X-ray Photoelectron Spectra Measurements Research Articles

Interface states at ultrathin oxide/Si(111) interfaces obtained from x-ray photoelectron spectroscopy measurements under biases

The energy distribution of interface states for Si(111)-based metal–oxide–semiconductor (MOS) devices with an ultrathin chemical oxide layer is obtained from measurements of x-ray photoelectron spectra under biases. All the observed interface states have discrete energy levels. The energy deviation of the interface state levels from the midgap is smaller than that for the Si(100)-based MOS devices; this is attributed to weaker interaction of the Si dangling bond with Si and oxygen atoms in the oxide layer. The densities of the interface states at the Si(111)/ultrathin oxide interface are comparable to those at the Si(100)/ultrathin oxide interface.

Interface states in the Si band-gap obtained from XPS measurements under biases

Measurements of X-ray photoelectron spectra were performed for 〈∼3 nm Pt/2.5–3.6 nm SiO 2/ n-Si(100)〉 biases between the Pt layer and the Si substrate. The Si 2p peaks due to the Si substrate and the oxide layer are both shifted by biasing, the magnitude of the shift of the former peak being much larger than that of the latter. The shifts are well correlated to each other, and are attributed to a change in the potential drop across the oxide layer caused by charges in interface states. Using the method developed by us, the interface states are found to have discrete energy levels with energies depending on the formation method of the silicon oxide layers, and are attributed to Si dangling bonds in various environments.

A new spectroscopic method for determination of energy distribution of interface states in the semiconductor band-gap

Measurements of X-ray photoelectron spectra (XPS) are performed for (3 nm-Pt/2.6 nm-oxide/p-InP(100)) and (2.5 nm-Pt/3.8 nm-oxide/n-GaAs(100)) MOS devices under biases. Upon applying a negative bias voltage to the InP (or GaAs) substrate with respect to the Pt layer, the substrate In 3d 5 2 (or As 3d 5 2 ) peak is shifted toward the lower binding energy, while it is shifted toward the higher binding energy by applying a positive bias. These shifts are caused by a change in the potential drop across the oxide layer due to accumulation of charges in interface states. The energy distribution of the interface states in the band-gap is obtained by analyzing the magnitudes of these shifts measured as a function of the bias voltage. The energy distribution has peaked-structure and the peaks are attributed to antisite and vacancy defects. The interface Fermi level of InP (or GaAs) is located near the energy level of the (+/0) transition of the P In (or As Ga) antisite defects.

Energy distribution of interface states in the band gap of GaAs determined from x-ray photoelectron spectra under biases.

The energy distribution of interface states in the GaAs band gap is determined for metal-oxide-semiconductor devices with an ultrathin thermal oxide layer of \ensuremath{\sim}3.8 nm, from measurements of x-ray photoelectron spectra under biases. The energy distribution has a peaked structure with four peaks at \ensuremath{\sim}0.15, \ensuremath{\sim}0.5, \ensuremath{\sim}0.75, and \ensuremath{\sim}1.1 eV above the valence-band maximum (VBM). The 0.75-eV peak has the highest density of \ensuremath{\sim}1.9\ifmmode\times\else\texttimes\fi{}${10}^{12}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ and is attributed to a (+/0) transition of ${\mathrm{As}}_{\mathrm{Ga}}$ antisite defects. The weak 0.5-eV peak is tentatively attributed to a (++/+) transition of the ${\mathrm{As}}_{\mathrm{Ga}}$ antisite defects. The 0.15- and 1.1-eV peaks that have densities of 1.3\ifmmode\times\else\texttimes\fi{}${10}^{12}$ and 0.8\ifmmode\times\else\texttimes\fi{}${10}^{12}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$, respectively, are attributed to ${\mathrm{Ga}}_{\mathrm{As}}$ antisite defects and Ga vacancy defects, respectively. The interface Fermi level of GaAs is located at 0.85 eV above the VBM, indicating that it is strongly affected by the ${\mathrm{As}}_{\mathrm{Ga}}$ antisite defects. From the density of the interface states near the Fermi level, i.e., \ensuremath{\sim}1\ifmmode\times\else\texttimes\fi{}${10}^{13}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ ${\mathrm{eV}}^{\mathrm{\ensuremath{-}}1}$, it is shown that d\ensuremath{\varphi}/d${\mathrm{\ensuremath{\chi}}}_{\mathit{M}}$ (\ensuremath{\varphi}: barrier height in GaAs, ${\mathrm{\ensuremath{\chi}}}_{\mathit{M}}$: metal electronegativity) is 0.24, indicating that the Fermi level is pinned partly by the ${\mathrm{As}}_{\mathrm{Ga}}$ antisite defects and that fixed oxide positive charges with a density of (2--3)\ifmmode\times\else\texttimes\fi{}${10}^{12}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ are present at the GaAs/oxide interface.

