Susumu Ikeda

Deformation of Thin Copper Crystals

Stress/strain curves of many number of copper crystals having various radii from 0.06 to 1 mm were measured. The range of easy glide increases considerably when the radius of crystal decreases. In the case of suitably oriented crystal the range of easy glide reaches to 50 per cent in shear, when the radius of crystal decreases less than 0.1 mm. The extrapolation of the range of easy glide to the infinitesimal radius gives a value between 40 to 80 per cent in shear irrespectively to the initial crystal orientation. The hardening rate in the easy glide region considerably decreases with the decreasing crystal radius. Meanwhile, the critical shear stress, the stress required for the transition from the easy glide to the rapid hardening region, the hardening rate in rapid hardening region reveal only slight dependence on the crystal radii, i.e. the former two slightly increase and the last slightly decreases with the decreasing crystal radii. These results are discussed qualitatively by introducing a concept ...

Surface-Mediated Visible-Light Photo-oxidation on Pure TiO2(001)

We used STM to observe visible light photo-oxidation reactions of formic acid on the ordered lattice-work structure of a TiO(2)(001) surface for the first time. The nanostructured surface makes the band gap significantly smaller than 3.0 eV only at the surface layer, and the surface state of the crystal enables a visible light response.

Three-dimensional study on the interconnection and shape of crystals in a graphic granite by X-ray CT and image analysis

Abstract The technique of investigating 3-dimensional interconnections and the shapes of crystals in a rock by X-ray computerized tomography (CT) and image analysis was developed using a graphic granite specimen as an example. Fifty 2-dimensional tomographic images (slices) of the graphic granite were obtained ‘non-destructively’ using a medical X-ray CT scanner. Since a CT value of the specimen was decreased with increasing cross-sectional sample area by the effect of beam-hardening, the CT value was corrected using the area of each slice. Binary images of the slices were made comparing one of them with a thin-section of the slice. Using the binary images, connection analysis of quartz rods in the graphic granite specimen was performed on the basis of percolation theory (cluster labelling). This analysis showed that at least 89.9% of the quartz rods were connected in three dimensions. Furthermore, the 3-dimensional shape of the quartz rods was analysed using the 2-point correlation function calculated from the binary images. The average shape of the quartz rods was obtained by fitting an ellipsoid to the high-value region of the 2-point correlation function. The elongation axis of the ellipsoid agreed well with the crystallographic c-axes of the quartz rods.

Low-energy excitations in amorphous polymers

In order to investigate low‐energy excitations below 10 meV, inelastic neutron‐scattering measurements have been carried out on various organic amorphous polymers at 10 and 50 K and three inorganic glasses at 150 and 295 K. It was found that a broad excitation peak is observed for all amorphous materials in the ω range of 1.5–4.0 meV irrespective of different chemical structures. On the other hand, highly crystalline polyethylene with a degree of crystallinity 0.96 shows no such broad peak, indicating that the low‐energy excitation is characteristic of amorphous materials. We have employed an asymmetric double‐well potential as a common origin for the low‐energy excitation in amorphous materials and analyzed the results of amorphous polyisobutylene to confirm validity of this model and alternatively to determine parameters of the potential. Analysis of the temperature dependence of the inelastic‐scattering intensity of the low‐energy excitation leads to a concept of phonon‐assisted tunneling in the asymmetric double‐well potential.

Quantitative evaluation of attenuation contrast of X-ray computed tomography images using monochromatized beams

Abstract A quantitative relation between the linear attenuation coefficient (LAC) obtained by Synchrotron Radiation X-ray computed tomography (observed LAC) and the theoretically calculated LAC (theoretical LAC) of standard materials (minerals and metals) has been obtained for an X-ray microtomographic system at BL20B2 of SPring-8, Japan. This system, called SP-μCT, uses highly monochromatized and well-collimated X-ray beams produced by a synchrotron radiation source. Three-dimensional images were obtained for samples 0.4.4 mm in size at X-ray energies of 15.35 keV with a voxel size of 5.83 × 5.83 × 5.83 μm3. A histogram of the observed LAC for each sample was well-fitted by a Gaussian curve except for heavy metals whose X-ray transmittance was insufficient. The contrast resolution of CT images is best (within 5% of the LAC value) at LACs of about 10.30 cm-1. A garnet schist was imaged with SP-μCT to verify the observed-theoretical LAC relation for minerals contained in a rock sample. The result was consistent with the relation obtained for the standards. The CT and back-scattered electron images of the rock sample were compared. The present results put restrictions on discrimination of mineral phases and estimation of chemical compositions (e.g., Mg/Fe ratio) of certain minerals forming solid solutions based on CT values. The present quantitative relationship between observed and theoretical LACs enables us to obtain an absolute elemental concentration map by imaging just above and below the X-ray absorption edge energy of the element (subtraction method).

