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The electronic structure of nearly stoichiometric Ni–Mn–Sn and Ni–Mn–In surface is investigated by inverse photoemission and photoemission spectroscopy. Comparison of the experimental and calculated inverse photoemission spectra shows that the dominant feature is related to Mn 3 d -like states. The overall shape and peak position of the theoretically obtained spectra show good agreement with the experimental ultraviolet photoemission valence band spectra. The changes in the composition dependent ultraviolet photoemission spectra reveal the change in degree of Ni 3 d and Mn 3 d band hybridization. Both inverse photoemission and ultraviolet photoemission study show a rigid band shift between Ni 2 MnIn and Ni 2 MnSn because of band filling, due to increase in the number of 5 p electrons from In to Sn. Mn 2 p and 3 s core-level reveal unambiguous existence of exchange splitting in both the materials.

Nanocrystalline zinc oxide (ZnO) thin films have attracted great attention due to their possible applications in optoelectronic devices. The dependence of size and catalyst (indium and fluorine) in ZnO thin films synthesized by spray pyrolysis technique was studied. To understand the chemical bonding structure and electronic states of the catalyst based ZnO thin films, XPS analysis was carried out. A comprehensive micro-Raman scattering study of the phonons in catalyst based ZnO thin films grown in ambient air was made. Low temperature dependent Raman spectroscopy studies were carried out for the detailed structures, vibrations, and in situ size variation of nanostructured thin films. The size and catalyst dependence of the coupling strength between electron and LO phonon was experimentally estimated. The coupling strength determined by the ratio of second to first-order Raman scattering cross sections was found to diminish with decreasing crystallite size, and the Frohlich interaction plays the vital role in electron–phonon-coupling in ZnO. Influence of catalyst on the luminescence properties was investigated.

The authors report a comparative study on ex situ passivation of a near-surface GaAs0.86P0.14/Al0.6Ga0.4As quantum well using various sulfide solutions and nitrogen plasma treatments. The built-in surface electric field is changed via band bending by applying various surface passivation conditions. The band bending is measured using x-ray photoelectron spectroscopy. Reduction in surface electric field in the range of 10–35 kV/cm is observed depending on different passivation conditions. The photoreflectance spectra show enhancement in intensity and blueshift of ∼3 meV accompanied by significant reduction in the broadening parameter of the observed e1-lh1 transitions. Among all the methods studied here, passivation by Na2S⋅xH2O is found to be most effective as it removes the native oxide layer completely leading to almost flat band condition.

Nanocrystalline cerium oxide (CeO 2 ) thin films were deposited onto the fluorine doped tin oxide coated glass substrates using methanolic solution of cerium nitrate hexahydrate precursor by a simple spray pyrolysis technique. Thermal analysis of the precursor salt showed the onset of crystallization of CeO 2 at 300 °C. Therefore, cerium dioxide thin films were prepared at different deposition temperatures from 300 to 450 °C. Films were transparent ( T ~ 80%), polycrystalline with cubic fluorite crystal structure and having band gap energy (Eg) in the range of 3.04–3.6 eV. The different morphological features of the film obtained at various deposition temperatures had pronounced effect on the ion storage capacity (ISC) and electrochemical stability. The larger film thickness coupled with adequate degree of porosity of CeO 2 films prepared at 400 °C showed higher ion storage capacity of 20.6 mC cm − 2 in 0.5 M LiClO 4 + PC electrolyte. Such films were also electrochemically more stable than the other studied samples. The Ce 4+ /Ce 3+ intervalancy charge transfer mechanism during the bleaching–lithiation of CeO 2 film was directly evidenced from X-ray photoelectron spectroscopy. The optically passive behavior of the CeO 2 film (prepared at 400 °C) is affirmed by its negligible transmission modulation upon Li + ion insertion/extraction, irrespective of the extent of Li + ion intercalation. The coloration efficiency of spray deposited tungsten oxide (WO 3 ) thin film is found to enhance from 47 to 53 cm 2 C − 1 when CeO 2 is coupled with WO 3 as a counter electrode in electrochromic device. Hence, CeO 2 can be a good candidate for optically passive counter electrode as an ion storage layer.

The irradiation effect in Ni 3 N/Si bilayers induced by 100 MeV Au ions at fluence 1.5 × 10 14 ions/cm 2 was investigated at room temperature. Grazing incidence X-ray diffraction determined the formation of Ni 2 Si and Si 3 N 4 phases at the interface. The roughness of the thin film was measured by atomic force microscopy. X-ray reflectivity was used to measure the thickness of thin films. X-ray photoelectron spectroscopy has provided the elemental binding energy of Ni 3 N thin films. It was observed that after irradiation (Ni 2p 3/2 ) peak shifted towards a lower binding energy. Optical properties of nickel nitride films, which were deposited onto Si (100) by ion beam sputtering at vacuum 1.2 × 10 −4 torr, were examined using Au ions. In-situ I – V measurements on Ni 3 N/Si samples were also undertaken at room temperature which showed that there is an increase in current after irradiation.

