Co-doped In2O3 thin films: Room temperature ferromagnets

Laser-ablated Co-doped In₂O₃ thin films were fabricated under various growth conditions on R-cut Al₂O₃ and MgO substrates. All Co:In₂O₃ films are well-crystallized, single phase, and room temperature ferromagnetic. Co atoms were well substituted for In atoms, and their distribution is greatly uniform over the whole thickness of the films. Films grown at 550 °C showed the largest magnetic moment of about 0.5 μ_B/Co, while films grown at higher temperatures have magnetic moments of one order smaller. The observed ferromagnetism above room temperature in Co:In₂O₃ thin films has confirmed that doping few percent of magnetic elements such as Co into In₂O₃ could result in a promising magnetic material.     

Ferromagnetism in carbon-doped In2O3 thin films

Carbon-doped In₂O₃ thin films exhibiting ferromagnetism at room temperature were prepared on Si (100) substrates by the rf-magnetron co-sputtering technique. The effects of carbon concentration as well as oxygen atmosphere on the ferromagnetic property of the thin films were investigated. The saturated magnetizations of thin films varied from 1.23 to 4.86 emu/cm³ with different carbon concentrations. The ferromagnetic signal was found stronger in samples with higher oxygen vacancy concentrations. In addition, deposition temperature and different types of substrates also affect the ferromagnetic properties of carbon-doped In₂O₃ thin films. This may be related to the oxygen vacancies in the thin film system. The experiment suggests that oxygen vacancies play an important role in introducing ferromagnetism in thin films.     

Chemical and structural properties of ternary post-transition metal oxide thin films: InZnO,InGaO and GaZnO

The chemical states of ternary post-transition metal oxide thin films of InGaO, GaZnO and InZnO were investigated using X-ray photoelectron spectroscopy. Detailed binding energy (BE) analyses revealed certain evolution in chemistry in the ternary oxides compared to the reference binary oxides of In₂O₃, ZnO, or Ga₂O₃. In particular, O 1s BEs were changed with the compositions, which suggests that the charge transfer (CT) between In³⁺/Ga³⁺/Zn²⁺ and O²⁻ ions is significant. Results of extended X-ray absorption fine structure analyses further showed that the first shell coordination (cation–O bond) is roughly maintained even though the ternary oxide films were structurally disordered. This implies that the CT process via O²⁻ ions can influence the charge reconstructions in the ternary oxide systems.     

Synthesis of monodisperse In2O3 nanoparticles and their d0 ferromagnetism

Monodisperse indium oxide (In₂O₃) nanoparticles (NPs) with the average diameter of 11 nm were prepared by a solvothermal method. The In₂O₃ NPs were characterized by X-ray diffraction, Raman and transmission electron microscopy. The intrinsic nature of ferromagnetism in In₂O₃ NPs has been established with the experimental observation of magnetic hysteresis loop. Photoluminescence and UV–visible studies were employed to evidence the presence of oxygen vacancies and revealed that the oxygen vacancies contribute to the ferromagnetism. The origin of ferromagnetism in In₂O₃ NPs may be due to exchange interactions among localized electron spin moments resulting from oxygen vacancies.     

Anomalous Hall effect in Cu and Fe codoped In2O3 and ITO thin films

We present a systematic study of the structure, magnetization, resistivity, and Hall effect properties of pulsed laser deposited Fe- and Cu-codoped In₂O₃ and indium-tin-oxide (ITO) thin films. Both the films show a clear ferromagnetism and anomalous Hall effect at 300 K. The saturated magnetic moments are almost the same for the two samples, but their remanent moments M_r and coercive fields H_C are quite different. M_r and H_C values of ITO film are much smaller than that of In₂O₃. The ITO sample shows a typical semiconducting behavior in whole studied temperature range, while the In₂O₃ thin film is metallic in the temperature range between 147 and 285 K. Analysis of different conduction mechanisms suggest that charge carriers are not localized in the present films. The profile of the anomalous Hall effect vs. magnetic field was found to be identical to the magnetic hysteresis loops, indicating the possible intrinsic nature of ferromagnetism in the present samples.     

