Surface morphology of CaF2 film grown up to 500 Å thickness on a Si(111) 7×7 substrate in the temperature range from room temperature (RT) to 700oC has been observed by atomic force microscopy (AFM) and reflection high-energy electron diffraction (RHEED). It was found that three dimensional (3 D) islands of CaF2 were grown at RT, however, relatively flat surface appears at over 300oC. Especially, at a high temperature of 700oC, equilateral triangular shape islands with wide flat terrace were formed. On the other hand, desorption process of the CaF2 film due to electron stimulated desorption (ESD) was also investigated. It was found as a remarkable point that equilateral triangular shape craters were formed on the film surface at 300oC by ESD.
TiO2 thin film photocatalysts that can be operated under visible light irradiation were successfully designed and developed by applying an ion engineering technique, i.e., the RF magnetron sputtering deposition method. These TiO2 thin film photocatalysts prepared at the relatively higher deposition temperatures were able to absorb light in visible regions efficiently and were observed to decompose NO into N2, O2 and N2O under visible light (λ > 450 nm) irradiation at 275 K. On the other hand, the TiO2 thin films prepared at the relatively lower deposition temperature exhibited a high transparency and high photocatalytic reactivity for the decomposition of NO under UV light (λ > 270 nm) irradiation at 275 K.
Initial growth stage of 3C-SiC, which was initiated by exposing a Si(001)-(2×1) surface to dimethylsilane (DMSi) at substrate temperature 650−750oC, was observed in situ using reflection high-energy electron diffraction (RHEED). From the observation of RHEED patterns, 3C-SiC spots appeared after incubation time (IT). During IT, Si(001)-c(4×4) structure was also observed. These changes were similar to the case using cracked propane. Therefore, it is considered that the carbon atoms from adsorbed DMSi molecules diffused into the Si substrate and formed Si1-xCx alloys in oder to relax the lattice mismatch between Si and 3C-SiC during IT. The activation energy calculated from the Arrhenius plot on the initial growth rate of 3C-SiC formation was close to that for hydrogen desorption from Si surface. The hydrogen atoms of DMSi molecules adsorbed on the surface transferred to the dangling bonds and afterwards they desorbed from Si-H bonds on the surface. The hydrogen desorption process is considered to be rate-limitting step.
Zeta potentials of Al and Al alloy plates are measured to investigate the relationship between zeta potentials and the structure of surface oxide layers. It is clarified that the formation of Boemite on the surface results in zeta potential decrease. It is also revealed that the pH-zeta potential curves of Al-Mg-Si alloy plates are in fair agreement with those of complex oxide particles of MgAl2O4 that are considers to be a model of surface oxide layers of the alloy. The plate surface of Al-Mg-Si is more negatively charged than that of Al-Mg in aqueous solutions above pH 4.
We propose that Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) can be applied to the characterization of initial oxidation on metal surface, because of its many advantages of quick data collection, parallel detection of wide mass range, high surface sensitivity, high mass accuracy, possibility for hydrogen and its compounds analysis, and so on. In this work, the initial oxidation on Gd surface has been studied through the oxygen exposure experiments, in order to detect surface compounds directly by their fragment ions. Under oxygen exposure of 1.0×10−5 Pa, positive and negative cluster ions, composed of Gd, O and H, were collected at every cycle of 1 s. Characteristic variation in intensities among the typical ions was observed both in positive and negative spectra, which was supposed to be related to the changes of Gd chemical structure. Based on the results obtained, the initial oxidation process on Gd surface was deduced as follows: at first, suboxide of Gd was generated, followed by hydroxide oxide, and finally Gd hydroxide was covered on the surface. In conclusion, ToF-SIMS can be used for in-situ monitering of initial oxidation as a powerful tool.
Two-photon photoemission spectroscopy (2 PPES) has been applied to benzene adsorbed Cu(111) surface and to Si(001) surface. 2 PPES for benzene adsorbed Cu(111) surface has revealed the adsorption induced bonding and antibonding states and the image state. Resonance width between the bonding state and the image state is found to be very narrow, about 0.1 eV full width at half maximum. Sharp resonant photoexcitaion has also been found for Si(001) bulk bands. These results demonstrate the capability of 2 PPES in determining pairs of occupied and unoccupied states. Importance of fine wavelength tuning in 2 PPES is emphasized.
