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Open AccessArticle

Thermally Stimulated Currents in Nanocrystalline Titania

1
Dipartimento di Fisica e Astronomia, Università di Firenze, Via G. Sansone 1, Sesto Fiorentino, 50019 Firenze, Italy
2
Albert-Ludwigs-Universität Freiburg, Experimentelle Teilchenphysik, Physikalisches Institut, Hermann-Herder Straße 3, 79104 Freiburg im Breisgau, Germany
3
Dipartimento di Ingegneria Industriale, Università di Firenze, Via S. Marta 3, 50139 Firenze, Italy
4
LBT Observatory, University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721, USA
5
Dipartimento di Ingegneria dell’Informazione, Università di Firenze, Via S. Marta 3, 50139 Firenze, Italy
*
Author to whom correspondence should be addressed.
Nanomaterials 2018, 8(1), 13; https://doi.org/10.3390/nano8010013
Received: 31 October 2017 / Revised: 12 December 2017 / Accepted: 12 December 2017 / Published: 5 January 2018
(This article belongs to the Special Issue ZnO and TiO2 Based Nanostructures)
A thorough study on the distribution of defect-related active energy levels has been performed on nanocrystalline TiO2. Films have been deposited on thick-alumina printed circuit boards equipped with electrical contacts, heater and temperature sensors, to carry out a detailed thermally stimulated currents analysis on a wide temperature range (5–630 K), in view to evidence contributions from shallow to deep energy levels within the gap. Data have been processed by numerically modelling electrical transport. The model considers both free and hopping contribution to conduction, a density of states characterized by an exponential tail of localized states below the conduction band and the convolution of standard Thermally Stimulated Currents (TSC) emissions with gaussian distributions to take into account the variability in energy due to local perturbations in the highly disordered network. Results show that in the low temperature range, up to 200 K, hopping within the exponential band tail represents the main contribution to electrical conduction. Above room temperature, electrical conduction is dominated by free carriers contribution and by emissions from deep energy levels, with a defect density ranging within 1014–1018 cm−3, associated with physio- and chemi-sorbed water vapour, OH groups and to oxygen vacancies. View Full-Text
Keywords: thermally stimulated currents; photocurrent; titanium dioxide; hopping; nanoporous film; desorption current; chemisorbed current thermally stimulated currents; photocurrent; titanium dioxide; hopping; nanoporous film; desorption current; chemisorbed current
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MDPI and ACS Style

Bruzzi, M.; Mori, R.; Baldi, A.; Carnevale, E.A.; Cavallaro, A.; Scaringella, M. Thermally Stimulated Currents in Nanocrystalline Titania. Nanomaterials 2018, 8, 13.

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