Iron Thin Films Research Articles

The bias effect on the frequency dispersion of microwave permeability of composites filled with metal films or flakes

A new method of studying microwave magnetic properties of metal particles and films is developed. The method is based on measurements with swept frequency under magnetic bias in a coaxial line. Application of the technique is illustrated by the data obtained for two types of samples, washer-shaped rolls of thin ferromagnetic films and composites filled with flake Sendust particles. The treatment of the measured data is performed with an account for sample demagnetization and anisotropy. The values of the anisotropy field and the saturation magnetization of thin iron films are calculated considering demagnetization of the sample. Because of the anisotropy of the composite samples, permeability depends slightly on the length of samples, and the saturation magnetization and the anisotropy field cannot be determined.

Plasmon resonance studies of iron coated gold films with and without an applied magnetic field

Surface plasmon excitations can result from the absorption of light incident on gold films. Adding a ferromagnetic metal, in our case iron, allows the surface plasmon resonance peak energy to be manipulated not only by the free electrons present in metals, but by an external magnetic field as well. Surface plasmon resonance is being used by devices found in industry, however manipulations of the surface plasmon resonance peak energy condition need further studies. Two experimental results are reported in this paper based on thin films of iron on gold/chromium, one based on the thickness of iron and the other with an application of a large 4000 Gauss DC magnetic field. Both of these changes result in a shift in the peak energy of the surface plasmon.

Effect of iron doping on structural and optical properties of TiO2thin film by sol–gel routed spin coating technique

Thin films of iron (Fe)-doped titanium dioxide (Fe:TiO[Formula: see text] were prepared by sol–gel spin coating technique and further calcined at 450[Formula: see text]C. The structural and optical properties of Fe-doped TiO2thin films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible spectroscopy (UV–vis) and atomic force microscopic (AFM) techniques. The XRD results confirm the nanostructured TiO2thin films having crystalline nature with anatase phase. The characterization results show that the calcined thin films having high crystallinity and the effect of iron substitution lead to decreased crystallinity. The SEM investigations of Fe-doped TiO2films also gave evidence that the films were continuous spherical shaped particles with a nanometric range of grain size and film was porous in nature. AFM analysis establishes that the uniformity of the TiO2thin film with average roughness values. The optical measurements show that the films having high transparency in the visible region and the optical band gap energy of Fe-doped TiO2film with iron (Fe) decrease with increase in iron content. These important requirements for the Fe:TiO2films are to be used as window layers in solar cells.

The Effects of Film Thickness and Substrate Resistivity on Corrosion of Iron Thin Films

This study investigated the corrosion behavior of Fe films with different thicknesses in NaCl solution. It has been reported that nanocrystalline metal thin films are more corrosion resistant than their coarser bulk counterparts, but the effect of thickness is not well characterized. Polarization curves were generated for three iron thin films with thicknesses of 10, 20, and 100 nm and bulk iron in aerated 3.5 wt% NaCl solution at 24 ˚C. All films were deposited on silica substrates, and 20 and 100 nm films were also deposited on silica substrates with a Pt conductive under-layer. The resistivity/conductivity of the samples were measured using a four point probe, and the effects of film and substrate resistivity on corrosion were addressed by comparing polarization curves of thin films with and without the Pt conductive layer. The extent of film corrosion was spatially varied and the variation in localized electrochemical response was measured using scanning vibrating electrode technique (SVET). The corroded films were also characterized by optical microscopy.

Influence of ion implantation parameters on the perpendicular magnetic anisotropy of Fe-N thin films with stripe domains

Nitrogen-martensite thin films are known to present a perpendicular magnetic anisotropy (PMA) depending on the nitrogen content. Additionally, weak magnetic stripe domains have been studied in Fe-N samples made by ion implantation. In this work, ion implantation proves to be a good technique to make nitrogen-martensite thin films presenting both tunable PMA and stripe domains. We report on the changes in magnetic and structural properties of nitrogen-implanted iron thin films, resulting from various implantation conditions. Fluences from 1.8 × 1016 N2+/cm2 to 3.5 × 1016 N2+/cm2 at 26 keV and 5.3 × 1016 N2+/cm2 at 40 keV were used to implant iron thin films epitaxially grown on ZnSe/GaAs(001). X-ray diffraction measurements disclosed the presence of body-centered tetragonal nitrogen-martensite whose c-axis is perpendicular to the thin film plane and the c-parameter increases with fluence. Vibrating sample magnetometer measurements revealed that nitrogen implantation induced strong changes in magnetic properties such as an increasing PMA with fluence. Therefore, this PMA may originate from the magnetocrystalline anisotropy of nitrogen-martensite and stress-induced anisotropy. Magnetic stripe domains are notably observed by magnetic force microscopy for the highest fluences. Furthermore, ferromagnetic resonance measurements lead to the magnetic anisotropy constants calculation. The results show a significant increase of the PMA, related to the presence of nitrogen-martensite whose c-parameter is close to that of α′-Fe8N, which reaches a maximum value of 4.9 × 106 erg/cm3. In addition, an interesting comparison is done between the anisotropy constants of Fe-N and Fe-Ga samples. Fe-Ga thin films are also well known to present PMA and stripe domains.

