K. Kono

Cupric oxide nanoparticles in SiO2 fabricated by copper-ion implantation combined with thermal oxidation

Cupric oxide (CuO) nanoparticles (NPs) are fabricated in silica glasses (SiO2) by Cu-ion implantation and following thermal oxidation. First, Cu metal NPs were formed in SiO2 by the implantation of Cu negative ions of 60 keV to ∼6×1016ions∕cm2, and then the Cu NPs were oxidized to CuO NPs by annealing at 400–1000 °C in oxygen-gas flow. After the oxidation at 600 °C for 1 h, the surface plasmon resonance peak of metallic Cu NPs disappears. Grazing-incidence x-ray diffraction confirms the disappearance of Cu NPs and the formation of CuO NPs, but excludes the formation of Cu2O NPs which are thermodynamically less stable under atmospheric oxygen pressure. The CuO NPs show higher thermal stability up to ∼1000°C than Cu NPs.

Negative copper ion implantation into silica glasses at high dose rates and the optical measurements

Abstract A technique of high-current implantation, with negative heavy ions, has been developed to attain efficient high-density implantation, especially for metal modification of dielectrics. The Cu− ions were implanted into silica glasses to study the dose rate dependence at a fixed dose of 3.0 × 1016 ion/cm2, up to a current density 260 μA/cm2. To dissipate the heat load onto the substrate, a masking method was developed using a multi-hole Cu plate. Optical absorption and reflection in a wavelength range, λ = 200–900 nm, showed a surface plasmon peak of Cu colloids at λ = 560 nm and a broad band of E′ centers, etc. Although the spectral shapes were similar, irrespective of the dose rate, the absorbance and the reflectivity at the peak showed a dose rate dependence, i.e., a two-humped variation. For X-ray fluorescence, the dose rate dependence had a fair correlation with the Cu-L variation. Besides the dose rate dependent precipitation, the Cu amount retained in the substrates may be affected by the mass transport around the beam-solid interface.

Production of Cu2O nanoparticles in SiO2 by ion implantation and two-step annealing at different oxygen pressures

Two different methods were applied to fabricate cuprous-oxide (Cu2O) nanoparticles (NPs) in silica glasses (SiO2), namely (i) low oxygen-pressure (LOP) oxidation of Cu NPs, which had previously been formed in SiO2by implantation of Cu ions and (ii) two-step annealing of Cu NPs in atmospheric-pressure oxygen gas (to convert Cu NPs to CuO) and in LOP-Ar gas (to convert CuO to Cu2O). The LOP oxidation at 800 °C converts a small portion of Cu NPs to the Cu2O phase, but most of the Cu NPs survive in the metallic state. By increasing the oxidation temperature to 900 °C, the Cu2O phase dissolves. On the other hand, the two-step annealing at different oxygen pressures converts all the Cu species to Cu2O NPs. Any diffraction peaks due to Cu NPs or CuO NPs, except Cu2O NPs, were not observed.

Particle-induced conductivity and photoconductivity of silicon under 17 MeV proton irradiation

Particle irradiation, as well as light illumination, to semiconductors increases electric conductivity. The particle-induced conductivity (PIC) of Si, under 17 MeV proton irradiation, has been studied measuring the dependence on proton fluence and flux. While the PIC of undoped Si rapidly deteriorates with proton fluence, that of doped Si does not greatly decrease below a certain fluence φC and steeply decreases above the fluence. The results are compared with photoconductivity (PC) in response to near-infrared light. The fluence dependence of the PIC is similar to that of the PC. The specific fluence φC coincides with the critical fluence in the PC evolution which we previously reported. The PIC is proportional to the square root of proton flux, while the PC follows a linear relation to the photon flux. Although the proton irradiation causes high-energy synergistic processes, the PIC is dominated by electron–hole production due to proton excitation. The PIC processes are elucidated in a similar manner to...

Interstitial carbon reactions in n-Si induced by high-energy proton irradiation

Abstract The effect of oxygen on the interstitial carbon reactions in n-Si created by high-energy proton irradiation was studied by an in situ DLTS measurement system. The suppression of Watkin’s replacement reaction by trapping of interstitial silicon was studied. The release of the interstitial silicon from interstitial oxygen complex and the following interstitial carbon was studied by in situ DLTS measurement. Also, the effects of interstitial carbon reactions on CCD performance is discussed as an example of application.

In situ photodetection in strong radiation fields: Simultaneous irradiation of Si by photons and high-energy protons

Photoconductivity (PC) of crystalline Si induced by ∼1 eV photon irradiation has been studied under simultaneous 17 MeV proton irradiation. The PC during simultaneous irradiation is suppressed to 20%–50% of the value without the proton irradiation. The PC-suppression rate depends on the photon energy, the proton flux, and the defect concentration. These dependences are explained with a saturated variation of conductivity increment Δσ during the proton irradiation. The saturation is mainly ascribed to bimolecular-type recombination of excess carriers under high-density excitation. The understanding of the PC-suppression process contributes to the development of photodetectors for use in strong radiation fields. Guidelines to limit the effect of the PC suppression are also discussed.

RADIATION PHOTONICS: A CASE OF METAL-NANOPARTICLE COMPOSITES

A multilayer non-linear optical structure based on the metal nanoparticles has been fabricated by sequential vapor deposition of silica and implantation of 60 keV Cu- ions. The multilayer structure showed an enhanced non-linear optical response.