Abstract
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 ∼1 μs for FTO glass substrate and ∼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.
Highlights
Microplasmas have recently gained significant attention for synthesis and processing of nanomaterials.[1,2] Due to the small probe separation, microplasmas can be produced at atmospheric pressure with small breakdown voltages[3] and can maintain the non-equilibrium state with low gas temperatures when short duration pulse voltages are applied.[4]
We have recently shown that Zinc oxide (ZnO) microplasmas are obtained when high electrical stress is applied using micrometer separated probes on ZnO nano-forests.[21,22]
We have studied the effects of the electrical stress parameters and substrate on the characteristics of ZnO microplasmas generated using this process, with particular interest on the possibility of controlling the gas temperature in plasma
Summary
Microplasmas have recently gained significant attention for synthesis and processing of nanomaterials.[1,2] Due to the small probe separation, microplasmas can be produced at atmospheric pressure with small breakdown voltages[3] and can maintain the non-equilibrium state with low gas temperatures (in transient cold plasmas) when short duration pulse voltages are applied.[4] Such atmospheric pressure cold plasmas have a wide range of biomedical applications.[5,6]. Zinc oxide (ZnO) in turn has numerous useful material properties, such as optoelectronic, semiconducting, and piezoelectric.[7] ZnO is abundant, inexpensive, anti-bacterial,[8] bio-compatible[9] and environment friendly.[10] Techniques to produce ZnO microplasmas can lead to various applications. Cold ZnO atmospheric pressure microplasmas can be used for sterilization,[11] medical.[12] and dental
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