Optoelectronic properties of layered titanate nanostructure and polyaniline impregnated devices

Abstract

Integrated structure of titanate nanotubes and nanosheets is investigated for their optical, electronic and optoelectronic properties when combined with HCl doped polyaniline (PANI). HR-TEM, SEM and XRD were employed for detailed morphological and microstructural understanding of the orthorhombic titanate nanostructure. Chemisorbed oxygeneous groups are probed with Raman spectroscopy which are found to desorb under UV-Vis treatment. We note a blue shift of Ti-O-Ti Raman frequency in contrast to Na-O-Ti stretching. Valence band region of titanate is analyzed for contribution of O2p, O2s, Na2p and Ti3p. Photoluminescence with different excitation energies revealed the presence of oxygen vacancy related defects in titanate. The highly occupied electronic states of PANI were also analyzed until 40 eV below the Fermi energy. XPS core-level analyses revealed ∼25 % doping density in PANI. Edges of valence band and HOMO are determined to be at 2.45 eV and 2.54 eV below Fermi energy for titanate and PANI, respectively. ITO/PANI/ITO has depicted negative photoresponse and the magnitude of which is reduced ∼4 times after combining with titanate nanostructure. Essentially the nanoscale architecture separates the emeraldine base and salt regions of PANI. This separation channelizes the charge carriers before trapping which reduces the magnitude of the negative photoresponse.