X-ray photoelectron spectroscopic study on initial oxidation of hafnium hydride fractured in an ultra-high vacuum

The initial oxidation of hafnium hydride was studied by X-ray photoelectron spectroscopy (XPS). The clean surface of hafnium hydride was obtained by fracturing the specimen in an XPS measurement chamber under a background pressure of 2.7 × 10⁻⁶ Pa. The fractured surface was oxidized in situ with the exposure to high-purity oxygen and the residual gases in an ultra-high vacuum chamber. The XPS spectra for the oxidized surfaces had the shoulder due to the oxidation, and the shoulder grew up with increase in exposure time even in the ultra-high vacuum. The factor analysis for the XPS spectra of the oxidized surface showed that the oxide formed in the chamber consists of only the hafnium dioxide, and no suboxide states are contained. The result corresponded to the oxide observed on hafnium hydride fractured in air.     

X-ray photoelectron spectroscopic studies on oxidation behavior of nickel and iron aluminides under oxygen atmosphere at low pressures

Oxidation behaviors of NiAl, Ni₃Al, and FeAl under oxygen atmosphere at low pressures were studied by X-ray photoelectron spectroscopy (XPS). Clean surfaces of these aluminides were prepared by fracturing in an ultra high vacuum, and then the fractured surfaces were oxidized by exposing to high-purity oxygen at pressures up to 1.3 Pa without exposing to air. The oxides formed on NiAl and FeAl surfaces were Al₂O₃, whereas the oxide on Ni₃Al was NiAl₂O₄. Aluminum, nickel, and iron on clean surfaces were oxidized even at a pressure of 1.3 × 10⁻⁶ Pa. The oxidation evolves with an increase in the pressure of oxygen, and further oxidation of aluminum occurs prior to that of nickel or iron. The oxidation behaviors under such oxygen atmosphere were similar to those of the aluminides oxidized in air, and these behaviors could be predicted from thermodynamic consideration.     

沉积态铀薄膜表面氧化的X射线光电子能谱

含铀(U)薄膜在激光惯性约束聚变的实验研究中有重要的用途.研究其在不同气氛下的氧化性能可以为微靶制备、储存及物理实验提供关键的实验数据.通过超高真空磁控溅射技术制备了纯U薄膜及金-铀(Au-U)复合平面膜,将其在大气、高纯氩(Ar)气及超高真空度环境中暴露一段时间后,利用X射线光电子能谱仪结合Ar~+束深度剖析技术考察U层中氧(O)元素分布及价态,分析氧化产物及机理.结果显示,初始状态的U薄膜中未检测到O的存在.Au-U复合薄膜中的微观缺陷减弱了Au防护层的屏蔽效果,使其在3周左右时间内严重氧化,产物为U表面致密的氧化膜及缺陷周围的点状腐蚀物,主要成分均为二氧化铀(UO_2).在高纯Ar气中纯U薄膜仅暴露6 h后表面即被严重氧化,生成厚度不均匀的UO_2.在超高真空度环境下保存12 h后,纯U薄膜表面也发生明显氧化,生成厚度不足1 nm的UO_2.Ar~+束对铀氧化物的刻蚀会因择优溅射效应而使UO_2被还原成非化学计量的UO_(2-x),但这种效应受O含量的影响.     

X-ray photoelectron spectroscopy studies on core-shell structured nanocomposites

Core-shell nanostructures were grown in silica-based glasses. Copper-copper oxide and iron-iron oxide structures had diameters in the range 3-6 nm, with shell thicknesses ∼1-2 nm. Silver-lithium niobate core-shell nanostructures had diameters in the range 4.2-46 nm and thicknesses varying from 2.2 to 22 nm. X-ray photoelectron spectroscopy studies were carried out on all these specimens. The analyses of these results show the presence of Cu⁺/Cu²⁺, Fe²⁺/Fe³⁺ and Nb⁴⁺/Nb⁵⁺ valence states in the above three systems. Electrical resistivity data were fitted satisfactorily to the small polaron hopping model in the case of copper and iron-containing specimens. The presence of ions in the lithium niobate shell provides direct evidence of the formation of localized states between which variable range hopping conduction can be effected.     

