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.
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