Growth and electronic structure of a 3d transition metal Mn on a free-electron-like metal Al(1 1 1) have been studied by photoelectron spectroscopy and low energy electron diffraction (LEED). A ( 3 × 3 ) R 30 ° LEED is observed at 6 ML Mn coverage, that is related to the α phase of bulk Mn. From the intensity of the adlayer and substrate core-level peaks and angle dependent studies, evidence of primarily layer by layer growth is observed. The Mn 2p core-level for 0.1 ML Mn coverage appears at 0.3 eV lower binding energy with respect to bulk Mn. With increasing Mn coverage, the Mn 2p binding energy increases. An extra component is observed at the lower binding energy side of the Al 2p spectra, that is related to interface alloying. The asymmetric line-shape of bulk-like Mn becomes symmetric for lower Mn coverages.

The formation of ⊥c texture of WS 2 thin films by solid state reaction between the spray deposited WO 3 and gaseous sulfur vapours with Ni interfacial layer has been reported. X-ray diffraction technique has been used to measure the degree of preferred orientation and texture of WS 2 films. Scanning electron microscopy, transmission electron microscopy and atomic force microscopy have been used to characterize the microstructure and morphology. The electronic structure and chemical composition was studied using X-ray photoelectron spectroscopy. The WS 2 films comprise single crystalline quality hexagonal crystallites of 15 μm × 15 μm size with their basal planes parallel to the substrate. The film consists of turbostratic stacking sequence of 2H and 3R polytypes of WS 2 . The tungsten-to-sulfur ratio was estimated to be 1:1.8. The various qualitative models used to explain promotional effects are briefly outlined and the plausible underlying mechanism of formation of ⊥c texture with nickel, in this study, is given.

Highly textured tungsten disulfide (WS2) thin films have been obtained by sulfurization of tungsten trioxide. The properties of WS2 thin films prepared with bismuth interfacial layer as texture promoter has been studied. The WS2 thin films were found to have predominant type-II orientation. The stacking of 2H-WS2 crystallites observed with scanning electron microscopy was not reported hitherto. The films can be pictured as an assembly of WS2 hexagonal crystallites. The energy dispersive X-ray analysis and X-ray photoelectron spectroscopy (XPS) studies confirm that the films are stoichiometric. The XPS analysis described the local environment of the tungsten atoms and the formal oxidation states of the tungsten and sulfur atoms were + 4 and − 2. Together with the high degree of crystallinity and excellent texture of the film, a relatively smooth morphology, on submicron scale, is revealed through atomic force microscopy study. The conditions for the desired textured growth with the van der Waals planes parallel to the substrate surface are reported.

The surface of Ni 2+x Mn 1-x Ga have been studied using X-ray photoelectron spectroscopy under different conditions of surface preparation. We find that the surface becomes Ni rich by argon ion sputtering. However, the change in surface composition due to sputtering can be reverted by annealing at appropriate temperature so that the bulk composition is restored at the surface. The origin of a satellite feature observed both in the valence band and the Ni 2p core-level spectra is discussed. The magnetic microstructures at the surface have been observed by using magnetic force microscopy.

The modifications in surface composition of Ni2.1Mn0.9Ga ferromagnetic shape memory alloy have been investigated using X-ray photoelectron spectroscopy (XPS) under various sputtering and annealing conditions. XPS core-level spectra show that sputtering makes the surface Ni rich. However, by annealing, the Mn content at the surface increases and at about 390 ° C the bulk composition is restored. The valence band spectra show evidence of Ni related extra states for the sputtered surface, which decrease with annealing. This behavior is in agreement with the change in surface composition derived from the core-level spectra.

The electronic structure of quasicrystalline Al–Pd–Mn is investigated by means of valence and core level photoelectron spectroscopy. Variations of the photoionization cross section in the constituents’ valence electronic levels as a function of photon energy are used to identify contributions from the different atomic species, in particular near the Pd 4d Cooper minimum. Resonant photoemission at the Mn 2p absorption edge shows the contribution of the Mn 3d states to the density of states in a region near the Fermi level. The asymmetry of Pd 3d and Mn 2p core level photoemission lines, and its difference for emission fro mm etallic and quasicrystalline phases, are utilized to infer the contributions of the different constituents to the density of states at the Fermi level.

