Iron Oxide Thin Films Research Articles

Effect of ruthenium alloy on the band gap value of FeS2-pyrite

In the aim of increasing the band gap value of FeS2-pyrite thin films having good crystallinity, high absorption coefficient (∼105cm−1) and a band gap of about 0.95eV, which were synthesized by a simple and low cost method consisting of sulphuration, under vacuum (≅10−4Pa), of amorphous iron oxide thin films pre-deposited by spray pyrolysis of FeCl3·6H2O (0.03M)-based aqueous solution onto glass substrates heated at 350°C, we draw attention in this work to the fabrication of these films after alloying with Ru. We followed two methods: the first one consists of spraying aqueous RuCl3·3H2O solution, during shorter time, on heated pre-deposited oxide layer at the same spray conditions with molar ratio as RuCl3·3H2O:FeCl3·6H2O=x:1−x (x=0.3966, 0.1586, 0.0396, 0.0317, 0.0156 and 0.00). The second consists of spraying on heated substrate, an aqueous solution prepared by dissolving ferric chloride (FeCl3·6H2O) and Ruthenium(III) chloride hydrate (RuCl3·3H2O) with molar ratio as RuCl3·3H2O:FeCl3·6H2O=x:1−x (x=0.3171, 0.1586, 0.234, 0.0119, 0.0051, 0.0025 and 0.00). Afterward, the as obtained films are sulphured at the optimum conditions (pressure≅10−4Pa, duration=6h, temperature=450°C). Dark layers having granular structure, were obtained. The effect of alloying on atomic structure, as well as optical properties of Ru-alloyed FeS2-pyrite films were examined by XRD, optical and MEB characterisations. Our results show that the band gap value of Fe1−xRuxS2 layers increases versus the alloy percentage. An optimum band gap value was obtained according to the first method of about 1.48eV for x=0.0156; which is considered a very interesting result for the photovoltaic applications of our films. An increase of the band gap value versus the Ru concentration with the second method was observed, as well.

Spatially resolved variations in reflectivity across iron oxide thin films

The spin polarising properties of the iron oxide magnetite (Fe3O4) make it attractive for use in spintronic devices, but its sensitivity to compositional and structural variations make it challenging to prepare reliably. Infrared microspectroscopy and modelling are used to determine the spatial variation in the chemical composition of three thin films of iron oxide; one prepared by pulsed laser deposition (PLD), one by molecular beam epitaxy (MBE) deposition of iron whilst simultaneously flowing oxygen into the chamber and one by flowing oxygen only once deposition is complete. The technique is easily able to distinguish between films which contain metallic iron and different iron oxide phases as well as spatial variations in composition across the films. The film grown by post-oxidising iron is spatially uniform but not fully oxidised, the film grown by simultaneously oxidising iron showed spatial variation in oxide composition while the film grown by PLD was spatially uniform magnetite.

Plasma Deposited Thin Iron Oxide Films as Electrocatalyst for Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells

The possibility of using plasma deposited thin films of iron oxides as electrocatalyst for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFC) was examined. Results of energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) analysis indicated that the plasma deposit consisted mainly of FeOX structures with the X parameter close to 1.5. For as deposited material iron atoms are almost exclusively in the Fe3+ oxidation state without annealing in oxygen containing atmosphere. However, the annealing procedure can be used to remove the remains of carbon deposit from surface. The single cell test (SCT) was performed to determine the suitability of the produced material for ORR. Preliminary results showed that power density of 0.23 mW/cm2 could be reached in the tested cell.DOI: http://dx.doi.org/10.5755/j01.ms.23.1.14406

Editors' Choice—A Methodology to Electrochemically Fabricate Fe-Ni-Co Nanotips

Fe-Ni-Co nanotips at the end of nanowires are fabricated at the interface of two Fe-Ni-Co regions via a combination of pulse electrodeposition, anodization and chemical etching. The conditions to electrodeposit and anodize the Fe-Ni-Co nanowires in polycarbonate templates were investigated with a rotating cylinder electrode (RCE) to inspect the polarization behavior of the thin film deposition. The wires were fabricated with three, consecutive electrochemical conditions, where first an Fe-Ni-Co wire segment is deposited, followed by an anodic potential to induce growth of an iron oxide thin film, and then followed by an applied, pulse cathodic current density to reduce the oxide and deposit another layer of Fe-Ni-Co. Upon etching, tips formed at the end of the last Fe-Ni-Co region, as evidenced by SEM. Potential transients during the last applied cathodic pulse current step, suggests that both the reduction of the oxide and metal occur, and that TEM/SAED confirm changes in the crystalline Fe-Ni-Co structure at the interfacial region between steps that contributes to the tip formation.

