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Title: Anomalous behavior of B{sub 1g} mode in highly transparent anatase nano-crystalline Nb-doped Titanium Dioxide (NTO) thin films

The effect of Niobium doping and size of crystallites on highly transparent nano-crystalline Niobium doped Titanium Dioxide (NTO) thin films with stable anatase phase are reported. The Nb doping concentration is varied within the solubility limit in TiO{sub 2} lattice. Films were annealed in controlled environment for improving the crystallinity and size of crystallites. Elemental and thickness analysis were carried out using Rutherford backscattering spectrometry and cross sectional field emission scanning electron microscopy. Structural characteristics reveal a substitutional incorporation of Nb{sup +5} in the TiO{sub 2} lattice which inhibits the anatase crystallites growth with increasing the doping percentage. The micro-Raman (MR) spectra of films with small size crystallites shows stiffening of about 4 cm{sup −1} for the E{sub g(1)} mode and is ascribed to phonon confinement and non-stoichiometry. In contrast, B{sub 1g} mode exhibits a large anomalous softening of 20 cm{sup −1} with asymmetrical broadening; which was not reported for the case of pure TiO{sub 2} crystallites. This anomalous behaviour is explained by contraction of the apical Ti-O bonds at the surface upon substitutional Nb{sup 5+} doping induced reduction of Ti{sup 4+} ions also known as hetero-coordination effect. The proposed hypotheses is manifested through studying the electronic structure and phononmore » dynamics by performing the near edge x-ray absorption fine structure (NEXAFS) and temperature dependent MR down to liquid nitrogen temperature on pure and 2.5 at.% doped NTO films, respectively.« less
Authors:
; ;  [1] ;  [2] ;  [3] ;  [4]
  1. Material Science Group, Inter University Accelerator Centre, New Delhi -110067 (India)
  2. Department of Electronic Science, University of Delhi South Campus, New Delhi - 110023 (India)
  3. Department of Physics, Bhagini Nivedita College, Delhi University, Delhi– 110043 (India)
  4. UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452017 (India)
Publication Date:
OSTI Identifier:
22492240
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Advances; Journal Volume: 5; Journal Issue: 12; Other Information: (c) 2015 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION SPECTROSCOPY; CONCENTRATION RATIO; DOPED MATERIALS; ELECTRONIC STRUCTURE; FIELD EMISSION; FINE STRUCTURE; NANOSTRUCTURES; NIOBIUM; NIOBIUM COMPOUNDS; NIOBIUM IONS; NITROGEN; PHONONS; RUTHERFORD BACKSCATTERING SPECTROSCOPY; SCANNING ELECTRON MICROSCOPY; SURFACES; TEMPERATURE DEPENDENCE; THIN FILMS; TITANIUM IONS; TITANIUM OXIDES; X-RAY SPECTROSCOPY