Yoshiko Miyagawa

Deposition of diamond-like carbon films using plasma based ion implantation with bipolar pulses

Plasma based ion implantation (PBII) with bipolar pulses has been proposed to improve a dose uniformity in an ion implantation on a three-dimensional target. A pulsed glow discharge plasma is produced around the target by a positive pulse at a gas pressure less than ∼0.5 Pa, and then ions are implanted into the target from all sides by the subsequent negative high-voltage pulse. It has been shown that ions produced by the positive pulse have been implanted effectively with the negative pulse. The PBII with bipolar pulses is applied to DLC coatings. A carbon mixing layer in the substrate surface is formed by the implantation to improve the adhesion of DLC films. Internal stress of DLC films slightly decreases with increasing frequencies of positive pulse. Moreover, it is shown that the PBII with bipolar pulses is possible to use for inner coating of DLC films on a stainless-steel pipe.

Dynamic MC simulation for a-C:H deposition in methane plasma based on subplantation model

Abstract We have applied dynamic Monte Carlo simulations to the synthesis of a-C:H films by PBII. Like our previous model, we assumed a surface reaction layer consisted of one or two monolayers of a-C:H, in which very low threshold displacement energies are used, so atoms are knocked on by the collisions with energetic ions much easier than in the bulk substrate. Only atoms with energy higher than the barrier can penetrate into the subsurface. The change from the previous model is in the treatment of sp 3 state forming. Our new model is based on the subplantation model proposed by J. Robertson [1] . The sp 3 state formation was assumed resulted from the density increase. In the subsurface, among the penetrated C atoms, only atoms with low energy which is not enough to induce collision cascade form sp 3 state together with the surrounding C atoms and the other C atoms with higher energy form sp 2 state because of the density relaxation induced by the dense collision cascades. In addition to the above assumption, release of the displaced H atom after the subsequent collision cascade is assumed. The calculation is centered on how the sp 3 fraction and the H concentration, and the growth rate depend on the incident energy, the ion/neutral ratio, threshold energy of sp 3 formation. The energy dependence obtained for both sp 3 fraction and H concentration agreed well with the experimental data.

Dynamic MC simulation of DLC films synthesis by PBII

Abstract Dynamic Monte Carlo simulations have been applied to the synthesis of diamond-like carbon films by plasma-based ion implantation (PBII). The direct chemical incorporation of the radicals, like CH 3 reacting with a diamond surface, is too low for the deposition of DLC films, so that the other reaction mechanisms should be responsible. We assumed a surface reaction layer consisted of several radical layers, in which radicals are dissociated by the collisions with energetic ions and some H and C atoms are released out and some H and C atoms are stitched into the subsurface and the stitched C atoms are assumed to form the sp 3 states. In the subsurface, it was assumed that sp 3 states atoms are released to the sp 2 state and H atoms are released out of the surface as a results of collision cascades induced by the energetic ions. The following was obtained by the simulation: the C atom stitching probability, which related with sp 3 state formation, has a maximum of near 500 eV independent of the dissociation energy of radicals, number of monolayers in the surface reaction layer, or ion/radical arrival ratio. It agrees with the experimental result. The stitching probability increases with the decrease of the dissociation energy and the increase of number of monolayers in the surface reaction layer and ion/radical ratio. The H concentration shows a maximum of near 300 eV. It also agrees with the experimental result.

Computer simulation of plasma for plasma immersed ion implantation and deposition with bipolar pulses

In order to analyze the plasma behavior under the plasma immersion ion implantation and deposition (PIIID when a negative pulse voltage is applied to a target, a weak plasma is generated around the target. In contrast, when a positive pulse voltage is applied, a more intense plasma is generated under the same conditions. The results obtained by simulation of the behavior of ions and electrons near a trench-shaped target are presented.

Computer Simulation of Range and Damage Distributions of He ions in SiC

The exrerimental projected ranges of various heavy ions in an amorphous Si target in the energy region where the nuclear stopping dominates are compared with calculations using the computer simulation program SASAMAL with the Lenz-Jensen, Moliere, Thomas-Fermi and Kalbitzer-Oetzmann (KO) screening parameters. In most cases, the best agreement was obtained with the KO screening parameters. The projected range distributions of He ions implanted in an SiC target were calculated using SASAMAL with KO screening parameters. The agreement between the SASAMAL(KO) results and our experimental data was satisfactory when the electronic stopping parameter k=1.3 kNS was used. The energy and the depth distributions of the primary knock-on atoms and the depth distributions of the recoil energy density with various values of the displacement energy Ed were also calculated using SASAMAL(KO) for He ions in SiC.

