Localized surface plasmons have been reported for periodic 2D monolayer black phosphorene (BP) nanoribbons in the infrared region. The anisotropic nature of BP causes different plasmonic effects depending on their orientation over select dielectric substrates, leading to tunability and promising future applications in imaging and other detectors. Computational models are used to demonstrate that by tuning the localized plasmonic resonance, as well as the orientation of the BP nanoribbon, it is possible to obtain desired coupled resonance modes and enhanced absorption capabilities. The modes obtained from the absorption spectra span the infrared range and extend our understanding of BP plasmons.
This work advances the fabrication capabilities of a two-step lithography technique known as nanomasking for patterning metallic nanoslit (nanogap) structures with sub-10-nm resolution, below the limit of the lithography tools used during the process. Control over structure and slit geometry is a key component of the reported method, exhibiting the control of lithographic methods while adding the potential for mass-production scale patterning speed during the secondary step of the process. The unique process allows for fabrication of interesting geometric combinations such as dual-width gratings that are otherwise difficult to create with the nanoscale resolution required for applications, such as nanoscale optics (plasmonics) and electronics. The method is advanced by introducing a bimetallic fabrication design concept and by demonstrating blanket nanomasking. Here, the need for the secondary lithography step is eliminated improving the mass-production capabilities of the technique. Analysis of the gap width and edge roughness is reported, with the average slit width measured at 7.4±2.2 nm. It was found that while no long-range correlation exists between the roughness of either gap edge, and there are ranges in the order of tens of nanometers over which the slit edge roughness is correlated or anticorrelated across the gap. This work helps quantify the nanomasking process, which aids in future fabrications and leads toward the development of more accurate computational models for the optical and electrical properties of fabricated devices.
Plasmonic nanodevices are metallic structures that exhibit plasmonic effects when exposed to light, causing scattering and enhancement of that light. These plasmons makes it possible for light to be focused below the diffraction limit. Dark-field spectroscopy has been used to capture the scattering spectra of these structures in order to examine the scattering and resonant frequencies of the plasmons provided by the devices. The geometries of the devices change which wavelengths of light are most readily able to couple to the device, resulting in a change in the wavelength of the scattered light. A variety of device geometries and configurations will be studied, including nanodiscs, nanowires, and plasmonic gratings, along with double-width nanogap plasmonic gratings. These new structures will have features below the fabrication limit of electron-beam lithography, i.e. sub-10 nanometer features. The polarization dependencies of these resonance modes are investigated as well. A relation between device geometry and wavelength will be drawn; in effect, this will allow the selection of geometry of the fabricated device based on the desired wavelength of light to be scattered. Preliminary Raman spectroscopy will also be performed in order to study the device response and usefulness for surface-enhanced Raman spectroscopy.
This work thoroughly investigates gold nanowires with various cross-sectional geometries and patterns. The study has determined the effect of the cross section aspect ratio on its maximum optical enhancement. The plasmonic optical enhancement properties of single gold nanowires and an array of three nanowires were investigated using finite element method simulations. The results indicate a significant dependence of the optical enhancement on both the thickness and width of the nanowires. From the simulation data, an equation for each geometry (single and triple array) was found that relates the dimensions and incident wavelength to the optical enhancement. These relationships can be a valuable resource while designing nanowires to optimize the dimensions and provide the maximum possible optical enhancement.
Making use of a newly established nanomasking technique, nanoscale features (sub-10 nm) have been fabricated with the potential to act as plasmonic enhancement structures. The technique makes use of a two-step lithography process to simultaneously produce many plasmonic hotspots with two-dimensional features over a large area, showing promise for mass production scalability. This technique is highly reproducible, reliably patterning multiple nanostructures and nanogaps over a potentially wafer-scale area without significantly increasing the number of steps required. Fabrication results show promise for scalability towards applications such as biosensing, photovoltaics, and enhanced spectroscopies.
Plasmonic structures can be used to enhance electromagnetic radiation, and nanoscale (<5 nm) gaps can increase this
enhancement even further. Fabrication of these desired structures involves using a relatively new, previously developed
self-aligned process to overcome typical electron beam lithography resolution limits. The resulting nanogap structures
have been shown to exhibit enhanced optical emission. This technique enables the fabrication of a large-area two-dimensional
matrix of such nanostructures which could prove useful for photovoltaics, plasmonically enhanced Raman
spectroscopy, biosensing, and other optoelectronic applications. Computational electromagnetic simulations of the
structures will prove useful for predicting behavior upon interaction with light and for experimental comparison.
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