Keiji Oyoshi

Formation of nanoscale phosphorus colloids in implanted SiO2 glass

Phosphorus ions were implanted to SiO 2 glasses at an energy of 180 keV to doses from 3 × 10 15 to 5 × 10 17 ions/cm 2 at room temperature. TEM observation revealed that amorphous red phosphorus (P red ) colloid particles of 2–4 nm in diameter are precipitated in the substrates implanted to doses 17 ions/cm 2 . Dissociation of the resulting P red into P 2 molecules was observed by optical absorption measured at temperatures > 550°C. After once heating to ∼ 600°C, the particle size of P red increased over two orders of magnitude and the optical band gap decreased from 2.5 eV to 2.2 eV, which is close to that of bulk P red .

Formation of buried oxynitride layers in silica glass by ion implantation

Buried oxynitride layers were formed in silica glass by N+ only or both N+‐ and Si+‐ion implantation. These samples were characterized by secondary‐ion mass spectroscopy, Rutherford backscattering spectrometry, x‐ray photoelectron spectroscopy, and scanning electron microscope. The depth profile of implanted N without Si implantation is a trapezoidal shape at a high‐dose condition (more than about 3 × 1016 ions/cm2). In the N+ implantation only, a part of implanted N reacts with Si, and forms a SiON layer which is thermally unstable. In both Si+ (100 keV, 1 × 1017 ions/cm2) and N+ (50 keV, 11× 1017 cm2) implantation, the depth profile of N is a Gaussian distribution, and the thermal stability of a SiON layer is dramatically improved. However, bubbles were generated near the projected range of Si and N at a high‐dose condition (the total dose was 4 × 1017 ion/cm2 and the dose ratio Si/N=3/4). The generation of bubbles was suppressed by two‐step N+ implantation (40 and 60 keV).

Smoothing of Silica Glass Surfaces by Ion Implantation

Enhancement of surface smoothness during ion implantation in rectangularly patterned silica glasses has been observed by scanning electron microscopy. The smoothness of the silica glass surface is significantly improved with increasing ion dose. The efficiency of ion beam smoothing strongly depends on the energy of the incident ion and ion species, whereas it depends weakly on dose rate and temperature. The efficiency of smoothing on the ion energy indicates a maximum when the range of the incident ion corresponds to the height of the rectangular step. Viscous flow is found to be a dominant process from analysis of the change in the surface profile.

Paramagnetic resonance of E′-type centers in Si-implanted amorphous SiO2. Si29 hyperfine structure and characteristics of Zeeman resonances☆

Abstract Electron paramagnetic resonance spectra were measured on SiO2 glasses implanted with Si ions to a fluence of 6 × 1016 cm−2 at an acceleration voltage of 160 kV. Three sets of doublets with different separation were observed in Si29-implanted substrates and were ascribed to primary hyperfine structures due to a Si29 nucleus ( nuclear spin = 1 2 ). The doublets with separation of 44.0 and 9.0 mT were attributed to ·Si29 ≡ O3 (E′-center, where the dot and three parallel lines denote the unpaired electron and three separate bonds, respectively) and ·Si29 ≡ Si3 (similar to D center in amorphous Si or Pb center in Si/SiO2 interface) radicals, respectively, and the doublet with a separation of ∼ 23 mT is tentatively assigned to a ·Si29 ≡ SinO3 − n (n = 1 or 2). The area intensity ratio of these three doublets was approximately 2.5 (44.0 mT): 2.5 (23.0 mT): 1.0 (9.0 mT). Zeeman resonances of E′ centers have a broader spread in g2 and are less saturable to microwave power than those of normal E′ resonances. It is suggested that these are common characteristics of E′ resonances in compacted amorphous SiO2.

