Alumina thin films are synthesized by combustion synthesis of mixtures of aluminium nitrate (ALN) and methylcarbazate (MCZ). The interdependence of the ratio of oxidizer and reducing agent on composition, microstructure and electronic properties of the resulting oxide layers is investigated. The dielectric and insulating behaviour is improved by addition of different amounts of MCZ (MCZ : ALN = 0.67 or 2.5). In this way films (thickness ∼140 nm) with a dielectric constant κ of 9.7 and a dielectric loss tan δ below 0.015 can be achieved. Medium concentrations of MCZ (MCZ : ALN = 1.0 or 1.5) lead to films with lower performance, though. Our studies indicate two opposing effects of the organic additive. Removal of organic residues during film formation as combustion gases is potentially detrimental. Larger amounts of MCZ, however, cause condensation reactions in the precusor mixture, which improve the microstructure. The porosity of the films can be sucessfully analyzed by positron annihilation liftetime studies. In this way the impact of the organic ligand sphere on the resulting microstructure can be quantified. Samples prepared from ALN alone exhibit mesopores and also larger micropores. In contrast, the formation of mesopores can be inhibited by addition of MCZ.

Abstract Zinc oxide thin films are fabricated by controlled oxidation of sputtered zinc metal films on a hotplate in air at temperatures between 250 and 450 °C. The nanocrystalline films possess high relative densities and show preferential growth in (100) orientation. Integration in thin‐film transistors reveals moderate charge carrier mobilities as high as 0.2 cm2 V−1s−1. The semiconducting properties depend on the calcination temperature, whereby the best performance is achieved at 450 °C. The defect structure of the thin ZnO film can be tracked by Doppler‐broadening positron annihilation spectroscopy as well as positron lifetime studies. Comparably long positron lifetimes suggest interaction of zinc vacancies (VZn) with one or more oxygen vacancies (VO) in larger structural entities. Such VO‐VZn defect clusters act as shallow acceptors, and thus, reduce the overall electron conductivity of the film. The concentration of these defect clusters decreases at higher calcination temperatures as indicated by changes in the S and W parameters. Such zinc oxide films obtained by conversion of metallic zinc can also be used as seed layers for solution deposition of zinc oxide nanowires employing a mild microwave‐assisted process. The functionality of the obtained nanowire arrays is tested in a UV sensor device. The best results with respect to sensor sensitivity are achieved with thinner seed layers for device construction.

Detection of combined defect cluster sites in zinc oxide: Oxidation of plasma sputtered zinc generates zinc oxide films in which Doppler broadening positron annihilation spectroscopy (PAS) and positron annihilation life-time studies (PALS) make it possible to detect oxygen vacancies (Vo) that are in close proximity to zinc vacancies (VZn). They form defect cluster sites acting as shallow acceptors reducing the overall electron conductivity. PAS and PALS is able to correlate semiconducting behavior and microstructure in ZnO thin film transistors. More information can be found in the Full Paper by J. J. Schneider et al. on page 5422.

Abstract Multilayered heterostructures comprising of In2O3, SnO2, and Al2O3 were studied for their application in thin‐film transistors (TFT). The compositional influence of tin oxide on the properties of the thin‐film, as well as on the TFT characteristics is investigated. The heterostructures are fabricated by atomic layer deposition (ALD) at 200 °C, employing trimethylindium (TMI), tetrakis(dimethylamino)tin (TDMASn), trimethylaluminum (TMA), and water as precursors. After post‐deposition annealing at 400 °C the thin‐films are found to be amorphous, however, they show a discrete layer structure of the individual oxides of uniform film thickness and high optical transparency in the visible region. Incorporation of only two monolayers of Al2O3 in the active semiconducting layer the formation of oxygen vacancies can be effectively suppressed, resulting in an improved semiconducting and switching behavior. The heterostacks comprising of In2O3/SnO2/Al2O3 are incorporated into TFT devices, exhibiting a saturation field‐effect mobility (μsat) of 2.0 cm2 ⋅ V−1 s−1, a threshold‐voltage (Vth) of 8.6 V, a high current on/off ratio (IOn/IOff) of 1.0×107, and a subthreshold swing (SS) of 485 mV ⋅ dec−1. The stability of the TFT under illumination is also altered to a significant extent. A change in the transfer characteristic towards conductive behavior is evident when illuminated with light of an energy of 3.1 eV (400 nm).

