なかのにっき

Many optical-based plasma diagnostic techniques require electron-impact excitation cross sections. In recent years, a considerable number of new results have become available for excitation of rare-gas atoms from both the ground state and metastable states. Using relatively simple techniques these cross sections can be combined with plasma emission measurements to extract many useful plasma parameters such as the electron temperature. Many of the limitations of simple plasma emission models such as the corona model can be overcome by using cross section measurements to select what particular emission lines to use in the analysis.

• The plasma-sheath boundary region
• Low-pressure gas discharge modelling
• Magnetron sputtering of transparent conductive zinc oxide: relation between the sputtering parameters and the electronic properties

Irradiation of high-OH containing amorphous SiO2 is known to introduce a broad absorption band at 4.8 eV and an associated sharp photoluminescence band in the visible red domain, at 1.9 eV. Both absorption and luminescence bands have been unambigously attributed to the nonbridging oxygen (NBO) center, a common defect in irradiated SiO2. Using results of first-principles calculations we show that the NBO center and the interstitial OH molecule (OHi) may both be responsible for the observed absorption and luminescence bands. Although the absorption spectra of the two defects are very similar, their luminescence spectra are different, but overlapping. We found that the NBO center has a sharp luminescence line centered around 1.8 eV in the visible red, whereas OHi molecules have a wide emission spectrum ranging from the infrared (0.8 eV) to visible red (1.8 eV). Investigation of the results show that the difference in the emission spectra is due to the different extent of atomic and electronic relaxations around the two defects: in the case of the NBO, site-independent electronic relaxations are responsible for the defect emitting a photon only at a particular energy, whereas in the case of OHi molecules an interplay between site-dependent atomic and (therefore site-dependent) electronic relaxations result in a wide emission spectrum. A further, intriguing result is that both defects show similar vibrational and polarization properties, therefore their contribution to the red luminescence band of irradiated amorphous SiO2 may not have been decoupled in previous studies.