Study of ion beam induced epitaxial crystallization of SrTiO3

Amorphous SrTiO3 on single crystal SrTiO3 (100) has been crystallized by He+, Ne+, or Ar+ ions with energy of 200 keV–2 MeV at a substrate temperature of 100–250 °C. Rutherford backscattering spectrometry in channeling geometry and x-ray diffraction were used to evaluate the crystallization. Ion-beam-induced epitaxial crystallization (IBIEC) of SrTiO3 was confirmed and the activation energy of IBIEC observed was about 0.1–0.3 eV, a value about 1/10 relative to thermal solid phase epitaxial crystallization. The observed IBIEC seems to be consistent with previously proposed models in which IBIEC is dominated by point defects produced by ion irradiation and their migration to the amorphous/crystal (a/c) interface. The IBIEC mechanism and point defect behavior are discussed by the use of simple models taking into account the rate limiting processes of IBIEC for both point defect diffusion and atomic rearrangement at a/c interface.

Crystallization of amorphous Si on a glass substrate through nucleation by Si+ ion implantation

Crystallization of amorphous Si films on a glass substrate by Si+ implantation (acceleration energy: 180 keV, beam current density: 10 μA/cm, ion dose: 1×1017 ions/cm2) was performed without external heating of the substrate. Transmission electron microscopy images of the crystallized specimens lead to the following conclusions: (1) crystallization was achieved through bulk nucleation by Si+ implantation, which is a low temperature and rapid process compared with the ordinary thermal process, (2) the crystallization is strongly related to the ion‐solid interaction, not due to ‘‘pure’’ thermal annealing by ion beam heating.

Roughness study of ion-irradiated silica glass surface

Abstract We have investigated the surface roughness of ion-irradiated silica glass by the use of atomic force microscopy (AFM). Highly polished synthetic silica glass was irradiated with 120 keV Ar+ ion at a dose range of1 × 1012−1 × 1017ions/cm2. The surface roughens progressively at an ion dose up to1 × 1014ions/cm2, whereas smoothing occurs at an ion dose above1 × 1014ions/cm2. The smoothing in the high dose region is attributed to the viscous relaxation induced by ion beam. As to roughening in the low dose region, two mechanisms both sputtering and compaction has been discussed. The roughening is thought of the compaction of the partial region in which each of the ion impacts cause structural changes.

The Dependence of Field Effect Mobilities on Substrate Temperature for Amorphous Silicon Deposition for Amorphous Silicon Thin Film Transistors

We evaluated the field effect mobility ( µFE) for a-Si TFTs at different temperatures for a-Si deposition (Tsub). The µFE showed a maximum in the temperature range of 200~250°C. We estimated the tail localized state distribution of the a-Si films for each Tsub value from theoretical curves modified by the measurement temperature dependence of µFE. The result of the fittings showed that the a-Si tail localized state was suppressed in the Tsub range 200~250°C.

Effects of ion beam irradiation on the crystallization of Si–C films

Radiation effects of 2 MeV Ar{sup +} ions on the crystallization of copper films were investigated with or without oxygen adsorption. Metal copper films of 1--5 nm thickness deposited on SrTiO{sub 3} (100) at 300 K by evaporation consisted of fine crystals with random orientation. The crystals were grown without epitaxial relationship to the substrate by ion irradiation. The epitaxial growth of copper crystals was achieved by the combined use of oxygen adsorption and ion irradiation. The epitaxial relationship between the film and the substrate was determined Cu (100){parallel}SrTiO{sub 3} (100) and Cu [001]{parallel}SrTiO{sub 3} [001].

Spectral investigation of nonlinear local field effects in Ag nanoparticles

The capability of Ag nanoparticles to modulate their optical resonance condition, by optical nonlinearity, without an external feedback system was experimentally demonstrated. These optical nonlinearities were studied in the vicinity of the localized surface plasmon resonance (LSPR), using femtosecond pump-and-probe spectroscopy with a white-light continuum probe. Transient transmission changes ΔT/T exhibited strong photon energy and particle size dependence and showed a complex and non-monotonic change with increasing pump light intensity. Peak position and change of sign redshift with increasing pump light intensity demonstrate the modulation of the LSPR. These features are discussed in terms of the intrinsic feedback via local field enhancement.