Tomohiro Aoyama

Reconstructions of 6H-SiC(0001) Surfaces Studied by Scanning Tunneling Microscopy and Reflection High-Energy Electron Diffraction

Surface reconstructions and surface decomposition of 6H-SiC(0001) covered with Si were observed using scanning tunneling microscopy (STM) and reflection high-energy electron diffraction (RHEED). The 3×3 structure terminated with Si atoms was obtained by annealing at 1050°C; this changed to a mixture of the graphite 1×1 and SiC 6×6 by annealing at 1300°C. The graphite 1×1 consisted of two types of graphite lattices, rotated 30° with respect to the SiC lattice and along the SiC lattice. The SiC 6×6 was terminated with C atoms. The RHEED spots due to the double diffraction between the SiC (02) spot and the graphite spot rotated by 30° with respect to the SiC lattice were observed. The thickness of the graphite layer and the area of the graphite region increased by successive annealing. String-shaped structures were formed along the steps at 1450°C. Further annealing up to 1800°C resulted in the formation of a thick graphite layer and amorphous carbon.

The (3×3)R30° reconstruction on hexagonal 6H–SiC(0001) surface with and without a Si flux

The (√3 x √3)R30° reconstruction on hexagonal 6H-SiC(0001) surface and its properties were studied by using reflection high-energy electron diffraction (RHEED) and RHEED multislice dynamical calculations. A Si coverage of 1/3 monolayer occupying the threefold-symmetric T 4 or H 3 sites develops upon a lower Si flux and/or at a higher annealing temperature and/or upon a longer time annealing. However, Si trimers centered on the T 4 positions with 1 monolayer coverage may be another appropriate candidate for the (√3 × √3)R30° reconstruction obtained under a very Si-rich condition and/or at a lower annealing temperature and/or upon a shorter time annealing.

Application of Air Cooling Technology and Minimum Quantity Lubrication to Relief Grinding of Cutting Tools

This study focuses on applying the environmentally friendly cooling-air grinding and minimum quantity lubricant (MQL) methods to relief surface tool grinding. The resultant grinding behavior is characterized. Grinding fluids have been commonly used during the grinding of tools for their cooling and lubricating effect since the hard, robust materials used for cutting tools are difficult to grind. Grinding fluids help to prevent a drop in hardness due to burning of the cutting edge and keep chipping to an absolute minimum. However, there is a heightened awareness of the need to improve the work environment and protect the global environment [1]. The present study is aimed at applying dry grinding, cooling-air grinding, and MQL to the relief surface grinding process. This new approach is compared with the conventional method that utilizes grinding fluid. The combination of cooling-air and MQL grinding is found to perform well and is better than the conventional grinding with grinding fluid.

Structural Study of the SiC(0001)(√3×√3)-R30\degree Surfaces by Reflection High-Energy Electron Diffraction Rocking Curves

Two types of √3×√3 surfaces, silicon-rich and carbon-rich, have been observed in a series of annealing processes. Rocking curves from the surface structures of both √3×√3 surfaces have been analyzed by reflection high-energy electron diffraction (RHEED) dynamical calculations. The silicon-rich √3×√3 surface is determined to be terminated with Si adatoms on T4 or H3 sites of the silicon terminated bulk surface. It is considered that the carbon-rich √3×√3 surface consists of a C honeycomb structure. From the results of Auger spectra and RHEED rocking curves, the phase transition from the silicon-rich to the carbon-rich √3×√3 phases is caused by adsorption of atomic hydrogen on the silicon-rich √3×√3 surface.

High Speed Drilling and Tapping using the Technique of Spindle Through MQL Supply

Abstract. The minimal quantity lubrication (MQL) technique is used in cutting processes in order to reduce the environmental pollution caused by cooling lubricants. In the usual case of MQL cutting, the oil mist is supplied to the cutting area by external supply nozzles. In the case of a high speed cutting process, however, the high speed peripheral air flow prevents the oil mist from reaching the cutting area. The spindle through coolant supply method gives a good solution to this problem. However, the small oil drops could stick to the inside of the rotating duct, separated from the air flow during high speed spindle rotation exceeding 10000 rpm, and do not reach the cutting point unless the spindle speed is reduced. In this study, a new spindle through lubricant supply system for MQL high speed cutting was developed and installed in a high speed spindle system. The performance of the developed system was evaluated by carrying out high speed drilling and tapping operations for aluminum alloy.

