CoO3 Thin Films Research Articles

Optical Properties Dependence on Deposition Time for CoO(OH) Thin Films Synthesized by CBD Technique

Optical Properties Dependence on Deposition Time for CoO(OH) Thin Films Synthesized by CBD Technique

Growth optimization and electronic structure of ultrathin CoO films on Ag(001): A LEED and photoemission study

We present here a detailed growth optimization of CoO thin film on Ag(001) involving the effects of different growth parameters on the electronic structure. A well-ordered stoichiometric growth of 5 ML CoO film has been observed at 473 K substrate temperature and 1 × 10−6 mbar oxygen partial pressure. The growth at lower substrate temperature and oxygen partial pressure show non-stoichiometric impurity phases which have been investigated further to correlate the growth parameters with surface electronic structure. The coverage dependent valence band electronic structure of the films grown at optimized condition reveals the presence of interfacial states near the Fermi edge (EF) for lower film coverages. Presence of interfacial states in the stoichiometric films rules out their defect-induced origin. We argue that this is an intrinsic feature of transition metal monoxides like NiO, CoO, MnO in the low coverage regime.

Effect of film thickness and strain state on the structure, magnetic and transport properties of La0.9Sr0.1CoO3 films

In this paper, we investigate the effects of film thickness and strain state on the structure, magnetism and electrical transport properties of La0.9Sr0.1CoO3 (LSCO) thin films. The x-ray diffraction analysis shows that the out-of-plane lattice parameters of LSCO films grown on different substrates gradually approach those of the bulk LSCO with increasing film thickness, indicating that the strain induced by the substrates is partially relaxed in thick films, i.e. 100 nm. The film magnetism is gradually enhanced with increasing film thickness. For the 20-nm-thick film, it is almost non-magnetic. However, the film becomes ferromagnetic when its thickness increases up to 100 nm. The magnetism is stronger for the film under compressive strain than that under tensile strain. The change in the magnetic properties of films is attributed to the lattice strain, which can affect the spin state of Co ions. Regarding the conductivity, all the samples show a semiconducting-like behavior, and the resistivity is inversely proportional to the film thickness. The electrical transport mechanism of the films with different thickness transforms from a three-dimensional variable range hopping (VRH) to a small-polaron hopping conduction (SPC) with increasing temperature. Fascinatingly, the temperature for transport mechanism transformation decreases gradually with increasing film thickness. This work could shed light on the electrical transport mechanism of LSCO films with different thickness.

One-Step Synthesis of Co3O4 Thin Film by Reactive Spray Deposition Technology for Efficient Electrochemical Water Splitting

ABSTRACTEfficient catalysts for the oxygen evolution reaction (OER) are widely applied in fuel cells and rechargeable lithium air batteries. It is desirable but challenging to achieve comparable activity to that of the noble-metal catalyst with non-precious metal catalyst. Highly active Co3O4 thin film electrodes have been successfully synthesized by a rapid one-step flame combustion synthesis method called Reactive Spray Deposition Technology. X-ray diffraction confirms the absence of any impurity phase with this synthesis process. The detailed morphology of the Co3O4 thin film is investigated with scanning electron microscopy and transmission electron microscopy. Cyclic voltammetry is used to investigate the redox activity of Co3+ to Co4+ which is crucial for the OER performance. The as-prepared Co3O4 catalyst demonstrates promising activity for OER, with an overpotential of 399 mV (at 10 mA cm-2) for OER.

Wurtzite CoO: a direct band gap oxide suitable for a photovoltaic absorber.

A direct band gap of 1.6 eV has been identified in wurtzite CoO thin films, which matches the required value to achieve a theoretically high conversion efficiency solar cell. Its p-type conduction has been determined and an intense sub-gap absorption between 0.7 and 1.1 eV has been observed.

Formation of Ruddlesden-Popper Faults and Their Effect on the Magnetic Properties in Pr0.5Sr0.5CoO3 Thin Films.

Epitaxial Pr0.5Sr0.5CoO3 thin films have been grown on single-crystalline (La0.289Sr0.712)(Al0.633Ta0.356)O3(001) substrates by the pulsed laser deposition technique. The magnetic properties and microstructure of these films are investigated. It is found that Ruddlesden-Popper faults (RP faults) can be introduced in the films by changing the laser repetition rate. The segregation of Pr at the RP faults is characterized by atomic-resolution chemical mapping. The formation of the RP faults not only contributes to the epitaxial strain relaxation but also significantly decreases the ferromagnetic long-range order of the films, resulting in lower magnetizations than those of the fault-free films. Our results provide a strategy for tuning the magnetic properties of cobalt-based perovskite films by modifying the microstructure through the film growth process.