Iron oxide grown by low-temperature atomic layer deposition

Atomic layer deposition (ALD) is a promising technology for fabricating conformal thin films of atomlevel thickness with chemical composition control over a variety of structures. This paper demonstrates the ALD of iron oxide thin films using a novel iron precursor, namely, bis[bis(trimethylsilyl)amide]iron [Fe(btmsa)2] and hydrogen peroxide as an oxygen source. The growth characteristics of iron oxide were investigated by varying the deposition temperatures from 100 to 225 °C, such that the ALD growth mode was observed at 150 to 175 °C with an average growth rate of 0.035±0.005 nm/cycle. The films deposited in ALD mode exhibited highly linear film thicknesses with the number of cycles and excellent conformality over high-aspect-ratio trenches. In addition, the deposited films were extremely pure and revealed a hematite phase without any subsequent heat treatment, even if the films were deposited at low temperatures.

α-Fe2O3 thin films by liquid phase deposition: low-cost option for supercapacitor

In the present study, iron oxide (α-Fe2O3) thin films with good adhesion on stainless steel substrates are deposited by liquid phase deposition (LPD) technique, which is additive and binder-free. Iron oxyhydroxide (FeOOH) thin films are formed by means of a ligand-exchange equilibrium reaction of metal-fluoro complex ions and an F−ions consuming reaction by using boric acid (H3BO3) as a scavenging agent. These films are annealed at 500 °C to get α-Fe2O3 thin films. The transformation from hydrophobic to hydrophilic nature of the films is observed due to annealing. The films are characterized by different techniques. The α-Fe2O3 film is checked for electrochemical supercapacitive performance in Na2SO3 solutions of various concentrations. Specific capacitance is calculated from cyclic voltammetry at numerous scan rates (5–200) mV s−1. The highest obtained value of specific capacitance is 582 F g−1 at 5 mV s−1 for 0.5 M Na2SO3 electrolyte. The maximum values of specific power and specific energy are 6.9 and 53.4 Wh kg−1 from the charge-discharge curve at the current density 2 mA cm−2 in 0.5 M Na2SO3 electrolyte.

THE EFFECTS OF pH ON STRUCTURAL AND OPTICAL CHARACTERIZATION OF IRON OXIDE THIN FILMS

In this study, the iron oxide thin films have been produced by chemical bath deposition (CBD) method as a function of pH onto amorphous glass substrates. The surface images of the films were investigated with scanning electron microscope (SEM). The crystal structures, orientation of crystallization, crystallite sizes, and dislocation density i.e. structural properties of the thin films were analyzed with X-ray diffraction (XRD). The optical band gap ([Formula: see text], optical transmission ([Formula: see text]%), reflectivity ([Formula: see text]%), absorption coefficient ([Formula: see text], refraction index ([Formula: see text]), extinction coefficient ([Formula: see text]) and dielectric constant ([Formula: see text]) of the thin films were investigated depending on pH, deposition time, solution temperature, substrate temperature, thickness of the films by UV–VIS spectrometer.

Effects of temperature on the optical properties of iron oxide (Fe2O3) thin films synthesized by chemical bath deposition

Synthesis of iron oxide (Fe2O3) thin films on glass substrates was carried out by chemical bath deposition technique, with a view to investigate the effects of variation of temperature on the optical properties of the films. Structural characterization of the films obtained by X-ray diffraction (XRD), revealed that they were γ-Fe2O3. The optical property study revealed that the as deposited films had a transmittance of about 75–90% in the VIS-NIR regions of electromagnetic spectrum, but this was slightly reduced to a range of about 70–83% in the same regions when treated with heat. Their band-gap was found to be 2.38eV for the unannealed, while it ranged from 2.55–2.68eV for the annealed films. A variation in other optical properties − refractive index, extinction coefficient etc –, was observed with heat treatment of the films, though not sequential. Their optical properties and band gaps make the films good materials for wide range of applications.

