Zinc Ferrite Thin Films Research Articles

Branched ZnFe2O4 nanorods grown via chemical spray pyrolysis technique for chemiresistive xylene gas sensor

In this work, we used a chemical spray pyrolysis technique to deposit zinc ferrite (ZF) thin films at different substrate temperatures to study xylene (C8H10) gas sensing properties. The focus is on the detection of xylene, a volatile organic compound (VOC) that is harmful to human health. It was found that the concentration of hazardous xylene gas was below the exposure limit. The substrate temperature has a notable impact on the sensor's performance, and ZF exhibits promise for discerning xylene selectively at 200 °C operating temperature. The results indicate that the ZF film deposited at 225 °C (ZF-B) exhibited a significant response (S = 47.4%) to a 50-ppm xylene concentration. Further analysis illustrates that the film substrate temperature deposited at 225 °C can have a unique morphology including thin branched rods, small nanorods with high surface area and roughness. These features contribute to enhanced sensing response by creating more active centers for gas molecule interactions. The stability test over 125 days indicates that the ZF-B film acts effectively as a xylene gas sensor, emphasizing the effectiveness of ZF thin films in detecting xylene in an air environment.

Effect of Oxidant Concentration on Properties of Ferrite Films by Spin-Spray Deposition

In response to the demands for high frequency, miniaturization, and high integration in electronic devices, such as inductors and DC-DC convertors, nickel–zinc ferrite thin films exhibit significant application value and development potential. For regulating the magnetic properties and microstructure of spin-sprayed polycrystalline ferrite materials, a comprehensive understanding of the impact of oxidant concentration on film reaction is essential. This study finds that as the concentration of the NaNO2 oxidant increases, the grain size of the nickel–zinc ferrite thin film samples progressively enlarges. Due to the preferential occupation of iron ions at the B sites, the saturation magnetization correspondingly increases. However, when the oxidant concentration becomes excessive, the preferential (222) orientation growth of the film is disrupted, leading to the agglomeration and uneven growth of grains, transitioning from triangular plate-like to spherical in shape. This increase in grain size alters the magnetization mechanism of the thin film, predominantly favoring domain wall movement. Upon analyzing the microstructure and magnetic characteristics, it becomes evident that the concentration of oxidant is a key determinant in the spin-spray deposition process.

Facile fabrication of low-defect spinel zinc ferrite oxide thin film for high-performance ultraviolet photodetector

ZnFe2O4 (ZFO) has gained much attention for numerous applications such as photocatalysis and lithium-ion batteries owing to its unique magnetic, optical, and electrical properties, low toxicity, and high chemical stability. However, current research on this material for the development of solid-state photodetectors is insufficient. For the first time, a high-purity and compact ZFO thin film was prepared via a simple sol-gel method and used as an efficient n-type photoactive material for ultraviolet A (UVA) detection. When ZFO is coupled with a p-type polymer, the high-quality p-n heterojunction can be used as a self-powered UV detector with a high on/off ratio of > 103, excellent detectivity of 3 × 1011 Jones, and a linear relationship between the photocurrent and light intensity. Accordingly, this study suggests that the novel ZFO-based photodiode prepared via a facile process could be industrially scalable and employed in practical UV detection applications.

Evidence of oxygen evolution over sputtered zinc ferrite (ZnFe2O4) thin film by enhanced lattice oxygen participation

We report evidence of oxygen evolution over zinc ferrite (ZnFe2O4) thin films grown on indium tin oxide and quartz substrates using the RF sputtering. The thin films are deposited at ambient temperature with different argon/oxygen gas ratios, specifically 1:0 (Z–Ar), 1:1 (Z–Ar:O), and 0:1 (Z–O). Structural characterization using grazing incidence x-ray diffraction at a 0.400° grazing angle confirmed the polycrystalline nature of the films. X-ray photoelectron spectroscopy scans of Zn 2p, Fe 2p, and O1s were conducted to investigate the lattice oxygen vacancies. The lattice oxygen vacancies in the Z–Ar film resulted in a lower bandgap of 2.05 eV than the Z–O film of 2.36 eV. The oxygen evolution reaction (OER) performances of the thin films are investigated to understand the effect of oxygen vacancies on electrochemical activity and observed that the Z–Ar film, with oxygen vacancies, exhibits a decrease in overpotential by ∼12.5% at 10 mA cm−2, eightfold increase in current density at 520 mV overpotential deduced from linear sweep voltammetry, and a 71.9% increase in donor density inferred from the Mott–Schottky plot, as compared to the Z–O film. The findings suggest that the Z–Ar film follows a “lattice oxygen participation mechanism” for the OER, instead of an “adsorbate evolution mechanism” observed in the Z–O film. The results highlight the significant impact of argon/oxygen gas ratios on the structural, optical, and electrochemical properties of zinc ferrite thin films and provide insight into the role of oxygen vacancies in modulating the OER performance for potential applications.

