Katsumi Nishimori

The preparation conditions and characteristics of the Bi−Sr−Ca−Cu−O single crystals

The 7 K, (7+80) K and 80 K phase lli-Sr-Ca-Cu-O single crystals were prepared by changing the composition of the starting materials using a self-flux method. The results of AES (Auger electron spectroscopy) measurements indicate that a part of the Sr would be substituted by Ca in the 7 K phase crystal. Plate-like crystals were observed by SEM (scanning electron microscope) in the as-grown 80 K phase crystal surface. This may be due to the fact that the specimen has a layer structure.

The electron mean free path (applicable to quantitative electron spectroscopy)

Abstract There are two well known methods accepted generally to establish the value of the electron mean free path. One is Seahs method where he compiled many published experimental data. The other is Penns method which is extensively theoretical. Besides, Tarng and Wehner showed that there is a significant difference between the observed electron mean free paths, according to whether the electron pass through Mo or W. Here, we propose a general method to calculate the electron mean free path for material of any atomic number, using Tarng and Wehners experimental results (Mo and W) and our experimental data for Cr. Then, we compare and review these three methods of Seah, Penn and ourselves to learn which method is the most accurate, using published AES and XPS experimental data. Among these three methods, our method shows values closest to the experimental ones. Finally, we must add the following sentence: When the AES experimental data are compared with the theoretical values, the attenuation length of the primary electron beam should be considered.

Optimal Feedback Control Design Using Genetic Algorithm in Multimachine Power System

Abstract This paper introduces an application of genetic algorithm (GA) to design weighting matrices Q and R elements in Linear Quadratic Regulator (LQR) optimization process. The weighting matrices Q and R are the most important components in LQR optimization. The performance of matrices Q and R determines the output performances of the system. Commonly, a trial-and-error method has been used to construct the matrices Q and R elements. This method is very simple, but very difficult to produce good control performances. Also it takes a long time to choose the best values in its processing. Because of this, in order to improve control performances by selecting the elements of matrices Q and R, the Bryson method can be employed to give better results in shorter time than the previous method. In this paper, we use GA to construct the weighting matrices Q and R properly. We design the weighting matrices of a power system optimization by using the trial-and-error method, Bryson method, and GA method and compare the control performances. It is shown that the GA calculation is the most useful among the three methods to improve system performances via matrices Q and R design to minimize settling time of control. This idea gives a new alternative procedure in time varying feedback control to improve the stability performances.

Determining the arrangement of fictitious charges in charge simulation method using genetic algorithms

Abstract In this paper, we propose a method to decide the appropriate arrangement of fictitious charges in the charge simulation method (CSM) by using a direct search method. The appropriate arrangement is achieved by using genetic algorithms (GA) as a search method. We describe the arrangement of the charges as chromosomes and place fictitious point-charges at random on the rotational axis of a spheroidal electrode. The charge arrangement is adjusted by using GA until the potential reaches a specified value over the surface of the electrode.

The difference between 6H-SiC (0001) and (0001) faces observed by AES, LEED and ESCA

Abstract 6H-SiC has a hexagonal structure. The top most surfaces of (0001) and (000 1 ) are only covered with Si and C atoms, respectively. The former is called a Si-rich surface and the latter is called a C-rich surface. These different surface polarities show different surface characteristics. These can also be observed by surface analytical techniques. Here, SiC surfaces were heated to several temperatures (RT-1100°C) for 10 min in an ultra-high vacuum (UHV) chamber. Then the surfaces were observed by LEED (low energy electron diffraction) and AES (Auger electron spectroscopy). The surfaces heated to 1000°C showed the cleanest surfaces. C(KVV)/Si(LVV) AES peak to peak (p-p) height ratio showed a minimum value at 1000°C for all SiC surfaces; on average it is 0.26 on a Si face and 0.38 on a C face. LEED patterns which were heated at 1000°C showed (√3 × √3 - R30°) structure on a Si-rich face and (3 × 3) structure on a C-rich face. After LEED and AES, ESCA experiments were carried out on these samples. C1s/Si2p peak area ratios were 1.2 and 2.0 on Si and C-rich faces, respectively. However, after Ar-ion sputter etching, the differences could not be observed.

