Abstract: Removed due to plagiarism
Abstract: As a typical multi-functional single crystal material, Lithium tantalite (LiTaO3 or LT) exhibits its excellent electro-optical, piezoelectric properties and has now been widely applied into many applications, such as surface acoustic wave (SAW) filters, isolators and other photoelectron devices. Compared with other functional crystals like silicon and sapphire, LT behaves much more brittle and softer. The knowledge of precision machining built on conventional hard-and-brittle materials is no longer applicable to this new type of soft-and-brittle crystal. In order to clarify the fundamental mechanical properties of LT, micro/nano-indentation tests are conducted in this study. The obtained results are analyzed and discussed to understand the behavior of this type of materials in their machining process.
Abstract: Finish machining of sintered steel is increasingly important for near net shape technology. However, the life of a cutting tool for machining sintered steel is generally much shorter than for carbon steel and thus, finish machining increases the manufacturing cost of sintered products. For this reason, wear characteristics of several grades of cutting tools in turning sintered steel were investigated under different lubrication conditions. As a result, it is found that a P10 grade of cermet and an S01 grade of AlTiN coated carbide are recommended for dry machining. When cutting fluid is necessary for chip control and disposal, air jet assisted wet machining with a K10 uncoated cemented carbide and wet machining with a P10 cermet are recommended. It is also found that a small amount of cutting fluid remained in the workpiece during wet machining caused an intense thermal impact to a P10 uncoated cemented carbide leading to short tool life.
Abstract: Single crystal SiC is one of the most attractive semiconductor materials for next generation power device applications. However, it is very difficult to be precisely machined due to its high hardness and chemical inertness. We evaluated the machining characteristics of 4H-SiC using different processes including diamond abrasives lapping, chemical mechanical polishing (CMP) and plasma assisted polishing (PAP). Scratches were introduced through diamond abrasives lapping due to the high hardness of diamond, which resulted in the worsening of surface roughness. A damage layer was observed in the cross-sectional transmission electron microscopy (XTEM) images. A scratch-free surface was obtained through CMP, but it’s not atomically flat since step/terrace structure couldn’t be clearly observed. PAP was newly proposed for the finishing of difficult to machine materials. In PAP, water vapor plasma oxidation and soft abrasive polishing were repeatedly conducted. Ceria which is much softer than SiC was used as the abrasive material. PAP was proved very effective to achieve surfaces out of scratches. Also, due to the low hardness of ceria, no damage layers were introduced. The roughness of PAP processed surface was decreased to about 0.1 nm rms. The surface was also observed by XTEM, which proved an atomically flat surface without crystallographical damage was obtained.
Abstract: In this study, we investigated the possibility of removing and smoothing a single-crystal silicon carbide (SiC) surface under ultraviolet (UV) irradiation in hydrogen peroxide (H2O2) solution. In this method, a SiC substrate was excited by UV irradiation that transmitted synthetic quartz, and then an oxide layer on the SiC substrate was formed by photochemical reaction. Simultaneously, hydroxyl radical (OH*) was generated by the decomposition of H2O2 solution by UV irradiation. OH* plays an important role of oxidation of SiC surface. With these chemical reactions, oxide layer was effectively formed on the SiC surface. Finally, the oxide layer generated on a SiC substrate was chemically and/or mechanically removed by synthetic quartz and solutions. The polishing characteristics of this method were investigated by controlling the process parameters. Additionally, surface quality and removal depth were measured and evaluated by a phase-shift interference microscopy. Obtained results show that the surface morphology and the removal rate are strongly dependent on the existence of the UV irradiation. Moreover, it is shown that the removal characteristics of the SiC substrate depend on the process parameters such as the process time, reciprocating speed, and contact load. The processed surface has revealed that many scratches on the preprocessed surface was completely removed. The microroughness of the processed surface was improved to 0.15 nm (Rms) and 1.62 nm (p-v), respectively. These results provide useful information for obtaining an atomically smooth SiC surface.
Abstract: Neutron beam generated by high intensity proton accelerator facility is powerful tool to investigate characteristics of soft and hard materials. However, neutron beam is not major tool for material science since intensity of neutron beam is very weak compared to that of X-rays. Neutron focusing device is required to increase in intensity of neutron beam. Aspherical supermirror is effective for neutron focusing with wide wavelength range without chromatic aberration. In this research, we proposed a fabrication process for large and cost-effective aspherical mirror substrate made of aluminum alloy because metal can be figured coarsely at low cost by using conventional machining. The mirror fabrication process proposed by us consists of grinding for coarse figuring, numerically controlled electrochemical machining (NC-ECM) to correct objective shape with form accuracy of sub-micrometer level and low-pressure polishing to decrease in surface roughness to sub-nanometer level. In the case of figure correction of the mirror substrate by NC-ECM, deterministic correction is realized because NC-ECM is a non-contact electrochemical removal process for metal materials, without workpiece deformation. In this paper, we report fundamental machining characteristics of ECM, which uses electrode with a diameter of 10 mm and NaNO3 electrolyte.
Abstract: Numerically controlled local wet etching (NC-LWE) is very promising technique for deterministic figuring of ultraprecision optical devices, such as aspherical lens, photo mask substrate and X-ray or neutron focusing mirror. NC-LWE technique is non-contact removal process using chemical reaction between etchant and surface of workpiece, so this technique enables us to figure the objective shape without introduction both substrate deformation and sub-surface damage. It is essential to measure temperature and concentration of the etchant to maintain the material removal rate constant over a processing time, since the etching rate of NC-LWE strongly depends on these parameters. Hydrofluoric (HF) acid solution is used as an etchant for synthesized quartz glass. We aim to develop an in situ monitoring system of etchant concentration using Raman spectroscopy and electric conductivity measurement. Raman spectroscopy measurement result indicates that there is a good linear relationship between HF concentration and intensity ratio of two specific Raman bands.
Abstract: A novel fabrication process was proposed to produce high-quality Bragg beam splitters for hard X-ray free-electron lasers (XFELs), which should consist of thin, bend-free, and robust Bragg-case crystals without any defects. A combination of a mechanical process and plasma chemical vaporization machining was employed. High crystalline perfection of the fabricated Si(110) crystal was verified with X-ray topography and rocking curve measurements. In addition, the thickness was evaluated to be 4.4 μm from the fringe period of the measured rocking curve. The crystal can be employed in Bragg beam splitters using the (220) Bragg reflection for X-ray pump-X-ray probe experiments with XFEL sources.
Abstract: We have developed a chemical process for atomic planarization of gallium nitride (GaN) using a platinum catalyst and ultraviolet (UV) light irradiation. The process is mediated by a hydrolysis reaction catalyzed by platinum as a solid catalyst. Because the reaction occurs selectively from the step edges, a flat surface composed of a straight step-and-terrace structure is obtained. In the absence of UV light, owing to the low step edge density, the removal rate is quite slow, approximately 1 nm/h. In contrast, under UV light, etch pits are formed on the terraces by photo-electrochemical etching causing an increase in the step edge density. We achieved surface planarization with a removal rate of 9.6 nm/h assisted by irradiation with UV light.