N2O decomposition on supported Rh catalysts (Rh/USY, Rh/SiO2, Rh/Al2O3) has been carried out to study the oxygen coverage (θo) dependence on the activity and to study the mechanism of O2 desorption using an isotopic tracer technique. The decomposition activity for all the Rh catalysts went down to the minimum (formation of only N2), but increased with increasing the coverage, and finally a high activity with steady-state O2 production was attained at high θo. In the isotope study, N216O was pulsed onto 18O/oxidized Rh catalyst at a low temperature (220oC), and desorbed O2 molecules were monitored by means of mass spectrometry. The 18O fraction in the desorbed oxygen had almost the same value as that on the surface oxygen. The result shows that the O2 desorption does not proceed via the Eley-Rideal mechanism, but via the Langmuir-Hinshelwood mechanism, i.e., the desorption of dioxygen through the recombination of adsorbed oxygen. On the other hand, O2-TPD measurement in He showed that desorption of oxygen from the Rh catalyst occurred at much higher temperatures (> 500oC). Therefore, it was proposed that reaction-assisted desorption of O2 takes place during N2O decomposition at the low temperature (220oC).
We have developed a time-of-flight X-ray photoelectron spectrometer (TOF-XPS) using short pulse X-ray, computer simulations of electron optics and X-ray mirror processing techniques. As a short pulse X-ray source, we adopted a characteristic plasma X-ray which radiates from a target by focused high-power short pulsed laser. For the TOF-XPS system, we adopted a magnetic-bottle method to collect the photoelectrons with high efficiency and high energy resolution. Along to this method, electron optics of the TOF-XPS system was realized by computer simulation techniques. And soft X-ray multilayered mirror with the high-precise surface roughness was produced for high focusing. Using the TOF-XPS system combined we measured the XPS spectra of silicon, gold and tungsten samples and confirmed characteristic peaks of these photoelectron spectra. We succeeded in measuring a chemical shift between tungsten and tungsten oxide at 4 f5/2 and 4 f7/2 peaks. The TOF-XPS system has achieved 0.5 μm spatial resolution with a Schwarzschild X-ray mirror for high spatial resolution.
Structures and properties of buff polished (BP) and mechano-chemically polished (MCP) titanium surfaces were investigated by using surface sensitive analysis. Optical micrographs of metal/scale cross-sections of titanium samples revealed a thick modified layer in the titanium surface region that is affected by the action of BP and MCP surface treatments. High density and wide distribution of hydrogen have been found in the thick modified layers by means of elastic recoil detection analysis (ERDA), and the chemical states of the hydrogen such as hydroxides were observed by using X-ray photoelectron spectroscopy (XPS) and electron stimulated desorption (ESD) with deuterium deposited on sample surfaces. Oxide layers on titanium surfaces of BP and MCP treatments were characterized using XPS and Auger electron spectroscopy (AES). The oxide layers had mixed up the structures of Ti, O and C, although thick oxygen and hydroxides layers were covered with thin carbon contamination and TiO2 layers. The modified layers have shown porous structures in terms of molecular scale.
We have observed for the first time non-thermal relaxation of the surface stress of Si induced by electron irradiation at room temperature. An atomically thin disordered layer was introduced by Ar ion bombardment. The surface stress change during the ion bombardment and the following electron irradiation of Si(100) was measured by means of an optical microcantilever technique. We have found that the compressive stress in the Si surface due to the disorder induced by ion bombardment was completely relaxed by electron irradiation at low energy. The criterion for complete relaxation is found not to be total energy deposition, but number of irradiated electrons.
Proteins and polypeptides were first covalently immobilized on a solid surface and then extended by a tensile force applied at the two ends of the polymer chain. The method consisted of introducing cysteine residues at N-and C-termini of protein molecules and covalently immobiling them on an amino-silanized surface of a crystalline silicon wafer. The other end of the protein molecule was cross-linked to a functionalized AFM (atomic force microscope) tip with covalent cross-linkers. The relationship between the tensile force and the extension length of the molecule was measured using the force curve mode of AFM. Results obtained with a polyglutamic acid that takes helical conformation in acidic and random coil state in neutral and alkaline media is described. Also the relationships measured with β-sheet globular protein, carbonic dehydratase are given.