Nagaaki Koshino

High rate synthesis of diamond by dc plasma jet chemical vapor deposition

This letter describes the first successful attempt at synthesizing diamond by chemical vapor deposition with the use of a dc plasma jet. A plasma jet, formed by the dc arc discharge of CH4 diluted with H2, was sprayed onto a water‐cooled substrate. The growth rate of the diamond film was 80 μm/h. The crystallinity measures well in terms of x‐ray diffraction and Raman spectroscopy. The quenching effect of the thermal plasma is discussed in relation to the high growth rate obtained.

Microstructure of sputtered garnet films for magneto‐optical recording media

Sputtered garnet films have a high potential for use as a magneto‐optical recording medium. However, the medium noise is thought to be large because of its crystal boundaries. We investigated the microstructure of films on GGG substrate, using TEM and SEM. The film crystallized by postannealing shows a rectangular hysteresis loop with high coercivity, and has an uneven surface. This is because the direction and size of each crystallite is not uniform. However, the film crystallized during deposition has quite a smooth surface, but does not have magnetic properties suitable for use in magneto‐optical recording. This film has a mosaiclike structure, in which all crystallites are uniformly oriented. We found that ion implantation of Ne+ and successive annealing of the film crystallized during deposition improved the magnetic properties without roughening the surface.Sputtered garnet films have a high potential for use as a magneto‐optical recording medium. However, the medium noise is thought to be large because of its crystal boundaries. We investigated the microstructure of films on GGG substrate, using TEM and SEM. The film crystallized by postannealing shows a rectangular hysteresis loop with high coercivity, and has an uneven surface. This is because the direction and size of each crystallite is not uniform. However, the film crystallized during deposition has quite a smooth surface, but does not have magnetic properties suitable for use in magneto‐optical recording. This film has a mosaiclike structure, in which all crystallites are uniformly oriented. We found that ion implantation of Ne+ and successive annealing of the film crystallized during deposition improved the magnetic properties without roughening the surface.

Magneto-optical recording of sputtered garnet films using laser diode

Sputtered garnet film is so transparent in the near-infrared region that recording using a laser diode was thought to be impossible. However, we have found that it is possible if Cr is applied to a thin garnet film. We investigated the sensitivity for static recording. The optical absorption of Cr film is 60% in the 0.8 μm wavelength range, and temperature elevation ocurrs easily. Recording becomes possible through the heat transfer from the Cr to the garnet film. The sensitivity depends mainly on the thickness of the Cr and garnet films. The optical absorption of the garnet film makes little contribution to the sensitivity. Recording needs only 6mW at a pulse width of 0.15 μs for a 0.1 μm thick garnet film by applying a bias field of 150 Oe. This sensitivity is considered to be sufficient for an optical disk mediun. Furthermore, dynamic recording was carried out using a 5-inch glass disk. We obtained a rather low C/N value of 30 dB. The reason for this low C/N value is due to both the irregular bit shape and the medium noise, resulting from the poor morphology of garnet film.

Optimized structure of sputtered garnet disks

The optimum structure of the sputtered garnet magnetooptical disk was investigated by numerical calculations and experiments. From the Faraday rotation, Faraday ellipticity, refractive index, and extinction coefficient, the authors determined the dielectric tensor elements of a sputtered garnet film. Using these values, they calculated the thickness dependence of the magnetooptical rotation angle, the reflectivity, and the reproduced signal amplitude of the disk with a reflecting layer. These results were then compared with measurements. The optimum garnet thickness and reflector material for a sputtered garnet disk were found. The optimum structure has a carrier/noise ratio of 60 dB at a carrier frequency of 0.6 MHz and possesses good recording sensitivity. >

Ce‐substituted garnet media for magneto‐optic recording

The magnetic and magneto‐optical properties of crystallized as‐deposited Ce‐substituted sputtered garnet films were measured as a function of temperature. The films were found to exhibit large Faraday rotation and high coercivity at room temperature. The small grain size and high squareness ratios of these films suggests that this media holds promise as a potential magneto‐optical recording media candidate for use at laser diode wavelengths. Furthermore, it was found that depending upon the value of the sputtering system background pressure prior to film deposition the compensation temperature of these films varied from below room temperature to the Curie point. The temperature dependence of magnetization of these two types of films was found to be very different and ESCA analysis was performed in order to ascertain the origin of these differences.

Photostimulated luminescence of BaBr2 : Eu

Abstract BaFBr : Eu is a well-known photostimulated luminescence (PSL) phosphor used as an X-ray image receptor for digital radiography systems. We fabricated BaBr 2 : Eu and confirmed that it is also a PSL phosphor. An image stored using BaBr 2 : Eu can be read using several different wavelengths; a 780 nm semiconductor laser is particularly attractive because it is very small and high powered.

Nitrogen introduced iron film with low coercive force prepared by ion plating

To produce an iron film with excellent magnetic properties, an RF ion-plating technique was used. Ion-plated iron films produced without introducing gas, have a high saturation magnetization(B s =2.2 T). The effects of introducing gases during iron deposition were also studied. Using a N 2 -Ar-He mixture gas, an iron film with low coercive force(H c =1 Oe) was obtained. Although, an iron nitride structure was not observed in this film, 3 at% of nitrogen has been detected in the sample. It is evident that a small amount of nitrogen reduces the coercive force of iron films.

Write-Erase Mechanism of Indium-Antimony Optical Disk Medium

Written and erased bits of the In-Sb phase change type optical disk medium were studied using transmission electron microscopy (TEN) and electron probe microanalysis (EPMA). Both the bits were separated into inner and outer areas and were composed of only rhombohedral Sb crystals and zinc blende In 50 Sb 50 crystals. The difference between the two bits were in crystal size and atomic distribution of the inner area. Models of the writing and erasing processes were derived from these observations and the In-Sb phase diagram. With these models, the thicknesses, grain sizes and optical contrasts of the both bits were consistently explained.

Selenium Alloy Film For New Erasable Optical Disk Media

Selenium film alloyed with indium and antimony has good characteristics for erasable optical disk media. Depending on the conditions of the irradiation directed to the film, it exibits two different reflectances and geometrical deformations,.and the change between these two states is reversible. The mechanism of the reversible changes is different from amorphous-to-crystalline phase transition. Both states are definitely crystalline, which have been confirmed by transmission electron microscope analysis. The film has a good durability of write-erase cycles and is chemically stable. The disk sample has been confirmed to be capable of writing and erasing at a speed of 600 rpm. The resolution is sufficient to record a bit of 1 pm length on the disk. Carrier-to-noise ratio is fairly good. This film also has a potential for higher signal transfer rates.

DyFeCo magneto-optical disks with a Ce-SiO2 protective film

We developed a DyFeCo magneto-optical disk using a protective film made of Ce-SiO2. The disk structure, composition, and sample preparation conditions were optimized to provide adequate read-write characteristics and reliability. Since DyFeCo is considerably less expensive than TbFeCo, our disks are practical alternative.