Abstract
In this paper, we use a finite difference time domain solver to simulate the near field optical properties of self-assembled microsphere arrays when exposed to an incoherent light source. Such arrays are typically used for microsphere lithography where each sphere acts as a ball lens, focusing ultraviolet light into an underlying photoresist layer. It is well known that arrays of circular features can be patterned using this technique. However, here, our simulations show that additional nanometer scale features can be introduced to the pattern by optimising the sphere dimensions and exposure conditions. These features are shown to arise from the contact points between the microspheres which produce paths for light leakage. For hexagonally close packed arrays, the six points of contact lead to star shapes in the photoresist. These star shapes have subfeature sizes comparable to the current achievable resolution of low-cost fabrication techniques.
Highlights
Self-assembled microsphere lithography (SA-MSL) is a cost effective, fast, highly ordered, repeatable, and innovative method of microarray fabrication, the origins of which lie in the work of Van Duyne’s group[1]
The microstar arrays could be utilised as an array itself or could be lifted off to be used as individual star shaped particles
nanosphere lithography (NSL) is already used for plasmonic enhancement by using deposition and lift off to form triangular shapes between the spheres[10]
Summary
Self-assembled microsphere lithography (SA-MSL) is a cost effective, fast, highly ordered, repeatable, and innovative method of microarray fabrication, the origins of which lie in the work of Van Duyne’s group[1]. Using NSL to produce star shaped arrays for plasmonic enhancement could provide more angular stability than its triangular counterpart. The unique shape of the microparticles produced here is expected to have a useful topology; the points of the star are of particular interest as they lend themselves to increasing the likelihood of tunnelling within composite materials[12].
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