Fabrication and Optical Properties of Periodic Ag Nano‐Pore and Nano‐Particle Arrays with Controlled Shape and Size over Macroscopic Length Scales

Abstract

A facile and economical route to preparation of highly ordered sliver pore or particle arrays with controlled pore‐shape and size extended over cm2 areas is described. The substrates are prepared at planar and curved surfaces via sphere‐imprinted polymer (PDMS) templating using polystyrene spheres with diameters of 820, 600, or 430 nm. Nano‐pore arrays are created by sputtering 80 nm of Ag directly onto the templates and nano‐particle arrays are prepared by electrode‐less deposition of Ag from Tollen's reagent. The shape of the nano‐pore or particles in the array conformed to that of the imprint of the sphere on the template. Stretching the flexible template enable creation of cuboid shaped nano‐voids and nano‐particles following Ag deposition. Diffuse reflectance from the spherical Ag nano‐cavity arrays showed absorbance maxima at wavelengths comparable similar to the diameter of the templating sphere, whereas reflectance from the cuboid arrays, showed little correlation with the sphere diameter. The cuboid nano‐particle arrays showed the most intense visible absorption which is red‐shifted compared to the spherical arrays. White light diffraction from the arrays, observed by rotating 1 cm2 substrates relative to a fixed light source, reflected exactly the symmetry axes of the periodic nano‐features in the arrays demonstrating the remarkable macroscopic order of the periodic structures. Raman spectra of 1‐benzenethiol adsorbed at the arrays indicated SERS enhancements from the substrates are attributed mainly to surface nano‐roughness with only moderate contributions from the periodically corrugated structures. Despite excitation at the major resonance dip in the reflectance spectrum, a weak, localized rim dipole mode is found to elicit a small increase in the SERS enhancement factor for the 430 nm diameter spherical arrays. FDTD studies of nano‐void arrays provided insights into various factors affecting the SERS experiment and confirmed the array's plasmonic spectra are dominated by propagating plasmon modes under microscope excitation/collection angles.

Flexible Surface‐Enhanced Raman Scattering Substrates: A Review on Constructions, Applications, and Challenges

“…Patterns on the surface of PDMS are another effective way for fabricating SERS‐active substrates. Silicon wafer with certain pattern, [ 17 ] highly ordered anodic aluminum oxide (AAO), [ 22,67 ] plant leaves, [ 68 ] assembled polystyrene spheres, [ 69 ] sapphire substrates, [ 70 ] digital video disk, [ 71 ] and even sandpaper [ 72 ] can be used as templates to prepare PDMS substrates with the multiscale surface. As illustrated by Figure , zigzag micropattern was first designed by UV photolithography on a silicon wafer, then the mixture of PDMS monomer and curing agent were poured on the above substrates.…”

Size and shape control of a variety of metallic nanostructures using tilted, rotating evaporation and lithographic lift-off techniques

“…Several types of techniques using e.g. lithographic masking 36–44 , stenciling 45,46 , and bottom-up masking 47–53 have been used to produce a wide range of nanostructuring. It is in this context that we investigate here the combination of electron beam (ebeam) lithography-derived masking and tilted, rotated thermal evaporation with lift-off processing for the novel fabrication of an assortment of metallic nanostructures having rotational symmetry with specific topographies and sizes depending on the particular lithographic mask dimensions and the rotation tilt angle employed during the evaporation.…”

Flow Behaviors of Polymer Colloids and Curing Resins Affect Pore Diameters and Heights of Periodic Porous Polymer Films to Direct Their Surface and Optical Characteristics

“…For this reason, these films have been used as super-hydrophobic substrates, − size-selective membranes, − templates for catalytic reactions or cell growth, − photonic crystal films, − photodetectors, photovoltaic devices, and optical sensors. − To date, the breath figure and replication methods are suggested to prepare the porous films. Breath figure methods produce pores by condensing water on the substrate surface, where solvents in the solvent–polymer mixtures are evaporated. ,,,− ,− Replication methods embed replicating components into either colloidal crystal monolayers or master templates having certain geometries and the porous structures are obtainable after removing the templates. ,,,,− ,− ,− Regardless of the preparation method, pore diameter is one of the important factors that determine the characteristics of the films. The breath figure method controls the pores by introducing humidity conditions and using different volumes of casting hydrophobic polymers. − Although the replication methods mostly modulate the pore diameters by using colloids of different sizes, other methods have also been suggested.…”