CoO3 Thin Films Research Articles

Ultrafast transverse thermoelectric response in c‐axis inclined epitaxial La0.5Sr0.5CoO3 thin films

AbstractUltrafast transverse thermoelectric voltage response has been observed in c‐axis inclined epitaxial La0.5Sr0.5CoO3thin films. Voltage signals with the rise time of 7 ns have been detected under the irradiation of pulse laser with duration of 28 ns. A concept, named response rate ratio, has been proposed to evaluate the intrinsic response rate, and this ratio in La0.5Sr0.5CoO3is smaller than that in other reported materials. The low resistivity is thought to be responsible for the ultrafast response, as low resistivity induces small optical penetration depth, and response time has a monotonous increasing relationship with this depth.magnified imageTransverse thermoelectric voltage with the rise time of 7 ns in La0.5Sr0.5CoO3thin film.(© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis and Characterization of Nanostructured Co(OH)<sub>2</sub> and Co<sub>3</sub>O<sub>4</sub> Thin Films by a Simple Solution Growth Process

Nanostructured Co(OH)2thin films were synthesized by a simple solution growth process. In experiment, F–and NH3were used as Co2+ordination agents, and hydroxyl ions were supplied by ammonia hydroxide solution for the hydrolysis reaction. The results showed that the solution pH and F/Co ratio had great influences on the morphologies of the thin films. The Co(OH)2thin films were constructed with lots of Co(OH)2nanoflakes. Nanostructured Co3O4 thin films were prepared by annealing the Co(OH)2thin films at 400°C for 2 h. The magnetic properties of Co3O4thin films were also investigated.

Substrate-biasing during plasma-assisted atomic layer deposition to tailor metal-oxide thin film growth

Two substrate-biasing techniques, i.e., substrate-tuned biasing and RF biasing, have been implemented in a remote plasma configuration, enabling control of the ion energy during plasma-assisted atomic layer deposition (ALD). With both techniques, substrate bias voltages up to −200 V have been reached, which allowed for ion energies up to 272 eV. Besides the bias voltage, the ion energy and the ion flux, also the electron temperature, the electron density, and the optical emission of the plasma have been measured. The effects of substrate biasing during plasma-assisted ALD have been investigated for Al2O3, Co3O4, and TiO2 thin films. The growth per cycle, the mass density, and the crystallinity have been investigated, and it was found that these process and material properties can be tailored using substrate biasing. Additionally, the residual stress in substrates coated with Al2O3 films varied with the substrate bias voltage. The results reported in this article demonstrate that substrate biasing is a promising technique to tailor the material properties of thin films synthesized by plasma-assisted ALD.

Oxide Coating of Alumina Nanoporous Structure Using ALD to Produce Highly Porous Spinel

AbstractIn this work we show that atomic layer deposition (ALD) stands out as a very promising method for coating nanomaterials and, more specifically, nanoporous materials of technological interest in heterogeneous catalysis. ALD is capable of coating extremely complex shapes with high conformality and high aspect ratios. The current work describes deposition of ZnO and CoO thin films on γ‐alumina nanoporous particles with sizes ranging from 20 to 100 µm in diameter, as well on aluminum membrane discs (anodiscs), and converting the surfaces into nanoporous, mechanically more robust spinel phases. We maintain the porosity of the supporting γ‐alumina particle, despite the addition of material to the 16 nm pores, by utilizing subsequent reactions between the coated layer and γ‐alumina, following the Kirkendall mechanism. The oxide thin film coatings are deposited at 175 and 167°C for ZnO and cobalt oxide, respectively, and thereafter annealed at from 600 to 1000°C for 3 h. This represents a new way to produce highly porous spinel particles and spinel‐coated membrane discs.

