Yasuyuki Egashira

Synthesis of ordered mesoporous carbons with channel structure from an organic–organic nanocomposite

Mesoporous carbons with ordered channel structure (COU-1) have been successfully fabricated via a direct carbonization of an organic-organic nanocomposite.

Chemical reaction engineering in the design of CVD reactors

The current status of modeling on CVD processes to produce thin films is summarized in this review. The experimental methodologies for extracting the essential chemistry in CVD reactors had been developed to efficiently design CVD reactors. Tubular wall deposition method provides information on the rate limiting step of the deposition process and the rate constants. Molecular size of film forming species can be estimated from the deposition rate profile in the tubular reactor if the process is limited by the gas phase diffusion. Microcavity-deposition method provides the tool to analyze the surface reactions. The microcavity-deposition method can be combined with macrocavity-deposition method to extract the important reaction pathways like as the intermediate deposition. The use of computer chemistry is also useful in detecting key reactions and it may be used to construct new deposition chemistry. The computer fluid dynamics coupled with the chemistries obtained from these approaches will be a powerful tool to design CVD reactors.

Growth mechanism of nanoparticles prepared by radio frequency sputtering

Growth mechanisms of nanometer-sized particles prepared by rf sputtering on silica glass layers were examined. Gold and gallium arsenide (GaAs) particles synthesized with varying sputtering times on a SiO2 sputtered layer were subsequently buried in a SiO2 film by sputtering a SiO2 target. Transmission electron microscopy showed that in both cases, with increasing sputtering time, the number density decreased and the distance between neighboring particles increased in the initial stage of the growth, which suggests that the particles migrate on the SiO2 surface and coalesce with each other as they grow. Differences of GaAs and gold particle formation suggest that the mobility of the GaAs particles is much larger than that of gold. The results suggest that the migration of nanoparticles is activated by the bond-formation energy released during the incorporation of precursors into growing particles.

Temperature dependence of the sticking probability and molecular size of the film growth species in an atmospheric chemical vapor deposition process to form AlN from AlCl3 and NH3

The sticking probability and molecular size of the growth species were determined as a function of deposition temperature ranging from 700 to 950 °C, in the AlN films prepared from AlCl3 and NH3. A novel method was developed, that includes the measurement of the film thickness profile on micron‐sized trenches and the molecular diffusivity of the growth species. The molecular size was about 1 nm at 700–850 °C and decreased gradually with increasing temperature. The sticking probability increased from 0.02 to 0.5 in the temperature range 700–950 °C and, surprisingly, obeyed the Arrhenius law in spite of this large probability of sticking. The activation energy amounted to 136 kJ/mol.

Development of the embryonic chicken thymus: I. Characteristic synchronous morphogenesis of lymphocytes accompanied by the appearance of an embryonic thymus-specific antigen

Abstract Differentiation of the lymphoid cells of embryonic chicken thymus was studied morphologically and serologically from the tenth day of incubation to hatching. Lymphoid cells became markedly smaller in size at two stages, from the eleventh to the thirteenth and from the fifteenth to the sixteenth days of incubation. During the first stage, lymphoid cells changed notably in other criteria as well. The mean generation time was prolonged from approximately 12 to 36 hr on Day 13. The proportion of those cells that possessed embryonic thymus-specific antigen synchronously increased from 4–7 to 60–75% during the 24-hr period between the twelfth and the thirteenth days and reached a plateau level on Day 14. Morphologically, cytoplasmic processes became conspicuous in lymphoid cells on Days 11 and 12. These processes probably separated from the main body of the actively transforming lymphoid cells. In this phenomenon, a septum composed of microfilaments and small vesicles was formed at the neck of the process. Between the twelfth and the thirteenth days, the majority of lymphoid cells took the features typical of differentiated lymphocytes, i.e., small round shapes with scanty cytoplasm and distinct heterochromatin in their nuclei.

Synthesis of GaAs nanoparticles by digital radio frequency sputtering

Nanometer‐sized GaAs particles embedded in SiO2 were prepared by a digital rf‐sputtering method, where GaAs and SiO2 targets were alternately sputtered in an Ar atmosphere. The GaAs deposition time was kept shorter than the time required to form a continuous layer. Transmission electron microscopy observations showed that the sizes of the GaAs particles can be controlled from 2 to 8 nm by changing the sputtering cycle time of the GaAs target. In spite of their small size, the GaAs particles have crystallinity similar to the target material without substrate heating or postannealing. The optical absorption spectra of the GaAs particles show a blue shift as large as 1.6 eV, corresponding to strong quantum confinement of electrons and holes.

