Semiconducting properties of In2O3 nanoparticle thin films in air and nitrogen

Oil soluble In₂O₃ nanoparticles were synthesized via the decomposition of indium acetylacetonate in organic solution. In₂O₃ nanoparticle thin films were prepared by spin-coating the dichloromethane solution of In₂O₃ on SiO₂/Si substrates and annealing at various temperatures. X-ray diffraction and scanning electron microscopy show that the In₂O₃ nanoparticles are spherical and the quality of thin film surface varies with annealing temperature and time. Field-effect transistor devices of the In₂O₃ nanoparticles were fabricated and their electronic characteristics were studied in air and nitrogen. The semiconducting properties can be tuned by modifying exposing time of the In₂O₃-based devices in air. The electron mobility and on–off current ratio have a dramatic change in the starting stage exposed in air, suggesting the device is sensitive to air due to the presence of nanostructures in the In₂O₃ thin films. The results suggest that the In₂O₃ thin film device may find applications in gas sensors.     

Influence of a heterolayered Al2O3–ZrO2/Al2O3 ceramic protective overcoat on the high temperature performance of PdCr thin film strain gauges

The application of PdCr thin film strain gauges on gas turbine engines requires protective overcoats to prevent the oxidation of the PdCr sensitive element. In this work, a heterolayered Al₂O₃–ZrO₂/Al₂O₃ ceramic film, which was fabricated by electron beam evaporation, is utilized as a protective overcoat over the PdCr sensitive thin film. The morphology and microstructure of the prepared films indicate that the composite Al₂O₃–ZrO₂ film is smooth and compact, and the interface between the composite Al₂O₃–ZrO₂ film and Al₂O₃ film is crack-free, which contributes to improving the protective performance of the heterolayered Al₂O₃–ZrO₂/Al₂O₃ ceramic protective overcoat at high temperature. Moreover, the PdCr thin film strain gauge with heterolayered Al₂O₃–ZrO₂/Al₂O₃ ceramic film as protective overcoat displays a minimum drift rate of less than 0.09%/h at 800 °C, and excellent cyclic repeatability such that the eight cyclic curves of the relative grid resistance are almost overlapped from room temperature to 800 °C, indicating the excellent protecting performance of the heterolayered Al₂O₃–ZrO₂/Al₂O₃ ceramic overcoat. It also reveals the smallest temperature coefficient of resistance of 155.3 ppm/°C compared to the monolayer Al₂O₃ overcoat and composite Al₂O₃–ZrO₂ overcoat.     

Fabrication and microstructure evolution of Al2O3/ZrBN-SiCN/Al2O3 high-temperature oxidation-resistant composite coating

The oxidation-resistance of thin film sensors, particularly at high temperatures, is critical for the lifetime and performance of the sensor. The preparation and oxidation-resistance of an Al₂O₃/ZrBN-SiCN/Al₂O₃ composite film with a sandwich-structure was performed using reactive magnetron sputtering. The microstructure evolution of the composite film is examined herein using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) analysis. Oxygen diffusion was significantly inhibited by the formation of crystalline Al₂SiO₅ and Zr-B-C amorphous phase inside the composite film. The Pt-13%Rh/Pt thin film thermocouple (TFTC) with the Al₂O₃/ZrBN-SiCN/Al₂O₃ composite film as a protective layer was fabricated and calibrated. Both the stability and lifetime of the TFTC was significantly enhanced for temperatures up to 1000?℃. The test error of the TFTC was reduced by half, compared with that of the TFTC with the Al₂O₃ protective layer, indicating an excellent oxidation-resistant performance of the composite film.     

The Influence of ZrO2 Additions on Al2O3 Evaporation and AlN Crystal Growth by Thermal Nitridation of Al2O3–ZrO2 Pellets

The effects of ZrO₂ additions to Al₂O₃ were investigated to improve the evaporation rate of Al₂O₃ for bulk AlN crystal growth. The evaporation rate of Al₂O₃ increased concomitantly with increasing ZrO₂ concentration under a nitrogen gas stream at 2223 K. The ZrO₂ was predominantly nitrided. The nitridation of ZrO₂ kept the local oxygen partial pressure high at the pellet surface, which suppressed the nitridation of Al₂O₃. The nitridation of ZrO₂ caused the outward diffusion of ZrO₂ (Zr⁴⁺ and O^2?) in the pellet, which was accelerated further by the presence of Al₂O₃–ZrO₂ liquid phase in grain boundaries, leading to the prompt formation of ZrN porous layer on the pellet surface. The suppressed nitridation of Al₂O₃ and the formation of porous ZrN layer were the reasons for the enhanced evaporation of Al₂O₃, leading to enhanced bulk AlN growth.     