Effect of annealing on the mobility and morphology of thermally activated pentacene thin film transistors

Pentacene thin film transistors (TFTs) were fabricated by the organic molecular beam deposition method. The TFTs were characterized in order to study the effect of thermal annealing on the morphology and carrier mobility of the transistors. For all the TFT samples the mobility exhibited an Arrhenius relationship with temperature, indicating a thermally activated transport that could be explained by the carrier trap and thermal release transport mechanism. Therefore, in order to investigate the annealing effect, we tested the data for a significant period of time after annealing until the temperature recovered to room temperature, so that the thermal activation effect was screened and possible effects of thermal expansion and stress were also ruled out. As a result, we found that only with a temperature below a critical temperature of approximately 45°C could annealing improve the mobility, while annealing with T>50°C would decrease the mobility compared to the value before annealing. Atomic force microsco...

Analysis of charge transport in a polycrystalline pentacene thin film transistor by temperature and gate bias dependent mobility and conductance

The gate bias and temperature dependent field-effect mobility and conductance of a polycrystalline pentacene thin film transistor (TFT) were analyzed to study the charge transport in the material. Since both heating and cooling can obviously change the film morphology, a relatively narrow temperature range was adopted to rule out the possible influence of structure variation on the device characterization. Both mobility and conductance values increased with the gate bias and showed a thermally activated Arrhenius-like behavior, while the threshold voltage deceased with temperature. Several models were compared, and it was found that the observations could only be well interpreted by a multiple trapping model, which suggests that the temperature and gate bias dependences should be attributed to the increased free charge carrier density. The density of trap states in the band gap was evaluated by the field-effect mobility as well as the field-effect conductance data. The results disclose a possible field-ef...

Growth of nanographite on Pt(111) and its edge state

The nanographite grains, the diameter of which was around 5nm, were formed on Pt(111) by exposing the Pt(111) substrate to benzene gas at room temperature and annealing it up to 850K. The increase of relative number of edge atoms enabled the observation of edge-derived electronic states. The measurement of ultraviolet photoelectron spectroscopy and near edge x-ray absorption fine structure on the nanographite revealed the appearance of the edge state located at the Fermi level.

Low-energy excitations in polyethylene: comparison between amorphous and crystalline phases

Abstract Neutron inelastic scattering measurements were carried out on semicrystalline and highly crystalline polyethylenes with degrees of crystallinity of 0.46 and 0.96, respectively, at 10 K to investigate low-energy excitations below 10 meV. It was found that the density of states G (ω) of the crystalline phase can be described by the Debye model but that of the amorphous phase shows an excess excitation peak at ≈2.5 meV. The calculated heat capacity C ( T ) of the amorphous phase shows a peak at ≈ 6 K in the plot of C ( T )/ T 3 versus T , while C ( T )/ T 3 for the crystalline phase is constant at low temperatures.

Nondestructive three-dimensional element-concentration mapping of a Cs-doped partially molten granite by X-ray computed tomography using synchrotron radiation

Abstract Nondestructive, three-dimensional (3-D) element-concentration mapping was performed and high spatial resolution and quantitative applicability were demonstrated. X-ray computed tomography using synchrotron radiation developed at SPring-8 (SP-μCT) enabled us to acquire high-resolution tomographic images with X-ray energies just above and below the absorption edge of an element. Concentration of the element could be calculated from the difference of these images with a correction using standard material. A 3-D Cs concentration map of a partially molten granite was obtained by this technique and compared with a 2-D element map produced by an electron-probe X-ray microanalyzer (EPMA), with respect to spatial and compositional resolution. A spatial resolution of about 20 μm was achieved by SP-μCT. The compositional resolution of ± 2.5 wt% was achieved using the following two calibration processes of linear attenuation coefficients (LAC): (1) calibration based on the empirical relationship between theoretical LACs and observed CT values, and (2) the calibration of spatial variation of observed mass attenuation coefficients (MAC) due to X-ray energy shift using a standard material (Cs-bearing solution). Using the Cs2O map obtained by SP-μCT, 3-D image analysis was demonstrated, for example, connectivity of melt was calculated and it was found that 88 vol% of melt was connected in three dimensions in the sample. Furthermore, the possibility of 3-D diffusion studies by SP-μCT was discussed based on the spatial and compositional resolutions. This “nondestructive” and “3-D” mapping technique can reveal the internal compositional distribution of precious samples such as extraterrestrial materials and cultural assets, and can solve many 3-D issues such as material transport in geological and industrial materials.