  Spatial confinement of matter in functional nanostructures has propelled
these systems to the forefront of nanoscience, both as a playground for exotic
physics and quantum phenomena and in multiple applications including
plasmonics, optoelectronics, and sensing. In parallel, the emergence of
monochromated electron energy loss spectroscopy (EELS) has enabled exploration
of local nanoplasmonic functionalities within single nanoparticles and the
collective response of nanoparticle assemblies, providing deep insight into the
associated mechanisms. However, modern synthesis processes for plasmonic
nanostructures are often limited in the types of accessible geometry and
materials, and even then, limited to spatial precisions on the order of tens of
nm, precluding the direct exploration of critical aspects of the
structure-property relationships. Here, we use the atomic-sized probe of the
scanning transmission electron microscope (STEM) to perform precise sculpting
and design of nanoparticle configurations. Furthermore, using low-loss (EELS),
we provide dynamic analyses of evolution of the plasmonic response during the
sculpting process. We show that within self-assembled systems of nanoparticles,
individual nanoparticles can be selectively removed, reshaped, or arbitrarily
patterned with nanometer-level resolution, effectively modifying the plasmonic
response in both space and energy domains. This process significantly increases
the scope for design possibilities and presents opportunities for arbitrary
structure development, which are ultimately key for nanophotonic design.
Nanosculpting introduces yet another capability to the electron microscope.
