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

Journal Article · Tue Dec 15 00:00:00 EST 2015 · AIP Advances

DOI:https://doi.org/10.1063/1.4938085· OSTI ID:22492240

Ojha, S.; Singh, Fouran ^[1]; Gautam, Naina ^[2]; Singh, R. G. ^[3]; Shukla, D. K. ^[4]

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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)

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 phonon 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.

• OSTI ID: 22492240
• Journal Information: AIP Advances, Vol. 5, Issue 12; Other Information: (c) 2015 Author(s); Country of input: International Atomic Energy Agency (IAEA); ISSN 2158-3226
• Country of Publication: United States
• Language: English

Related Subjects

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