Large third-order optical nonlinearities in iron oxide thin films synthesized by reactive pulsed laser deposition

We report on a study of the third-order nonlinear optical properties of Fe2O3 thin films, grown by the method of laser deposition on silica (SiO2) substrates. The films were synthesized on substrates at different temperatures (293 K and 800 K) and under different oxygen pressures (0.1 Pa, 0.5 Pa, 1.0 Pa). The resulting films were amorphous, if grown on cold substrates (293 K), or polycrystalline otherwise. The third-order optical susceptibility χ(3) of the films was determined by the Z-scan method at the wavelengths of 1064 nm and 532 nm and the laser pulse width of 20 ns. Remarkably high χ(3) values on the order of 10−4 esu at 1064 nm are obtained. The results show that Fe2O3 thin films are promising nonlinear materials for contemporary optoelectronics.

Kinetics versus Charge Separation: Improving the Activity of Stoichiometric and Non-Stoichiometric Hematite Photoanodes Using a Molecular Iridium Water Oxidation Catalyst

Oxygen-deficient iron oxide thin films, which have recently been shown to be highly active for photoelectrochemical water oxidation, were surface-functionalized with a monolayer of a molecular iridium water oxidation cocatalyst. The iridium catalyst was found to dramatically improve the kinetics of the water oxidation reaction at both stoichiometric and nonstoichiometric α-Fe2O3-x surfaces. This was found to be the case in both the dark and in the light as evidenced by cyclic voltammetry, Tafel analysis, and electrochemical impedance spectroscopy (EIS). Oxygen evolution measurements under working conditions confirmed high Faradaic efficiencies of 69–100% and good stability over 22 h of operation for the functionalized electrodes. The resulting ∼200–300 mV shift in onset potential for the iridium-functionalized sample was attributed to improved interfacial charge transfer and oxygen evolution kinetics. Mott–Schottky plots revealed that there was no shift in flat-band potential or change in donor density fo...

Phase transformations in thin iron oxide films: Spectromicroscopic study of velocity and shape of the reaction fronts

Combining low energy electron microscopy (LEEM) with low energy electron diffraction (LEED) and x-ray photoemission electron microscopy (XPEEM), we studied the phase transformations between Fe3O4, γ-Fe2O3, and α-Fe2O3, grown as 10nm thin oxide films on Pt(111) and Ag(111) single crystals. These transformations occur as moving reaction fronts in most cases, the shapes and velocities of which show strong dependences on temperature and oxygen pressure, but also on defects like step bunches of the supporting substrate and domain boundaries in the initial oxide film. While the non-uniform moving fronts make quantitative analysis difficult, we have extracted approximate values for the average front velocities. We discuss these as well as the qualitative information on the non-uniform fronts in terms of the known geometric situations and the likely motional steps.

Charge-Transfer Complexes and Photochemistry of Ozone with Ferrocene and n-Butylferrocene: A UV-vis Matrix-Isolation Study.

The reactions of ozone with ferrocene (cp2Fe) and with n-butylferrocene (n-butyl cp2Fe) were studied using matrix isolation, UV-vis spectroscopy, and theoretical calculations. The codeposition of cp2Fe with O3 and of n-butyl cp2Fe with O3 into an argon matrix led to the production of 1:1 charge-transfer complexes with absorptions at 765 and 815 nm, respectively. These absorptions contribute to the green matrix color observed upon initial deposition. The charge-transfer complexes underwent photochemical reactions upon irradiation with red light (λ ≥ 600 nm). Theoretical UV-vis spectra of the charge-transfer complexes and photochemical products were calculated using TD-DFT at the B3LYP/6-311G++(d,2p) level of theory. The calculated UV-vis spectra were in good agreement with the experimental results. MO analysis of these long-wavelength transitions showed them to be n→ π* on the ozone subunit in the complex and indicated that the formation of the charge-transfer complex between ozone and cp2Fe or n-butyl cp2Fe affects how readily the π* orbital on O3 is populated when red light (λ ≥ 600 nm) is absorbed. 1:1 complexes of cp2Fe and n-butyl cp2Fe with O2 were also observed experimentally and calculated theoretically. These results support and enhance previous infrared studies of the mechanism of photooxidation of ferrocene by ozone, a reaction that has considerable significance for the formation of iron oxide thin films for a range of applications.

