Scattering-type Scanning Near Field Optical Microscopy (s-SNOM) has been demonstrated as a valuable tool for revealing important properties of materials at nanoscale. Recent proof-of-concept experiments have shown that, among others, s-SNOM can provide quantitative information on the real and imaginary parts of the dielectric function, and hence of intrinsic optical properties of materials and biological samples. In this work we further explored these capabilities in several experiments dealing with microcapsules for drug delivery, ultra-thin optical coatings with tunable color properties, and two types of nanoparticles with important applications in energy storage and conversion, or biosensing and theranostics.
We experimentally demonstrate photocurrent generation from a titanium nitride thin film forming an interface to a zinc
oxide thin film by the illumination of visible light up to 800 nm in wavelength. The photocurrent is attributed to hot
electrons excited in titanium nitride whose excitation is not limited by the bandgap of zinc oxide. Our result paves the
way to use titanium nitride instead of metals for phototectors and solar photocatalysis.
We demonstrate the development of colloidal lithography technique to fabricate large-area plasmonic perfect absorbers using Al, which is an earth abundant low-cost plasmonic material in contrast to Au and Ag. Using numerical electromagnetic simulations, we optimize the geometrical parameters of Al perfect absorbers (AlPAs) with resonances at desired wavelengths depending on the applications. The fabricated AlPAs exhibit narrowband absorptions with high efficiency up to 98 %. By tuning AlPAs parameters, the resonance of AlPAs can be tuned from the visible to the middle infrared region. The AlPAs can be applied for spectrally selective infrared devices such as selective thermal emitters, selective surface-enhanced vibrational spectroscopy (SEIRA) for molecular sensing and selective IR detectors. In this report, we demonstrate applications of AlPAs for selective thermal emitters and SEIRA. The results obtained here reveal a simple technique to fabricate scalable plasmonic perfect absorbers as well as their potential applications in optoelectronic and photonic devices.
Nanosphere lithography (NSL) uses self-assembled layers of monodisperse micro-/nano-spheres as masks to fabricate
plasmonic metal nanoparticles. Different variants of NSL have been proposed with the combination with dry etching
and/or angled-deposition. These techniques have employed to fabricate a wide variety of plasmonic nanoparticles or
nanostructures. Here we report another promising extension - moiré nanosphere lithography (MNSL), which
incorporates in-plane twisting between neighboring monolayers, to extend the patterning capability of conventional
NSL. In conventional NSL, the masks, either a monolayer or bilayer, are formed by spontaneous self-assembly.
Therefore, the resulted colloidal crystal configurations are limited. In this work we used sequential stacking of
polystyrene nanosphere monolayers to form a bilayer crystal at the air/water interfaces. During this layer-by-layer
stacking process, a crystal domain in the top layer gains the freedom to positon itself in a relative angle to that in the
bottom layer allowing for the formation of moiré patterns. Subsequent O2 plasma etching results in a variety of complex
nanostructures that have not been reported before. Using etched moiré patterns as masks, we further fabricated the
corresponding gold nanostructures and characterized their scattering optical properties. We believe this facile technique
provides a new strategy to fabricate novel and complex plasmonic nanostructures or metasurfaces.
Engineering of quantum emissions is regarded as the heart of nano-optics and photonics; local density of optical states (LDOS) around the quantum emitters are critical to engineer quantum emissions, thus detection of the LDOS will impact areas related to illumination, communication, energy, and even quantum-informatics. In this report, we demonstrated a far-field approach to detect and quantify the near-field LDOS of a nanorod via using CdTe quantum dots (QDs) tethered to the surface of nanorods as beacons for optical read-outs. The spontaneous decay of QD emission in the proximity of nanorod was used as a ruler for elucidating the LDOS. Our analysis indicates that the LDOS of the nanorod at its ends is 2.35 times greater than that at the waist. Our approach can be applied for further evaluation and elucidation of the optical states of other programmed nanostructures.