Three-dimensional patterning and morphological control of porous nanomaterials by gray-scale direct imprinting

Abstract

We present a method for direct three-dimensional (3D) patterning of porous nanomaterials through the application of a premastered and reusable gray-scale stamp. Four classes of 3D nanostructures are demonstrated for the first time in porous media: gradient profiles, digital patterns, curves and lens shapes, and sharp features including v-grooves, nano-pits, and ‘cookie-cutter’ particles. Further, we demonstrate this technique enables morphological tuning and direct tailoring of nanomaterial properties, including porosity, average pore size, dielectric constant, and plasmonic response. This work opens a rapid and low-cost route for fabricating novel nanostructures and devices utilizing porous nanomaterials, with promising applications spanning diffractive and plasmonic sensing, holography, micro- and transformation optics, and drug delivery and imaging.

Direct Imprinting of Porous Silicon via Metal‐Assisted Chemical Etching

“…Further, unlike reported purely mechanical imprinting processes for PS, [ 17,18 ] it does so with minimal mechanical forces and no resulting plastic deformation or residual stresses. Like current formats of implementation of MACE, it is capable of centimeter-scale parallel patterning with sub-20 nm nanometer resolution, however, unlike them, it avoids need for lithographic patterning of the metal catalyst for each substrate to be patterned by using a reusable imprinting stamp.…”

“…During photolithography and micromachining, photoresist, developers, and etchants infi ltrate the pores, leading to contamination of the substrate, poor sidewall control and over-etching and, in general, poor fi delity of pattern transfer. [ 12 ] To circumvent these issues, micro-contact printing (MP), [ 15 ] dry-removal soft-lithography (DWSL), [ 16 ] and direct imprinting of PS (DIPS) [ 17,18 ] methods have been developed to pattern PS. The patterned photoresist fi lm is used as a mask during the anodization step leading to 2D embedded PS patterns with micron-scale resolution.…”

“…Recipes for dry etching methods must be specifi cally tailored to a particular pore morphology of the PS being etched and high-aspect ratio features are seldom reported. [ 12 ] To circumvent these issues, micro-contact printing (MP), [ 15 ] dry-removal soft-lithography (DWSL), [ 16 ] and direct imprinting of PS (DIPS) [ 17,18 ] methods have been developed to pattern PS. The MP method uses a stamp that blocks diffusion of reactants during anodization of the silicon surface.…”

Monolithic nanoporous gold disks with large surface area and high-density plasmonic hot-spots

“…[21], [13] The fabrication scheme is shown in Figure 1. A film of gold and silver alloy approximately 120 nm thick was first sputtered onto the substrate (e.g., silicon wafer or glass slide) using an Ag82.5Au17.5 (atomic percentage) alloy target.…”

Nanoporous silicon-based surface patterns fabricated by UV laser interference techniques for biological applications

“…In the case of nanoPS, different patterns have been developed for such applications as photonic devices, diffraction gratings, high-sensitivity biosensors, etc [8][9][10]. In order to fabricate these patterns, various techniques such as dry soft 2 lithography [11], press stamp [12], ion bombardment [13], or microstructuring crystalline silicon before electrochemical etching [14] have been used. One of the most used and precise technique is the combination of focused high-energy proton beams and electrochemical etching [15].…”