The surface electronic structure of Ag has been studied using angle and energy resolved photoyield (AERPY) using low photon energies (2.7-18 eV). The adlayer standing-wave-like bulk plasmon mode is clearly observed in Ag(1 1 1) and Ag(1 0 0) thin films. A feature at 3.7 eV, observed both on Ag adlayers and bulk crystal surface, is assigned to the multipole plasmon mode. No signature of the multipole plasmon is observed around 6.7 eV, which is in disagreement with the prediction of the s-d polarization model.

Argon ion bombardment on Al(1 1 1) leads to formation of adatoms and sub-surface bubbles. From X-ray photoemission spectroscopy study, we find that the Ar core-levels exhibit a systematic shift in binding energy and change in the line shape as function of ion incidence energy. This is related to the increase in size of the sub-surface bubbles created by argon ion bombardment where the Ar atoms are trapped. Low energy electron diffraction pattern for Al(1 1 1) exhibits broadened spots and enhanced background intensity after bombardment which is related to the formation of random steps and terraces on the surface.

Photons are an alternative probe to electrons or ions for the detection of surface and interface collective modes. We have used synchrotron radiation in conjunction with angle resolved photoyield measurements to study the evolution of overlayer excitation modes in thin alkali layers. Our experimental results show clear evidence of collective modes such as the multipole plasmon, bulk overlayer plasmon and threshold excitation. Both the energy and lineshape of these photoyield resonances show strong thickness dependence. The response of the hidden substrate is rather different. The Al multipole peak shows no energy shift as a function of coverage confirming the absence of an intermediate charge density. We discuss our results in terms of previous dynamical calculations of the surface response.

The annealing temperature dependence of the core-level spectra of the rare gas bubbles implanted in the sub-surface region of Al(111) has been investigated by x-ray photoelectron spectroscopy. A systematic change in the binding energy of the rare gas core-level has been observed, as a function of annealing temperature. The change in binding energy is explained by the increase in bubble size with annealing temperature. Al conduction electron screening of the rare gas core-hole decreases in the photoemission final state with increase in bubble size. We have also observed the decrease in concentration of the rare gas with annealing temperature. The Ne 1s spectra show two components separated by about 1.2 eV and change in intensity with temperature, which is possibly related to a near-surface and a sub-surface distribution of Ne bubbles. The near-surface component gets desorbed faster than the sub-surface component with annealing.

The use of angle- and energy-resolved photoyield experiments for the study of collective excitations at clean metal surfaces and in thin metal films is discussed by recourse to recent experiments. It is shown that photoyield experiments, when compared with theoretical predictions based on the nonlocal corrections to the Fresnel optics, can provide a detailed interpretation of the experimental results for clean surfaces and thin films of simple metals such as Al and the alkali metals. The excitation of so-called multipole plasmons, bulk-like plasmons in thin films, and related multielectron excitations in Al and the heavier alkalis can be quantitatively understood on the basis of jellium-type calculations, whereas lattice effects are shown to be important for a description of the photoyield in Li. Apart from multielectron excitations, features above the plasmon excitations threshold can be understood in terms of single-particle transitions, and the excitation of bulk plasmons with q≠0 by the incident light. Finally, experimental observations of collective modes in more complex surface structures are presented, and the influence of surface electronic structure on the energy of the multipole plasmon is discussed.

High-energy electron energy-loss spectroscopy in transmission has been applied to obtain the absorption spectra at the B 1s, C 1s and Ni 2 p 3 2 excitation edges of bulk polycrystalline YNi2B2C. We find a close similarity in the near-edge structures and confirm the strongly covalent character of the bonding between Ni, B and C. We compare our results to band structure calculations of the local unoccupied density of states generated within the local density approximation. From x-ray photoemission spectroscopy measurements we determine the core level binding energies and from a comparison of photoemission and Auger spectroscopic measurements we derive a value of the Ni d-d Coulomb energy UA of about 4eV.

Electronic structures of gallium and indium in the solid and liquid states have been investigated using photoemission and bremsstrahlung isochromat spectroscopies yielding information concerning the occupied and unoccupied parts of the density of states. Experimental results are compared with various calculations in order to obtain a detailed description. X-ray photoemission spectra of Ga 2p and In 3d core levels exhibit shifts across the solid- liquid transition, arising from changes in screening.