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 and X-ray Auger electron spectroscopy studies of heavy ion irradiated C60 films

The influence of 200 MeV Au ion irradiation on the surface properties of polycrystalline fullerene films has been investigated. The X-ray photoelectron and X-ray Auger electron spectroscopies are employed to study the ion-induced modification of the fullerene, near the surface region. The shift of C 1s core level and decrease in intensity of shake-up satellite were used to investigate the structural changes (like sp² to sp³ conversion) and reduction of π electrons, respectively, under heavy ion irradiation. Further, X-ray Auger electron spectroscopy was employed to investigate hybridization conversion qualitatively as a function of ion fluence.     

X-ray photoelectron spectroscopic studies on phase identification and quantification of nickel aluminides

Core-level XPS spectra for clean surfaces of Ni₃Al, NiAl, and NiAl₃ alloys were studied. The clean surfaces were obtained by fracturing in the ultra-high vacuum chamber. The positive chemical shifts of Ni 2p_3/2 peak for NiAl and NiAl₃ from Ni metal were 0.2 and 1.0 eV, respectively. The negative shift for Al 2p peak and the positive shift for Ni 3p peaks increased with the decreasing concentration of the corresponding elements. The peak position of the bulk plasmon loss peak for Al 2s peak shifted toward higher energy side, and further, the intensity ratio decreased with the decrease in aluminum concentration. Both the peak intensity ratios of Al 2p to Ni 3p determined by factor analysis and convenient separation are proportional to the atomic ratio of aluminum to nickel. The results indicate that the intensity ratio of Al 2p to Ni 3p determined by these two methods can be applied to the quantification for the surface of the nickel-aluminum alloys.     

X-ray photoelectron spectroscopy studies of Co-doped ZnO-Ga2O3-SiO2 nano-glass-ceramic composites

Co-doped ZnO-Ga₂O₃-SiO₂ nano-glass-ceramic composites were prepared by sol-gel method. X-ray diffraction patterns showed that the crystallization temperature was 800 °C. X-ray photoelectron spectroscopy (XPS) was used to study the effect of heat-treatment temperature on the electronic structure of Co-doped ZnO-Ga₂O₃-SiO₂ nano-glass-ceramic composites. The Zn (2p_3/2), Ga (2p_3/2) and O (1s) XPS spectra for the glass-ceramics heat-treated at 800-1000 °C could be deconvoluted into two peaks corresponding to these elements in glass network and in nanocrystals, respectively. The results indicate that the material is composed of an amorphous silicate network and ZnGa₂O₄ nanocrystalline particles. The amount of nanocrystals increases with the annealing temperature. The photoelectron peak of Si (2p) shifts to higher binding energy at higher annealing temperature, revealing the charge transfer from Si to O increased. The relationship between the microstructure of Co-doped ZnO-Ga₂O₃-SiO₂ sample and its absorption properties was discussed, and the suitable heat-treatment temperature was proposed.     

Monolayer vs. multilayer self-assembled alkylphosphonate films: X-ray photoelectron spectroscopy studies

Combining functional organic self-assembled monolayers (SAMs) with conventional semiconductor materials is a key step in the development of integrated electronics-based devices. T-BAG (Tethering by Aggregation and Growth) has been shown to be a simple and reliable method to grow SAMs of alkylphosphonates on oxide surfaces. However, distinguishing SAMs from ultra-thin multilayers is a challenge for most conventional surface characterization techniques.Self-assembled films of octadecylphosphonic acid (ODPA) were deposited on oxide-covered silicon coupons, converted to the corresponding phosphonates, and characterized by high resolution angularly resolved X-ray photoelectron spectroscopy (XPS). It was our goal to distinguish among different bonding configurations for phosphorous in the phosphonate head groups, namely, mono-dentate, bi-dentate or tri-dentate interactions with the oxide surface, as well as to assess quantitatively the near-surface layer composition.We also present an innovative method that allows us to distinguish between monolayer and multilayer films of ODPA on silicon oxide surfaces. This method is based on differential surface charging effects in XPS. It was found that variation in the ODPA film thickness causes differential responses of various spectral characteristics to an electrical bias applied to the sample during XPS measurements. Both positive and negative applied biases were found to affect the carbon core-level (C1s) line-shape and intensity in the case of the multilayer ODPA film, whereas line-shapes and intensities of all XPS lines measured for the monolayer film were unaffected by the application of a dc bias in the ±30 V range.     