Fabrication and characterization of MOCVD (In1-xAlx)2O3 (0.1≤x≤0.6) ternary films

A series of (In_1-xAl_x)₂O₃ (0.1 ≤ x ≤ 0.6) films with tunable bandgap were grown on MgO (100) substrates by MOCVD. The influences of chemical compositions and growth temperatures on the film properties were studied systematically. XRD analyses indicated that the film quality degraded from crystalline to amorphous structure as Al concentration (x) increased. The (In_1-xAl_x)₂O₃ films prepared at 700 °C exhibited better film crystallinity than those of the ones grown at 600 °C. The films prepared at 700 °C with x = 0.1–0.3 showed an epitaxial In₂O₃ <111> orientation with the corresponding growth relationship of In₂O₃ (111)∥MgO (100). The film with x = 0.2 exhibited the best crystallinity and the largest grain size of 25.9 nm. The Hall mobilities and resistivities of the films were influenced evidently by Al concentrations. The Hall mobility showed a monotonous decrease from 12 to 1.1 cm²V^?1s^?1 as x increased from 0.1 to 0.6. The lowest resistivity of 9.2 × 10^?3 Ω cm was acquired for the film with x = 0.2. The average transmittances in the visible region for all the films were beyond 83%. The bandgap of the (In_1-xAl_x)₂O₃ films can be regulated in the range of 3.85–4.88 eV by changing Al concentrations from 0.1 to 0.6.     

Growth of nanolaminate structure of tetragonal zirconia by pulsed laser deposition

Alumina/zirconia (Al₂O₃/ZrO₂) multilayer thin films were deposited on Si (100) substrates at an optimized oxygen partial pressure of 3 Pa at room temperature by pulsed laser deposition. The Al₂O₃/ZrO₂ multilayers of 10:10, 5:10, 5:5, and 4:4 nm with 40 bilayers were deposited alternately in order to stabilize a high-temperature phase of zirconia at room temperature. All these films were characterized by X-ray diffraction (XRD), cross-sectional transmission electron microscopy (XTEM), and atomic force microscopy. The XRD studies of all the multilayer films showed only a tetragonal structure of zirconia and amorphous alumina. The high-temperature XRD studies of a typical 5:5-nm film indicated the formation of tetragonal zirconia at room temperature and high thermal stability. It was found that the critical layer thickness of zirconia is ≤10 nm, below which tetragonal zirconia is formed at room temperature. The XTEM studies on the as-deposited (Al₂O₃/ZrO₂) 5:10-nm multilayer film showed distinct formation of multilayers with sharp interface and consists of mainly tetragonal phase and amorphous alumina, whereas the annealed film (5:10 nm) showed the inter-diffusion of layers at the interface.     

A new sol-gel route to prepare dense Al2O3 thin films

Anew sol-gel route has been applied to synthetize dense Al₂O₃thin films from aluminum isopropoxide (Al(OPri)₃)as raw precursor material. The results show that, in the solution, acetylacetone (AcAc) and aluminum form a complex compound which effectively suppresses the growth of colloidal particles and makes the sol very stable. Al₂O₃thin films fabricated by spin-coating method and calcined at 500 °C for 3 h possess an amorphous structure and exhibit a highly homogeneous surface texture without evidence of holes or cracks throughout the film. Moreover, the prepared films display a low leakage current and a high transmittance. This new sol-gel route appears to be a highly promising method to synthetize dense Al₂O₃ thin films from Al(OPrⁱ)₃, and could provide a wide range of optical and electric applications.     