The Fabrication of La<sub>0.9</sub>Sr<sub>0.1</sub>CoO<sub>3</sub> Thin Films and its LITV Effect Applications

High quality La0.9Sr0.1CoO3 (LSCO) thin films grown on 5° vicinal cut LaAlO3 (LAO) (100) substrates were deposited by pulse laser deposition (PLD). Laser induced thermoelectric voltage (LITV) was detected instantly with fast response time and extremely narrow full width at half maximum (FWHM) when 248 nm pulse laser radiated on the surface of LSCO thin films. These merits of LSCO thin films make it one ideal material to fabricate light detectors and photosensitive device. With the increase of pulse laser energy, the peak voltages increase linearly, so LSCO thin films can be used to make high precision laser energy/power meter.

Tunable strain effect and ferroelectric field effect on the electronic transport properties of La0.5Sr0.5CoO3 thin films

Tensiled La0.5Sr0.5CoO3 (LSCO) thin films were epitaxially grown on piezoelectric 0.67Pb (Mg1/3Nb2/3)O3-0.33PbTiO3 (PMN-PT) single-crystal substrates. Due to the epitaxial nature of the interface, the lattice strain induced by ferroelectric poling or the converse piezoelectric effect in the PMN-PT substrate is effectively transferred to the LSCO film and thus reduces the tensile strain of the film, giving rise to a decrease in the resistivity of the LSCO film. We discuss these strain effects within the framework of the spin state transition of Co3+ ions and modification of the electronic bandwidth that is relevant to the induced strain. By simultaneously measuring the strain and the resistivity, quantitative relationship between the resistivity and the strain was established for the LSCO film. Both theoretical calculation and experimental results demonstrate that the ferroelectric field effect at room temperature in the LSCO/PMN-PT field-effect transistor is minor and could be neglected. Nevertheless, with decreasing temperature, the ferroelectric field effect competes with the strain effect and plays a more and more important role in influencing the electronic transport properties of the LSCO film, which we interpreted as due to the localization of charge carriers at low temperature.

Erratum: “Effects of Li content on the structural, optical, and electrical properties of LiZnMgO films” [J. Appl. Phys. 107, 113717 (2010)

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Synthesis of Co3O4 nanosheets via electrodeposition followed by ozone treatment and their application to high-performance supercapacitors

A thin film of Co3O4 nanosheets is electrodeposited on a flexible Ti substrate by a one-step potentiostatic method, followed by an UV–ozone treatment for 30 min. The films before and after the UV–ozone treatment are characterized with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The film is composed of Co(OH)2 before UV–ozone treatment, and of Co3O4 after the treatment. The morphologies of both films are examined by scanning electron microscopy (SEM) and transmission electron microscope (TEM). The obtained films are composed of nanosheets, and there is no change in their sheet-like morphology before and after the UV–ozone treatment. When applied for a supercapacitor, the Co3O4 modified Ti electrode (Co3O4/Ti) shows a far higher capacitance than that of the Co(OH)2 modified Ti electrode. The electrodeposition time and NaOH concentration in the electrolyte are optimized. A remarkably high specific capacitance of 1033.3 F g−1 is obtained for the Co3O4 thin film at a charge–discharge current density of 2.5 A g−1. The long-term stability data shows that there is still 77% of specific capacitance remaining after 3000 repeated charge–discharge cycles. The high specific capacitance and long-term stability suggest the potential use of Co3O4/Ti for making a flexible supercapacitor.

Perpendicular magnetization in CoO (111) layers induced by exchange interaction with ferromagnetic Co and Ni60Cu40 nanoclusters

The magnetization reversal of ferromagnetic nanoparticles coupled by exchange with a CoO (111) thin film has been studied. The interfacial exchange interaction triggers the appearance of an out-of-plane magnetization in the CoO (111) film. Co and Ni60Cu40 particles were chosen, as they present an order of magnitude difference in the saturation magnetization and Curie temperatures that surround the Néel temperature of CoO. In both cases, the exchange coupling leads to an increase of the coercive field, up to 200% in Co particles, and small exchange bias of 100 Oe when the external magnetic field is applied in the CoO (111) plane. When the field is applied along the CoO [111] direction, an unexpected net magnetization of the CoO (111) layer is revealed. Interestingly, it scales with the particles magnetization. The results are explained in terms of a large interfacial interaction and an induced canting of the CoO spins in the close region of the interface. The large value of the CoO magnetization indicates that the canting settles over an extended thickness of at least 3.7 nm and 1.2 nm in the cases of Co and Ni60Cu40 particles, respectively, which is consistent with a compensated antiferromagnetic spins surface.

