Aperiodic Multilayer Graphene Based Tunable and Switchable Thermal Emitter at Mid-infrared Frequencies

Over the past few decades, there have been tremendous innovations in electronics and photonics. The development of these ultra-fast growing technologies mostly relies on fundamental understanding of novel materials with unique properties as well as new designs of device architectures with more diverse and better functionalities. In this regard, the promising approach for next-generation nanoscale electronics and photonics is to exploit the extraordinary characteristics of novel nanomaterials. There has been an explosion of interest in graphene for photonic applications as it provides a degree of freedom to manipulate electromagnetic waves. In this thesis, to tailor the broadband blackbody radiation, new aperiodic multilayer structures composed of multiple layers of graphene and hexagonal boron nitride (hBN) are proposed as selective, tunable and switchable thermal emitters. To obtain the layer thicknesses of these aperiodic multilayer structures for maximum emittance/absorptance, a hybrid optimization algorithm coupled to a transfer matrix code is employed. The device simulation indicates that perfect absorption efficiency of unity can be achieved at very narrow frequency bands in the infrared under normal incidence. It has been shown that the chemical potential in graphene enables a promising way to design electrically controllable absorption/emission, resulting in selective, tunable and switchable thermal emitters at infrared frequencies. By simulating different aperiodic thermal emitters with different numbers of graphene layers, the effect of the number of graphene layers on selectivity, tunability, and switchability of thermal emittance is investigated. This study may contribute towards the realization of wavelength selective detectors with switchable intensity for sensing applications

Electrically injected quantum dot photonic crystal microcavity light emitters and microcavity arrays

Progress in the design, fabrication and characterization of electrically injected photonic-crystal quantum-dot microcavity light sources is described. In the devices investigated in this study, the carriers are injected directly into the photonic crystal microcavity, avoiding the surface state recombination in the photonic crystal pattern. A novel and robust air-bridge contact technology is demonstrated. Spectral linewidths ∼2–3 nm are observed from hexagonal microcavities of varying sizes in the output spectra of oxide-clad microcavity devices. Narrower linewidths ∼1.3 nm are observed from air-clad devices. Results on arrays of densely packed oxide-clad photonic crystal microcavities are also presented. Spectral characteristics of oxide-clad and air-clad devices are compared.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58142/2/d7_9_S09.pd

Engineering Tunable Plasmonic Nanostructures To Enhance Upconversion Luminescence

Plasmonic nanostructures, which can confine and manipulate light below the diffraction limit, are becoming increasingly important in many areas of optical physics and devices. One of the areas that can greatly benefit from surface-plasmon mediated confinement of optical fields is the enhancement of emission in low quantum yield materials. The resonant wavelength for plasmonic structures used for emission enhancement is either the excitation or emission wavelengths of the luminescent material. Therefore, a key component in designing plasmonic structures used in luminescent enhancement applications is the ability to engineer and tune plasmonic building blocks to create structures resonant at the desired wavelength. In this thesis, we have used two approaches to build tunable structures for luminescent enhancement: 1) using already synthesized metallic nanocrystals resonant at the desired wavelengths as building blocks, we designed structures that would result in maximum emission enhancement. 2) Designing arrays of plasmonic nanostructures with the help of simulation software to be resonant at the desired wavelength and then fabricating them with top-down nanoscale fabrication techniques. In either approach, the resulting large area structures were macroscopically studied by steady state and time-resolved photoluminescence measurements to quantify the plasmonic effects on enhancement. We were able to achieve high enhancement factors in almost all of the structures and designs. Furthermore, we were able to identify and study various effects that play a role in plasmonic enhancement processes

Infrared Energy Harvesting for Optoplasmonics from Nanostructured Metamaterials

Metamaterials exhibit unique optical resonance characteristics which permit precise engineering of energy pathways within a device. The ability of plasmonic nanostructures to guide electromagnetism offers a platform to reduce global dependence on fossil fuels by harvesting waste heat, which comprises 60% of generated energy around the world. Plasmonic metamaterials were hypothesized to support an exchange of energy between resonance modes, enabling generation of higher energy photons from waste infrared energy. Infrared irradiation of a metamaterial at the Fano coupling lattice resonance was anticipated to re-emit as higher energy visible light at the plasmon resonance. Photonic signals from harvested thermal energy could be used to power wearable medical monitors or off-grid excursions, for example. This thesis developed the design, fabrication, and characterization methods to realize nanostructured metamaterials which permit resonance exchange for infrared energy harvesting applications

One-dimensional carbon nanostructures for terahertz electron-beam radiation

One-dimensional carbon nanostructures such as nanotubes and nanoribbons can feature near-ballistic electronic transport over micron-scale distances even at room temperature. As a result, these materials provide a uniquely suited solid-state platform for radiation mechanisms that so far have been the exclusive domain of electron beams in vacuum. Here we consider the generation of terahertz light based on two such mechanisms, namely, the emission of cyclotronlike radiation in a sinusoidally corrugated nanowire (where periodic angular motion is produced by the mechanical corrugation rather than an externally applied magnetic field), and the Smith-Purcell effect in a rectilinear nanowire over a dielectric grating. In both cases, the radiation properties of the individual charge carriers are investigated via full-wave electrodynamic simulations, including dephasing effects caused by carrier collisions. The overall light output is then computed with a standard model of charge transport for two particularly suitable types of carbon nanostructures, i.e., zigzag graphene nanoribbons and armchair single-wall nanotubes. Relatively sharp emission peaks at geometrically tunable terahertz frequencies are obtained in each case. The corresponding output powers are experimentally accessible even with individual nanowires, and can be scaled to technologically significant levels using array configurations. These radiation mechanisms therefore represent a promising paradigm for light emission in condensed matter, which may find important applications in nanoelectronics and terahertz photonics.DMR-1308659/National Science Foundationhttp://ultra.bu.edu/papers/Tantiwanichapan-2016-PRB-CNT-THz.pd