Substrate temperature dependent ammonia gas sensing performance of zinc ferrite thin films prepared by spray pyrolysis technique

Ammonia (NH3) production, storage, and transportation are prone to leaks, and exposure to NH3 levels above the Occupational Safety and Health Administration (OSHA) limit can affect the environment and be hazardous to human life. It is crucial to eliminate health risks by detecting NH3 within the exposure limit. In this work, thin films of zinc ferrite (ZF) having the morphology of nanorods with laminated cubes and rectangular grains with laminated sheets were deposited using spray pyrolysis approach at various substrate temperatures (225–300 °C). Then employed the grown films to detect harmful NH3 gas below the OSHA exposure limit at room temperature. In this study, it was noted that the substrate temperature has a significant impact on the performance of the proposed sensor. Among the four temperatures, a good sensing response of S = 1.91 towards 25 ppm of NH3 was obtained for the film deposited at 225 °C. The enhancement was mainly due to the formation of films with a large surface-to-volume ratio and surface roughness with a tiny nanorod structure. For stability checking, the response of the sensor was recorded after 90 days towards 25 ppm of NH3. The results of stability also indicate that coated ZF225 film is an effective NH3 gas sensor. This research reveals that ZF thin films can efficiently detect the presence of NH3 in the environment.

Manganese doped two-dimensional zinc ferrite thin films as chemiresistive trimethylamine gas sensors.

Trimethylamine (TMA) is highly toxic and can have lethal effects on living organisms. Detecting the presence of TMA in air is very important because, if the TMA level exceeds the OSHA (Occupational Safety and Health Administration) limit, it may harm the environment and endanger human life. Doping is an appropriate flexible way to change the electrical structures of metal oxide semiconductors (MOSs) and improve their ability to detect toxic gases. In this work, Mn-doped zinc ferrite thin film nanorods with agglomerated morphology were fabricated by a spray pyrolysis technique. For the first time, a comprehensive investigation was done on the gas sensing capabilities of Mn-doped ZnFe2O4 thin films. The findings showed that ZFM1 had the best gas sensing characteristics, with high sensitivity (S = 6.24), good selectivity, and quick recovery, towards 10 ppm TMA at ambient temperature. The alternate Mn-ZF sites are responsible for the rapid recovery because they can significantly increase the concentration of oxygen vacancies in the ZF crystal. 0.1 Mn doped ZnFe2O4 (ZFM1) thin film exhibits greatly enhanced gas sensing properties towards TMA, because of its high surface-to-volume ratio and rough surface with a small nanorod structure. The sensor's response to 10 ppm TMA was measured 13 weeks later for stability testing. The stability test results show that the coated ZFM1 film works well as a TMA gas sensor. This work shows that ZF thin films are effective in detecting TMA in the atmosphere.

Effect of Oxygen Vacancies and Cationic Inversion on Magnetic Properties of Pulsed Laser Deposited Zinc Ferrite Thin Films

Effect of Oxygen Vacancies and Cationic Inversion on Magnetic Properties of Pulsed Laser Deposited Zinc Ferrite Thin Films

Oxygen vacancies induced ferromagnetism in RF-sputtered and hydrothermally annealed zinc ferrite (ZnFe2O4) thin films

