An Al-containing ordered alloy, NiAl(110), was oxidized under various conditions of ultra high vacuum. The crystallinity and thickness of the formed alumina films were evaluated. The two-step growth process, where a specimen was oxidized at about 600 K being followed by annealing at ca. 1100 K, is well known. We examined the effect of oxygen pressure, substrate temperature and annealing conditions. A one-step process, where a specimen was oxidized at around annealing temperature so that oxidation and crystallization proceeded simultaneously, has been newly developed. The effects of oxygen pressure and substrate temperature in the one-step growth were clarified. It was revealed that a flat well-ordered alumina film thicker than 0.5 nm (known) could be grown by this new method.
The two-point-resolution of a novel two-color far-field super-resolution fluorescence microscopy has been evaluated. This microscopy is based on a combination of two-color fluorescence dip spectroscopy and a phase modulation technique for the laser beam. The two-point-resolution of the microscopy has been evaluated by using the fluorescent beads of which the size is specified by the observation with AFM. By introducing two color lasers, the observed fluorescence image shrunk down beyond the diffraction limit. In the observation of neighboring two fluorescence beads, pronounced separation between two individual fluorescence spots has been investigated. By taking the focal depth into consideration, FWHM and profile of the fluorescence images were well reproduced. It is proved that our technique breaks the diffraction limit and the spatial resolution of the optical fluorescence microscope can be improved by 2 times higher than the diffraction limit.
Hydrogenation of single-crystal yttrium (Y) thin films was studied with nuclear reaction analysis (NRA), and low energy electron diffraction (LEED). The Y(0001) thin film with 20 nm thickness was epitaxially grown on W(110). Hydrogenation was carried out by exposing the Y films to molecular and atomic hydrogen. Absorption rate of hydrogen under exposure to molecular hydrogen was the same as that to atomic hydrogen at 700 K indicating that the dissociation of H2 is not the rate-determining step. The hydrogen concentration was found to saturate at H/Y=1.7, and the trihydride γ-YH3 phase was not formed above 450 K in 10−3 Pa H2. At a low temperature (≈100 K), on the other hand, the dihydride (β-YH2) formation was suppressed, and only the α-phase was found to grow. The depth profile of the absorbed hydrogen indicates that the absorbed hydrogen is distributed uniformly in the depth direction of the Y thin films.
Surface electronic states of a stepped Cu(755) surface were studied by angle-resolved ultraviolet photoelectron spectroscopy using synchrotron radiation (SR-ARUPS). We have observed an isotropic free-electron-like surface state below the Fermi level. Unlike to the stepped Ni(755) surface with the same surface structure, no electronic state localized at the step edges was found. This experimental fact shows that the valence-band structure plays an important role in inducing step-localized states. In addition, we tried to prepare Co atomic chains on the stepped Cu(755) surface by vacuum deposition. However, the analysis of low-electron-energy-diffraction (LEED) patterns shows that the Co atoms grow in island-growth mode into epitaxial triangular nanoislands. The Co electronic structure in these Co nanoislands is investigated also by SR-ARUPS. Below 0.2 ML, two Co-derived zero-dimensional peaks were clearly resolved at around 0.3 and 1.1 eV. With coverage increasing, these peaks shift toward each other. This peak shift dependent on the Co coverage is explained in terms of the enhanced exchange splitting that is caused to reduce unavoidably increased Coulomb interaction between Co electrons with flat-band localized in thesmall Co nanoislands at low coverages.
Hydride evolution in annealing the Si(001) surface after adsorption of silane/germane at room temperature has been investigated by using multiple-internal-reflection IR absorption spectroscopy. For both silane and germane adsorptions, it was found that major species existing above 300oC are Si-Si doubly occupied dimers (DOD) and step-edge SiH. For further annealings above 300oC, the DOD kept its original intensity or even evolved until 370−400oC, but eventually decayed at 450oC with the hydrogen desorption. The onset of the DOD decay was concurrent with depletion of the step-edge SiH, which suggests a role of the step-edge SiH as being a “reservoir” for DOD states. Possible transfer of hydrogen atoms from the step-edge SiH to DOD can be related to adatom migrations, which include exchange between adatoms and substrate atoms. It is highly probable that low-temperature hydrogen desorption from germane-adsorbed Si surface is rate-limited by diffusion of Ge adatoms.
