Here, we employ a combination of 27 Al solidstate nuclear magnetic resonance (SSNMR) and conventional spectroscopic and microscopic techniques to investigate the structural evolution of aqueous aluminum precursors to a uniform and smooth aluminum oxide film. The route involves no organic ligands and relies on dehydration, dehydroxylation, and nitrate loss for condensation and formation of the threedimensional aluminum oxide structure. Local chemical environments are tracked as films evolve over the temperature range 200−1100 °C. 27 Al SSNMR reveals that Al centers are predominantly four-and five-coordinate in amorphous films annealed between 200 and 800 °C and four-and six-coordinate in crystalline phases that form above 800 °C. The Al coordination of the aqueous-deposited aluminum oxide films are compared to data from SSNMR studies on vapor-phasedeposited aluminum oxide thin films. Additionally, dielectric constants of aluminum oxide-based capacitors are measured and correlated with the SSNMR results. Aluminum oxide is an important material for protective coatings, catalysis, and microelectronic applications. For the latter application, amorphous materials are preferred, but a lack of long-range order complicates structural characterization and determination of structure−property relationships. Solution deposition approaches are attractive alternatives to traditional vapor-phase deposition methods because precursors are commonly stable in air, and they enable printing and direct lithographic patterning on common semiconductor wafers as well as large-area and flexible substratesuseful for scale-up to applications in windows and photovoltaic devices.

Multimeric oxo-hydroxo Al clusters function as models for common mineral structures and reactions. Cluster research, however, is often slowed by a lack of methods to prepare clusters in pure form and in large amounts. Herein, we report a facile synthesis of the little known cluster Al (OH) (H O) (SO ) (Al ) through a simple dissolution method. We confirm its structure by single-crystal X-ray diffraction and show by Al NMR spectroscopy, electrospray-ionization mass spectrometry, and small- and wide-angle X-ray scattering that it also exists in solution. We speculate that Al may form in natural water systems through the dissolution of aluminum-containing minerals in acidic sulfate solutions, such as those that could result from acid rain or mine drainage. Additionally, the dissolution method produces a discrete Al cluster on a scale suitable for studies and applications in materials science.

Herein, we report hydrolysis and condensation chemistries of C 4 H 9 SnCl 3 to molecular clusters and gel films. Precursor speciation plays a key role in film formation and quality toward realization of atomically smooth surfaces. Density functional theory investigations of C 4 H 9 SnCl 3 and its reactions show that hydrolysis of the dimer (C 4 H 9 Sn) 2 (OH) 2 Cl 4 (H 2 O) 2 has a high energetic penalty in the gas phase and when using a polarizable continuum solvation model based on density. These computations support our observed stability of the dimeric cluster in air, in various solvents, and through initial film deposition. It hydrolyzes and condenses to the [(C 4 H 9 Sn) 12 O 14 (OH) 6 ] 2+ dodecamer on-chip after a post film-deposition bake at 80 °C. Consequently, film surface smoothness is uniquely retained through on-wafer condensation.

Metal-oxide thin films find many uses in (opto)­electronic and renewable energy technologies. Their deposition by solution methods aims to reduce manufacturing costs relative to vacuum deposition while achieving comparable electronic properties. Solution deposition on temperature-sensitive substrates (e.g., plastics), however, remains difficult due to the need to produce dense films with minimal thermal input. Here, we investigate combustion thin-film deposition, which has been proposed to produce high-quality metal-oxide films with little externally applied heat, thereby enabling low-temperature fabrication. We compare chemical composition, chemical structure, and evolved species from reactions of several metal nitrate [In­(NO3)3, Y­(NO3)3, and Mg­(NO3)2] and fuel additive (acetylacetone and glycine) mixtures in bulk and thin-film forms. We observe combustion in bulk materials but not in films. It appears acetylacetone is removed from the films before the nitrates, whereas glycine persists in the film beyond the annealing temperatures required for ignition in the bulk system. From analysis of X-ray photoelectron spectra, the oxide and nitrate content as a function of temperature are also inconsistent with combustion reactions occurring in the films. In­(NO3)3 decomposes alone at low temperature (∼200–250 °C) without fuel, and Y­(NO3)3 and Mg­(NO3)2 do not decompose fully until high temperature even in the presence of fuel when used to make thin films. This study therefore distinguishes bulk and thin-film reactivity for several model oxidizer-fuel systems, and we propose ways in which fuel additives may alter the film formation reaction pathway.

We describe a process to produce aqueous precursor solutions of the flat -Al 13 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 flat -Al 13 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.