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.     

Ethanol sensing properties of networked In2O3 nanorods decorated with Cr2O3-nanoparticles

In₂O₃ nanorods decorated with Cr₂O₃ nanoparticles were synthesized by thermal evaporation of In₂S₃ powder in an oxidizing atmosphere followed by solvothermal deposition of Cr₂O₃ and their ethanol gas sensing properties were examined. The pristine and Cr₂O₃-decorated In₂O₃ nanorods exhibited responses of ~524% and ~1053%, respectively, to 500-ppm ethanol at 200 °C. The Cr₂O₃-decorated In₂O₃ nanorod sensor showed stronger electrical response to ethanol gas at 200 °C than the pristine In₂O₃ nanorod counterpart. The former also showed faster response and recovery than the latter. The pristine and Cr₂O₃-decorated In₂O₃ nanorod sensors showed the strongest response to ethanol gas at 250 and 200 °C, respectively. The Cr₂O₃-decorated In₂O₃ nanorod sensor showed selectivity for ethanol gas over other reducing gases. The underlying mechanism for the enhanced response, sensing speed and selectivity of the Cr₂O₃-decorated In₂O₃ nanorod sensor for ethanol gas is discussed.     

In2O3:Ga and In2O3:P-based one-electrode gas sensors: Comparative study

Gas sensing characteristics of one-electrode sensors based on the In₂O₃ ceramics doped by gallium and phosphorus have been discussed. In₂O₃-based ceramic was prepared by sol–gel technology. Ozone, CO, CH₄ and H₂ were used as tested gases. The doping concentration effect on the sensor parameters such as magnitude of response, operating temperature, response and recovery times, sensitivity to the air humidity, and selectivity have been analyzed. It was shown that In₂O₃ doping by Ga and P could be used for the sensor performance optimization. It was assumed that the appearance of the second phase (InPO₄ and Ga₂O₃) and the change of structural parameters, taking place during doping process, were the main factors controlling the change of operating characteristics in In₂O₃:P and In₂O₃:Ga-based sensors.     

In2O3 nanosheets array directly grown on Al2O3 ceramic tube and their gas sensing performance

Arrayed In₂O₃ nanosheets were synthesized directly via a two-step solution approach on an Al₂O₃ ceramic tube. Their morphology and structure were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV–Vis absorption spectroscopy, and scanning electron microscopy (SEM). The results reveal that the length of each nanosheet is about 1 µm, the width of the bottom of nanosheet is about 200 nm. Importantly, the In₂O₃ nanosheets with large specific surface area possess highly sensing performance for ethanol detection. The response value to 100 ppm ethanol is about 45 at an operating temperature of 280 °C, and the response and recovery time are extremely short. It is expected that the directly grown In₂O₃ nanosheets with large specific surface area and excellent sensing properties will become a promising functional material in monitoring and detecting ethanol.     

Electric field enhancements in In2O3-coated single-walled carbon nanotubes

In₂O₃ nanoparticles are coated on the surfaces of single-walled carbon nanotubes (SWCNTs) by a successive ionic layer adsorption and reaction process. The thickness of the In₂O₃ nanoparticle film is tuned by controlling the number of coating cycles. The electric field around the In₂O₃-coated SWCNTs is compared with that of pristine SWCNTs. Field enhancement of the In₂O₃-coated SWCNTs is confirmed by conductive atomic force microscopy at low electric field (contact mode: 1 V to −1 V) and also field emission (FE) analysis at high electric field (0–4.2 V/μm). The uniformity and emission stability are also measured via FE analysis. Near infrared and X-ray photoemission spectroscopy data are suggested to explain the charge transfer, bandgap change between the In₂O₃ nanoparticles and SWCNTs, and the electric field enhancements in the In₂O₃-coated SWCNTs at both low and high electric field.     

High temperature failure modes of In2O3 thin films and improved thermal stability using Al2O3/ZrO2 protective layers

The limiting temperature of an In₂O₃ thin film sensor is much lower than its melting point. Herein, the failure modes of In₂O₃ thin films at high temperatures, including sublimation and changes in composition, have been studied. The edge and surface layer sublimation rates increased dramatically at 1350 °C, indicating that it is the limiting temperature of no-protection In₂O₃ films. In addition, oxygen atoms will escape from In₂O₃ thin films at high temperatures, forming oxygen vacancies. As the main current carrier type in In₂O₃, the increasing number of oxygen vacancies affects the resistance of In₂O₃ thin film sensors. To solve these problems and promote the high temperature performance of In₂O₃ thin films, protection methods based on Al₂O₃ and ZrO₂ layers have been investigated. The ZrO₂ protective layer alleviated the serious considerable sublimation of In₂O₃ thin films at high temperatures, and the Al₂O₃ protective layer was beneficial for reduction the escape of oxygen atoms. Finally, different protection layers were evaluated by in-situ resistivity measurements of In₂O₃ thin films at high temperatures. The resistance of the In₂O₃ thin film resistor with a protective multilayer consisting of Al₂O₃ and ZrO₂ remained stable at 1360 °C, verifying the protection method effectively increased the thermal stability of In₂O₃ thin films.     