Microstructural Investigations of Ca and La Doped CoO Thin Films Prepared by Pulsed Laser Deposition Technique

Two types of different oxides multifunctional thin films were deposited by PLD technique on the surface of Si and MgO substrates. First of them was CoO doped with Ca content characterized by fcc (halite) structure and second one was perovskite-type LaCoO3 compound. Their microstructure, chemical/phase composition and morphology were examined by means of diverse techniques (SEM, TEM, EDS). For the surface topography observations of thin films the Atomic Force Microscopy (AFM) was applied. Nanohardness and scratch tests (adhesion measurements) were also performed for estimation of (Co,Ca)O and LaCoO3 films mechanical properties and quality. Obtained results confirm that using PLD technique it is possible to carry stoichiometric composition of different compounds from the target to single crystal substrate however the microstructure and properties of obtained thin films are highly influenced by the substrate’s material and laser ablation parameters (laser wavelength, energy density, time and target-substrate distance).

Effect of Concentration on the Optical and Solid State Properties of CoO Thin Films Deposited Using the Aqueous Chemical Growth (ACG) Method

Thin films of Cobalt(II) Oxide were deposited from equimolar concentrations of Cobalt Chloride, and Hexamethylenetetramine on clean glass substrates using the Aqueous Chemical Growth method in order to determine the effect of precursor concentration on their optical and solid state properties. The analytical tools used for the study include, Rutherford Back Scattering (RBS) spectroscopy for elemental analysis and determination of film thickness, X-Ray Difftraction (XRD) for crystallographic structure, a UV-VIS spectrophotometer for optical and other solid state properties and a photomicroscope for photomicrographs. The results indicate that an increase in the concentration of precursor materials makes ACG CoO thin film a better absorber of ultraviolet radiation, a better transmitter of infra-red radiation, a reflector of visible radiation and a material having an increased band gap. The ACG CoO thin film deposited from 0.1 M precursor concentration was found to be a suitable material for the construction of thermographic devices, poultry houses etc. It can also serve as window layer in solar cells among other optoelectronic applications.

Synthesis and Characterization of Co<sub>3</sub>O<sub>4</sub> Thin Film

Nanosized Co3O4 thin films were prepared on glass substrates by using sol-gel spin coating technique. The effect of annealing temperature (400°C - 700°C) on structural, morphological, electrical and optical properties of Co3O4 thin films were studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Electrical conductivity and UV-visible Spectroscopy (UV-Vis). XRD measurements show that all the films are nanocrystallized in the cubic spinel structure and present a random orientation. Six prominent peaks, corresponding to the (111) phase (2θ ≈ 18.90°), (220) phase (2θ ≈ 31.29°), (311) phase (2θ ≈ 36.81°), (222) phase (2θ ≈ 38.54°), (400) phase (2θ ≈ 44.80°), (511) phase (2θ ≈ 59.37°) and (440) phase (2θ ≈ 65.27°) appear on the diffractograms. The crystallite size increases with increasing annealing temperature. These modifications influence the optical properties. The morphology of the sol gel derived Co3O4 shows nanocrystalline grains with some overgrown clusters and it varies with annealing temperature. The optical band gap has been determined from the absorption coefficient. We found that the optical band gap energy decreases from 2.58 eV to 2.07 eV with increasing annealing temperature between 400°C - 700°C. These mean that the optical quality of Co3O4 films is improved by annealing. The dc electrical conductivity of Co3O4 thin films were increased from 10–4 to 10–2 (Ω.cm)–1 with increase in annealing temperature. The electron carrier concentration (n) and mobility (μ) of Co3O4 films annealed at 400°C - 700°C were estimated to be of the order of 2.4 to 4.5 × 1019 cm–3 and 5.2 to 7.0 × 10–5 cm2.V–1.s–1 respectively. It is observed that Co3O4 thin film annealing at 700°C after deposition provide a smooth and flat texture suited for optoelectronic applications.

