Approved for public release; distribution is unlimited / Knowledge of transport parameters is important to the development of new optoelectronic materials and devices, such as ultraviolet (UV) semiconductor lasers and advanced solar cells. A series of experiments was performed to measure fundamental transport parameters in luminescent semiconductor materials. Using a technique that couples a scanning electron microscope (SEM) in spot mode with a charge coupled display (CCD) camera, it is possible to image the recombination of charge created at a point. The goal is to extract fundamental transport parameters, such as minority carrier diffusion length (Ldiffusion)) and drift length (Ldrift), with high spatial resolution. Direct transport imaging was used to study diffusion without bias and drift under a range of applied electric fields. The recombination distribution as a function of applied bias was imaged. For the unbiased measurements, the results showed that for bulk n-type GaAs the spotwidth was independent of probe current indicating the luminescence distribution is primarily a function of generation volume and not diffusion length. For thin layer samples that could be approximated as two dimensional (2D), it was found that the spotwidth changed as a function of probe current indicating the potential to extract diffusion length data. Results are compared to numerical modeling of charge transport and the feasibility and limitations of this method for contact-free measurements of lifetime ()̥ and mobility (æ) are assessed. / DOD Civilian, NAWCWD China Lake, California

Wan, Xi. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

No description available.

This thesis presents novel results in the field of plasmonics and optoelectronics application. Plasmonics is the rapidly expanding branch of photonics. It opens up capabilities of electronic and photonic device implementation within the same integrated circuits as well as enhances the limit of detection for chemical and biological-based sensors. The first finding lies in solving the dilemma in search of ultimate plasmonics materials for plasmonics application. It is well known that Cu and Ag are metals that have incredible electric and optic properties. However, they are easily oxidized in contact with air. Both experimental and theoretical findings demonstrate that application of a mono or bilayer graphene protects Cu and Ag from oxidation and degradation of its plasmonic properties. The performance of each metal is evaluated based on the quality factor Q and the minima in amplitude of reflection intensity Rmin of the Surface plasmon-polariton (SPP) curve. The second novelty of this thesis comprises the fabrication of low loss, high efficient broadband, as well as narrowband, graphene-based electro-absorption modulators. The studied graphene-based modulators made use of Fabry-Perot resonator geometries. It has been shown that high-k dielectric hafnium dioxide (HfO2) provides solid state “supercapacitor” effects and allows to observe light modulation from the near-infrared to shorter wavelengths close to the visible spectrum with remarkably low gate voltages (~4 V). The electro-absorption modulators based on Fabry-Perot resonator geometry reached the modulation depth in transmission mode of 28% at a wavelength of 1.1 Âμm.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Optical trapping is an important tool for studying and manipulating nanoscale objects. Recent experiments have shown that subwavelength control of nanoparticles is possible by using patterned plasmonic nanostructures, rather than using a laser directly, to generate the electric fields necessary for particle trapping. In this thesis we present a theoretical model and experimental evidence for plasmonic optical trapping in nanoscale metal junctions. Further, we examine the use of the resultant devices as ultrasmall photodectors. Electromigrated nanojunctions, or “nanogaps”, have a well-established plasmon resonance in the near-IR, leading to electric field enhancements large enough for single-molecule sensitivity in Surface-Enhance Raman (SERS) measurements. While molecule-based devices have been carefully studied, optically and electrically probing individual quantum dots in nanoscale metal junctions remains relatively unexplored. Plasmon-based optical trapping of quantum dots into prefabricated structures could allow for inexpensive, scalable luminescent devices which are fully integrable into established silicon-based fabrication techniques. Additionally, these metal-nanocrystal-metal structures are ideal candidates to study optoelectronics in ultrasmall nanocrystals-based structures, as well as more exotic nanoscale phenomena such as blinking, plasmon-exciton interactions, and surface-enhanced fluorescence (SEF). We present experimental data supporting plasmon-based optical trapping in the nanogap geometry, and a corresponding numerical model of the electric field-generated forces in the nanogap geometry. Further, we give proof-of-concept measurements of photoconductance in the resultant quantum dot-based devices, as well as challenges and improvements moving forward.

