Letter pubs.acs.org/NanoLett
Ten-Nanometer Dense Hole Arrays Generated by Nanoparticle Lithography Tianlong Wen, Ryan A. Booth, and Sara A. Majetich* Physics Department, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States S Supporting Information *
ABSTRACT: Large area dense hole arrays with a feature size of ∼10 nm were generated using self-assembled monolayers of nanoparticles as etch masks. To fabricate the hole arrays, monolayers of nanoparticles were irradiated by electron beam to turn surfactants into amorphous carbon, treated by acid to remove the nanoparticle cores, and then etched by CF4 to deepen the holes. Evaporated gold films preferentially diffuse into the holes to generate gold nanoparticle arrays. However no obvious diffusion into holes was observed for a sputtered iron platinum film. KEYWORDS: Nanoparticle lithography, hole arrays, self-assembly, monolayers, etching, gold nanoparticle arrays
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nanoparticles as etch masks.16 However, when small nanoparticles self-assemble into dense arrays, the gaps between nanoparticles are usually very small (∼2 nm). There is no convenient method to shrink the size of these small nanoparticles and widen the gaps as microsphere lithography does, making the etching extremely difficult through the small gaps compared to large microspheres and sparse nanoparticles due to an aspect ratio dependent etch rate.17 In our processing, dense hole arrays with ∼10 nm features were obtained by using ∼12 nm magnetite nanoparticles as etch masks. While there have been many previous studies of nanoparticle arrays,18,19 there are several motivations for transferring the pattern of the nanoparticles into an underlying substrate.20 Selfassembly leads to random crystallographic orientations. However, this would lead to extra noise in magnetic recording media, due to variations in the perpendicular magnetization, and to a spread in the ferromagnetic resonance (FMR) peak, which has plagued fundamental studies of high frequency response in nanoparticles. The ability to transfer patterns of nanoscale features would enable electronic measurements on single nanoparticles using scanning probe microscopy. It is extremely difficult to attach electrodes to a single nanoparticle, but this becomes feasible with the patterning of a trilayer film, where the top and bottom layers are the electrodes and a scanning probe tip is used to make electrical contact. Until now electronic measurements on nanoparticles require tunneling through a surfactant barrier that may be nonuniform. Many interesting nanostructures in optics, electronics, and magnetics require layers of different materials and quality interface to minimize electron scattering and maximize exchange coupling.
echniques to generate two-dimensional (2D) periodic arrays with feature sizes of 10 nm or smaller are in great demand for pattern miniaturization in applications such as bit patterned media1,2 and nanoplasmonics.3 Available techniques include electron beam (or e-beam) lithography4 and block copolymer lithography.5,6 Here we report that self-assembled monolayers of nanoparticles can be used as templates to make large area and high density 2D hole arrays with feature sizes