Electrical and ferromagnetic properties of Tb-doped indium-tin oxide films fabricated by sol-gel method

The electrical and ferromagnetic properties of (In_0.9−xTb_xSn_0.1)₂O₃ and (In_0.99−yTb_0.01Sn_y)₂O₃ films fabricated by sol-gel method have been investigated. All the films show room temperature ferromagnetism. The magnetic moment per Tb ion of (In_0.9−xTb_xSn_0.1)₂O₃ films first increases and then decreases with the increasing Tb content. The variation of conductivity with Tb content is coincident with that of the magnetic moment. Furthermore, the conductivity and magnetic moment variations with Sn content y in (In_0.99−yTb_0.01Sn_y)₂O₃ films also have the similar trend. These results imply that the ferromagnetism may originate from the carrier-mediated mechanism.     

Intrinsic magnetic properties of In2O3 and transition metal-doped-In2O3

This paper reports on the influence of the sintering temperature and atmosphere and transition-metal doping on the magnetic properties of nanocrystalline and bulk In₂O₃. Undoped nanocrystalline In₂O₃ is diamagnetic whatever the sintering temperature and atmosphere. All single-phase transition-metal-doped In₂O₃ samples are paramagnetic, with a paramagnetic effective moment originating from weakly interacting transition metal ions. No trace of ferromagnetism has been detected even with samples sintered under argon, except extrinsic ferromagnetism for samples with magnetic dopant concentrations exceeding the solubility limit.     

Role of defects in magnetic properties of Fe-doped SnO2 films fabricated by the Sol--Gel method

This paper obtains the room temperature ferromagnetism in Sn1 xFexO2 films fabricated by the Sol-Gel method.X-ray diffraction results show that Fe doping inhibits the growth of SnO2 and Fe3+ ions occupy the Sn sites.The measurement of resistance excludes the free carrier inducing ferromagnetism.Moreover,the temperature dependence of magnetization has been better fitted by the Curie-Weiss law and bound magnetic polaron(BMP) theory.An enhancement of ferromagnetism is achieved by annealing the samples with x = 7.1% in H2,and a decrease of oxygen flow rate.All these results prove that the BMP model depending on defects can explain ferromagnetism in diluted magnetic oxides.     

Ferromagnetism in transition-metal-doped semiconducting oxide thin films

A rather complete work on transition-metal (TM)-doped TiO₂ thin films has been done and room ferromagnetism (FM) is found in the whole series of Sc/V/Cr/Mn/Fe/Co/Ni-doped TiO₂ films. Not only is it remarkable that for the first time, FM at high temperature was achieved in TM-doped TiO₂, but also a very big magnetic moment of 4.2μ_B/atom could be obtained, and direct evidences of real ferromagnets with big domains were shown as well. A similar chemical trend was achieved in TM-doped In₂O₃ films, however, the observed magnetic moment is rather modest, with the maximal value is of only 0.7μ_B/atom for Ni-doped In₂O₃ films. As regards TM-doped SnO₂ films, observed magnetic moments could be very large, with the maximum saturation of 6μ_B per impurity atom for Cr-doped SnO₂ thin films, but it could be influenced very much depending on substrate types. On the other hand, results on TM-doped ZnO films interestingly have revealed that in these systems, the magnetism more likely resulted from defects and/or oxygen vacancies.     

Effect of thermal treatment on the electrotransport properties of thin-film In<Subscript>2</Subscript>O<Subscript>3</Subscript>, ZnO materials and the multilayer (In<Subscript>2</Subscript>O<Subscript>3</Subscript>/ZnO)<Subscript>83</Subscript> heterostructure

The effect heat treatment has on the electrotransport mechanisms in films of ZnO and In₂O₃, and in a multilayer (In₂O₃/ZnO)₈₃ structure obtained via ion-beam sputtering, is studied. It is shown that there is a mechanism of weak electron localization in the In₂O₃ and (In₂O₃/ZnO)₈₃ samples. The relaxation processes that occur during the heat treatment of In₂O₃ films are found to increase the length of elastic electron scattering, but to reduce this parameter in multilayer heterostructures.     

Regularities of formation of cubic zirconia stabilized with calcium,yttrium, and indium oxides under mechanochemical treatment

An effect of the composition of reacting components during mechanochemical activation on the ZrO₂ structure stabilized with additives of In₂O₃, CaO, and Y₂O₃ oxides has been revealed. It is established that mechanochemical activation of oxide mixtures leads to the formation of dispersed solid solutions based on cubic zirconia. It is shown that interaction depth of the components during mechanochemical activation increases in the series of oxides In₂O₃ < CaO < Y₂O₃.     

