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We investigated aqueous solutions containing nitrite ions and DMPO (5,5-dimethyl-1-pyrroline-N-oxide) by electron spin resonance (ESR) in the pH range from 1 to 6. A DMPO-OH signal was observed below pH 3.0 in the presence of nitrite ions, whereas in the absence of nitrite ion, an extremely weak signal was observed below pH 1.5. Addition of methanol, a hydroxyl radical scavenger, to this system did not lead to the appearance of a detectable DMPO-CHOH signal. The possibility of this DMPO-OH signal being due to a genuine spin trapping process with hydroxyl radical was, therefore, ruled out. The reactivities of reactive nitrogen species (RNS) in this system with DMPO have also been investigated by density functional theory (DFT) at the IEFPCM (water)/B3LYP/6-311 + G ** level of theory. On the basis of the pH dependence of the signal intensity and the redox potential E° (versus SHE) calculated by DFT theory, we propose that the origin of this signal is "inverted spin trapping" via one-electron oxidation of DMPO by HONO, followed by the nucleophilic addition of water. Prevention of these false-positive results when detecting hydroxyl radical using ESR spin trapping requires an awareness of both the presence of nitrite ions in the solution and the solution pH.

The film property distributions along the thickness direction of the catalyst-generated atomic hydrogen (Cat-H*) treatment effects on hydrogenated amorphous silicon (a-Si:H) fabricated by plasma-enhanced chemical vapor deposition (plasma-CVD) and liquid-Si printing (LSP) were systematically investigated. The a-Si:H films fabricated by LSP (L-a-Si:H) had nanosize voids; however, these films showed a decrease in void size around the surface region after Cat-H* treatment, in contrast to stable plasma-CVD films without voids. The decrease in nonaffected area by Cat-H* treatment in

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