Engineering of solution-grown metal oxide heterointerfaces presents an alternative strategy for thin-film transistor development.

The use of ultrasonic spray pyrolysis is demonstrated for the growth of polycrystalline, highly uniform indium oxide films at temperatures in the range of 200-300 °C in air using an aqueous In(NO3)3 precursor solution. Electrical characterization of as-deposited films by field-effect measurements reveals a strong dependence of the electron mobility on deposition temperature. Transistors fabricated at ∼250 °C exhibit optimum performance with maximum electron mobility values in the range of 15-20 cm(2) V (-1) s(-1) and current on/off ratio in excess of 10(6). Structural and compositional analysis of as-grown films by means of X-ray diffraction, diffuse scattering, and X-ray photoelectron spectroscopy reveal that layers deposited at 250 °C are denser and contain a reduced amount of hydroxyl groups as compared to films grown at either lower or higher temperatures. Microstructural analysis of semiconducting films deposited at 250 °C by high resolution cross-sectional transmission electron microscopy reveals that as-grown layers are extremely thin (∼7 nm) and composed of laterally large (30-60 nm) highly crystalline In2O3 domains. These unique characteristics of the In2O3 films are believed to be responsible for the high electron mobilities obtained from transistors fabricated at 250 °C. Our work demonstrates the ability to grow high quality low-dimensional In2O3 films and devices via ultrasonic spray pyrolysis over large area substrates while at the same time it provides guidelines for further material and device improvements.

Metal oxide thin-film transistors are fast becoming a ubiquitous technology for application in driving backplanes of organic light-emitting diode displays. Currently all commercial products rely on metal oxides processed via physical vapor deposition methods. Transition to simpler, higher throughput manufacturing methods such as solution-based processes, are currently been explored as cost-effective alternatives. However, developing printable oxide transistors with high carrier mobility and bias-stable operation has proved challenging. Here we show that hybrid multilayer channels composed of alternating ultra-thin layers (≤4 nm) of indium oxide, zinc oxide nanoparticles, ozone-treated polystyrene and a compact zinc oxide layer, all solution-processed in ambient atmosphere, can be used to create TFTs with remarkably high electron mobility (50 cm 2 /Vs) and record operational stability. Insertion of the ozone-treated polystyrene interlayer is shown to reduce the concentration of electron traps at the metal oxide surfaces and heterointerfaces. The resulting transistors exhibit dramatically enhanced bias stability over 24 h continuous operation and while subjected to large electric-field flux density (2.1×10 -6 C/cm 2 ) with no adverse effects on the electron mobility. Density functional theory calculations identify the origin of this enhanced stability as the passivation of the oxygen vacancy-related gap states due to interaction between ozonolyzed styrene moieties and the oxides. Our results sets new design guidelines for bias-stress resilient metal oxide transistors. Main textMoving away from sophisticated, capital intensive manufacturing processes, soluble semiconductors 1,2,3 not only promise to deliver devices with unusual physical characteristics and enhanced performance, but also trigger a paradigm shift in manufacturing philosophy by embracing scalable, cost-effective processes such as chemical spray pyrolysis, 4 ink-jet printing, 5 slot-die coating, 6 among others. As consequence the interest in solution-based manufacturing of consumer electronics is rapidly increasing with global tech giants investing heavily in emerging forms of printed electronics. 7 Among a variety of soluble electronic materials, oxide semiconductors offer a breadth of intriguing assets, including high charge carrier mobility, 8 optical transparency, 9 versatile synthesis, 10 low manufacturing cost 11 etc., the combination of which makes them ideal for use in a range of rapidly emerging applications in the field of printed electronics. Among them, thin-film transistor (TFTs) technologies are a priority for solution processable oxides as they promise to amplify the technological impact of their vacuum-grown counterparts 11 by reducing the manufacturing cost. For these reasons, continuous research efforts have been devoted to improving the operating characteristics of

