Papers by Author: Takeyuki Yamamoto

Abstract: This study aims to develop a cutting method, which enables to generate a localized hydrostatic pressure field in the vicinity of cutting zone in order to improve the machined surface integrity without causing unnecessary plastic deformation. In the previous work, a molecular dynamics simulation was performed using a newly developed cutting tool equipped with a planer jig with a rectangular hole for the cutting chip elimination, and it was confirmed that the developed cutting tool has advantages in giving a relatively high-hydrostatic stress field in the vicinity of the cutting zone and in suppressing the burr formation. In this report, further molecular dynamics simulation was performed in order to clarify the influence of jig shape on the cutting phenomena and machined surface integrity. As a result, it is found that a cutting tool of which front and side except for the rectangular hole are covered by the planer jig is the most advantageous for supplying high hydrostatic pressure and suppressing burr formation.

Abstract: It is known that the TiO2 has some photocatalytic functions, even though they are relatively weak and their further enhancements are necessary for wider practical usages. On the other hand, improving materials surface functions by introducing microtextures is of great interest in various fields. Under such circumstances, the present study is aiming at developing a high-functional photocatalytic surface by earning the real surface area and reducing the light reflection and so on with the support of microtexturing technique. In this work, a pure Ti plate surface, which was covered with numerous micro impressions and micro pile-ups formed by the vibration-assisted microscratching, was anodized in order to obtain a regularly microtextured TiO2 film on the uppermost surface of Ti plate, and its wettabilty was evaluated in order to investigate its potential as the photocatalyst. As a result, it was found that the wettability of the TiO2 film surface regularly microtextured by the vibration-assisted microscratching was superior to those of the mirror finished one under the irradiation environment by the ultraviolet rays.

Abstract: mproving materials surface function by introducing nano/micro surface textures is of great interest in various fields. The authors have also achieved an improvement in the photocatalytic surface function by introducing the microcutting grooves texture on the titanium dioxide surfaces. In this report, the authors performed the vibration assisted cutting to fabricate finer surface microtextures anticipating future usage as microtexture moulds for the nanoimprinting and/or injection moulding. In the experiment, a pure copper plate was cut using a sharply pointed triangular diamond tip vibrated by a fast tool servo system in the direction of cutting depth with μm order amplitude and kHz order frequency. As a result, it was found that the periodical micro concave-convex patterns with the combinations of impressions and pileups can be obtained by the proposed method using almost the same vibration amplitude as the cutting depth. It was also achieved that a micro-textured surface with numerous concave-convex patterns less than 1 μm in height with 3 μm in pitch.

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: This study aims to develop a high-functional photocatalytic film, of which surface is regularly textured by the micro machining technique in order to earn the real surface area. In this work, a regularly textured TiO2 film surface was fabricated by anodic oxidizing a pure titanium plate with regularly arrayed micro cutting grooves, and its wettabilty was evaluated. Micro cutting grooves were machined by a 3-axis NC control precision machine tool with a single point diamond cutter. Anodic oxidation experiments were conducted by using the self-developed equipment with diluted acetic acid as the electrolyte. As a result, it was found that the wettability of the TiO2 film surface regularly textured by synchronized 3-axial micro cutting was superior to those of the mirror finished or irregularly textured surfaces under the irradiation environment by the ultraviolet rays.

Abstract: The MEMS technology for various nano/micro devices often requires special facilities and complicated and multistage processes, thus the fabrication cost is extremely high. This research aimed to fabricate nanoscale basic structures on silicon substrates using nanoscratching, which can be potentially used to make nano/micro molds for nanoimprint lithography. In this study, various nano/micro-scale structures, such as groove and, single and multiple layer structures were generated on the silicon substrate using an atomic force microscope equipped with a sharp probe made of monocrystalline diamond. The nanoimprint experiment was also performed using the fabricated single-step mold and silicon-resin to fabricate single island structures.

Abstract: This study aims to study the influence of surface topography on the photocatalytic reaction of TiO2 film surfaces. In this work, a textured TiO2 film surface was fabricated by anodic oxidizing a titanium plate with micro grooves, and its wettabilty was evaluated. Micro grooves were machined on a 3-axis NC control precision machine tool using a single point diamond cutter with a tip radius of several hundred nanometers. Anodic oxidation experiments were conducted by using the self-developed equipment with diluted acetic acid as the electrolyte. It was found that the wettability of the TiO2 film surface textured by microcutting was superior to that textured by polishing under the irradiation environment of ultraviolet rays. The wettability of photocatalytic film surfaces could be improved by increasing the surface area.

Abstract: This study aims to clarify the friction and wear phenomena, which are of great importance in abrasive machining with atomic-scale material removal, such as polishing of magnetic disk substrates and CMP of semiconductor substrates. Various phenomena that occurred when a well-defined copper surface rubbed by an extremely fine rigid diamond abrasive, such asthe sliding without removal and the atomic-scale wear, were analyzed using a molecular dynamics model, in which the abrasive grain was connected to a three-dimensional spring and the holding rigidity of the abrasive grain was taken into account. A series of simulations using different indentation depths clarified that the one- or two-dimensional atomic-scale stick-slip phenomenon in proportion to the period of atomic arrays of workpiece surface occurred in the sliding processes without atomic removal. The results also demonstrated that the period and amplitude of the fundamental stick-slip wave varied when accompanied with atomic removal due to the increase in normal load.

Abstract: This paper reports a molecular dynamics simulation of chemo-mechanical grinding (CMG) of silicon wafer by controlling the interatomic potential parameters to imitate the chemo-mechanical or mechano-chemical reactions between an abrasive grain and a Si wafer. Some comparisons between diamond grinding and CMG were made by using the proposed simulation model. From the simulation results, reductions of surface damages, wears of abrasive grain and scratching forces in CMG were confirmed to be same as observed in actual experiments by a CeO2 abrasive wheel, and the availability of proposed simulation model was verified.