Ultrathin Wetting Layer-Free Plasmonic Gold Films

Abstract

Ultrathin gold films are attractive for plasmonic and metamaterial devices, thanks to their useful optical and optoelectronic properties. However, deposition of ultrathin continuous Au films of a few nanometer thickness is challenging and generally requires wetting layers, resulting in increased optical losses and incompatibility with optoelectronic device requirements. We demonstrate wetting layer-free plasmonic gold films with thicknesses down to 3 nm obtained by deposition on substrates cooled to cryogenic temperatures. We systematically study the effect of substrate temperature on the properties of the deposited Au films and show that substrate cooling suppresses the Volmer−Weber growth mode of Au, promoting early stage formation of continuous Au films with improved surface morphology and enhanced optoelectronic properties. Our results pave the way for straightforward implementation of ultrathin Au-based optoelectronic and plasmonic devices, as well as metamaterials and metasurfaces.

Plasma Enhanced Atomic Layer Deposition of Plasmonic TiN Ultrathin Films Using TDMATi and NH3

“…Importantly, we introduced a hydrogen-plasma post-deposition treatment to further alter the optical properties of TiN while maintaining the thermal budget at the low temperature of 250 • C. We found that such plasma treatments greatly improved the metallic quality of the films, increasing the ε 1 slope by 1.3 times, from −0.015 to −0.021, on MgO and two times, from −0.012 to −0.024, on Si (100) for 11 nm thick films. Our work demonstrates the feasibility of developing metallic and plasmonic ultrathin TiN films with a PE-ALD deposition and post-deposition treatment that is substrate insensitive and with a low temperature of 250 • C. Our work opens up potentials of investigating a CMOS compatible ultrathin plasmonic material, which have been of interest for flexible transparent optoelectronic devices [19,20] and nonlinear optical applications [21,22].…”

Thin‐Metal‐Film‐Based Transparent Conductors: Material Preparation, Optical Design, and Device Applications

“…Reproduced with permission. [ 48 ] Copyright 2015, American Chemical Society. c) SEM images of Ag and oxygen‐doped Ag layers of different thicknesses on ZnO films.…”

“…Studies have shown that substrate cooling is indeed beneficial for high‐quality, ultrathin metal film formation. [ 48,96,160 ] Lemasters et al. have found that by cooling the substrate to cryogenic temperatures (≈−195 °C), wetting‐layer‐free plasmonic Au films with thicknesses down to 3 nm can be obtained.…”

“…have found that by cooling the substrate to cryogenic temperatures (≈−195 °C), wetting‐layer‐free plasmonic Au films with thicknesses down to 3 nm can be obtained. [ 48 ] As shown in Figure 15b, as the substrate temperature goes down, the surface morphology of 5 nm thick Au films gets improved and at the same time, the associated sheet resistance gets reduced.…”

“…While there are ongoing researches to improve the optoelectronic properties and mechanical flexibilities of ITO on flexible substrates by investigating the underlying mechanism, [ 8,9 ] adjusting its deposition procedure, [ 10–12 ] or exploiting hybrid structures incorporating ITO and other conductive materials, [ 13–18 ] more intensive research efforts have been devoted to developing flexible transparent conductors based on ITO‐free materials, such as conductive polymers, [ 19–21 ] carbon‐based materials, [ 22–25 ] patterned metal grids, [ 26–33 ] metal nanowires, [ 34–42 ] and thin metal films. [ 43–48 ] Though conductive polymers and carbon‐based materials improve the mechanical flexibility of transparent conductors, their relatively low conductivity could limit the conductors’ electrical performance. [ 21,25,49,50 ] Metal grids and nanowires offer advantages of high transmittance and low sheet resistance.…”