Effect of high-energy Si+ ion irradiation on the crystallization behavior of amorphous strontium titanate films

Abstract Amorphous strontium titanate (STO) films deposited on Si substrates by magnetron sputtering at room temperature were irradiated with 2 MeV Si ions at doses of 5×10 16 –1.5×10 17 Si + /cm 2 and post-annealed at 450 °C in vacuum. The compositional and structural changes of STO films after the ion irradiation were examined by Rutherford backscattering spectrometry, scanning electron microscopy and X-ray diffraction measurements. The Sr:Ti:O ratio of the as-deposited films was found to be approximately 0.8:1:3. Ion irradiation did not affect the amount of Sr and Ti significantly and the films remained amorphous. After annealing, however, the formation of STO crystals was observed and Sr and O were slightly lost from the films. As compared to the un-irradiated STO films, the ion-irradiated ones showed significantly enhanced crystallization behaviors upon vacuum annealing.

Annealing of silica glasses implanted with high-energy copper ions

Silica glasses were implanted with 1.8 MeV Cu ions at a dose of 0.32–1.3×1017 ions/cm2 at a temperature of less than 300° C. The thermal annealing of the samples was carried out in air in the range of 300–1100° C, and the effects on the formation and growth of Cu nanoparticles were examined as a function of ion dose and annealing temperature using Rutherford backscattering spectrometry and optical absorption measurements. It was found that the broad absorption band between 250–400 nm was increased and the average radius of Cu particles was slightly decreased where the total concentration of Cu was not changed up to 700° C. This suggests that small Cu precipitates were generated. The surface plasmon resonance absorption at approximately 570 nm was clearly developed at 800° C. In addition, the average radius of Cu particles increased as the annealing temperature increased from 800–1000° C. However, the concentration of Cu began to decrease at temperatures above 800° C. The plasmon absorption also decreased in intensity with increasing temperature, which indicated that the amount of Cu particles had decreased. The decrease of the amount of Cu particles was affected by ion dose.

Effect of High-Energy Carbon Ion Irradiation in Aligned and Random Directions on Microstructure of (111) Au Films

(111)-Oriented Au films were irradiated with 1.8 MeV C ion beams in -aligned and random directions at 450 and 650° C. The structural changes induced by the irradiations were examined. The results showed that the grain growth and the reduction of dislocations and stacking faults occurred upon irradiation. Furthermore, the aligned irradiation more strongly effected the structural changes of the Au films than the random irradiation at 450° C.

Influence of high-energy Si+ ion irradiation on microstructure and mechanical properties of alumina films

Abstract Amorphous alumina films, approximately 600 nm in thickness, prepared on Si(100) substrates by RF magnetron sputtering were irradiated with 2.0 MeV Si + ions at a dose of 1×10 17 ions/cm 2 and the influence on the composition, microstructure, and mechanical properties was examined by Rutherford backscattering, X-ray diffraction and nano-indentation measurements. It was found that the O/Al ratio in the films was approximately 1.5, and there was no significant alteration in this ratio after ion irradiation. However, a structural change from amorphous to the crystalline γ-alumina was observed. Hardness and elastic modulus of the irradiated film were significantly increased from approximately 11 and 181 GPa up to approximately 25 and 246 GPa, respectively.

Plasma analysis for the plasma immersion ion implantation processing by a PIC-MCC simulation

Abstract In order to analyze the plasma behavior during PIII processing, a computer simulation has been carried out using the simulation software “PEGASUS”. The software uses a Particle-in-Cell (PIC) method for the movement of charged particles in the electromagnetic field and a Monte Carlo method for collisions of ions, electrons, and neutrals in the plasma and also a Monte Carlo method to analyze the background gas behavior for a low density gas system. This approach is based on the weighting collision simulation scheme allowing for disparate number densities of different species. The spatial distributions of potential and densities of ions, electrons and radicals in the coating system were calculated together with the flux of ions and electrons on the surface of the object. The gas pressure was 0.01 to 50 Pa and a negative and/or a positive pulse voltage ( V max = 0.1 to 20 kV) was applied to the object. The calculation is fully self-consistent. A two-dimensional Cartesian and a cylindrical coordinate system were used. The effects of gas pressure, applied voltage, and secondary electron emission coefficient by ion impact (γ) on the sheath thickness, the spatial distribution of densities of electron, ion, and neutral atoms, the ion flux and its spatial distribution, etc. were studied for PIII processing of a trench shaped object, inner wall of a pipe and a PET bottle.