Intrinsic Carrier Parameters and Optical Carrier Injection Method in High-Purity Diamonds

Diamond attracts increasing attentions as a semiconductor, since high-purity synthesized diamonds have become commercially available in these decades. For appropriate design of any devices, the basic carrier transport parameters should be known. However, it has been difficult to determine carrier parameters in diamond, because the controlled doping and Ohmic contact formation have been hard to achieve. In this chapter, a modern experimental method to measure basic carrier parameters, such as the effective mass, scattering times, and mobility of intrinsic diamonds, is introduced. The method, i.e., nanosecond time-resolved cyclotron resonance (TRCR), is applicable to optically injected carriers in intrinsic diamonds without wire connection. Following the key technique of optical carrier injection, detailed analysis methods for the cyclotron resonance spectra are introduced. The extracted basic parameters of diamond are summarized in comparison to those of silicon and germanium in the same group-IV semiconductor family. This is worthy for triggering further ideas in application-oriented researches using widespread materials

Application of Liquid Laser Ablation: Organic Nanoparticle Formation and Hydrogen Gas Generation

Laser ablation is induced by a heating process of materials through the absorption of laser light and results in an explosive expansion of materials. For materials located in liquid, in contrast to those in vacuum, laser ablation proceeds under rather mild conditions via a cycle of heating and cooling by mediated solvent; therefore, it is applicable for organic solids to fragment into nanoparticles. Alternatively, for effective light absorbers, the irradiated site becomes the reaction centre of a photochemical reaction even in liquids, resulting in hydrogen gas generation. In this chapter, two topics of laser ablation in the liquid phase are presented: nanoparticle formation of organic materials and hydrogen gas generation from solid carbon in water. Thereby, the extended abilities of liquid laser ablation to transform ordinary materials into functional ones are introduced

DHEA Administration Activates Local Bioactive Androgen Metabolism in Cancellous Site of Tibia of Ovariectomized Rats

It is not known whether local androgen metabolism is involved in the mechanisms underlying the dehydroepiandrosterone (DHEA) administration-induced improvement of bone mineral density (BMD) in an estrogen-deficiency state. The aim of the present study was to clarify whether DHEA administration would improve local androgen metabolism and BMD in cancellous site of tibia of ovariectomized (OVX) rats. Twenty-two female rats, 6 weeks old, were randomized into three groups: sham-operated rats, OVX control rats, and OVX rats that received DHEA treatment. DHEA was administered intraperitoneally at 20 mg/kg body weight for 8 weeks. The concentrations of free testosterone and dihydrotestosterone (DHT) in cancellous site of tibia did not change as a result of ovariectomy, while the DHT concentration increased following DHEA administration. We revealed that DHEA administration improved the reduction of 17β- and 3β-hydroxysteroid dehydrogenases and clearly reversed the reduction of 5α-reductase types 1 and 2 and androgen receptor in the cancellous site of tibia of OVX rats. DHEA administration suppressed estrogen deficiency relative to the decrease in the cancellous BMD, which was positively associated with local DHT concentration. These findings indicate that DHEA administration enhances local bioactive androgen metabolism in the cancellous tibia of young OVX rats, suggesting that local DHT may play a part in the DHEA administration-induced improvement of cancellous BMD

Genetic characterization of type A enterotoxigenic Clostridium perfringens strains

Clostridium perfringens type A, is both a ubiquitous environmental bacterium and a major cause of human gastrointestinal disease, which usually involves strains producing C. perfringens enterotoxin (CPE). The gene (cpe) encoding this toxin can be carried on the chromosome or a large plasmid. Interestingly, strains carrying cpe on the chromosome and strains carrying cpe on a plasmid often exhibit different biological characteristics, such as resistance properties against heat. In this study, we investigated the genetic properties of C. perfringens by PCR-surveying 21 housekeeping genes and genes on representative plasmids and then confirmed those results by Southern blot assay (SB) of five genes. Furthermore, sequencing analysis of eight housekeeping genes and multilocus sequence typing (MLST) analysis were also performed. Fifty-eight C. perfringens strains were examined, including isolates from: food poisoning cases, human gastrointestinal disease cases, foods in Japan or the USA, or feces of healthy humans. In the PCR survey, eight of eleven housekeeping genes amplified positive reactions in all strains tested. However, by PCR survey and SB assay, one representative virulence gene, pfoA, was not detected in any strains carrying cpe on the chromosome. Genes involved in conjugative transfer of the cpe plasmid were also absent from almost all chromosomal cpe strains. MLST showed that, regardless of their geographic origin, date of isolation, or isolation source, chromosomal cpe isolates, i) assemble into one definitive cluster ii) lack pfoA and iii) lack a plasmid related to the cpe plasmid. Similarly, independent of their origin, strains carrying a cpe plasmid also appear to be related, but are more variable than chromosomal cpe strains, possibly because of the instability of cpe-borne plasmid(s) and/or the conjugative transfer of cpe-plasmid(s) into unrelated C. perfringens strains. © 2009 Deguchi et al

Hydrogen Generation by Laser Irradiation of Carbon Powder in Water

We report the photochemical activity of carbon powder in the generation of hydrogen from water by laser irradiation, without any electrodes and photocatalysts. The gas was obtained by laser irradiation in the VIS-NIR range and was dependent nonlinearly on the laser power density. From a gas component analysis and a repeated irradiation experiment, it was found that the carbon powder was oxidized and acted as a sacrificial reagent in the photochemical hydrogen generation. In addition, a highly carbonized charcoal, known as Bincho-tan, was found to effectively work for the hydrogen generation

Quantitative relevance of substitutional impurities to carrier dynamics in diamond

International audienceWe have quantified substitutional impurity concentrations in synthetic diamond crystals down to sub-partsper-billion levels. The capture lifetimes of electrons and excitons injected via photoexcitation were compared for several samples with different impurity concentrations. Based on the assessed impurity concentrations, we have determined the capture cross section of electrons for boron impurity, σ A = 1 × 10 −14 cm 2 , and that of excitons for nitrogen impurity, σ ex D = 3 × 10 −14 cm 2. The general tendency of the mobility values for different carrier species is successfully reproduced by including carrier scattering by impurities and excitons

Low-temperature mobility-lifetime product in synthetic diamond

The mobility-lifetime (μτ) product is an important parameter that determines the performance of electronic and photonic devices. To overcome the previously reported difficulties in measuring the μτ product at cryogenic temperatures, we implement a time-resolved cyclotron resonance method to determine the carrier lifetime τ. After clarifying the difference between the AC and DC mobilities measured by cyclotron resonance and time-of-flight methods, respectively, we demonstrate an inverse temperature dependence of the μτ product. The highest recorded μτ product of 0.2 cm2/V, which is approximately 100 times the room-temperature value, was obtained at 2 K for chemical-vapor-deposition diamond of the highest currently available purity