Takahiro Kondo

So far, poly(L-lactic acid), PLLA nanosheets proved to be promising for wound healing. Such biodegradable materials are easy to prepare, bio-friendly, cost-effective, simple to apply and were shown to protect burn wounds and facilitate their healing. At the same time, certain metal ions are known to be essential for wound healing, which is why this study was motivated by the idea of incorporating PLLA nanosheets with Zn2+ ion containing nanoparticles. Upon being applied on wound, such polymer nanosheets should release Zn2+ ions, which is expected to improve wound healing. The work thus focused on preparing PLLA nanosheets embedded with several kinds of Zn-containing nanoparticles, their characterization and ion-release behavior. ZnCl2 and ZnO nanoparticles were chosen because of their different solubility in water, with the intention to see the dynamics of their Zn2+ ion release in liquid medium with pH around 7.4. Interestingly, the prepared PLLA nanosheets demonstrated quit similar ion release rates, reaching the maximum concentration after about 10 h. This finding implies that such polymer materials can be promising as they are expected to release ions within several hours after their application on skin.

Longitudinal strains in epitaxial monolayer graphene (EMG) grown on SiC substrates were evaluated by z-polarization Raman microscopy. Due to the covalent bonds formed at the interface between graphene and the substrate, strong compressive strains were loaded on the EMG, which were sensitively detected by Raman spectroscopy. Our polarization Raman microscope was specially designed for evaluating the longitudinal (z-polarization) strain, as well as the lateral (xy-polarization). Z-polarization Raman microscopy revealed the relationship between the fluctuation of the local strains and the sample morphology in the SiC-graphene through submicron spatial resolution mapping. The amount of strain estimated through Raman shift and its spatial inhomogeneity have critical influence on the mobility of electrons, which are essential for future device applications of EMG.

Mixed oxides of Zn and Sn are of interest for gas sensing and diverse optoelectronic applications, and therefore new approaches to prepare such nanomaterials are anticipated. This study reports, for the first time, on the use of laser ablation in liquid applied to a Sn-Zn alloy and describes obtained products. Core@shell Sn@SnO and ZnO nanoparticles are shown to be produced by millisecond pulsed laser upon ablating eutectic Sn-Zn alloy in water. The as-prepared materials were found to contain surface hydroxide layers which were dehydrated to SnOx and ZnO when higher laser energy fluence was applied or when the products were post-treated at 200C in air. The morphology, shape and size distribution, phase and chemical composition of prepared nanoparticles were studied as a function of laser parameters used during their preparation. Increase in pulse energy was found to result in fabrication of finer particles. It was found that while both metallic Sn and SnOx were presented in the product, zinc was always oxidized to its oxide ZnO. In addition, when properly annealed, the produced nanomaterial demonstrated gas sensing response towards ammonia at room temperature.

We investigated two-dimensional lipid bilayers by spectroscopic imaging with surface enhanced Raman spectroscopy (SERS). A DSPC lipid bilayer incubated on a glass substrate was coated with a thin layer of silver. Due to the strong electromagnetic enhancement of the silver film and the affinity to lipid molecules, the Raman spectrum of a single bilayer was obtained in a 1 s exposure time with 0.1 mW of incident laser power. In the C-H vibrational region of the spectra, which is sensitive to bilayer configurations, a randomly stacked area was dominated by the CH3 asymmetric-stretch mode, whereas flat areas including double bilayers showed typical SERS spectra. The spectral features of the randomly stacked area are explained by the existence of many free lipid molecules, which is supported by DFT calculations of paired DSPC molecules. Our method can be applied to reveal the local crystallinity of single lipid bilayers, which is difficult to assess by conventional Raman imaging.

