Akio Itoh

Mechanical property changes in sapphire by nickel ion implantation and their dependence on implantation temperature

Sapphire plates, cut parallel to an {0001} plane, have been implanted with 300 keV nickel ions to doses ranging from 5×1012 to 1×1017 Ni cm−2 at specimen temperatures of 100, 300 and 523 K, in order to investigate the effect of implantation temperature on the mechanical property changes in sapphire caused by ion implantation. The measured changes in surface hardness, surface fracture toughness and bulk flexural strength were found to depend strongly on the implantation temperature, and were largely correlated with the residual surface compressive stress measured by using a cantilever beam technique. The surface amorphization that occurred only by the implantation at 100 K and at doses larger than ∼2×10s15 Ni cm−2 reduced the hardness to ∼0.6 relative to the value of the unimplanted sapphire, and considerably increased the surface plasticity. Furthermore, the amorphization was found to involve a large volume expansion of ∼30% and to change drastically the apparent shape and size of a Knoop indentation flaw made prior to implantation. This effect was suggested to reduce stress concentrations at surface flaws and hence to increase the flexural strength.

Tribology of carbonaceous films formed by ion-beam- assisted deposition of organic material☆

Abstract By combining the vapour deposition of a silicone oil (pentaphenyltrimethyltrisiloxane) and simultaneous energetic ion irradiation, carbonaceous films (i-silicone films) 0.1-0.3 μm thick were coated on disc samples of hardened SUJ2 (AISI 52100). As the ions for irradiation, 1.5 MeV Ar+, 400 keVTi+ were used. The frictional properties of the i-silicone coated disc, in particular the dependence of the friction coefficient μ on humidity, were tested with a pin-on-disc method using a hardened SUJ2 pin. All the i-silicone coatings prepared by using the three ion beams exhibited similarly low values of μ−0.05 in ambient atmosphere. In both air and nitrogen gas the i-silicone coating exhibited a low value of μ≈0.05 for a relative humidity range from 70% to 20%, the lowest humidity available. On the contrary, diamond-like carbon prepared by plasma- enhanced chemical vapour deposition displayed a value of μ≈0.2 for the same humidity range. In dry nitrogen, both the i-silicone and the diamond-like carbon exhibited an extremely low value of μ⩽0.02. Reasons for the moisture-insensitive frictional properties of i-silicone and features of the ion-beam-assisted deposition coating process of organic materials are discussed.

Effect of ion implantation on fracture stress of Al2O3

Abstract Effects of ion implantation and subsequent thermal annealing on the fracture stress of single-crystalline α-Al2O3 have been investigated for 400 keV N and 300 keV Ni ions. Upon N or Ni implantation, the flexural strength of a specimen 7 × 25 × 1 mm3 in size increased by 20 to 60% in the ion dose range from 1 × 1015 to 1 × 1017 ions cm 2 . By post-implantation thermal annealing, the relative flexural strength for the N implanted specimen recovered gradually with annealing temperature followed by a complete recovery at around 1300°C. This behavior of recovery for flexural strength has been found to be similar to that for radiation damage. On the other hand no recovery of flexural strength has been observed for the Ni implanted specimen, in which a spinel compound NiAl2O4 formed upon thermal annealing at temperatures above 1000°C. In N implantation, the strengthening results entirely from the effect of radiation damage, whereas in Ni implantation the formation of a surface NiAl2O4 layer with post-implantation thermal annealing is also effective in the strengthening.

Structure and properties of c-BN film deposited by activated reactive evaporation with a gas activation nozzle

Abstract This paper describes the structure and properties of cubic boron nitride (c-BN) film deposited using activated reactive evaporation with a gas activation nozzle. c-BN films deposited directly on various substrates showed very poor adhesion. It was found that a hexagonal phase of a few hundreda˚ngstroms thick was formed before the c-BN phase appeared and this resulted in poor adhesion. The adhesion characteristics of the c-BN film to the substrate were significantly improved by inserting silicon nitride interlayer. The micro Vickers hardness of a c-BN film of thickness 1.5μm was 5500– 6300 kg mm-2. As verified by a scratch test, a high substrate temperature effected good adhesion. The coefficient of friction for the c-BN film in contact with stainless steel was about 0.35 in air at ambient temperature, whereas at 1.7 × 10-3 Pa at 400 °C it was extremely low, 0.02.

