Structural study by solid-state (71)Ga NMR of thin film transistor precursors.

Solid-state (71)Ga NMR was used to investigate the structures of several heterometallic Group 13 hydroxo-aquo clusters, [Ga13-xInx (µ3-OH)6(µ2-OH)18(H2O)24](NO3)15 which are envisioned for thin film transistors. The characterization of these clusters in the solid state provides additional information in understanding the synthesis, structure and speciation of these precursors for high-quality, ultrasmooth thin films. Yet important structural information regarding these clusters - including the exact composition, isomeric structure, and coordination environments - were unknown prior to this precise NMR spectroscopy study. These molecular species, termed "Ga13-xInx", contain three types of six-coordinate metal sites, with bridging OH(-) groups and H2O as capping ligands, and we report results on Ga7In6, Ga8In5, Ga10In3, Ga11In2, Ga12In1, and Ga13. Utilizing two magnetic fields (13.9 T and 21.1 T), the solid-state NMR spectra were interpreted in conjunction with computational modeling (using CASTEP) and simulation of spectral lineshapes (using Dmfit). The metal sites are best represented as distorted octahedra, and they exhibit a range of quadrupolar couplings and asymmetry parameters, which can be addressed using longitudinal strain analysis. Until now, there has been speculation about the sites for transmetallation within the synthetic cluster community. Here, we show that Ga NMR is a powerful technique to monitor the transmetallation of In for Ga in the Ga13-xInx clusters, specifically substituting in the "outer ring" sites, and not the "core" or "middle ring".

An overview of selected current approaches to the characterization of aqueous inorganic clusters.

This Perspective article highlights some of the traditional and non-traditional analytical tools that are presently used to characterize aqueous inorganic nanoscale clusters and polyoxometalate ions. The techniques discussed in this article include nuclear magnetic resonance spectroscopy (NMR), small angle X-ray scattering (SAXS), dynamic and phase analysis light scattering (DLS and PALS), Raman spectroscopy, and quantum mechanical computations (QMC). For each method we briefly describe how it functions and illustrate how these techniques are used to study cluster species in the solid state and in solution through several representative case studies. In addition to highlighting the utility of these techniques, we also discuss limitations of each approach and measures that can be applied to circumvent such limits as it pertains to aqueous inorganic cluster characterization.

Synthesis and solid-state structural characterization of a series of aqueous heterometallic tridecameric group 13 clusters.

The synthesis and solid-state characterization of a complete series of new heterometallic aqueous nanoscale Ga/In tridecameric clusters is presented. These hydroxo-aquo species significantly expand the library of discrete, aqueous group 13 clusters. This report details the synthetic and structural characterization of these compounds, which are of interest as precursors (inks) for thin-film oxides with materials applications. Single-crystal X-ray diffraction (XRD) data show that the hexagonal unit cell lengths of these clusters fall within the range a, b = 20.134-20.694 Å and c = 18.266-18.490 Å. The unit cell volumes become larger (V = 6494-6774 A(3)) with increasing indium occupancy. The compositions of several Ga/In clusters determined by electron probe microanalysis and elemental analysis are in agreement with single-crystal XRD results. The transformation of the Ga/In clusters to metal oxides at high temperature was studied using variable-temperature powder XRD. With heating, the Ga/In clusters with lower indium occupancies convert to the ß-Ga2O3 structure. For clusters with higher indium occupancies, phase separation occurs, and an In2O3 bixbyite-type structure forms. The stoichiometric control at the molecular level demonstrated herein is important in designing functional thin films of metal oxides due to the tunable nature of these heterometallic solution precursors. In addition, information about the solid-state structure of these compounds leads to a fundamental understanding of the materials properties of these clusters for future thin-film and precursor development.

Transmetalation of aqueous inorganic clusters: a useful route to the synthesis of heterometallic aluminum and indium hydroxo-aquo clusters.

[AlxIny(µ3-OH)6(µ-OH)18(H2O)24](NO3)15 hydroxy-aquo clusters (AlxIn13-x) are synthesized through the evaporation of stoichiometrically varied solutions of Al13 and In(NO3)3 using a transmetalation reaction. Several spectroscopic techniques ((1)H NMR, (1)H-diffusion ordered spectroscopy, dynamic light scattering, and Raman) are used to compare AlxIn13-x to its Al13 counterpart. A thin film of aluminum indium oxide was prepared from an Al7In6 cluster ink, showing its utility as a precursor for materials.