Planar microplasma optical emission gas spectroscopy based on selective growth of ZnO nanowires

Abstract

The present study demonstrates a novel miniature planar device by the selective growth of ZnO nanowires for microplasma optical emission gas spectroscopy. Gold electrodes are fabricated on the silicon substrate by thermal evaporation and photolithography process with a 15 μm gap size. Zinc oxide (ZnO) nanowires, are selectively grown on the electrodes without using a seeding layer by a hydrothermal method which is a cost-effective approach. Growth of vertically aligned ZnO nanowires on electrodes with sharp tips reinforce the field emission enhancement factor which results in lower microplasma generation voltage. The SEM characterizations reveals that ZnO nanowires are grown on electrodes, selectively. The diameter range and length of nanowires vary between 50 and 250 nm and 3 and 5 μm, respectively. Also, the gap distance between electrodes decreases from 15 μm to about 4–10 μm due to the growth of vertically aligned nanowires. The experimental tests are implemented for helium, nitrogen, and carbon dioxide gases at room temperature and atmospheric pressure. The results successfully exhibit the characteristic peaks and repeatable responses for all the samples. In addition, the required working voltage for microplasma formation of He, N2, and CO2 reduce 32%, 22%, and 20%, respectively, after ZnO nanowires growth. Besides, the electrodes sputtering rate significantly decreases during the tests due to the thermal stability of ZnO nanowires. According to the device performance, the proposed structure could be a promising candidate for relative low voltage, highly selective and stable optical emission spectroscopy for gas detection applications.