We report the inception of substantial magnetization of 4107 G in rf-sputtered and annealed hydrothermally at 180 °C zinc ferrite (ZFO) thin films. The value of electron-phonon coupling strength (λ) calculated using Raman A1g and F32g modes contended the shift of inverse spinel structure of the as-prepared thin films to the normal spinel structure with the enhancement in annealing duration. The shift in spinel structure was further affirmed by X-ray photoelectron spectroscopy (XPS) where inversion parameter, i.e., a fraction of the Zn2+ ions occupied by octahedral sites reduced from 0.18 of as-deposited film to 0.13 of air annealed and 0.14 for hydrothermally annealed films. Additionally, the ZFO thin film annealed hydrothermally for 4 h showed lower value of λ of 0.11 for A1g Raman mode and a high value of the ratio of surface hydroxyl (OH− groups) oxygen ions (Oii) to the lattice oxide (Fe/Zn–O) oxygen ions (Oi) in XPS spectra confirmed the presence of enormous oxygen vacancies. The magnetization analysis suggested that the presence of high oxygen vacancies in 4 h of hydrothermally annealed sample promotes the direct ferromagnetic interaction in Fe3+ ions in octahedral sites leading to a high value of saturation magnetization unlike the air annealed samples.

Resonance frequency above 20 GHz in superparamagnetic NiZn-ferrite

We investigate the frequency dispersion of complex permeability in the GHz range in superparamagnetic nickel–zinc ferrite thin films with different Ni/Zn ratios using a microstrip probe. The films, comprising crystallites as small as 3 nm and deposited by a microwave-irradiation-assisted solvothermal method, exhibit the coexistence of two resonance characteristics—a ferromagnetic resonance peak (fr) at ∼2 GHz and a superparamagnetic resonance peak (fb) above 20 GHz, breaching Snoek's limit. The high value of fr is attributed to the high surface anisotropy and far-from-equilibrium distribution of cations in the lattice, while fb is attributed to the thermally driven superparamagnetic relaxation of ferrite nanocrystallites in the thin films. This work demonstrates the feasibility of employing superparamagnetic ferrite thin films so deposited as excellent CMOS-integrable magnetic components for high-speed and high-frequency electromagnetic device applications.

Twofold and fourfold anisotropies in zinc ferrite thin films investigated by ferromagnetic resonance

By means of the ferromagnetic resonance (FMR) technique (at the $X$ band) we investigated the magnetic properties of ${\mathrm{ZnFe}}_{2}{\mathrm{O}}_{4}$ (ZFO) films grown on different substrates. Angular dependence of the FMR field showed the existence of twofold and fourfold anisotropies for the same material, grown on Si(111), MgO(100), and STO(100), respectively. By using a model that takes into consideration the relevant contributions to the energy, we were able to extract the following parameters: effective magnetization ${M}_{\mathrm{eff}}$, cubic magnetocrystalline anisotropy field, in-plane and out of plane uniaxial anisotropy fields, and the $g$ factor. The samples deposited on Si showed a twofold in-plane anisotropy while a fourfold magnetic anisotropy was observed for the ZFO/MgO and ZFO/${\mathrm{SrTiO}}_{3}$ samples. All samples showed a strong perpendicular uniaxial anisotropy above 1 kOe and low in-plane uniaxial and cubic anisotropy field, on the order of tens of oersteds. The FMR linewidth ($\mathrm{\ensuremath{\Delta}}H$) fitted from FMR data shows $\mathrm{\ensuremath{\Delta}}H$ values above 190 Oe for all samples, indicating high damping of this material to be $\ensuremath{\sim}{10}^{\ensuremath{-}2}$ for the ZFO/MgO. The present analysis compared the FMR data obtained for the in-plane and out of plane measurements. Likewise, the effective magnetization and perpendicular uniaxial anisotropy field by FMR were compared with the magnetic response obtained by a vibrating sample magnetometer.

Structure and dielectric properties of thin nanocrystalline ZnFe2O4 films

Optically transparent high-quality nanosized crystalline zinc ferrite thin films on different substrates have been synthesized by the decomposition of organic zinc and iron (III) compounds. According to scanning probe microscopy study, the films are 40-50 nm thick and their surface consists of densely spaced uniformly oriented crystallites with morphology depending on the substrate. X-ray diffraction analysis has shown that the films are polycrystalline and ZnFe2O4 has a cubic spinel structure. The dielectric constant lies in the range of 53 ÷ 54. The films are spontaneously polarized with a residual polarization of about 0.59 ÷ 0.69 μC⋅cm−2 , the coercive field is (8 ÷ 12)·104 V/cm.

