured thin films and superlattices. Neutrons provide a different contrast between the elements than X-rays and, in addition, are sensitive to the magnetization in the sample. Using polarized neutrons, magnetic as well as chemical profiles can be probed. In this review a basic introduction into the theory of X-ray and neutron reflectivity is provided along with some recent examples including the oxidation of Fe films and the structural and magnetic properties of Co/Cu superlattices.     

X-ray reflectivity study of hydrogen implanted silicon

The X-ray reflectivity (XRR) technique was used to study monocrystalline silicon samples implanted with H₂ ions at an energy of 31 keV and to the dose of 2 × 10¹⁶ hydrogen atoms/cm². All samples were subsequently isochronally annealed in vacuum at different temperatures in the range from 100 to 900 °C. Although the hydrogen depth distribution was expected to be smooth initially, fringes in the XRR spectra were observed already in the implanted but not annealed sample, revealing the presence of a well-defined film-like structure. Annealing enhances the film top to bottom interface correlation due to structural relaxation, resulting in the appearance of fringes in the larger angular range, already at low annealing temperatures. The thickness of the film decreases slowly up to 350 °C where substantial changes in the roughness are observed, probably due to the onset of larger clusters formation. Further annealing at higher temperatures restores the high correlation of the film interfaces, while the thickness decreases with the temperature more rapidly.     

Deconvolution in X-ray photoelectron spectroscopy

Published Mg and Al Kα X-ray lineshapes have been used to study the removal of the effects of X-ray broadening in XPS spectra by deconvolution. These results are compared with spectra obtained for the same specimens in the same instrument using a monochromatic X-ray source. The use of deconvolution to remove analyzer broadening from spectra has also been examined, and it has been verified experimentally that the maximum improvement in the full width at half-maximum of a peak that can be achieved is 30%. Deconvolution has also been examined as a means to remove backgrounds from XPS spectra over wide energy ranges, up to 100 eV.     

Surface sensitivity of Auger-electron spectroscopy and X-ray photoelectron spectroscopy

A convenient measure of surface sensitivity in Auger-electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) is the mean escape depth (MED). If the effects of elastic-electron scattering are neglected, the MED is equal to the electron inelastic mean free path (IMFP) multiplied by the cosine of the emission angle with respect to the surface normal, and depends on the material and electron energy of interest. An overview is given here of recent calculations of IMFPs for 50–2000 eV electrons in a range of materials. This work has led to the development of a predictive formula based on the Bethe equation for inelastic electron scattering in matter from which IMFPs can be determined. Estimates show, however, that elastic-electron scattering can significantly modify the MED. Thus, for AES, the MED will be reduced by up to about 35%. For XPS, however, the MED can be changed by up to ±30% for common measurement conditions although it can be much larger (by up to a factor of 2) for near-grazing emission angles. Ratios of MED values, calculated with elastic scattering considered and neglected for XPS from the 3s, 3p, and 3d subshells of silver with Mg Kα X-rays are approximately constant (to about 10%) over a range of emission angles that varies from 40° to 60° depending on the subshell and the angle of X-ray incidence. Recommendations are given on how to determine the optimum range of emission angles for satisfactory analysis of angle-resolved XPS (ARXPS) data. Definitions are included of three terms often used for describing surface sensitivity (IMFP, MED, and effective attenuation length (EAL)), and examples are given of the varying magnitudes of these quantities for different analytical conditions.     

X-ray photoelectron spectroscopy of rare-earth compounds

A variety of rare-earth (RE) compounds (oxides, sulfates and oxalates) have been studied by X-ray photoelectron spectroscopy. Except for Eu, the binding energies (BE's) of the RE 3d and 4d peaks for the sulfates and oxalates are respectively almost equal to and 1.3–3.1 eV higher than those for the oxides. In the Eu 3d spectrum of europium(II) oxalate, distinct shake-down satellite peaks are present, and the BE's of these peaks are 1̃0 eV lower than the parent ones. For the oxides, appreciable differences are found in the BE's of the O 1s peaks, and a specific “inclined W” form is observed in plots of BE versus 1/R (where R is the mean distance from the oxygen atom to the neighboring RE atom) and versus the RE oxidation-reduction potential (ORP). No characteristic differences are seen in the BE's (C 1s, S 2s and S 2p) of the other ligands.     

X-ray photoelectron spectroscopy of FeP phosphide

The structure of the outer and inner electron spectra of iron (2p, 3p, 3s, and 3d) and phosphorus (3s and 3p) atoms in FeP monophosphide is studied in detail by the X-ray photoelectron spectroscopy (XPS) method. On the basis of the analysis of the binding energy of electrons, as well as the parameters characterizing the structure of experimental spectra, a conclusion is made that Fe³⁺ (d ⁵) cations in FeP are stabilized in a state with intermediate value of the total spin (IS, S = 3/2). The range of values of intra-atomic parameters (10Dq, J _H ) is established in which the consideration of the high degree of covalence of Fe–P bonds may lead to the stabilization of (FeP₆)^15– clusters in the IS state.     