Magnetism in epitaxial PrCoO3 and Pr0.7Y0.3CoO3 thin films

Lattice distortions can stabilize magnetic ground states not observed in the bulk for thin films of undoped cobalt perovskites ACoO3. We have found that lattice distortions, in the form of tensile epitaxial strain, can stabilize a ferromagnetic ground state in PrCoO3 thin films below 65 K. However, in Pr0.7Y0.3CoO3, which has a smaller unit cell, similar levels of tensile strain are insufficient to induce ferromagnetism. These results indicate the importance of A-site cation choice for Co spin-state and Co-O-Co exchange interactions, offering another dimension to tune magnetic order in thin film cobalt perovskites.

In situ Fourier Transform Infrared Spectroscopy Diagnostic for Characterization and Performance Test of Catalysts

The present work establishes a systematic approach based on the application of in-situ Fourier transform infrared spectroscopy (FTIR) for the investigation of the crystal structure, thermal stability, redox behavior (temperature-programmed reduction/temperature-programmed re-oxidation) as well as the catalytic properties of Co3O4 thin films. The syntheses of Co3O4 were achieved by chemical vapor deposition in the temperature range of 400–500 °C. The structure analysis of the as-prepared material revealed the presence of two prominent IR bands peaking at 544 cm−1 (v1) and 650 cm−1 (v2) respectively, which originate from the stretching vibrations of the Co−O bond, characteristic of the Co3O4 spinel. The lattice stability limit of Co3O4 was estimated to be above 650 °C. The redox properties of the spinel structure were determined by integrating the area under the emission bands v1 and v2 as a function of the temperature. Moreover, Co3O4 has been successfully tested as a catalyst towards complete oxidation of dimethyl ether below 340 °C. The exhaust gas analysis during the catalytic process by in situ absorption FTIR revealed that only CO2 and H2O were detected as the final products in the catalytic reaction. The redox behavior suggests that the oxidation of dimethyl ether over Co3O4 follows a Mars-van Krevelen type mechanism. The comprehensive application of in situ FTIR provides a novel diagnostic tool in characterization and performance test of catalysts.

Reactive sputtering growth of Co3O4 thin films for all metal oxide device: a semitransparent and self-powered ultraviolet photodetector

All-oxide photodetectors-based on Co3O4 thin films are optimized and fabricated using large area reactive sputtering method. In particular, optical measurements of Co3O4 thin films show the presence of dual band gaps (Eg1 ~1.5eV and Eg2 ~2eV) and an average transmittance of 70% over the broad spectral range (300 − 1300nm) is useful to realize the semitransparent all metal oxide photoelectric device. A Co3O4-based semitransparent, high-performing, self-biased, ultraviolet-operated photodetector with Co3O4/ZnO/ITO architecture presented. Addition to this, Co3O4 device over-coated by MoO3 as hole transporter shows advantage of selective contact, resulting three times improvement in the photoresponse with fast UV detection (33 ms). This study will pave the way to design cost-effective, semitransparent, and efficient cobalt oxide-based photodetectors as well as photovoltaics.

Influence of Co-doping on optical properties and traps localization of ZnO films obtained by spray pyrolysis

We report a systematic investigation on the structural and optical properties of Co-doped ZnO and Co3O4 thin films grown by spray pyrolysis using acetates as precursors in low molarity solutions. XRD and optical transmittance measurements do not show secondary phases. Optical measurements exhibit the Co2+ signatures related to tetrahedral coordination in absorption and emission. Temperature-dependent PL shows the influence of traps up to 200K when they are shielded by thermal energy. The qualitative potential fluctuations model allows the evaluation of traps depth of as tenths of meV and the influence of Co-doping in the neighborhood of optically active Co2+.