Effect of hydrogenation vs. re-heating on intrinsic magnetization of Co doped In2O3

Influence of Co doping for In in In₂O₃ matrix has been investigated to study the effect on magnetic vs. electronic properties. Rietveld refinement of X-ray diffraction patterns confirmed formation of single phase cubic bixbyite structure without any parasitic phase. Photoelectron spectroscopy and refinement results further revealed that dopant Co²⁺ ions are well incorporated at the In³⁺ sites in In₂O₃ lattice and also ruled out formation of cluster in the doped samples. Magnetization measurements infer that pure In₂O₃ is diamagnetic and turns to weak ferromagnetic upon Co doping. Hydrogenation further induces a huge ferromagnetism at 300 K that vanishes upon re-heating. Experimental findings confirm the induced ferromagnetism to be intrinsic, and the magnetic moments to be associated with the point defects (oxygen vacancies V_o) or bound magnetic polarons around the dopant ions.     

The effect of annealing on the room temperature ferromagnetism in co-sputtered In2O3: C thin films

In this paper, we report investigation of room temperature (RT) ferromagnetism in In₂O₃ (InO) thin films doped with carbon prepared by the co-sputtering method. InO thin films both undoped and C doped with varied thicknesses in the range of 45 to 80 nm were synthesized on Si substrates with varied C concentrations. The carbon concentration was varied from 1.6 to 9.3 at%. The undoped InO films showed no trace of ferromagnetism. Carbon doped films (InO:C) exhibited ferromagnetism at RT, which was of the orders of 10⁻⁵ emu and varied strongly with C concentrations. It is observed that the magnetization reached a maximum value of 5.7 emu/cm³ at 4 at% C. Annealing of the InO:C films in an oxygen environment resulted in a decrease in the magnetization, indicating the crucial role of oxygen vacancies in the films. It is concluded that the oxygen vacancies were important and compete with C substitution for the RT ferromagnetism.     

Transparent conductive electrodes for electrochromic devices: A review

This paper reviews the optical and electrical performance of thin films that are useful as transparent electrodes in electrochromic devices. The properties of certain heavily doped wide-bandgap semiconductor oxides (especially In₂O₃:Sn) and of certain coinage metal films are discussed.     

A close correlation between induced ferromagnetism and oxygen deficiency in Fe doped In2O3

We report on the reversible manipulation of room temperature ferromagnetism in Fe (5%) doped In₂O₃ polycrystalline magnetic semiconductor. The X-ray diffraction and photoemission measurements confirm that the Fe ions are well incorporated into the lattice, substituting the In³⁺ ions. The magnetization measurements show that the host In₂O₃ has a diamagnetic ground state, while it shows weak ferromagnetism at 300 K upon Fe doping. The as-prepared sample was then sequentially annealed in hydrogen, air, vacuum and finally in air. The ferromagnetic signal shoots up by hydrogenation as well as vacuum annealing and bounces back upon re-annealing the samples in air. The sequence of ferromagnetism shows a close inter-relationship with the behavior of oxygen vacancies (V_o). The Fe ions tend to a transform from 3+ to 2+ state during the giant ferromagnetic induction, as revealed by photoemission spectroscopy. A careful characterization of the structure, purity, magnetic, and transport properties confirms that the ferromagnetism is due to neither impurities nor clusters but directly related to the oxygen vacancies. The ferromagnetism can be reversibly controlled by these vacancies while a parallel variation of carrier concentration, as revealed by resistance measurements, appears to be a side effect of the oxygen vacancy variation.     

Characterization of interface between CuInSe2 and In2O3

CuInSe₂/In₂O₃ structures were formed by depositing CuInSe₂ films by stepwise flash evaporation onto In₂O₃ films, which were grown by DC reactive sputtering of In target in presence of (Ar+O₂) gas mixture. Phase purity of the CuInSe₂ and In₂O₃ films was confirmed by Transmission Electron Microscopy (TEM) studies. X-ray diffraction (XRD) results on CuInSe₂/In₂O₃/glass structures showed sharp peaks corresponding to (112) plane of CuInSe₂ and (222) plane of In₂O_3. Rutherford Backscattering Spectrometry (RBS) investigations were carried out on CuInSe₂/In₂O₃/Si structures in order to characterize the interface between In₂O₃ and CuInSe₂. The results show that the CuInSe₂ films were near stoichoimetric and In₂O₃ films had oxygen deficient composition. CuInSe₂/In₂O₃ interface was found to include a ∼20 nm thick region consisting of copper, indium and oxygen. Also, the In₂O₃/Si interface showed the formation of ∼20 nm thick region consisting of silicon, indium and oxygen. The results are explained on the basis of diffusion/reaction taking place at the respective interfaces.     

