Sputtering temperature dependent growth kinetics and CO2 sensing properties of ZnO deposited over porous silicon

• Homogenous distribution of the ZnO nanoparticles grown over macroporous Si utilizing magnetron sputtering.
• Grain growth analysis confirms Ostwald ripening process and surface diffusion of add-atoms at 400 and 600 °C, respectively.
• Porous substrate induced increased surface area enhanced the sensitivity 4 times as compared to cSi substrates.
• High sensitivities ∼9.9 with faster response time ∼57s were achieved for films sputtered at 400 °C.

We report the growth kinetics and sensing properties of ZnO deposited over macro-porous silicon substrates at 400 and 600 °C using magnetron-sputtering technique. Scanning electron microscopy was employed to investigate the morphology and the particle size of the ZnO nanoparticles (NPs). The grain growth kinetics was analyzed with the help of the phenomenological equation rn=k0texp(−Q/RT)rn=k0texp(−Q/RT) finding an activation energy Q = 13.92 kJ/mol. The grain growth exponent (n = 2.85) for the growth at 400 °C corresponds to an Ostwald ripening process, while the growth at 600 °C is described by n = 1.66 implying a higher growth rate attributed to a high surface diffusion of add-atoms contributing to the formation of larger grains. The sensing response of the complete structure has been tested at different temperatures. The highest sensitivity, S ∼10, was obtained at a sensor temperature of 300 °C on the ZnO NPs sputtered on to the porous silicon substrate at 400 °C. The high response is attributed to the infiltration, uniform and homogenous distribution of the ZnO NPs into the pores. ZnO NPs sputtered at 400 °C are found to be smaller than those grown at 600 °C, exhibiting a larger surface-area/volume ratio and hence increasing the oxygen adsorption resulting in an enhanced CO2 sensitivity.