Abstract
Monolayer nano-sphere arrays attract great research interest as they can be used as templates to fabricate various nano-structures. Plasma etching, and in particular high-frequency plasma etching, is the most commonly used method to obtain non-close-packed monolayer arrays. However, the method is still limited in terms of cost and efficiency. In this study, we demonstrate that a low frequency (40 kHz) plasma etching system can be used to fabricate non-close-packed monolayer arrays of polystyrene (PS) nano-spheres with smooth surfaces and that the etching rate is nearly doubled compared to that of the high-frequency systems. The study reveals that the low-frequency plasma etching process is dominated by a thermal evaporation etching mechanism, which is different from the atom-scale dissociation mechanism that underlines the high-frequency plasma etching. It is found that the polystyrene nano-sphere size can be precisely controlled by either adjusting the etching time or power. Through introducing oxygen as the assisting gas in the low frequency plasma etching system, we achieved a coalesced polystyrene nano-sphere array and used it as a template for metal-assisted chemical etching. We demonstrate that the method can significantly improve the aspect ratio of the silicon nanowires to over 200 due to the improved flexure rigidity.
Highlights
Monolayer nano-sphere arrays attract great interest in both academic research and industry development, as the array structure can be widely utilized in applications such as photovoltaics [1,2], biosensing [3] and micro/nano-structure fabrication [4]
By dip-coating [5,6], spin-coating [7], or air–water interface self-assembling [8,9,10,11], close-packed monolayer nano-sphere arrays can be facilely achieved on substrates like silicon wafers and glass panels, and used as templates for subsequent procedures
A non-close-packed monolayer array can be derived from a close-packed monolayer array through shrinking technologies such as chemical etching [19,20], heat treatment [21], plasma etching [22,23,24,25,26,27,28,29], and so on
Summary
Monolayer nano-sphere arrays attract great interest in both academic research and industry development, as the array structure can be widely utilized in applications such as photovoltaics [1,2], biosensing [3] and micro/nano-structure fabrication [4]. A non-close-packed monolayer array can be derived from a close-packed monolayer array through shrinking technologies such as chemical etching [19,20], heat treatment [21], plasma etching [22,23,24,25,26,27,28,29], and so on. We demonstrate that a low frequency (40 kHz) plasma etching system can be used to achieve non-close-packed monolayer arrays of polystyrene (PS) nano-spheres with smooth surfaces. Using the non-close-packed monolayer array of PS nano-spheres as a template for metal-assisted chemical etching, we have achieved silicon (Si) nanowires with a high aspect ratio of over 200
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