Surface modified zinc ferrite as a carbon-alternative negative electrode for high-energy hybrid supercapacitor

The limited energy storage capacities of carbon-based negative electrodes, which rely on conventional double layer charge storage mechanisms, have limited the electrochemical performances of hybrid supercapacitors (HSCs). The development of nanostructured redox-active materials that serve as alternatives to carbon-based negative electrodes is crucial to overcome the limitations of current HSCs. In this work, a coordination chemistry approach is utilized to tune the nanostructure of zinc ferrite thin films on flexible stainless steel (SS) foil by using several zinc salt precursors, including ZnCl2·6H2O, Zn(NO3)2·6H2O, and ZnSO4·6H2O, while using the same iron precursor (FeCl2·4H2O). Materials prepared with the ZnCl2·6H2O metal salt form porous nanosheets with groundnut-like structures that exhibit maximum specific capacities of 544 mA h/g (454 F/g) at current density of 2.5 A/g. Redox-active solid-state HSCs are assembled by using zinc ferrite as a negative electrode, MnO2 nanoflakes as a positive electrode, and a polymer gel as the electrolyte. The developed solid-state HSC cells show excellent performance as exemplified by a maximum specific capacitance of 123.8 F/g and an energy density of 55.72 Wh/kg, both of which are superior to those of conventional carbon-based symmetric and HSCs.

Chemiresistive Gas Sensing Properties of Copper Substituted Zinc Ferrite Thin Films Deposited by Spray Pyrolysis

Gas sensors working at lower temperatures are considered better since they consume less energy. Many transition metal oxides have received greater attention in the development of potential gas sensors. In this work, we deposited copper substituted zinc ferrite thin films by spray pyrolysis at an optimized 375°C substrate temperature. The structural and physical properties of films were characterized by x-ray diffractometry (XRD), Field emission scanning electron microscopy (FE-SEM), and spectroscopic ellipsometry (SE). The chemiresistive gas sensing study revealed the effect of copper content on gas response and operating temperature. The zinc ferrite thin film sensor with no copper content shows a 25.1% response at 150°C operating temperature, but the film with 10% copper substitution (i.e. Cu0.1Zn0.9Fe2O4) shows a higher response (47.5%) at a lower 120°C operating temperature with satisfactory selectivity to SO2 gas. The optimized thin film sensor shows a linear response for exposed gas in the range 5 ppm to 200 ppm, which afterward bends to saturation. The mechanism of saturation of response is discussed in the paper. The results offer a potentially attractive candidate material for effective sensing of SO2 gas at a relatively low operating temperature.

Insight into magnetic properties in zinc ferrite thin films by tuning oxygen content

In this investigation ZnFe2O4 thin films were fabricated by RF magnetron sputtering and the magnetic behavior was examined under the influence of the growth conditions in three types of atmospheres, using near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and vibrating sample magnetometry (VSM). XPS revealed that films under an Ar/O2 ratio 1:2 and 2:1 have Fe/Zn atomic ratios similar to the Fe/Zn stoichiometric composition; while the films deposited in pure Ar atmosphere, showed a formation of Fe ions (Fe0) reduced by Ar ion sputtering. VSM revealed an enhancing of the saturation magnetization for the ZFO in thin films unlike the samples in bulk, suggesting that Fe ions migrate to A sites and the interaction JAB dominates the magnetic properties instead of JBB interaction.

Cobalt metal doped magnesium ferrite and zinc ferrite thin films grown by Spray Pyrolysis

The transition metal doped magnesium ferrite and zinc ferrite as the most common form of iron oxide become an especially important photoanode material for photoelectrochemical water splitting, due to its comparatively small band gap (Eg = 2.0 eV) that can absorb visible light and its perfect chemical stability in watery solutions. Spinel ferrites have the general formula of AFe2O4 (where A2+:Fe, Co, Ni, Zn, etc.). Thin films were synthesized on different substrates by Spray Pyrolysis (SP) technique. The technique of SP is easier, cheaper and faster than other method. Spinel ferrites, AFe2O4, are technologically important group of materials due to their optical, magnetic, and electrical properties. Among the different spinel ferrites, magnesium ferrite have unique properties. The effects of doped cobalt metal on the thin films were analyzed through Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray Diffraction (XRD) and UV–Vis double beam spectrophotometer and for electrical properties of films were used Van der Pauw technique.

