Ryusuke Nishitani

Topographic study on staging transition in H2SO4-graphite intercalation compound by in situ Raman scattering measurements

The staging kinetics in H 2 SO 4 -GICs has been investigated experimentally by time-and space-dependent Raman scattering measurements. The stage transition from stage n to n -1 begins at the interface between the intercalant reservoir and the a -face of the graphite crystal. The lower stage-( n - 1) domains emerge at the interface and proceed toward the inner region of the crystal. A narrow phase-boundary between different stage domains exists in the localized region and move toward the inner region as the stage transformation progresses. The present results support the model [R. Nishitani, Y. Uno and H. Suematsu: Synth. Met. 7 (1983) 13] that the stage transformation proceeds via propagation of the boundary between well-staged regions. The origin of the stage disorder is also discussed.

STM induced photon emission at the liquid-solid interface

Abstract We have observed STM-induced photon emission at the liquid–solid interface. The luminescence spectra as well as the photon intensity are recorded simultaneously with the measurement of the scanning tunneling microscopy (STM) topography image using an intensified charge coupled device detector and a spectrograph for the spectrum measurements, and a photomultiplier for the photon intensity measurements. The measurements STM induced luminescence are made in non-aqueous liquid which has a wide potential window. The luminescence could only be recorded for 1,4-dioxane at the STM bias voltage at 5xa0V, but other liquids were also tried. The reason behind this result is discussed in relation to the dielectric constant of the liquid.

In-situ STM observation of coalescence of metal particles in liquid

We have madein-situ observation of electrodeposition on the graphite surface in electrolyte(0.5 mM-Bi2O3, 10 mM-HClO4) by means of Scanning Tunneling Microscopy(STM). We have observed the growth and the stripping of Bi metal particles of about 10 nm in diameter, with increase and decrease in the electrode potential, respectively. The STM images are taken in real time in a period of about 30 sec. They show that small particles grow in the initial stage, come in contact with each other, and coalesce in the contact area connecting two neighboring particles.

Vibrational modes of C60 fullerene on Si(111)7×7 surface : estimation of charge transfer from silicon dangling bonds to C60 molecules

We have investigated vibrational modes of C60 monolayer film adsorbed on the Si(111)7×7 surface using high-resolution electron-energy-loss spectroscopy in combination with scanning tunneling microscopy. The differences in energies and in oscillator strengths from a thick C60 film (i.e., bulk C60) are discussed in terms of the charge transfer from silicon dangling bonds to C60 molecules. The amount of charge transfer is estimated to be 1±1 electron(s) compared with the infrared absorption spectra of alkaline-doped C60 fullerides and with the weak electron-molecular-vibration coupling calculation.

Study of the Growth Mechanism of Nanocrystalline Si:H Films Prepared by Reactive Hydrogen Plasma Sputtering of Silicon.

The growth mechanism of hydrogenated nanocrystalline silicon (nc-Si:H) films prepared by reactive hydrogen plasma sputtering of silicon has been studied by means of X-ray diffraction, Raman scattering, and infrared absorption (FT-IR) measurements and SEM observation, and by the diagnosis of the plasma. The nc-Si:H films obtained consist of aggregations of nanocrystalline silicon surrounded by hydrogen atoms. We have found that growth rate and various properties of the nc-Si:H films such as grain size, hydrogen content and morphology are associated both with the incident flux densities of hydrogen ions and the SiHx (x=0–4) species.

Study on Enhancement of Tunnelling-Induced Fluorescence from Porphyrin Film by Substrate Plasmon

We have studied the effect of the plasmon field on the STM-induced luminescence from porphyrin (H2TBPP) film on Au substrate. We have measured the spectrally resolved photon intensity map for the STM-induced luminescence, and found the similarity of their contrast for the photon maps for different spectral regions with different spectral origins, i.e. molecular fluorescence and the local plasmon induced luminescence from the substrate. This fact indicates that the molecular fluorescence is closely related with the plasmon field of the substrate, and supports that the STM-induced fluorescence from porphyrin film on Au is enhanced by the local plasmon field of the Au substrate.

MEASUREMENTS OF SPECTRAL RESOLVED PHOTON INTENSITY MAP FOR METAL PARTICLES BY STM

We have measured for the first time the spectral resolved photon maps of the light induced by scanning tunneling microscopy (STM) of noble metal particles on the graphite surface. The photon intensity as a whole is linearly correlated with the height of the topography of the samples. The photon map changes depending on the wavelength of the light collected. The position-dependent contrast besides the height-dependent contrast is obtained by normalizing the photon map with the corresponding STM topography. The normalized photon maps show that the spectral modes of the light emitted are varied with the tip position on the particles. The result shows that the contrast of the photon map is dependent on both the sample topography and the tip shape. A measurement of an isochromat photon map is also made for the mixture of gold and silver metals for a chemical analysis.

Temperature-Dependent Reaction of rf Hydrogen Plasma with Silicon

The reaction of rf hydrogen plasma with silicon has been studied by characterizing the reaction products as a function of silicon target temperature (80–300° C), hydrogen gas pressure (20–200 Pa) and rf power (50–400 W). It was found that the reaction rate of rf hydrogen plasma with silicon increased at temperatures below 200° C. Major products in the reaction are SiH2 and SiH3 species, and their sputtering rates depend strongly on the silicon target temperature rather than plasma density under the present sputtering conditions. The temperature dependence can be explained in terms of the chemical reaction rate of hydrogen with silicon and the surface density of adsorbed hydrogen on the silicon surface. The plasma bombardment effects on the reaction rate and the desorption rate of adsorbed hydrogen are also discussed.

Measurements of photon intensity map for metal particles by scanning tunneling microscopy

We have measured maps of the photon intensity emitted from gold metal particles in scanning tunneling microscopy (STM) of metal films in ultra high vacuum. The photon images are obtained with a spatial resolution in a nanometer scale. The photon intensity is recorded simultaneously with the measurements of a topography image of the film by STM. We have measured photon images for various morphologies of the film. The observed photon maps are well correlated with the morphology. The photon maps for the dense aggregation of small particles show similar contrasting particles to those on the corresponding morphology. The photon intensity for the rough surface is influenced by the surface geometry of the tip and the particles, and the contrast of the photon map is modified from the morphology. We have observed that the photon intensity is dependent on the material and the grain of the material. The effect of the asymmetry of the tip shape on the photon map is found.

Study of Sputtering Mechanism of Silicon with Hydrogen Plasma Controlled by Magnetic Field

The sputtering mechanism of silicon in rf hydrogen plasma has been studied by controlling plasma density at silicon surface. The amounts of ionic and neutral species have been measured as functions of the magnetic field. We have observed that the amount of each neutral species shows a different dependence on the magnetic field. It is found that the silicon target is sputtered by mainly forming neutral SiH2 and SiH3 species into plasma. The amount of ionic species changes linearly with increase in the magnetic field. There is no direct relationship between the amount of ionic species and the corresponding neutral species.