Kohji ABE (阿部 浩二)

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (B), Fund Type: -, Overall Grant Amount: - (direct: 15900000, indirect: -)
High-quality single-crystal films of α-Al_2O_3 9A thick and SiO_2 30 A thick have been fabricated on metal surfaces of Ru(0001) and Ni(111), respectively. α-Al_2O_3 was fabricated by a phase transition from γ- to α-Al_]2O_3 having a commensurate structure with Ru(0001). Atomic hydrogen during initial growth of an amorphous SiO_2 film and ambient oxygen atmosphere during annealing of this film were essential in forming the single-crystal SiO_2 film on Ni(111). An extraordinary result that the band gap for the oxide layer decreases with decreasing oxide thickness was preliminarily observed using scanning tunneling spectroscopy (STS). This result was confirmed by medium-resolution electron energy loss spectroscopy, in. which the oxide thickness V. dependence of the band gap was measured by α-Al_2O_3 films with various oxide thicknesses below 35 A. For growing ultra-thin films of transition metals on a single-crystal oxide, i.e. a wide band gap crystal, we have, utilized the band gap narrowing and succeeded in making a monoatomic layer (ML) of a Pt film on α-Al_2O_3(9 A)/Ru(0001). We have investigated electronic properties of the oxide layer using C-O vibrational frequencies of CO adsorbed on Pt(1 ML)/α-Al_2O_3(9 A)/Ru(0001) measured by reflection absorption infrared spectroscopy. On the other hand, the crystal structure of SiO_2 film thick 40 A was investigated by grazing incidence X-ray diffraction using syncrotron radiation. A nice single crystal film of β-quartz is fabricated with a thickness of 30 A and a polycrystalline Ni silicide film 10 A thick is formed with a mosaic structure at the interface. These single-crystal oxide films on metal surfaces are new surface materials, which will open a window against other fields of solid state physics and chemistry.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (C), Fund Type: -, Overall Grant Amount: - (direct: 3700000, indirect: -)
The aim of this project is to show that the effect of phase fluctuation plays the crucial role in appearance of incommensurate structure in crystals. We propose a new model to explain the origin of the incommensurate phase transition in quartz. In this model, the intensity of the satellite intensity observed in diffraction experiments is strongly attenuated due to the decrease of Debye-Waller factor, which is attributed to the phase fluctuation. In this research we have proved this model from the following method.
(1) From the detailed investigation of low frequency Raman spectrum in the high symmetry beta phase, the temperature dependence of the integrated intensity was found not to exactly follow the Curie-Weiss law ,but deviates from 30K above the incommensurate phase transition temperature. This is consistent with our model.
(2) The MD calculation was performed using Tsuneyuki potential. The result shows that the short period modulation is more likely to appear than long wave modulation in contrast to the currently accepted model.
(3) The characteristics of incommensurate structure in' dielectric crystals are explained by the rotational degree of freedom of certain group of atoms. The elastically hinged molecule (EHM) model was proposed. The dynamics of the transition is investigated by the computer simulation using the EHM model. The negative poison ratio and several non-linear soliton-like behavior of lattice were also investigated by this and similar models.

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (C), Fund Type: -, Overall Grant Amount: - (direct: 2200000, indirect: -)
In this study, we have established a new fluorescence method which can be used for the study of proton dynamics in ice crystals. 2-naphthol molecule was chosen ad the fluorescence probe to be excited by a pico-second pulse laser. The following results were obtained.
(1) The decay curves of the fluorescence after the pulsed excitation were well explained by the ESPT (excited state proton transfer) model.
(2) A stepwise decrease in the flurescence lifetime from 5ns to 2ns was observed near 120K,which is consistent with the increase in the mobility of the proton in ice above 120K.They were both attributable to the L-defect mobility increase.
(3) The lifetime shortening as well as the increase of the intensity ratio between the fast and slow components were observed around 72K.This temperature is identified as the proton ordering transition, which have been observed only in KOH-dopedice in dielectric and calorimetric measurements. The precent result shows that our fluorescence mothod has high sensitivity to detect the local tendency of proton ordering near the probe naphthol moleculesince the fluctuation increase near the transition makes the excited state of the probe molecule less stable and makes the lifetime short. We conclude that the inclusion of the probe molecule would locally break the so-called ice rule and stimulate the proton ordering eve without KOH-doping.
(4) In order to see how the naphthol molecule is included in ice crystal, we grew a pure naphthol crystal by a vacuum sublimation method. From the comparison of the naphthol-doped ice spectra, we have assigned the vibrational structure in the fluorescence spectra. The result shows that there is a characteristic zero phonon shift depending on the type of inclusion, which will be useful for the continuing study on the melting transition of ice.
These results were partly published in several journals and also presented in the International Meeting on the Physics an Chemistry of Ice held in New Hampshire in Aug.1996. (Proc.will be soon published in J.Phys.Chem.)

Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for General Scientific Research (C), Fund Type: -, Overall Grant Amount: - (direct: 2500000, indirect: -)
Using a newly developed method for the studies on the dynamic of phase transitions, the following results were obtained.
(1).A molecular crystal 'Sucrose' was investigated with a pico-second pulsed laser. It was found the lifetime of the fluorescence sharply decreases as the melting point is approached. By comparing with the X-ray study, it was found that the onset of the observed shortening from a temparature about 25K below Tm was an indication of the collapsing process of the regular crystal structure into an amorphous state. This would be the first measurement of a precursor of a melting transition by light.
(2) A single crystal of ice(Ih) doped with 2-naphthol(2-C8H10(0H)) molecules was grown. The fluorescence lifetime measurements recealed that a stepwise decrease of lifetime from 5ns to 2ns occurs between 130K and 200K.The behavior was analyzed by a model which takes into account the relaxation of the proton configurations in the neighborhood of the naphthol molecules. The analysis allowed us to estimate the activation energy for the generation of L-defects in ice.
(3) A structural phase transition of a single crystal biphenyl was investigated by a similar method. The lifetime shows a minimum at the transition temperature Tc=40K, where biphenyl undergoes a second order incommensurate phase transition. In conrast to the significant change in the lifetime of the broadband fluorescence, a sharp zero-phono line at lambda=533nm was found to have a rather long lifetime without any critical temperature depenedence.
All the results confirmed that that the present method can be a sensitive probe of fluctuations associated with the phase transitions and would be able to be applied to variety of phase transitions. The results were reported, e.g.in the 8th International Meeting on Ferroelectricity and will appear in several journal(in press and submitted).