Non‐enzymatic Fructose Sensor Based on Co3O4 Thin Film

AbstractIn this study, we report on the selective of fructose on Co3O4 thin film electrode surface. A facile chemical solution deposition technique was used to fabricate Co3O4 thin film on fluorine doped tin oxide, FTO, glass. Electrode characterization was done using XRD, HRTEM, SEM, AFM, and EIS. The constructed sensor exhibited two distinctive linear ranges (0.021–1.74 mM; 1.74–∼15 mM) covering a wide linear range of up to ∼15 mM at an applied potential of +0.6 V vs Ag/AgCl in 0.1 M NaOH solution. The sensor demonstrated high, reproducible and repeatable (R.S.D of <5 %) sensitivity of 495 (lower concentration range) & 53 (higher concentration range) μA cm−2 mM−1. The sensor produced a low detection limit of ∼1.7 μM (S/N=3). The electrode was characterised by a fast response time of <6 s and long term stability. The repeatability and stability of the electrode resulted from the chemical stability of Co3O4 thin film. The sensor was highly selective towards fructose compared to the presence of other key interferences i. e. AA, AC, UA. The ease of the electrode fabrication coupled with good electrochemical activity makes Co3O4 thin film, a promising candidate for non‐enzymatic fructose detection.

Room Temperature Ferromagnetism in Sm0.5Sr0.5CoO3 Thin Films Deposited by Pulsed Laser Deposition

Room Temperature Ferromagnetism in Sm_0.5Sr_0.5CoO₃ Thin Films Deposited by Pulsed Laser Deposition

Structural, optical, electrical and electrochemical properties of Fe:Co3O4 thin films for supercapacitor applications

Cubic structured pure and Fe-doped cobalt oxide thin film electrodes are successfully prepared by nebulizer spray pyrolysis technique. Single phase polycrystalline cubic structure with (220) plane orientation are observed in the XRD analysis for pure and Fe-doped cobalt oxide films. From the optical analysis, two bandgaps are observed in the range 1.366–1.713 eV and 2.846–2.925 eV for lower and higher energy regions respectively. HR-SEM images revealed the formation of well covered and spherical shaped particles in the formed films. The increase of electrical conductivity with Fe doping concentration has been confirmed at room temperature. The maximum specific capacitance value is observed in the 2.5 wt% of Fe doped Co3O4 thin film electrode at the scan rate of 2 mV/s.

Pulsed photonic fabrication of nanostructured metal oxide thin films

Nanostructured metal oxide thin films with a large specific surface area are preferable for practical device applications in energy conversion and storage. Herein, we report instantaneous (milliseconds) photonic synthesis of three-dimensional (3-D) nanostructured metal oxide thin films through the pulsed photoinitiated pyrolysis of organometallic precursor films made by chemical solution deposition. High wall-plug efficiency-pulsed photonic irradiation (xenon flash lamp, pulse width of 1.93 ms, fluence of 7.7 J/cm2 and frequency of 1.2 Hz) is used for scalable photonic processing. The photothermal effect of subsequent pulses rapidly improves the crystalline quality of nanocrystalline metal oxide thin films in minutes. The following paper highlights pulsed photonic fabrication of 3-D nanostructured TiO2, Co3O4, and Fe2O3 thin films, exemplifying a promising new method for the low-cost and high-throughput manufacturing of nanostructured metal oxide thin films for energy applications.

Preparation of p-type semiconductor perovskite La1–xSrxCoO3 films and their p–n heterostructure devices

Semiconductor La0.67Sr0.33CoO3 thin films has been investigated as function of oxygen atmosphere during film growth in pulsed laser deposition. While amount of oxygen greatly depends on an oxygen atmosphere during film growth, in condition of oxygen atmosphere from 4Pa to 100Pa, the carrier in La0.67Sr0.33CoO3 thin films were found to be positive, exhibiting p-type conduction. Furthermore, we prepared (p)-La0.67Sr0.33CoO3/(i)-CeO2/(n)-InGaZnOx heterostructure devices and investigated electrical properties. These results showed rectifying behavior was clearly observed in heterostructure at room temperature. The sharp increase of current with voltage, when voltage exceeds diffusion potential, indicates the conductive resistance was small. p-type semiconductor La0.67Sr0.33CoO3 thin films and their p–n heterostructure devices with rectifying behavior may aid in the development of various semiconductor devices such as three terminal transistors, light emitted diode (LED) and solar cell.

