This paper deals with some topics on the materials and the vapor-phase growth processes in the field of spinelectronics, where both charge and spin degrees of freedom of an electron realize various storage devices. First, a tunnel magneto-resistance effect is described to show how spinelectronic materials are utilized in the device. Second, a half-metallic ferromagnet, which improves the performance of spinelectronic devices drastically, and its growth process are explained. A molecular-beam epitaxy (MBE), one of non-equilibrium vapor-phase growth processes, plays an indispensable role in synthesizing the material. For example, a new class of half-metallic ferromagnet, previously nonexistent zinc-blende CrAs designed by ab initio calculations, was successfully grown by MBE.
Monodispersed silicon nanoparticles with high crystallinity were successfully synthesized by a continuous system of pulsed-laser ablation, in-situ annealing and a size classification using differential mobility analyzer. Transmission electron microscopy and Raman scattering measurement revealed that the in-situ annealing was effective in improving both morphological uniformity and crystallinity of the nanoparticles. The silicon nanoparticles showed clearly size-dependent photoluminescence in near IR and visible region at room temperature, due to the quantum confinement effect. The full-width at the half-maximum of the PL spectrum was as narrow as 200 meV reflecting the sharp size distribution of the emitting particles.
Monodisperse metal nanoparticles have been used as a catalyst for growing carbon nanotubes (CNTs). The nanoparticles were generated by laser ablation and size-classified with a differential mobility analyzer at low pressures (1-1.5 kPa). CNTs were grown by hot filament or thermal chemical vapor deposition at temperatures of 510-610 °C using acetylene. First, multi-walled carbon nanotubes (MWNTs) were grown from 5-nm nickel particles on a silicon substrate. The MWNTs had outer diameters matching the particle sizes, indicating that the current method can produce diameter-controlled MWNTs. Secondly, for applications of CNTs to LSI interconnects, 5-nm cobalt particles were injected into via holes of LSI interconnects by utilizing a directed particle beam. The directed particle beam was produced by introducing the particles into a high vacuum chamber using differential pumping. The particles were deposited at the bottom of the holes with a diameter as small as 100 nm. Aligned MWNTs were successfully grown in the holes. Finally, titanium-cobalt bimetallic particles were used to grow MWNTs to study the effects of titanium on the growth. It was found that titanium enhances the MWNT growth significantly. There is an optimum titanium fraction for the growth, as confirmed by evaluating the growth probabilities of MWNTs.
Electrospray (ES) technique is one of the few known schemes capable of atomizing a liquid into ultrafine droplets. By this method, a meniscus of conducting solution formed at the tip of a capillary tube becomes conical in shape when high voltage is applied between the tip and the counter electrode. Droplets are generated by the continuous breakup of a liquid jet at the apex of the cone. The most common use of ES has been as the ion source for mass spectrometry. This paper first reviews various applications of ES in nanoparticle synthesis. ES is also a tool to transfer inorganic or/and organic matters in a liquid into a gas-phase. In the present work, the size distribution of the generated aerosol was determined by a differential mobility analyzer (DMA) and a counter system. The results show that the ES-DMA system is a convenient and reliable tool for the rapid size determination of colloidal nanoparticles or water-soluble polymers, being capable of simultaneously measuring the mobility distribution and concentration of total residue present in the sample waters.
A framework is presented for understanding the performance of modern analytical and high-resolution microscopy techniques, which are applicable to nano scale particle evaluation. With sub-nano meter spatial resolution, modern microscopy techniques could provide critical feedbacks on the fabrication processes, for example, direct measurement of particle size and its distribution, morphology, crystallinity and surface condition of nano particles. This paper discusses the practical application of modern microscopy techniques to laser-synthesized ultra-fine silicon and iron particles, i.e., the structural evaluation and the direct quantitative chemical analysis of surface oxide layer on nano particles.