Effect of CeO2 and Al2O3 contents on Ce‐ZrO2/Al2O3 composites

Effect of CeO₂ and Al₂O₃ contents on phase composition, microstructures, and mechanical properties of Ce–ZrO₂/Al₂O₃ composites was studied. The CeO₂ content in CeO₂–ZrO₂ varied from 7 to 16 mol%, and the Al₂O₃ content in Ce‐ZrO₂/Al₂O₃ composites were 7 and 22 wt%. When CeO₂ content was ≤10 mol%, high Al₂O₃ content contributed to hinder the tetragonal‐to‐monoclinic ZrO₂ phase transformation during cooling and decrease the density of microcracks in the composites. Tetragonal ZrO₂ single‐phase was obtained in the composites with ≥12 mol% CeO₂, regardless of the Al₂O₃ content. Hardness, flexural strength, and toughness were dependent on CeO₂ and Al₂O₃ contents which were related to the microcracks, grain size, and phase transformation. The high flexural strength and toughness of the composites with 7wt% Al₂O₃ could be obtained at an optimum CeO₂ content of 12 mol%, whereas those of the composites with 22 wt% Al₂O₃ could be achieved in the wide CeO₂ content range of 8.5‐12 mol%.     

Growth of AlN Crystals on SiC Substrates by Thermal Nitridation of Al2O3

The growth of AlN crystals on c‐plane 6H–SiC substrates by thermal nitridation of Al₂O₃ pellets in the presence of graphite and ZrO₂ was demonstrated. Addition of graphite and ZrO₂ effectively accelerated the evaporation of Al₂O₃, yielding c‐axis oriented AlN films on SiC substrates. The SiC substrate was severely deteriorated at 2173 K, which produced a porous interface between the AlN film and substrate, resulting in low‐quality AlN crystals. The deterioration of SiC was successfully suppressed by introducing a pre‐deposited homo‐buffer layer, allowing two‐dimensional‐like growth of AlN. The buffer layer promoted the formation of a high‐quality AlN film. At 2173 K, the full‐width at half maximum of the X‐ray rocking curves of the (0002) and (10–10) planes of the AlN film was 360 and 425 arcsec, respectively.     

Resistive switching behavior in Lu2O3 thin film for advanced flexible memory applications

In this article, the resistive switching (RS) behaviors in Lu₂O₃ thin film for advanced flexible nonvolatile memory applications are investigated. Amorphous Lu₂O₃ thin films with a thickness of 20 nm were deposited at room temperature by radio-frequency magnetron sputtering on flexible polyethylene terephthalate substrate. The structural and morphological changes of the Lu₂O₃ thin film were characterized by x-ray diffraction, atomic force microscopy, and x-ray photoelectron spectroscopy analyses. The Ru/Lu₂O₃/ITO flexible memory device shows promising RS behavior with low-voltage operation and small distribution of switching parameters. The dominant switching current conduction mechanism in the Lu₂O₃ thin film was determined as bulk-controlled space-charge-limited-current with activation energy of traps of 0.33 eV. The oxygen vacancies assisted filament conduction model was described for RS behavior in Lu₂O₃ thin film. The memory reliability characteristics of switching endurance, data retention, good flexibility, and mechanical endurance show promising applications in future advanced memory.     

Production of Al2O3‐Stabilized Tetragonal ZrO2 Nanoparticles for Thermal Barrier Coating

Al₂O₃‐stabilized tetragonal ZrO₂ nanoparticles were obtained through hot‐air spray pyrolysis and characterized after postsynthesized treatments. The produced nanoparticles were 26 nm in size with surface area of 59 m²/g. A multilayer thermal barrier coating of nanostructured Al₂O₃‐ZrO₂‐embedded silicate was applied to the mild steel (EN3) specimen using spin‐coating technique and characterized comprehensively employing X‐ray diffraction and scanning electron microscope. The Al₂O₃‐stabilized ZrO₂ with silicate matrix facilitates the formation of zirconium silicate nanostructured surface‐protective coating on EN3 specimen. The Al₂O₃‐ZrO₂/SiO₂ matrix‐based hybrid inorganic coating shows effective thermal barrier for EN3 after firing at a high temperature of 600°C.     

