Limitation of Auger electron spectroscopy in the determination of the metal-on-oxide growth mode: Pd on MgO(100)

A discussion on the use of Auger electron spectroscopy as a quantitative tool to determine the growth mode of metals on single crystal oxide surfaces is presented. In the case of Pd grown epitaxially on MgO(100), the three-dimensional character of the growth is easily seen at coverage above one monolayer. However, in the submonolayer regime, and mainly at low substrate temperatures, the AES results are ambiguous. The combination of AES with the more sensitive helium-atom diffraction method allows us to demonstrate that the growth is three-dimensional from the early stages, the particles becoming flatter when the substrate temperature decreases. We compare our results with other growth studies on different metal/oxide systems. At low temperature, the ideal growth modes are not always observed, the final morphology of the films being determined mainly by kinetic effects. Thus a pseudo-Stranski-Krastanov growth mode is often obtained with formation of 2D islands followed by 3D clustering from a critical submonolayer coverage.     

Nonconvergence of the 1/N expansion for SU(N) gauge fields on a lattice

We present specific examples that demonstrate the non-convergence of the 1/N expansion for the lattice theory of SU(N) gauge fields.     

Electronic structure of Ti metal and TiO2 powder studied by hard and soft (Cu Kα1 and Al Kα1) X-ray photoelectron and Auger spectroscopy

High-energy X-ray photoelectron spectroscopy (XPS) is of particular importance for minimizing the effects of surface contamination by increasing photoelectron escape depths. In this study high-resolution high-energy Cu Kα₁ and soft Al Kα₁ XPS and Auger electron spectroscopy were used to compare the electronic structure of Ti in TiO₂ powder and Ti metal. The Ti 1s in TiO₂ XPS line is narrower and more symmetric than in Ti metal. A comparison of the relative intensities of the L₂₃M₂₃M₄₅ and L₂₃M₂₃M₂₃ Auger transitions in Ti metal and TiO₂ is consistent with the expected transfer of Ti 3d electrons away from the Ti site in the oxide. The satellites accompanying the Ti 1s XPS line excited by Cu Kα₁ X-rays occur at the same energies as the satellites accompanying the Ti 2s and 2p XPS lines excited by Al Kα₁ X-rays indicating that they do not depend on the core-level, the experimental resolution or inelastic scattering processes.     

有机锡化合物的光电子能谱（XPS）和质谱（MS）研究Ⅱ

本文报道了７种新合成的（Ｚ）－１－（２－（三芳基锡）乙烯基）－１－环庚醇有机锡化合物的ＸＰＳ和ＭＳ结果，通过ＸＰＳ讨论了化合物中不同取代基的存在，对锡内层电子的影响及取在对Ｏｈ结合能化学位移的作用，结果表明，卤素在这里起着得要的作用，通过ＭＳ和ＸＰＳ讨论了不同取代基对Ｏ→Ｓｎ键的影响。     

Non-perturbative effects and infrared renormalons within the 1/N expansion of the O(N) non-linear sigma model

We analyze the structure of the Borel transform of the two-dimensional O(N) non-linear σ model within its $\text{1}\text{N}$ expansion. We check the existence of IR singularities (IR renormalons) and the presence of non-perturbative terms which organize themselves in an operator expansion à la Shifman-Vainshtein-Zakharov. We prove that renormalons cancel between the different terms of the operator expansion, so that there is a well-defined resummation procedure of the perturbative series. We suggest that this mechanism provides a general solution of the IR renormalons problem for massless UV free field theories.     

X-ray photoelectron and Raman studies of microwave Plasma Assisted Chemical Vapour Deposition (PACVD) diamond films

X-ray photoelectron and Raman spectroscopies were used to investigate the chemical and the structural properties of thin diamond films synthesised by Plasma Assisted Chemical Vapour Deposition (PACVD). Continuous polycrystalline diamond films were grown under different plasma conditions and based on the combination of detailed XPS and Raman spectroscopic analysis two main topics are highlighted (i) the stress measurements were discussed by distinguishing clearly the chemical effects from the mechanical effects; (ii) an electronic gap at 2.7 eV probed by Raman resonance that corresponds to an energy loss peak on the XPS carbon signal, was related to the surface hydrogenation.     