Repeatable intensity calibration of an X-ray photoelectron spectrometer

Ten years ago, NPL developed an infrastructure for calibrating the intensity response functions of electron spectrometers for Auger electron and for X-ray photoelectron spectroscopies. Two software systems were developed: one for Auger electron spectrometers or for Auger electron and X-ray photoelectron spectrometers combined, and one for X-ray photoelectron spectrometers on their own; the latter being applied if no suitable electron gun is available. The system for Auger electron and X-ray photoelectron spectrometers combined has been used regularly to calibrate the Metrology Spectrometer II at NPL and experience shows that this gives an instrumental intensity consistency of 0.4% over 10 years. Evaluations have not previously been reported at this level. The system for Auger electron and X-ray photoelectron spectrometers combined is used here in preference to the system solely for X-ray photoelectron spectrometers since it is more robust to the sample condition and can be used over a wider energy range. These issues, and how observed variations in the instrument intensity response may arise, are explained.     

Near surface composition of some alloys by X-ray photoelectron spectroscopy

Chemical compositions of the alloys of CuNi (Cu_0.10Ni_0.90, Cu_0.30Ni_0.70, Cu_0.70Ni_0.30) and BiSb (Bi_0.80Sb_0.20, Bi_0.64Sb_0.34, Bi_0.55Sb_0.45) are determined by X-ray photoelectron spectroscopy. The stoichiometries are determined and are compared with the bulk compositions. Possible sources of systematic errors contributing to the results are discussed. Errors arising out of preferential etching in these alloys have been investigated. It has been inferred from such studies that the preferential etching does not enrich the surface composition with a particular component for the two systems reported here. Quantitative results of CuNi system indicate that the surface regions of the Cu_0.70Ni_0.30 alloy is Cu-rich, although no such evidence is observed in case of BiSb system.     

A study of the formation and oxidation of PtSi by SR-PES

In the paper we present the results on the formation of platinum silicide (PtSi) by means of synchrotron radiation photoelectron spectroscopy (SR-PES) and show the effect of a Pt/Si sample exposure to both a low and high-pressure oxygen atmosphere at the end of an annealing process. We have carried out a detailed analysis of high resolution photoelectron spectra of the Pt 4f and Si 2p peaks which were taken during the sample annealing at specific temperatures. In addition to the generally known Pt₂Si and PtSi phases we have recognized an additional intermediate phase during the formation of Pt₂Si and attributed it to the Pt₃Si phase. We have proved that silicon diffuses towards the sample surface. The results of a low-pressure oxygen experiment have shown that oxygen binds only to surface silicon, however, in the case of a PtSi sample prepared externally in the ON Semiconductor labs under nitrogen/oxygen atmosphere oxygen binds not only to surface silicon but also takes over Si atoms out of the PtSi phase which results in the formation of a SiO₂ layer on almost pure platinum.     

