X-ray Angle-resolved Photoemission Research Articles

Annealing-temperature Dependence of Compositional Depth Profiles and Chemical Bonding States of CeOx/LaOx/Si and LaOx/CeOx/Si Structure

We have investigated the influence of post deposition annealing (PDA) on compositional depth profiles and chemical structures of CeOx/LaOx/Si(100) and LaOx/CeOx/Si(100) interfaces by angle-resolved X-ray photoemission spectroscopy. Analyses of Ce 3d and O 1s spectra show that a Ce oxidation state changes from Ce4+ to Ce3+ by PDA in N2 at and above 500{degree sign}C and changes from Ce3+ to Ce4+ by PDA in O2 at 300{degree sign}C. This implies that a Ce oxidation state can be controlled by changing the condition of PDA. The diffusion of Ce and La atom occurs at CeOx/LaOx interface by PDA above 500{degree sign}C.

X-ray Photoelectron Spectroscopy characterization of native and RCA-treated Si (111) substrates and their influence on surface chemistry of copper phthalocyanine thin films

In this paper native and RCA-treated n- and p-doped Si(111) substrates and ultra-thin 16-nm copper phthalocyanine (CuPc) layers deposited thereon were investigated using X-ray Photoemission Spectroscopy and Angle-Resolved X-ray Photoemission Spectroscopy. The oxide layer thickness was determined to be 1.3 nm on the RCA-treated substrates and 0.8 nm on the native ones. The analysis of substrate carbon contamination showed the existence of C–H, C–OH and COOH components on all substrates. The RCA clean removes more readily the carbon components with the OH group from the n-type Si and causes the segregation of the contaminants. The initial carbon species propagate in the evaporated CuPc layer up to a thickness of about 5 nm affecting the shape of the C1s peak. Additionally, the behavior of the binding energy difference between N1s and Si2p peaks upon the CuPc growth shows that there may occur various CuPc molecule adsorption modes on investigated Si substrates. It could be a useful information, from the technological point of view, especially for low dimensional electronic device preparation.

Anisotropic Electric Conductivity of DelafossitePdCoO2Studied by Angle-Resolved Photoemission Spectroscopy

An explicit connection between the electronic structure and the anisotropic high conductivity of delafossite-type PdCoO2 has been established by angle-resolved photoemission spectroscopy (ARPES) and core-level x-ray photoemission spectroscopy. The ARPES spectra show that a large hexagonal electronlike Fermi surface (FS) consists of very dispersive Pd 4d states. The carrier velocity and lifetime are determined from the ARPES data, and the conductivity is calculated by a solution of the Boltzmann equation, which demonstrates that the high anisotropic conductivity originates from the high carrier velocity, the large two-dimensional FS, and the long lifetime of the carriers.

Annealing-temperature Dependence of Compositional Depth Profile and Chemical Structures of LaOx/ScOx/Si and ScOx/LaOx/Si Interfacial Transition Layer

We have investigated the effects of post deposition annealing (PDA) on chemical structures of 4nm-LaOx, 4nm-ScOx/Si, 2nm-LaOx/2nm-ScOx/Si and 2nm-ScOx/2nm-LaOx/Si interfaces by angle-resolved X-ray photoemission spectroscopy. Analyses of Si 2s spectra show that the reactivity between ScOx and Si substrate is lower than that between LaOx and Si substrate. Analyses of O 1s spectra show that the absorption of moisture in the LaOx is suppressed by 2nm-ScOx/2nm-LaOx/Si structure. In addition, the electronic band structure of ScOx/Si(100) was decided.

Comparative Sb and As segregation at the InP on GaAsSb interface

We study the formation of the InP on GaAsSb interface grown by molecular beam epitaxy at 450 °C. Using angle resolved x-ray photoemission spectroscopy (XPS), we show that Sb strongly segregates whereas As does not, leading to a Sb-rich InP surface. Similarly, XPS spectra recorded on air-exposed samples reveal oxidized Sb but no oxidized As. We perform a quantitative analysis and determine a Sb segregation coefficient very near to 1. This result is in good agreement with previous reflectance anisotropy spectroscopy observations on the same interface.

