![]() (13) So far, there is no consensus on the origin of formation of the superficial AuO x layer, as its thickness, chemical composition, stability, and the coexistence of different oxygen species are dependent on the oxidation method and on gold morphology (size and shape). (12) This oxidation occurs despite the fact that the heat of formation is estimated to be around +19.3 kJ/mol. Several papers have reported the formation of gold oxide (Au 2O 3) on UTMFs and nanoparticles of Au in processes such as pulsed laser deposition (PLD) and sputtering in an oxygen atmosphere, (8,9) or after exposure to highly reactive chemical environments such as ozone, (10) high frequency activated O 2 (11) or dc-glow discharge oxygen plasma. 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. 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. 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. Here we show that the resistance, reflectance, and resonant optical response of Au UTMFs is changed significantly by ultraviolet light. ![]() It is also known that oxidized thin films and nanostructures of Au can be reduced by irradiating with short-wavelength light. 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. ![]() Ultrathin metal films (UTMFs) are used in a wide range of applications, from transparent electrodes to infrared mirrors and metasurfaces.
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