Contents lists available at ScienceDirect Materials Science in Semiconductor Processing journal homepage: www.elsevier.com/locate/mssp Electron transport in surface modiﬁed TiO 2 nanoparticles V. Lionas a , T. Georgakopoulos a , N. Todorova b , S. Karapati b , K. Pomoni a, ⁎ , C. Trapalis b a Department of Physics, University of Patras, 26504 Patras, Greece b Institute of Nanoscience and Nanotechnology, National Centre for Scientiﬁc Research “Demokritos”, 15343 Ag. Paraskevi, Attikis, Greece ARTICLE INFO Keywords: TiO 2 Modiﬁcation Electrical conductivity Conduction mechanisms ABSTRACT Surface modiﬁed nanoparticles of P25 Evonik Degussa TiO 2 with silane coupling agent 3-(2-aminoethylamino) propyltrimethoxysilane (AAPTMS) were prepared at low temperature conditions. The samples were character- ized using the BET technique. Their temperature dependent dc electrical conductivity was investigated in the temperature range 195–440 K. In order to investigate the inﬂuence of the environment, measurements were conducted in vacuum and in air. A change of conductivity with the molar ratio of AAPTMS/P25 is shown. Moreover, a decrease of conductivity is exhibited when compared to that of P25 nanopowder, attributed to the presence of silica in AAPTMS. The modiﬁed samples show a signiﬁcant decrease of conductivity in air. In ad- dition, the conductivity dependence on temperature diﬀers from that in vacuum, suggesting the competition between the adsorption of oxygen and water from the surrounding atmosphere. It was demonstrated that the electrical conduction was controlled by the grain boundaries and the small polaron hopping at the high and intermediate temperatures whereas Mott's variable range hopping was the main conduction mechanism at the lower temperature regime. 1. Introduction Titanium dioxide (TiO 2 ) is one of the more fascinating materials with a wide range of applications in several ﬁelds such as photocatalysis [1–4], gas sensors [5–7], air puriﬁcation [8–10], solar cells [11–13], removal of inorganic and organic pollutants [14–16], self cleaning [17,18] etc. TiO 2 is an inexpensive, nontoxic wide-band gap semi- conductor (~ 3.2 eV) with physical and chemical stability, and high photocatalytic eﬃciency. It crystallizes in three diﬀerent crystalline phases, anatase (tetragonal), rutile (tetragonal) and brookite (orthor- hombic) [19]. Intensive eﬀorts have been made to overcome the low photoeﬃciency and the lack of visible light activity of bare TiO 2 . To date, surface modiﬁcation is one of the most eﬀective approaches on promoting the TiO 2 photocatalytic performance. Surface modiﬁcation can be achieved by several techniques. Among them is the loading of nanosized metals as Pt, Au, Pd and Ag at TiO 2 surface via photo- deposition [20–22], the partial replacement of oxygen by doping with transition metals [23–25] and non-metallic elements [26–28], the polymer TiO 2 nanocomposites [29], and the morphological control, speciﬁcally the exposed {001} facets [30,31]. The surface charge of TiO 2 can also be modiﬁed using metal oxides such as silica, alumina and zirconia. The surface charge modiﬁcation inﬂuences the photo- catalytic reaction rate and mechanism and silica is one of the common inorganic surface charge TiO 2 modiﬁers [4]. The last years a number of studies with silica as TiO 2 surface modiﬁer have been conducted which conﬁrm the enhancement of photocatalytic properties [4,32,33]. On the other hand, the suppression of the photocatalytic activity was reported by some others [34–36] that was attributed to the creation of coating around TiO 2 nanoparticles because of the formation of Ti–O–Si che- mical bonding at the interface of TiO 2 and SiO 2 . Karapati et al. modiﬁed commercial titania P25 nanoparticles modiﬁed with alkaline surfactant AAPTMS [3-(2-aminoethylamino) propyltrimethoxysilane] in water media [10]. The results demonstrated that during modiﬁcation TiO 2 interacted with the amino-groups (–NH 2 ) of AAPTMS and a coating of –SiOH groups was formed around the TiO 2 nanoparticles. The modiﬁed titania powders exhibited improved photocatalytic activity in NO oxi- dation and NO x removal. Apart the study of the optical and structural properties of transition metal oxides, the understanding of their electrical transport mechan- isms is essential for the successful fabrication, performance and eﬃ- ciency of semiconductor devices. The studies of the electrical con- ductivity of the modiﬁed TiO 2 are limited when compared to the considerable amount of research work carried out to improve its pho- tocatalytic activity. The most of them refer to the inﬂuence of doping with transition metals and non-metallic elements and the results de- pend on the preparation technique, the TiO 2 phase, the kind and amount of doping element as well as on the annealing temperature. Joskowska et al. have found an increase of more than three orders of https://doi.org/10.1016/j.mssp.2018.04.012 Received 13 February 2018; Received in revised form 3 April 2018; Accepted 12 April 2018 ⁎ Corresponding author. E-mail address: pomoni@physics.upatras.gr (K. Pomoni). Materials Science in Semiconductor Processing 83 (2018) 63–69 1369-8001/ © 2018 Elsevier Ltd. All rights reserved. T