Photoinduced formation of thin-film structures in titanium alkoxides via direct deposition from solution and from spin-c
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J. Boyle Sandia National Laboratories, Advanced Materials Laboratory, Albuquerque, New Mexico 87106 (Received 15 July 2010; accepted 28 September 2010)
The photoinduced formation of thin film structures from a Ti-alkoxide precursor (OPy)2Ti(TAP)2, where OPy 5 OC6H6N, TAP 5 OC6H2[CH2N(CH3)2]3-2,4,6, was demonstrated via direct deposition from a pyridine-based solution and by optical illumination of a solid-state spin-coated thin film of the compound. Photopatterned physical relief structures were produced using both of these deposition methods and feature sizes as small as ;1 lm were readily achieved. Surface investigations of the material’s nanostructure revealed that films photo-deposited from solution exhibited nanometer-scale surface roughness with evenly distributed surface porosity (;10 nm sized pores) while films produced through the illumination of spin-coated thin films exhibited, in comparison, a reduction in surface roughness. Vibrational spectra were compared with the results of quantum chemical computations (density-functional theory) of potential photoproducts in an attempt to identify and distinguish the dominant structural groups resulting from the optical processing of each precursor form (i.e., solution versus solid-state). It was determined that ultraviolet irradiation for both thin-film formation techniques resulted in a disruption of the ligand groups, facilitating the initiation of hydrolysis and condensation reactions in the films.
I. INTRODUCTION
The creation of physical relief structures in metal oxide materials via in situ optical processing enables the photopatterning of diverse structures with the potential to impact a broad range of optical (gratings and waveguides),1–4 chemical, and biological, that is, bioselective interfaces and growth media (cellular scaffolding)5 applications. Specifically, the ability to manipulate the thin film structure at the onset of material formation is key to controlling molecular assembly over multiple length scales and can further influence the thin film’s physical, chemical, and optical properties. Photo-mediated processes have been seen to influence molecular structures in a variety of different metal-oxide systems.1–4,6–19 For example, metaloxide gel films that have been chemically modified with additives, such as β-diketones or hydroxyl-substituted aromatic ketones, have been known to exhibit photosensitivity as well as to suppress hydrolysis and condensation reactions at the ligand sites.3,4,7–13 Illumination of these films with UV irradiation has resulted in the decomposition of the chelate rings, altering the solubility of the film in organic solvents or acidic solutions.3,4,7–13 As a result, a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2010.34 754
J. Mater. Res., Vol. 26, No. 6, Mar 28, 2011
http://journals.cambridge.org
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patterned optical exposures with subsequent chemical etching have been used to form spatially defined relief structures.3,4,7–13 Past research has demonstrated that (O
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