Aluminum pigments were coated with Fe2O3 and CuO by solution-based thermal decomposition of the urea nitrate compounds hexakisureairon(III)nitrate and tetrakisureacopper(II)nitrate. The deposition process was optimized to obtain homogeneously coated aluminum pigments. The growth of the surface coatings was controlled by investigation with scanning electron microscopy, energy dispersive X-ray spectroscopy and static light scattering as well as infrared, X-ray diffraction and thermogravimetric analysis. The iron precursor showed an incomplete decomposition in solution, incorporating traces of urea molecules inside the coatings while the copper precursor showed complete dissociation accompanied by in situ formation of amine complexes. The amount of organic residues resulting from ligand fragments in the final oxide coatings could be reduced to 22 % for the iron oxide and 12 % for the copper oxide by further temperature treatment in solution (259 °C). Colorimetric investigations of the obtained pigments revealed an excellent hiding power, outperforming the pigments used in current state-of-the-art formulations.

Cobalt-doped zinc oxide single crystals with the shape of hexagonal platelets were synthesized by thermohydrolysis of zinc acetate, cobalt acetate, and hexamethylenetetramine (HMTA) in mixtures of ethanol and water. The mineralization proceeds by a low-temperature dissolution-reprecipitation process from the liquid phase by the formation of basic cobalt zinc salts as intermediates. The crystal shape as well as twin formation of the resulting oxide phase can be influenced by careful choice of the solvent mixture and the amount of doping. An understanding of the course of the reaction was achieved by comprehensive employment of analytical techniques (i.e., SEM, XRD, IR) including an in-depth HRTEM study of precipitates from various reaction stages. In addition, EPR as well as UV/Vis spectroscopic measurements provide information about the insertion of the cobalt dopant into the zincite lattice. The Langmuir-Blodgett (LB) technique is shown to be suitable for depositing coatings of the platelets on glass substrates functionalized with polyelectrolyte multilayers and hence is applied for the formation of monolayers containing domains with ordered tessellation. No major differences are found between deposits on substrates with anionic or cationic surface modification. The adherence to the substrates is sufficient to determine the absolute orientation of the deposited polar single crystals by piezoresponse force microscopy (PFM) and Kelvin probe force microscopy (KPFM) studies.

Generation of dielectric amorphous aluminum oxide using a novel chimie douce molecular precursor route is reported.

Bioinspired mineralization for the production of new functional materials offers mild reaction conditions suitable for integrating biological templates and build hierarchically organized hybrid nanostructures with defined properties. In this respect, the tobacco mosaic virus (TMV) stands out due to its unique structural dimensions. Here, the authors present a novel mineralization pathway for the synthesis of virus-based zinc oxide (ZnO) hybrids with multifunctional properties. Wild-type TMV, two TMV mutants (E50Q and TMV-Cys) and amino-functionalized self-assembled monolayers (NH2-SAMs), as a reference, were used as templates. This mineralization approach allows control of the particle size of the inorganic phase. Further, the virus contributes additionally to the texturing of zinc oxide. Field-effect transistors (FETs) built from the hybrid films, obtained at close to ambient conditions, showed reproducible results at optimized conditions and without posttreatment. This significantly reduced the threshold voltage of the E50Q/zinc oxide FET compared to that of the NH2-SAMs/zinc oxide FET points to the impact of the organic template on FET performance. Nacre-like virus-based zinc oxide multilayers and corresponding monolithic references were prepared. The mechanical properties, namely, Young's modulus, hardness and fracture toughness, were determined and an improvement in the mechanical performance by genetic modification was observed.

Combustion synthesis of dielectric yttrium oxide and aluminium oxide thin films is possible by introducing a molecular single-source precursor approach employing a newly designed nitro functionalized malonato complex of yttrium (Y-DEM-NO(2)1) as well as defined urea nitrate coordination compounds of yttrium (Y-UN 2) and aluminium (Al-UN 3). All new precursor compounds were extensively characterized by spectroscopic techniques (NMR/IR) as well as by single-crystal structure analysis for both urea nitrate coordination compounds. The thermal decomposition of the precursors 1-3 was studied by means of differential scanning calorimetry (DSC) and thermogravimetry coupled with mass spectrometry and infrared spectroscopy (TG-MS/IR). As a result, a controlled thermal conversion of the precursors into dielectric thin films could be achieved. These oxidic thin films integrated within capacitor devices are exhibiting excellent dielectric behaviour in the temperature range between 250 and 350 degrees C, with areal capacity values up to 250 nF cm(-2), leakage current densities below 1.0 x 10(-9) A cm(-2) (at 1 MV cm(-1)) and breakdown voltages above 2 MV cm(-1). Thereby the increase in performance at higher temperatures can be attributed to the gradual conversion of the intermediate hydroxy species into the respective metal oxide which is confirmed by X-ray photoelectron spectroscopy (XPS). Finally, a solution-processed YxOy based TFT was fabricated employing the precursor Y-DEM-NO(2)1. The device exhibits decent TFT characteristics with a saturation mobility (mu(sat)) of 2.1 cm(2) V-1 s(-1), a threshold voltage (V-th) of 6.9 V and an on/off current ratio (I-on/off) of 7.6 x 10(5).