Surface analysis for LiBq4 growing on ITO and CuPc film using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS)

We have investigated the morphology and surface electron states of LiBq₄ deposited on ITO and CuPc/ITO, using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The AFM observations indicate that LiBq₄ can form a much more uniform film on CuPc than that on ITO. Furthermore, X-ray photoelectron spectroscopy (XPS) is utilized to further demonstrate the AFM results. From the analysis of XPS, we found that LiBq₄ molecules have poor thermal stability, they are seriously oxidized during depositing; but when a CuPc layer is inserted between LiBq₄ and ITO film, the oxidation and surface contamination of LiBq₄ are significantly reduced. It is then concluded that the introduction of a CuPc buffer layer under the LiBq₄ film can improve the film quality of LiBq₄.The XPS results also testified the fact that no coordination bonds between N atoms and B atoms are formed in LiBq₄ molecules, which make LiBq₄ to be potential blue organic light-emitting material.     

Mass gap and universality for euclidean O(N) and CPN−1 models

From a suitably defined correlation function we evaluate the strong coupling expansion for the mass gap of an euclidean version of the O(N) models in 2D. Good agreement is found for N = 0, 1 and 2 with the known values of the critical temperature and for N ? 3 with the continuum mass gap as evaluated in an hamiltonian approach. Another test of universality based on the use of an asymmetric lattice also yields good results. An analogous discussion for the CP^N?1 models is performed.     

C~+离子内壳激发共振态1s2s(~3S)2p~3的Auger能量和Auger分支率(英文)

利用精确的鞍点变分波函数和鞍点复数转动方法,计算了C⁺离子五电子原子系统内壳激发共振态1s2s（³S）2p^32,4P°,^2,4D°的俄歇能量和俄歇分支率,考察了俄歇跃迁的收敛性,对300 keV C⁺离子和CH₄气体碰撞实验产生的高分辨率俄歇电子谱进行了标定,并指出这些类硼C⁺离子的内壳激发共振态对253～273 eV范围的实验谱线有重要贡献.本文计算结果与实验数据符合得很好.     

C+离子内壳激发共振态1s2s(3S)2p3的Auger能量和Auger分支率

利用精确的鞍点变分波函数和鞍点复数转动方法,计算了C+离子五电子原子系统内壳激发共振态1s2s(3S)2p3 2,4Po, 2,4Do 的俄歇能量和俄歇分支率,考察了俄歇跃迁的收敛性,对300-keV C+离子和CH4气体碰撞实验产生的高分辨率俄歇电子谱进行了标定,并指出这些类硼C+离子的内壳激发共振态对253-273eV范围的实验谱线有重要贡献. 本文计算结果与实验数据符合得很好.     

Surface analysis for catalyst layer (PT/PTFE/C) and diffusion layer (PTFE/C) for proton exchange membrane fuel cells systems (PEMFCs)

X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) studies have been used to analyze the surface of diffusion layer (PTFE/C) and catalyst layer (Pt/C/PTFE) of electrode. Detail analysis of carbon C_1s peak showed that the carbon was of the form of C, C-O, CO, CF, CF₂ and CF₃ with CF₂ is more dominated on the surface compared to CF and CF₃. The oxygen O_1s photoelectron peak showed that the oxygen was of the form of CO and C-O. The platinum was of the form of Pt⁰ with some Pt oxidized to PtO. The scanning electron microscopy was used to observe the dispersion of Teflon in the diffusion layer, the distribution of platinum in the catalyst layer loaded with 0.38 mg Pt/cm² and also the cross section of the membrane electrode assembly. The prepared electrode delivers a superior performance compared with the commercial electrode (E-TEK). The difference in performance between the two electrodes is due to the good localization of the platinum particles.     