A quantitative auger electron spectroscopy method (applied to a thin film monolayer overgrowth)

Abstract When a thin film grows in a monolayer overgrowth fashion, the AES signal versus film thickness is calculated by a quantitative AES method. The method is applied to the Cases of Ag on Au, Mo on W and Be on Cu. The calculated results agree very well with the experimnetal results. In this method, the following points are considered: (1) the attenuation of a primary beam, (2) the effects of back-scattered and forward-scattered electrons both from thin film and substrate materials, (3) the escape depths of any electrons, and (4) the effect of the three-dimensional movements of secondary electrons and Auger electrons in the solid. Consequently, especially from the above effect (4), the curve of Auger electron signal intensity versus film thickness can be estimated for the various optics (e.g. Cylindrical Mirror Analyzer (CMA), Low Energy Electron Diffraction (LEED) optics,…) used for the usual Auger experiments. Electron mean free paths can be obtained by the interpolation or the extrapolation for the different atomic numbers and the different energies from the published experimental result of Mo and W. The result by this method has a similar tendency as the result obtained by Penn. Also, the number of back-scattered and forward-scattered electrons can be estimated by the coefficient of secondary electrons with energy above the ionization electron energy E C to produce Auger electrons. Then, the values of the secondary electron coefficients are measured and tabulated for the 20 different elements from Be to U as a function of the ionization electron energy.

Automatic arrangement of fictitious charges and contour points in charge simulation method for two spherical electrodes

Abstract We propose a method to decide the appropriate arrangement of both fictitious charges and contour points in the charge simulation method for the case that the shape of electrodes can be expressed in the spherical coordinates. In this paper, we use genetic algorithm (GA), which is inspired by the mechanism of natural selection where stronger individuals are likely the winners in a competing environment, as a search method. We calculated the potential distribution around two spherical electrodes with different potentials above a grounded electrode plate. The surface potentials of the electrodes were assumed to be 5000 and 30 V , respectively, for example. The total number of the charges was 22 for the electrode system. First, we placed fictitious point-charges and contour points at random inside the electrodes and on the surfaces of electrodes, respectively. The arrangement was automatically adjusted by using GA until the potential reached the desired values at all the test points placed on the electrode surfaces. We show that the GA can be useful to determine the appropriate arrangement of both fictitious charges and contour points simultaneously.

Comparison of escape depths between Auger electron and disappearance potential spectroscopy electron

Abstract The escape depths of the characteristic electrons of the Auger electron and the quasielastically reflected electron were determined by Auger electron spectroscopy (AES) and disappearance potential spectroscopy (DAPS), respectively, for a Cr overlayer onto Ti and Fe substrates. For the case of Cr on Fe, in-situ measurements of AES and DAPS were carried out. From the results, the mean free paths of 455, 575 and 710 eV electrons through Cr were obtained as 9.6, 13 and 15 A, respectively. The attenuation length of a 2.5 keV primary electron of AES through Cr was also obtained and the value was 62 A. In addition, the mean free paths of electrons with the same energy depend on the scattering materials of Cr, Mo and W (material dependence). The phenomena are useful for a quantitative electron spectroscopy of surfaces.

Crystal Growth of Bi-Sr-Ca-Cu-O (c0=39 Å) Single Crystals

Bi-Sr-Ca-Cu-O (Bi-based) single crystals were prepared by the self-flux method with a temperature-holding process. The prepared Bi-based single crystals were platelike with a size of about 2×2 mm2. From the X-ray diffraction patterns, we found that the Bi-based single crystal had a c-axis unit cell length of about 39 A.

LEED-AES and XPS Studies of Bi-Sr-Ca-Cu-O Single Crystal Surfaces

The well-defined clean surface in the 80K-phase Bi-Sr-Ca-Cu-O single crystal was obtained by cleaving it in air and heating it at 350°C in ultrahigh vacuum (UHV). The low-energy electron diffraction (LEED) pattern from the clean surface showed the perfect single domain of a 1×5 structure. From the Auger electron spectroscopy (AES) measurements, the cleaved surface might be a Bi-O layer and O atoms will be removed more easily than the other elements of Sr, Ca and Cu by Ar+ sputter etching. In the clean surface of the single crystal, Cu2+ was dominant. The X-ray photoelectron spectroscopy (XPS) spectrum of O 1s consists of the OH(~531 eV) and OL(~529 eV) components, and the OH component is smaller than the OL component.