The Formation Mechanism and Step Coverage Quality of Tetraethylorthosilicate ‐ SiO2 Films Studied by the Micro/Macrocavity Method

The formation mechanism and step-coverage quality of SiO 2 films formed by the pyrolysis of tetraethylorthosilicate (TEOS) were studied, using a novel experimental technique called the «multi-layered micro/macrocavity method.» The growth rate profiles at millimeter (macrocavity) and submicron (microtrench) sales deposited under a total pressure ranging from 2 to 760 Torr were simultaneously analyzed. The step coverage approaches conformal deposition either with decreasing volume-to-surface ratio (V/S) of the macrocavity reaction zone or with increasing total pressure. Combining these results with the growth-rate profiles of the macrocavity shows that two kinds of intermediate species participate in deposition. One is a high-activity species with a surface sticking probability near 1, and the other is a low-activity

Pore size distributions of silylated mesoporous silica MCM-48 membranes

Abstract Mesoporous silica MCM-48 membranes were synthesized on a porous alumina support using surfactant molecules which act as template for the polymerization of silica. Higher synthetic temperatures resulted in thicker silica wall. However, the average pore size of MCM-48 was independent of the synthetic temperature. The permeation of N 2 through the calcined MCM-48 membrane was governed by the Knudsen diffusion. There was no contribution of viscous flow, which can be observed in large pinholes. The pore size distributions of silylated mesoporous silica MCM-48 membranes were evaluated by permporometry measurements in which N 2 flux was monitored in the presence of methanol vapor. A sharp decrease in the N 2 flux at a relative vapor pressure of methanol equal to 0.5 was observed, indicating a narrow pore size distribution of the MCM-48 membrane. The corresponding Kelvin diameter of the membranes was about 2.0 nm, which is consistent with the value for the silylated MCM-48 powder calculated with Barrett–Joyner–Halenda (BJH) method using N 2 adsorption isotherm.

Mesoporous MCM-48 membrane synthesized on a porous stainless steel support

A mesoporous MCM-48 membrane with high thermal stability has been synthesized on a porous stainless steel support by hydrothermal treatment.

Serological Studies on the Major Histocompatibility Complex of New Inbred Strains of the Guinea Pig

New inbred strains of guinea pigs, JY 1, JY 2, JY 3, JY 6, JY 9 and JY 10 have been established in this Institute. Serologic studies of guinea pig leukocyte antigens (GPLA antigens) were carried out in order to examine their major histocompatibility complex (GPLA complex). Antisera specific for Ia antigens were raised by cross‐immunization of NIH strain 2 (NIH 2) and NIH strain 13 (NIH 13) guinea pigs, well known inbred guinea pigs. The sera identified four distinct Ia specificities, which were designated as Ia.2a, Ia.2b, Ia.13a and Ia.13b. Six antigenic specificities different from the above Ia specificities were identified by sera obtained by appropriate immunization of the inbred guinea pigs and were designated as P.1, P.2, P.3, P.4, P.5 and P.6. Antigenic specificities of GPLA antigens recognized in inbred guinea pigs were: NIH 2 (Ia.2a, Ia.2b, P.1, P.2, P.3, P.4), NIH 13 (Ia.13a, Ia.13b, P.1, P.2, P.3, P.4), JY 1 (Ia.13a, Ia.13b, P.5), JY 2 (Ia.2b, Ia.13b, P.3, P.4, P.6), JY 3 (Ia.13a, Ia.13b, P.2, P.4, P.5), JY 6 (Ia.2b, Ia.13b, P.3, P.6), JY 9 (Ia.13a, Ia.13b, P.4, P.5), JY 10 (Ia.13a, Ia.13b, P.2, P.3, P.4, P.6). The correspondence of these specificities to those already reported was discussed and the P.2 or P.4 was considered to be an additional specificity of GPLA antigens that have not been reported yet. As the new inbred strains of guinea pigs were thus found to possess characteristic GPLA complex, which differ from each other and from those of NIH 2 and NIH 13 strain, they should be useful for studies of roles of the major histocompatibility complex in the immune system.