A Facile, Low-Cost Plasma Etching Method for Achieving Size Controlled Non-Close-Packed Monolayer Arrays of Polystyrene Nano-Spheres

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.

Nanosphere Lithography for Structuring Polycrystalline Diamond Films

“…We believe that NLS represents a promising method for ingenious designs, and that exploring new procedures for nano-/micro-structuring diamond will open new fields of diamond applications, such as photonic materials [3,22,29,53], Raman or fluorescence plasmonic structures [12,14,18,38], metasurfaces [37,54], biomimetic surfaces (e.g., moth-eye structure) [24], biological and chemical sensors [13,54,55], surfaces with specific wetting properties (e.g., superhydrophobicity, anti-fogging, self-cleaning) [12,19], and many others.…”

“…After a short etching time, sphere-like structures were obtained ( Figure 3a) with a smooth surface (e.g., PS_1 μm for 30 s, Figure 3a). For more details about the plasma etching (various systems, the effect of process parameters) of the PS spheres, see [24,25]. The produced non-close-packed monolayers with isolated PS spheres can be used as the mask for further structuring.…”

“…The produced non-close-packed monolayers with isolated PS spheres can be used as the mask for further structuring. These kinds of templates are commonly used for nanowire fabrication [24].…”

“…The nanosphere assembly is followed by various post-processing steps, which can be modified on demand [23]. The most common step is plasma etching, which is used to alter the size and geometry of the spheres in the close-packed array without changing their relative placement [20,24,25]. Furthermore, deposition (e.g., metal evaporation, sputtering, pulsed laser deposition, electrochemical deposition), thermal annealing, lift-off techniques, and 3D printing are used to obtain the most common features, such as triangular, honeycomb, pyramid structures, holes, pillars, rods, rings, and cones [11,14,18,21,22,26].…”

Colloidal Lithography for Photovoltaics: An Attractive Route for Light Management

“…(2) allow highly-selective etching (RIE) in step b) of Figure 2; and (3) can be easily removed by chemical lift-off in step d) [54,[57][58][59][60][61][62][63][64]. In view of that, the most synthesized particle materials for use in CL have been polystyrene (PS), polymethyl methacrylate (PMMA), and silica [65].…”