Simple Holographic Patterning for High‐Aspect‐Ratio Three‐Dimensional Nanostructures with Large Coverage Area

Abstract

Using the vertical standing wave phenomena commonly regarded as a deterrent in holographic lithography, multifaceted three‐dimensional (3D) nanostructures are fabricated on polymeric photoresist materials using a simple two‐beam interferometer. Large‐area 3D nanostructures with high aspect ratios (greater than 10) are readily produced using this methodology, including grating, pillar and pore patterns. Furthermore, manipulation of the lithography process conditions results in unique sidewall profiles of the nanostructures. Such 3D holographic control even produces highly porous polymer membranes composed of 3D interconnected pore networks, which resembles the 3D photonic crystal compound nanostructures that were previously attainable only with limited pattern coverage area using complex multibeam holographic lithography processes. Such well‐tailored high‐aspect‐ratio 3D nanostructures with large pattern coverage area further enable the fabrication of novel nanostructures for functionalized materials via various additive and subtractive pattern transfer techniques such as etching, deposition, and molding. In particular, direct molding followed by thermal decomposition process leads to the synthesis of hierarchical titanium oxide nanostructures of tunable 3D geometry, which would be of great significance in applications of photonic crystals, photovoltaic solar cells, and photocatalyst in water decontamination.

Fabrication of hierarchical nanostructures using free-standing trilayer membrane

“…Not only a thin nanoporous membrane but also a thick microporous membrane can be prepared and employed for such processes to realize more various types of 3D hierarchical nanopatterns. Such wellregulated hierarchical nanostructures attainable by the introduced fabrication technique will advance many scientific and engineering applications including dry adhesives, 1-3 superhydrophobic surfaces, 4-9 nano-optics/photonics, [10][11][12] self-assembly of nanomateirals, 13 …”

“…[35][36][37] The interference lithography systems and processes used in this study were especially developed for the large-area (i.e., full wafer-scale) nanopatterning, as reported earlier. 12,[38][39][40][41][42][43] In this work, the nanopore patterns of two different periods (500 and 900 nm) were prepared by using a He-Cd laser of a wavelength of 325 nm (IK3501R-G, Kimmon Koha Co., Ltd.). After the exposure, the samples were postexposure baked on a hotplate at 100 C for 1 min.…”

“…Recently, three-dimensional (3D) hierarchical nanostructures have drawn great interests due to their advanced applicability to many science and engineering applications including dry adhesives, 1-3 superhydrophobic surfaces, [4][5][6][7][8][9] antireflective moth-eye structures, 10 photonic crystals, 11,12 and self-assembly of nanomaterials. [13][14][15] Modified with highaspect-ratio nanostructures, the surface properties of devices can be tuned and tailored to enhance the performance and mimic the multifunctional biological systems in nature.…”

“…The bilayer film is patterned to be nanoporous by using laser interference (holography) lithography for the top photoresist layer and then reactive ion etching (RIE) for the bottom ARC layer, respectively. The ARC is used to reduce the standing-wave issues associated with the interference lithography process 12 and to enhance the mechanical robustness of the bilayer polymer membrane. A thin Cr layer is further deposited (using e-beam evaporation in this study) on top of the nanoporous bilayer film, forming a trilayer stack.…”

One-step patterning of double tone high contrast and high refractive index inorganic spin-on resist

“…According to the traditional lift-off process, titanium dioxide was firstly micro structured using conventional UV resist pattern as a mold. 10 Endeavors to simplifying the traditional complex lift-off process were made by Cuisin et al and Wathuthanthri et al 11,12 who used the sol--gel filling technique in resist templates prepared by X-ray lithography or two-beam interferometer that can be calcinated to produce three-dimensional titania patterns. Furthermore, Masuda et al [13][14][15] and Sukenik's group 16,17 obtained micropatterned TiO 2 by depositing titania from aqueous solution onto photopatterned self-assembled monolayer (SAM) films.…”