Novel Sn Doped Co3O4 Thin Film for Nonenzymatic Glucose Bio‐Sensor and Fuel Cell

AbstractA facile chemical solution deposition via two‐step spin coating technique was used to fabricate nano‐particulate novel Sn doped Co3O4 thin film for glucose sensor and fuel cell applications. Substitution of Sn into Co3O4 host lattice lead to a remarkable increase in the electrocatalytic activity of the Co3O4 electrode material. Film thickness played a significant role in enhancing the charge transferability of the electrode as was observed from electrochemical impedance spectroscopy (EIS). The best sensor exhibited two wide linear response ranges (2 μM up to ∼0.5 mM and 0.6 mM up to ∼5.5 mM respectively) with sensitivities of 921 and 265 μA cm−2 mM−1 respectively and low limit of detection of 100 nM (S/N=3). The sensor was very selective towards glucose in the presence of various interference and showed long term stability. Moreover, the developed thin film modified electrode could generate one electron current in nonenzymatic fuel cell setup at room temperature.

Electrochemical performance of potentio-dynamically deposited Co3O4 electrodes: influence of annealing temperature

Co3O4 thin films were deposited potentiodynamically on to the stainless steel substrate. Prepared samples were annealed within the temperature range 473 K to 873 K by the interval of 100 K. XRD study reveals cubic crystal structure of Co3O4. FE-SEM showed compact agglomerated granular type morphology. Electrochemical characterization of electrodes showed pseudo capacitive behavior. Maximum value of specific capacitance (441.17 F/g) was achieved at the scan rate 2 mV/s in 1 M KOH with 87.88% stability. Charge–discharge curves showed nonlinear behavior and used to calculate the specific energy, specific power and columbic efficiency which were 20.98 W/kg, 15.96 kW/kg and 86.63% respectively. EIS of complex impedance spectra showed internal resistance ~0.9435 Ω.

Synthesis of cobalt oxide (Co3O4) thin films by electrostatic spray pyrolysis technique (ESP)

The fabrication of cobalt oxide (Co3O4) thin films has received considerable attention. The crystalline quality of Co3O4 plays an important role in the properties of the fabricated film. This paper reports on the performance of a local electrostatic spray pyrolysis system to prepare Co3O4 thin films on glass substrates. The effect of applying an electric field during deposition on the structural growth and optical properties of Co3O4 thin films was studied. An improvement in the structure and optical properties was observed for the films deposited using an electric field, primarily because of the reduction in the droplet size. The results showed that applying a suitable electric field led to films formed with a smoother surface that were highly crystalline, with larger grain size, higher stoichiometry, and good optical properties that differed from those of the Co3O4 film deposited with no electric field. It was found that the grain size increased with the applied electric field. Optical absorption results revealed direct and indirect transitions for the Co3O4 thin films, and the band gap energy decreased with the applied electric field.

Stabilization of TiO2–Co3O4 thin films on a glass fiber material by introduction of silica into the matrix

The TiO2–Co3O4–SiO2 oxide system supported on glass fiber was synthesized and studied. The oxide layers attached to the glass fiber surface have a porous structure. Characteristics of thin-film coatings on the glass fiber substrate (oxide layer phase composition and adhesion to the glass fiber surface) depend on the silica concentration. The obtained materials are catalytically active towards the exhaustive oxidation of propane.

Facile Synthesis of Nanostructured Co3O4 thin Films at Low Temperature for High-Performance Pseudocapacitors

Co3O4 as a low cost, environmental friendly and nice corrosion resistant electrode material for pseudocapacitors, owns a high theoretical specific capacitance up to 3650 F g-1. However, the actual specific capacitance of Co3O4 is much lower than its theoretical value according to the present literatures. In order to improve the electrochemical performance of Co3O4 electrodes, various binder-free and self-supported Co3O4 thin films with distinct nanostructures were prepared by facile chemical bath deposition at low temperature (Figure.1). The diverse morphologies of Co3O4 thin films (3D thorn-like structure, porous nanoplates, nanoparticles and ultrathin nanosheets) were controlled by the different anions (SO4 2-, NO3 -, Cl- and CH3COO-) of cobalt sources used in synthesis procedure. Among them, the cobalt acetate derived Co3O4 thin film electrodes (A-Co3O4) exhibit the best electrochemical performances in 2 M KOH electrolyte (Figure. 2), such as a high specific capacitance (1545 F g-1) and nice cycling stability (84.6 % retention after 1000 charge-discharges at a high current density of 4 A g-1). Figure 1