Effects of low-dose γ-irradiation on the structural, morphological, and optical properties of fluorine-doped tin oxide thin films

• Published in: Radiation physics and chemistry (Oxford, England : 1993) Vol. 176; p. 109077
• Main Authors: Oryema, Bosco, Jurua, Edward, Madiba, Itani G., Nkosi, Mlungisi, Sackey, Juliet, Maaza, Malik
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-11-2020; Elsevier BV
• Subjects: Bulk density; Carrier density; Commercial spacecraft; Crystallites; Crystallization; Fluorine; Fluorine-doped tin oxide thin films; Gamma irradiation; Glass substrates; Low-dose γ-irradiation; Morphology; Optical properties; Optical property; Radiation dosage; Room temperature; Spacecraft thermal control coating; Structural property; Surface morphology; Surface properties; Surface roughness; Thermal control coatings; Thin films; Tin oxides; Transmittance; Fluorine-doped tin oxide thin films; Optical property; Spacecraft thermal control coating; Structural property; Low-dose γ-irradiation; Surface morphology
• ISSN: 0969-806X; 1879-0895
• DOI: 10.1016/j.radphyschem.2020.109077

This paper presents the effects of low-dose γ-irradiation on the structural, morphological, and optical properties of Fluorine-doped tin oxide (FTO) thin films for application as a passive thermal control coating in future miniaturized lightweight spacecraft. Commercial-grade FTO films on glass substrate (Pilkington Ltd, UK) with a bulk density of 2.5 g/cm3, sheet resistance of 12 Ω.sq-1, coating thickness of 450 nm, optical band-gap of 3.80 eV, a carrier concentration of 1.50×1020 cm−3 and a mobility of 15 cm2/Vs were irradiated at room temperature and atmospheric pressure using a 60Co gamma source (with gamma energies of 1.17 MeV and 1.33 MeV) at iThemba Laboratory for Accelerator Based Sciences, Cape Town, South Africa. Each sample was exposed to γ-rays for a different span of time to achieve a series of different integrated absorbed doses of 20, 30, and 50 Gy, at a dose rate of 0.207 Gy/min. Evolution in structural properties of the films was characterized using a Bruker AXS D8 Advance XRD with Cu-Kα (λ = 1.54056 Å) scanned in the 2θ degree range of 20 – 80 degrees. Surface properties were analyzed using a VEECO Dimension 1100 AFM machine. Meanwhile, variations in optical transmittance of the films was investigated using a Cary 5000 UV-vis-NIR spectrophotometer of Varian, Inc. model internal DRA- 2500 in the wavelength range of 200 – 2500 nm. XRD results indicate an enhancement of crystallization after irradiation, slight peak shifts, and variations in crystallite sizes with increasing dose. Surface roughness decreased with increasing dose and the grain structures also seen to vary with dose. No significant variations in optical transmittance of the FTO films.
•Gamma radiation had substantial impacts on the structure and morphology of FTO.•No amorphous phase transformations occurred, and no new peaks emerged in films.•Crystallinity of the films increased without altering the basic crystal structure.•Variations in lattice parameters of the films were observed.•Transmittance analysis shows no substantial impact on the optical property.