Tilted exposure microsphere nanolithography for high-throughput and mask-less fabrication of plasmonic molecules

Abstract

Fabrication of nanostructures for applications such as plasmonics and metamaterials are typically accompanied by a slow production and limited area due to the required sub-micron feature sizes. In these applications, periodic array of metal/dielectric features can produce optical resonance responses such as optical field enhancement response, Fano response, chiral response, and negative refractive index. Here, we propose a mask-less photolithography technique that can produce a variety of periodic nanostructure clusters. The method is based on microsphere nanolithography, which focuses UV field into the so-called photonic jet which is a propagative intensive field underneath the sphere. The position of photonic jet can be moved by changing the angle of exposure. The method introduces a controllable scheme to realize nano-gap size by controlling the angle of exposure. The feature sizes generated by this method are about one third of exposure wavelength. The method is compatible with highthroughput nano-manufacturing schemes, such as roll-to-roll production. Here we present some examples to demonstrate the capabilities of this method in producing an array of complex plasmonic molecules over a large area. The periodicity of array and element's diameter can be tuned by microsphere size and exposure/developing time, respectively. Tilted exposure lithography inherently is self-aligned and readily extendible to deep UV lithography due to absent of mask and optical elements. FDTD simulation agrees well with our experimental results, and suggests that much smaller feature sizes can be achieved at shorter wavelengths.

Recent advancement on micro-/nano-spherical lens photolithography based on monolayer colloidal crystals

“…Fig. 4c and e, respectively [88]. Recently, it was shown that tilted exposure could also be carried out in DUV projection SLPL technique by inducing the formation of a photonic nanojet with different angles of incidence [87].…”

“…This approach is actually a derivative of the conventional SLPL. Mohseni et al [88] demonstrated the capabilities of this method in producing an array of complex plasmonic molecules over a large area. The classical schematic of the fabrication process is illustrated in Fig.…”