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 <i><b>flat</b></i><b>-Al</b>_<b>13</b> hydroxo cluster (Al₁₃(μ₃-OH)₆(μ₂-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 <i><b>flat</b></i><b>-Al</b>_<b>13</b> cluster in the bulk. ²⁷Al 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/cm²) and dielectric constants expected for amorphous Al₂O₃. Because the precursor preparation requires no postsynthesis purification, it is readily scalable to large volumes