ZnO-enhanced In2O3-based sensors for n-butanol gas

A series of high-response and fast-response/recovery n-butanol gas sensors was fabricated by adding ZnO to In₂O₃ in varying molar ratios to form ZnO-In₂O₃ nanocomposites via a facile co-precipitation hydrothermal method. Morphological characterizations revealed that the shape of pure In₂O₃ was changed from irregular cubes into irregular nanoparticles, 30–50?nm in size, with the addition of ZnO. Compared with the pure In₂O₃ gas sensor, the ZnO-In₂O₃ gas sensor exhibits superior n-butanol sensing performance. With the introduction of ZnO, the response of the sensor to n-butanol was improved from 17 to 99.5 at 180?°C for a [Zn]:[In] molar ratio of 1:1. In addition, the ZnO-In₂O₃ gas sensors show a reduced optimal working temperature, excellent selectivity to n-butanol, and good repeatability. The response of the ZnO-enhanced In₂O₃-based sensors showed a strong linear relationship with the n-butanol gas concentration, allowing for the quantitative detection of n-butanol gas.     

Preparation and characterization of multiwalled carbon nanotube/In2O3 composites

We have prepared multiwalled carbon nanotube (MWCNT)/In₂O₃ composites using a simple impregnation method. The precursor compound indium(III) chloride (InCl₃) was used to cover the surface of MWCNTs and distilled water was used as solvent. The applied mass ratio was 4:1 (In₂O₃/MWCNT), and during the calcination process different temperatures (300, 350 and 400 °C) were investigated. The produced materials were characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, transmission and scanning electron microscopy, and a thermogravimetric analysis was executed also. The average thickness of the produced surface layer and the average sizes of the In₂O₃ particles were calculated with the Scherrer formula and the ImageJ-program. The results show that the heat treatment temperature affected the characteristic morphology and the crystal structure of the as-prepared composite. These multiwalled carbon nanotube-based composites are promising candidates as gas sensors and catalyst.     

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.     

Synthesis of In2O3 porous nanoplates for photocatalytic decomposition of perfluorooctanoic acid (PFOA)

Indium oxide (In₂O₃) porous nanoplates (PNPs) were synthesized by an ethylenediamine-assisted hydrothermal process followed by calcination at 270 °C. Compared with In₂O₃ non-porous nanoplates (NPs) obtained at higher temperature (500 °C), PNPs possessed a high value of specific surface area (156.9 m² g^− 1) and a meso-microporous structure. As-synthesized In₂O₃ PNPs showed a superior activity for photocatalytic decomposition of an emerging persistent organic pollutant-perfluorooctanoic acid (PFOA), the decomposition half-life of PFOA was shortened to 4.4 min.     

Field emission properties and growth mechanism of In2O3 nanostructures

Four kinds of nanostructures, nanoneedles, nanohooks, nanorods, and nanotowers of In₂O₃, have been grown by the vapor transport process with Au catalysts or without any catalysts. The morphology and structure of the prepared nanostructures are determined on the basis of field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD), and transmission electron microscopy (TEM). The growth direction of the In₂O₃ nanoneedles is along the [001], and those of the other three nanostructures are along the [100]. The growth mechanism of the nanoneedles is the vapor-liquid–solid (VLS), and those of the other three nanostructures are the vapor-solid (VS) processes. The field emission properties of four kinds of In₂O₃ nanostructures have been investigated. Among them, the nanoneedles have the best field emission properties with the lowest turn-on field of 4.9 V/μm and the threshold field of 12 V/μm due to possessing the smallest emitter tip radius and the weakest screening effect.     

NO2 gas sensing responses of In2O3 nanoparticles decorated on GO nanosheets

Nanomaterials offer a wide range of applications in environmental nanotechnology. Hazardous pollutants in the environment are needed to be detected and controlled effectively to avoid human health risks. In this paper, we described the fine-controlled growth of In₂O₃ nanoparticles embedded on GO nanosheets by a facile precipitation method. The In₂O₃@GO nanocomposites exhibited outstanding gas sensing performance as compared with pure In₂O₃ nanoparticles towards NO₂. At 225 °C, the sensor displayed high selectivity, best response (78) to 40 ppm NO₂, quick response, and recovery times of 106s/42s. The improved sensing performances of the nanocomposite were attributed to large surface area, high gas adsorption-desorption capability, and the formation of p-n heterojunctions between In₂O₃ nanoparticles and GO nanosheets. The excellent gas detecting activities validate In₂O₃@GO nanocomposites as a promising candidate in the NO₂ gas sensor industry.     

