Abstract
We recently demonstrated a sub-bandgap photoresponse with our wafer-scale
Au/TiO2 metallic-semiconductor photonic crystals (MSPhC). The
sub-bandgap energy with 590 nm peak could be absorbed in the form of hot
electron and injected to TiO2, which provides 5.28 times more energy
for photolysis than that of energy absorbed to flat TiO2. If the
solar energy already absorbed above 700 nm could be injected to the catalyst,
higher than 10 times improvement will be achieved, and above 20% solar to fuel
efficiency will be feasible with the robust but inefficient TiO2
catalyst. In order to achieve photocurrent near and above 700 nm spectrum, we
deposited gold nanorods on the surface of MSPhC to incur localized surface
plasmon (LSP) modes absorption and subsequent injection to the TiO2
catalyst. We used electrophoretic deposition (EPD) method to deposit nanorods on
the top, sidewall and bottom well surface of the photonic nanocavities. The
deposition of nanorods was achieved reasonably uniform and sparse not to block
the optical cavities of MSPhC. Flat gold surfaces were tested at 4 different
suspension densities to get the optimum gold nanorods density. Under 10V applied
electric field, positively charged gold nanorods at the concentration of
6.52×1013 #/mL could deposit MSPhC surface
with the density of 230 #/µm2, which was reasonably
uniform and sparse. Preliminary tests show an absorbance increase near 700 nm on
flat device coated with gold nanorods. Photocurrent measurement is under way to
demonstrate the enhanced hot electron transfer over full visible light and
near-infrared solar spectrum.