Magnetic field induced one-dimensional nano/micro structures growth on the surface of iron oxide thin film

The influence of external magnetic field on the morphology of α-Fe2O3 thin film formed at liquid–vapor interface has been investigated. Application of magnetic field during the growth of film resulted in the magnetic moment ordering of constituent nanoparticles. Thus formed α-Fe2O3 thin film was transferred to a glass substrate, which upon annealing converted into one dimensional (1D) nanostructured thin film due to the oriented attachment of magnetically ordered nanoparticles. The effect of dopants viz. Ni2+ and Co2+ on the directional growth, and magnetic properties of nanostructures has also been investigated. The Ni2+ and Co2+ doped α-Fe2O3 1D nanostructured thin films show superparamagnetic and ferromagnetic behavior, respectively, whereas undoped α-Fe2O3 film exhibits superparamagnetism. From the room temperature magnetization measurements of films, it is found that the magnetization depends upon the morphology and magneto-crystalline anisotropy attributes of the film nanostructures.

Iron oxide thin films: MBE growth in low oxygen pressure and electrical and magnetic properties

Epitaxial iron oxide films were grown on MgO(001) substrate by using molecular beam epitaxy. The growth modes, magnetism and transport properties of the films were strongly dependent on the oxygen pressure during film growth. Fe3O4 film was grown in oxygen poor environment (2.3×10−7Torr), while γ-Fe2O3 film was grown in 8.2×10−6Torr oxygen. The average roughness decreases from 1.02 to 0.26nm with oxygen pressure during growth.

Morphology, structural and optical properties of iron oxide thin film photoanodes in photoelectrochemical cell: Effect of electrochemical oxidation

Hematite (α-Fe2O3) is a promising semiconductor as photoanode in solar hydrogen production from photoelectrolysis of water due to its appropriate band gap, low cost and high electrochemical stability in aqueous caustic electrolytes. Operation of such photoanode in a biased photoelectrochemical cell constitutes an anodization with consequent redox reactions at the electrode surface. α-Fe2O3 thin film photoanodes were prepared by simple and inexpensive dip coating method on fluorine doped tin oxide (FTO) glass substrate, annealed in air at 500°C for 2h, then electrochemically oxidized (anodized) in 1M KOH at 500mV for 1min in dark and light conditions. Changes in structural properties and morphology of α-Fe2O3 nanoparticles films were investigated by XRD, Raman spectroscopy and a high resolution FE-SEM. The average grain size was observed to increase from ~57nm for pristine samples to 73 and 77nm for anodized samples in dark and light respectively. Broadening and red shift in Raman spectra in anodized samples may be attributed to lattice expansion upon oxidation. The UV–visible measurements revealed enhanced absorption in the photoanodes after the treatment. The findings suggest that the anodization of the photoelectrode in a biased cell causes not only changes of the molecular structure at the surface, but also changes in the crystallographic structure which can be detected with x-ray diffractometry.

Low-cost flexible supercapacitors with high-energy density based on nanostructured MnO2 and Fe2O3 thin films directly fabricated onto stainless steel.

The facile and economical electrochemical and successive ionic layer adsorption and reaction (SILAR) methods have been employed in order to prepare manganese oxide (MnO2) and iron oxide (Fe2O3) thin films, respectively with the fine optimized nanostructures on highly flexible stainless steel sheet. The symmetric and asymmetric flexible-solid-state supercapacitors (FSS-SCs) of nanostructured (nanosheets for MnO2 and nanoparticles for Fe2O3) electrodes with Na2SO4/Carboxymethyl cellulose (CMC) gel as a separator and electrolyte were assembled. MnO2 as positive and negative electrodes were used to fabricate symmetric SC, while the asymmetric SC was assembled by employing MnO2 as positive and Fe2O3 as negative electrode. Furthermore, the electrochemical features of symmetric and asymmetric SCs are systematically investigated. The results verify that the fabricated symmetric and asymmetric FSS-SCs present excellent reversibility (within the voltage window of 0–1 V and 0–2 V, respectively) and good cycling stability (83 and 91%, respectively for 3000 of CV cycles). Additionally, the asymmetric SC shows maximum specific capacitance of 92 Fg−1, about 2-fold of higher energy density (41.8 Wh kg−1) than symmetric SC and excellent mechanical flexibility. Furthermore, the “real-life” demonstration of fabricated SCs to the panel of SUK confirms that asymmetric SC has 2-fold higher energy density compare to symmetric SC.

