Electron-stimulated desorption of argon and krypton adsorbed on Pt (111) was studied for the electron energy range from 10 to 120 eV. The ion species investigated were Ar+, Ar2+, Ar2+ for argon, and Kr+ for krypton. The threshold energy for Ar2+ desorption was found to be 83 eV, which is interpreted in terms of the formation of Ar3+ followed by the Coulomb repulsion of two adjacent ions produced by the curve crossing from Ar3+ Ar to Ar2+ Ar+ or Ar2+* Ar+. For the desorption of Ar+ and Ar2+, resonant excitations with onsets at 24.2, 25.4, 34, and 50 eV have been found. The first two thresholds are interpreted as pairs of interacting surface and bulk excitons, respectively. The details of the desorption mechanism are discussed in connection with the threshold energies and the thickness dependences of desorption intensities.
The surface contaminants or residues on silicon wafers were investigated by a new combined technique of secondary ion mass spectrometry (SIMS) and electron stimulated desorption mass spectrometry (ESDMS) together with the field limiting method. The appearing peaks in the ESDMS spectra were due to the adsorbed species alone while those in the SIMS spectra were due to the substrate constituents as well as adsorbed species. Analysis by ESDMS was particularly useful for the detection and identification of the outermost layer species and for the evaluation of the surface cleanliness. The present combined technique can be a useful tool for analyzing complementarily the substrate by SIMS and the surface by ESDMS.
In an effort to develop a semiconductor type NH3 sensor, the NH3 sensing properties of WO3 semiconductors loaded with colloidal noble metals were investigated. Among the various noble metals tested, Au was proven to be the most excellent promoter for the WO3-based NH3 sensor, whereas Pt gave a very high NH3 sensitivity at 200°C, but the response was too slow. Thus Au-WO3 element could respond to NH3 in air over a wide NH3 concentration range of 5 ppb-50 ppm at 450°C, showing excellent characteristics in both NH3 sensitivity and response rate. An optimum Au loading amount was shown to be 0.8 wt % with respect to the NH3 sensitivity. The electrical resistance of Au-WO3 element in air increased with an increase in Au loading. From the measure-ments of Seebeck coefficients it was revealed that the Au particles loaded interact with WO3 and take the conduction electrons away when exposed to air, while those electrons are given back to WO3 on exposure to NH3-containing atmospheres. It is concluded that such an electronic interac-tion between Au and WO3, susceptible to a change in atmosphere, is responsible for the prominent promoter action of Au.
Real-time Raman measurements have been performed on graphite under 3-keV He+ irradiation. Time dependence of the change in phonon correlation length has been studied from the change in the first-order Raman spectrum. Lattice disorder caused by irradiation is explained in terms of a reduction in the phonon correlation length due to defects induced by ion irradiation.
We synthesized MgO/TiOx ceramics superlattices of the combination of various thicknesses of TiOx layers and MgO layers on MgO(100) single crystal substrates by a pulsed-molecular-evaporation method; this is a novel reactive deposition method using a pulsed molecular beam source of oxygen. We determined the structure of TiOx, the periodicity and the interface structure of the superlattices by means of reflection high energy electron diffraction (RHEED), X-ray diffraction (XRD) and Atomic Force Microscope (AFM). XRD analysis revealed that TiOx takes the form of pseudomorphic anatase effected by the substrate. TiOx grew in the form of c-axial orientated islands from the first unit layer. MgO deposited on TiOx layer grew epitaxially from a few angstrom of the deposition and recovered the smooth surface; as was confirmed by the observation of RHEED and AFM. On the basis of this interesting growth mechanism, superlattices could be composed by materials having different crystal forms like TiOx and MgO.
Terraced surfaces of Bi-Co complex oxide, (Bi, Pb)2Sr2CoOy, are examined by means of high-resolution transmission electron microscope (HRTEM) profile imaging method. The outermost surface of each step is a single (BiO) layer, which preserves wavy fluctuations of atom-plane almost in the same manner as those in the bulk-modulation. Some of (BiO)-layers near the edge of the crystal are not double but single (BiO) layers. In addition, an extremely small crystal of Bi2 (Sr, Ca)3Cu2Oy with unit-cell-size width is found to have the modulated structure almost identical with the bulk-modulation.
A new method of three dimensional (3-D) analysis by Auger electron spectroscopy (AES) is proposed. The 3-D data for a specimen surface layer are compiled by repeating Auger image acquisition and ion sputtering alternatively. Three different techniques for extracting revealing hidden information from the compiled data are shown. 1) Cross-sectional images were constructed by looking at the intensity distribution along a line for each of the stored images. 2) The selected spaces (e. g. grain boundaries) of the 3-D data were quantified. An binary image generated by processing a secondary electron image simultaneously acquired were used to cut out the desired data space as a mask. 3) Depth profiles for the specified area were also constructed. Although 3-D data acquisition takes a long time, the data processed over a wide space shows high reliability, because it is substantially accumulated a large number of data.
This paper presents the perpendicular magnetic properties and microscopic structures of Co-ferrite films prepared by a heat-oxidation process of evaporated Fe-Co multi-layered thin films. The oxi-dation temperature is less than 550°C. Thin films are oxidized in 760 Torr O2 atmosphere under a magnetic field of 1 kG applied in the perpendicular direction to the film surface. Co-ferrite films are evaluated using as follows: (a) the crystal structure is analyzed using an X-ray diffractometer, (b) a SEM is used in observations of surfaces and cross-sections, (c) composition distributions in the film depth direction are investigated by AES and XPS, (d) a VSM is used to measure hysteresis loops, and (e) a magneto-optical property is measured from Kerr-rotation angle. One cause of the perpendicular magnetic anisotropy of the oxide films is thought to be the effect of the columnar grain growth of oxide particles which facilitated by growing vertically along grain boundaries.
We have studied the surface structures of Al/Si(100) system by observing the I-V curves and intensity line profiles of LEED. For the 2×3 phase a streaky LEED pattern was observed, and it is interpreted that Al dimer rows are not arranged perfectly in every other Si dimer. The resemblance of I-V curves of the integral order spots between the Al-4×1 and Al-7×1 phases indicates the correlation of the atomic geometry of the Si substrate between the Al-4×1 and Al-7×1 structures.
This paper demonstrates that an electro-chemical process is suitable for fabrication of Ni/GaAs Schottky contacts in a controlled manner. Nearly ideal I-V characterisitics have been achieved by means of an anodic-etching process, prior to electroplating in the same bath as for electroplating. The Schottky barrier height for the almost ideal Ni/n-GaAs contact prepared by the above process has been found to be 0.81±0.01 eV.
Surface atomic composition and chemical state have been investigated for Si (100) bombarded with 5 keV ions (B+, C+, N+, O+, F+, Ne+). The XPS observations reveal that the tendencies of surface chemical change by the irradiation are divided into three types. These are, 1) formation of monatomic layer composed of bombarding ions (B+, C+), 2) formation of new compounds between silicon and bombarding ions (N+, O+), and 3) no chemical change observed (F+, Ne+). The changes in surface atomic compositions are discussed in connection with irradiation-induced surface segre-gation of the implanted atoms and free energy (ΔG) or sublimation energy of the Si compounds.
Natural MoS2 (001) surface structure was investigated by coaxial impact-collision ion scattering Spectroscopy (CAICISS), low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) under ultra high vacuum. It was found that the surface reconstruction of MoS2 (001) does not occur. There is the same stacking sequence (2H structure) in the bulk. However, we found the contractions of 3.6±0.4% at the top surface interlayer (d12) and of 0∼2% at the subsequent interlayer (d23).