Tsunetaka Sumomogi

Evaluation of surface and subsurface cracks on nano-scale machined brittle materials by scanning force microscope and scanning laser microscope

Nano-scale machining by ultra precision grinding and cutting, known as ductile mode machining, has the potential of overcoming limitations of conventional machining technology. In this study, the nano-scale layers of single crystal silicon and glass surface were machined by a sharply pointed diamond tool, and the subsurface cracks as well as the surface cracks were observed by a scanning force microscope and a scanning laser microscope. The transition point determined by the subsurface cracks is found to be shallower than that by the surface cracks. Therefore the evaluation of the subsurface cracks is important especially in finish machining.

Effect of O2 gas partial pressure on mechanical properties of SiO2 films deposited by radio frequency magnetron sputtering

The effect of O2 partial pressure on the mechanical properties of SiO2 films deposited by rf magnetron sputtering is studied. The sputtering rate of SiO2 in argon gas with added O2 gas is lower than that in pure argon gas, whereas the rate is independent of O2 partial pressure. The internal stresses in films are compressive, and the magnitude decreases from 0.8 GPa for films sputtered in pure argon gas to 0.4 GPa for films sputtered in argon gas with O2 gas partial pressure above 9×10−3 Pa. Although the internal stress decreases with increasing O2 partial pressure, the magnitudes of hardness and adhesion increase conversely. X-ray diffraction measurements indicate that the crystal structure of sputtered SiO2 films is amorphous at all O2 partial pressures investigated. The argon content in the film obtained from an electron probe microanalyzer decreases with increasing O2 partial pressure. An atomic force microscopy observation reveals that the surface topography of sputtered SiO2 films show a turnover fro...

Effect of O2 gas partial pressure on mechanical properties of Al2O3 films deposited by inductively coupled plasma-assisted radio frequency magnetron sputtering

The effect of O2 partial pressure on the mechanical properties of Al2O3 films is studied. Using films prepared by inductively coupled plasma-assisted radio frequency magnetron sputtering, the deposition rate of Al2O3 decreases rapidly when oxygen is added to the argon sputtering gas. The internal stresses in the films are compressive, with magnitude decreasing steeply from 1.6 GPa for films sputtered in pure argon gas to 0.5 GPa for films sputtered in argon gas at an O2 partial pressure of 0.89 × 10−2 Pa. Stress increases gradually with increasing O2 partial pressure. Using a nanoindentation tester with a Berkovich indenter, film hardness was measured to be about 14 GPa for films sputtered in pure argon gas. Hardness decreases rapidly on the addition of O2 gas, but increases when the O2 partial pressure is increased. Adhesion, measured using a Vickers microhardness tester, increases with increasing O2 partial pressure. Electron probe microanalyzer measurements reveal that the argon content of films decrea...

Evaluation of surface and subsurface cracks in nanoscale-machined single-crystal silicon by scanning force microscope and scanning laser microscope

Abstract Studies of nanoscale machining of brittle materials, such as silicon, have come into prominence in recent years. Material removal with plastic deformation, known as ductile mode machining, has been achieved by a very small depth of cut. When surface cracks occurred with increasing cut depth, the machining has been commonly considered to be of brittle mode. In the present study, the ductile–brittle transition point in the nanoscale machining of single-crystal silicon was examined by the observations not only on the surface cracks but also on the subsurface cracks. A scanning force microscope was used to measure the depth of the grooves and to observe the surface cracks. The distance from the surfaces to the deepest point of the subsurface cracks on obliquely sectioned and then etched surfaces were measured by a scanning laser microscope. The transition point determined by the subsurface cracks was found to occur at a shallower depth of cut compared with the transition point from the surface cracks. Therefore, evaluation of subsurface cracks is important especially in the finish shape of machining.

Characteristics of newly developed scanning tunneling microscopy/spectroscopy at low temperatures

A ceramics tunneling unit and a cryostat are newly designed for variable‐temperature experiments of scanning tunneling microscopy/spectroscopy (STM/STS) at low temperatures. The unit has high symmetry and rigidity. Coarse adjustment of sample‐tip position is made using a ceramics differential screw and a stacked piezoelectric transducer, attached to the unit. The unit is succesfully tested at room and low temperatures in He gas, not directly being immersed into cryogenes. The stability is suitable also for STS measurements using a lock‐in amplifier.

Purity-dependent structures of Al nanoclusters on HOPG observed by STM

Abstract Nanoclusters with a diameter of 2–10 nm were deposited from highly pure Al and Al–50%Cu targets onto highly oriented pyrolitic graphite (HOPG) by pulsed laser ablation. The structures and atomic configurations of these nanoclusters were then investigated with atomic resolution using a scanning tunneling microscope. On the pure Al nanoclusters, hexagonal two-dimensional configurations were found over a large area around a three-dimensional nanocluster. These two-dimensional structures were oriented at 30° to the graphite lattice and the atomic distance was estimated to be 0.424 nm. On the other hand, two-dimensional atomic configurations were not observed around the Al–50%Cu nanoclusters and the atomic distance was almost the same as that of highly oriented pyrolytic graphite visible in the STM. Thus, the initial growth and structures were completely different between the two materials.

Purification of 6N Aluminum by Ultrahigh Vacuum Melting

In order to improve the purity of 6N aluminum, it was melted in a vacuum of 3-6×10−6 Pa for 30 min and solidified gradually. The melted samples were cut into several pieces and the residual impurities of each part were analyzed by Glow Discharge Mass Spectrometry (GDMS). The Residual Resistivity Ratio (RRR) of each part was measured and the relationship of RRR with residual impurities is discussed. The purity of the melted sample was improved in comparison with that of the raw material, and the measured RRR almost doubled to 40000. GDMS analysis revealed that the amounts of elements of partition coefficient k 1 were not reduced. While each impurity concentration ratio in this study is about one-tenth of that in the previous report, the purification efficiency of each element in this study and that in the previous report matched well. Although the estimated RRR values from composition analyses were larger than the measured RRR values, both showed similar tendencies with regard to specimen position and also corresponded well with regard to impurity distribution.