Growth mechanism of AlN crystals via thermal nitridation of sintered Al2O3–ZrO2 plates

The crystal growth of AlN from aluminum oxides was studied using a thermal nitridation method. Four types of aluminum oxides, sintered Al₂O₃, ZrO₂-containing sintered Al₂O₃, and a- and c-plane sapphires, were used as a source material. As observed, millimeter-sized AlN crystal grains were successfully grown from the ZrO₂-containing sintered Al₂O₃ only at temperatures ranging from 2223 to 2323 K. The growth mechanism, including the role of ZrO₂ additive, was discussed from a thermodynamic viewpoint. The following growth model was proposed: predominant nitridation of ZrO₂ in Al₂O₃ suppresses Al₂O₃ nitridation, and the ZrO₂–Al₂O₃ liquid phase forms, which promotes the formation of Al₂O(g) and Al(g) from Al₂O₃. These Al-based gases react with CN(g) and/or N₂(g) to form AlN crystals on the Al₂O₃–ZrO₂ plate.     

Impact of oxygen partial pressure on resistive switching characteristics of PLD deposited ZnFe2O4 thin films for RRAM devices

In this paper we show resistive switching characteristics of ZnFe₂O₄ thin films grown by pulsed laser deposition at various oxygen partial pressures. We discuss how the microstructure, surface roughness, oxidation condition, and resistive switching properties of ZnFe₂O₄ thin films are influenced by the oxygen partial pressure prevalent in the chamber during the deposition process. The films were deposited at oxygen partial pressure (pO₂) of 0.0013, 0.013, 0.13 and 1.3 mbar. The ZnFe₂O₄ thin film deposited at the lowest pO₂ (0.0013 mbar) did not display a resistive switching characteristic. The ZnFe₂O₄ device deposited at 0.13 mbar yielded the best results. These devices have a low SET variance and a large memory window (more than 2 orders of magnitude) due to an optimum amount of oxygen vacancies/ions contained in the ZnFe₂O₄ film, which is helpful for better resistive switching, than devices deposited at other oxygen pressures. We also find that the migration of oxygen vacancies is linked to the resistive switching process.     

Gold Sensitized In2O3 nanocubes for ppb level NO2 gas sensing

Hydrothermally synthesized In₂O₃ nanocubes were sensitized with Au and gas sensing performance is analyzed. The Au sensitization was done using sputtering and gas sensing performance is studied as function of different sputtering time. The catalytic activity of Au particles on In₂O₃ films increases with the sputtering time but acquires saturation at high sputtering time. The Au sensitization with sputtering time of 5 s was found to show improved sensor response (R_g/R_a) of 8435 than the sensor response of 6876 for pure In₂O₃ film. The improved sensor response was attributed to the catalytic activity of Au particles on the In₂O₃ film surface. In addition, Au sensitized In₂O₃ also demonstrates the sensor response at 60 ppb.     

Phase-formation processes in the Al2O3-ZrO2-SiO2 system in heating

The specifics of the phase-formation processes and material structure formation based on Al₂O₃, ZrO₂, and Si₂O₂ are investigated. The possibility of using these materials to protect various construction materials from gas corrosion at high temperatures is demonstrated.     

Performance of CuO/Al2O3 Catalysts Promoted by SnO2 and ZrO2 in the Selective Oxidation of Carbon Monoxide

The effect of added SnO₂ and ZrO₂ to CuO/Al₂O₃ catalysts was investigated with reference to the oxygen spillover phenomena in the selective oxidation of carbon monoxide. The TPR and TPO analyses indicated that SnO₂ and ZrO₂ addition caused oxygen migration and induced the formation of high concentrations of active oxygen species on the SnO₂ and ZrO₂ surface. The catalytic activities of SnO₂ and ZrO₂ supported CuO/Al₂O₃ catalysts were superior to that for CuO/Al₂O₃ catalysts in the selective oxidation of carbon monoxide. Oxygen, when absorbed to the SnO₂ and ZrO₂ surface can spill over to the CuO phase and easily react with carbon monoxide. Consequently, the addition of SnO₂ and ZrO₂ led to significantly improved activities. This can be attributed to the enhanced migration of oxygen to the catalyst surface.     