A study is made of the electrooxidation of methanol in sulfuric acid on carbon-supported electrodes containing platinum-tin bimetal catalysts that are prepared by an in situ potentiometric-characterization route. The catalysts are investigated by employing chemical analyses, X-ray diffraction (XRD), X-ray absorption-near-edge spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS) data in conjunction with electrochemical measurements. From the electrochemical data, it is inferred that while an electrode with (3:1) Pt-Sn/C catalyst involves a two-electron rate-limiting step akin to platinum-on-carbon electrodes, it is shifted to a one-electron mechanism on electrodes with (3:2)Pt-Sn/C, (3:3)Pt-Sn/C, and (3:4)Pt-Sn/C catalysts. The study suggests that the tin content in the platinum-tin bimetal catalyst produces: (i) a charge transfer from tin to platinum; (ii) an increase in the coverage of adsorbed methanolic residues with increase in the tin content, as indicated by the shift in rest potential of the electrodes towards the reversible value for oxidation of methanol (0.043 V versus SHE), and (iii) a decrease in the overall content of higher valent platinum sites in the catalyst. © 1994.

Pseudomorphic growth of thin elemental metal films is often observed on a variety of crystalline solids. On quasicrystalline surfaces with their complex structure and the absence of translational periodicity, the situation is different since elemental metals do not exhibit quasicrystalline order, and hence the specific interaction between overlayer and substrate is decisive. Here we study the growth of manganese films on an icosahedral i-Al-Pd-Mn alloy with a view to establishing the growth mode and electronic structure. Although we observe an exponential intensity variation of the adlayer and substrate related x-ray photoemission spectroscopy (XPS) peaks, low energy electron diffraction (LEED) shows that Mn adlayers do not exhibit quasicrystallinity. The detailed structure of the Mn 2p core level line reveals considerable electronic structure differences between the quasicrystalline and elemental metal environment. Evidence of a substantial local magnetic moment on the Mn atoms in the overlayer (about 2.8 µ(B)) is obtained from the Mn 3s exchange splitting.

We present a design of a compact and versatile sample holder meant for studying complex (ternary) metallic crystals that require sputtering and annealing to high temperatures under ultrahigh vacuum (10(-10) mbar range) for obtaining the clean, ordered and stoichiometric surface. A resistive heater is fixed to the sample holder and not to the sample plate, and thus can be thoroughly degassed initially to high temperatures without heating the sample. The heater, which is mounted vertically on the sample holder frame, slides into the sample plate of rectangular cross-section during sample transfer. For efficient cooling that is required for adlayer deposition, Cu braids can be pressed on the sample plate from both sides through a screw mechanism. The sample holder has 5 degrees of freedom including a tilt rotation. The sample holder has been used to study different metal surfaces such as ferromagnetic shape memory alloys, alkali metal and Mn adlayers on Al-Pd-Mn quasicrystal, aluminum metal, and Al-Mn alloys. Here, our recent results on temperature dependent low energy electron diffraction study of Ni(2)MnGa(100) are presented.

The authors report a comparative study of the L3-M45M45 Auger spectra of Cu, Cu2O and CuO. The large intensity of the uncorrelated two-hole band-like spectrum in the L3-M45M45 Auger spectra of Cu2O and CuO and the spectral shapes for these transitions indicate strong Cu 3d-O 2p hybridization in the oxides. The L2-L3M45 CK rates obtained for these compounds indicate the stability of the Cu 3d level with increasing oxidation state of Cu. They also provide a quantitative estimate of the contributions of the different processes that lead to the formation of the L3-M45M45 Auger satellite in Cu, Cu2O and CuO.

Aluminum bulk, surface, and multiple plasmons have been observed in the core-level spectra of rare gas (Ne, Ar, and Xe) nanobubbles in Al, whose intensities are even higher than those of Al metal. Both intrinsic and extrinsic bulk plasmons are detected, but they exhibit diametrically opposite intensity variation due to change in the size and implantation depth of the bubbles. Furthermore, the existence of bubble surface plasmon is demonstrated.

Ne 1s core-level photoelectron spectra from Ne nanobubbles implanted in aluminum exhibit two peaks whose binding energies and relative intensities change with implantation energy, isochronal annealing, and sputtering. These changes in the core-level spectra are manifestations of the nanometer size of the bubbles since the screening of the photohole by the Al conduction electrons depends on the bubble size. Existence of a bimodal depth and size distribution of Ne nanobubbles is demonstrated in this work: smaller bubbles of about 4 A in radius are formed close to the Al(111) surface while the larger sized bubbles of 20 A in radius exist deeper below in the beneath subsurface region. A general relation between the radius of the rare-gas bubbles and their core-level binding energies is established.