Doping evolution of the electronic structure in the single-layer cuprateBi2Sr2−xLaxCuO6+δ: Comparison with other single-layer cuprates

We have performed angle-resolved photoemission and core-level x-ray photoemission studies of the single-layer cuprate ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{La}}_{x}\mathrm{Cu}{\mathrm{O}}_{6+\ensuremath{\delta}}$ (Bi2201) and revealed the doping evolution of the electronic structure from the lightly doped to optimally doped regions. We have observed the formation of the dispersive quasiparticle band, evolution of the Fermi ``arc'' into the Fermi surface, and the shift of the chemical potential with hole doping as in other cuprates. The doping evolution in Bi2201 is similar to that in ${\mathrm{Ca}}_{2\ensuremath{-}x}{\mathrm{Na}}_{x}\mathrm{Cu}{\mathrm{O}}_{2}{\mathrm{Cl}}_{2}$ (Na-CCOC), where a rapid chemical potential shift toward the lower Hubbard band of the parent insulator has been observed, but is quite different from that in ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}$ (LSCO), where the chemical potential does not shift, yet the dispersive band and the Fermi arc and/or surface are formed around the Fermi level already in the lightly doped region. The (underlying) Fermi surface shape and band dispersions are quantitatively analyzed using tight-binding fit, and the deduced next-nearest-neighbor hopping integral ${t}^{\ensuremath{'}}$ also confirms the similarity to Na-CCOC and the difference from LSCO.

Epitaxial Growth and Surface Properties of Half‐Metal NiMnSb Films

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Aluminum diffusion and reaction in thin films of perylene-3,4,9,10-tetracarboxylic dianhydride: Depth profiles and time-dependent diffusion coefficients

Diffusion and reaction of aluminum metal species (Al) vacuum deposited on perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) thin films were investigated using angle resolved x-ray photoemission spectroscopy. The acquired data were analyzed assuming that the diffusion of Al is described by a one-dimensional diffusion equation with a time-dependent diffusion coefficient. Depth profiles and diffusion coefficients are obtained for reacted and metallic Al separately. The results show that the metallic Al diffuses rapidly during the deposition while the metal diffusion continues at a lower rate even after the deposition at room temperature. On the other hand, the reacted Al does not diffuse further into the PTCDA layers.

Epitaxial growth and surface properties of half-metal NiMnSb films

We present, herein, an extended study of the half-Heusler alloy NiMnSb, starting with thedeposition technique, continuing with the basic structural and magnetic properties of thethin films, and finishing with the electronic and compositional properties of their surfaces.The experimental methods we apply combine magnetization and magnetoresistivitymeasurements, atomic force microscopy, ferromagnetic resonance, x-ray and neutrondiffraction, low energy electron diffraction, angle resolved x-ray photoemission, extendedx-ray absorption fine structure spectroscopy, soft x-ray magnetic circular dichroism andspin polarized inverse photoemission spectroscopy. We find that stoichiometric surfacesexhibit close to 100% spin polarization at the centre of the surface Brillouin zone at theFermi edge at ambient temperatures. There is strong evidence for a moment reorderingtransition at around 80 K which marks the crossover from a high polarization state(T<80 K) to a more representative metallic ferromagnetic state(T>80 K). The results from the different experimental techniques are successively reviewed, withspecial emphasis on the interplay between composition and electronic structure of theNiMnSb film surfaces. Surface segregation, consistent with a difference in free enthalpybetween the surface and the bulk, is induced by annealing treatments. This surfacesegregation greatly reduces the surface polarization.

Angle resolved X-ray photoemission spectroscopy double layer model for in situ characterization of metal organic chemical vapour deposition nanometric films

In situ Angle Resolved X-ray Photoemission Spectroscopy (ARXPS) characterizations of TiO 2 thin films grown on silicon by Metal Organic Chemical Vapour Deposition were performed in order to get information on interfacial reactions at the first stages of the growth, one of the aims being to understand the influence of deposition conditions. Thickness measurements were also carried out from ARXPS analyses. As the real structure of the films was shown to be a double layer system such as TiO 2/SiO 2/Si, an ARXPS model of thickness and surface coverage determination was applied to each layer independently. However, the application of this model to very thin films underestimates the surface coverage of the interfacial layer. A “Double Layer” model taking into account the attenuation of the silicon oxide and substrate signals by the external layer was also developed.

