Tsuyoshi Onuma

Co/Pd multilayer media with Pd inorganic granular seed layer for perpendicular recording

We have investigated the Co/Pd multilayer media with a Pd–SiN granular seed layer as perpendicular recording media. The Pd–SiN granular seed layer and the Co(0.2 nm)/Pd(0.8 nm) multilayer were formed by dc and rf sputtering at room temperature on a FeTaC soft magnetic underlayer. The Pd–SiN granular seed layer of 3 nm was very effective to get good magnetic properties with coercivity of 3.9 kOe, a nucleation field of −2.1 kOe, and a M–H slope parameter 4π(dM/dH)H=Hc of 1.4. In addition, it was found that growth of multilayer grains is sensitive to surface conditions of the soft magnetic underlayer. The average column diameter of 13.7 nm with a dispersion of 21.7% was evaluated from the plan-view transmission electron microscope image of well-separated Co/Pd columns with a boundary, which was grown on the Pd–SiN seed layer and the soft magnetic underlayer with Ar plasma etching. Atomic force microscope measurements showed that mean roughness (Ra) of the FeTaC surface decreased from 0.46 to 0.39 nm by the p...

Perpendicular magnetic recording media based on Co-Pd multilayer with granular seed layer

We have investigated Co-Pd multilayers deposited on a Pd-SiN granular seed layer and a FeTaC soft magnetic underlayer (SUL) for perpendicular magnetic recording. The Pd-SiN granular seed layer of 3 nm was found to be very effective for good magnetic properties with coercivity of 3.9 kOe, a negative nucleation field of -2.1 kOe, and a M-H loop slope parameter 4/spl pi/ (dM/dH)/sub H=Hc/ of 1.3. The average column diameter of 13.7 nm with a dispersion of 21.7% was evaluated from the transmission electron microscopy image of well-separated columns with a clear boundary. This Co-Pd medium gave better playback performances by a merged ring giant magnetoresistive head compared to the medium with a Pd seed layer. The effect of Ar plasma etching on the SUL was also investigated to improve playback performance.

Development of an Ultrashort-Pulse Reflectometer for Density Profile Measurements on GAMMA 10.

An ultrashort-pulse reflectometer is under development for electron density profile and fluctuation measurements on the GAMMA 10 tandem mirror. At the heart of the system is an impulse generator which creates an 8 V, 65 ps full-width half-maximum pulse. Data was taken at the midplane of the GAMMA 10 central cell. The incident wave was launched with ordinary-mode polarization and frequency components of the reflected wave in the range 8–10 GHz were detected. The observed values of the time-of-flight are in rough agreement with those obtained from calculations using the Abel-inverted profile obtained from a 70 GHz microwave interferometer. These results suggest that the present system can be expanded to yield a reliable diagnostic for electron density profile measurements.

Initial Measurements from an Ultrashort-Pulse Reflectometer on GAMMA 10

Initial results from an ultrashort-pulse reflectometer on the GAMMA 10 tandem mirror are presented. The diagnostic uses an impulse generator (8 V, 65 ps full-width at half maximum) as its microwave source, and the four-channel receiver system measures the time-of-flight for ordinary-mode polarized reflected waves at 8, 9, 10 and 11 GHz. The reflectometer tracks electron density fluctuations well over portions of the discharge, while overall values of the time-of-flight are in rough agreement with calculated values using Abel-inverted profiles from interferometry data. These results demonstrate the potential of the current system for time-resolved electron density profile measurements on GAMMA 10.

Multilayer Disk Reduced Interlayer Crosstalk with Wide Disk-Fabrication Margin

To reduce interlayer crosstalk caused by the ghost spot which appears in a multilayer optical disk with more than three information layers, a multilayer disk structure which reduces interlayer crosstalk with a wide disk-fabrication margin was proposed in which the backward reflectivity of the information layers is sufficiently low. It was confirmed that the interlayer crosstalk caused by the ghost spot was reduced to less than the crosstalk from the adjacent layer by controlling backward reflectivity. The wide disk-fabrication margin of the proposed disk structure was indicated by experimentally confirming that the tolerance of the maximum deviation of the spacer-layer thickness is four times larger than that in the previous multilayer disk.

Cross-sectional control of boron contents and the microstructures of Co/Pd multilayer perpendicular magnetic recording media

The effects of cross-sectional modulated boron segregation on Co/PdB multilayer perpendicular magnetic recording media have been studied. Gradually reduced boron contents from thin PdB seed layer (33 at.%) to the top of the Co(0.2 nm)/PdB (0.8-nm) multilayer (12.5 at.% at the center of the multilayer) were successively achieved and confirmed by the depth-profile of X-ray photoelectron spectroscopy (XPS). Observed magnetic properties and magnetic force microscopy images suggested that this gradient diffusion supports reduction of intergrain exchange coupling and improvement of the magnetic properties. The signal-to-noise ratio over 22 dB was obtained at 450 kFCI in playback tests, in combination with amorphous cobalt boron soft-magnetic underlayer (SUL). It is suggested that these properties are brought by a combination of the dispersed nucleation sites with rich boron content in the initial layer and decreasing boron content during the growth of the multilayer. In addition, this simple medium, which consists of only three elements, Co, Pd, B, for the SUL, the seed layer, and the magnetic layer, has a very unique feature of the dull interfaces, observed by a transmission electron microscope.

Non-contact measurement of electric potential of PV modules

PV module characterization by non-contact electrostatic potential measurement method is investigated. The method can be carried out by a portable equipment under various outdoor operating conditions as well as in laboratories. The electric potential of the cells in various crystalline silicon and thin film PV modules can be determined in a noncontact configuration such as through their cover glass and backsheet. Basic repeatability of the electrostatic voltage measurement was confirmed to be within about ±0.5 V for indoor measurements, which is better than the output voltage of a component cell. The repeatability was typically within the voltage corresponding to 2 to 3 times the component cells even under changeable outdoor conditions. The present study demonstrates that the method is applicable to PV module characterization, such as identifying a hotspot cell in a PV module and determining degraded modules in a PV array, through monitoring the distribution of their electric potential under outdoor conditions without interrupting the grid-connected operation of the system.

Non-contact measurement of electric potential of photovoltaic cells in a module and novel characterization technologies

A novel noncontact method of measuring the electric potential of component cells in photovoltaic (PV) modules is investigated using electrostatic field measurement technology. Experimental results for various kinds of PV cells and modules are presented, and their measurement principle as well as practical factors that affect the measurement results are discussed. It is demonstrated that the DC electric potential of the cells in various crystalline silicon and thin-film PV modules can be measured indoors through their cover glass or backsheet within a resolution of the output voltage of about 1 cell. The method is also applicable to the outdoor measurement of PV modules under grid-connected operation, and enables various kinds of characterization such as identifying low-performance cells in a PV module and degraded modules in a PV array, and determining the balance of their output current under outdoor operating conditions. Different distributions of electric potential measured from the front and back surfaces are observed for some types of modules. These differences are suggested, by the results of the analysis of experiments and numerical simulations, to originate from the modification of the modules surface electric potential by slight current flow through its component materials such as the cover glass, ethylene vinyl acetate (EVA), and backsheet.

Microstructure and segregation effect of Co/Pd multilayer perpendicular magnetic recording media

In this report, we have investigated addition of boron with modulated contents in depth profile and microstructure by a transmission electron microscopy (TEM) with high annular angle dark field (HAADF) detector to evaluate segregation effect.