To analyze the interference effects on the oscillation of four-probe resistance of one-dimensional nanostructures in experiments, we performed numerical simulation of a nanoscale four-probe system consisting of monatomic carbon chains using self-consistent charge density-functional tight-binding method and nonequilibrium Green's function method. We constructed spectra of the peak spacing of calculated four-probe resistance spectra, and compared them with those expected from a simple model of interference due to multiple reflections between sample-probe contacts. From the peak spacing spectra, the interference effects caused by the multiple reflections and by resonant scattering at the sample-probe contacts are extracted separately. This result suggests that the peak spacing analysis is a potential tool to understand four-probe resistance measurements.
Strontium (Sr) is a well-known template on Si for a highly-desirable transistor gate material SrTiO3. Sr layers are grown epitaxially on hydrogen-terminated Si(111) surface despite the large lattice mismatch of 12%. However, there are still many unclear points concerning the specific interface structure. We need to study how the buried monatomic hydrogen layer behaves to manage the large mismatch. In order to clarify its buried hetero-interface structure related to monatomic hydrogen layer, Si-H bonding states are in situ monitored during Sr growth by Multiple Internal Reflection Fourier Transform Infrared (MIR-FTIR) spectroscopy, and the buried hetero-interface between Sr layer and Si(111) surface is investigated by ex situ neutron reflectometry (NR). FTIR has shown change of Si-H bonding states caused by the Sr growth at the initial monolayer growth stage. Furthermore, we have found the difference in neutron reflectivity profiles between the Sr layers grown on H- and D-terminated Si substrates. These results suggest the existence of buried monatomic hydrogen layer at the hetero-interface acting as an effective component of interface structure to manage the high lattice mismatch.
Depth profiling of multilayered Si/Ti samples using resonance-enhanced multiphoton ionization-sputtered neutral mass spectrometry (REMPI-SNMS) has been compared with that using SIMS to study matrix effects of REMPI-SNMS. We have discussed matrix effects at interface and in the Ti bulk containing oxygen by using Ar+ and O2+ beam as primary ion beam. It is found that the matrix effect at the interface for REMPI-SNMS has been negligible small. On the other hand, the result of REMPI-SNMS measurement has been affected by oxygen in the bulk due to the drastically change of secondary ion yield. We suggest that SIMS/SNMS depth profiles with different primary ions are useful to understand matrix effects.
In order to address the question if the proliferative ability of MSCs is able to be enhanced by surface topology, mesenchymal stem cells from rat adult bone marrow (r-MSCs) were cultured on polystyrene and polybutadiene honeycomb films without cytokines for cell growth. SEM, AFM and time laps phase contrast imaging demonstrated the anomalous cellular adhesion morphology and division on the honeycomb films that have not been observed so far in vitro culture on 2 dimensional scaffolds.; r-MSCs did not spread at all keeping semispherical shape along culture and divided directly in the semispherical cell bodies. The proliferative ability on polystyrene honeycomb films was about 1.5 times higher than that on the control flat film and commercially available polystyrene culture plates, whereas the polybutadiene honeycomb films did not affect the proliferative ability. The polymer dependence of the proliferative ability might be ascribed to the stiffness of the honeycomb structure dependent on polymer. These results led us to the hypothesis that the polystyrene honeycomb films mimic the topography and stiffness of the niche for r-MSCs, inducing the characteristic cell shape and division which may be similar to those in vivo.
We have investigated the acetylene-plasma deposition of amorphous carbon film using “in-situ”, “real-time” infrared absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS). We showed that sp-hydrocarbons are dominant species at the initial stages of deposition, while sp3-hydrocarbon components increase their densities with film growth. IRAS data obtained for the deposited amorphous carbon film exposed to deuterium plasma showed that the density of the sp-hydrocarbon components is relatively high in the vicinity of the film surface. On the basis of the present experimental results, we suggest that the sp-hydrocarbons are transformed into the sp2-, sp3-hydrocarbon components at the film surface through the addition reaction.
The function of proteins is engendered through their dynamic structural changes and dynamic interactions with other molecules. Although their direct real-space and real-time visualization is a straightforward approach to understanding the dynamic molecular processes, the lack of techniques has precluded it. Atomic force microscopy (AFM) is a versatile technique to image proteins in liquids at sub-molecular resolution, but its poor temporal resolution has meant an availability of only static or slow time-lapse images of proteins. Recently, this situation is, however, quickly changing. Over the past 15 years, studies toward increasing the scan speed of AFM and making high-speed imaging compatible with low-invasive imaging have been carried out at my lab. As a result, high-speed imaging, which is 1000 times faster than before, is achieved. This report presents exemplification of dynamic imaging of functioning biological samples.