Innovation on human-machine interfacing technologies is critical for the development of smart, multifunctional and efficient electronic/optoelectronic systems. The effect of piezotronics is a newly started field of study, which utilizes piezoelectric polarization that is mechanically induced inside a piezoelectric semiconductor to regulate electron transport across electronic contact interfaces. With the concept coined in 2006, many efforts have been contributed to studying the underlying physical mechanism of this effect as well as demonstrating various applications based on single nanowire piezotronic devices. This thesis selects ZnO as the material foundation and was started by firstly studying flexible, controllable and scalable synthesis methods for ZnO nanowires array and thin film. By replacing the use of random, individual nanowires with these materials, novel piezotronic and piezophototronic devices were designed, fabricated and tested to achieve the function of strain sensing, tactile imaging, piezo-enhanced photodetection and solar energy harvesting. The adoption of nanowires array and thin film materials over single nanowires leads to significant advantages in terms of scalable fabrication, industrial compatibility and broader functionality. By consistently going down this route, we believe that the field of piezotronics will eventually make revolutionary impact on MEMS, optoelectronics, multifunctional sensor networks, human-machine interfacing and so on.

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

No description available.

This thesis focuses on the investigation of the optoelectronic, photo and thermal- responsive properties of organoboron compounds. In search of blue phosphors for phosphorescent organic light emitting diodes, new triarylboron functionalized phosphorescent Pt(II) complexes were synthesized and their device performances were evaluated. In Pt(II) complexes with the 2-phenylpyridyl N,C-chelate ligand and an acetylacetonato ancillary ligand, it was found that BMes2 substitution at the 4’ position of the phenyl ring can increase the phosphorescent emission energy, compared to the 5’-BMes2 substituted analogue. This occurred without substantial loss of luminescent quantum efficiency. At 100 cdm-2 luminance, electroluminescence devices with the newly synthesized Pt(II) complexes as emitters have achieved external quantum efficiency of ~ 4.7-13.4%. Tuning of the photo-responsive properties of biaryl N,C-chelate dimesitylboron compounds was achieved by functionalization with either a bisthienyl moiety or ferrocene unit. It was demonstrated that the bisthienyl unit has the ability to completely stabilize a N,C-chelate boryl chromophore toward photoisomerization. With the ferrocene unit being part of the chelation backbone of BMes2 moiety, the B−N bond of molecule B(2-ferrocenyl-N-Me-benzimidazolyl)Mes2 was found to undergo a dynamic dissociation/association process in solution, leading to its slow hydrolysis under ambient conditions. The oxidized ferrocenium species has a notable spin delocalization through space from the Fe(III) center to a flanking mesityl group. To further expand the photochromic family based on pyridyl N,C-chelate dimesityboron compounds, a systematic study was carried out with the pyridyl N donor replaced by N-heterocyclic carbene donor and azolyl, benzoazolyl N donors. These new classes of organoboranes all underwent transformation to their corresponding dark isomer in a similar fashion as the pyridyl N,C-chelate dimesitylboron. However, a second-step photoisomerization was observed in the NHC,C-chelate dark isomer via a “borylene”-like intermediate. The thiazolyl, benzoazolyl N,C-chelate dark isomers demonstrate multi-structural transformations, which include hydrogen atom transfer, 1,3-boryl shift and diastereomer interconversion via a spiropyran type ring-opening/closure process. The imidazolyl N,C-chelate dark isomer exhibits a consecutive photochromism phenomenon, namely an interconversion between azaboratabisnorcaradiene and azabenzotropilidene derivatives. The calculated mechanism for this bares an interesting resemblance to that of the “walk” rearrangement in norcaradiene. / Thesis (Ph.D, Chemistry) -- Queen's University, 2014-06-23 20:55:20.399