Yusuke Yajima

Theoretical formulation of the vacuum ultraviolet production efficiency in a plasma display panel

The theoretical formulation given in this article allows the vacuum ultraviolet (VUV) production efficiency to be calculated from the electron temperature of the plasma and the gas parameters including gas mixing ratio, excitation energies, and excitation cross sections using the separately determined conversion efficiency of the plasma input power into the electron heating power. The VUV production efficiencies calculated for (Ne+Xe) mixture (neon (Ne) and xenon (Xe) mixture) discharge gases using the formulation show that the efficiency can be increased by decreasing the electron temperature and by increasing the amount of Xe in the gas mixture. A method for determining the electron temperature of the plasma display panel (PDP) plasma from emission intensity measurements was also given, and was used to show that the electron temperature in the ordinary PDP plasma is 3 eV.

17.3: Improvement of the Speed of Address Discharges in Ne‐Xe‐He Discharge Gases for ACPDPs

The time lag of address discharges is discussed in terms of its relation with discharge gas composition. We measured the discharge time lag in ACPDPs with Ne-Xe-He mixed gases. As the concentration of helium increases, the address discharge time lag becomes shortened because helium atoms reduce mostly the formative time lag of the discharge. The formative time lag depends on the ion drift velocity at the initial stage of discharge formation. This ion drift velocity becomes lager with higher helium atom concentration.

Scanning Lorentz electron microscope with high resolution and observation of bit profiles recorded on sputtered longitudinal media (invited)

A transmission electron microscope operating with a cold field emission source has been modified to facilitate differential phase contrast mapping and applied to the observation of microscopic magnetic features appearing in recorded longitudinal media. After describing the design and performance of the scanning Lorentz electron microscope, as we call it, results on the observation of bit patterns delineated on Co‐based sputtered longitudinal media are presented. Relations of observed bit profiles to macroscopic magnetic properties of media and to device performance are discussed. Then, magnetization fluctuation on a scale of magnetic crystallites constituting the medium is examined. Also given is an account of a stray field effect inherent in hard magnetic materials.

Observation of Magnetic Head Fields Using Distorted Transmission Electron Microscopy Images

We have observed magnetic fields generated from a thin film magnetic head using transmission electron microscopy (TEM) images. The image in which the shadow of the head appears together with the projected pattern of a reference film is acquired with the use of appropriate defocus. From the pattern distortion in the image, both strong and weak components of the head field can be detected. Furthermore, this method makes it possible to quantitatively analyze, with high spatial resolution, the magnetic field strength which depends on distance from the air bearing surface of the head.

Observation of magnetic induction distribution by scanning interference electron microscopy

A scanning interference electron microscope (SIEM) capable of observing magnetic induction distribution with high sensitivity and spatial resolution has been developed. The SIEM uses a pair of fine coherent scanning probes and detects their relative phase change by magnetic induction, giving raster images of microscopic magnetic distributions. Its performance has been demonstrated by observing magnetic induction distributed near the edge of a recorded magnetic storage medium. Obtained images are compared with corresponding images taken in the scanning Lorentz electron microscope mode using the same microscope, and the differences between them are discussed.

Structural properties of polycrystalline Co–Cr–X (X=Pt and/or Ta)/Cr-alloy magnetic recording media

The grain size distributions of {11.0} textured Co–Cr–Pt and Co–Cr–Pt–Ta magnetic layers with Cr-alloy underlayers have been investigated by high-resolution transmission electron microscopy. The grain size distribution of the Co–Cr–Pt layer can be best described by the Rosin–Rammlar function. On the other hand, the Co–Cr–Pt–Ta layer is best described by the log–normal function which has a longer tail in the large-grain-size region than the Rosin–Rammlar function has. The size distribution tended to broaden as the average grain size of the magnetic layer decreased.

Nonmagnetic contrast in scanning Lorentz electron microscopy of polycrystalline magnetic films

The effect of the probe beam defocus on scanning Lorentz electron microscopy images has been investigated. Wave optical analyses show that, given a finite defocus, the variation of the transmission amplitude across the illuminated area on the specimen causes nonmagnetic contrast in the differential phase contrast (DPC) images. This nonmagnetic contrast depends on the sign and the amount of defocus. Since this contrast is virtually proportional to the gradient of the transmission amplitude, it should appear similar to the differentiated contrast of the bright‐field scanning transmission electron microscope (STEM) image. Therefore, the nonmagnetic noise appearing in the defocused DPC image can be substantially reduced by subtracting a suitably weighted differentiated bright‐field STEM image of the same area. This noise reduction procedure has been demonstrated by applying it to the unintentionally defocused DPC image of a recorded longitudinal magnetic storage medium.

Quantification of local remanence magnetization in perpendicular magnetic recording film by scanning interference electron microscopy

The local remanence magnetization of perpendicular magnetic recording bit patterns has been quantified by scanning interference electron microscopy. When two coherent probes run across each bit, the interference image contrast changes periodically with a unit of h/e (h: Planck’s constant, e: electron charge). Our numerical analysis shows that the magnetic field effect on the image contrast is less than 1/1000 that of the magnetization under the experimental conditions. This allows the local remanence magnetization of the film to be determined accurately by averaging the periodic contrast change measured over repetitive bit patterns. From the interference image of bit patterns on a Co (0.4 nm)/Pt (1.2 nm)×18 layered film, a value of 1.4×10−8 T m was obtained as the product of the remanence and the film thickness.

Distribution of paramagnetic defects formed in silicon by MeV ion implantations

Abstract Two different types of paramagnetic centers in silicon, Si-P3 (neutral {110} planar tetravacancies) in a well defined crystalline structure and point defects with poorly defined local structure in substantially damaged crystalline environments, formed by 3 MeV phosphorus and silicon ion implantations up to a dose of 1 × 10 14 cm −2 have been compared both in the dose dependence of area densities and in depth profiles. When the dose reaches to 1 × 10 14 cm −2 , the area density of Si-P3 starts to saturate while that of “indefinite” point defects keeps increasing. Also at this dose, the mean concentration of Si-P3 decreases as a function of depth from the surface whereas that of “indefinite” point defects increases. These results are discussed in terms of a damage overlap model in conjunction with a Monte Carlo simulation of lattice disorder.

Analysis of magnetic induction distribution by scanning Lorentz/interference electron microscopy

A new observation technique of magnetic induction base on the combination of differential phase contrast and interface electron microscopy has been developed. This technique can be used to clearly to visualize the magnetic induction distribution in and around the specimen. Furthermore, the quantitative determination of induction strength with a unit of h/e (h: Plancks constant, e: electron charge) can also be made possible.