Heizo Tokutaka

Observation of Josephson Junctionlike Behavior in Single-Crystal (Bi, Pb)2Sr2CaCu2Oy

The dependences of critical current on the temperature and magnetic field and the current-voltage characteristics in response to incident microwave radiation are measured in the direction of the c-axis of the 80 K superconducting phase (Bi, Pb)2Sr2CaCu2Oy bulk single crystal. Josephson junctionlike behavior is successfully observed, and it shows that the single crystal itself is composed of Josephson junctions along the c-direction and that its electrical transport in this direction is limited by intrinsic tunnel barriers existing in the single crystal.

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.

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.

Effects of temperatures and periods for melting on growth of Bi2Sr2CaCu2Oy single crystals

Abstract We prepared Bi 2 Sr 2 CaCu 2 O y single crystals by a self-flux method using a crucible with a cap. From the results, we found that the optimum temperature and period for melting the starting materials were 1000°C and 5 h, respectively. Plate-like Bi 2 Sr 2 CaCu 2 O y single crystals with the size of 6 × 2 mm 2 were obtained and had an 80 K single-phase.

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.

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.

Growth of Bi2Sr2CaCu2Oy single crystals by a vertical Bridgman method and their characterization

Abstract We prepared Bi 2 Sr 2 CaCu 2 O y single crystals by a vertical Bridgman method and investigated their characterization. From the results, we found that the plate-like Bi 2 Sr 2 CaCu 2 O y single crystal with the size of 4 × 10mm 2 was a single phase. The as-grown Bi 2 Sr 2 CaCu 2 O y single crystals had a superconductivity without any annealing after crystal growth. In addition, the single Bi 2 Sr 2 CaCu 2 O y crystal did not contain any impurities and its surface morphology was flat.

Characteristics of TiN Films Sputtered under Optimized Conditions of Metallic Mode Deposition

We prepared TiN films by metallic or nitride mode sputtering using a collimator, and investigated the characteristics of the films. Resistivity, density, thermal stress, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) measurements and transmission electron microscope (TEM) observation were carried out. The characteristics of the TiN films depended on the N2/Ar flow ratio. TiN deposition rates in the metallic mode with N2/Ar flow ratios from 0.2 to 0.5 were 3 times higher than those in the conventional nitride mode with N2/Ar ratios from 0.75 to 1.0. By depositing the film under the best metallic mode conditions with N2/Ar=0.5, the TiN film with a minimum resistivity and a maximum film density was formed. The TiN films, which were prepared under optimized conditions of metallic mode deposition, had a small concentration of oxide in the TiN, strong (111)-preferred orientation and good crystallinity.

Application of self‐organizing maps (SOM) to Auger electron spectroscopy (AES)

The self-organizing map (SOM) method that was developed by Kohonen has been examined preliminarily by applying some problems of chemical analysis using AES data, leading to promising results: using a two-dimensional SOM, the items that are described qualitatively by linguistic expressions can be explained more quantitatively by the position of the spectral data on the SOM, together with a grey level expression. The composition of an unknown sample also can be determined precisely by a SOM that has been constructed using spectra from samples of known composition.