Atmospheric pressure microplasmas in ZnO nanoforests under high voltage stress

Atmospheric pressure ZnO microplasmas have been generated by high amplitude single pulses and DC voltages applied using micrometer-separated probes on ZnO nanoforests. The high voltage stress triggers plasma breakdown and breakdown in the surrounding air followed by sublimation of ZnO resulting in strong blue and white light emission with sharp spectral lines and non-linear current-voltage characteristics. The nanoforests are made of ZnO nanorods (NRs) grown on fluorine doped tin oxide (FTO) glass, poly-crystalline silicon and bulk p-type silicon substrates. The characteristics of the microplasmas depend strongly on the substrate and voltage parameters. Plasmas can be obtained with pulse durations as short as similar to 1 mu s for FTO glass substrate and similar to 100 ms for the silicon substrates. Besides enabling plasma generation with shorter pulses, NRs on FTO glass substrate also lead to better tunability of the operating gas temperature. Hot and cold ZnO microplasmas have been observed with these NRs on FTO glass substrate. Sputtering of nanomaterials during plasma generation in the regions surrounding the test area has also been noticed and result in interesting ZnO nanostructures ('nano-flowers' and 'nano-cauliflowers'). A practical way of generating atmospheric pressure ZnO microplasmas may lead to various lighting, biomedical and material processing applications.