posted on 2023-11-21, 17:03authored byBrian G. Willis, John Grasso, Chengwu Zhang, Rahul Raman
Plasmonic materials exhibit localized plasmon resonances
that collect
light and concentrate electric fields around nanostructures. The field
enhancements are useful for applications such as spectroscopy, catalysis,
and photodetection. Electric field enhancements are dependent on the
materials, geometric designs, and positioning of nanostructures. Plasmonic
dimers are especially effective to concentrate electric fields between
nanostructures, and there is significant interest to develop nanofabrication
strategies to control interparticle distances with subnanometer precision
for arbitrary designs. In this work, we investigate arrays of interconnected
plasmonic dimers with sub-10 nm nanogaps achieved by Cu area-selective
atomic layer deposition (ALD). Nanostructures are made by conventional
nanofabrication methods and subsequently coated with conformal layers
of Cu to control the interparticle distances. Au and Pd layers are
used to activate Cu deposition for homodimer and heterodimer combinations
with and without interconnects. Optical extinction measurements before
and after growth experiments show how plasmon resonances change when
Cu layers expand nanostructures and reduce nanogaps formed between
dimer pairs. Finite difference time domain simulations are used to
model experiments and study how modifications of nanostructure sizes,
thicknesses, and shapes affect plasmonic properties. Our findings
show that Cu ALD can reduce nanogaps below 10 nm for both interconnected
and unconnected nanorods and that interconnected plasmonic dimers
have optical properties similar to unconnected dimers. Moreover, the
ALD process can scale to large arrays of nanostructures. Results are
promising for achieving subnanometer control of interparticle distances
for devices that combine electrical and optical functions with intense
electric fields generated by localized surface plasmon resonances.