Recent studies on Pd L3-edge X-ray Absorption Near Edge Structure (XANES) spectra for pure Pd small clusters show that the spectra are greatly influenced by hydrogen adsorption and absorption. In this paper the full multiple scattering method is applied to study the difference in measured spectra. The calculated XANES spectra are not so sensitive to the detailed positions and the electronic structures of the interacting hydrogen atoms, whereas they are sensitive to the induced structural and electronic state change in the host Pd small clusters. The size effect on the peak at ∼7 eV is well explained in terms of the induced lattice expansion after hydrogen absorption.
Dependence of interaction force between condensed polystyrene-latex (PSL) particles and atomic force microscope (AFM) tip on diameter of PSL particle is studied from the force curve measured in dry atmosphere. In the diameter range of PSL particle from 42 nm to 1 μm, it is found that this dependence is different from that of geometric mean radius which is derived from DMT theory. These results can be analyzed in terms of PSL particle deformation effect and contribution of surrounding PSL particles.
We have developed a real time in situ imaging system for LEEM, PEEM, SEEM, AEEM and XPEEM to image surface elements and chemical species in chemical and physical processes. AEEM and XPEEM can provide the surface mapping of elements and chemical states. We have designed the system to be operated in a chamber of low pressures ambient gas at high temperatures to follow chemical reactions on the surface.
The internal energy distribution of C02 produced and desorbed in the steady-state CO oxidation (∼10-2 Torr) on well-defined single crystal Pd surfaces were successfully measured by using infrared (IR) chemiluminescence technique. The CO2 molecules produced on flat surface such as Pd(111) were highly excited (especially in terms of bending mode) than those on Pd(110) (1×1) which has atomically rough surface. These results show that the dynamics of CO oxidation on Pd surfaces is structure-sensitive. The difference in the vibrational distribution of the desorbing CO2 indicates that a structure of activated complex of CO2 is more bent on Pd(111) and relatively linear on Pd(110). Also, the kinetics of the steady-state CO oxidation is structure-sensitive. Furthermore, the IR chemiluminescence technique was applied to the study of CO2 on Pd(335) having both (111) terrace and step properties. The IR study on Pd(335) revealed that the steady-state CO oxidation is proceeding at step sites under higher surface temperature condition (850 K), and the active site of CO+O recombination reaction shifts to the terrace site with increasing CO coverage.
Atomic force microscope (AFM) and electrochemical scanning tunneling microscope (EC-STM) were used to examine the surface structure of zeolites (mordenite, heulandite, Linde Type A) and Cu(111), respectively. The (001) surface of mordenite had several deep grooves and was coated with impurities. After this coating material was scraped off, the ordered pore structure was observed. The surface structure of Linde Type A crystal indicated that the double 4-rings are the building key unit for crystal growth. AFM images of the morphological changes on the (010) surface of heulandite due to dissolution in a 0.2 N H2SO4 aqueous solution revealed the unique dissolution process that resulted from the characteristic pore structure. EC-STM could reveal the surface structure of Cu(111) with electrochemically created hydroxyl species in an alkaline aqueous solution. Two kinds of lattice structures were observed. AFM and EC-STM can provide the microscopic-level information of the surface structure of zeolite and metal catalysts.
Chemical adsorption of ions on SiO2 and Al2O3 in aqueous solution is examined. It is revealed that sulfate ions adsorb both on Si and Al oxide surfaces and that the adsorption results in zeta potential decrease. Decrease in zeta potential of Al2O3 in NaHCO3 solutions indicates a chemical adsorption of HCO3- ions on the Al oxides. When two different ions, for example, Al(III) and sulfate ions are contained in a SiO2 dispersed solution, the quantity of each adsorbant on the SiO2 is almost same as that in the case they are contained separately. Profiles of zeta potential pH for a coexisting system reflect that of a solely existing system.
A spin sensitive tip is needed to realize the spin-polarized STM, which can resolve the spin-polarization of surface density of states. GaAs and its related compound semiconductors are well known as spin-polarized electron sources and are also candidates for the spin probe. We made a GaAs thin film tip by cleavage. Since the GaAs film is thin enough, circular polarized light can illuminate through the tip and efficiently excite spin-polarized electrons near its apex. Because an atomically resolved Si(111) 7×7 surface was observed with the tip, the tip is mechanically stable. Optical responses of the tip were studied with Fe thin films grown on a MgO(001) surface. Using this magnetic thin film, we demonstrated that spin-dependent tunneling could be detected with the tip.
Quantitative analysis of shallow plasma doped boron was carried out by Quad SIMS under several bombardment conditions of primary oxygen beam. Energy of oxygen primary beam was in a range of sub keV and the incident angle was evaluated at glancing angle under the condition of oxygen leak and also at near normal angle on the sample surfaces. By using shallow implanted standard, average sputtering rate and RSF were obtained. The results of quantitative analysis at the depth deeper than 2-4 nm were similar under all measuring conditions. Also it was found that angle dependence on sputtering yield of oxygen beam at 250 eV was smaller than that at 10 keV energy.