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Thorough understanding of the electronic and optical properties of single-walled carbon nanotubes (SWCNTs) will no doubt benefit future technological applications. Since the discovery of band gap photoluminescence from isolated semiconducting SWCNTs, significant progresses in studying the optical properties of SWCNTs have been made (e.g. linear polarization along the tube axis for the absorption and emission of light, excitonic nature in SWCNT excitation). However, there are still several controversial parameters of SWCNTs (e.g. quantum efficiency, absorption cross section, radiative lifetime, and Auger recombination lifetime). With the advancement in SWCNT sample preparation, studies of SWCNT intrinsic properties have shifted from ensemble to a single tube level, in which the ambiguities in elucidating intrinsic properties posed by the assortment of different tube species can be minimized. By examining individual SWCNTs suspended in air, in contrast to micelle-encapsulated SWCNTs, we believe that the environmental effects can be reduced. This thesis will demonstrate the capability of doing spectroscopy on a single semiconducting air-suspended SWCNT. In continuous-wave excitation, the photoluminescence excitation map and high resolution photoluminescence (PL) image of a SWCNT can be constructed, and PL polarization is proven. Quantum efficiency of 5% is experimentally estimated for (9,8) and (10,8) chiral SWCNTs. Pulse excitation allows us to study the intrinsic exciton dynamics of a SWCNT. To gain insight into exciton nonlinear decay processes, PL saturation in pump power dependence measurement is investigated and compared to the simulated results from stochastic models of exciton dynamics. Femtosecond excitation correlation spectroscopy with 150 fs time resolution is employed to time-resolve the PL of a single tube suspended in air. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2008-08-29 13:10:49.045

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vii, 106 leaves : ill. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics, 1968

Metal-polymer nanocomposite materials were found to have highly tunable opti- cal properties. Density functional theory-based calculations were employed to study trends in Ag/polyvinylidene fluoride nanocomposite optical properties. The frequency- dependent imaginary part of the dielectric constant was calculated from dipolar inter- band transitions. The metallic inclusion introduced both occupied and unoccupied states into the large polymer band gap. Thus, higher inclusion volume fractions generally led to stronger composite optical response. Spectra from monodisperse sys- tems correlated well with nanoparticle quantum confinement models. A polydisperse system exhibited optical properties that correlated best with interparticle distances along the field direction. Nanodisk and nanorod-shaped inclusions had tunable re- sponse from field polarization, aspect ratio, crystallographic projections, and nanorod end-cap morphology. / Graduate / 0495

M.Sc. (Physics) / Silicon thin films can be manufactured with the aid of various deposition techniques, each with its own unique properties. In this study the optical properties of silicon manufactured with physical vapour deposition from an electron beam source were studied as a function of layer thickness, deposition rate and substrate temperature. The index of refraction (n and k) as well as optical gap eg. were determined with the aid of characterization models derived specific for optical techniques. These models are covered extensively in the thesis. It was found that the layers were homogeneous and stable, but that the deposition rate and substrate temperature did have a large influence on the properties of the layers. The results show that structural changes, first from the collumnar structure to an amorphous structure and with a further increase in substrate temperature, also a transition from the amorphous to a microcrystalline structure do occure at temperatures considerably lower than what was previously anticipated. With variations in deposition rate it was found that the disorder in the coating will increase with an increase in rate resulting in a reverse transition from the microcrystalline structure to the amorphous structure. Optical gaps in the range 1. 12eV to approximately 1. 38eV were found to be possible with the correct choice of deposition parameters...