Sensors for the nitrogen oxides, NO2, NO and N2O, based on In2O3 and WO3 nanowires

Sensing characteristics of ZnO, In₂O₃ and WO₃ nanowires have been investigated for the three nitrogen oxides, NO₂, NO and N₂O. In₂O₃ nanowires of ∼20 nm diameter prepared by using porous alumina membranes are found to have a sensitivity (defined as the ratio of the sensor resistance in the gas concerned to that in air) of about 60 for 10 ppm of all the three gases at a relatively low temperature of 150 °C. The response and recovery times are around 20 s. The sensitivity of these In₂O₃ nanowires is around 40 for 0.1 ppm of NO₂ and N₂O at 150 °C. WO₃ nanowires of 5–15 nm diameter, prepared by the solvothermal process show a sensitivity of 20–25 for 10 ppm of the three nitrogen oxides at 250 °C. The response and recovery times are 10 s and 60 s, respectively. The sensitivity is around 10 for 0.1 ppm of NO₂ at 250 °C. The sensitivity of In₂O₃ and WO₃ nanowires is not affected by humidity even up to 90% relative humidity. The study also reveals that the sensing mechanism for the three nitrogen oxides have a commonality in that the desorption of oxygen is a crucial step in all the cases. PACS 07.07.Df; 85.35.-p; 82.35.Np     

Synthesis,structural and ellipsometric evaluation of oxygen-deficient and nearly stoichiometric zinc oxide and indium oxide nanowires/nanoparticles

Oxygen-deficient (OD) and nearly stoichiometric (NST) ZnO and In₂O₃ nanowires/nanoparticles were synthesized by chemical vapor deposition on Au-coated silicon substrates. The OD ZnO and OD In₂O₃ nanowires were synthesized at 750 and 950°C, respectively, using Ar flow at ambient pressure. A mixture of flowing Ar and O₂ was used for synthesizing NST ZnO nanowires and NST In₂O₃ nanoparticles. Growth of OD ZnO nanowires and NST In₂O₃ nanoparticles was found to be via a vapor–solid (VS) mechanism and the growth of NST ZnO nanowires was via a vapor–liquid–solid mechanism (VLS). However, it was uncertain whether the growth of OD In₂O₃ nanowires was via a VS or VLS mechanism. The optical constants, thickness and surface roughness of the prepared nanostructured films were determined by spectroscopic ellipsometry measurements. A three-layered model was used to fit the calculated data to the experimental ellipsometric spectra. The refractive index of OD ZnO, NST ZnO nanowires and NST In₂O₃ nanoparticles films displayed normal dispersion behavior. The calculated optical band gap values for OD ZnO, NST ZnO, OD In₂O₃ nanowires and NST In₂O₃ nanoparticles films were 3.03, 3.55, 2.81 and 3.52?eV, respectively.     

An extreme change in structural and optical properties of indium oxynitride deposited by reactive gas-timing RF magnetron sputtering

The indium oxynitride (InON) films were achieved by reactive RF magnetron sputtering indium target which has the purity of 99.999% with a novel reactive gas-timing technique. The structural, optical and electrical properties in a series of polycrystalline InON films affected by gas-timing of reactive N₂ and O₂ gases introduced to the chamber were observed. The X-ray photoelectron spectroscopy revealed that the oxygen content in thin films that compounded to indium and nitrogen, which increased from 10% in indium nitride (InN) to 66% in indium oxide (In₂O₃) films. The X-ray diffraction peaks show that the phase of deposited films changes from InN to InON and to In₂O₃ with an increasing oxygen timing. The hexagonal structure of InN films with predominant (0 0 2) and (0 0 4) orientation was observed when pure nitrogen is only used as sputtering gas, while InON and In₂O₃ seem to demonstrate body-center cubic polycrystalline structures depending on gas-timing. The surface morphologies investigated from atomic force microscope of deposited films with varying gas-timing of O₂:N₂ show indifferent. The numerical algorithm method was used to define the optical bandgap of films from transmittance results. The increasing oxygen gas-timing affects extremely to the change of crystallinity phase from InN to InON and to In₂O₃, the increase of optical bandgap from 1.4 to 3.4 eV and the rise of sheet resistance from 15 Ω/□ to insulator.