This paper introduces the activities of Nanotechnology support project conducted by The Nanotechnology Researchers Network Center of Japan and 14 facility centers composed of universities and national research institutes. There are two important activities in this project. They are nano foundries presented by facility centers to researchers and the service of nanotechnology information to nanotechnology related people. People can utilize the facilities of 4 nanotechnology research fields in the 14 research laboratories. In the 4 fields, there are ultra-HV TEM (ultra high voltage electron microscope), two different types of synchrotron radiation equipment, nano-fabrication for metals, semiconductors like silicon and compounds, and oxides, and molecular synthesis of fine chemicals at nanometer level. The information service is done by The Nanotechnology Researchers Network Center of Japan whose mission is to survey nanotechnology related research trends, provide support and acceleration of international communication among researchers, and to spread the status of nanotechnology in Japan. In this paper, one of the nanotechnology research surveys is introduced as part of the center's activity.
A super-sonic impactor using a Laval nozzle, which was developed for size control of ultra-fine aerosol particles down to nano-size range, was applied to the sampling of ultra-fine ambient aerosol. Ambient aerosol was classified into two size fractions by the super-sonic impactor and PAHs in each fraction were analyzed as a typical index of anthropogenic air pollutants. The concentrations of individual PAH compounds in the particles collected by the supersonic impactor were compared with those collected on the backup filter and those of total suspended particulates in order to evaluate the wall loss as well as the influence of super-saturation of vapor components in the supersonic flow. As a result, ambient particles were successfully classified into two size fractions at 200-300 nm using the supersonic impactor. When the air was humid, the concentration of PAHs with benzene rings more than four in the smaller size fraction collected on the backup filter was decreased because the condensation of water vapor onto particles led to an increase in particle size. It was also suggested that there is a possibility of increased collection of semi-volatile compounds on the backup filter due to the super-saturation.
To clarify mechanisms of dry deposition in a forest, the vertical profiles of gaseous and particulate matter in a Japanese cypress forest in Kiryu experimental watershed, located in the southern part of Shiga Prefecture, Japan, were studied. From January 2000 to January 2002, gaseous and particulate matter were collected for 2 to 3 weeks successively using a 4-stage filter and pump system at 6 different locations above (30.0, 28.0, 21.0 m), in (14.0 m) and below (5.0, 1.2 m) the forest canopy. The ionic concentrations of the water-soluble constituents of particulate matter (Na+, NH4+, K+, Ca2+, Mg2+, Cl-, NO3-, SO42-) and concentrations of some trace gases (HNO3, HCl, NH3, SO2) averaged over 2 to 3 weeks were measured by ion chromatography. As a result of measurements, the concentrations of HNO3, HCl, NH3 and SO2 were found to decrease at the canopy. The concentrations of inorganic ionic constituents of particulate matter below the canopy showed specific temporal variation being independent of the concentrations above the canopy. The composition of inorganic ionic constituents of the particulate matter did not change significantly among the measured heights. The particulate matter below the canopy seemed to be constantly supplied from the canopy by the resuspension of deposited particles because of stable wind below the canopy.
An increase in storage capacity of hard disk drives (HDDs) resulted in a reduction in flying height (clearance between hard disk (HD) and magnetic head) to be in the order of nanometer. The small flying height made the HDs more sensitive to the surface contamination, which very often led to fatal failures. The present work studied the HD surface contamination with SO2 by exposing lubricant-coated HDs to cleanroom (CR) air as well as to SO2-containing test air. As a result, the adsorption of SO2 in CR air was expressed by an adsorption kinetic equation based on Langmuir isotherm, while the equation was not applicable to the adsorption of SO2 in test air. The sticking probability of SO2 in test air onto the lubricated HD was found to be about one tenth of that for SO2 in CR. The difference may be attributed to the enhanced adsorption of SO2 by basic gases present in CR. This result suggests that SO2 adsorption onto HD surface should be evaluated by the exposure to CR air and that the data obtained by the exposure to model gas might be misleading. For the suppression of HD surface contamination by SO2, it is necessary to equip CR with an integrated air purification system for basic gases and SO2.
Hypersensitivity pneumonitis is a common type IV, or delayed allergic reaction caused by inhalation of aerosol fungi, solvents or chemical substances; multiple epithelioid cell granulomas are formed in the lungs of patients with this disease. In its early stage most of the cases are reversible if the etiologic agent is identified and removed from environment. However, it can progress to irreversible fibrosis if exposure continuous. In this study, the concept of type IV allergy reaction and the features of and further responses to such allergies including hypersentivity pneumonitis are described.