Kenji Hirakuri

Size-Tunable Silicon/Iron Oxide Hybrid Nanoparticles with Fluorescence, Superparamagnetism, and Biocompatibility

Magnetic/fluorescent composite materials have become one of the most important tools in the imaging modality in vivo using magnetic resonance imaging (MRI) monitoring and fluorescence optical imaging. We report herein on a simplified procedure to synthesize hybrid nanoparticles (HNPs) that combine silicon and magnetic iron oxides consisting of magnetite (Fe(3)O(4)) and maghemite (γ-Fe(2)O(3)). Intriguingly, our unique synthetic approach can control magnetic and optical behaviors by reducing the particle size, demonstrating that the HNPs with the mean diameter of 3.0 nm exhibit superparamagnetic behavior and green fluorescence in an aqueous solution, ambient air, and a cellular environment, whereas the HNPs with the mean diameter more than 5.0 nm indicate ferromagnetic behavior without fluorescence. Additionally, both HNPs with different diameters possess excellent magnetic responsivity for external applied magnetic field and good biocompatibility due to the low cytotoxicity. Our biocompatible HNPs with the superparamagnetism can provide an attractive approach for diagnostic imaging system in vivo.

Improved blood compatibility of DLC coated polymeric material.

There is currently an increasing interest in the use of DLC (diamond like carbon) films in biomedical applications. These investigations making use of DLC in the biomedical area indicate its attractive properties. In this study, we succeeded in depositing DLC on polymer substrates and found the best conditions and method for this application. We evaluated the blood compatibility of polycarbonate substrates coated by DLC (PC-DLC) under different conditions by using epifluorescent video microscopy (EVM) combined with a parallel plate flow chamber. Segmented polyurethane (SPU), which has been used to fabricate medical devices including an artificial heart, and proven to have acceptable blood compatibility, was compared with polycarbonate substrates coated with DLC film. The EVM system measured platelet adhesion on the surface of the DLC, by using whole human blood containing Mepacrine labeled platelets perfuse at a wall shear rate of 100 s-1 at 1 min intervals for a period of 20 min. PC-DLC demonstrated that Tecoflex showed higher complement activation than PC-DLC. There were significant differences between the PC-DLC substrates. On the basis of these results, it is recommended for use as a coating material in implantable blood contacting devices such as artificial hearts, pacemakers, and other devices. This DLC seems to be a promising candidate for biomaterials applications and merits further investigation.

Roughness and deposition mechanism of DLC films prepared by r.f. plasma glow discharge

Abstract Due to the attractive properties, diamond-like amorphous carbon (DLC) films have been developed as resist material for photo lithography and as hard coatings. For these applications flat surfaces are required. In this work, the surface morphology and the deposition mechanism of DLC films have been investigated. Using parallel plate r.f. plasma glow discharge, methane gas was decomposed for deposition of DLC films on the third electrode located perpendicularly to the two parallel plates. The DLC films were deposited on Si substrates at various distances from the plasma discharge and different bias voltages. IR spectra of the DLC films were taken with an FTIR spectrometer. Determination of the roughness was performed by atomic force microscopy (AFM). An optical emission profile taken between plasma edge and substrate surface was employed to monitor the occurrence of neutral radicals.

The synthesis and structural characterization of boron-doped silicon-nanocrystals with enhanced electroconductivity

Boron (B)-doped silicon-nanocrystals (Si-NCs) with wavelength-tunable photoluminescence (PL) properties in the visible region are successfully prepared for the first time, leading to significant enhancement of electroconductivities. The B-doped Si-NCs are prepared on a p-type Si(100) substrate by co-deposition of p-type Si(100) chips/boron chips/silica disk targets. As the number of the B chips used as the target is increased, the amount of doped B content increases gradually. Here the amount of doped B content in the Si-NCs is controlled from 0 to 0.4, 0.7, 2.3 at.%. The B elemental states, compositional ratios, and surface condition of the obtained Si-NCs are fully characterized by high-resolution transmission electron microscopy (HRTEM) observations, micro-Raman scattering spectroscopic analysis, etc. Our B-doped Si-NCs possess both the continuous luminescence property in the visible region and enhanced electroconductivity. The red-shift of the PL peak is confirmed by the increase of the amount of doped B content. This paper should be very important from the viewpoint of application to optoelectronic devices and electroluminescent (EL) displays.

Influence of the methane concentration on HF-CVD diamond under atmospheric pressure

Abstract The most common approach for chemical vapor deposition (CVD) of diamond is the utilization of hydrocarbon gases highly diluted in hydrogen at low pressure (e.g. several thousands of Pascals (Pa)). The quality and growth rate of diamond strongly depends on the methane gas concentration, especially at high pressure, because the generation of atomic hydrogen sharply decreases with increasing pressure. In order to increase the growth rate, we have carried out CVD diamond growth under atmospheric pressure. A dramatic increase of the growth rate could be achieved when using the hot-filament (HF)–CVD technique at atmospheric pressure. Such an increase could already be observed in a previous experiment, however, under varying pressure and at a constant methane concentration of 0.5%. Furthermore, the crystalline quality of the diamond grains could be improved by hydrogen etching at atmospheric pressure. In the current study, the methane volume concentration was varied from 0.03% to 2.0% in order to estimate its effect on diamond growth. The relationship between the quality of the deposited diamond and the methane concentration has been investigated by Raman spectroscopy. The amount of activated hydrogen was estimated from the etching rate of non-diamond components. At high atmospheric pressure, high growth rates could be achieved up to a methane concentration of 0.3%. Moreover, the growth rate has also been shown to depend on the residence time of the precursor in the reactor. Finally, Raman analysis revealed an increasing quality of diamond with decreasing methane concentration.

