Fabrication of metallic nanodisc hexagonal arrays using nanosphere lithography and two-step lift-off

Abstract

Nanosphere lithography (NSL) has been widely used as an inexpensive method to create periodic arrays of metallic nanoparticles or nanodiscs on substrates. However, most nanodisc arrays derived from a NSL template are restricted to hexagonally-ordered triangular arrays because the metal layer is deposited onto the interstices between the nanospheres. Metallic nanodisc arrays with the same arrangement as the original nanosphere array have been rarely reported. Here, we demonstrate a facile, low-cost method to fabricate large-area hexagonal arrays of metallic nanodiscs using an NSL template combined with a two-step lift-off process. We employ a bi-layer of two dissimilar metals to create a re-entrant sidewall profile to undercut the sacrificial layer and facilitate the final lift-off of the metallic nanodiscs. The quality of the nanodisc pattern and the array periodicity is determined using statistical image analysis and compared to the original nanosphere array in terms of size distribution, surface smoothness, and array pitch. This nanodisc array is used as an etch mask to create a vertically-aligned Si nanowire array. This combined approach is a scalable and inexpensive fabrication method for creating relatively large-area, ordered arrays of various nanostructures.

Metal enhanced fluorescence biosensing: from ultra-violet towards second near-infrared window

“…114 The variability of structures that can be produced is still expanding and ranges from rod arrays to rings, discs and crescents. 27,[115][116][117] In 2016, the amplification of light in NIR-II from Ag 2 S quantum dots was reported for the first time, achieving an enhancement of over 100 times when conjugated to nanotriangular arrays as produced via colloidal lithography. 67 Most notably, in 2017, protein microarrays based on NIR plasmonic gold nanostructures were reported for the highly sensitive detection of the pancreatic biomarker CA19-9.…”

Free-standing Ag triangle arrays a configurable vertical gap for surface enhanced Raman spectroscopy

“…Many methods have been used to fabricate large-area and well-ordered arrays of planar metallic nanostructures, including photolithography [11], laser ablation [12,13], and template-based methods using an anodized alumina membrane [14,15] or nanosphere lithography (NSL) [16][17][18]. Among them, NSL is a versatile and economical way to create large-area, periodic plasmonic arrays which are inherently uniform in shape and size, such as a nanocap [19,20], nanohole [21], nanodisc [22], nanopillar [23], nanoring [24] and nanotriangle [25] etc. These periodic metallic nanoparticles have been widely applied to SERS [26,27].…”

Pitch Control of Hexagonal Non-Close-Packed Nanosphere Arrays Using Isotropic Deformation of an Elastomer

“…Such nanostructure arrays, if constructed out of noble metals, exhibit plasmonic properties and optical (i.e., Raman, fluorescent) enhancements and are therefore widely used in sensing − and optoelectronic applications. − However, the type of the nanostructures derived from the close-packed array is rather limited, and more complex nanostructure arrays can be obtained by separating the spheres and carrying out additional processes such as soft lithography, (angled) evaporation, etching, and annealing . Examples of the resulting nanostructures generated from the non-close-packed monolayers include honeycomb patterns, , ordered porous films, , and arrays of nanodisks, , nanorings, , nanocrescents, − nanocones, and nanowires. − Non-close-packed monolayers significantly increase the versatility of colloidal lithography and the available types of nanostructures over structures derived from a closed-packed monolayer.…”