Hiroaki Niwa

HIGH-ENERGY CU AND O ION CO-IMPLANTATION INTO SILICA GLASSES

Abstract Optical and structural changes of silica glass substrates implanted with Cu and O ions and subjected to thermal annealing, are examined as a function of the implantation sequence by optical absorption, Rutherford Backscattering Spectrometry (RBS) and thin film X-ray diffraction (XRD) measurements. Before annealing, the distribution of Cu is affected by the implantation sequence and O- followed by Cu-implantation leads to fewer Cu nanoparticles than the Cu- followed by O ion implantation. After annealing, however, the redistribution behavior of Cu and optical absorption features are similar for both co-implanted samples. Nanocrystals of Cu2O are mainly formed by annealing and the absorption peaks at about 340, 450 and 480 nm are observed for the co-implanted samples. The peaks are possibly evidence for the presence of the copper oxide nanocrystals.

Formation of β‐Si3N4 by nitrogen implantation into SiC

Polycrystalline β‐SiC samples were implanted with 50 keV 15N ions with fluences ranging from 3×1017 to 1.5×1018 ions/cm2 at elevated temperature up to 1100 °C. Nitrogen depth profiles were measured as a function of implantation temperature and annealing temperature using nuclear reaction analysis, Rutherford backscattering spectroscopy, and Auger electron spectroscopy. It was found that the maximum concentration and the width of nitrogen depth profiles implanted at 1100 °C were reduced distinctly in comparison with the profiles implanted below 930 °C or annealed at 1100 °C. The redistribution of nitrogen implanted in SiC at 1100 °C was ascribed to the formation of β‐Si3N4 crystallites in SiC, which was confirmed by x‐ray diffraction at glancing incidence.

Thermal behaviour of nitrogen implanted into zirconium

Abstract Zirconium films were implanted with 15 N ions of energy 50 keV to a total fluence of 1 × 10 18 ions cm -2 in an attempt to study the formation process and thermal stability of ZrN layers produced by high fluence implantation of nitrogen. Subsequent to the implantation at room temperature, samples were annealed at temperatures of 300 °C–900 °C. The depth profiles of the implanted nitrogen were measured by nuclear reaction analysis using the 15 N(p,αγ) 12 C at E R = 429 keV, and the surfaces were examined by thin film X-ray diffraction (XRD) and scanning electron microscopy. There were many blisters 0.2–0.4 μm in diameter on the surface of the as-implanted samples and double peaks were observed in the nitrogen depth profiles; they were in both sides of the mean projected range. It was found that most of the blisters became extinct after annealing above 400 °C, and the XRD peak (111) intensity was increased with the increase in the annealing temperature. Moreover, 14 N and 15 N implantations were superimposed on Zr samples in order to study the atomic migration of nitrogen at each stage of high fluence implantation. It was found that the decrease in the peak at the deeper layers was related to blister extinction and nitrogen diffusion into underling zirconium which could be correlated with radiation damage induced by post-implanted ions.

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.

High-energy co-implantation of Ti and O ions into sapphire

Abstract Optical and structural changes of sapphire(0001) substrates implanted with Ti ions or with Ti and 0 ions and subjected to thermal annealing, are examined by optical absorption, RBS-channeling and XRD measurements. The transmittance of the co-implanted sample was larger than that of the Ti-implanted sample. After annealing at 1000 °C, rutile-type TiO 2 microcrystals with (200) orientation were formed in the co-implanted sample of Ti and O ions. Furthermore, a broad optical absorption at 220–340 nm in the co-implanted sample was increased after the annealing. This was possibly due to the formation of TiO2 microcrystals in the sapphire substrate. In contrast to this result, no evidence of the formation of titanium oxide in a crystal structure was obtained for the Ti-implanted sample after the annealing.

Microstructure of germanium films crystallized by high energy ion irradiation

Abstract Amorphous (a-)Ge films deposited on air-cleaved CaF 2 (111) substrates were irradiated with 1.8 MeV Si ions, and the microstructure of the irradiated Ge films was examined by using Rutherford backscattering spectrometry combined with channeling technique, X-ray diffraction measurement and transmission electron microscopy. It was found that the ion irradiation can induce solid phase epitaxial growth (SPEG) of Ge (111) films even at low sample temperature ( T s ) of approximately 200°C, although the films included some randomly oriented crystals. In contrast to this, a-Ge films practically did not crystallize during heat treatment at 200°C and the polycrystal films were only obtained when temperatures reached more than 500°C. These results suggest that ion irradiation enhances the SPEG of a-Ge/CaF 2 heterosystem at relatively low T s values.

Growth of epitaxial TiN films on MgO(100) by high current discharge plasma

High current discharge plasma produced by the Ta‐LaB6 cathode was used for ion plating of TiN films. The dependence of the deposition rate of TiN on the substrate dc bias potential was measured using the Rutherford backscattering spectrometry (RBS) method. The results indicate that the particles impinging on the substrate, i.e., vaporized particles (Ti) and reactive gases (N2), could be ionized at high efficiency of 70%. Epitaxial TiN films were grown at temperatures between 400 and 700 °C on cleaved MgO(100) substrate supplied with negative dc anf rf potential. Structures of the epitaxial film were investigated by RBS and ion channeling, and scanning tunneling microscope (STM). The minimum channeling yields for (100) and (110) axes obtained at a substrate temperature of 550 °C with the growth rate of 40 A/s were found to be 1.4% and 2.0%, respectively, which were almost the same as that of the MgO substrate. Atomically resolved tunneling images of (100) surface of the epitaxial TiN film were observed by STM.

APPLICATION OF HEAVY-ION RBS TO COMPOSITIONAL ANALYSIS OF THIN FILMS

Abstract A 8 MeV multicharged carbon or oxygen beam was used for Rutherford Backscattering Spectrometry (RBS) compositional analysis. Thin films of Co, Cu, Si, and NiCr of a few nm thickness were deposited on carbon substrates by vacuum evaporation or Ar sputtering. The measured results demonstrate that the mass resolution is much better for the heavy-ion RBS than for the He-RBS analysis. For the compositional analysis, a fitting function formula is proposed based on a simple model in which the thin film consists of many islands. The calculated results agree with the measured spectra, which show asymmetry of the peaks. Numerical analyses using the fitting function give reasonable agreement between the expected and measured ratios of mass elements in the films.

Damage Production and Reduction of Single-Crystalline TiN Films by 1.8 MeV Carbon Beam Irradiation

By means of an in-situ Rutherford-backscattering-spectrometry (RBS) channeling technique, we have investigated creation and reduction of irradiation damage in single-crystalline TiN films induced by 1.8 MeV carbon beam. Both the effects of ion channeling and of beam heating on variation of damage level are shown briefly by successive irradiations on the order of 1017 C+/cm2 under different conditions. It is shown that the aligned irradiation with a high-intensity beam repairs almost completely the damage produced by random irradiation where the sample is heated to about 450^°Cbythebeam, whereassimpleheattreatmentupto 600^°Cresultsinlessreductionofthedamage.