The ability to reverse the inherent tendency of noble metals to grow in an uncontrolled three-dimensional (3D) fashion on weakly interacting substrates, including two-dimensional (2D) materials and oxides, is essential for the fabrication of high-quality multifunctional metal contacts in key enabling devices. In this study, we show that this can be effectively achieved by deploying nitrogen (N2) gas with high temporal precision during magnetron sputtering of nanoscale silver (Ag) islands and layers on silicon dioxide (SiO2) substrates. We employ real-time in situ film growth monitoring using spectroscopic ellipsometry, along with optical modeling in the framework of the finite-difference time-domain method, and establish that localized surface plasmon resonance (LSPR) from nanoscale Ag islands can be used to gauge the evolution of surface morphology of discontinuous layers up to a SiO2 substrate area coverage of ∼70%. Such analysis, in combination with data on the evolution of room-temperature resistivity of electrically conductive layers, reveals that presence of N2 in the sputtering gas atmosphere throughout all film-formation stages: (i) promotes 2D growth and smooth film surfaces and (ii) leads to an increase of the continuous-layer electrical resistivity by ∼30% compared to Ag films grown in a pure argon (Ar) ambient atmosphere. Detailed ex situ nanoscale structural analyses suggest that N2 favors 2D morphology by suppressing island coalescence rates during initial growth stages, while it causes interruption of local epitaxial growth on Ag crystals. Using these insights, we deposit Ag layers by deploying N2 selectively, either during the early precoalescence growth stages or after coalescence completion. We show that early N2 deployment leads to 2D morphology without affecting the Ag-layer resistivity, while postcoalescence introduction of N2 in the gas atmosphere further promotes formation of three-dimensional (3D) nanostructures and roughness at the film growth front. In a broader context this study generates knowledge that is relevant for the development of (i) single-step growth manipulation strategies based on selective deployment of surfactant species and (ii) real-time methodologies for tracking film and nanostructure morphological evolution using LSPR.

Nano-structuring of metals is one of the greatest challenges for the future of plasmonic and photonic devices. Such a technological challenge calls for the development of ultra-fast, high-throughput and low-cost fabrication techniques. Laser processing, accounts for the aforementioned properties, representing an unrivalled tool towards the anticipated arrival of modules based in metallic nanostructures, with an extra advantage: the ease of scalability. In the present work we take advantage of the ability to tune the laser wavelength to either match the absorption spectral profile of the metal or to be resonant with the plasma oscillation frequency, and demonstrate the utilization of different optical absorption mechanisms that are size-selective and enable the fabrication of pre-determined patterns of metal nanostructures. Thus, we overcome the greatest challenge of Laser Induced Self Assembly by combining simultaneously large-scale character with atomic-scale precision. The proposed process can serve as a platform that will stimulate further progress towards the engineering of plasmonic devices.

IrO2 shell–Ir−Ni core particulate films (denoted as IrO2 (Ir−Ni)) have been prepared by galvanic replacement of Ni layers electrodeposited on glassy carbon (GC) electrodes. The method involves three steps: immersion of the Ni/GC electrode into a deaerated solution of Ir­(IV) at 65 °C for 15 min (galvanic replacement); electrochemical treatment of the resulting Ir−Ni/GC electrode for anodic dissolution of nonreacted surface Ni and surface enrichment in Ir (formation of a precursor core–shell structure denoted as Ir (Ir−Ni)); anodization of the resulting Ir (Ir−Ni)/GC system (iridium dioxide formation). The resulting IrO2 (Ir−Ni)/GC electrodes have been characterized by SEM/EDS, AFM, and XPS, revealing a particulate morphology (submicron particles), an Ir-rich bulk atomic composition (Ir/Ni atomic ratio of ca. 5), and a thin IrO2 shell. Electrochemical characterization in acid solutions in both the H adsorption/desorption and the oxide formation/reduction potential ranges points to complete surface coverage by IrO2. The prepared IrO2 (Ir−Ni)/GC electrodes have been tested as anodes for oxygen evolution (OER) from acid solutions by means of EIS and steady-state current–potential plots; they have been proven to exhibit superior intrinsic catalytic activity for OER compared to that of plain IrO2 anodically grown on bulk Ir.

The growth mechanism of indium oxide (In 2 O 3 ) layers processed via spray pyrolysis of an aqueous precursor solution in the temperature range of 100-300 °C and the impact on their electron transporting properties are studied. Analysis of the droplet impingement sites on the substrate's surface as a function of its temperature reveals that Leidenfrost effect dominated boiling plays a crucial role in the growth of smooth, continuous, and highly crystalline In 2 O 3 layers via a vapor phase-like process. By careful optimization of the precursor formulation, deposition conditions, and choice of substrate, this effect is exploited and ultrathin and exceptionally smooth layers of In 2 O 3 are grown over large area substrates at temperatures as low as 252 °C. Thin-film transistors (TFTs) fabricated using these optimized In 2 O 3 layers exhibit superior electron transport characteristics with the electron mobility reaching up to 40 cm 2 V −1 s −1 , a value amongst the highest reported to date for solution-processed In 2 O 3 TFTs. The present work contributes enormously to the basic understanding of spray pyrolysis and highlights its tremendous potential for large-volume manufacturing of high-performance metal oxide thin-film transistor electronics.

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