Minerals to Materials: Bulk Synthesis of Aqueous Aluminum Clusters and Their Use as Precursors for Metal Oxide Thin Films

We describe a process to produce aqueous precursor solutions of the flat-Al-13 hydroxo cluster (Al-13(mu(3)-OH)(6)(mu(2)-OH)(18)(H2O)(24)(NO3)(15)) via stoichiometric dissolution of bulk Al(OH)(3)(s) in HNO3(aq). We highlight its facility by demonstrating high yields and large-scale synthesis. X-ray diffraction confirms formation of a single-phase product, and Raman spectra show characteristic O-Al-O vibrational modes, both techniques confirming the identity of the flat-Al-13 cluster in the bulk. Al-27 NMR spectroscopy and dynamic light scattering also confirm the presence of the cluster in aqueous solution. We show the as-prepared solution produces smooth and continuous thin films via spin-coating. In capacitors, the films exhibit low leakage currents (near 10 nA/cm(2)) and dielectric constants expected for amorphous Al2O3. Because the precursor preparation requires no postsynthesis purification, it is readily scalable to large volumes.