Tatsumi Hioki

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.

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.

The effect of oxygen deficiency on the structural phase transition and electronic and magnetic properties of the spinel

The effect of oxygen deficiency on a phase transition from cubic to tetragonal phase has been investigated for the spinels with by measurements of differential scanning calorimetry (DSC), magnetic susceptibility nuclear magnetic resonance ( NMR) and electronic resistivity . According to the DSC measurements, the transition temperature for a stoichiometric compound is determined to be K. As increases from zero to 0.066, the magnitude of is found to decrease by about 4 K; then, the magnitude of increases by about 41 K with further increase of up to 0.10; thus, the curve exhibits a broad minimum at around . This relationship between and is also observed by the measurements of NMR and . The dependence of on is considered to be a result of a competition between a decrease in the average valence of Mn ions and a dilution of the nearest-neighbour interaction between Mn ions. Both effects are caused by the oxygen deficiency; the former raises , whereas the latter reduces it.

Oxygen nonstoichiometry of spinel LiMn2O4 − δ

Abstract Oxygen nonstoichiometry δ has been determined for a spinel LiMn 2 O 4 − δ sample as a function of oxygen partial pressure P O 2 in the temperature range between 873 and 1123 K, using a thermogravimetric analysis and a chemical titration analysis. The maximum oxygen deficiency of LiMn 2 O 4 − δ was found to be δ cr. ∼ 0.2. For the samples obtained at 1023 K, as δ increased from zero, the tetragonal spinel phase appeared around δ = 0.07, while only the cubic spinel phase was observed for the samples with δ ⩽ 0.07. Partial molar enthalpy Δ H O 2 and entropy Δ S O 2 of oxygen in the LiMn 2 O 4 − δ samples with 0.05 ⩽ δ ⩽ 0.2 were estimated to be −208 to −277 kJ mol −1 and −168 to −219 J K −1 mol −1 respectively. The dependence of δ on P O 2 was expressed as δ ∼ P O 2 (−0.67±0.06) ; to explain this relation, we employed a defect cluster model. In contrast, the sample with δ = 0.67 was found to decompose to LiMnO 2 and Mn 3 O 4 . The change in standard enthalpy for the decomposition ΔH 0 was estimated to be 84 kJ mol −1 .

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.

Nuclear Spin Relaxation of Impurities in Dilute Ferromagnetic Alloys

The nuclear spin lattice relaxation time T 1 of the 3 d - and 4 d -series impurities (V, Mn, Co, Cu, Nb, Mo, Ru, Rh, and Pd) dissolved dilutely in Fe metal has been measured as a function of external magnetic field strength by pulsed NMR technique. The relaxation mechanisms for these impurities in high external magnetic field are discussed in terms of the hyperfine interactions with the s - and the d -band electrons. The density of states of the impurity d - electrons in the Fe metal is calculated using the Wolff and Clogston model and used for the calculation of the relaxation time. External field dependence of the relaxation time was discussed by the spin wave mechanism. The relaxation mechanism in the ferromagnetic metal proposed by Weger has been also derived by the susceptibility formalism.

Nonlinear optical properties of Sn+ ion-implanted silica glass

Abstract The absolute value of the third-order nonlinear optical susceptibility, ¦χ (3) ¦, of Sn + ion-implanted silica glass was found to be ∼ 10 −6 esu. This value is as large as those reported for semiconductor-doped glasses. Silica glass substrates were implanted with Sn + ions at an acceleration energy of 400 keV to a dose of 2 × 10 17 ions/cm 2 at room temperature. Metallic Sn microcrystallites of 4–20 nm in diameter were found to be embedded in the silica glass matrix. The average volume fraction of the Sn microcrystallites was evaluated to be 28%. ¦χ (3) ¦and the imaginary part of the dielectric function, Im ϵ, had peaks at the same wavelength of 500 nm owing to surface plasmon resonance. The peak width of ¦χ (3) ¦was nearly half of that of Im ϵ, which can be explained by an effective medium theory.