Nature of the well screened state in hard X-ray Mn 2p core-level photoemission measurements of La1-xSrxMnO3 films

Using hard x-ray (HX; hnu=5.95 keV) synchrotron photoemission spectroscopy (PES), we study the intrinsic electronic structure of La(1-x)Sr(x)MnO(3) (LSMO) thin films. Comparison of Mn 2p core-levels with soft x-ray (SX; hnu approximately 1000 eV) PES shows a clear additional well-screened feature only in HX PES. Takeoff-angle dependent data indicate its bulk (> or =20 A) character. The doping and temperature dependence track the ferromagnetism and metallicity of the LSMO series. Cluster model calculations including charge transfer from doping-induced states show good agreement, confirming this picture of bulk properties reflected in Mn 2p core-levels using HX PES.     

Vanadium-induced decrease in the magnetization of a VxCo1−x alloy film on the W(110) surface

The magnetic and structural properties of a series of V_xCo_1?x alloy films prepared in a variety of compositions on a W(110) surface were investigated using spin-resolved photoemission spectroscopy (SRPES) and low-energy electron diffraction (LEED) measurements. The epitaxial structures of the films were preserved over all V concentrations, despite the observation of a structural phase transition (SPT: hcp/bcc at x = 0.38), which was apparent from the LEED images. A magnetic phase transition (MPT) from ferromagnetic to paramagnetic occurred in the Co-rich region at x = 0.38. The SPT (from hcp and bcc) and MPT (from ferromagnetic to paramagnetic) were clearly correlated at x = 0.38, possibly due to changes in the electronic and magnetic structures of the valence band, as monitored by SRPES and LEED. The magnetization in the V_xCo_1?x alloy films on a W(110) surface varied systematically with the V concentration, and correlations between the structural changes and magnetic properties were revealed using SRPES and LEED.     

Dominance of the final state in photoemission mapping of the fermi surface of Co/Cu(001)

The Fermi surface of tetragonally distorted fcc Co films grown on Cu(001) has been investigated with first-principles calculations and compared with an experimental determination using angle-resolved photoemission. The angular distributions for hnu=21-45 eV are dominated by the structure of the final states rather than by the shape of the Fermi surface. Theoretical estimates of the photoemission matrix elements support this observation. This suggests that photoemission can have limitations in mapping Fermi surfaces, especially for materials that exhibit flat, closely spaced valence bands.     

砷化镓上银和金膜的价带光电子谱

木文测量了光子能量为21.2eV,40.8eV和1486.6eV的光电子谱,得到了关于GaAs(110)解理面上银膜的价带能谱新数据,并得到金膜价带能谱的补充数据,蒸发的银膜和金膜的厚度范围为0.l?到1000?,实验上发现并讨论了下面的现象:GaAs(110)面上金膜和银膜的紫外价带光电子谱的强度与膜厚的关系曲线中出现极大峰。 关键词：     

Work function changes of W(110) with temperature and Sm adsorption using electron beam retarding potential technique

We have studied the work function changes (ΔΦ) of W(110) by Sm adsorption as a function of Sm thickness at room temperature and also that of the Sm-covered W(110) as a function of temperature. The work function change was monitored using the electron beam retarding potential technique in conjunction with low energy electron diffraction (LEED). It is found that the work function of W(110) decreases rapidly at lower dose (0.75 Å) of Sm, touches a minima (ΔΦ=0.32 eV), then increases slightly and is saturated with further Sm dosing. Besides, it was also found that the work function of W(110) reduces by 0.3 eV at a particular dose of Sm with substrate temperature up to 523 K. These results show a strong dependence of the work function of W(110) on its temperature and adsorption of Sm and this can be used to advantage in the making of emitters.     