Surface oxidation of NiCo alloy: A comparative X-ray photoelectron spectroscopy study in a wide pressure range

Oxidation of NiCo alloy has been studied under two pressure regimes, 5 × 10⁻¹⁰ and 5 × 10⁻¹ bar, by X-ray photoelectron spectroscopy (XPS). The aim of this work is to investigate the synergetic effect between the two alloy components during the initial stages of oxidation. The results showed that at low oxygen pressure, segregation and preferential oxidation of cobalt takes place, while oxidation of nickel is largely suppressed. The species dominating the surface is CoO but small amount of metallic cobalt still remains even after prolonged oxidation at 670 K. At 0.5 bar O₂ pressure, alloy oxidation was found to be temperature depended. From 420 K to 520 K, cobalt is completely transformed to CoO and the Ni:Co atomic ratio at the surface approaches a minimum, similar to the observations at low pressure regime. However, at higher temperatures (from 520 K to 720 K), nickel is re-segregated on the surface, in the expense of cobalt, while CoO is further oxidized to Co₃O₄. At this temperature range formation of mixed Ni-Co-O spinel-like oxides is probable as supported by the characteristic modifications of the Ni 2p_3/2 photoelectron peak and the increase of the Ni:Co atomic ratio.     

The iron oxidation state in Mg-Al-Fe mixed oxides derived from layered double hydroxides: An XPS study

Mixed oxides with large surface area and high thermal stability can be obtained by thermal treatment of the layered double hydroxides (LDH). Mg-Al-Fe mixed oxide samples with varying Mg/Al ratio and 5 mol.% of Fe were prepared in this way and the iron oxidation state (Fe_ox) in these compounds was studied by X-ray photoelectron spectroscopy (XPS), using a calibration based on the relation of Fe_ox to the splitting between the O 1s and Fe 2p_3/2 centroids. The XPS results confirm Fe³⁺ as a dominant oxidation state in the studied mixed oxides. A vacuum-induced reduction of iron in the Fe₂O₃ and Mg-Al-Fe oxide samples has been observed and an influence of the Mg:Al ratio on this effect in mixed oxides has been detected. The role of the local variations of the electron density distribution in the close neighbourhood of the surface oxygen atoms in the mixed oxides in the reduction processes is discussed.     

Photoelectron escape from iron oxide

Iron oxide of nanometer thickness were grown in situ by step-by-step oxidation of an iron foil to measure the escape probabilities of O 1s photoelectrons as a function of depth of origin, the so-called emission depth distribution function (EDDF), and the mean escape depth (MED). To record photoelectron spectra for a wide range of emission angles, the X-ray excitation source was positioned on the opposite side of the iron foil with respect to the analyzer. To excite photoelectrons on the side of the foil surface adjacent to the analyzer, the foil was made thin enough to be semitransparent to the X-ray radiation. The O 1s spectra were recorded for a wide range of oxide thicknesses until no features of metallic iron were recognized in the photoelectron spectra. The escape probability of the O 1s photoelectrons in the iron oxide was derived from the oxide-thickness dependence of the O 1s peak areas. The resulting EDDF reached a maximum beneath the oxide surface for X-ray incidence and electron-emission angles located along the surface normal. For the same incidence angle and an emission angle of 60°, the escape probability could be well approximated by a simple exponential function. The mean escape depths were obtained for both experimental geometries and agreed well with the available theory.     

Valence band and core level X-ray photoelectron spectroscopy of lead sulfide nanoparticle-polymer composites

Valence band and core level X-ray photoelectron spectroscopy (XPS) were used to probe lead sulfide (PbS) nanoparticle-polymer nanocomposites. Composite materials were prepared by trapping commercially available monodisperse 3 and 10 nm PbS nanoparticles in two polymers, the non-conducting polymer, polystyrene, and the conjugated polymer, poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene (referred to below as MEH-PPV). The nanocomposites prepared from commercial nanoparticles underwent oxidation, mainly to form lead sulfate. However, the narrow size distributions of the commercial nanoparticles allowed observation of distinct changes in the valence band from the 3 to 10 nm nanoparticles. Nanocomposites of 2-5 and 4-7 nm PbS nanoparticles were synthesized by growing the particles in poly(vinyl alcohol) (referred to below as PVA) and MEH-PPV, respectively. These composites both indicated the formation of lead sulfide nanoparticles. Furthermore, the XP spectra for the PVA/PbS composite displayed bonding between the PbS nanoparticles and the polymer while MEH-PPV showed no PbS-polymer bonding. The nanoparticles synthesized in MEH-PPV did not undergo oxidation. The particle size distributions of the synthesized nanoparticles were too broad to display size-dependent changes in the valence band.     