High quality chemical vapor deposition diamond growth on iron and stainless steel substrates

Due to the catalytic effect and the rapid diffusion coefficients of carbon species into iron-based materials such as iron and 18-8 stainless steel [18% chrome (Cr) and 8% nickel (Ni)], it is very difficult to produce diamond grains on such substrates. However, diamond growth on iron-based materials is extremely important for mechanical and electrical applications, since these materials are widely used in industrial field and fundamental science. In our previous study, diamond nucleation and subsequent growth have been precisely controlled by the residence time of the source gas, which is an essential parameter. Here, we have carried out diamond growth on iron-based materials using the hot-filament chemical vapor deposition technique with varying residence times. At low residence times, diamond grains with practically useful growth rate are grown. The growth rate of diamond grains on stainless steel substrates was a factor of about 10 greater than that on a regular silicon substrate at optimum conditions. ...

Application of diamond-like carbon films to the integrated circuit fabrication process

Abstract On account of their attractive properties, amorphous diamond-like carbon (DLC) films have been developed as resist materials for lithography and as hard coatings. In this paper, we investigate the etching properties of DLC films and the electrical properties of a pn junction fabricated using DLC films. Using a parallel-plate radio frequency plasma glow discharge, methane gas was decomposed for the deposition of the DLC films on a silicon substrate. Then oxygen was used to etch the films. Properties, such as the etching rate and the cross-sectional profile, were evaluated by atomic force microscopy (AFM). In order to produce the diode, DLC films were applied to resist materials as a part of the fabrication process. The etching rate of DLC films increases with decreasing oxygen pressure. We suspect that the high etching rate at low pressure from the negative bias voltage originates from the sputtering of accelerated ionic species. The bias voltage also increases with decreasing oxygen pressure. In order to estimate the shape of the etched edge, AFM images and cross-sectional profiles of etched DLC films were investigated as a function of oxygen pressure. At high pressure, isotropic etching by neutral radicals occurred, as the shape of the etched edge was not vertical. The top and bottom edges coincided vertically at low pressure because of the high bias voltage. The yield of excellent pn junctions fabricated using DLC films as resist materials was investigated as a function of deposition and etching pressure. From the results of the characteristics of the pn junction and the yield, for the integrated circuit fabrication process the optimum condition for both deposition and etching is at low pressure.

Surface properties and field emission characteristics of chemical vapor deposition diamond grown on Fe/Si substrates

Electron field emission characteristics of diamond grains fabricated on iron dot-patterned silicon (Fe/Si) substrates at different methane concentrations have been investigated. The characteristics of the samples could be improved by control of the methane concentration during diamond fabrication. Etching treatment of the as-grown diamond has enhanced the emission properties both with respect to current and threshold voltage. In order to study the influence of etching effects on the field emission characteristics, the respective surfaces were studied by Raman spectroscopy, Auger electron spectroscopy, and electron spectroscopy for chemical analysis (ESCA). ESCA revealed intensive graphite and FeOx peaks on the sample surface grown at high methane concentration. For the etched samples, the peaks of diamond and silicon carbide were observed, and the peaks of nondiamond carbon disappeared. The experimental results show that the etching process removes graphitic and nondiamond carbon components.

Effects of silica and titanium oxide particles on a human neural stem cell line: morphology, mitochondrial activity, and gene expression of differentiation markers.

Several in vivo studies suggest that nanoparticles (smaller than 100 nm) have the ability to reach the brain tissue. Moreover, some nanoparticles can penetrate into the brains of murine fetuses through the placenta by intravenous administration to pregnant mice. However, it is not clear whether the penetrated nanoparticles affect neurogenesis or brain function. To evaluate its effects on neural stem cells, we assayed a human neural stem cell (hNSCs) line exposed in vitro to three types of silica particles (30 nm, 70 nm, and <44 μm) and two types of titanium oxide particles (80 nm and < 44 μm). Our results show that hNSCs aggregated and exhibited abnormal morphology when exposed to the particles at concentrations ≥ 0.1 mg/mL for 7 days. Moreover, all the particles affected the gene expression of Nestin (stem cell marker) and neurofilament heavy polypeptide (NF-H, neuron marker) at 0.1 mg/mL. In contrast, only 30-nm silica particles at 1.0 mg/mL significantly reduced mitochondrial activity. Notably, 30-nm silica particles exhibited acute membrane permeability at concentrations ≥62.5 μg/mL in 24 h. Although these concentrations are higher than the expected concentrations of nanoparticles in the brain from in vivo experiments in a short period, these thresholds may indicate the potential toxicity of accumulated particles for long-term usage or continuous exposure.

The effect of ultrasonic vibration on CVD diamond nucleation

Abstract Nucleation and subsequent growth of chemical vapor deposition (CVD) diamond particles on silicon substrates under ultrasonic vibration have been investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Ramas spectroscopy. The diamond nucleation density with the ultrasonic vibration was higher than without vibration. AFM observations showed that, in the initial phase, growth on vibrated substrates leads to rougher surface than conventional growth. At lower substrate temperature diamond particles could only be grown under ultrasonic vibration. Raman spectra revealed that the quality of diamonds grown on vibrated substrates at low substrate temperature is comparable to that of diamonds produced at normal conditions.