RESUMO
Due to the influence of refraction effects on the escape probability of the Back-Scattered Electrons (BSE), an expression of the fraction of these BSE is given as a function of the beam energy, E°, and emission angle (with respect to the normal) α. It has been shown that these effects are very sensitive to a local change of the work function in particular for low emerging angles. This sensitivity suggests a new type of contrast in Low Voltage Scanning Electron Microscopy (LVSEM for E°<2 keV): the work function contrast. Involving the change of φ with crystalline orientation, this possibility is supported by a new interpretation of a few published images. Some other correlated contrasts are also suggested. These are topographical contrasts or contrasts due to subsurface particles and cracks. Practical considerations of the detection system and its optimization are indicated.
RESUMO
The high resolution transmission electron microscope (HRTEM) imaging of short range order (SRO) in Ni4Mo was investigated by means of multi-slice image simulations. The HRTEM images of Ni4Mo exhibit locally bright dot patterns corresponding to the [001] projections of the N2M2-type (chalcopyrite-like) structure. The multi-slice simulations revealed that the N2M2 patterns are rationalized as the projection patterns of the SRO structure which consists of subunit cell clusters of D1a, D022 and Pt2Mo structures. The N2M2-type image contrast appears when both the fundamental fcc lattice reflections and the 1 1/2 0 diffuse scattering of SRO contribute enough to imaging. This suggests that a good coincidence in intensity distribution between the Fourier power spectra of HRTEM images and the electron diffraction patterns is one of the conditions for the image contrast of SRO to be interpreted in terms of the projection contrast.
RESUMO
The state of short-range order (SRO) and the ordering process in Cu3Pt have been studied by the in-situ transmission electron microscope observation method. In order to detect weak diffraction-patterns and weak image-contrasts, an imaging plate system and/or digital-process of video-recorded signals were applied. It is confirmed that above the critical temperature for ordering, Tc, the alloy shows diffuse scattering in its electron diffraction pattern. The appearance of the diffuse scattering indicates that the "disordered" Cu3Pt (designated as A1) has an SRO-state in thermoequilibrium. Dark field images taken by using the diffuse scattering shows a fine dot-contrast, which indicates the presence of "microdomains". The dot-contrast is flickering at higher temperatures, but the rate of flickering decreases with falling temperature and finally stops before reaching Tc. On further decreasing temperature, some of the microdomains grow up to large domains of the long period superstructure (L12-s) phase. This indicates that the transformation to L12-s via SRO proceeds without a process of nucleation even though the transformation is of a first-order.
RESUMO
Treatment of the head and neck cancer has surprisingly developed in the last decade. The most possible reasons were the development of the more effective anticancer drugs and new combination therapy including immunotherapy. FAR therapy, which was applied to the head and neck cancer in our clinic since 1972, was a combination of vitamin A, 5-FU and radiation. We have already reported the results and the problems of FAR therapy. But, recently we have developed the clinical application of vitamin A to the chemotherapy so as to overcome the resistance of the tumor cells to the anticancer drugs. In this paper, vitamin A was focused as a potentiating agent and the possible material to overcome the resistance to the anticancer drugs.