A Controlled Atmosphere Cutting Apparatus for Understanding Tribological Behavior of Lubricants in Near-Dry Machining

Minimal Quantity Lubrication (MQL) cutting is a successful example of near-dry machining operations. Using actual milling operations, this study shows that equivalent or sometimes superior cutting performance of MQL cutting with a biodegradable synthetic ester lubricant can be achieved in comparison with the conventional cutting with flood coolant supply. There is little investigation on reasons for the preferable performance, such as increase in tool life and the improvement in surface finish. With an extremely low quantity of a lubricant, this study also aims at understanding fundamentally the tribological behavior of a small amount of lubricants during metal cutting. For this purpose, a controlled atmosphere cutting apparatus is developed. The apparatus can introduce a small amount of lubricants in vapor phase into the cutting chamber and can measure their adsorption characteristics by a mass spectrometer. Based on the results obtained by this apparatus, the tribological behavior of a model ester is discussed in connection with the effectiveness of the synthetic ester, which is a suitable lubricant for MQL cutting. Furthermore, the modified version of the apparatus equipped with a cutting force dynamometer is proposed to evaluate the cutting performance in a controlled atmosphere.

Atomic models of (∛×∛)R30° reconstruction on hexagonal 6H–SiC(0001) surface

By using reflection high-energy electron diffraction (RHEED) and RHEED multislice dynamical calculations, the atomic structures of the (∛×∛)R30° reconstruction on 6H–SiC(0001) surface were solved. Both the simple adatom structure with a Si coverage of one-third monolayer occupying the threefold-symmetric T4 or H3 sites and a bit complex structure with Si trimers centered on the T4 positions with 1 monolayer coverage are all compatible with our results.

Initial Oxidation of 6H-SiC (0001) (3 x 3)-R30° and 3 x 3 Surfaces Studied by AES and RHEED

Initial oxidation of the SiC (0001) (√3×√3)-R30° and 3×3 surfaces at various temperatures is studied by using Auger electron spectroscopy (AES) and reflection high-energy electron diffraction (RHEED). The results show that the 3×3 surface oxidizes with maintaining its original periodicity, while the √3×√3 surface changes into a 1×1 structure. Moreover, the √3×√3 surface loses almost all Si-Si bonds by a low oxygen exposure, in contrast the 3×3 surface does not. There is no significant difference among the Auger spectra at different sample temperatures in the case of the √3×√3 surface, while thermal activation is found in the 3×3 case at 500°C.

Reconstruction of the 6H–SiC(0001) √3×√3-R30° surfaces by adsorption of hydrogen in ultra high vacuum

Reconstruction of the 6H/SiC(0001)3/3-R308 surfaces in ultra high vacuum (UHV) has been studied by rocking curves of reflection high energy electron diffraction (RHEED) intensities and Auger electron spectroscopy (AES). It is found that the silicon rich 3/3 surface is unstable in UHV. This 3/3 surface transforms into the carbon rich 1/1 surface in rather short time. The phase transition is concluded to be caused by atomic hydrogen adsorbed on the silicon rich surface. Annealing the 1/1 surface leads to the carbon rich 3/3 surface, which transforms into the silicon rich 3/3 surface by successive annealing in UHV. The results show that silicon adatoms on the silicon rich 3/3 surface is not etched by the adsoption of hydrogen but reside on the surface as silicon clusters in the reconstruction process to work as a silicon source in the successive annealing. # 2002 Elsevier Science B.V. All rights reserved.

Low-Voltage Scanning Electron Microscopy as a Tool for Surface Imaging and Analysis of Practical Materials

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