Gi-Dong Kim

Optical property modification of PMMA by ion-beam implantation

Polymeric waveguides were fabricated by proton implantation on poly(methyl methacrylate) (PMMA). Depth profiles of the refractive indices of modified regions were obtained and were found to be in good agreement with the stopping power curve of protons in PMMA. It means that the waveguides are formed at the depths where the stopping power is the maximum value. Light losses for 635 nm wavelength were measured using planar waveguides to verify if the transmittance is enough for the application of the technique to optical devices.

Enhancement effect of photoluminescence in Si nanocrystals by phosphorus implantation

Different from bulk silicon crystal, nano-sized Si crystalline embedded in dielectric medium is known as an efficient light emitting center. In nano-crystalline Si, excitonic electron-hole pairs are considered to be attributed to radiative recombination. But the defects surrounding crystalline nc-Si suppress light emitting, which works as a non-radiative decay path. Hydrogen is usually utilized in order to encapsulate the dangling bonds in the Si:SiO 2 interface, dramatically enhancing luminescence yield from nc-Si embedded in dielectric medium. Unfortunately because hydrogen has higher mobility in the matrix, subsequent thermal processes may reduce the enhancement effect. Thus instead of easily reversible hydrogen, phosphorus was introduced by implantation, and was to have the same effect and to be resistive to thermal treatments. Samples were prepared by 400 keV Si implantation with dose of 1 × 10 17 Si /cm 2 and by multi-energy P implantation to make relatively uniform P concentration in the region where implanted Si ions are distributed. Precipitation of crystalline silicon was obtained by annealing at 1100°C for 2 hour in pure Ar environment. Experimental data such as enhancement effect of PL yield, decay time, peak shift for the phosphorus implanted nano-crystalline Si are shown, and the possible mechanisms are discussed.

Fast neutron facility of KIGAM

The Korea Institute of Geoscience and Mineral Resources (KIGAM) neutron facility, which is based on an electrostatic tandem accelerator, was designed and has been installed for the production of nuclear data for the structure materials of a fusion reactor. The main nuclear reaction for generating neutron beams is the H(p,n)He reaction. This system generates both DC neutron beams and pulsed neutron beams with energies from 1.4 MeV to 2.6 MeV, which are determined by measuring resonance energies for neutron absorption yields on C and Si and comparing these energies with the resonance energies for total neutron cross sections. Neutron fluxes at these energies were about 10 neutrons/sr/sec based on a MeV neutron activation method on Au. The neutron energy spread (full width at tenth maximum: FW1/10M) at a neutron energy of 2.146 MeV is obtained to be about 220 keV, which is determined using measurements of the neutron flight time.