Photoluminescence properties of porous Si aged in ethanol solution and porous Si films aged in ambient air were studied. It was shown that the photoluminescence properties of porous Si strongly depend on aging time and environmental conditions. The photoluminescence intensity of porous Si dispersed in ethanol solution increases 50-fold with aging for 7 d. This increase is accompanied by increases in Si–O bond density and lifetime, indicating that the electron–hole pair is strongly confined by the formation of surface oxide thin films. The photoluminescence intensity of porous Si films decreases with aging in ambient air, suggesting that nonradiative recombination centers are formed by natural oxidation.

Nitrogen (N) atomic density is measured by an actinometry method in the toroidal shaped plasma device NAGDIS-T, where the plasma produced in a DC arc discharge is cooled as spiraling down inside the vacuum vessel. The plasma was characterized with an electrostatic probe, and we applied the actinometry method to obtain the N density using the deduced electron density and temperature. The actinometry method used the Ar line emissions at 750.4 or 811.5 nm and N emission at 746.8 nm. The measured N densities from the actinometry was compared with that from the vacuum ultraviolet absorption spectroscopy.

We studied the photoluminescence (PL) of porous Si powder via oxidation in distilled water and organic solvents of ethanol, acetone and hexane. Porous Si powder aged in an ethanol solution increased in PL intensity up to 50 times over 4 days. Even though the PL intensity of porous Si aged in acetone and hexane solutions also increased, the increase was smaller than that of seen in the ethanol solution. Porous Si powder oxidized in an ethanol solution shows the best improvement in PL intensity for all the used solvents. However, the PL intensity of porous Si aged in distilled water decreased. The PL intensity of porous Si aged in deaerated ethanol slowly increased indicating that the surface oxidation of porous Si was caused by the oxygen dissolved in the organic solvents. Oxidation of a porous Si surface strongly depends on the type of organic solvent.

For the development of a high nitrogen atom density source, we produced nitrogen plasmas and measured the nitrogen atom density using vacuum ultraviolet absorption spectroscopy (VUVAS) at high neutral gas pressure (>1.5 mTorr) and discharge power (>500 W) in the NAGDIS-T, which could generate spiral-shaped dissociative recombining plasmas. It was seen that the nitrogen atom density increases with increasing neutral gas pressure and discharge power, and it reached 6.2 × 10 17 m −3 . In the low gas pressure case, the estimated atom density was confirmed to be consistent with that measured by the actinometry method.

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