  In this work, the influence of Au plasmonics on photocurrent generation in
the visible wavelength range in integrated thiol-linked CdSe quantum dot/Au
nanogap structures is demonstrated. The plasmonic absorption is sensed
utilizing photoacoustic (PA) detection technique. The laser diode is modulated
to generate the PA excitation that oscillates the air-filled cell. When light
absorption increases, an enhanced acoustic signal is captured by a microphone.
The observed enhancement in the PA response is related to plasmonic absorption
by the Au layers and the response is further enhanced by about 20% due to CdSe
QDs. In our structure, the surface plasmon resonance (SPR) wavelength is
approximately 500 nm. The SPR is utilized for generating photocurrents in CdSe
quantum dots. Due to energy transfer from the dot to closely spaced Au surface
through thiol links, a smooth transmission channel of electrons is established
that forms a detectable photocurrent, which can be tuned by a bias voltage.
These plasmonic nanogap structures can enable higher sensitivity in
photovoltaics, photodetection and sensing.
