Tuning of Ultra-Thin Gold Films by Photoreduction

Abstract

Ultrathin metal films (UTMFs) are used in a wide range of applications, from transparent electrodes to infrared mirrors and metasurfaces. Due to their small thickness (<5 nm), the electrical and optical properties of UTMFs can be changed by external stimuli, for example, by applying an electric field through an ion gel. It is also known that oxidized thin films and nanostructures of Au can be reduced by irradiating with short-wavelength light. Here we show that the resistance, reflectance, and resonant optical response of Au UTMFs is changed significantly by ultraviolet light. More specifically, photoreduction and oxidation processes can be sequentially applied for continuous tuning, with observed modulation ranges for sheet resistance (Rs) and reflectance of more than 40% and 30%, respectively. The proposed method has the potential for achieving reconfigurable UTMF structures and trimming their response to specific working points, e.g., a predetermined resonance wavelength and amplitude. This is also important for large scale deployment of such surfaces as one can compensate material nonuniformity, morphological, and structural dimension errors occurring during fabrication.

Multispectral Holographic Intensity and Phase Imaging of Semitransparent Ultrathin Films

“…An ongoing trend in photonics is the transition from thin to ultrathin films and atomically thin materials . In this paper, special attention has also been given to ultrathin metal films (UTMFs), as these show strong potential for use in optoelectronic devices due to their high conductivity and transparency, and also their tunable properties. − …”

“…As a prototypical application and to demonstrate this method for the analysis of semitransparent thin films, we fabricated and characterized cupric oxide (CuO) seeded gold UTMFs − with mass-equivalent thicknesses from 2 to 27 nm. These films have peak T in the range of 40–80%, depending on the thickness of the gold, and additionally a strong interaction with the phase of the transmitted light.…”