Seiichiro Higashi

Milk fermented by Lactobacillus gasseri SBT2055 influences adipocyte size via inhibition of dietary fat absorption in Zucker rats.

We have demonstrated previously that a diet containing skimmed milk (SM) fermented by Lactobacillus gasseri SBT2055 (LGSP) reduces adipocyte size in Sprague-Dawley rats. Two experiments were conducted to extend these observations in order to elucidate the mechanism involved. In experiment 1, lean and obese Zucker rats were fed a diet containing SM or LGSP for 4 weeks. The LGSP diet, compared with the SM diet, resulted in lowering of the mesenteric adipose tissue weight (23 %; P < 0.05), adipocyte sizes (28 %; P < 0.001) and serum leptin concentration (36 %; P < 0.05) in lean rats. Obese Zucker rats did not display such dietary effects. Only the number of smaller adipocytes was increased (P < 0.05) by the LGSP diet in the subcutaneous adipose tissue of obese rats. The LGSP diet significantly reduced the serum and hepatic cholesterol in rats. In addition, the LGSP diet led to an increased excretion of faecal fatty acids and total neutral faecal sterols in both rat strains. In experiment 2, Sprague-Dawley rats with permanent cannulation of the thoracic duct were fed either the SM or LGSP diets and their lymph was collected. The LGSP diet lowered the maximum transport rate of TAG and phospholipids. These results indicate that fermented milk regulates adipose tissue growth through inhibition at the stage of dietary fat absorption in lean Zucker rats.

Pulsed-Laser-Induced Microcrystallization and Amorphization of Silicon Thin Films.

Pulsed-laser-induced microcrystallization and amorphization of Si thin films were investigated by transient reflectance and conductance measurements. It was clarified experimentally that the complete melting of a Si film and subsequent supercooling induces both microcrystallization and amorphization. In the case of the microcrystallization of a 49.1-nm-thick Si film, nucleation among supercooled liquid Si was observed. The nucleation temperature and resulting nucleation rate under the microcrystallization condition were estimated to be 1047 K and 1.67×1025 events/(cm3s), respectively. On the other hand, no significant nucleation was observed in the case of a laser amorphization of 20.7-nm-thick Si film although the film was melted for the relatively long duration of about 80 ns. Extremely fast quench of liquid Si films seems to suppress nucleation and results in solidification in amorphous phase.

Heat Treatment with High-Pressure H2O Vapor of Pulsed Laser Crystallized Silicon Films.

In this paper, we discuss the carrier generation and reduction of defects for lightly phosphorus-doped pulsed laser crystallized silicon films by heat treatment with high-pressure H2O vapor. Change in the electrical conductivity caused by reduction of the density of localized defect states is presented. Reduction of the spin density is also reported for undoped films. We also discuss the electrical conductivity of the polycrystalline films using a statistical thermodynamical calculation program. 2. Experimental

High-Quality SiO2/Si Interface Formation and Its Application to Fabrication of Low-Temperature-Processed Polycrystalline Si Thin-Film Transistor

Improvement of SiO2/Si interface quality and its effect on the performance of low-temperature-processed polycrystalline silicon thin-film transistors (poly-Si TFTs) are investigated. Two gate SiO2 formation conditions for realizing the density of interface states (Dit) at mid-gap of 1.4×1011 and 4.1×1010 cm-2eV-1 were applied to a 425°C TFT fabrication process using electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition (PECVD). By reducing Dit, reduction of threshold voltage from 1.97 to 1.12 V, reduction of sub-threshold swing from 303 to 250 mV/decade and increase of mobility from 196 to 309 cm2V-1s-1 were observed. The analysis of TFT characteristics indicated the decrease of both deep and shallow level trap states. As a result, not only threshold voltage and sub-threshold swing, but also the mobility of the poly-Si TFT was significantly improved. The results indicate that low-temperature process technologies for forming a high-quality SiO2/Si interface are important for next-generation high-performance poly-Si TFTs.

Stress in Pulsed-Laser-Crystallized Silicon Films

Stress in pulsed-laser-crystallized silicon films was investigated using high-resolution Raman scattering measurements. Film stress was evaluated based on the peak shift of transverse optical (TO) phonon of crystalline silicon in Raman scattering spectra. The tensile stress in laser-crystallized 50-nm-thick silicon films on glass substrates increased from 3.5×108 Pa to 9.7×108 Pa as the film deposition temperature increased from 200°C to 480°C. The peak shift of laser-crystallized microcrystalline silicon (µc-Si) films revealed that the tensile stress introduced by laser irradiation was 2.3×108 Pa at most. These results indicate that the strong tensile stress is introduced by the silicon film deposition rather than by the pulsed-laser crystallization. Also, the authors demonstrate that pulsed-laser crystallization maintains the existing stress at the growth initiation sites in the bottom region of silicon films.

