Hisakazu Nozoye

Adsorption state of dimethyl disulfide on Au(111): Evidence for adsorption as thiolate at the bridge site

We studied the adsorption state of dimethyl disulfide and methylthiolate on the Au(111) surface by means of the density functional theory (DFT) within a generalized gradient approximation and experimental high-resolution electron energy loss spectroscopy (HREELS) techniques. It turns out that the methylthiolate adsorption is more stable than the dimethyl disulfide adsorption and that the most stable adsorption site for the methylthiolate is the bridge site slightly off-centered towards the fcc-hollow site with its S–C bond tilted from the surface normal by 53°. HREELS results are in excellent agreement with the DFT results, providing very strong support to the depicted adsorption scenario.

Deposition at low substrate temperatures of high-quality TiO2 films by radical beam-assisted evaporation.

We deposited high-quality TiO2 films by an oxygen-radical beam-assisted evaporation (RBE) method at a lower substrate temperature (Ts) than that for a TiO2 film deposited by conventional thermal evaporation (TE) with neutral-oxygen gas. The films were then evaluated in terms of refractive index, shift of wavelength of a peak in the reflection curve, and absorption coefficient. The TiO2 films deposited by RBE at Ts < 473 K showed higher refractive indices, were more compact, and had lower absorption coefficients than the film deposited by TE at Ts = 473 K.

Decomposition of alkanethiols adsorbed on Au (1 1 1) at low temperature

The adsorption and desorption of butanethiol (CH 3 (CH 2 ) 3 SH: C4), hexanethiol (CH 3 (CH 2 ) 5 SH: C6) and octanethiol (CH 3 (CH 2 ) 7 SH: C8) on Au (1 1 1) under vacuum condition have been studied by temperature programmed desorption (TPD). Desorptions of thiolate radical species were observed for C6 and C8. Connecting the desorption temperatures of parent thiols from the first layer and that of hydrogen, we were able to find a condition for thiolate radicals to be desorbed from the surface.

Peculiar decomposition behavior of N2O on Ni(755)

The adsorption and decomposition behavior of N 2 O on Ni(755) has been investigated by TPD and XPS. Decomposition of N 2 O (into N 2 and atomic oxygen) is observed between 96 and 200 K. There are two desorption peaks of N 2 at 170 and 120 K. The saturated amount of N 2 produced from N 2 O is quite close to the step density of Ni(755). The molecular desorption of N 2 O occurs only for large exposures of N 2 O where the desorption peak of N 2 is saturated. The desorption peak at 170 K is due to desorption of adsorbed N 2 which is formed at bare step sites from initial dissociation of N 2 O below 105 K. On the other hand, the peak at 120 K comes from spontaneous desorption of N 2 by decomposition of molecular N 2 O at oxygen-modified step sites.

Interaction of CO with the SmOX/Ru(001) interface

The effect of an interface of rare earth oxide transition metal upon CO adsorption was investigated on the Ru(001) surface partially covered with SmO x . which was prepared by means of the selective oxidation of Sm in a Sm + CO coadsorption system on Ru(001). Temperature programmed desorption and ultraviolet photoelectron spectroscopy results indicated that two characteristic adsorption states of CO presented at the interface of SmO x /Ru(001) depending on the coverage of preadsorbed Sm. For the low Sm coverage below ∼0.3 monolayer, the interface was completely oxidized and the CO species placed at the interface site desorbed at lower temperature than that on a bare Ru site. For the higher Sm coverage, in contrast, the boundary of SmOx island was defective in oxygen and the interface of SmO x /Ru(001) yielded more tightly CO bonding state compared with the bare Ru site.

CH bond weakening of cyclohexane on Ni(111) by coadsorbed CO

The effect of coadsorbed CO on the activation of the CH bond of cyclohexane adsorbed on Ni(1 1 1) was investigated by temperature programmed desorption and Fourier transform infrared reflection absorption spectroscopy. Coadsorption of CO caused an upward shift of desorption temperature of cyclohexane and a downward shift of vibrational frequency of the CH stretching. These results indicate that the CH bonds, which point toward the metal surface, are weakened by coadsorbed CO.

Synthesis of Epitaxial TiO2 Thin Films on MgO(100) Using a Combination of an Oxygen-Radical Beam and a Tetra-isopropoxy Titanium Molecular Beam

We synthesized epitaxial titanium oxide thin films on MgO (100) using a combination of a metalorganic pulsed molecular beam and an oxygen-radical beam. At temperatures below 350°C, titanium oxide (TiO2) thin films were exclusively deposited only when an oxygen-radical beam was irradiated along with Ti(i-OC3H7)4. Above this temperature, TiO2 thin films were deposited both in the presence and absence of the oxygen-radical beam; however, the oxygen-radical beam enhanced the deposition rate as well as the crystallinity of the titanium oxide thin films.

Synthesis of TiO2 thin films by metalorganic pulsed molecular beam deposition with an oxygen-radical beam source

Abstract Titanium oxide (TiO 2 ) thin films were synthesized on glass substrates by a metalorganic (Ti(i-OC 3 H 7 ) 4 ) pulsed molecular beam deposition method with an oxygen-radical beam source. The deposition rates of TiO 2 were studied at various substrate temperatures with or without discharging the oxygen-radical beam source. Below the substrate temperatures of 320°C, TiO 2 thin films were deposited only when the radical beam was impinged on the substrate. Above the substrate temperatures of 380°C, self decomposition of Ti(i-OC 3 H 7 ) 4 was the dominant decomposition channel. Dependence of the crystallinity of the films on the deposition conditions was discussed.

Adsorption of CO on Sm-modified Ru(001): formation of unusual adsorption states of CO

Abstract The adsorption behavior of CO over a Sm-preadsorbed Ru(001) surface was studied using photoemission spectroscopy. In addition to the usual CO adsorption upon Ru(001), both more tight and very weak adsorption states of CO appeared at about 105 K. The weakly bound CO was found to yield exceedingly high binding energy (BE) emissions in both core and valence regions compared to CO adsorption on metal surfaces. It is likely that the tightly bound CO attractively interacts with the Sm atom, resulting in the formation of Sm + CO islands over the Ru(001) substrate. This two-dimensional Sm + CO composite produces an adsorption site for the weakly bound state of the CO molecule.

Determination of nitrogen-radical flux by nitridation of Al

Abstract AlN thin films were synthesized on MgO substrates by means of direct nitridation of Al with a newly designed nitrogen-radical beam radio-frequency source while Al was evaporated at a substrate temperature of 380–550°C and an Al deposition rate of 0.1–2.0 A/s. Without using the nitrogen radical beam source, AlN thin films were not synthesized. The nitridation ratio ( N Al ) was determined by electron probe micro analysis (EPMA) and X-ray photoelectron spectroscopy (XPS). From the dependence of the N Al ratio on the deposition rate of Al, the maximum nitrogen radical flux was estimated to be 2.1 × 1014 radicals/cm2 · s. Although Al was completely nitrated no clear evidence of the crystalline phase of AlN was observed in X-ray diffraction (XRD).