Characterization of aluminium nitride thin films

Aluminium nitride (AlN) thin films have been synthesized by evaporation of aluminium and simultaneous irradiation with nitrogen ions, ion-vapour deposition method, at the substrate temperature of room temperature or 473K. The kinetic energy of the incident nitrogen ion beam has been kept at 0.5 keV and the deposition rate has been varied from 0.075 to 0.28 nm/s. The structure of the synthesized films has been examined by X-ray diffraction (XRD) and the surface morphology has been characterized by atomic force microscopy (AFM). In the XRD patterns of both films synthesized at room temperature and 473K, the diffraction lines due to the AlN(10.0), (00.2) and (10.1) planes have been discerned. AFM observations reveal that the surface of the films synthesized at 473K becomes rough as compared with the films synthesized at room temperature. This may be attributed to growth of AlN particles on the substrate kept at 473K. Furthermore, in the films synthesized at the 473K substrate, several aggregated protrusions can be observed on the relatively smooth surface at the deposition rate of 0.28 nm/s, while the surface of the films is uniform on nanometre scale at the deposition rate of less than 0.12 nm/s. The present results suggest that the synthesis of the AlN films with uniform surface is feasible by controlling the substrate temperature and the deposition rate.     

Psychosocial evaluation on the correct recollection of periodic medical checkups of workers. 1. The ratio of correctly recalled results of medical checkups

To investigate the usefulness of a periodic medical checkup at the workplace from the standpoint of remembering the results, a survey was performed by a self-rating questionnaire on 424 industrial workers in a certain manufacturing company. The questionnaire included several items, such as their recalled abnormal medical findings and follow-up toward them, Breslow's 7 health practices, Goldberg's 12 selected items from the Japanese version of the General Health Questionnaire, and other original health related items. The study was conducted a month after the workers received their results. A total of 391 (290 males and 101 females) or 92.2% responded to the questionnaire. Several factors, such as age, gender, the type of occupation, and perceived health status were significantly correlated to the recalled results of medical checkups, but, only age and the way of observing the results were in accordance with the actual results. Only forty-nine percent of the responders correctly remembered their results. Age and perceived health status were significantly correlated to the exact recollection of the results. In particular, those who had poor perceived health status tended to have a wrong understanding of their medical results. Furthermore, there were those with the highest averaged GHQ scores who responded as having some abnormal findings even though no abnormalities were discovered in the medical checkups. On the other hand, there were those with the lowest averaged GHQ scores who answered that they had no abnormal findings even though some abnormalities were revealed in the medical checkups. The frequency of correct follow-up of the results was lower than the exact recalling of the results. In addition, those who made a mistake in the follow-up were inclined to have an optimistic view. Therefore, comprehensive health care for precise recalling of the results of medical checkups should be required to improve abnormal findings or maintain a good health status.     

Numerical plate testing for linear two‐scale analyses of composite plates with in‐plane periodicity

A method of numerical plate testing (NPT) for composite plates with in‐plane periodic heterogeneity is proposed. In the two‐scale boundary value problem, a thick plate model is employed at macroscale, while three‐dimensional solids are assumed at microscale. The NPT, which is nothing more or less than the homogenization analysis, is in fact a series of microscopic analyses on a unit cell that evaluates the macroscopic plate stiffnesses. The specific functional forms of microscopic displacements are originally presented so that the relationship between the macroscopic resultant stresses/moments and strains/curvatures to be consistent with the microscopic equilibrated state. In order to perform NPT by using general‐purpose FEM programs, we introduce control nodes to facilitate the multiple‐point constraints for in‐plane periodicity. Numerical examples are presented to verify that the proposed method of NPT reproduces the plate stiffnesses in classical plate and laminate theories. We also perform a series of homogenization, macroscopic, and localization analyses for an in‐plane heterogeneous composite plate to demonstrate the performance of the proposed method. Copyright © 2015 John Wiley & Sons, Ltd.     

