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 (μ 3 -OH) 6 (μ 2 -OH) 18 (H 2 O) 24 (NO 3 ) 15 ) via stoichiometric dissolution of bulk Al(OH) 3 (s) in HNO 3 (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. 27 Al 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 Al 2 O 3 . Because the precursor preparation requires no postsynthesis purification, it is readily scalable to large volumes.