Dual-scale rough multifunctional superhydrophobic ITO coatings prepared by air annealing of sputtered indium–tin alloy thin films

• Published in: Applied surface science 2012-10, Vol.258 (24), p.9723-9731
• Main Authors: Gupta, Nitant, Sasikala, S., Mahadik, D.B., Rao, A.V., Barshilia, Harish C.
• Format: Article
• Language: English
• Subjects: Coatings; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Contact angle; Cross-disciplinary physics: materials science; rheology; Deposition; Dual-scale roughness; Exact sciences and technology; Indium tin oxide; Indium-Tin; Multifunctional; Nanostructure; Physics; Roughness; Superhydrophobic surface; Thin films; Three dimensional; X-rays
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2012.06.019

► Sputtered indium–tin coatings were annealed in air to generate superhydrophobic surfaces. ► The coatings also showed multifunctional properties, viz., semi-transparency, conductivity and photoluminescence. ► Dual scale roughness of the samples was detected using FESEM, rendering the drops to be in Cassie wetting state. ► Chemical nature and structure of the coatings was examined by XRD, XPS and micro-Raman analyses. ► The other properties were examined by absorption spectra, sheet resistance and PL spectra measurements. A novel method to fabricate multifunctional indium tin oxide (ITO) coatings is discussed. Superhydrophobic ITO coatings are fabricated by radio frequency balanced magnetron sputter deposition of indium–tin alloy on glass substrates followed by complete oxidation of the samples in air. The chemical nature and structure of the coatings are verified by X-ray diffraction, X-ray photoelectron spectroscopy and micro-Raman spectroscopy. Field emission scanning electron microscopic studies of the coatings display rod-like and blob-like microstructures, together with fractal-like nanostructures infused on top. Microscale roughness of the ITO coatings is measured by three-dimensional profilometry and is found to be in the range of 0.1–3μm. Thus the presence of micro- and nano- sized structures result in dual-scale roughness. The variation in the contact angle with the deposition time is studied using a contact angle goniometer. High water contact angles (>160°) and low contact angle hysteresis (5°) are obtained at an optimum microscale roughness. The ITO coatings also exhibit other functional properties, such as low sheet resistance and semi-transparent behaviour in the visible region. The loss in the transparency of the ITO coatings is attributed to the presence of higher scale of roughness. The photoluminescence measurements show large photoemission in the visible region. It is expected that further improvements in the multifunctional properties of transparent conducting oxides will open new frontiers in designing novel materials with exotic properties.