Influence of Preparation Methods of In2O3/Al2O3 Catalyst on Selective Catalytic Reduction of NO by Propene in the Presence of Oxygen

Selective catalytic reduction of NO with propene was investigated over In₂O₃/Al₂O₃ catalysts prepared by three methods, namely, a single sol-gel (SG), impregnation (IM), and co-precipitation method (CP). The catalysts were characterized by means of BET, XRD, XPS, and TPD. The maximum NO conversion over In₂O₃/Al₂ O₃ prepared by sol-gel method was 95% at 400 °C in the absence of H₂O, and the activity decreased slightly in the presence of H₂O, and it was still 76% even in the presence of H₂O and SO₂. Although the retarding effect of SO₂ on the activity was observed for the three catalysts, In₂O₃/Al₂O₃ (SG) showed relatively high activity. It is found that the high surface area and low average pore diameter are important to the catalytic activity, and the strong interaction between indium and alumina for In₂O₃/Al₂O₃ catalyst prepared by sol-gel method may be the reason of high activity for NO reduction. The reaction and surface studies showed that NO₃⁻ and partially oxidized hydrocarbons (RCOO⁻ species) are mainly intermediates, and the oxidation C₃H₆ to RCOO⁻ species maybe the key reaction process in the SCR of NO with C₃H₆.     

Preparation, Electrical Conductivity, and Sensory Properties of Oxide Films in the In2O3–SnO2 and In2O3–ZrO2 Systems

Nanostructured polycrystalline films in the In₂O₃–SnO₂ and In₂O₃–ZrO₂ systems, which are of interest for use in sensors for determining the content of strongly oxidizing media (such as ozone) and in electrode materials, are grown by the hydropyrolytic method from metal nitrates and through vacuum deposition of metals. Chemically interacting nanocomposites based on indium oxide are studied. The surface morphology of films and the structure of polycrystalline grains are investigated using electron microscopy and X-ray diffractometry.     

Synthesis of In2O3/GNPs nanocomposites with integrated approaches to tune overall performance of electrochemical devices

The electroactive material with a porous structure, good electrical conductivity, hybrid composition, and a higher surface is considered more suitable for applications as an electrode in the energy storage device. Herein, we report the preparation of In₂O₃ nanoparticles via a simple chemical route and their nanocomposites with 10% (IOG-10), 30% (IOG-30), 50% (IOG-50), 70% (IOG-70), and 100% G-100 graphene nanoplatelets (GNPs) via ultra-sonication. The presence of GNPs in the nanocomposite samples was verified by powder X-ray diffraction (PXRD), Raman, and scanning electron microscopy (SEM) results. The prepared samples were loaded onto the porous 3D nickel foam (NF) substrate to manufacture the working electrode for electrochemical testing. The cyclic voltammetry (CV), as well as galvanostatic charge/discharge (GCD), results proposed the IOG-30@NF as a suitable electrode for electrochemical applications. More precisely, the IOG-30@NF electrode shows a specific capacitance of 1768 Fg^-1 at 1 Ag^-1, which is considerably higher than that of either G-100@NF or In₂O₃@NF electrodes. Besides, the IOG-30@NF electrode shows good cyclic stability of 92.2% after 4000 GCD tests completed at 12 Ag^-1. When increasing the current density value from 1 to 4, the IOG-30@NF electrode maintains a specific capability of 81%, ensuring its exceptional rate capability. The higher specific capacity, higher rate-performance, and better cyclic activity of the IOG-30@NF electrode can be ascribed to its hybrid-composition, nanoarchitecture In₂O₃, 3D but porous nickel foam substrate, appropriate graphene content, and interaction between In₂O₃ nanoparticles and GNPs nanosheets.     

Metal-organic-framework-derived In2O3 microcolumnar structures embedded with Pt nanoparticles for NO2 detection near room temperature

A novel synthesis of In₂O₃ porous microcolumnar structures (MCs) by a self-sacrificial template route was carried out using MIL-68. Using a modified calcination strategy, the samples could maintain the original metal organic frame work (MOF) morphology with a high gas accessibility after a slow decomposition of organic ligands. Pt nanoparticles (NPs) were loaded on the samples before or after the MOF calcination, leading to different contact states of the Pt NPs and In₂O₃ matrix. The gas sensing properties of the samples were systematically investigated using a dynamic testing system. Particularly, sample Pt/In₂O₃ MCs-1 exhibited a superior NO₂ sensing performance near room temperature (R_g/R_a?=?44.9?at 1 part-per-million and 5.2?at 100 parts-per-billion (ppb)). The sensor resistance could recover to its baseline even at 40?°C after purging with air without any additional treatment. This can be attributed to the chemical sensitisation of the Pt NPs as well as large contents of pores and channels for gas diffusion. The introduction of humidity in the gas mixture could remarkably decrease the sensor response and recovery times owing to the ‘wet’ NO₂ adsorption mechanism. This study demonstrated a novel synthesis route of Pt-loaded In₂O₃ porous columnar structures and its potential applications in near-room-temperature detection of ppb-level NO₂.     