Understanding the effect of reactive oxygen species (ROS), such as singlet oxygen molecule and atomic oxygen, on polyimide (PI) film properties, such as wettability, morphology, and chemical bonding state, is essential for further development of PI-based surfaces. We investigated the effect of different ROS generated during ultraviolet (UV) and plasma treatment in oxygen gas on surface modification of Kapton PI. Different surface modification techniques, UV and plasma treatment, are known to generate different ROS. In this work, we demonstrate the effect of different ROS on PI surface modification. From the diagnostics of ROS by means of electron spin resonance and optical emission spectroscopy, we confirmed that during UV treatment, excited singlet oxygen molecules are the main ROS, while plasma treatment mainly generated atomic oxygen. The wettability of PI surface treated by UV and plasma resulted in hydrophilic PI surfaces. XPS results show that the wettability of PI samples is mainly determined by their surface O/C ratio. However, chemical bonding states were different: while UV treatment tended to generate C=O bonds, while plasma treatment tended to generate both C?O and C=O bonds. Singlet oxygen molecules are concluded to be the main oxidant during UV treatment, and their main reaction with PI was concluded to be of the addition type, leading to an increase of C=O groups on the surface of PI film. Meanwhile, atomic oxygen species were the main oxidant during plasma treatment, reacting with the PI surface through both etching and addition reaction, resulting in a wider variety of bonds, including both C?O and C=O groups.

In this study, nanomaterials prepared via laser ablation of tin in water are systematically studied and compared. Tin targets were ablated by both millisecond and nanosecond pulsed lasers, resulting in core@shell product nanostructures with different chemistries and morphologies. Depending on laser fluence, the obtained core@shell nanoparticles had either Sn or SnO cores and SnOx shells with varied surface hydration degree. Optical emission spectra of laser-generated plasmas were taken, giving additional support to nanoparticle formation mechanisms. Finally, gas sensing at room temperature is demonstrated as one of the potential applications for such nanostructures.

The present work reports on room-temperature ethanol sensing performance of ZnO nanospheres and nanorods prepared using pulsed laser ablation in water. Nanosecond and millisecond lasers were used to prepare ZnO nanomaterials with hexagonal wurtzite crystal structure. The two contrasting nanostructures were tested as gas sensors towards volatile compounds such as ethanol, ammonia, and acetone. At room temperature, devices based on both ZnO nanomaterials demonstrated selectivity for ethanol vapor. The sensitivity of nanospheres was somewhat higher compared to that of nanorods, with response values of similar to 19 and similar to 14, respectively, towards 250 ppm. Concentrations as low as 50 ppm could be easily detected. (C) 2017 The Japan Society of Applied Physics.

Highly-reactive gas-phase species, such as OH, O-3 and NOx, present at the air/water interface, play a crucial role in natural environments. Unique hydrogen bond structures, not seen in the bulk, exist at the air/water interface. Here, by means of vibrational sum-frequency generation spectroscopy, we probe the interfacial water structure, and demonstrate how reactive gas-phase species interact with the water surface. We found that the reactive gas-phase species supplied to the water surface largely influenced the water surface structure. Furthermore, we suggest a higher density of reactive species at the water surface as compared to the bulk.

Effects of an externally applied electric field on orientation polarization of the water molecules at an insulator-solution interface were studied using sum-frequency generation (SFG) spectroscopy. Orientation of water molecules that have a structure causing a signal at similar to 3100 cm(-1) in the SFG spectra are strongly affected by an applied electric field. Moreover, the water dipole flips when an electric field is applied in the opposite direction of the electric field generated from the surface charge of a solid insulator (calcium fluoride). The required electric field is extremely low compared to that expected by the zeta potential, implying that the structure of the SFG signal is formed not on the calcium fluoride surface, where the electric field is expected to be the strongest, but further from the interface. (C) 2014 AIP Publishing LLC.

Effects of a rotating magnetic field (RMF) on the electron energy distribution function (EEDF) and on the electron density are investigated with the aim of controlling the radical composition of inductively coupled plasmas. By adjusting the RMF frequency and generation power, the desired electron density and electron energy shift are obtained. Consequently, the amount and fraction of high-energy electrons, which are mostly responsible for direct dissociation processes of raw molecules, will be controlled externally. This controllability, with no electrode exposed to plasma, will enable us to control radical components and their flux during plasma processing. (C) 2013 AIP Publishing LLC.

The effects of a rotating magnetic field (RMF) on the electron energy distribution function (EEDF) are studied with the aim of controlling the EEDF of radio-frequency (rf) inductively coupled plasmas. In order to obtain the EEDF correctly, the external filter and the reference electrode of the probe system are used to compensate for the effect of the rf (13.56 MHz) and the RMF (1.7-2.9 MHz) fluctuations of the plasma potential. With increasing RMF frequency, the high energy component of the EEDF increases. Space potential and effective electron temperature also tend to increase with increasing RMF frequency. (C) 2012 Elsevier B. V. All rights reserved.