High-Throughput Continuous Hydrothermal Synthesis of Transparent Conducting Aluminum and Gallium Co-doped Zinc Oxides.

High-throughput continuous hydrothermal flow synthesis was used to generate a library of aluminum and gallium-codoped zinc oxide nanoparticles of specific atomic ratios. Resistivities of the materials were determined by Hall Effect measurements on heat-treated pressed discs and the results collated into a conductivity-composition map. Optimal resistivities of ∼9 × 10-3 Ω cm were reproducibly achieved for several samples, for example, codoped ZnO with 2 at% Ga and 1 at% Al. The optimum sample on balance of performance and cost was deemed to be ZnO codoped with 3 at% Al and 1 at% Ga.

A single-source precursor approach to solution processed indium arsenide thin films.

This paper reports the synthesis of the novel single-source precursor, [{(MeInAs t Bu)3}2(Me2InAs( t Bu)H)2] and the subsequent first report of aerosol-assisted chemical vapour deposition of InAs thin films. Owing to the use of the single-source precursor, highly crystalline and stoichiometric films were grown at a relatively low deposition temperature of 450 °C. Core level XPS depth profiling studies showed some partial oxidation of the film surface, however this was self-limiting and disappeared on etch profiles. Valence band XPS analysis matched well with the simulated density of state spectrum. Hall effect measurements performed on the films showed that the films were n-type with promising resistivity (3.6 × 10-3 Ω cm) and carrier mobility (410 cm2 V-1 s-1) values despite growth on amorphous glass substrates.

High-Throughput Synthesis, Screening, and Scale-Up of Optimized Conducting Indium Tin Oxides.

A high-throughput optimization and subsequent scale-up methodology has been used for the synthesis of conductive tin-doped indium oxide (known as ITO) nanoparticles. ITO nanoparticles with up to 12 at % Sn were synthesized using a laboratory scale (15 g/hour by dry mass) continuous hydrothermal synthesis process, and the as-synthesized powders were characterized by powder X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray analysis, and X-ray photoelectron spectroscopy. Under standard synthetic conditions, either the cubic In2O3 phase, or a mixture of InO(OH) and In2O3 phases were observed in the as-synthesized materials. These materials were pressed into compacts and heat-treated in an inert atmosphere, and their electrical resistivities were then measured using the Van der Pauw method. Sn doping yielded resistivities of ∼ 10(-2) Ω cm for most samples with the lowest resistivity of 6.0 × 10(-3) Ω cm (exceptionally conductive for such pressed nanopowders) at a Sn concentration of 10 at %. Thereafter, the optimized lab-scale composition was scaled-up using a pilot-scale continuous hydrothermal synthesis process (at a rate of 100 g/hour by dry mass), and a comparable resistivity of 9.4 × 10(-3) Ω cm was obtained. The use of the synthesized TCO nanomaterials for thin film fabrication was finally demonstrated by deposition of a transparent, conductive film using a simple spin-coating process.

Synthesis and Structural characterization of ß-ketoiminate-stabilized gallium hydrides for chemical vapor deposition applications.

Bis-ß-ketoimine ligands of the form [(CH2 )n {N(H)C(Me)CHC(Me)O}2 ] (L(n) H2 , n=2, 3 and 4) were employed in the formation of a range of gallium complexes [Ga(L(n) )X] (X=Cl, Me, H), which were characterised by NMR spectroscopy, mass spectrometry and single-crystal X-ray diffraction analysis. The ß-ketoimine ligands have also been used for the stabilisation of rare gallium hydride species [Ga(L(n) )H] (n=2 (7); n=3 (8)), which have been structurally characterised for the first time, confirming the formation of five-coordinate, monomeric species. The stability of these hydrides has been probed through thermal analysis, revealing stability at temperatures in excess of 200 °C. The efficacy of all the gallium ß-ketoiminate complexes as molecular precursors for the deposition of gallium oxide thin films by chemical vapour deposition (CVD) has been investigated through thermogravimetric analysis and deposition studies, with the best results being found for a bimetallic gallium methyl complex [L(3) {GaMe2 }2 ] (5) and the hydride [Ga(L(3) )H] (8). The resulting films (F5 and F8, respectively) were amorphous as-deposited and thus were characterised primarily by XPS, EDXA and SEM techniques, which showed the formation of stoichiometric (F5) and oxygen-deficient (F8) Ga2 O3 thin films.

Aerosol-assisted delivery of precursors for chemical vapour deposition: expanding the scope of CVD for materials fabrication.

The production of thin films of materials has become the attention of a great deal of research throughout academia and industry worldwide owing to the array of applications which utilise them, including electronic devices, gas sensors, solar cells, window coatings and catalytic systems. Whilst a number of deposition techniques are in common use, chemical vapour deposition (CVD) is an attractive process for the production of a wide range of materials due to the control it offers over film composition, coverage and uniformity, even on large scales. Conventional CVD processes can be limited, however, by the need for suitably volatile precursors. Aerosol-assisted (AA)CVD is a solution-based process which relies on the solubility of the precursor, rather than its volatility and thus vastly extends the range of potentially applicable precursors. In addition, AACVD offers extra means to control film morphology and concurrently the properties of the deposited materials. In this perspective we discuss the AACVD process, the influence of deposition conditions on film characteristics and a number of materials and applications to which AACVD has been found beneficial.

Group 13 ß-ketoiminate compounds: gallium hydride derivatives as molecular precursors to thin films of Ga2O3.

Bis(ß-ketoimine) ligands, [R{N(H)C(Me)-CHC(Me)═O}(2)] (L(1)H(2), R = (CH(2))(2); L(2)H(2), R = (CH(2))(3)), linked by ethylene (L(1)) and propylene (L(2)) bridges have been used to form aluminum, gallium, and indium chloride complexes [Al(L(1))Cl] (3), [Ga(L(n))Cl] (4, n = 1; 6, n = 2) and [In(L(n))Cl] (5, n = 1; 7, n = 2). Ligand L(1) has also been used to form a gallium hydride derivative [Ga(L(1))H] (8), but indium analogues could not be made. ß-ketoimine ligands, [Me(2)N(CH(2))(3)N(H)C(R')-CHC(R')═O] (L(3)H, R' = Me; L(4)H, R' = Ph), with a donor-functionalized Lewis base have also been synthesized and used to form gallium and indium alkyl complexes, [Ga(L(3))Me(2)] (9) and [In(L(3))Me(2)] (10), which were isolated as oils. The related gallium hydride complexes, [Ga(L(n))H(2)] (11, n = 3; 12, n = 4), were also prepared, but again no indium hydride species could be made. The complexes were characterized mainly by NMR spectroscopy, mass spectrometry, and single crystal X-ray diffraction. The ß-ketoiminate gallium hydride compounds (8 and 11) have been used as single-source precursors for the deposition of Ga(2)O(3) by aerosol-assisted (AA)CVD with toluene as the solvent. The quality of the films varied according to the precursor used, with the complex [Ga(L(1))H] (8) giving by far the best quality films. Although the films were amorphous as deposited, they could be annealed at 1000 °C to form crystalline Ga(2)O(3). The films were analyzed by powder XRD, SEM, and EDX.