Improvement of Electrical Properties of Pulsed Laser Crystallized Silicon Films by Oxygen Plasma Treatment

tageous for the fabrication of devices such as polycrystalline silicon thin film transistors (poly-Si TFTs) at low temperatures. However rapid and local heating using pulsed laser can cause a large number of defect states in laser crystallized silicon films. To overcome this problem, many investigations using hydrogenation have been reported. 4‐10) In this paper, we report the passivation phenomena of grain boundaries of laser crystallized silicon films by oxygen plasma treatment. We present changes in the electrical properties of laser crystallized lightly doped silicon films associated with the reduction of the density of defect states by oxygen plasma treatment. Increases in the carrier density and the carrier mobility are reported. Reduction of the potential barrier height at grain boundaries is also discussed. Moreover, thermal stability in the electrical conductivity is discussed. 2. Experimental

Self-Assembling Formation of Ni Nanodots on SiO2 Induced by Remote H2 Plasma Treatment and Their Electrical Charging Characteristics

We fabricated nanometer-scale Ni dots and NiSi dots on an ultrathin SiO2 layer using remote H2 plasma and demonstrated the feasibility of remote H2 plasma treatment for controlling the areal density of the dots. 1.8-nm-thick-Ni/SiO2 and Ni/Si-quantum dots (QDs)/SiO2 layer were treated with remote H2 plasma generated by the inductive coupling between an external single-turn antenna and a 60 MHz generator. When a Ni/SiO2 was treated with remote H2 plasma at room temperature, Ni nanodot density could be controlled in the range of 109 to 1012 cm-2 by adjusting the plasma conditions. After the remote H2 plasma treatment of the Ni/Si-QDs, the formation of electrically isolated NiSi dots with an areal density of ~1011 cm-2 was confirmed. These results imply that hydrogen radicals generated in H2 plasma play an important role in improving surface diffusion caused by energy reduction at the Ni/SiO2 interface. The surface potential of the Ni nanodots changes stepwise with the tip bias. This is due to the multistep electron injection into and extraction of Ni nanodots. The minimum tip biases for electron injection into Ni nanodots, NiSi dots and Si-QDs were -0.2, -0.7, and -1.0 V, respectively. This reflected the difference in electron affinity among Ni, NiSi and Si.

Electrical Properties of Pulsed Laser Crystallized Silicon Films

Electrical properties of phosphorus-doped laser-crystallized silicon films were investigated. The analysis of free carrier optical absorption revealed that crystalline grains formed at laser energies of 360–375 mJ/cm2 had high carrier mobilities of 40–50 cm2/Vs, which were close to that of doped single crystalline silicon. The mobility did not depend on the number of laser pulses. On the other hand, Hall effect measurements showed a marked increase in the carrier mobility of electrical current traversing grain boundaries from 3 to 28 cm2/Vs as the laser energy density increased from 160 to 375 mJ/cm2. The Hall mobility also increased as the number of laser pulses increased, although a single pulse irradiation resulted in a maximum carrier mobility of 15 cm2/Vs. These results suggest that a high laser energy density as well as numbers of multiple pulses are necessary to reduce disordered amorphous states and improve grain boundary properties.

Application of Plasma Jet Crystallization Technique to Fabrication of Thin-Film Transistor

The crystallization of a-Si films on glass substrates using the plasma jet crystallization (PJC) technique and its application to thin-film transistor fabrication were studied. Amorphous Si (a-Si) films deposited by plasma-enhanced chemical vapor deposition (PECVD) of 50% SiH4 diluted with H2 were crystallized by thermal plasma jet under the power of 1.6 to 2.6 kW input to the plasma source and the substrate scan speed of 170 to 1000 mm/s. The crystallinity of the films was improved by treating the films at a higher input power for a longer duration. Thin-film transistors (TFTs) fabricated using the crystallized films showed good electrical characteristics. By increasing the input power from 1.86 to 2.29 kW in the crystallization, the average field-effect mobility was increased from 42 to 61 cm2V-1s-1, and the threshold voltage was decreased from 4.0 to 3.4 V. These results indicate that the PJC technique is a very promising low-temperature process technology.

Analysis of Transient Temperature Profile During Thermal Plasma Jet Annealing of Si Films on Quartz Substrate

The transient temperature profile during thermal plasma jet annealing has been investigated by optical reflectivity measurements. The transient reflectivity measured during the annealing shows oscillation, which originates from the changes in the refractive indices of a Si film and a quartz substrate with temperature. By analyzing the oscillation, we have successfully obtained the temperature profile during the annealing with a time resolution of milliseconds. As a result of such analysis when the power input to a plasma source is 2.2 kW, the surface temperature has been observed to increase from 1300 to 1560 K by decreasing the scan speed from 1000 to 500 mm/s.