Abstract
Fluorine-doped tin oxide (FTO) thin films were deposited on glass substrates using ultrasonic spray pyrolysis (USP) at a fixed substrate temperature of 400 °C and various Fluorine/Tin (F/Sn) atomic ratios of 0, 0.1, 0.5, and 1.0. Effects of F/Sn atomic ratios on structural-morphological, compositional, electrical, optical, and nanomechanical properties of the FTO thin films were systematically studied. The FTO films exhibited a tetragonal structure with preferred orientations of (110), (200), and (211), and polycrystalline morphology with spear-like or coconut shell-like particles on the surfaces. The presence of F-doping was confirmed by XPS results with clear F1s peaks, and F-concentration was determined to be 0.7% for F/Sn = 0.1 and 5.1% for F/Sn = 0.5. Moreover, the resistivity of FTO films reduced remarkably from 4.1 mΩcm at F/Sn = 0 to 0.7 mΩcm at F/Sn = 1, primarily due to the corresponding increase of carrier concentration from 2 × 1020 cm−3 to 1.2 × 1021 cm−3. The average optical transmittance of the films prepared at F/Sn of 0–0.5 was over 90%, and it decreased to 84.4% for the film prepared at F/Sn = 1. The hardness (H) and Young’s modulus (E) of the FTO films increased when the F/Sn ratios increased from 0 to 0.5, reaching maximum values of H = 12.3 ± 0.4 GPa, E = 131.7 ± 8.0 GPa at F/Sn = 0.5. Meanwhile, the H and E reduced considerably when the F/Sn ratio further increased to 1.0, following the inverse Hall-Petch effect approximately, suggesting that the grain boundary effect played a primary role in manipulating the nanomechanical properties of the FTO films. Furthermore, favorable mechanical properties with large H/Ef and ratios were found for the FTO film prepared at F/Sn = 0.5, which possessed high crystallinity, large grain size, and compact morphology.
Highlights
Florine-doped tin oxide (FTO) thin films have attracted considerable attention because of their high electronic conduction and optical transparency in the visible region for technological applications, such as flat displays, thin-film solar cells, sensors, organic light emitting diodes, transparent heaters, and architectural glass [1,2,3,4]
Spray pyrolysis deposition (SPD) is a simple, economical, and commonly used method to prepare self-textured FTO thin films with a simple scalable deposition and easy doping process that is achieved by manipulating the substrate temperature, calcinations, gas pressure, and flow rate [1]
Nanomechanical properties hardness and Young’s modulus) of the FTO concentration thin films were (n) and a Gaussian-Lorentzian peak shape. (i.e., In-plane electrical conductivity, carrier obtained by nanoindentation tests (MTS NanoXP® system, MTS Cooperation, Nano Instruments mobility (μ) were measured at room temperature by using a Hall system (Bio-Rad HL5500PC, Hercules, Innovation Center, Oak Ridge, TN, USA)
Summary
Florine-doped tin oxide (FTO) thin films have attracted considerable attention because of their high electronic conduction and optical transparency in the visible region for technological applications, such as flat displays, thin-film solar cells, sensors, organic light emitting diodes, transparent heaters, and architectural glass [1,2,3,4]. Spray pyrolysis deposition (SPD) is a simple, economical, and commonly used method to prepare self-textured FTO thin films with a simple scalable deposition and easy doping process that is achieved by manipulating the substrate temperature, calcinations, gas pressure, and flow rate [1]. To the best of our knowledge, the F-doping- dependent nanomechanical properties of FTO films prepared by USP have not been studied yet. We successfully employed ultrasonic spray pyrolysis (USP, a modified SPD technique) to fabricate FTO thin films on glass substrates. The structural, morphological, compositional, electrical, optical, and nanomechanical properties of polycrystalline FTO thin films prepared at F/Sn atomic ratios of 0, 0.1, 0.5, and 1.0 were systematically studied. The results in this study will provide a strategy for fabricating high-quality FTO thin films with the enhanced both desired material and nanomechanical properties for applications
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