GaAs表面硫化学钝化,CH3CSNH2处理新探

应用同步辐射光电子谱（SRPES）和光致荧光（PL）方法探讨不同钝化条件对GaAs表面键合状态和电子态的影响．发现无论在酸性溶液或碱性溶液条件下，经过CH₃CSNH₂处理的GaAs表面S都与Ga和As成键，形成硫化物钝化层；钝化层形成后，PL谱的强度明显增强，表明GaAs表面复合中心的减少和缺陷态密度的降低 关键词：     

The trapping of K and Na atoms by a clean W(110) surface trajectory calculations

The fraction of K and Na atoms initially trapped by the W(110) surface has been measured as a function of the incident energy (0.5–15 eV) and as a function of the incident angle. The trapping probability equals one at low incident energies (E_i ? 0.5 eV) and decreases with increasing energy. The measurements show an increase of trapping with increasing angle of incidence θ_i (measured from the surface normal). Simultaneously the desorption energies Q_i were determined from the temperature dependence of the measured mean residence time on the W(110) surface. We obtained for K: Q_i = 2.05 ± 0.02 eV, and for Na: Q_i = 2.60 ± 0.04 eV.The trapping phenomenon at a solid surface was approximated in a theoretical way by calculating the in-plane trajectory of a projectile scattered from a diatomic surface-molecule. The important feature which showed up was the conversion of tangential to normal momentum of the projectile, and thus the inapplicability of cube models. As a function of the angle of incidence two regimes can be distinguished: at the smaller angles the scattering is governed by simultaneous interaction of the projectile with two neighbouring surface atoms, and at the higher angles of incidence the single particle interaction contributes most to the momentum transfer.     

Surface state scattering at a buried interface

The free-electron-like surface state of Mg(0001) is strongly modified in thin films grown on W(110). The long bulk penetration length of its wave function makes it sensitive to the reflective properties of the buried interface, and hence to the complex electronic structure of the substrate. In particular we find a many-fold splitting of the Mg surface band by entering a wide projected band gap of W(110). There is a strong thickness-dependent two-band splitting, which is a clear signature of the formation of a surface-interface resonant state. An additional split-off from these two surface bands is explained by the substrate induced spin-orbit interaction.     

Oxidation kinetics of thin titanium films grown on tungsten

Growth of thin Ti films on (100)W and the kinetics of their oxidation are studied using thermal-desorption spectroscopy and Auger electron spectroscopy. Titanium films grow nearly layer by layer on the (100)W face at room temperature. The activation energy for desorption of Ti atoms decreases from 5.2 eV for coverage θ=0.1 to 4.9 eV in a multilayer film. Oxidation of a thin (θ=6) titanium film starts with dissolution of oxygen atoms in its bulk to the limiting concentration for a given temperature, after which the film oxidizes to TiO, with the TiO₂ oxide starting to grow when exposure of the film to oxygen is prolonged. The thermal desorption of oxides follows zero-order kinetics and is characterized by desorption activation energies of 5.1 (TiO) and 5.9 eV (TiO₂).     

Low-energy electron energy-loss spectroscopy with Ge:GaAs (110) heterostructures

Electronic properties and chemical composition of Ge films grown by molecular beam epitaxy on GaAs (110) surfaces were studied in situ by electron energy-loss spectroscopy. The loss peaks involving core-level excitations proved that As atoms segregate at the surface of the growing film. The well known 20 eV loss peak of the clean GaAs (110) surface, being attributed to transitions from Ga(3d) to Frenkel-type excitons of dangling-bond surface states, was found to persist, slightly shifted to 19.7 eV, with the growing Ge (110) film. Since the Ga coverage amounts to below approximately 0.05 of a monolayer this transition seems to contain a strong intraatom contribution.     

Initial growth of Cu films on oxygen covered W(110)

The growth of Cu films on the p(2 × 1)O-W(110) and (1 × 1)O-W(110) surfaces has been monitored using specular He scattering. Deposition at temperatures below 200 K leads to rough films on both surfaces. Deposition at T > 300 K leads to phase separation of Cu and O on the p(2 × 1)O-W(110) surface. Deposition at 300 K on the higher oxygen coverage surface leads to films which are nearly as smooth as these deposited on clean W(110). Deposition at 800 K leads to needle-like crystallite formation without an initial continuous film.     

