Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf Effects of bath temperature and deposition time on Co 3 O 4 thin films produced by chemical bath deposition Evren Turan a, ⁎ , Esra Zeybekoğlu b , Metin Kul a a Department of Physics, Eskişehir Technical University, Eskişehir, Turkey b Department of Physics, Giresun University, Giresun, Turkey ARTICLE INFO Keywords: Cobalt oxide Chemical bath deposition Structural properties Optical transitions Dielectric constants Cobalt oxide films have been produced by chemical bath deposition technique at various bath temperatures for different deposition times onto glass substrates. The as-grown Co 3 O 4 films were annealed at 300 °C for 1 h and investigated via x-ray diffraction, field emission scanning electron microscopy. The x-ray diffraction patterns have revealed that the annealed samples are polycrystalline with face-centered-cubic structure. The cubic phase is clearly seen in the form of long rods from micrographs. The band gap of the Co 3 O 4 thin films was determined using absorption spectra. The samples have exhibited direct transition with the band gap values lying in the range between E opt1 = 1.40–1.49 eV and E opt2 = 2.02–2.19 eV. The refractive index and extinction coefficient as a function of wavelength were investigated from reflectance spectrum by applying the envelope method. The optical parameters of the Co 3 O 4 film, such as dielectric constants, plasma frequency, and carrier concentration, were also evaluated. The electrical properties of the samples constructed planar structure have been measured in the dark at room temperature by applying the voltage values between 1 and 100 V. 1. Introduction Metal oxides are attractive materials for thin film electronic and optoelectronic applications due to their compatibility with synthesis on large-area inexpensive glass and flexible plastic substrate. Metal oxides, especially transition metal oxides, comprise a very diverse and fasci- nating class of compounds with properties covering almost all aspects of material science and physics [1]. Among the transition metal oxides, spinel type cobalt oxide (Co 3 O 4 ) is one of the most versatile oxide materials. It has drawn much attention due to its distinctive char- acteristics, which include antiferromagnetic behaviour [2], the ability to act as a p-type semiconductor, and other applications in various fields. Co 3 O 4 has immense potential in a number of applications, such as solar selective absorbers [3], electrochromic devices [4], magnetic materials [5], and gas sensors [6]. In recent years, semiconducting nanoparticles, related to smaller than 100 nm characteristic dimen- sions, have drawn considerable interest owing to their unique optical and electrical properties in comparison with their bulk counterparts. In particular, the synthesis and characterization of transition metal oxide nanoparticles have been an active and challenging subject in materials science and other fields with regard to their physical properties [7]. The nanosized transition metal oxides are expected to lead to even more attractive applications in the conjunction of their traditional arena and nanotechnology [8]. Different techniques have been used for the production of Co 3 O 4 nanoparticles including electrodeposition [9], precipitation [10], rf reactive sputtering [11], spray pyrolysis [12] and chemical bath de- position (CBD) [13, 14]. The CBD is a chemical deposition technique, in which semiconductor films are deposited onto substrates immersed in dilute solutions. The CBD technique has been a more attractive tech- nology because of its simplicity in comparison with conditions re- quiring vacuum or complex equipment. It is a well suited technique for large area coating, low temperature processing and low process cost. Films prepared by this technique are generally polycrystalline in structure and their properties are extremely influenced by the deposi- tion process. Selection of deposition parameters makes it possible to obtain films with a wide variety of features. The major deposition variables are the precursor properties and concentrations, pH, sub- strates, bath temperature, deposition time and annealing. Many experimental studies have been focused on the synthesis, structural and optoelectronic properties of Co 3 O 4 films. As known from the literature, there have been many works on the physical properties of Co 3 O 4 films deposited by the chemical bath technique reported so far [13, 14]. However, there are few investigations about the effects of both bath temperature and deposition time on Co 3 O 4 films to modify the structural and optical properties of the films in the literature. https://doi.org/10.1016/j.tsf.2019.137632 Received 22 June 2018; Received in revised form 6 July 2019; Accepted 10 October 2019 ⁎ Corresponding author. E-mail address: earabaci@anadolu.edu.tr (E. Turan). Thin Solid Films 692 (2019) 137632 0040-6090/ © 2019 Elsevier B.V. All rights reserved. T