Modification of X-ray excited photoelectron and C KVV Auger spectra during radiative carbonization of poly(vinylidene fluoride)

Modifications of the photoelectron and C KVV Auger spectra during the long-term surface degradation of partially crystalline PVDF under simultaneous soft X-ray and electron followed by ion irradiation are reported. Deep radiative carbonization brings about the formation of carbynoid structures (chain-like carbon) in the surface, while the number of interchain cross-links is insignificant. As a result, the shape of the electron emission spectra of carbon in the carbonized sample essentially differs from that of graphite and PVDF. The ion bombardment of the carbonized sample destroys one-dimensional structure due to the formation of cross-links. Thus, carbon atoms transit into sp²-hybrid state and, therefore, the photoelectron and Auger spectra show features characteristic for microcrystalline graphite.     

PTCDA/ITO表面和界面的X射线光电子能谱分析

利用X射线光电子能谱对PTCDA/p-Si有机/无机光电探测器中PTCDA/ITO表面和界面进行了测试分析。结果表明,苝环上的C原子的结合能为284.6 eV,酸酐中的C原子的结合能为288.7 eV,并存在来源于ITO膜中的氧对C原子的氧化现象,界面处C(1s)谱中较高结合能峰消失,且峰值向低结合能发生化学位移;CO键中O原子的结合能为531.5 eV,C—O—C键中的O原子的结合能为533.4 eV。     

Scaling behavior of island density in submonolayer growth of CaF2 on vicinal Si(1 1 1)

We have studied the scaling behavior of two-dimensional island density during submonolayer growth of CaF₂ on vicinal Si(1 1 1) surfaces using scanning tunneling microscopy. We have analyzed the morphology of the Si(1 1 1) surfaces where CaF₂ partial monolayers with coverages of about 0.1 monolayer are deposited at ∼600 °C. The number density of terrace nucleated islands increases with substrate terrace width l as ∼l⁴ in a low island density regime. This scaling behavior is consistent with predictions for the case of the irreversible growth of islands.     

The effect of adsorbed atomic hydrogen on the growth of ultrathin silicon films on Ge(100) studied by positron-annihilation-induced Auger electron spectroscopy (PAES)

The effects of adsorbed atomic hydrogen on the stability of silicon films grown on a Ge(100) substrate were studied by using positron-annihilation-induced Auger electron spectroscopy (PAES) and electron-induced Auger electron spectroscopy (EAES). PAES is almost exclusively sensitive to the topmost atomic layer due to the trapping of positrons in an image potential well just outside the surface before annihilation. This surface specificity was exploited in the study of film stability and interfacial mixing during the growth of silicon on Ge(100). The PAES results show that the prior adsorption of hydrogen prevented the segregation of germanium on top of the deposited silicon, and that the hydrogen adsorption was useful in growing a thermally stable structure.     

Nucleation, growth and properties of Co nanostructures electrodeposited on n-Si(1 1 1)

In the present work, cobalt thin films deposited directly on n-Si(1 1 1) surfaces by electrodeposition in Watts bath have been investigated. The electrochemical deposition and properties of deposits were studied using cyclic voltammetry (CV), chronoamperometry (CA), ex situ atomic force microscopy (AFM), X-ray diffraction (XRD) and alternating gradient field magnetometer (AGFM) techniques. The nucleation and growth kinetics at the initial stages of Co studied by current transients indicate a 3D island growth (Volmer-Weber); it is characterized by an instantaneous nucleation mechanism followed by diffusion limited growth. According to this model, the estimated nucleus density and diffusion coefficient are on the order of magnitude of 10⁶ cm⁻² and 10⁻⁵ cm² s⁻¹, respectively. AFM characterization of the deposits shows a granular structure of the electrodeposited layers. XRD measurements indicate a small grain size with the presence of a mixture of hcp and fcc Co structures. The hysteresis loops with a magnetic field in the parallel and perpendicular direction and showed that the easy magnetization axis of Co thin film is in the film plane.     

