One-Step Formation of Crystalline TiO2 Nanotubular Arrays with Intrinsic p-n Junctions

It,is highly desired to fabricate crystalline TiO2 nanotubes by anodization Without subsequent annealing that may result in cracking and the formation of an interfacial barrier between the nanotubular arrays and the substrate, thus improving the structural integrity and corresponding photoelectric properties. In this work, an attempt was made to fabricate crystalline TiO2 nanotubular arrays through anodization in a. NH4F-containing glycerol electrolyte at room temperature (RT) and 100 degrees C. It was demonstrated that crystalline: nanotubes. were successfully,fabricated at both RT and 100 degrees C. Photocurrent and surface photovoltage spectra of the nanotubes were measured to investigate their photoinduced charge separation efficiency and semiconductor characteristics. It was interesting to observe that the as, fabricated TiO2 nanotubes at RT consisted of both rutile and anatase, confirmed by SAD of TEM, which showed apparent p-type semiconductor characteristics. The mechanism for the formation of crystallites at RT and the possibility to develop intrinsic nanoscale p-n Junctions were discussed. However, the nanotubes anodized at 100 degrees C were in the state of anatase, exhibiting n-type semiconductor characteristics.