X-ray photoelectron spectroscopy of copper compounds

The X-ray photoelectron spectra of some forty-six copper compounds and complexes have been measured. The chemical shifts obtained from accurate determinations of the binding energies have been qualitatively explained on the basis of the Pauling electronegativity concept using the group electronegatives of Huheey for the polyatomic counter anions. The chemical shifts of the copper atoms as well as the atoms in the ligands were found to be dependent not only on the oxidation state but also on the kind and number of ligand atoms.

Intense satellite lines were found in the 2p and 2s bands of the cupric compounds; the number and splitting of the satellites were found to be sensitive to the chemical environment. A correlation was found between the satellite splitting and the binding energies and this is explained by a 3d→4s, 4p ‘shake-up’ mechanism.     

Inelastic effects in X-ray photoelectron spectroscopy

Inelastic scattering of excited electrons and deep holes in X-ray photoemission, and especially the problem of electron attenuation lengths and escape     

Shake-up satellites in X-ray photoelectron spectroscopy

Shake-up satellite peaks have been reported in the core electron spectra of various types of molecules. The specific valence excitation(s) giving rise to this extra structure has been assigned largely as a result of the application of the sudden approximation coupled with other considerations, e.g. transition energies. Satellite peaks appearing in the core electron spectra of first row transition metal complexes appear to be particularly interesting since existing data indicate that their positions and intensities convey information regarding some important properties of the complex.In this work reported shake-up satellite peaks are described and analyzed. In addition, some areas requiring more experimental work are pointed out, and a few potential applications of satellite peak data are mentioned.     

Electronic structure of carbyne studied by X-ray photoelectron spectroscopy and X-ray emission spectroscopy

The electronic structure of amorphous carbyne has been investigated by X-ray photoelectron spectroscopy and X-ray emission spectroscopy. Carbyne band structure has been calculated semiempirically and the experimental data have been interpreted on the basis of the calculation results. The valence band width was found to be about 20 eV which is the same as that in all other condensed carbon structures. The fine satellite structure near the 1s line of carbon has been studied. It is shown that the energy bands in carbyne are arranged in a mirror-like way relative to the Fermi level. The real carbyne structure is susceptible to conformations which affect primarily the π-subband structure.     

X-ray photoelectron spectroscopy of tin oxide nanolayers

X-ray photoelectron spectra of 30- and 100-nm nanolayers, recorded in the energy range 0–35 eV, show a strong dependence of both the distribution of the density of Sn 5s, p+ O₂ p valence states and the change in the intensity ratio for the Sn 4d and O 2s subvalence states on the annealing temperature and nanolayer thickness. In the nanolayers fabricated at an annealing temperature of 450°C, an unusually strong band of O 2s states of unbound oxygen is observed, which is retained for nanolayers doped with palladium and disappears for nanolayers doped with gold and silver.     

X-ray photoelectron spectroscopy of nitroanilines and their derivatives

N 1s core-electron spectra have been studied for nitroanilines and related compounds. The spectral data are qualitatively interpreted by means of the molecules-in-molecule method, which describes the interaction between the aromatic amine part (donor moiety) and the nitro group (acceptor moiety) in terms of a composite system consisting of a donor and an acceptor. It was found that the nitro-N 1s spectra and the separation between the nitro-N 1s and the amino-N 1s ionization energies depend upon the magnitude of the intramolecular charge-transfer interaction in the ground state. A similarity between the relaxation effect in the nitro-N 1s or nitro-O 1s core-hole ion and a nitration reaction of the donor moiety is demonstrated.     

X-ray photoelectron spectroscopy study of magnetic films

Ta/NiO_x/Ni₈₁Fe₁₉/Ta films were prepared by rf reactive and dc magnetron sputtering. The exchange coupling field H_ex and the coercivity H_c of NiO_x/Ni₈₁Fe₁₉ as a function of the ratio of Ar to O₂ during the deposition process were studied. The composition and the chemical states in the interface region of NiO_x/NiFe were also investigated using X-ray photoelectron spectroscopy (XPS) and the peak decomposition technique. The results show that the ratio of Ar to O₂ has a great effect on the chemical states of nickel in NiO_x films. The exchange coupling field H_ex and the coercivity H_c of Ta/NiO_x/Ni₈₁Fe₁₉/Ta are thus seriously affected. XPS is shown to be a powerful tool for characterizing magnetic films. Received: 18 July 2001 / Accepted: 21 December 2001 / Published online: 3 June 2002 RID="*" ID="*"Corresponding author. Fax: +86-010/6232-7283, E-mail: guanghua_yu@263.net     

X-ray photoelectron spectroscopy applied to insular films

For a given experimental arrangement, X-ray photoelectron spectra measured at different points on a sample surface may show fluctuations which cannot be attributed to counting statistics. These fluctuations are caused by overlayers having an insular structure. The XPS information obtained can be evaluated by a statistical method to yield the dimensions of the islands.     

X-ray photoelectron spectroscopy studies on solid xanthates

Two commonly used xanthates, potassium ethyl xanthate (KEX) and sodium isopropyl xanthate (NaiPX) were characterized by comparing their bulk and surface composition. The XPS spectra were recorded using Al K and Mg K excitation and potential sources of contamination were accounted for. Sulfate and carbonate contaminations were identified, both in the bulk and on the surface of the KEX sample. NaiPX contained hydroxyl- and carbonyl-type contaminations. The earlier published XPS spectral data on xanthates were compiled and compared with the results of this work.