Crystal-chemistry from XPS analysis of carbide-derived Mn+1AXn (n=1) nano-laminate compounds

The M_n+1AX_n layered carbide/nitride-derived phases, where M is an early transition metal, A is an A-group element and X is N or C, have an unusual combination of mechanical, electrical and thermal properties. The surface and crystal-chemistries of several recently synthesized n=1 members have been investigated by X-ray photoelectron spectroscopy. The results show that the constituent species are characterized by low binding energies, sometimes exceptionally so. The C 1s energies are in the lower end of the range for carbides, at 281.1-282.0 eV. The M-species—Ti, V, Nb and Hf—have binding energies at or below those corresponding to the elemental metallic state. The binding energies of the A-species in apparent planar coordination—In, Ge, As and Al—are quite exceptional, being 0.5-2 eV below those corresponding to the elemental state. Those results suggest that screening of the A-group species is derived from out-of-plane interactions, while the XPS signatures of the species associated with the MX blocks are reminiscent of those obtained from the relevant carbide phases.     

Systematic study of the product((E(2_2~+)/E(2_1~+)) * B(E2)↑) through the asymmetric rotor model

A systematic study of the product((E(2_2~+)/E(2_1~+))*B(E2)↑) is carried out in the major shell space Z=50-82,N=82-126 within the framework of the asymmetric rotor model where the asymmetry parameter γ0reflects change in the nuclear structure.A systematic study of the product((E(2+)/E(2+))*B(E2)↑) with neutron number N is also discussed.The product((E(2_2~+)/E(2_1~+))*B(E2)↑) provides a direct correlation with the asymmetry parameter γ0.The effect of subshells is visible in Ba-Gd nuclei with N 82,but not in Hf-Pt nuclei with N 104.We study,for the first time,the dependency of the product((E(2_2~+)/E(2_1~+))*B(E2)↑) on the asymmetry parameterγ0.     

Ultrathin film growth and spectroscopic characterization of VOx (0.8x1.3) on Pt(1 1 1)

VO_x ultrathin epitaxial films (0.8x1.3) have been grown on Pt(1 1 1) by evaporating vanadium in a low and well-controlled water background (1×10⁻⁷ Pa). X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and X-ray excited auger electron spectroscopy data strongly indicate that vanadium(II) in the predominant oxidation state. Angle-scanned photoelectron diffraction data are compatible with a single domain film, bearing a rock-salt VO structure and exposing the (1 1 1) plane. Such films evolve toward more oxidized species within hours, probably due to oxidation by residual water in the chamber.     

Fluorination of diamond — C4F9I and CF3I photochemistry on diamond (100)

The radiation-induced decomposition of C₄F₉I and CF₃I overlayers at 119 K on diamond (100) surfaces has been shown to be an efficient route to fluorination of the diamond surface. X-ray photoelectron spectroscopy has been used for photoactivation as well as for studying the photodecomposition of the fluoroalkyl iodide molecules, the attachment of the photofragments to the diamond surface, and the thermal decomposition of the fluoroalkyl ligands. Measured chemical shifts agree well with ab initio calculations of both C 1s and F 1s binding energies. It is found that chemisorbed CF₃ groups on diamond (100) decompose by 300 K whereas C₄F₉ groups decompose over the range 300 to 700 K and this reactivity difference is rationalized on steric grounds. Both of these thermal decomposition processes produce surface C---F bonds on the diamond. The surface C---F species thermally decompose over a wide temperature range extending up to 1500 K. Hydrogen passivation of the diamond surface is ineffective in preventing free radical attack from the photodissociated products of the fluoroalkyl iodides; I atoms produced photolytically abstract H from surface C---H bonds to yield hydrogen iodide at 119 K allowing diamond fluorination. The attachment of chemisorbed F species to the diamond (100) surface causes band bending as the surface states are occupied as a result of chemisorption. This results in a shift to higher binding energy of the diamond-related C 1s levels present in the surface and subsurface regions which are sampled by XPS on the diamond. The use of photoactivation of fluoroalkyl iodides for the fluorination of diamond surfaces provides a convenient route compared to other methods involving the action of atomic F, molecular F₂, XeF₂ and F-containing plasmas.