Modification of the mechanical properties of ceramics by ion implantation

Abstract The effects of ion implantation on the mechanical properties are reviewed for alumina, silicon carbide and fully-stabilized zirconia. It is demonstrated that by ion implantation, (a) hardness of the near surface layer is varied over a wide range, depending on ion dose and implantation temperature, (b) significant increases in the flexural strength are observed, (c) the resistivity against the crack initiation and propagation associated with Vickers indentation is increased, (d) the resistivity against lateral and radial crackings associated with scratching by a loaded diamond stylus is increased, (e) a reduction in the friction coefficient from 0.6 to 0.15 is observed for polycrystalline silicon carbide in sliding contact with a steel. These results are discussed in terms of microstructural changes, surface compression stress and amorphized surface layer of an increased plasticity.

Tribological properties of ion implanted SiC ceramics

Abstract Polycrystalline α-silicon carbide disks were implanted with 800 keV A.r + or 400 keV Ag + ions, and the friction and wear behaviour was investigated by sliding SUJ2 steel pins against the disks. The results obtained are as follows: 1) by implanting the ions into SiC, the coefficient of friction, μ, is reduced from 0.6 to 0.15, 2) the wear rate of the steel pin is also reduced to ∼ 0.2 relative to the value of the pin sliding against an unimplanted disk, 3) the duration of the sliding state with μ ⋍ 0.15 is more than 1 × 10 5 cycles for the disk implanted with 800 keV Ar + ions to a dose of 1 × 10 16 ions/cm 2 .

Photoresist Chemical Mechanical Polishing for Shallow Trench Isolation

We investigated the chemical mechanical polishing (CMP) characteristics of photoresist for the first time. It was found that photoresist polishing rates are strongly dependent on photoresist baking temperature. The photoresist polishing rate exceeded 7000 nm/min, which is 87 times higher than the value for SiO2, after baking at 170°C, but matched that of SiO2 after baking at 220°C at a polishing pressure of 230 g/cm2. The photoresist polishing rate after baking at 240°C was lower than that of SiO2. Using these photoresist CMP characteristics, a simple shallow trench isolation (STI) process was achieved.

Vibrating Sample Magnetometry of High-Tc Superconductor Y-Ba-Cu Oxide

Magnetic properties of a high-Tc superconductor Y-Ba-Cu oxide are studied by using a vibrating sample magnetometer. The specimen prepared shows a rapid resistivity drop at 95 K and zero-resistance state at 91 K. A diamagnetic susceptibility as large as 43% of the perfect diamagnetism is observed at a temperature as high as 84 K. At this temperature, the lower critical field is about 200 Oe and the upper critical field is suggested to be higher than 10 T.

Tribological Properties of Ceramics Modified by Ion Implantation and by Ion Beam-Assisted Deposition of Organic Material

Ceramic materials are increasingly being used as rolling or sliding parts of machines, for example, as bearings or seals, and surface treatments to enhance the friction and wear performance of ceramics have become more and more important.

Diamond film deposition by a substrate-stabilized flat flame

A diamond film deposition system with a C2H2H2O2 flat flame was improved to extend the stable region of the flat flame in several deposition factors: the volume ratio of C2H2 to O2 in the reactant gas (C/O ratio), the substrate temperature (Ts), the total reactant gas flow rate (Vg) and the distance between the burner nozzle tip and the substrate (L). Effects of these deposition factors on the deposition rate and the quality of the diamond film were studied. As Ts increased, the deposition rate increased at the expense of the film quality for the C/O ratios of 1.03 and 1.05 while the deposition rate increased without deterioration of the film quality for the C/O ratio of 1.01. The maximum deposition rate was 80–90 μm h−1 for the C/O ratios of 1.03 and 1.05 and 50 μm h−1 for the C/O ratio of 1.01. When the Vg increased by 30%, the deposition rate and the uniformly deposited area increased by ca 90% and 30%, respectively. The uniformly deposited area was found to nearly coincide with the flat flame area. For the thermal stress-free self-standing polycrystalline diamond films, it was found that the full width at half-maximum (FWHM) of the diamond Raman peak at 1332 cm−1 becomes narrower with decreasing the amount of the non-diamond carbon in the films. The narrowest FWHM of 2.6 cm−1 obtained in this work was comparable to that of a high quality single crystal diamond.