Direct Observation of Sink-Dependent Defect Evolution in Nanocrystalline Iron under Irradiation

Crystal defects generated during irradiation can result in severe changes in morphology and an overall degradation of mechanical properties in a given material. Nanomaterials have been proposed as radiation damage tolerant materials, due to the hypothesis that defect density decreases with grain size refinement due to the increase in grain boundary surface area. The lower defect density should arise from grain boundary-point defect absorption and enhancement of interstitial-vacancy annihilation. In this study, low energy helium ion irradiation on free-standing iron thin films were performed at 573 K. Interstitial loops of a0/2 [111] Burgers vector were directly observed as a result of the displacement damage. Loop density trends with grain size demonstrated an increase in the nanocrystalline (<100 nm) regime, but scattered behavior in the transition from the nanocrystalline to the ultra-fine regime (100–500 nm). To examine the validity of such trends, loop density and area for different grains at various irradiation doses were compared and revealed efficient defect absorption in the nanocrystalline grain size regime, but loop coalescence in the ultra-fine grain size regime. A relationship between the denuded zone formation, a measure of grain boundary absorption efficiency, grain size, grain boundary type and misorientation angle is determined.

The Effect of Film Thickness and Substrate Resistivity on Corrosion of Fe Thin Films

This study investigated the corrosion behavior of Fe films with different thickness in NaCl solution. It has been reported that nanocrystalline metal thin films are more corrosion resistant than their coarser or bulk counterparts, but the effect of thickness is not well characterized. Polarization curves were measured for three iron thin film with thicknesses of 10, 20, and 100 nm and bulk iron in aerated 3.5 wt% NaCl solution at 24 ˚C. Each film thickness was deposited on silica substrates, and 20 and 100 nm films were also deposited on silica substrates with a Pt conductive layer. The resistivity/conductivity of the samples were measured using four point resistivity measurement, and the effect of film and substrate resistivity on corrosion was addressed by comparing polarization curves of thin films with and without the platinum conduction layer. The extent of film corrosion was spatially varied and the variation in localized electrochemical response was measured using scanning vibrating electrode technique. The corroded films were also characterized by SEM.

Nanostructuring of iron thin films by high flux low energy helium plasma

High flux, low energy He plasma exposure is proven to nanostructure iron thin films over their entire thickness to a highly open structure with large surface area. From a large set of plasma exposure parameters, the ion flux, the surface temperature, and the plasma exposure time are found to be the most relevant parameters to process mechanically stable, nanostructured Fe thin films on brittle glass substrates. The nanostructure stays stable during oxidation. Different surface morphologies are found, depending on the location where the plasma plume interacts with the thin film. This method paves the way to a new direction in top down nanostructuring of thin films, which can be adopted for many functional materials in diverse applications that require a high ratio of active to projected surface area.

Development of 2000 K Class High Temperature In Situ Transmission Electron Microscopy of Nanostructured Materials via Resistive Heating

We report the development of a new type of a 2000 K class high temperature stage for transmission electron microscopy (TEM) of various shaped nanostructured materials, i.e., nanometer-sized isolated nanostructures, such as particles, fibers, and thin films, and nanocrystalline bulk materials. The maximum temperature of the heating stage was 300–700 K higher than that of prevailing heating stages. In addition, we found that since the structure of the developed heating stage is simple, the stage can be applied to most of transmission electron microscopes without any additional modification. The stability of the heating stage was confirmed by In Situ high-resolution observation of the lattice fringes of the zirconium dioxide nanoparticles heated at 1183 K. We observed In Situ the nanoscale structural variation of titanium plate surfaces around 900 K and the melting of nanocrystalline iron thin films around 1808 K by this method. It was demonstrated that the heating stage is useful for the analysis of high temperature structural dynamics of various shaped nanostructured materials.