Direct photopatterning of indium zinc oxide (IZO) and zinc tin oxide (ZTO) semiconductors is realized using Schiff‐base complexes of indium, zinc, and tin(II) with methoxyiminopropionato ligands as precursors. These precursor complexes are stable under visible light, but they interestingly decompose in the UV region, thereby facilitating a site‐selective photopatterning and its subsequent conversion to the desired amorphous oxides. Thin film transistors (TFTs) with photopatterned IZO and ZTO layers exhibit high performance after post‐annealing at relatively low temperatures between 250 and 350 °C, with charge‐carrier mobilities ( µ sat ) of 7.8 and 3.6 cm 2 (V s) −1 for IZO and ZTO, respectively. The mechanism of the photodecomposition of the precursor films is studied by attenuated total reflectance–Infrared spectroscopy. Apart from the electrical characterization, the resultant UV‐patterned oxide thin films are characterized by transmission electron microscopy micrographs of focussed ion beam (FIB)‐prepared cross sections, atomic force microscopy, as well as Auger depth profiles. X‐ray photoelectron spectroscopy investigations elucidate the influence of surface hydroxylation on the TFT performance. The straightforward approach of facile precursor UV‐photopatterning demonstrates its potential feasibility as a low‐cost method toward integration of such solution–processed oxide films into large‐area electronics.

Electrophoretic deposition provides an attractive access to semiconductor/conductor bilayers which can be complemented to functional devices like MOS capacitors.

Combustion synthesis of semiconducting amorphous indium gallium zinc oxide IGZO (In:Ga:Zn, 7:1:1.5) thin films was carried out using urea nitrate precursor compounds of indium(III), gallium(III) and zinc(II). This approach provides further understanding towards the oxide formation process under a moderate temperature regime by employment of well-defined coordination compounds. All precursor compounds were fully characterized by spectroscopic techniques as well as by single crystal structure analysis. Their intrinsic thermal decomposition was studied by a combination of differential scanning calorimetry (DSC) and thermogravimetry coupled with mass spectrometry and infrared spectroscopy (TG-MS/IR). For all precursors a multistep decomposition involving a complex redox-reaction pathway under in situ formation of nitrogen containing molecular species was observed. Controlled thermal conversion of a mixture of the indium, gallium and zinc urea nitrate complexes into ternary amorphous IGZO films could thus be achieved. Thin film transistors (TFTs) were fabricated from a defined compositional mixture of the molecular precursors. The TFT devices exhibited decent charge carrier mobilities of 0.4 and 3.1 cm(2)/(Vs) after annealing of the deposited films at temperatures as low as 250 and 350 degrees C, respectively. This approach represents a significant step further towards a low temperature solution processing of semiconducting thin films.

Amorphous zinc tin oxide (ZTO) thin films are accessible by a molecular precursor approach using mononuclear zinc(II) and tin(II) compounds with methoxyiminopropionic acid ligands. Solution processing of two precursor solutions containing a mixture of zinc and tin(II)-methoxyiminopropinato complexes results in the formation of smooth homogeneous thin films, which upon calcination are converted into the desired semiconducting amorphous ZTO thin films. ZTO films integrated within a field-effect transistor (FET) device exhibit an active semiconducting behavior in the temperature range between 250 and 400 °C, giving an increased performance, with mobility values between μ = 0.03 and 5.5 cm2/V s, with on/off ratios increasing from 105 to 108 when going from 250 to 400 °C. Herein, our main emphasis, however, was on an improved understanding of the material transformation pathway from weak to high performance of the semiconductor in a solution-processed FET as a function of the processing temperature. We have correlated this with the chemical composition and defects states within the microstructure of the obtained ZTO thin film via photoelectron spectroscopy (X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy), Auger electron spectroscopy, electron paramagnetic resonance spectroscopy, atomic force microscopy, and photoluminescence investigations. The critical factor observed for the improved performance within this ZTO material could be attributed to a higher tin concentration, wherein the contributions of point defects arising from the tin oxide within the final amorphous ZTO material play the dominant role in governing the transistor performance.