Transmission of low-energy (< 10 eV) O ions through Au films on TiO2(110)

In an attempt to identify the fundamental processes that influence ion transport through metallic surface layers, we have studied the transmission of O⁺ ions through discontinuous Au films adsorbed on TiO₂(110). A low energy (< 10 eV) O⁺ ion beam is generated via electron stimulated desorption when an Au-dosed TiO₂(110) substrate is bombarded with a focused 250 eV electron beam. Low energy ion scattering data indicate that Au evaporated under ultrahigh vacuum conditions at 300 K forms three-dimensional clusters on TiO₂(110). As the Au coverage increases, the formation of Au clusters on TiO₂(110) blocks a fraction of the TiO₂ surface and the O⁺ yield is attenuated. However, for high coverages (≥30% Au covered substrate) the O⁺ signal decreases at a faster rate than the TiO₂ open area fraction. We attribute the attenuation of the O⁺ yield for high Au coverages mainly to blocking of O⁺ by Au clusters, to deflection of trajectories by the image force between ions and Au clusters, and to charge transfer between desorbing O⁺ and neighboring Au clusters.     

A study of local density of states of atom clusters on the W(110) surface

The kinetic energy distributions of field desorbed He ions from tungsten clusters of one to five atoms on a W(110) surface are measured using a high resolution pulsed-laser time-of-flight atom probe. The He field ion energy distribution from the single W adatom shows an extra peak-like feature centered at 2.7 eV above the Fermi level. It has a full width at half maximum (fwhm) of 2.3 eV. The data from two tungsten adatoms separated by two lattice constants have nearly the same feature with the extra peak located at 2.5 eV above the Fermi level. These peaks arise from resonance tunneling with the adatom local density of states (LDOS). The He ion energy distribution of a tungsten dimer has an extra peak centered at 1.5 eV above the Fermi level. The fwhm is about 4 eV. The spectra from four and five tungsten adatom clusters show only one peak each, similar to that from a flat plane.     

The study on Schottky contact between Au and clean CdZnTe

Au Schottky contact was deposited on the clean CZT (1 1 0) and (1 1 1) A surface by molecular beam epitaxy (MBE). The real Schottky barrier heights were measured to be 0.738 eV and 0.566 eV by Synchrotron radiation photoemission spectroscopy (SRPES) respectively. The constituents of (1 1 0) and (1 1 1) A surfaces were measured by XPS. The Te concentration on (1 1 1) A surface is higher than that of (1 1 0) surface. And the difference of chemical reactivity and charge transfer were identified by Au 4f_7/2, Cd 4d, Te 4d_5/2 core level shifts using SRPES. Using metal-induced gap states model, the results of experiment were explained.     

Spectra of quantum states in thin metal films and their modification: Al/W(110) system

The modification of spectra of quantum well states of sp-type in thin Al films on the W(110) surface was experimentally investigated by angular-resolved photoelectron spectroscopy both during deposition and in dependence of the detection angle. Quantum well states are observed for the partially filled band of valence states in the range of binding energies from 4.4 eV to the Fermi level. An Al film with a thickness of 11 monolayers exhibits a jump of the dispersion relations of quantum well states in the local W(110) band gap in the ΓS direction and splitting of these relations due to the effect of substrate electronic structure on the formed spectrum of quantum states and their possible spin polarization.     

Coexistence of strongly mixed-valence and heavy-fermion character in SmOs4Sb12 studied by soft- and hard-X-ray spectroscopy

Sm-based heavy-fermion compound SmOs4Sb12 has been investigated by soft x-ray (hnu=1070-1600 eV) and hard x-ray (HX; hnu=7932 eV) spectroscopy. The HX photoemission spectroscopy clearly demonstrates that the strongly mixed-valence state and the heavy-fermion state coexist in the bulk. It is found that the Sm valence decreases below 100 K, indicating that the Kondo coherence develops with approaching the proposed Kondo temperature. Our theoretical analyses suggest that the origin of the coexistence in SmOs4Sb12 is the coincidence of two conditions, namely, (i) the energy difference between Sm divalent and trivalent states is very small and (ii) the hybridization between Sm 4f and conduction electrons is weak.     

