The adsorption structure of methylthiolate (CH3S) on Au(111) with (√3×√3)R30o periodicity was studied by S 2p photoelectron diffraction. Both of scanned-energy and scanned-angle photoelectron diffractions indicated that the methylthiolate molecules are bound at atop sites. The S-Au distance was determined to be 2.42±0.03 Å and the S-C bond is tilted by approximately 50o from the surface normal towards [−211] and [−12−1] (nearest-neighbor thiolate) directions. Recently proposed “disulfide” model and the “vacancy” model, in which periodic vacancies are formed in the Au first layer, have been also investigated but found to be inconsistent with the experimental results.
We demonstrate that CoSi2 directly grows epitaxially on H-terminated Si(001) and the interface is atomically flat. The hydrogen present on the Si surface seems to suppress the direct reaction of Co with Si up to ∼400oC. Thus, the hydrogen at the Co/Si interface hinders the formation of low temperature (metal-rich) phases such as Co2Si and CoSi. Upon thermal desorption of hydrogen at around ∼460oC, the direct epitaxial growth of CoSi2 on Si(001) occurs. However, with the increase of initial Co film thickness, cracks are formed partially due to a strong tensile stress. More detailed study is needed concerning the effects of such defects for the practical applications to VLSI.
The infrared chemiluminescence technique was applied to the steady-state CO oxidation by NO on Pd(111) and Pd(110) to measure the internal energy of CO2 desorbed from surfaces. In this paper, on the basis of the results of CO oxidation by O2, we elucidate the CO2 formation mechanism of CO + NO reaction. From the comparison of IR emission spectra of CO2 between CO + NO and CO + O2 reactions, it is found that the vibrational energy states of CO2 in CO + NO reaction are similar to those in CO + O2 reaction. This indicates that the reaction path of CO2 formation in CO + NO is the same as that in CO + O2. The vibrational states are much dependent on the surface structure: the CO2 molecules produced on flat Pd(111) were highly excited (especially bending mode) than those on Pd(110) which has atomically rough surface.
A theoretical framework for calculating XPD intensity that incorporates relativistic effect is developed. The theory is applicable to the cases where relativistic effects become important, for example, such a case as heavy elements (Z > 50) are present or circularly polarized photons are used in initial excitation of photoelectrons. The theory is based on short-range-order-multiple-scattering approach so that it is practically useful in analyzing experimental data in order to obtain structural information. In this framework relativistic Dirac Green's function is expanded in terms of full non-relativistic Green's functions using Gestzesy expansion. Using this formalism explicit formulae for spin-resolved XPD from s (l = 0) core levels are given by truncating the expansion at first few terms, which is sufficient in most cases. Numerical examples for direct (atomic) photoemission and single scattering XPD in two-atom models are presented. The theory has an advantage that we can use well-defined Debye-Waller factors and optical potentials developed within the framework of non-relativistic theory because the expansion is possible in terms of non-relativistic Green's functions.
A c(4×4) structure formed by exposing monomethylsilane (MMSi) to a Si(001)-(2×1) surface at substrate temperature of 700oC was measured using scanning tunneling microscopy (STM). At the stage that the spots originated from c(4×4) structure were brightly observed by reflection high energy electron diffraction (RHEED), both c(4×4) and (2×1) domains coexisted. From the evaluation of the c(4×4) and the (2×1) structures by lineprofile of STM images, the c(4×4) structure was revealed to be contracted, while the distance between the (2×1) dimer rows was expanded. Using X-ray photoelectron spectroscopy (XPS), we have confirmed that the carbon atoms included in MMSi diffused into Si substrate. It can therefore be assumed that the contraction of the c(4×4) surface was originated from the diffusion of carbon into Si subsurface. Because of small lattice constant of SiC compared to Si, the c(4×4) structure was predicted to become the site that enhances the nucleation of SiC islands.
Polycrystalline thin films with an oriented direction of ε-Mn4N along the (111) axis and of η-Mn3N2 along the (113) axis were prepared as a single phase by RF reactive magnetron sputtering method. A comparison of XPS spectral analysis with discrete Variational-Xα method showed that the N atoms in Mn-N compounds behave as a donor and govern the magnetic properties of the films. The ε-Mn4N films was a single phase perovskait type crystal with lattice parameter 0.386 nm, and this films had properties of the ferrimagnetism with 1.1 μB per unit cell. The η-Mn3N2 films was face center tetragonal (a = 0.4205 nm, c = 1.2131 nm), and it had properties of antiferromagnetism with 0.4 μB per unit cell.
In order to estimate surface functions of biosensors, surface analytical tools such as time-of-flight secondary ion mass spectrometry (TOF-SIMS) are required for evaluating, identifying and quantifying the biochemical structures of biosensor surfaces. Surface of an optic immunosensor that uses the enhancement of fluorescein isothiocyanate (FITC) fluorescence caused by reactions between proteins, was investigated with TOF-SIMS for estimating and modifying the protein immobilization processes. Secondary ion images of TOF-SIMS show that protein distribution on the sensor surface is not homogeneous. The results indicate that the fluorescence background may be high when proteins are localized on specific area on the biosensor, because a part of immobilized proteins, covered with other proteins, are not able to contribute the reaction with immunoglobulin G (IgG). Thus the estimation of protein immobilization on the biosensor surface with TOF-SIMS clarifies the performance of the biosensor and will contribute to the development of biosensors.
The interaction of CH4 with a Pt(111)-(2×2)-O surface has been investigated by a supersonic molecular beam scattering technique. It was found that the CH4 irradiation completely removes oxygen atoms from the surface via CH4 oxidation reaction, CH4 + O → CO + H2, which is translationally activated. The oxidation probability of CH4 on Pt(111)-(2×2)-O is found roughly of an order of magnitude greater than the initial dissociative chemisorption probability of CH4 on Pt(111), especially under a low incident kinetic energy condition. From the angular intensity distribution and the time-of-flight distribution measurements of scattered CH4, no significant difference in the collision dynamics of CH4 both on Pt(111) and on Pt(111)-(2×2)-O is recognized.
Temperature dependence of the initial oxidation kinetics of Ti(0001) surface was investigated by low energy electron diffraction (LEED) and real-time photoelectron spectroscopy using synchrotron radiation of surface- and bulk-sensitive photon energies. LEED observation revealed that oxide layers grow epitaxially with different surface structures depending on temperature: 1×1 at 200oC and √3×√3 at 400oC. From the oxygen uptake curve measured by O 1s photoelectron intensity, it was clarified that oxygen diffusion through the epitaxially grown oxide layer is significantly enhanced with raising temperature, making the oxide layer thicker than 70 Å at 400oC. The chemical shift components observed for Ti 2p showed that TiO2 becomes predominant at the subsurface with O2 dose, while the stoichiometry of oxide near the interface is maintained as TiO and Ti2O3, for both cases at 200oC and 400oC. Thus it is concluded that the epitaxial growth of a very thin oxide on the Ti(0001) surface proceeds not only at the interface but also in the oxide layer by increasing the oxidation number to that of TiO2.
EXPEEM (energy-selected X-ray photoemission electron microscopy) has a potential to give surface chemical mapping by analyzing the X-ray photoelectron kinetic energies. We have successfully observed EXPEEM images of Au islands deposited on a Ta substrate by using a Wien filter type energy analyzer and an undulator synchrotron radiation with a photon energy as high as 2300 eV. The energy and spatial resolution of the EXPEEM were estimated to be 1 eV and 1.6 μm, respectively.