Adsorption and diffusion of ammonia on an ice/Pt(111) surface were studied using Fourier transform infrared spectroscopy (FTIR) and thermal desorption spectroscopy (TDS). After exposing the crystalline ice film to ammonia molecules at 45 K, we have detected an intriguing feature at 1470 cm−1 in the FTIR spectra. This feature is derived from the ammonia adsorption on the ice with a characteristic structure which appears in thin film region. The peak intensity decreases gradually as the thickness of the substrate ice increases. In addition, we have detected a feature at 1260 cm−1 that appears after flashing the film to 113 K. The feature corresponds to the ammonia molecules which penetrate the ice surface and reach the ice/Pt(111) interface. Intriguingly, the intensity of this feature decreases with the ice thickness and there is a linear relation of the peak intensity of the features at 1470 cm−1 and 1260 cm−1. We propose a model that the solubility of the ammonia molecules is much higher for the thin ice film, whose structure is deformed from the ideal ice due to the presence of the metal substrate, than that for the ideal ice.
In an attempt to develop materials to remove phosphorus that causes eutrophication or red tide, boehmite (aluminum oxide hydroxide) was surface-treated with sulfuric acid, nitric acid, hydrochloric acid, and sulfates, and the adsorption rates and adsorption isotherms of phosphate ions onto them were measured. The amount of phosphate ions adsorbed onto the boehmite, which was treated with sulfuric acid, was the greatest. This suggests that hydroxyl groups located in the boehmite are exchanged for sulfate groups by the sulfuric acid treatment. When boehmite was surface-treated with sulfuric acid of different concentrations, the amount of phosphate ions adsorbed increase with the increasing concentration of sulfuric acid. This result indicates that the adsorption of phosphate ions can be controlled by the amount of sulfate groups introduced in boehmite. The sulfate group of boehmite could also be introduced by an acidic sulfate solution treatment. When boehmite was treated with sulfuric acid, its capacity to adsorb a low concentration of phosphate ions from sea water increased to approximately 3 times that of the untreated boehmite. This suggests that the boehmite after the treatment of sulfuric acid or an acidic sulfate solution could be utilized for removing phosphate ions from sea water.
The selective catalytic reduction (SCR) of N2O with CH4 in the presence of excess O2 was studied over ion-exchanged Fe-BEA catalyst by the observation of reaction intermediates in order to elucidate the reaction mechanism. From the results of activity tests, SCR of N2O with CH4 in the presence of excess O2 proceeded at much lower reaction temperature than N2O decomposition over the Fe-BEA catalyst. The profiles of temperature programmed desorption of O2 after N2O pretreatment gave a new desorption peak at lower desorption temperatures compared to the case of O2 pretreatment. However, the oxygen species desorbed at the lower temperatures did not react with CH4 in the profiles of temperature programmed reaction. From the structural analysis by means of extended X-ray absorption fine structure, a Fe-Fe bond was observed on the Fe-BEA catalyst after N2O treatment. This suggests that binuclear species can be formed over the Fe-BEA catalyst. In the in-situ FTIR observation, the methoxy and formate species were observed during the SCR reaction. We measured the reaction rates of these surface species with N2O and O2, and this is related to the selective reduction of N2O with CH4.
We have carried out displacement current measurements to investigate the electrical properties of pentacene OFET (organic field-effect transistors) and their carrier injection behavior. We demonstrate that an analysis of displacement current provides us with information about (i) carrier injection from the metal electrodes to pentacene, (ii) the voltage at which carrier injection takes place, (iii) spatial distribution in the organic film of injected carriers, (iv) the amount of stored charge, and so on. We confirm that holes are injected from the Au electrode into the pentacene layer, which is consistent with the p-channel operation previously observed for pentacene OFET. We find that the gate voltage at which storage of injected charge at the gate oxide interface begins, is nearly equal to the onset voltage of the OFET, which suggests that carrier injection correlates with the operation of the FET. We also find that the electrical characteristics of pentacene FET greatly change due to exposure of the FET to oxygen. This change can be interpreted as being due to the carrier injection of the oxygen molecules adsorbed on the pentacene layer. We demonstrate that the drain current depends on the amount of injected carriers.
We applied scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) to analyze the initial process of graphitization at 6H-SiC(000-1) surfaces. There appeared a (4×4) periodicity in the LEED pattern of the 6H-SiC(000-1) surface annealed at 1050oC. In the STM image, many protrusions with (4×4) periodicity were observed on the graphite formed on the 6H-SiC(000-1) surface.