Porogen induced formation of mesoporous zinc ferrite thin films and their chemiresistive properties

The semiconducting metal oxides are the most studied chemiresistive sensing materials. Their surface morphology plays an important role in sensing response. The porous nature of the material can significantly enhance their sensing ability. With this aim, ZnFe2O4 thin films were deposited on glass substrates by spray pyrolysis technique. The added NH4Cl porogen made pores in the film. The chemiresistive response of these porogen induced films for SO2 gas and liquid glucose were found better as compared to compact films; which were deposited without porogen. The reaction mechanism and pore formation are explained in the paper.

Anisotropic growth and magnetic properties of nickel–zinc ferrite thin film by spin spray deposition

NiZn ferrite thin films with different compositions were prepared by spin spray deposition on an enhanced ultrasonic system and significant improvements in microstructure and magnetic properties of spin-sprayed thin-films were observed and explained. The formation of triangular grain morphology as a result of anisotropic growth was discussed based on a thin-film growth mechanism, and the preferred (222) anisotropic growth was deduced as the consequence of a uniform, fast-rate deposition of high-quality ferrite thin film by spin spray. First-order reversal curve measurement was adopted to investigate the grain size distribution of the abnormal microstructure. Moreover, a transition of magnetization mechanism took place along the increment of iron concentration which resulted in a larger permeability at high frequency. These findings provide a valuable reference for an in-depth understanding of spin spray deposition and an effective way to tune the performance of ferrite thin-film material.

Electrochemical Performance of Nanocrystalline Zinc Ferrite Films Synthesized Using Electrodeposition

Nanocrystalline spinel zinc ferrite ZnFe2O4 thin film has been studied and synthesized via the electrodeposition-anodization process. Electrodeposited ZnFe2 alloys were obtained from aqueous sulphate bath. The resulted alloys were electrochemically oxidized in strong alkaline solution (1 M KOH) at room temperature to the analogous hydroxides. The electroanodized ZnFe2 alloy film was annealed in air at 400 °C for 2 h to get the required zinc ferrite. The electrochemical factors controlling of the electrodeposition of ZnFe2 alloys such as the bath temperature, agitation, the current density were studied and optimized. The crystal structure, crystal size and microstructure of the produced ferrites were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The deposited film was mainly composed of ZnFe2O4 based on XRD studies. The produced film had a spinel structure and the crystallite size was 4.9 nm. SEM micrograph of the resulted zinc ferrite particles shows compact crystallites shapes and agglomerated chains with smallest semicircular particles like morphology.

Impact of Defects on Magnetic Properties of Spinel Zinc Ferrite Thin Films

The recent developments in the study of magnetic properties in the spinel zinc ferrite system are explored. Engineering of ionic valence and site distribution allows tailoring of magnetic interactions. Recent literature is reviewed, and own investigations are presented for a conclusive understanding of the mechanisms responsible for the magnetic behavior in this material system. By varying the Zn‐to‐Fe ratio, the deposition, as well as thermal annealing conditions, ZnFe2O4 thin films with a wide range of crystalline quality are produced. In particular, the focus is on the magnetic structure in relation to spectroscopic properties of disordered ZnFe2O4 thin films. Comparing the cation distribution in film bulk (optical transitions in the dielectric function) and near‐surface region (X‐ray absorption), it is found that an inhomogeneous cation distribution leads to a weaker magnetic response in films of inverse configuration, whereas defects in the normal spinel are likely to be found at the film surface. The results show that it is possible to engineer the defect distribution in the magnetic spinel ferrite film structure and tailor their magnetic properties on demand. It is demonstrated that these properties can be read out optically, which allows controlled growth of the material and applications in future magneto‐optical devices.

Synergetic effect of thermal and electromagnetic energy on electrical properties of zinc ferrite thin film

In this study, the nanocrystalline ZnFe2O4 thin films were deposited using spray pyrolysis technique. The structure, morphology, and optical and electrical properties of the sample were analyzed. The film shows higher conductivity for selective illumination having wavelength corresponding to the bang gap energy. In case of thermal excitation the rapid increase in conductivity was observed after 500 K. The combined exposure of heat and light affects the conductivity without changing activation energy of the material.