The adsorption of CO and oxygen on Cu layers on a W(110) surface

The adsorption of CO, and to a lesser extent that of oxygen on Cu layers deposited on a W(110) surface has been investigated by thermal desorption. Auger, and XPS measurements. For CO the amount adsorbed decreases monotonically with Cu thickness from 1–5 layers. For O there is a slight increase for 1 layer, followed by a steep decrease up to 4 Cu layers where the amount adsorbed levels off. CO adsorption shifts the core levels of Cu (observed for 1 layer of Cu) to higher binding energy by 0.4 eV; the O 1s level of CO is also shifted to higher binding energy by 1.5 eV, relative to CO/W(110) suggesting that electron transfer from CO occurs but is passed on to the underlying W. For O adsorption there is very little shift in the Cu core levels or in the O 1s level, relative to O/W(110). Thermal desorption of CO at saturation coverage from Cu/W(110) shows desorption peaks at 195, 227 and 266 K, as well as small peaks associated with CO desorption from clean W, namely a peak at 363 K and β-desorption peaks at 1080 and 1180 K. As CO coverage is decreased the 195 and 227 K peaks disappear successively; the W-like peaks remain unchanged in intensity. It is argued that the latter may be due to adsorption on bare W at domain boundaries of the Cu overlayer, while the 190–266 K peaks are associated with adsorption on Cu, but probably involve reconstruction of the Cu layer. For n = 2–8 a single but composite peak is seen, shifting from 180 to 150 K as Cu thickness increases as well as a minor peak at 278 K, which virtually vanishes on annealing the Cu deposit at 850 K. The effect of tungsten electronic structure on the behavior of adsorbates on the Cu overlayers, as well as similar effects in other snadwich systems are discussed.     

体心立方金属W薄膜晶体取向的膜厚尺寸效应及其表面映射

体心立方W膜(110)织构系数T₁₁₀的变化存在非单调的厚度尺寸效应，这依赖于薄膜中晶粒形核和长大时表面能和应变能的相互作用，薄膜表面结构演变反映了两者的竞争过程.应用小波变换结合分形几何描述薄膜表面结构各向异性行为，用此法构建了薄膜织构系数T₁₁₀与表面结构各向异性的关系，表明薄膜晶体取向存在表面映射. 关键词： 金属薄膜 晶体取向 膜厚 表面形貌     

低覆盖度的Au/GaN(0001)界面的同步辐射研究

利用同步辐射光电子能谱研究了低覆盖度Au在GaN(0001)表面的初始生长模式,肖特基势垒高 度以及界面的电子结构.结果表明，Au沉积初始阶段有界面的化学反应,随后呈三维岛状生长 .由光电子能谱实验确定的肖特基势垒高度为14 eV. 通过对界面价带谱和Au 4f芯能级谱 的分析,确定了界面化学反应的存在.利用线性缀加平面波方法计算了GaN(0001)和Au的价带 态密度并分析了化学反应产生的机理,认为在初始阶段界面形成了Au_Ga合金. 关键词： 同步辐射 光电子能谱 Au/GaN欧姆接触 态密度     

Properties of ultrathin layers of palladium on a tungsten {110} surface

The growth mode, structure, thermal stability and work function of Pd films up to several monolayers in thickness on a W{110} surface are studied. At room temperature, layer-by-layer growth occurs, at least up to 4 layers. Layers in excess of the first monolayer are metastable and agglomerate at substrate temperatures above 700 K. Pd-W and Pd-Pd interactions within the first layer are investigated with thermal desorption techniques. The binding energy for single Pd atoms to the substrate is 3.6 eV/atom, the energy per lateral bond between nearest Pd atoms is about 0.05–0.12 eV/bond dependent upon range of interaction. These data are based on a phase transition occurring during the desorption of the first layer. The desorption of Pd in excess of the first monolayer is similar to the sublimation of bulk Pd.