Electrochemical corrosion of thin ferromagnetic Fe—N films in neutral solution

A model experiment was conducted in order to determine an interplay between inherent strains and electrochemical corrosion rate in nitrogen-doped iron thin films. 150 and 300 nm thick films, used in the experiment, were obtained by means of DC magnetron sputtering. In order to study the influence of substrate on inherent strains in metal, these films were deposited onto flexible polymer and rigid glass substrates. It was found, that the rigidity of the substrate increased the corrosion rate of thin iron films in a neutral electrolytic solution. It was proven using X-ray diffraction, that the greater rigidity was, the stronger were the internal strains within the films. That effect was especially pronounced in thinner films, where the increase in the rate of dissolution was accompanied by a localization of corrosion. Characteristics of electrochemical processes were measured using a three-electrode cell. The comparison of the films free surface energy was performed by measuring water contact angle.

Effect of defects, magnetocrystalline anisotropy, and shape anisotropy on magnetic structure of iron thin films by magnetic force microscopy

Microstructures of magnetic materials, including defects and crystallographic orientations, are known to strongly influence magnetic domain structures. Measurement techniques such as magnetic force microscopy (MFM) thus allow study of correlations between microstructural and magnetic properties. The present work probes effects of anisotropy and artificial defects on the evolution of domain structure with applied field. Single crystal iron thin films on MgO substrates were milled by Focused Ion Beam (FIB) to create different magnetically isolated squares and rectangles in [110] crystallographic orientations, having their easy axis 45° from the sample edge. To investigate domain wall response on encountering non-magnetic defects, a 150 nm diameter hole was created in the center of some samples. By simultaneously varying crystal orientation and shape, both magnetocrystalline anisotropy and shape anisotropy, as well as their interaction, could be studied. Shape anisotropy was found to be important primarily for the longer edge of rectangular samples, which exaggerated the FIB edge effects and provided nucleation sites for spike domains in non-easy axis oriented samples. Center holes acted as pinning sites for domain walls until large applied magnetic fields. The present studies are aimed at deepening the understanding of the propagation of different types of domain walls in the presence of defects and different crystal orientations.

Growth and optical properties of Fe2O3 thin films: A study of quantum confinement effects by experiment and theory

Thin iron films in the thickness range 0.7–48nm have been deposited on high quality Corning glass and Si(100) substrates by radio frequency magnetron sputtering. The films were then oxidized by annealing at temperatures of 400−450°C in a furnace in air. X-ray diffraction experiments revealed the formation of single-phase α-Fe2O3. The films were continuous and present negligible surface roughness. Ultraviolet-visible light absorption spectroscopy has shown a blue shift of both, the indirect and direct band gaps of hematite. The experimental results are interpreted as evidences of quantum confinement effects. This is facilitated by theoretical calculations based on Hartree Fock approximation as applied for an electron-hole system, in the framework of effective mass approximation. The agreement between theory and experiment supports the quantum confinement interpretation.

Synthesis, Structural, and Magnetic Properties of Fe Thin Films

A series of iron thin films have been deposited under vacuum, by thermal evaporation, onto polycrystalline Cu substrates. The film thickness ranges from 13 to 69 nm. An X-ray diffraction (XRD) technique, working in the 𝜃–2𝜃 mode with the K α Cu radiation (λ = 1.54056 A), has been used to perform the structural properties. The static magnetic measurements were carried out using a vibrating sample magnetometer (VSM), with the external magnetic field applied parallel and normal to the surface of the films. All the films are polycrystalline and present well-defined Bragg peaks. The easy magnetization axis lies in the film plane for all the samples, and no in-plane magnetic anisotropy has been detected for all films. High values of squareness have been measured in the longitudinal configuration. All the findings will be presented and discussed.

Structural and electrical properties of nickel–iron thin film on copper substrate for dynamic random access memory applications

Using pulse electrodeposition technique, nano crystalline NiFe films were deposited on conductive copper substrates, under galvanostatic mode in an ultrasonic field at different conditions such as pulse current magnitude, deposition time and ultrasonic bath temperature. As-prepared NiFe/Cu thin films were characterized for phase analysis, surface morphology, surface roughness and resistivity measurements. The results show that the use of ultrasonic bath at room temperature has reduced the surface roughness, resistivity, average grain size and crystallite size of NiFe/Cu thin films. The resistivity is reduced with increasing deposition current from 44.2 µΩ cm at 40 mA to 33.0 µΩ cm at 100 mA. On the other hand, a significant drop of the resistivity from 35.7 to 9.4 µΩ cm is observed if the deposition time was reduced from 5 to 3 min.

