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Bulk single crystals of CdZnTe compound semiconductor is used for room temperature radiation detection in commercial radiation sensors. A large volume of detector material with low defect density is required for increasing the detection efficiency. Manufacture of such a bulky detector-quality material with low defect density is expensive. In this communication, synthesis of nanowires arrays of CdZnTe that can be used for detecting low energy radiation is reported for the first time. CdZnTe ternary compound semiconductor, referred as CZT, was electrodeposited in the form of nanowires onto a TiO2 nanotubular template in non-aqueous electrolytes using a pulse-reverse process at 130 oC. Very high electrical resistivity of the CZT nanowires (in the order of 10 10 Ω-cm) was obtained. Such a high resistivity was attributed to the presence of deep defect states such as cadmium vacancies created by the anodic cycle of the pulse-reverse electrodeposition process. Stacks of series connected CZT nanowire arrays were impressed with different bias potentials. The leakage current was in the order of tens of PicoAmperes. When exposed to a radiation source (Am -241, 60 keV), the current flow in the circuit increased. The preliminary results indicate that the CZT nanowire arrays can be used as radiation detector materials at room temperature with a much low bias potential (0.7 – 2.3 V) as against 300 – 500 V applied to the bulk detector materials.

The sonoelectrochemical method is a highly efficient technique for the synthesis of well ordered and robust titanium dioxide nanotube arrays. Self ordered arrays of TiO 2 nanotubes of various diameters and length can be rapidly synthesized under an applied potential of 5-20 V in the presence of organic electrolyte solvents like ethylene glycol. The TiO 2 nanotubes prepared in the organic electrolytes and annealed under N 2 atmospheres give a TiO 2 – x C x type of semiconductor materials having a band gap of 2.0 eV. The hybride nanotubes demonstrated promising efficiency in splitting water in the presence of solar light. In addition, the modeling of titania nanotubes using the first principles of the Density Functional Theory (DFT) approach is underway for calculating electronic properties of the TiO 2 nanotubular structure. It is envisioned that the DFT modeling will yield valuable information in developing improved titania photoanodes for high efficiency photoelectrochemical splitting of water. Keywords: titanium dioxide nanotube, photoelectrochemical water splitting, density functional theory

Anodization of Ti in acidified fluoride solution resulted in a vertically oriented and an ordered nanotubular titanium oxide surface. Annealing of the TiO2 nanotubular arrays in a carbonaceous or nitrogen containing atmosphere presumably resulted in band-gap states, which enhanced the photo-activity. Composite electrode of nanotubular TiO2 + carbon doping resulted in a photocurrent density of more than 2.75 mA/cm2 at 0.2 V(Ag/AgCl) under simulated solar light illumination. The enhanced photo-activity of the carbon-modified nanotubular TiO2 is highly reproducible and sustainable for longer duration. The charge carrier densities, calculated based on the Mott-Schottky analyses, were in the range of 1-3 x 1019 cm-3 for both the carbon modified and the nitrogen-annealed nanotubular TiO2 samples. The asanodized and oxygen-annealed samples showed a charge carrier density of 5 x 1017 and 1.2 x1015 cm-3 respectively. In this study, the measured photo current density was not directly related to the charge carrier densities of the nanotubes. Presence of different phases, such as amorphous, anatase and rutile, influenced the photo activity more than the charge carrier density.