Growth, Structural and Mechanical Characterization and Reliability of Chemical Vapor Deposited Co and Co<sub>3</sub>O<sub>4</sub> Thin Films as Candidate Materials for Sensing Applications

The adhesion and mechanical stability of thin film coatings on substrates is increasingly becoming a key issue in device reliability as magnetic and storage technology driven products demand smaller, thinner and more complex functional coatings. In the present study, chemical vapor deposited Co and Co3O4thin films on SiO2and Si substrates are produced, respectively. Chemical vapor deposition is the most widely used deposition technique which produces thin films well adherent to the substrate. Co and Co3O4thin films can be used in innovative applications such as magnetic sensors, data storage devices and protective layers. The produced thin films are characterized using nanoindentation technique and their nanomechanical properties (hardness and elastic modulus) are obtained. Finally, an evaluation of the reliability of each thin film (wear analysis) is performed using the hardness to elastic modulus ratio in correlation to the ratio of irreversible work to total work for a complete loading-unloading procedure.

Fabrication of Thermoelectric La0.95Sr0.05CoO3 Thin Film and Seebeck Coefficient Measurement

The p-type perovskite oxides La1-xSrxCoO3 are a promising group of complex oxide thermoelectric materials because of its higher Seebeck coefficient. In this paper, the La0.95Sr0.05CoO3 thin film was prepared by spin coating. A custom-made micro-electromechanical system based device was used to measure the voltage output and Seebeck coefficient of the thin film. The measured Seebeck coefficient of the thin film was 350 μV/K.

Surface Electronic Structure Transitions at High Temperature on Perovskite Oxides: The Case of Strained La0.8Sr0.2CoO3 Thin Films

In-depth probing of the surface electronic structure on solid oxide fuel cell (SOFC) cathodes, considering the effects of high temperature, oxygen pressure, and material strain state, is essential toward advancing our understanding of the oxygen reduction activity on them. Here, we report the surface structure, chemical state, and electronic structure of a model transition metal perovskite oxide system, strained La(0.8)Sr(0.2)CoO(3) (LSC) thin films, as a function of temperature up to 450 °C in oxygen partial pressure of 10(-3) mbar. Both the tensile and the compressively strained LSC film surfaces transition from a semiconducting state with an energy gap of 0.8-1.5 eV at room temperature to a metallic-like state with no energy gap at 200-300 °C, as identified by in situ scanning tunneling spectroscopy. The tensile strained LSC surface exhibits a more enhanced electronic density of states (DOS) near the Fermi level following this transition, indicating a more highly active surface for electron transfer in oxygen reduction. The transition to the metallic-like state and the relatively more enhanced DOS on the tensile strained LSC at elevated temperatures result from the formation of oxygen vacancy defects, as supported by both our X-ray photoelectron spectroscopy measurements and density functional theory calculations. The reversibility of the semiconducting-to-metallic transitions of the electronic structure discovered here, coupled to the strain state and temperature, underscores the necessity of in situ investigations on SOFC cathode material surfaces.

