Lee Butler

Nanoscale characteristics of single crystal zinc oxide nanowires

In this work, we report the growth and nanoscale characterization of single crystal zinc oxide nanowires synthesized by thermal chemical vapor deposition. Scanning electron microscopy, high-resolution transmission electron microscopy, x-ray diffraction, photoluminescence and Raman spectroscopy confirmed the high quality nature of the materials. To analyze their electrical properties, terahertz time domain spectroscopy was used. Atom probe tomography experiments and analysis were successfully developed and carried out, for the first time, on individual ZnO nanowires. This analysis revealed the incorporation of small concentration levels of atomic nitrogen homogeneously in nanowires grown when nitrogen gas was present during synthesis. Atom probe tomography can yield valuable information on the distribution of dopants and other impurities in wide bandgap semiconductor nanostructures and thus help understand better the material characteristics at the nanoscale.

Design, simulation, and characterization of THz metamaterial absorber

In recent years a great amount of research has been focused on metamaterials, initially for fabrication of left-handed materials (LHM) for use in devices such as superlenses, or electromagnetic cloaking device. [1, 2]. Such devices have been developed and demonstrated in regimes from radio frequency all the way up to infrared and near optical frequencies [3–5]. Metamaterials can be characterized by electric permittivity, e(ω), and magnetic permeability, μ(ω). By manipulating these properties, metamaterials can be engineered to exhibit un-natural phenomena such as negative index of refraction (n eff = Z 0 ), the reflection at some resonance frequency, ω 0 , can be minimized.

Photovoltaic devices based on quantum dot functionalized nanowire arrays embedded in an organic matrix

Quantum dot (QD) functionalized nanowire arrays are attractive structures for low cost high efficiency solar cells. QDs have the potential for higher quantum efficiency, increased stability and lifetime compared to traditional dyes, as well as the potential for multiple electron generation per photon. Nanowire array scaffolds constitute efficient, low resistance electron transport pathways which minimize the hopping mechanism in the charge transport process of quantum dot solar cells. However, the use of liquid electrolytes as a hole transport medium within such scaffold device structures have led to significant degradation of the QDs. In this work, we first present the synthesis uniform single crystalline ZnO nanowire arrays and their functionalization with InP/ZnS core-shell quantum dots. The structures are characterized using electron microscopy, optical absorption, photoluminescence and Raman spectroscopy. Complementing photoluminescence, transmission electron microanalysis is used to reveal the successful QD attachment process and the atomistic interface between the ZnO and the QD. Energy dispersive spectroscopy reveals the co-localized presence of indium, phosphorus, and sulphur, suggestive of the core-shell nature of the QDs. The functionalized nanowire arrays are subsequently embedded in a poly-3(hexylthiophene) hole transport matrix with a high degree of polymer infiltration to complete the device structure prior to measurement.

Quantum dot functionalized ZnO nanowire/P3HT hybrid photovoltaic devices

We report hybrid inorganic/organic photovoltaic heterojunction structures based on quantum dot functionalized nanowires. Single crystalline ZnO nanowires were first functionalized with InP/ZnS core-shell quantum dots and then embedded in a conductive polymer hole matrix to achieve a low cost, high efficiency device structure. The device structures were characterized by scanning electron microscopy, transmission electron microscopy, confocal Raman and photoluminescence spectroscopy. The obtained results show excellent interface properties between the QDs and the ZnO nanowires, a high degree of polymer infiltration into the nanowire array and improved planarization of the polymer matrix.