pubs.acs.org/Langmuir © 2010 American Chemical Society
Bioinspired Deposition of TiO2 Thin Films Induced by Hydrophobins D. Santhiya,*,†,‡ Z. Burghard,† C. Greiner,† Lars P. H. Jeurgens,‡ T. Subkowski,§ and J. Bill† †
Institute for Materials Science, University of Stuttgart, and ‡Department Mittemeijer, Max-Planck-Institute for Metals Research, Heisenbergstrasse 3, 70569 Stuttgart, Germany, and §BASF-SE, GVF/C A-30, D-67056 Ludwigshafen, Germany Received October 19, 2009. Revised Manuscript Received January 4, 2010
The deposition of ceramic thin films from aqueous solutions at low temperature using biopolymers as templates has attracted much attention due to economic and environmental benefits. Titanium dioxide is one of the most attractive functional materials and shows a wide range of applications across vastly different areas because of its unique chemical, optical, and electrical properties. In the present work, we deposited smooth, nanocrystalline titania thin films by an aqueous deposition method on surface active and amphipathic proteins of fungal origin called hydrophobins. Initially, the hydrophobin molecules were self-assembled on a silicon substrate and characterized by angle-resolved X-ray photoelectron spectroscopy (AR-XPS), atomic force microscopy (AFM) and surface potential measurements. Thin films of titanium dioxide were deposited on the surface of hydrophobin self-assembled monolayers from aqueous titanium(IV) bis(ammonium lactate) dihydroxide solution at near-ambient conditions. The microstructure of the asdeposited films was analyzed by AFM, scanning and transmission electron microscopy, which revealed the presence of nanocrystals. The titania films were also characterized using AR-XPS and Fourier transform infrared spectroscopic (FTIR) techniques. Appropriate mechanisms involved in film deposition are suggested. Additionally, nanoindentation tests on as deposited titania films showed their high resistance against mechanical stress.
Introduction Favorable optical, electrical, and chemical properties of titania, for example, high refractive index, permittivity, excellent transmittance of visible light, remarkable solar energy conversion, and photocatalysis, are widely exploited for diverse applications such as microelectronic devices, photonic materials, high-efficiency catalysts, gas sensors, hydrogen storage, inorganic membranes, environmental remediation, ductile ceramics, pigmentation, optical devices, microorganism photolysis, and medical treatments.1-15 Because of these attractive applications, the interest on the fabrication of titania thin films is increasing. There are numerous conventional methods for the deposition of such films, including sol-gel chemistry, vapor-phase deposition, dip-coating processes, and spray pyrolysis. All these techniques have several *To whom correspondence should be addressed. E-mail: deenan.santhiya@ gmail.com. (1) Fujishima, A.; Honda, K. Nature 1972, 238, 37–38. (2) Meng, Q.-B.; Fu, C.-H.; Einaga, Y.; Gu, Z.-Z.; Fujishima, A.; Sato, O. Chem. Mater. 2002, 14, 83–88. (3) Fujishima, A.; Rao, T. N.; Tryk, D. A. Electrochim. Acta 2000, 45, 4683– 4690. (4) Wijnhoven, J. E. G. J.; Vos, W. L. Science 1998, 281, 802–804. (5) Bach, U.; Lupo, D.; Comte, P.; Moser, J. E.; Weiss€ortel; Salbeck, J.; Spreitzer, H.; Gr€atzel, M. Nature 1998, 395, 583–585. (6) Gr€atzel, M. Nature 2003, 421, 586–587. (7) Lakshmi, B. B.; Patrissi, C. J.; Martin, C. R. Chem. Mater. 1997, 9, 2544– 2550. (8) Seo, J. W.; Chung, H.; Kim, M. Y.; Lee, J.; Choi, I. H.; Cheon, J. Small 2007, 3, 850–853. (9) Matsunaga, T.; Tomoda, R.; Nakajima, T.; Nakamura, N.; Komine, T. Appl. Environ. Microbiol. 1988, 54, 1330–1333. (10) Girshevitz, O.; Nitzan, Y.; Sukenik, C. N. Chem. Mater. 2008, 20, 1390– 1396. (11) Larbot, A.; Fabre, J. P.; Guizard, C.; Cot, L. J. Am. Ceram. Soc. 1989, 72, 257–261. (12) Agoudjil, N.; Benkacem, T. Desalination 2007, 206, 531–537. (13) Gouma, P. I.; Mills, M. J.; Sandhage, K. H. J. Am. Ceram. Soc. 2000, 83, 1007–1009. (14) Zhou, Z.; Shinar, R.; Allison, A. J.; Shinar, J. Adv. Funct. Mater. 2007, 17, 3530–3537. (15) Sato, S.; White, J. M. J. Phys. Chem. 1981, 85, 592–594.
6494 DOI: 10.1021/la9039557
drawbacks, such as expensive vacuum equipment, the limitations of line-of-sight deposition, the need to heat the substrates above 400 °C to crystallize the films, and usage of toxic chemicals.16-20 Hence, an attractive alternative approach involves aqueous deposition methods, which allow film formation at low temperatures (
