Arash Mohammadpour

Coaxing solid-state phosphorescence from tellurophenes.

The synthesis of the first examples of tellurophenes exhibiting phosphorescence in the solid state and under ambient conditions (room temperature and in air) is reported. Each of these main-group-element-based emitters feature pinacolboronates (BPin) as ring-appended side groups. The nature of the luminescence observed was also investigated using computational methods.

Anodic TiO2 nanotube arrays with optical wavelength-sized apertures

We report on the fabrication and optical properties of very large diameter titanium dioxide nanotube (NT) arrays with inner diameters as large as 900 nm, which surpass the largest inner diameter reported thus far for anodically formed self-organized TiO2 NTs by a factor of 2.5.

Magnetic field-assisted electroless anodization: TiO2 nanotube growth on discontinuous, patterned Ti films

We present a magnetic field-assisted oxidation and etching process that transforms Ti thin films on arbitrary substrates into self-organized TiO2 nanotube arrays without the direct application of an anodization voltage between the cathode and the Ti film/substrate. In effect, the Ti film/substrate electrode is at a floating potential determined by the ionic Hall voltage. The development of such a magnetic field-assisted electroless anodization process, frees the anodization technique of forming nanostructured semiconductors and metal oxides from the constraints of substrate conductivity and film continuity imposed by the traditional anodization process, and allows the creation of uniform anodic nanostructures on pre-existing high-aspect ratio patterns as well as on substrates containing both conductive and non-conductive areas. Using magnetic field assisted electroless anodization, we demonstrate the formation of microscale patterns of high quality TiO2 nanotubes from discontinuous Ti films deposited on thermal oxide-coated Si substrates and patterned by a lift-off process.

Reduced Ensemble Plasmon Line Widths and Enhanced Two-Photon Luminescence in Anodically Formed High Surface Area Au–TiO2 3D Nanocomposites

Localized surface plasmon resonances (LSPR) in TiO2 nanorod and nanotube arrays decorated by gold nanoparticles can be exploited to improve photocatalytic activity, enhance nonlinear optical coefficients, and increase light harvesting in solar cells. However, the LSPR typically has a low quality factor, and the resonance is often obscured by the Urbach tail of the TiO2 band gap absorption. Attempts to increase the LSPR extinction intensity by increasing the density of gold nanoparticles on the surface of the TiO2 nanostructures invariably produce peak broadening due to the effects of either agglomeration or polydispersity. We present a new class of hybrid nanostructures containing gold nanoparticles (NPs) partially embedded in nanoporous/nanotubular TiO2 by performing the anodization of cosputtered Ti-Au thin films containing a relatively high ratio of Au:Ti. Our method of anodizing thin film stacks containing alternate layers of Ti and TiAu results in very distinctive LSPR peaks with quality factors as high as 6.9 and ensemble line widths as small as 0.33 eV even in the presence of an Urbach tail. Unusual features in the anodization of such films are observed and explained, including oscillatory current transients and the observation of coherent heterointerfaces between the Au NPs and anatase TiO2. We further show that such a plasmonic NP-embedded nanotube structure dramatically outperforms a plasmonic NP-decorated anodic nanotube structure in terms of the extinction coefficient, and achieves a strongly enhanced two-photon fluorescence due to the high density of gold nanoparticles in the composite film and the plasmonic local field enhancement.