LETTERS nature materials | VOL 3 | AUGUST 2004 | www.nature.com/naturematerials 529 M etal oxides are emerging as important materials for their versatile properties such as high-temperature superconductivity, ferroelectricity, ferromagnetism, piezoelectricity and semiconductivity. Metal-oxide films are conventionally grown by physical and chemical vapour deposition 1,2 . However, the high cost of necessary equipment and restriction of coatings on a relatively small area have limited their potential applications. Chemical-solution depositions such as sol–gel are more cost-effective 3 , but many metal oxides cannot be deposited and the control of stoichiometry is not always possible owing to differences in chemical reactivity among the metals. Here we report a novel process to grow metal-oxide films in large areas at low cost using polymer- assisted deposition (PAD), where the polymer controls the viscosity and binds metal ions, resulting in a homogeneous distribution of metal precursors in the solution and the formation of uniform metal–organic films. The latter feature makes it possible to grow simple and complex crack-free epitaxial metal-oxides. One of the challenges in solution-based processes of complex metal- oxide films has been to produce high-quality films with desired chemical composition. We have used a strategy that controls the distribution of metals in solution at a molecular level. We use a mixture of metal precursor and soluble polymer to form a solution with desired viscosity without gelling. The polymer actively binds the metal and serves to both encapsulate the metal to prevent chemical reaction and maintain an even distribution of the metal in solution. This ensures a homogeneous metal distribution and prevents unwanted reactivity that can lead to the formation of undesired phases. These solutions can remain stable for months even when multiple metals are used. In the deposition process reported here, the solution is applied onto a substrate through either spin-coating or dipping. The coated substrate is then treated at a desired Polymer-assisted deposition of metal-oxide films Q. X. JIA 1 *, T. M. MCCLESKEY 2 , A. K. BURRELL 2 , Y. LIN 1 , G. E. COLLIS 2 , H. WANG 1 , A. D. Q. LI 3 AND S. R. FOLTYN 1 1 Superconductivity Technology Center,Division of Materials Science and Technology,and 2 Structural and Inorganic Chemistry, Division of Chemistry, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA 3 Deptartment of Chemistry,Washington State University, Pullman,Washington 99164, USA *e-mail: qxjia@lanl.gov Published online: 18 July 2004; doi:10.1038/nmat1163 Ti O O O O O O Ti 2 – + H 2 N + NH NH 2 N N N O O O O O O N H Sr O O O O O O O O N N 2 – H 2 N + + NH NH 2 a b c Figure 1 A schematic illustration of metals (titanium - green; strontium - yellow) as simple salts or complexes bound to polymers. a,b,Titanium bound to PEI as a catecholate complex (a) and to PEIC (red) directly (b). c, Strontium bound to PEI (blue) as an EDTA complex. ©2004 Nature Publishing Group