RETRACTED ARTICLE: Sol–gel derived Co3O4 thin films: effect of annealing on structural, morphological and optoelectronic properties

Nanocrystalline Co3O4 thin films were prepared on glass substrates by using sol–gel spin coating technique. The effect of annealing temperature (400–700 °C) on structural, morphological, electrical and optical properties of Co3O4 thin films were studied by X-ray diffraction (XRD), Scanning Electron Microscopy, Electrical conductivity and UV–visible Spectroscopy. XRD measurements show that all the films are nanocrystallized in the cubic spinel structure and present a random orientation. The crystallite size increases with increasing annealing temperature (53–69 nm). These modifications influence the optical properties. The morphology of the sol–gel derived Co3O4 shows nanocrystalline grains with some overgrown clusters and it varies with annealing temperature. The optical band gap has been determined from the absorption coefficient. We found that the optical band gap energy decreases from 2.58 to 2.07 eV with increasing annealing temperature between 400 and 700 °C. These mean that the optical quality of Co3O4 films is improved by annealing. The dc electrical conductivity of Co3O4 thin films were increased from 10−4 to 10−2 (Ω cm)−1 with increase in annealing temperature. The electron carrier concentration (n) and mobility (μ) of Co3O4 films annealed at 400–700 °C were estimated to be of the order of 2.4–4.5 × 1019 cm−3 and 5.2–7.0 × 10−5 cm2 V−1 s−1 respectively. It is observed that Co3O4 thin film annealing at 700 °C after deposition provide a smooth and flat texture suited for optoelectronic applications.

Growth temperature control of the epitaxy, magnetism, and transport in SrTiO3(001)/La0.5Sr0.5CoO3 thin films

The authors report a detailed study of the influence of deposition temperature on the microstructure, phase purity, nanoscale chemical homogeneity, stoichiometry, and magnetic and electronic properties of epitaxial La0.5Sr0.5CoO3 thin films grown on SrTiO3(001) substrates via reactive dc magnetron sputtering. The results are interpreted in terms of the temperature-dependent interplay between crystallization, strain relaxation, and cation mobility (which improve with increasing deposition temperature), and oxygenation (which deteriorates at the highest deposition temperatures). In addition to the established approach to epitaxial sputter deposition based on high temperature deposition combined with subsequent ex situ annealing in O2, our results also identify a narrow deposition temperature window ∼600–625 °C, where single phase, highly crystalline, low surface roughness epitaxial films can be obtained with close to ideal stoichiometry without postdeposition annealing. Electronic and magnetic properties similar to bulk single crystals can be obtained in this region.

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Total-Reflection Inelastic X-Ray Scattering from a 10-nm ThickLa0.6Sr0.4CoO3Thin Film

To study equilibrium changes in composition, valence, and electronic structure near the surface and into the bulk, we demonstrate the use of a new approach, total-reflection inelastic x-ray scattering, as a sub-keV spectroscopy capable of depth profiling chemical changes in thin films with nanometer resolution. By comparing data acquired under total x-ray reflection and penetrating conditions, we are able to separate the O K-edge spectra from a 10 nm La0.6Sr0.4CoO3 thin film from that of the underlying SrTiO3 substrate. With a smaller wavelength probe than comparable soft x-ray absorption measurements, we also describe the ability to easily access dipole-forbidden final states, using the dramatic evolution of the La N4,5 edge with momentum transfer as an example.

Strongly oriented Co3O4 thin films on MgO(100) and MgAl2O4(100) substrates by PE-CVD

Co3O4 thin films were grown on MgO(100) and MgAl2O4(100) by plasma enhanced-chemical vapor deposition (PE-CVD) from the [Co(dpm)2] precursor. Depositions on both single crystal substrates were performed from Ar/O2 plasmas at temperatures between 100 and 400 °C in order to tailor the chemical and physical properties of the synthesized films. The composition, morphology and structure of the Co3O4 systems were thoroughly analyzed by XPS, SIMS, FE-SEM and bidimensional XRD. The obtained results evidenced the formation of high-purity and strongly oriented Co3O4 thin films, with features dependent on the used substrate and the adopted growth temperature.