Electron spin resonance (ESR) study of Li-doped polyacenic semiconductive (PAS) material processed with heat treatment

The electron spin resonance (ESR) spectral change of Li-doped polyacenic semiconductive (PAS) materials has been examined before and after heat treatment to elucidate the decrease in the discharging amount of the heat-treated Li-doped PAS electrodes. Decrease in the peak-to-peak line width of the ESR lineshape has been observed for all the Li-doped PAS electrodes, indicating partial degradation of Li-dopants. These results strongly suggest the existence of two kinds of Li-dopants in the highly Li-doped PAS electrodes: heat-resistant and heat-labile ones.     

Characterization of electrode/electrolyte interface using in situ X-ray reflectometry and LiNi0.8Co0.2O2 epitaxial film electrode synthesized by pulsed laser deposition method

An in situ experimental technique was developed for detecting structure changes at the electrode/electrolyte interface of lithium cell using synchrotron X-ray reflectometry and two-dimensional model electrodes with a restricted lattice plane. The electrode was constructed with an epitaxial film of LiNi_0.8Co_0.2O₂ synthesized by the pulsed laser deposition method. The orientation of the epitaxial film depends on the substrate plane; the 2D layer of LiNi_0.8Co_0.2O₂ is parallel to the SrTiO₃ (1 1 1) substrate ((0 0 3)_{LiCo0.2Ni0.8O2}//(1 1 1)SrTiO₃), while the 2D layer is perpendicular to the SrTiO₃ (1 1 0) substrate ((1 1 0)_{LiCo0.2Ni0.8O2}//(1 1 0)SrTiO₃). These films provided an ideal reaction field suitable for detecting structure changes at the electrode/electrolyte interface during the electrochemical reaction. The X-ray reflectometry indicated a formation of a thin-film layer at the LiNi_0.8Co_0.2O₂ (1 1 0)/electrolyte interface during the first charge-discharge cycle, while the LiNi_0.8Co_0.2O₂ (0 0 3) surface showed an increase in the surface roughness without forming the surface thin-film layer. The reaction mechanism at the electrode/electrolyte interface is discussed based on our new experimental technique for lithium batteries.     

Effect of surface structure on cell growth prepared by the terminal immobilization method

Substrate effects of surface morphology and chemical structure for cell cultures prepared by molecular terminal immobilization method were studied. When we focused attention on a phenyl group as a functional moiety, the cell growth on the surface prepared by the immobilization method showed a better proliferation rate than that of a substrate prepared by the casting method. Further, from the results of mouse fibroblast L929 cell (L‐cell) growth on poly(amino acid)‐immobilized surfaces in Dulbecco's minimal essential medium containing 10% FBS, it was indicated that the amino group was more effective than the phenyl group, and that a slight difference of chemical structure had a substantial influence on cell growth. In addition, mouse bone marrow–derived Sp2/0‐Ag14 cell (Sp2/0 cell) culture in ASF‐104 serum‐free medium, poly(amino acid)‐immobilized substrates showed an almost equal proliferation rate to that in a serum‐containing medium. These results showed that effective cell growth can occur on immobilized surfaces, and that detection of a weak interaction depends on the functional groups. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3001–3008, 2004     

Network of γ-irradiated poly(vinyl alcohol) beads

The crosslinking of poly(vinyl alcohol) beads was performed by γ-ray irradiation. The maximum molecular size, M_lim, which can permeate through beads, was obtained by eluting poly(ethylene glycol) through a column packed with beads. The root-mean-square of the end-to-end distance $\text{(}\text{r}{}^2\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and that of the hydrodynamic radius $\text{(}\text{s}{}^2\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ were also calculated. Meanwhile, the average size of the network of the beads, r_c, was estimated from the average molecular weight between crosslinkages, M_c, which was derived from the glass transition temperatures of crosslinked and non-crosslinked poly(vinyl alcohol) beads. r_c values of poly(vinyl alcohol) beads decreased as the total dose of γ-irradiation increased when dry poly(vinyl alcohol) beads were γ-irradiated, while the values were almost constant when poly(vinyl alcohol) beads swollen in water were γ-irradiated. Further, linear relations were obtained among r_c, $\text{(}\text{r}{}^2\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, and $\text{(}\text{s}{}^2\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ covering the wide range of total dose.