Facile synthesis of In2O3 nanoparticles with high response to formaldehyde at low temperature

In₂O₃ nanoparticles with uniform particle size (10-25 nm) were obtained using the facile precipitation strategy at room temperature with following calcined treatment. The gas-sensing performance of In₂O₃ nanoparticles with different calcined temperatures was investigated. The results demonstrated that the In₂O₃ nanoparticles calcined at 500°C exhibited highest sensing response (R_a/R_g = 68.1) to 10 ppm HCHO at 100°C with good selectivity, stability, reproducibility, and ultra-low limit of detection (1 ppm). The results of XPS, UV, and other characterizations indicated that In₂O₃-500 possessed the most absorbed oxygen species, the highest carrier mobility, and lowest band gap energies. Our work offers new insights into the development of sensing materials to the detection of volatile organic compounds (VOCs).     

High‐Performance Ferroelectric Solid Solution Crystals: Pb(In1/2Nb1/2)O3–Pb(Zn1/3Nb2/3)O3–PbTiO3

A series of regular shaped Pb(Zn_1/3Nb_2/3)O₃‐based ternary ferroelectric single crystals (1 ? x)Pb(In_1/2Nb_1/2)O₃–0.33Pb(Zn_1/3Nb_2/3)O₃–xPbTiO₃ (PIN–PZN–PT) have been grown by means of the top‐seeded solution growth method that prevented pyrochlore phase and promoted [001] or [111] growth. The nucleation and crystallization behavior of the Pb(Zn_1/3Nb_2/3)O₃‐based ferroelectric single crystals differed from other relaxor‐based ferroelectric single crystals was discovered. Di‐/piezo‐/ferro‐/pyroelectric properties were characterized systematically. The PIN–PZN–PT single crystals showed large coercive fields E_c, high Curie temperature T_C and high pyroelectric coefficient P, presenting similar performance but better thermal stability compared with the PZN–PT single crystals, and making it a promising material for transducers and IR detectors in a wider temperature range.     

Fabrication of Ti3C2Tx/In2O3 nanocomposites for enhanced ammonia sensing at room temperature

Ti₃C₂T_x, as a novel two-dimensional material, displays promising prospects in NH₃ detection at room temperature. However, the NH₃ detection limit of pristine Ti₃C₂T_x is still a major research concern. Therefore, it is important to explore new Ti₃C₂T_x-based nanocomposites for better NH₃-sensing performance. In the present experiment, Ti₃C₂T_x/In₂O₃ nanocomposites were successfully synthesized by ultrasonication and characterized by XRD, FESEM, TEM, XPS, and BET. The optimal Ti₃C₂T_x/In₂O₃-based sensor had a high response of 63.8% (30.4 times higher than that of pristine Ti₃C₂T_x) to 30 ppm NH₃ at room temperature. In addition, the optimal Ti₃C₂T_x/In₂O₃-based sensor had stable repeatability, excellent selectivity, and long-term stability, while exhibiting excellent potential for NH₃ detection at room temperature.     

Conductive coating films based on low density In2O3 powders and polymer latexes

Several kinds of conductive coating films were prepared from a low-density indium(III) oxide powder (which was employed because it provides a much higher volume for the same weight) and polymer latexes. The low-density In₂O₃, which is an electrically conductive pigment, was prepared by pyrolysis followed by the combustion of water-swellable polymer microspheres imbibed with In(NO₃)₃, the precursor of In₂O₃. Either acrylamide/N,N'-methylenebisacrylamide or poly(vinylalcohol)/glutaricdialdehyde was used to generate spherical hydrogel particles. The polymer latexes with which the In₂O₃ was mixed had a soft core and a hard shell structure to ensure that the coating film has suitable mechanical properties in addition to conductivity. Acrylonitrile/butadiene/styrene copolymer ABS or acrylonitrile/butylacrylate/styrene copolymer ABAS latexes were used as binders for the conductive pigment. The powder coating followed by hot pressing, the water-borne coating consisting of low-density In₂O₃ and polymer latexes followed by curing, or the colloidal dispersion coating was used to deposit flexible conductive coating films on polyester sheets. The conductive pigment density and the polymer latexes' size and flowability are the factors that affect the characteristics of the film. We found that the colloidal suspension coating procedure based on ABAS latexes achieves better electrical and mechanical properties for the coating films. © 1996 John Wiley & Sons, Inc.