We studied the adsorption and dynamical behavior of pyrene molecules on single-wall carbon nanotubes (CNT), using both first-principles density functional theory (DFT) and classical molecular dynamics methods. For the energetics, the van der Waals corrected DFT-D2 method was used to determine the stable adsorption sites and adsorption energies. In the (6,6) CNT/pyrene system, the adsorption energy was determined to be 0.73 eV by DFT-D2, in comparison to the result of 0.46 eV within local density approximation. This has shown that it is hard to peel pyrene from CNT at room temperatures. On the other hand, finite-temperature nonequilibrium molecular dynamics simulation has revealed that following the temperature gradient the pyrene molecule can readily move along the CNT sidewall, indicating that it is plausible to peel pyrene when it has moved to the end of the CNT. We have also studied the effect of pyrene adsorption on the thermal conductivity of CNT.
A gap mode in surface enhanced Raman scattering (SERS) can provide single molecule sensitivity and spatial resolution of a few nanometers. To establish a gap mode Raman spectroscopy, we investigated three distinct geometries of a flocculate of silver nanoparticles (AgNP), a gap mode with a metal substrate/molecule/metal nanoparticle sample under an external, and attenuated total reflection (ATR) geometry. We succeeded to elucidate adsorbed state of different thiol molecules in flocculates of AgNPs as well as counter ions in solutions. A large number of AgNPs were immobilized on Ag films via various thiol molecules using van der Waals and electrostatic interaction, which provided enormous SERS enhancement of 108-109 at a nanogap. A propagating surface plasmon (PSP) combined with a gap mode under ATR geometry yielded significantly larger SERS enhancement than that under an external geometry.
In recent years, the analysis of biological samples has been extensively performed in pharmacokinetic and metabolic studies. The use of Secondary Ion Mass Spectrometry (SIMS) with conventional monomer ion beams, such as Ar+, Cs+ or Ga+, in biological applications is difficult because of the low secondary ion yield of large organic molecules and the complicated fragment ion signals. The use of cluster ions as primary projectiles in SIMS has spread dramatically in the past decade. Bismuth (Bi) cluster ions are now the most familiarized primary ions in cluster SIMS because of the high convergence property and the high molecular ion yield. Argon gas cluster ion beam (Ar-GCIB) is also one of the most attractive primary projectiles for biological application because of the soft sputtering without damage accumulation. However, our knowledge of detection limit and sensitivity is still insufficient for the practical analysis of complex biological samples with cluster SIMS. In addition, imaging mass spectrometry with high spatial resolution is crucially essential for tissue and cell analysis. In this study, lipid standard samples were measured in order to examine the detection limit and the spatial resolution of our Ar-GCIB SIMS, and the results were compared with those of the commercial Bi cluster SIMS. The results indicated that Ar-GCIB SIMS has a capability to obtain the valuable information in biological analysis, however, the improvement on spatial resolution and sensitivity is still required.
We fabricated resistive random access memory (ReRAM) structure of Pt/Bi2Sr2CaCu2O8+δ(Bi−2212) bulk single crystal/Pt, and investigated Cu electronic states of the Bi−2212 by X−ray absorption near−edge structure. Hydrogen atoms are efficiently introduced into Bi−2212 with the assistance of catalytic effect of Pt by annealing Pt/Bi−2212 structure in hydrogen atmosphere. Resistive switching effect was generated by the reduction of Cu valence due to the formation of chemical bonding between in−plane oxygen of CuO2 layer and hydrogen (O−H bond), which corresponds to the formation of Cu(OH)2−like material, in the Bi−2212 in the vicinity of the Pt electrode. It is, therefore, suggested that the resistive switching effect occurred by bonding/dissociation of the O−H bond due to the migration of the hydrogen ions.
We employed hard X-ray photoelectron spectroscopy in operating devices. This method allows us to investigate bias dependent electronic states while keeping device structures intact. Using this method we have investigated electronic states and potential distribution in a Pt gate metal/high-k gate stack structure under device operation. We have found that a potential gradient was formed at the Pt/HfO2 interface by analyzing the shifts of the core levels as a function of the applied bias voltage. Angle resolved photoelectron spectroscopy revealed that a SiO2 layer was formed at the Pt/HfO2 interface, which is the origin of the potential gradient formed at the Pt/HfO2 interface.
We have developed a totally flexible, sheet-shaped biofuel cell by stacking a bioanode fabric, a hydrogel sheet containing electrolyte and fuel (fructose), and an O2-diffusion biocathode fabric. The results presented include two strategies to improve the performance of the device. (1) An anode modified with an appropriate CNT dispersion showed higher activity. (2) The gas-diffusion biocathode was improved by optimizing its hydrophobicity. The improved biofuel cell sheet produced a maximum power density of 1.0 mW cm−2 at 0.36 V even when bent. Such a flexible, sheet-shaped power source could be combined in the future with flexible electronic to make wearable devices.
We report direct observations of laser-induced coherent lattice vibration in gold nanocrystals on the fused quartz substrate using picoseconds time-resolved X-ray diffraction. The single-layered gold nanocrystal film is formed by means of vapor-evaporated gold film. The lattice constant change and vibration period of lattice constants of 111, 200, 311, 220, and 222 of gold nanocrystals after femtosecond laser irradiation at 400 nm are almost similar within nanosecond region. These results indicate that the strain generated from laser-induced expansion within a few picoseconds and propagates into the finite size gold crystals. The feature of these photo-induced lattice vibrations in gold nanocrystals is discussed.
An outstanding challenging in nanomagnetism is the quantitative understanding of magnetization reversal process of nanostructures. We investigate the magnetization reversal of individual Co islands on Cu(111). We measure switching fields HSW of single Co islands using spin-polarized scanning tunneling microscopy/spectroscopy at 8 K. The switching field changes with island size. The switching field increases with size and reaches a maximum value of 2.4 T at a size of 5500 atoms, and decreases for larger islands. To discuss magnetization reversal processes, we extract the energy barrier ΔE for magnetization reversal as a function of island size. Our analysis reveals a crossover of the magnetization reversal from an exchange-spring behavior to domain wall formation with increasing size at around 7500 atoms.
Aim at nanoscale mapping of organic matters, a novel Laser-SNMS instrument was developed by combining an FIB-TOF-SIMS with high lateral resolution and a femtosecond laser with high power. The phase separation structure of polystylene/polyhydroxystylene polymer alloy was analyzed. In case of conventional SIMS mode, the fragmentation signals of the two kinds of polymer were observed. The obtained fragment signal has little quantity, the acquired constituent distribution counts cannot be recognized two polymers. In case of Laser-SNMS, the monomer signal of each polymer was clearly observed. The acquired constituent distribution was able to distinguish each polymer in phase separation structure.