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This work reports the growth of stable TiO 2 nanotube arrays on flexible Kapton substrates by electrochemical anodization of a sputtered Ti (titanium) film. Although such nanotubes are conventionally fabricated on Ti foils, obtaining these on polymer-based flexible substrates remained a challenge because of higher annealing temperature not compatible with thermal stability of the substrates. Here, we demonstrate the fabrication of TiO 2 nanotubes (1.5 μm long and 80 nm diameter) by anodization of the Ti film deposited using the RF sputtering technique at two different substrate temperatures (room temperature and 300 °C). Nanoindentation and nanoscratch techniques reveal better adhesion of the Ti film with an underlying Kapton substrate for 300 °C deposition temperature. Such investigations reveal a more than twofold enhancement of the "rear pileup" for the Ti film deposited at elevated temperature compared to that at room temperature. The amorphous TiO 2 nanotubes are crystallized at 220 °C for 3 h using a solvothermal technique that allows crystallization at temperatures much lower than the annealing temperature. Application of these nanotubes for photoelectrochemical water splitting reveals a photocurrent density of 18 μA/cm 2 under AM 1.5 G conditions. Furthermore, the charge density and flat band potential (V FB ) are calculated from Mott−Schottky analysis, showing features comparable to the TiO 2 nanotubes on the Ti foil crystallized through thermal annealing. The present work establishes a scalable approach for developing TiO 2 nanotube arrays on the flexible substrate and its use for photo-electrochemical solar energy conversion.

Current manuscript describes porous alumina (PA) template assisted electrodeposition of high aspect ratio nanowires and dense hierarchical structures of CdTe. We demonstrate here for the first time that simple structural engineering of a PA template can lead to electrochemical growth of diverse shapes of CdTe nanostructures. Facile and cost-effective modifications have been implemented for the fabrication of self-organized through-hole PA membrane and its transfer onto any rough substrate. These modifications have facilitated extended duration (30 minute to 1 hour) electrodeposition of CdTe nanostructures at high bath temperature of 60 • C without delaminating the PA membrane. High aspect ratio nanowires of 60 nm diameter and 2.8 μm length were growth through the self-ordered PA membrane without any underlying metal coating i.e. without altering its optical properties. An average of 56% optical absorption (within 350 nm -1400 nm wavelength) and a moderate photoluminescence was observed for the CdTe nanowires. Minor variation in the anodization process resulted into a non-uniform/branched PA template that enabled the formation of dense 3D hierarchical structures of CdTe using similar electrodeposition conditions as that used for CdTe nanowires. The hierarchical CdTe nanostructures exhibited very high total optical absorption of ∼90% within 350 nm -1400 nm wavelength and a strong photoluminescence was also demonstrated that was almost 10 fold more intense than the CdTe nanowires. CdTe, CdS, CdSe are well established II-VI periodic group optically active chalcogenide semiconductor materials with immense applications in optoelectronic, photonics and bio-labelling applications. Intervention of Nanoscience and Nanotechnology has enabled realization of low dimensional nanostructures of Cadmium chalcogenides (CdS, CdSe, or CdTe) with enhanced surface area to volume ratio that have attracted major appreciation with their unique and enhanced electronic and optical properties.1-3 Specifically, 1D Cadmium chalcogenide nanowires/nanorods have demonstrated highperformance optoelectronic applications such as optical waveguides, lasers, photoluminescence, photodetectors (visible, NIR), solar cells, etc. [4][5][6][7][8][9][10][11][12][13][14][15] It is realized that a precise control over the size and the structure of nanostructures enables vast tuning of the energy band gaps and generates unique optical properties.16 Unlike 2D structures, nanowires can accommodate large amount of mismatch related strain via radial expansion or contraction. It is known that nanowires with high aspect ratio can provide efficient absorption even with smaller depth that can increase the efficacy of photovoltaic devices.17 Especially, CdTe nanowires holds potential for low-cost photovoltaic due to its high absorption coefficient, with a capability of absorbing significant amount of sunlight in a layer thickness of only ∼1 μm, as compared to ∼10 μm for Si. Overall, it is apparent that there has been a major focus onto controlling the structural param...