Thesis (Ph.D.)--University of Texas at Dallas, 2007. / Includes vita. Includes bibliographical references (leaves 94-96).

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (M.S.)--Baylor University, 2006. / Includes bibliographical references (p. 77-80).

Thesis (M.S.) OGI School of Science & Engineering at OHSU, September 2007. / Includes bibliographical references (leaves 72-74).

Thesis (Ph. D.)--Washington State University, May 2007. / Includes bibliographical references (p. 234-257).

Proefschrift Universiteit Maastricht. / Met bibliogr., lit. opg. - Met samenvatting in het Nederlands.

No description available.

Thesis (Ph.D.)--Kent State University, 2008. / Title from PDF t.p. (viewed Oct. 5, 2009). Advisor: D. Mark Manley. Keywords: partial-wave analysis; multichannel; KN scattering; crystal ball. Includes bibliographical references (p. 125-127).

Semiconductor nanowires are of great interest as active components in numerous optoelectronic devices. Therefore, accurate characterisation and control of the nanowire transport properties is of paramount importance for the realisation of nanowire-based devices. With this aim in mind, this thesis presents THz spectroscopy as an ideal, non-contact technique for probing the nanowire electrical conductivity and carrier dynamics, with particular focus on the effect of doping and crystal structure on key device parameters, such as carrier mobilities and lifetimes. Firstly, the effect of 'bulk' n-type and p-type shell doping is investigated in GaAs nanowires. For the first time using an optical pump terahertz probe technique, high extrinsic carrier concentrations on the order of 10¹⁸cm^-3 are extracted for these doped nanowires. An increase in carrier lifetime is demonstrated as a direct result of doping-induced bandbending, highlighting controlled doping as a method for reducing parasitic surface recombination in optoelectronic nanowire-based devices. This result is particularly promising for the development of nanowire solar cells and nanowire lasers, where long carrier lifetimes are required. However, this 'bulk' shell doping technique is synonymous with a reduction in the carrier mobility within the nanowire by over an order of magnitude in comparison to an undoped reference, as a direct result of increased impurity scattering due to doping. As a solution to this inherent reduction in electron mobility associated with 'bulk' doping, modulation doping in GaAs/AlGaAs core-shell nanowires is presented. Enhanced carrier lifetimes are again observed, as dopant electrons passivate trap states at the core-shell interface. Yet, for this doping technique, a lower extrinsic carrier concentration of 10¹⁶cm^-3 is extracted. More importantly, a minimal reduction in the electron mobility is observed compared to an undoped reference sample. By physically separating the donor ions from the photoexcited electrons, impurity scattering is reduced and a high electron mobility maintained. Temperature-dependent terahertz and photoluminescence measurements confirm that the dominant scattering mechanism affecting the electron mobility in these modulation doped nanowires is longitudinal optical phonon scattering, with impurity scattering reduced in comparison to an undoped reference. From these measurements, the dopant activation energy in these nanowires is extracted for the first time via the terahertz spectroscopy, coinciding with literature values for the donors in bulk AlGaAs. An increase in carrier lifetime and radiative efficiency was observed with increasing temperature above the dopant ionisation temperature. This demonstrates the suppression of non-radiative recombination routes in these nanowires, as dopants act to passivate trap states at the core-shell interface, making modulation doped nanowires promising candidates for use in nanowire-based optoelectronic devices. Secondly, the effect of crystal structure in InAsSb nanowires is investigated. Antimony incorporation in InAs nanowires is presented as a method for achieving catalyst-free growth of quasi-pure phase nanowires, where the transport properties of the nanowire are unaffected by defects in the nanowire crystal structure. Utilising an optical pump terahertz-probe technique, an increase in carrier lifetime with increasing antimony content is demonstrated for the first time, which directly correlates with a reduction in defect density due to antimony incorporation. The electron mobilities are also extracted and an increase in mobility with increasing antimony content is observed. This is a direct result of the reduced electron effective mass at higher antimony concentrations, as well as the reduction of interface and defect scattering, associated with decreased defect density at high antimony concentrations. As interface and defect scattering dominates at low temperatures, further enhancement of the electron mobility is expected at low temperatures. Finally, from the knowledge gained from these studies of the nanowire carrier dynamics, two applications of III-V nanowires in terahertz devices are explored. Single-nanowire terahertz detectors based on InP nanowires are demonstrated, with a broad detection bandwidth of up to 2THz and signal to noise ratio of 40, comparable to bulk InP terahertz receivers. An ultrafast terahertz polarisation modulator based on GaAs nanowires is also demonstrated for the first time with picosecond optical switching speeds, a high extinction ratio of 18%, modulation depth of -8dB and dynamic range of -9dB. The performance of these nanowire-based terahertz modulators are comparable to graphene-based terahertz modulators and far surpasses those based on carbon nanotubes, providing a nanoscale platform for ultrafast THz wireless communication.

Fourier Transform Infrared Attenuated Total Reflection Spectroscopy (FTIR-ATR) and Raman microscopy were employed to study the distribution and leaching of the fungicide fluorfolpet in plasticised poly(vinyl chloride) (pPVC) matrixes, along with the diffusion and perturbation of water molecules in the matrixes. Raman mapping and depth profiling were used to determine the molecular distribution of fluorfolpet on the surface and in the bulk of the films respectively. The films were examined both before and after treatment with water at 25°C, in order to study the effect of the leaching of fluorfolpet and its distribution and that of the plasticiser dioctylphthalate (DOP). It was found that the degree of leaching was strongly dependent upon the concentration of DOP in the films, and that leaching occurred from the surface (i.e. film/solvent interface). The distribution of the additives was determined to be "heterogeneous" on the microscopic scale, but "homogeneous" on the macroscopic scale. Additional information such as the rate of migration of the biocide inside the film was obtained using FTIR spectroscopy and the rotating disc method in conjunction with UV spectroscopy. FTIR-ATR was used to investigate the hydration and dehydration of plasticised PVC films. Monitoring of the time dependent change in the nu(OH) mode of water was used to determine the mode of sorption of water into PVC. A dual mode sorption model was found to fit the data well. Diffusion rates of water were found to be strongly dependent on the DOP concentration in the film. It was shown that the "free volume" and the "number of potential binding sites" were determining factors for the diffusion of water in PVC films. A systematic FTIR-ATR study of the perturbation of water sorbed into PVC polymer as a function of plasticiser content and time is reported. The nu(OH) band of water in the polymer has been fitted to individual components, corresponding to those recently found for pure water itself. A detailed quantitative analysis of the frequency shifts and relative intensities of these bands yields direct evidence for the breaking of the water network in the polymer matrix.