Zinc complexes with multidentate Schiff base ligands are suitable precursors for ZnO in microwave-assisted transformation reactions. [Bis(acetylacetonato)ethylenediimine]zinc(II) and [bis(methylacetoacetato)ethylenediimine]zinc(II) have been synthesized with high purity and good yield from the direct reaction of the respective diimine ligand with diethylzinc in tetrahydrofuran. The thermal decay is studied by thermogravimetry coupled with online infrared spectroscopy. The ceramization reaction in ethoxyethanol yields stable dispersions of spherical ZnO nanoparticles with very small particle sizes (around 5-6 nm), which can be employed for coating and thin-film deposition processes. Field-effect transistors (FETs) composed of thin films fabricated from these semiconducting ZnO particles possess charge-carrier mobilities of 6.0 × 10-3 and 5.4 × 10-2 cm2/(V s) after processing at 350 and 450 °C, respectively. Electrophoretic deposition affords dense film coatings composed of these ZnO nanoparticles with thicknesses of 30-90 nm on ITO (indium tin oxide) glass-electrodes. The positive ζ-potentials of the ZnO nanoparticles in these dispersions are in agreement with the electrocoating process at the cathode.

The solution deposition of ZrO2 thin films from a single-source precursor with oximato ligands allowed the deposition of very uniform and homogenous films. Variation of the film thickness by either employing higher precursor concentrations or the succeeding deposition of multiple layers did not lead to any observable changes in the film morphology. Measurements were carried out using scanning electron microscopy as well as white light interferometry. Detailed investigations of the electrical properties by impedance spectroscopy of capacitors revealed that the relative permittivity is not affected by the processing procedure. No influence of the particular thickness and the number of the individual layers in a stack could be determined. In all cases, the dielectric constant of the amorphous ZrO2 had a value ~ 14.8, as extracted from the impedance at 10 kHz. The method seems attractive for the application in printed electronics as it is robust against changes in the deposition conditions.

Variation of the ligand framework in 1,3-substituted zinc-diketonates provides a straightforward way to control size, morphology and electronic properties of semiconducting zinc oxide nanoparticles.

Amorphous indium zinc oxide (IZO) thin films are accessible by solution-deposition of mixtures of molecular single-source precursors with dimethyl 2-hydroxyimino- and 2-nitromalonato ligands (dmm-NOH and Hdmm-NO2, respectively). Thermal combustion of the precursor molecules In3O3(dmm-NO2)(3)center dot(toluene) and [Zn4O(dmm-NO)(6)] leads to a highly exothermic decomposition reaction yielding amorphous indium zinc oxide (IZO) even at a temperature of 150 degrees C. The main aim of the present investigation is to correlate the electronic performance in such solution processed field-effect transistors (FET) with the presence of surface groups and bulk defects depending on the processing temperatures of the resulting IZO films (250 to 400 degrees C). In depth electronic characterization using X-Ray-and Photoelectron Emission Spectroscopy (XPS and UPS) reveals major electronic changes during thin film formation in the temperature range between 275 and 300 degrees C. These findings are confirmed by Positron Annihilation Spectroscopy (PAS) which allows the monitoring of defects in a picometer range in the resulting functional IZO thin films. Resulting transistor mobilities (mu) of the semiconducting IZO films are in the range of those of amorphous silicon even at a processing temperature of 250 degrees C and increase up to 6 and 9.5 cm(2) (V s)(-1) at 350 and 400 degrees C with on/off ratios of 105 up to 107, respectively.

Heterogeneous dirhodium(II) catalysts based on environmentally benign and biocompatible cellulose nanocrystals (CNC-Rh2) as support material were obtained by ligand exchange between carboxyl groups on the CNC surface and Rh2(OOCCF3)4, as was confirmed by solid-state (19)F and (13)C NMR spectroscopy. On average, two CF3COO(-) groups are replaced during ligand exchange, which is consistent with quantitative analysis by a combination of (19)F NMR spectroscopy and thermogravimetry. CNC-Rh2 catalysts performed well in a model cyclopropanation reaction, in spite of the low dirhodium(II) content on the CNC surface (0.23 mmol g(-1)). The immobilization through covalent bonding combined with the separate locations of binding positions and active sites of CNC-Rh2 guarantees a high stability against leaching and allows the recovery and reuse of the catalyst during the cyclopropanation reaction.