Interface States for Si-Based MOS Devices with an Ultrathin Oxide Layer: X-Ray Photoelectron Spectroscopic Measurements under Biases

Energy distributions of interface states for <30-Å-thick Pt/ 25∼35-Å-thick silicon oxide/ n-Si(100)> metal-oxide-semiconductor (MOS) devices have been obtained from measurements of X-ray photoelectron (XPS) spectra under biases. Upon applying bias voltages, the substrate Si(2p) peak is shifted because of a change in the occupancy of interface states by electrons, inducing a change in the potential drop across the silicon oxide layer. Devices with a native oxide layer have high interface state density near the midgap, which is attributed to isolated dangling-bond states. For MOS devices with a thermal oxide layer grown at 550° C in a wet-oxygen atmosphere, the interface states have two density maxima, one below and the other above the midgap. For devices with a thermal oxide layer formed at 700° C in wet oxygen, two density maxima of the interface states are also observed with reduced density.

Chemical Vapor Surface Modification of Porous Glass with Fluoroalkyl-Functionalized Silanes. 2. Resistance to Water

Smooth and porous glass surface substrates were modified with fluoroalkyltrichlorosilanes (CF 3 (CF 2 ) n -CH 2 CH 2 SiCl 3 , n=0, 3, 7, FAS) by means of chemical adsorption from the gas phase to give rise to highly hydrophobic surfaces. The hydrophobicity was found to increase with increasing molecular size of the adsorbates, accompanied by the more regular molecular orientation confirmed by the analysis of the X-ray photoelectron spectra (XPS). The resistance of the FAS layer to liquid H 2 O was examined by following the variations in the contact and critical tilting angles with time after immersion in boiling H 2 O. In all the samples tested, the contact angle (θ s ) decreases and the critical tilting angle (α) increases with time. For the same FAS treatment, the decreasing rate of θ s is much smaller in the surface porous substrate, while the increasing rate of α is greater. These noticeable facts were rationalized in terms of the data of Fourier-transformed infrared attenuated total reflection and XPS measurements. Also, the former data reveal that the FAS molecules are anchored via interfacial Si s -O-Si bonds and intermolecular Si c -O-Si c bonds in the monolayer formation process and partially desorbed by hydrolysis during immersion in HaO. Molecular orbital calculations of the clusters employed as a model of the FAS molecule chemically bonding to the surface of SiO 2 were also carried out in order to obtain information on the electronic distribution and the reactivity with H 2 O, suggesting that the crucial step of the deterioration is the nucleophilic attack of the interfacial Si atoms accompanied by cleavage of the intermolecular Si c -O-Si, bonds. On the basis of these results, the deterioration mechanism was discussed

New method for determination of energy distribution of surface states in the semiconductor band-gap: XPS measurements under biases

The energy distribution of surface states in the semiconductor bandgap has been obtained spectroscopically from measurements of X-ray photoelectron spectra (XPS) under biases. The XPS measurements are performed for [ca. 30 A ̊ - thick Pt ca. 25 A ̊ - thick oxide/p- InP (1 0 0)] MIS diodes. The difference in binding energy between the In(3 d) and Pt(4 f) peaks, E In E Pt, is changes by applying biases, because of accumulation of charges in the surface states. The energy distribution of the surface states is determined by analyzing the amount of the biasinduced shift in E In E Pt. The density of the surface states is high near the mid-gap, near the conduction band minimum and near the valence band maximum.

