Thesis advisor: Michael J. Naughton / The nanoscale morphology of metals can enable special functionality in plasmonic and electrochemical devices, with applications in energy conversion and storage, sensors, and computers. In particular, sharp edges on metal nano and microstructures are understood to affect the density of electrons on the metal surface. The associated concentration of electric field can concentrate surface plasmon polaritons (SPPs) and enable waveguiding of the SPPs, as we show in this thesis for sharp ridges along aluminum nanowires. Also important is the presence of facets on the metal structures, which determines the orbitals that electrons occupy on the metal surface. Changes in both the electron density and orbitals can affect the binding of molecules to the metal, which can improve reaction kinetics in catalysis. We demonstrate this on gold dendrite and plate electrocatalysts for CO2 electrolysis. Regarding metal nanostructure fabrication, electrochemical deposition and corrosion have demonstrated promising control over the morphology, including the topography, crystallinity, grain boundaries, and crystal faceting. This is important, because existing methods for metal nanostructure fabrication can only produce a circumscribed assortment of morphologies. In contrast, semiconductors and insulators have many new deposition techniques that produce a wide range of controlled morphologies. Of further appeal, electrochemical techniques are solution-based and typically operate at room temperature and pressure, allowing facile scale-up to industrial production. Here we demonstrate and discuss the mechanisms of two new techniques, which produce the aluminum nanowires and gold dendrites and plates discussed above. / Thesis (PhD) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

<div>Miniaturization of optical components with low power consumption fabricated using a CMOS foundry process can pave the way for dense photonic integrated circuits and on-chip quantum information processing. Optical waveguides, modulators/switches, and single-photon detectors are the key components in any photonic circuits, and miniaturizing them is challenging. This requires strong control of evanescent waves to reduce the cross-talk and bending loss as well as low mode volumes to increase light-matter interaction.</div><div><br></div><div><div>In this thesis, we propose a paradigm shift in light connement strategy using transparent all-dielectric metamaterials. Our approach relies on controlling the optical</div><div>momentum of evanescent waves, an important electromagnetic property overlooked in photonic devices. For practical applications, we experimentally demonstrate</div><div>photonic skin-depth engineering on a silicon chip to conne light and to reduce the cross-talk and bending loss in a dense photonic integrated circuit.</div></div><div><br></div><div><div>We demonstrate that due to the strong light connement in the proposed waveguides, it is possible to miniaturize and integrate superconducting nanowire singlephoton detectors (SNSPDs) into a silicon chip. The timing jitter and dark-count</div><div>rate in these miniaturized SNSPDs can be considerably reduced. Here, we propose a theoretical model to understand the fundamental limits of these nanoscale SNSPDs and the trade-off between timing jitter, dark-count, and quantum effciency in these detectors. We propose experimental tests to verify the validity of our model.</div></div><div><br></div><div><div>Switching/modulating cavity Purcell factor on-chip is challenging, so we have proposed a nonlinear approach to switch Purcell factors in epsilon near zero (ENZ) materials. We demonstrate fourfold change in the Purcell factor with a switching time of 50 fs. The work in this thesis can lead to a unique platform for on-chip quantum nanophotonics.</div></div>