Microwave hybrid and conventional sintering of Al2O3 and Al2O3/ZrO2 multilayers fabricated by aqueous tape casting

In this study, microwave hybrid sintering and conventional sintering of Al₂O₃- and Al₂O₃/ZrO₂-laminated structures fabricated via aqueous tape casting were investigated. A combination of process temperature control rings and thermocouples was used to measure the sample surface temperatures more accurately. Microwave hybrid sintering caused higher densification and resulted in higher hardness in Al₂O₃ and Al₂O₃/ZrO₂ than in their conventionally sintered counterparts. The flexural strength of microwave-hybrid-sintered Al₂O₃/ZrO₂ was 70.9% higher than that of the conventionally sintered composite, despite a lower sintering temperature. The fracture toughness of the microwave-hybrid-sintered Al₂O₃ increased remarkably by 107.8% despite a decrease in the relative density when only 3 wt.% t-ZrO₂ was added. The fracture toughness of the microwave-hybrid-sintered Al₂O₃/ZrO₂ was significantly higher (247.7%) than that of the conventionally sintered composite. A higher particle coordination and voids elimination due to the tape casting and the lamination processes, the microwave effect, the stress-induced martensitic phase transformation, and the grain refinement phenomenon are regarded as the main reasons for the mentioned outcomes.     

Significantly enhanced energy density of amorphous alumina thin films via silicon and magnesium co-doping

The different Si-Mg co-doping content was explored to improve the dielectric properties of amorphous Al₂O₃ thin film. According to the analysis of DSC, FT-IR, and XPS spectra, it can be confirmed that a novel structure of glass network is formed in the co-doped Al₂O₃ thin film. More importantly, compared to Al₂O₃ thin film, the leakage current of (Al_.97Si_.02Mg_.01)₂O_y thin film is reduced by 2 orders of magnitude and the breakdown strength is improved from 276?MV/m to 544?MV/m. The corresponding energy density of the modified sample is up to 9.2?J/cm³, which is an enhancement of 6.2?J/cm³ over that of the undoped Al₂O₃ thin film. Based on finite element analysis, the simulation results show that the applied electric field is mainly focused on the glass network, which could strengthen the stability of Al₂O₃ structure and decrease the breakdown probability of the films. From the viewpoint of defect chemistry, another reason for the enhancement of the dielectric properties is that Si-Mg co-doping results in the generation of cation vacancies and thus the formation of oxygen vacancies could be effectively prevented. This work could provide a new design strategy for high-performance dielectric capacitor devices.     

Extremely Thin Al2O3 Surface‐Passivated Nanocrystalline ZnO Thin‐Film Transistors Designed for Low Process Temperature

Nanocrystalline ZnO (nc‐ZnO) thin‐film transistors (TFTs) exhibit inherent instability under bias/photo stresses, which originates from the oxygen molecules adsorbed on the surface of the crystal grains. The space charge region at nanocrystal surfaces that is induced by adsorbed oxygen molecules produces a high electrical potential barrier and significantly interrupts charge transport between the source and drain in nc‐ZnO TFTs. In this article, we developed high‐performance TFTs via the continuous deposition of an extremely thin Al₂O₃ layer on a nc‐ZnO channel. These devices were fabricated by atomic layer deposition at an extremely low process temperature of 150°C, including both the deposition and postannealing temperatures. The nc‐ZnO TFT with an extremely thin Al₂O₃ layer (1.8 nm) showed a significantly higher mobility (25 cm²/Vs) compared to devices without an Al₂O₃ layer (3.6 cm²/Vs). This dramatic difference was ascribed to the suppression of the chemisorption of oxygen molecules at the nanocrystal surface during thermal annealing (reducing the potential barrier width/height between adjacent nanocrystals). Furthermore, ultrathin Al₂O₃‐covered nc‐ZnO TFTs exhibited considerably enhanced electrical/photo stability due to the reduction in adsorption/desorption events of oxygen molecules on the nanocrystal surfaces (with no change in the depletion width after illumination) under gate bias or illumination stress.     

Effect of SiO2, Fe2O3, and TiO2 on stabilization of cubic ZrO2 in the presence of Al2O3

Several compositions are investigated in order to determine the essence of the phase transformations occurring at temperatures up to 1600°C in the ZrO₂ — Ln₂O₃ (Ln is Nd, Y, Yb) — Al₂O₃ — SiO₂ (Fe₂O₃, TiO₂) systems. The efficiency of using Y₂O₃ and Yb₂O₃ to stabilize cubic ZrO₂ in the presence of a mixture of Al₂O₃ and SiO₂ (Fe₂O₃, TiO₂) is shown. Data show the possibility of fabricating high-quality zirconium-corundum articles with any proportion of Al₂O₃ and ZrO₂.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 6, pp. 17 – 20, June 1996.