Study of Structure, Morphology and Optical Properties of Cobalt-Doped and Co/Al-co-Doped ZnO Thin Films Deposited by Electrospray Method

Abstract

A versatile electrospray method was utilized for deposition of thin ZnO films doped with Co (5%) (CZO) or co-doped with Co (2.5%) and Al (2.5%) (CAZO). Thin polycrystalline films with approximate thickness of 200 nm and high transmittance (more than 80%) were obtained. No additional XRD peaks due to dopant impurities or dopant oxides were observed. The cobalt doping led to decrease in grain size and increase in crystallite size from 22 nm to 29 nm in the (101) direction. Smaller changes were observed for the CAZO films. Surface roughness of the films was measured using a 3D optical profiler. Surface roughness of the doped films was from 5 nm to 9 nm higher than that of the pure films. Refractive index, extinction coefficient and thickness of the films were calculated using ellipsometric measurements and were further used for determination of optical band gap and Urbach energy. Refractive index and optical band gap increased with doping from 1.86 and 3.29 eV for pure ZnO to 2.00 and 3.35 eV for CZO and 1.97 and 3.33 eV for CAZO films. Through calculation of Urbach energy (119 meV for pure ZnO, 236 meV for CZO and 138 meV for CAZO), it was demonstrated that doping leads to an increase in structural disorder, most pronounced in the case of Co doping.

Optimization of Electrospray Deposition Conditions of ZnO Thin Films for Ammonia Sensing

“…Assuming direct transitions, the calculated values for Eg were 3.3 ± 0.1 eV for both R2Z5 and R2Z3 thin films. These values are in very good agreement with the value of 3.29 eV previously obtained for thin transparent ZnO films with roughness of 26 nm deposited on silicon substrate at substrate temperature of 300 • C, feed rate of 15 µL/min and voltage of 18 kV [30]. Therefore, a conclusion could be drawn that the experimental deposition parameters of electrospray do not significantly influence the optical band gap of thin ZnO films.…”

“…The measured diffuse reflectance values Rd were used for calculation of optical band gap, Eg, according to the theory of P. Kubelka and F. Munk [40]. Generally, Eg for ZnO was calculated using the Tauc plot [41], assuming direct transition between valence and conduction bands [30,31]. This means that (α*E) 2 , where α is the absorption coeffi- Figure 4c presents the diffuse reflectance, R d , of R2Z5 and R2Z3 thin films.…”

“…The measured diffuse reflectance values R d were used for calculation of optical band gap, Eg, according to the theory of P. Kubelka and F. Munk [40]. Generally, Eg for ZnO was calculated using the Tauc plot [41], assuming direct transition between valence and conduction bands [30,31]. This means that (α*E) 2 , where α is the absorption coefficient in cm −1 and E is the light energy in eV, is plotted versus E. The value of optical band gap, Eg, is calculated from the cross point of the linear approximation of the plot with x-axis at y-axis value of zero.…”

“…Recently, we used the electrospray method for the deposition of ZnO with well-controlled properties [ 30 , 31 , 32 ]. The method belongs to the family of the so-called “wet” deposition methods because it utilizes solution processing.…”

Enhanced photocatalytic and electrochemical performance of hydrothermally prepared NiO‐doped Co nanocomposites

“…These complexes are valuable because they serve as precursors to metal oxides and provide a good source of cobalt. Nanoparticles from these complexes exhibit distinct optical, structural, and magnetic properties [25][26][27][28][29][30]. Electrochemical techniques like cyclic voltammetry (CV) and impedance spectroscopy are used to understand their electrocatalytic properties better.…”