Jun-ichi Kawamoto

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.

Electrical and optical properties of ion‐irradiated organic polymer Kapton H

An organic polymer Kapton H film was irradiated with high‐energy (∼MeV) N+2 ions. The specific resistivity of the film irradiated to a dose ∼1017 N/cm2 was estimated to be ∼10−2 Ω cm, which is about 20 orders of magnitude smaller than that of the unirradiated film. With increase of dose, the irradiated region of the film became grayish silver with a remarkable metallic luster. It is suggested that the alterations of the electrical and optical properties of the film result from the decomposition and the subsequent carbonization of the polymer induced by ion irradiation. The properties of the irradiated film are compared with those of the pyrolyzed one.

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.

Recrystallization‐driven migration of implanted ions in sapphire and resultant‐oriented precipitation

The migration of Cr, Mn, Ni, and Xe implanted in sapphire during post‐implantation thermal annealing is investigated by Rutherford backscattering (RBS)/channeling studies. Thermal annealing was performed in air or in vacuum. It is shown that the epitaxial recrystallization of the implantation‐damaged region dominantly causes the migration of the implanted ions when there is little or no solid solubility of the ion species in sapphire. This migration mechanism strongly relates to the formation of oriented precipitates. When the implanted ions migrate toward the surface, surface precipitates of oxides are formed with annealing in air. On the other hand, when the implanted ions concentrate around the projected range at an elevated temperature, metals mainly precipitate in the substrate. The following crystallographic relations are found between the precipitates and the substrates: (111) MnAl2O4, (111) NiAl2O4, (111) Ni or (110) Cr∥(0001) Al2O3, and (103) Mn3O4∥(1120) Al2O3.

Versatile computer programs for analysis of random and channeling backscattering spectra

Two types of computer programs have been developed to simulate random and channeling backscattering spectra with high speed. One is applicable to analysis of multielemental and multilayered structures. Depth profiles of interdiffusion and of impurities distributed inhomogeneously can be analyzed simultaneously with this program. Another allows the simulation of channeling spectrum from a perfect or partially damaged single crystal whose top surface consists of an amorphous layer with an arbitrary thickness. These simulation programs are applied to determine the thicknesses of the ten‐layered structure of Ag/Al/Ag/.../Al, the mixing rates for the Al/Sb system irradiated with Xe ions, and the damage profile of GaP induced by Ar+ irradiation.

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.

Oxygen content control for as‐deposited YBa2Cu3Ox thin films by oxygen pressure during rapid cooling following laser deposition

As‐deposited epitaxial YBa2Cu3Ox thin films have been prepared by ArF excimer laser deposition followed by a rapid cooling with controlled oxygen pressure. The best film after the rapid cooling has a Tc with a zero resistance of 88 K and a Jc (77 K) of 5.5×105 A/cm2. It has been observed that the c‐lattice parameter decreases, that is, the oxygen content x increases from ∼6 to 7, with increasing oxygen pressure during the rapid cooling. The relation between x and oxygen pressure is almost consistent with that for a powder sample being in a thermal equilibrium. We conclude that the oxygen content in the as‐deposited films is determined by the thermal equilibrium oxygen content during the cooling process.

Tribological properties of metals modified by ion-beam assisted deposition of silicone oil

Silicone oil vapor deposition and Ar + ion irradiation can form an adhesive carbonaceous film on a steel substrate. The friction coefficient μ of the coated substrate is found to be very low for sliding against a steel ball both in air (μ ∼ 0.04) and in N 2 gas (μ 3 –1.5 × 10 4 cycles for a film 0.15 μm thick. X-ray photoemission spectroscopy, infrared reflection spectra, and Raman measurements indicate that the film mainly consists of amorphous carbon containing Si and O.

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.

Magnetic properties of Fe-implanted sapphire

Vibrating sample magnetometry has been used to investigate the magnetic properties of sapphire implanted with 400‐keV 56Fe ions to a dose of 1×1017 ions/cm2 and isochronally annealed at temperature ranging from 700 to 1450 °C in vacuum for 1 h. The specimens are superparamagnetic or ferromagnetic, depending upon the annealing temperature or the size of α‐Fe particles precipitated inside sapphire. The precipitation of α‐Fe has been confirmed by x‐ray diffraction. From x‐ray diffraction line broadening, it has been confirmed that the size of α‐Fe particles monotonically increases from 3.5 to 38 nm with annealing temperature. The critical size for superparamagnetic behavior has been roughly determined to be 7 nm. The saturation magnetic moment suggests that after the annealings at 850 to 1200 °C, 92%±8% of the implanted Fe ions exist as α‐Fe.