  Advances in understanding chemical and physical driving forces in
self-assembly allow the fabrication of unique nanoarchitectures with
subwavelength building blocks as the basis for plasmonic and metamaterial
devices. Chemical crosslinking of colloidal nanospheres has produced among the
smallest gap spacings, necessary to obtain regions of greatly enhanced electric
field, hotspots, which are critical to tailor light-matter interactions.
However, obtaining uniform electromagnetic response of dense nanoantennas over
large area for use in devices remains challenging. In this work,
electrohydrodynamic (EHD) flow and chemical crosslinking is combined to form
dense, yet discrete, Au nanosphere clusters (oligomers) on a working electrode.
EHD provides a long range driving force to bring nanospheres together and
anhydride crosslinking yields 0.9 nm gap spacings. Using selective chemistry,
nanospheres are simultaneously crosslinked onto a block copolymer template,
producing oligomers with a narrower wavelength band width and higher hotspot
intensity than monolayer structures produced without a template. We investigate
nanoantenna response via full wave simulations, ultraviolet-visible
spectroscopy, and surface enhanced Raman scattering (SERS). Nanoantennas
exhibit uniform hotspot intensity and gap spacing. Simulations show field
enhancements of 600, correlating well with measured average SERS enhancement of
1.4x10^9. Nanoantenna substrates produce a SERS signal with a relative standard
deviation of 10% measured over a 1 mm2 area, crucial for nano-optical devices
such as optical sensors, among other applications. Understanding long range
(EHD flow) and short range (chemical crosslinking) driving forces provides the
control for assembling colloidal nanoparticles in architectures for large area
plasmonic and metasurface device fabrication.