Characterization of potassium-doped nickel catalysts and activity for selective hydrogenation of 1,6-hexanedinitrile

Studies of the chemical preparation, BET surface areas, X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), temperature-programmed reduction (TPR) and catalytic activities of several nickel catalysts were carried out for the catalytic hydrogenation of adiponitrile, in a continuous process at 1 atm pressure, 443 K, and in the absence of ammonia. Surface areas decrease with NiO reduction temperature. XRD, XPS and TPR measurements detect NiO incipient reduction at 473–498 K, a NiO reducibility inhibitor character for potassium, and 99.9% reduction degrees above 573 K. Selectivities of 100% with respect to 6-aminohexanenitrile are obtained at 60% conversion for catalysts with potassium contents of 10.5 × 10 −4 g K 2O/g Ni.

Photoelectrochemical Investigations on Al and In Co-doped ZnS Thin Film Electrodes in an Aqueous Electrolyte

Al doped and Al-In co-doped ZnS thin film electrodes were grown by electron-beam evaporation on ITO (indium-tin oxide) glass substrate, and their photoelectrochemical properties were investigated. These thin films were also characterized by optical absorption, X-ray diffraction (XRD) and X-ray photoelectron spectrum (XPS) measurements. The doping of the ZnS film with Al alone did not result in a satisfactory n-type semiconductor. For Al-In co-doped ZnS thin films prepared by the thermal diffusion of a thin In layer which was deposited previously on the ITO-glass substrate, however, the barrier resistance between ITO and ZnS was lowered, and a clear n-type semiconductor characteristic was observed. The efficiencies of both the photocurrent and photocorrosion of ZnS in an aqueous electrolyte were increased with higher Al concentration.

Computed tomography for quantitative NDE: 37610 Streit, R.D.; Clark, G.A.; Brase, J.M. Mechanical Engineering, Vol. 109, No. 9, pp. 56–64 (Sep. 1987)

The results of X-ray photoelectron spectra (XPS valence band and core levels) measurements for Ge+ implanted SiO2/Si heterostructures are presented. These heterostructures have a 30 nm thick Ge+ ion implanted amorphous SiO2 layer on p-type Si. The chemical-state transformation of the host-matrix composition after Ge+ ion implantation and rapid thermal annealing (RTA) are discussed. The XPS-analysis performed allows to conclude the formation of Ge0 and GeOx clusters within the samples under study. It was established, that the annealing time strongly affects the degree of oxidation states of Ge-atoms.

5s-electron excitation energies in the rare-earth metals

We report calculations of $5s$ electron excitation energies for the rare-earth metals. Aside from the lack of a direct estimate of correlation effects, the method is quite similar to that we have used in calculating $4f$ level positions which are in excellent correspondence with experiment. Our aim here is to assess the applicability of the technique to closed-shell core states, and we have chosen the $5s$ levels in view of the simplicity of their x-ray photoelectron spectra (XPS). Within the approximation of a completely screened final state, in which the atomic cell having the $5s$ hole is electrically neutral, the results are in good qualitative and semiquantitative agreement with XPS measurements. The disparity between theory and experiment is about 4 eV across the lanthanide series, and its sign is consistent with correlation effects. Available free-atom information only permits us to estimate the correlation energy associated with $5s$ excitation in ionized Cs; the estimate is of the proper sign and magnitude to bring our results into accord with experiment. We also assess the effect of the complete screening assumption by estimating excitation energies corresponding to ionized final-state cells; we find that the presence of a screening electron lowers the $5s$ binding energy by 4-5 eV.