ALBERT

Notes: A new thermomagnetic recording method using tunneling current in a scanning tunneling microscope as a heating source is proposed. In the experiment, pulse voltage of from 2–8 V with a pulse width of 1 ms is applied to the sample, while the probe position is kept at a bias voltage of 0.2 V and a tunneling current of 0.3 nA. As a result, we have demonstrated that thermally recorded magnetic domains are formed in a Pt/Co multilayered film and minimum domains as small as 0.2 μm in diameter are observed using a polarized optical microscope. © 1995 American Institute of Physics.

Notes: In the field of material sciences, it has long been desired to develope the equipment to obtain crystallographic information of micrometer-size crystalline substances. Synchrotron radiation (SR) could be a candidate to deal with such a small specimen other than electron microscope. It seems more advantageous to utilize SR from the viewpoint that the processing of the diffraction data that has already been established for identification of the materials, structure analysis, and refinement. Even in the case of SR, special care should be taken for the measurement of very weak diffracted intensities. In the case not using SR, the size of 50 μm might be the limit for the specimen to be examined by the diffraction method. The diffracted intensity is proportional to the volume of the specimen, and that of micrometer-size crystal is estimated as 10−5 times of that of the limit mentioned above. The noise level of the experiment, therefore, should be as low as possible. If the noise level becomes negligibly small, the signal could be accumulated continually to the desired intensity level by adjusting measuring time. The experiment, for the purpose, should be carried out in vacuum with the stational crystal method and with very narrow collimated x-ray beams.The Laue method is employed by the above reason, as well as the fact that the intensity of each Bragg reflection on a reciprocal row passing through the origin of the reciprocal space is superposed with each other, which also intensifies a diffraction spot on the photographic plate. The Laue camera is set up at BL-4B of Photon Factory, sealed in vacuum and installed with a very narrow collimater. The development of the system has been performed to the level which several Bragg reflections of molybdenum single crystal with 0.8 μm in its diameter can be taken on the imaging plate for 50-min exposure with ring current from 128 to 125 mA. The origin of diamonds in meteorites has been a controversy as to whether they are formed from carbonaceous materials by impact shock or directly formed from vapor. Recent discovery of vapor-growth diamonds in carbonaceous chondrites has generated a renewed interest in the origin of ureilite diamonds. Two types of micrometer-size diamonds were prepared. One of them was grown under low pressure by chemical vapor deposition (CVD) from gaseous mixtures of H2 and CH4, and another was synthesized by shock effect (kindly offered by Nippon Oil & Fats Co., Ltd.) The micro-Laue method was applied to them in order to get information about their microstructures. Two characteristics are recognized in profiles of reflections themselves and in whole patterns of the Laue photographs. The reflections of CVD diamonds are elongated but symmetric in their profiles and are distributed regularly as they are indexed by the diamond lattice, while those of shock effect are also elongated and asymmetric, and are distributed at random as they cannot be indexed. The characteristics observed by the method may be useful to ascribe the origin to CVD or shock effect.

Notes: Silicon was oxidized by a collimated hyperthermal ozone beam produced by pulsed-laser ablation of solid ozone to increase the controllability of the silicon dioxide film thickness and to achieve low-temperature oxidation. The oxidation rate could be accurately controlled by the number of laser shots to which the number of supplied ozone molecules was proportional. Ozone molecules with a translational energy of around 1 eV obtained by laser ablation produced an initially rapid oxidized region with no temperature dependence in which a 0.6 nm silicon dioxide film could be synthesized at room temperature with only 200 laser shots. Higher-efficiency oxidation was also achieved in comparison with that by using a spray of ozone with thermal energy. © 2001 American Institute of Physics.

Notes: A system for analyzing and refining the crystal structure of a submicrometer-sized specimen has been developed at the Photon Factory, KEK, employing a Laue method with an imaging plate. The system was evaluated using two molybdenum spheres with diameters of 0.8 μm and 0.27 μm3 in volume. The result showed that the isotropic temperature factors of both spheres were successfully refined, and that one of the samples was found to be twinned. The smaller domain of the twin was determined to be 0.02 μm3 in volume, which means that the smaller domain is composed of only 109 Mo atoms. The system was applied to a 5-μm-sized icosahedral CVD diamond as a first application. Analysis of several Laue patterns revealed that the sample is composed of more than 17 domains. Among them, 16 domains are twinned with each other, and the mode of twinning is of the spinel twin type.