Electronic Structure at Tetratetracontane/Au(111) Interface

AbstractModification of the quasi two-dimensional surface state on Au(111) surface with adsorption of n-alkane molecule, tetratetracontane: TTC was investigated by angle-resolved photoemission spectroscopy (ARUPS) and X-ray photoemission spectroscopy (XPS). From ARUPS the energy band structure of the surface state of Au(111) surface is found to be significantly affected by TTC adsorption. The modified surface potential on Au(111) surface by the adsorption confines the surface electrons into the quantum well newly established between TTC wide energy gap and sp band gap of the Au(111) surface increasing its localization nature. Clear chemical shift in C 1s core level was observed in XPS spectrum for TTC layer right at the interface and small back-donation from Au(111) surface to TTC unoccupied states is suspected. On the other hand, a large interface dipole layer about 0.72 eV was observed by TTC adsorption. From these results, Pauli repulsion effect is expected not to have dominant effect on such large dipole formation on TTC adsorption.

Interaction of alkali metals with perylene-3,4,9,10- tetracarboxylic–dianhydride thin films

n doping of the molecular organic semiconductor perylene-3,4,9,10-tetracarboxylic–dianhydride (PTCDA) is often achieved by use of alkali metals as dopants. This doping process is commonly performed in two steps. In the first the dopant is evaporated onto the surface of the PTCDA film. As it has been believed that the dopant shows an inhomogeneous diffusion profile through the layer with most of the dopant accumulated in the first few layers, a subsequent annealing step has been performed in order to reach a homogeneous distribution of the dopant in the whole layer. In this paper experimental results concerning chemical composition ((angle resolved) X-ray photoemission spectroscopy, secondary-ion-mass spectrometry, Fourier transform infrared spectroscopy), electronic structure (ultraviolet photoemission spectroscopy, inverse photoemission spectroscopy), as well as electrical properties (conductivity, Seebeck coefficient) are shown before and after doping and before and after annealing. These results suggest that the deposited dopant is redistributed and partially removed during the annealing step. A model for the dopant distribution is suggested.

Distinguishing magnetic-moment and magnetic-ordering behavior in transition metal alloys

We report dichroism in angle-resolved X-ray photoemission with linearly polarized synchrotron radiation (MLDAD) of the 3p core levels of the ferromagnetic metals Fe, Ni, and their binary alloys. This technique is characterized by elemental specificity and surface sensitivity. A method has been introduced to accurately measure the magnetic dichroism asymmetry peak-to-peak amplitudes, AMLDAD, and the spectral width, WMLDAD. AMLDAD is a measure of the overall saturation magnetization, while WMLDAD reflects the magnitude of elemental magnetic moments. Deviations at the Invar composition Fe65Ni35 are due to changes in magnetic order.

Scalability and Electrical Properties of Germanium Oxynitride MOS Dielectrics

In this letter, we present a fundamental study on the scalability and electrical properties of germanium oxynitride dielectrics for metal-oxide-semiconductor device applications. The nitrogen depth profile within the oxynitride dielectric layers was first monitored using angle-resolved x-ray photoemission spectroscopy and the dielectric permittivity variation was therefore identified. After thinning down the lower permittivity portion of these dielectrics, we successfully scaled down the capacitance-based equivalent SiO/sub 2/ thickness, in Ge MOS capacitors, to 1.9 nm without suffering from gate leakage. We have also investigated the effects of thermal annealing on various capacitor electrical properties. For instance, we measured a flat-band voltage shift of as much as -0.8 V from the ideal value on as-deposited capacitors and the recovery of the theoretical value, with acceptably small amount of oxide fixed charge, after subsequent thermal annealing. Lastly, we have benchmarked the performance of these oxynitride insulators with the advanced high-/spl kappa/ dielectrics on Ge and discussed the impacts on future scaling.

Interface composition and electronic properties of chromium (III, IV) oxides junctions

Air oxidation of chromium films is investigated as an alternative technique for making chromium (III, IV) oxides junctions, of interest for magnetoelectronics applications. Characterization of the surface by angle-resolved X-ray photoemission spectroscopy (ARXPS) shows that a surface layer of insulating Cr 2O 3 is covering metallic CrO 2. The phase separation of the two types of oxides is more pronounced after increased oxidation. Low-temperature electric transport curve confirms the zero-bias anomaly observed in the past on oxidized chromium junctions.