Epitaxially stabilized iron thin films via effective strain relief from steps

We show a new way to stabilize epitaxial structures against transforming bulk stable phases for Fe thin films on a vicinal Cu(001) surface. Atomically-resolved observations by scanning tunneling microscopy reveal that high-density Cu steps serve as strain relievers for keeping epitaxially-stabilized Fe fcc(001) lattice even at a transient thickness towards the bulk stable bcc(110) lattice. Spectroscopic measurements further clarify the intrinsic electronic properties of the fcc Fe thin film in real space, implying electronic differences between 6 and 7 monolayer thick films induced by the modification of the lattice constant in the topmost layers.

X-ray fluorescence determination of the surface density of thin chromium and iron films using reference samples of elements with close atomic numbers

In X-ray fluorescence determinations of the surface density of thin chromium and iron films, we studied the possibility of using an approach based on the application of reference samples of elements with close atomic numbers. It was shown that the proposed diagnostic approach ensures the determination of the surface density of films with rather high precision.

Study of high-temperature oxidation of ultrathin fe films on Pt(100) by using X-ray photoelectron spectroscopy

High-temperature oxidation of iron thin films deposited on Pt(100) surfaces was studied by using X-ray photoelectron spectroscopy (XPS). Upon an oxygen exposure of 300 Langmuir onto a 7.5- monolayer (ML) Fe film at 830 K, about 2 monolayers of the Fe film were oxidized as Fe3O4 while the remaining Fe atoms diffused into the substrate. For 1.25-, 2.5-, and 3.75-monolayer Fe films, only about a monolayer of the Fe film was oxidized as FeO, regardless of the number of Fe atoms. The oxide layers on the 7.5-monolayer Fe film were observed to be stable upon post-annealing at 1030 K.

Magnetic anisotropy and relaxation of single Fe/FexOy core/shell- nanocubes: A ferromagnetic resonance investigation

In this work a full angle dependent Ferromagnetic Resonance (FMR) investigation on a system of 20 separated Fe/FexOy nanocubes without dipolar coupling is reported. The angular magnetic field dependence of FMR spectra of 20 single particles and 2 dimers were recorded using a microresonator setup with a sensitivity of 106 μB at X-band frequencies. We determine an effective magnetocrystalline anisotropy field of 2K4,eff/M = 50 mT ± 5 mT for selected particles, which is smaller than the one of bulk Fe due to the core shell morphology of the particles. The FMR resonances have a linewidth of 4 mT ± 1 mT, corresponding to a magnetic effective damping parameter α = 0.0045 ± 0.0005 matching the values of high quality iron thin films. Numerical calculations taking into account the different angular orientations of the 24 particles with respect to the external magnetic field yield a good agreement to the experiment.

Local X-ray magnetic circular dichroism study of Fe/Cu(111) using a tunneling smart tip.

Localized spectroscopy with simultaneous topographic, elemental and magnetic information is presented. A synchrotron X-ray scanning tunneling microscope has been employed for the local study of the X-ray magnetic circular dichroism at the Fe L2,3-edges of a thin iron film grown on Cu(111). Polarization-dependent X-ray absorption spectra have been obtained through a tunneling smart tip that serves as a photoelectron detector. In contrast to conventional spin-polarized scanning tunneling microscopy, X-ray excitations provide magnetic contrast even with a non-magnetic tip. Intensity variations in the photoexcited tip current point to chemical variations within a single magnetic Fedomain.

Modeling of magnetic properties of iron thin films deposited by RF magnetron sputtering using Preisach model

Iron thin films were deposited on glass substrates using RF magnetron sputtering and their optimal deposition conditions were determined. The structure properties were analyzed using x-ray diffraction (XRD) and their magnetic hysteresis loops were obtained by Vibrating Sample Magnetometer (VSM) at room temperature. In this situation, the magnetic field is either parallel or perpendicular to the substrate plane. The main contribution of this work is to characterize the thin layers and present a mathematical model that can get best fit of the characteristics B(H). By using Preisach model, good agreement was obtained between theoretical and experimental results in both cases.