Fabrication of Thin Films of α-Fe2O3 via Atomic Layer Deposition Using Iron Bisamidinate and Water under Mild Growth Conditions.

Atomic layer deposition (ALD) has been shown to be an excellent method for depositing thin films of iron oxide. With limited iron precursors available, the methods widely used require harsh conditions such as high temperatures and/or the use of oxidants such as ozone or peroxide. This letter aims to show that bis(N,N'-di-t-butylacetamidinato) iron(II) (iron bisamidinate or FeAMD) is an ideal ALD precursor because of its reactivity with water and relative volatility. Using in situ QCM analysis, we show outstanding conformal self-limiting growth of FeOx using FeAMD and water at temperatures lower than 200 °C. By annealing thin films of FeOx at 500 °C, we observe the formation of α-Fe2O3, confirming that we can use FeAMD to fabricate thin films of catalytically promising iron oxide materials using moderate growth conditions.

Inhibitory Effect Evaluation of Glycerol‐Iron Oxide Thin Films on Methicillin‐Resistant Staphylococcus aureus

The main purpose of this study was to evaluate the inhibitory effect of glycerol‐ iron oxide thin films on Methicillin-Resistant Staphylococcus aureus (MRSA). Our results suggest that glycerol‐iron oxide thin films could be used in the future for various biomedical and pharmaceutical applications. The glycerol‐iron oxide thin films have been deposited by spin coating method on a silicon (111) substrate. The structural properties have been studied by X‐ray diffraction (XRD) and scanning electron spectroscopy (SEM). The XRD investigations of the prepared thin films demonstrate that the crystal structure of glycerol‐iron oxide nanoparticles was not changed after spin coating deposition. On the other hand, the SEM micrographs suggest that the size of the glycerol‐iron oxide microspheres increased with the increase of glycerol exhibiting narrow size distributions. The qualitative depth profile of glycerol‐iron oxide thin films was identified by glow discharge optical emission spectroscopy (GDOES). The GDOES spectra revealed the presence of the main elements: Fe, O, C, H, and Si. The antimicrobial activity of glycerol‐iron oxide thin films was evaluated by measuring the zone of inhibition. After 18 hours of incubation at 37°C, the diameters of the zones of complete inhibition have been measured obtaining values around 25 mm.

Optical and Magnetic Properties of Iron Oxide Thin Films

Iron oxide thin film has been prepared by sol-gel dip coating method. The film is deposited at withdrawal speed of 250 mms-1 on glass substrate. The film is further characterized using UV-Visible spectroscopy Scanning electron microscopy (SEM), and Vibrating sample magnetometer (VSM) for the study of their optical and magnetic properties. The optical absorption showed direct band gap of 1.9eV. The smooth and homogenous surface of film was observed by SEM. The VSM studies reveal that film is ferromagnetic in nature.

Study of Phase Transition in Iron Oxide Thin Films

We here report preparation and characterization of iron oxide thin films using sol-gel method. Iron nitrate is used as precursor whereas water and ethylene glycol as solvent. Three different sols are prepared with pH 1 (Acidic), 7 (neutral) and 13 (basic). The films are spin coated on copper substrate and annealed at 300˚C for 60mins. XRD results indicate the formation of phase pure Fe3O4 at pH 1 while phase transition from Fe3O4 to γ-Fe2O3 is observed with change in pH from 1 to 7. Whereas in the basic medium (pH 13) α-Fe2O3 phase is obtained. These transitions between different phases of iron oxide strongly affect the magnetic properties. Films with pH 1 show highest saturation magnetization while decrease in saturation magnetization is observed as pH is increased to 7, indicative of phase transition from Fe3O4 to γ-Fe2O3. Further decrease in saturation magnetization in basic medium is associated with phase transition to α-Fe2O3 phase.