Catalyst-free surface-roughness-assisted growth of large-scale vertically aligned zinc oxide nanowires by thermal evaporation

This study reports the successful growth of large-scale vertically aligned ZnO nanowires on sapphire, glass, and Si substrates by direct thermal evaporation without the employment of either metal catalysts or seed layers via a surface-roughness-assisted vapor-solid mechanism. Simple processing steps including mechanical scratching, mechanical polishing, and chemical etching have been utilized to demonstrate the effectiveness of the present approach. The advantages include easy achievement of vertically aligned nanowires and applicability on various types of substrates.