Fabrication of InN/Si heterojunctions with rectifying characteristics

InN/Si heterojunctions consisting of InN with an oxygen concentration of ∼3% and a bandgap of 1.8 ∼ 2.0 eV were formed by MBE. The band alignment of the heterojunctions turned out be type II with a band discontinuity of 1.49 ∼ 1.60 eV. A SiNx intermediate layer with a thickness of 2.1 nm was observed by angle-resolved X-ray photoemission spectroscopy. The heterojunction showed good rectifying characteristics with a reverse current of 1 × 10−7 A/cm2. Separation of the InN/Si interface and the p–n interface by insertion of n-Si layer with a thickness of 200 nm resulted in a reduction of the reverse current in the heterojunction.

Interfaces with vapor-evaporated polyaniline thin films

Interfaces with vapor-deposited polyaniline thin films are investigated using angle-resolved X-ray photoemission spectroscopy. We demonstrate that a diffuse interface is formed with sodium deposited on top of polyaniline, and the distribution of sodium atoms, in the near surface region of the polyaniline thin film, is quite uniform. In comparison, the interface between polyaniline and another polymer, PVDF-TrFE, is rather abrupt and a flat-band model can be applied to the interface band structure.

Study of ultrathin silicon oxide films by FTIR‐ATR and ARXPS after wet chemical cleaning processes

AbstractThe narrowest feature on current integrated circuits is the gate oxide—the thin dielectric layer that forms the basis of field effect device structures. Silicon dioxide is the dielectric of choice and, if the present miniaturization trend continues, the projected oxide thickness will be &lt;1 nm in 2005. Therefore, ultrathin silicon oxide layers using various preparation conditions have been studied by angle‐resolved x‐ray photoemission spectroscopy (ARXPS) and Fourier transform infrared attenuated total reflection (FTIR‐ATR).The silicon oxides obtained by wet chemical treatments such as RCA (SC1 + SC2), SC1 (standard clean), RHO3 (RCA + HF + O3) and DDC (diluted dynamic clean) are characterized in terms of chemical oxide quality before and after thermal annealing. The presence of suboxides (SiOx), as revealed by XPS results, is correlated with Ox–Si–H bonds observed by FTIR‐ATR. The FTIR‐ATR spectra, deconvoluted into four peaks in the asymmetrical stretching SiO bond region (1000–1200 cm−1), show differences between all these chemical oxides. The AS1 (in phase) and AS2 (out of phase) vibrations are compared in terms of position and intensity. The influence of thermal annealing on the chemical oxide quality is also presented. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Chemical depth profile of ultrathin nitrided SiO2 films

Ultrathin nitrided SiO2/Si(001) films were studied using angle-resolved x-ray photoemission spectroscopy. The structure of the oxynitride depended on the nitridation process. Under one type of nitridation the film kept the structure of the SiO2, with N assuming O sites. By taking advantage of the nonuniformity on the chemical depth profile, the Si 2p chemical shift was determined for those Si atoms bonded to three O and one N atom, and for those bonded to two O and two N atoms. The stoichiometry depth profile was recognized through a simple method that allowed the input of physical constrains.

The colossal magnetoresistance (La xSn 1− x) yMnO 3− δ films studied by X-ray photoemission spectroscopy

(La x Sn 1− x ) y MnO 3− δ (LSnMO) epitaxial films have been successfully grown on single-crystal (1 0 0) LaAlO 3 substrates by pulsed-laser deposition (PLD). Measurements of magnetic and transport properties show that this material has colossal magnetoresistance (CMR) effect near the insulator–metal (IM) transition and paramagnetic–ferromagnetic (PF) phase transition. The core levels and the valence band of the film have been studied by X-ray photoemission spectroscopy (XPS). Through the study of angle-resolved X-ray photoemission spectroscopy (ARXPS), we find that the terminal layer of LSnMO film is the MnO atomic plane and there is a slight tin separating out in the film surface. On the basis of the above results and the crystalline structure of perovskite oxides, the growth mechanism of the LSnMO heteroepitaxy on (1 0 0) LaAlO 3 substrate has been discussed.