Using high-resolution core-level photoelectron spectroscopy and modified Anderson impurity model calculations, we study the $\mathrm{Mn}\phantom{\rule{0.2em}{0ex}}2p$ spectrum of manganese metal and resolve the current debate about its spectral shape. An unusual satellite feature, $1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ from the main peak, is observed in the $\mathrm{Mn}\phantom{\rule{0.2em}{0ex}}2{p}_{3∕2}$ spectrum of a thick Mn layer grown on Al. It originates from intra-atomic multiplet effect related to Mn atoms with large local moment. The satellite decreases in intensity for thin Mn layers and for Al deposition on bulklike Mn because of enhanced $\mathrm{Mn}\phantom{\rule{0.2em}{0ex}}3d$ hybridization with Al $s,p$ bandlike states. The reason for the absence of a charge-transfer satellite is discussed.

The valence band discontinuity of the n-type cubic GaN/GaAs heterojunction is measured by means of angle-resolved photoemission spectroscopy using synchrotron radiation. High quality cubic GaN films are grown on GaAs(100) substrates by nitrogen plasma-assisted molecular beam epitaxy, and the valence band discontinuity is determined by a combination of core and valence level spectra. A value of ΔEV=(1.84±0.1) eV across the GaN/GaAs heterojunction is obtained, which means that the discontinuity in the conduction bands at this interface is very small, such that a vertical contact scheme may be realized for GaN/GaAs heterojunctions.

Performance and characteristics of a band-pass photon detector using acetone gas and CaF_2 window (acetone/CaF_2) have been studied and compared with an ethanol/MgF_2 detector. The optimal operating conditions are found to be 4 mbar acetone pressure and 745+/-20 V anode voltage. The count rate obtained by us is about a factor of 3 higher than what has been reported earlier for the acetone detector. Unlike other gas filled detectors, this detector works in the proportional region with very small dead time (4 micro sec). A detector band-pass of 0.48+/-0.01 eV FWHM is obtained., Review of Scientific Instruments 76, 066102 (2005)

Two fundamental manifestations of Al conduction electron response to Ar atom core hole in the final state of photoemission have been studied in implanted Ar bubbles in Al(111). Ar $2p$ binding energy and the Doniach-\ifmmode \check{S}\else \v{S}\fi{}unji\ifmmode \acute{c}\else \'{c}\fi{} asymmetry of the core-level line shape vary systematically as functions of ${\mathrm{Ar}}^{+}$ implantation energy and number of ions bombarded (fluence). The observations are explained by relating the strength of Al conduction electron screening to the size of the Ar nanobubbles.

Large blueshift was observed in a near-surface GaAs0.86P0.14/Al0.7Ga0.3As quantum well upon treatment with Na2S·xH2O solution. Very slow etching with simultaneous surface passivation of the quantum well was obtained using this chemical treatment. Photoreflectance (PR) spectra exhibit maximum blueshift of 28 meV after treating the quantum well surface with Na2S·xH2O solution for 30 min (top layer thickness reduced to 10 A). The blueshift is attributed to an increase in the confinement and/or an image charge effect due to the penetration of the wave function into vacuum. The blueshift is accompanied by a significant reduction in the broadening parameter of the observed e1-lh1 transition in PR spectra indicating effective passivation along with an increase in the confinement.

The formation of Ar bubbles in Al has been investigated by using depth-resolved positron annihilation spectroscopy and transmission electron microscopy. Due to Ar bubble formation, the Doppler-broadening S parameter decreases, while the W parameter increases compared to the reference unimplanted Al sample. The effect of Ar ion fluence and annealing temperature on these parameters has been investigated. The presence of Ar at near-surface region has been confirmed by Rutherford backscattering spectroscopy. Transmission electron microscopy also shows that the Ar bubbles are in solid state with fcc structure after annealing at 870 K. The average diameter and lattice parameter of these solid Ar bubbles are estimated to be about 4±1 nm and 0.495±0.005 nm, respectively.

The temperature-dependent nucleation and growth mechanism of electrodeposited zinc oxide (ZnO) thin films on fluorine-doped tin-oxide-coated (10–20 Ω cm−2) glass substrates from an acetate solution was studied by using the chronoamperometry technique. The morphological, compositional and structural properties were studied by scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS) and x-ray diffraction techniques. The current transients were analyzed by fitting chronoamperometric data into the Scharifker–Hills nucleation model, which reveals a change in the nucleation and growth mechanism from progressive to intermediate (progressive + instantaneous) to instantaneous with a rise in bath temperature (from 25 °C to 75 °C). The SEM study showed hexagonal grains for the films obtained at 35 °C. The x-ray diffraction spectra revealed the formation of phase-pure ZnO thin films. The chemical state of the deposit was confirmed by XPS measurements.