The reflectivity of large single crystals of protonated and deuterated (TMTSF)₂Re0₄ and (TMTSF)₂BF₄ has been measured from ≈ 30 cm-¹ to ≈ 8000 cm-¹ using a Bruker IFS 113V Fourier Transform Interferometer for E / a and E / b' above and below the metal--insulator transitions at 177 K and 39 K respectively. The infrared powder absorption spectra of protonated and deuterated (TMTSF)₂Re0₄ has been measured from 200 cm˗¹ to 2000 cm˗¹. The Kramers-Kronig optical conductivity has been calculated from the reflectivity using Drude extrapolations to high frequency. The results for the conductivity for E / a show a one-dimensional density of states, characteristic of a one-dimensional semiconductor with strong electron-phonon coupling, with the vibrations appearing as resonances below the gap and as antiresonances above. The E / b' conductivity is smaller by almost two orders of magnitude than that for E / a, but displays the same semiconducting behavior. The phonons active in the E / b' polarization appear only as resonances. A normal coordinate analysis has been performed for protonated and deuterated TMTSF⁰ and TMTSF⁺. The results have been used to infer the frequencies of vibration and the deuterium shifts of TMTSF⁺⁰ׄ⁵. The molecular frequencies of vibration have been assigned on the basis of their observed frequencies and optical polarization, as well as their deuterium shifts. Some external phonons have also been assigned. The observation that many of the internal and external vibrations are split is due to the eightfold increase in the size of the unit cell (and subsequent reduction of the Brillouin zone) below the metal-insulator transition. The optical properties of the semiconducting state have been modelled for a one--dimensional molecular conductor with a twofold-commensurate charge-density wave, which accurately reproduces the effects of the lattice dimerization and the potential due to the anion chains. The calculations yield the electron-molecular-vibrational coupling constants for the totally symmetric a[formula omitted] vibrations of the TMTSF molecule. The model also yields a transfer integral of 1400 cm-¹ for both materials and semiconducting energy gaps of 2Δ = 1700 cm˗¹ and 2Δ = 1120 cm˗¹ for (TMTSF)₂ReO₄ and (TMTSF)₂BF₄ respectively. The optical conductivity in the E / b' polarization has been discussed in -terms of a two-dimensional band structure with anisotropic transfer integrals. The band structure calculations show the same general features as the measured spectra. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Structural engineering plays an essential role in controlling the optical properties of nanostructures, which are of fundamental and practical interest in nanoscience and technology. In this study, two kinds of nanostructural engineering were investigated systematically to enrich nano-optics research: structural helicity was imposed on plasmonic nanoparticles (NPs) with chiroptical activity engineerable in the ultraviolet (UV)-visible region, and porosification was imposed on silicon nanowires (SiNWs) to tune optical interaction and photoluminescence (PL).. The generation of helical metamaterials, which have strong, engineerable chiroptical activity in the UV-visible region, has attracted increasing attention due to the manipulation of the circular polarization state of light to develop diverse homochirality-associated bio-applications. Glancing-angle deposition with fast substrate rotation is performed to generate plasmonic helical NPs (PhNPs) with a helical pitch (P) of less than 10 nm, which is so much smaller than the wire diameter (d) that the PhNPs appear to be achiral NPs. The PhNPs exhibit chiroptical activity that originates intrinsically from hidden helicity, characterized by circular dichroism (CD). With an increase of P from 3 to 66 nm, the plasmonic CD signals barely shift but show a logarithmic amplification. PhNPs made of aluminum, silver, and copper exhibit a stable chiroptical response from the deep UV (~220 nm) region to the visible region. When an achiral plasmonic nanostructure guest is coated on a PhNP host (i.e., a chiral host@achiral guest nanostructure is created), the achiral guest becomes chiroptically active due to helicity transfer from the chiral host to the achiral guest. Such a helicity transfer can be generally adapted to diverse plasmonic metals to tailor the plasmonic chiroptical response flexibly in the UV-visible region. Furthermore, an amplification of the near-field optical chirality induced by the PhNPs would pave a novel way to performing asymmetric syntheses, for which investigations are currently lacking. Silver PhNPs are used to effectively mediate the enantioselective photocyclodimerization of 2-anthracenecarboxylate: left-handed silver PhNPs lead to a positive ee (enantiomeric excess) value, and right-handed silver PhNPs give rise to a negative ee value. The enantioselectivity is enhanced with a decreasing P. The PhNP-mediated enantioselective photocyclodimerization is ascribed to the synergistic contribution from chirally helical surface-induced enantioselective adsorption of 2-anthracenecarboxylate and chiroptically active nanoplasmon-enhanced optical chirality of near-field circularly polarized light.. Metal-assisted chemical etching (MACE) is carried out to generate mesoporous SiNWs (mp-SiNWs) with mesopores from 2 to 50 nm. The porosification imposes two prominent properties onto SiNWs: a high surface-to-volume ratio and quantum confinement ascribed to the shrinkage of silicon skeletons. Hence, engineering the porosity of SiNWs is of fundamental importance. Here, a new method is devised to reduce the porosity of mp-SiNWs without changes in the MACE conditions. After generating the mp-SiNWs with high porosity, the mp-SiNWs are removed from the mother Si wafers with sticky tape, followed by MACE under the same conditions to produce low-porosity mp-SiNWs. Less porous mp-SiNWs reduce optical scattering from the porous Si skeletons and vertically protrude on the wafer without aggregation to facilitate optical trapping. Consequently, low-porosity mp-SiNWs effectively reduce UV-visible reflection loss. Furthermore, optical applications require surface modification of mp-SiNWs with functional chemicals, which has a prerequisite to passivate mp-SiNWs with H-termination using 5% hydrogen fluoride. 40% NH4F, which has been widely used to passivate Si(111) wafers with H-termination, tends to unexpectedly etch mp-SiNWs attributed to surface F-termination caused by the nucleophilic attack of F− anions to Si atoms. It has been used to study systematically the NH4F-etching rate as a function of the doping levels of SiNWs, surface crystalline orientations, and porosity. At a modest temperature of 110°C, 1,4-diethynylbenzene (DEBZ) is grafted via monosilylation grafted on H-terminated mp-SiNWs. The modified mp-SiNWs with chemically active monolayers is facilely subjected to further chemical modification and surface functionalization. In addition, the monosilylation encodes mp-SiNWs with PL of DEBZ, opening a door to flexible engineering of PL of mp-SiNWs for optoelectronic and bio-detection applications.

A research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg in partial fulfilment of the requirements for the degree of Master of Science / The aim of this work was to evaluate the measurement of the optical properties as a means of obtaining information on the growth history of synthetic diamond. A suite of sample! of known synthesis origin representing the different types of commercially produced synthetic diamond was analysed hy photoluminescence. The photoluminescence intensity was normalising by using the area of tbe Raman peak. This allowed a semi-quantitative comparison of the defect concentration. Three photoluminescent centres were identified, H3, 575 run and 1.945 eV (with zero-phonon lines at 2.463 eV, 2.156 eV, and 1.945 eV respectively). Differences between the intensities of the luminescence due to these centres were observed as a function of the type ot diamond. The H3 amd the 1.945 eV intensity was found to increase with the proporticn of cubic growth sector, In addition the 1.945 eV intensity was found to increase with heat treatment and was higher in {lOO}than in {111} growth sectors. as all three defects detected involve vacancies and nitrogen impurity, an analysis was done to quantify any correlation between the luminescent intensities from the different defects in the same SDA powder sample. The 1.945 eV and 575 nm intensities were observed to be correlated. An additional correlation was found between the 575 nm and the H3 intensities in the case of finer particle size samples. The luminescence intensity for all three defect types was observed to be a function of the particle size of the sample. The shapes and widths of zero-phonon lines were related to the types and concentration of lattice defects present in a crystal according to line broadening theory. An attempt was made to explain the results in the context of the known synthesis origin and growth conditions. / AC2018

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