Optik 144 (2017) 271–280 Contents lists available at ScienceDirect Optik j ourna l ho me pa ge: www.elsevier.de/ijleo Original research article Structural, optical and electrical properties of crystalline V 2 O 5 films deposited by thermal evaporation and effects of temperature on UV–vis and Raman spectra Ravish K. Jain, Atul Khanna ∗ Sensors and Glass Physics Laboratory, Department of Physics, Guru Nanak Dev University, Amrtisar-143005, Punjab, India a r t i c l e i n f o Article history: Received 17 March 2017 Received in revised form 24 June 2017 Accepted 25 June 2017 PACS: 78.20.Nv 61.10.Kw 61.10.Nz 78.20.-e 33.20.Fb Keywords: V2O5 thin films Thermo-optical effect XRR GIXRD Optical properties Raman spectra a b s t r a c t Crystalline V 2 O 5 films of thicknesses in the range: 78–119 nm were prepared on glass sub- strates by thermal evaporation with in-situ substrate heating at 350 ◦ C. XRD studies found the growth of highly oriented orthorhombic V 2 O 5 films with two peaks corresponding to (001) and (002) crystal planes. Raman studies also confirmed the formation of orthorhom- bic V 2 O 5 phase. Electrical studies by two-probe study showed an increase in conductivity with temperature indicating the semiconducting nature of the samples. Optical studies found that UV–vis transmittance is maximum and the reflectance is minimum in film with lowest thickness. The values of activation energy for conduction are 0.15 eV, 0.16 eV and 0.19 eV and those of optical band gap are 2.85 eV, 2.63 eV and 2.67 eV for films of thick- nesses: 78 nm, 88 nm and 119 nm respectively. Grazing incidence X-ray reflectivity studies on the film samples showed that the surface roughness increases with increase in thickness and that the density of the samples is 70.6% of that of the bulk V 2 O 5 . In-situ high temper- ature Raman studies up to 60 ◦ C found that the Raman bands at 283 cm −1 and 305 cm −1 broaden considerably and decrease in intensity with increase in temperature; these bands however recover their original shape on cooling. Both peak broadening and recovery effects occur with time lag of ∼30 min and ∼20 min respectively. A decrease in average UV–vis-NIR transmission of ∼1% was observed with increase in temperature, and this thermo-optical effect is reversible. © 2017 Elsevier GmbH. All rights reserved. 1. Introduction Vanadium has an interesting property of existing in more than one stable oxidation state (multi-valency) and it forms as many as 15 oxide compounds such as VO 2 , V 2 O 3 , V 2 O 5 , V 6 O 13 etc. [1–3]. The oxides of vanadium have several useful properties such as electro-chromic and thermo-chromic behaviour, metal to insulator transition and high temperature coefficient of resistance. Due to these technologically useful properties, vanadium oxides have wide range of applications in bolometers, optoelectronic devices, optical switches, temperature and gas sensors and energy efficient smart windows [1–6]. It is well known that V 2 O 5 exhibits semiconductor to metallic transition at 257 ◦ C, similar to that shown by VO 2 at 68 ◦ C [7]. Kang et al. reported that V 2 O 5 film undergoes metal-insulator transition without any structural phase transition [8]. V 2 O 5 is the most stable oxide phase of vanadium and is a wide band gap (2.3 eV) n-type semiconductor [9]. Various ∗ Corresponding author. E-mail address: atul.phy@gndu.ac.in (A. Khanna). http://dx.doi.org/10.1016/j.ijleo.2017.06.104 0030-4026/© 2017 Elsevier GmbH. All rights reserved.