双原子填充式skutterudite化合物的结构及X射线光电子能谱分析

用高温熔融、淬火、扩散退火结合放电等离子烧结(SPS)法合成了Ca和Ce复合填充的单相Ca_mCe_nFe_xCo_4-xSb₁₂(m=0.17—0.27，n=0.05—0.25，x=1.5)化合物，并结合Rietveld结构解析以及X射线光电子能谱(XPS)分析研究了两种原子复合填充skutterudite化合物的结构与填充状态.Rietveld结构解析表明，Ca_mCe_nFe_1.5Co_2.5Sb₁₂化合物具有skutterudite结构，Ca和Ce原子填充到了Sb的二十面体空洞中，填充原子热振动参数B_Ca/Ce远大于框架原子的热振动参数B_Fe/Co和B_Sb.XPS元素窄区谱分析结果表明，Sb原子在结构中有五种化学状态，每种化学状态的相对含量主要由总填充分数决定，填充原子Ca在Sb的二十面体空洞出现概率有三种可能，但在中心位置出现的概率最大. 关键词： skutterudite化合物 双原子复合填充 结构 X射线光电子能谱分析     

X-ray photoelectron study of Sn1−xMnxTe semimagnetic semiconductors

X-ray photoelectron (XPS) studies of core-levels in Sn_1−xMn_xTe (x < 0.1) semimagnetic semiconductors have been performed. The spectra were acquired under UHV conditions from the clean (as-cleaved or in-situ scraped) crystal surface. The single-phase NaCl structure of the alloys studied was verified by X-ray diffraction (XRD). The structure of Sn 3d and Te 3d core-levels in SnMnTe was found fully consistent with that of SnTe. Remarkable qualitative similarity of the Mn 2p spectrum of Sn_1−xMn_xTe (x = 0.09) with the case of zinc-blende MnTe [R.J. Iwanowski, M.H. Heinonen, E. Janik, Chem. Phys. Lett. 387 (2004) 110] has been shown: (1) the same binding energies (BEs) of the main contributions to the Mn 2p_3/2 line, related to Mn²⁺ state of the bulk MnTe bond; (2) occurrence of low BE component in the Mn 2p spectrum, indicative of clean-surface species containing reduced-valence Mn ions (i.e. Mn^q+, where 0 < q < 2); (3) strong satellites of the 2p_3/2 (Mn²⁺ related) parent lines. In SnMnTe, the highest intensity ratio of the satellite to main peak (ever reported for Mn 2p photoelectron spectrum) was revealed; this was interpreted in terms of the so-called charge-transfer model.     

The effects of the lithium intercalation on the X-ray photoelectron spectra of NiPS3

Summary A detailed XPS study of the lithium-intercalated NiPS₃ specimens was performed at the 2p, 3p, 3s core levels of the nickel atoms and at the 2p core levels of the sulphur and phosphorous atoms for various lithium contents. Comparison of the Ni 2p, 3p and 3s XPS spectra corresponding to NiPS₃ and Li _x NiPS₃ systems shows some evident trends. In particular, a shift of the Ni main line towards lower binding energies, a decrease in the intensity of the Ni 3p, 2p satellite structures and a change in the full width at half maximum of the Ni 3s band with lithium content are observed. All these findings suggest a change in the 3d electron configuration for high lithium concentrations. As regards the cluster (P₂S₆)⁴⁻, with the addition of lithium, a P 2p main line shift towards higher binding energies is noted, while the S 2p peak shifts towards lower binding energies. These results are discussed in comparison with previous physical measurements concerning the nickel reduction process and the related electronic modifications. The authors of this paper have agreed to not receive the proofs for correction.