Iron Films Research Articles

Stabilization of nanoscale iron films by self-terminated electrodeposition in sulfate electrolyte

Iron and iron oxide nanostructures are of broad interest for numerous applications, such as in the fields of magnetic data storage, spintronics, biosensing and catalysis. In all of these cases, defined deposition on nanometer scale is essential for functionality. For conventional electrodeposition of transition metals, precise thickness control and layer stability at the nanoscale are difficult due to dissolution tendencies in acidic electrolytes after the voltage is switched off. In contrast to previous studies that focused on self-termination of Ni and Ni-based alloys, we investigate the thickness control of nanoscale iron oxide/iron layers using self-terminated electrodeposition from sulfate electrolytes. Electrochemical quartz crystal microbalance measurements show that self-terminated thickness can be controlled by both deposition potential and iron ion concentration. Comparison of experimental results with model calculations based on diffusion theory reveal two different growth modes for self-termination. At low iron ion concentration, self-termination of iron proceeds via the formation of an ultrathin iron hydroxide layer. At larger iron ion concentration, precipitation of bulk Fe(OH)2 dominates the film growth and self-termination is shifted to more negative potentials. All self-terminated layers exhibit enhanced stability in the electrolyte after the voltage is switched off compared to those deposited in the conventional deposition regime. With in situ Rutherford backscattering spectrometry measurements, we can follow the self-terminating deposition and the stability after voltage switch-off for longer times online. Surface analytical and morphological analyses show that the self-terminated layers exhibit a higher iron oxide/iron ratio and are smoother than layers obtained by conventional electrodeposition.

Microstructural dependence of defect formation in iron-oxide thin films

Passivating iron-oxide films are grown atop iron films simulating the corrosion process in a nuclear reactor environment. Two oxide films grown via physical vapor deposition at 600 °C and room temperature exhibited dense-epitactic and columnar-polycrystalline, microstructures respectively. A third oxide film grown in open air at 600 °C exhibited an eqiuaxed, porous morphology. Cubic maghemite and magnetite phases in each oxide film were identified via grazing incidence X-ray diffraction. Positron annihilation spectroscopy was used to characterize point defects and measure their depth and size distributions in each oxide layer and showed a range of average positron lifetimes from 0.23 ns in the high temperature, vapor deposited film, 0.35 ns in the room temperature-grown film, and 0.31 ns in the thermally grown oxide. These data indicate that the film morphology, which varies greatly in these films, leads to very different defect content. Finally, four-dimensional scanning transmission electron microscopy was used to measure the internal stress of each film and was correlated to the strain state presented in the X-ray diffraction spectra. The defect formation in each film is reasoned through using a thin film growth model.

Propagating backward-volume spin waves in epitaxial Fe films

The propagation characteristics of backward-volume magnetostatic spin-waves in epitaxial Fe(001) films were studied by frequency-domain and time-domain spin-wave propagation spectroscopies using a vector network analyser. Due to the combination of cubic-magnetocrystalline anisotropy and anisotropic spin-wave dispersion, the backward-volume spin-wave exhibited a complicated packet propagation. For the hard-axis propagation, the group velocity of the spin wave was greatly enhanced at low external magnetic fields and propagation occurred even under no magnetic field. By analysing within a theoretical model and micromagnetic simulations, these transmission character of the backward-volume magnetostatic spin-waves in an epitaxial iron film was well reproduced. The observed characteristics are essential information to promote two-dimensional magnonic devices utilizing cubic-anisotropic materials.

Elastoplastic and Polymorphic Transformations in Iron Films Loaded by Ultrashort Laser Shock Waves

Elastoplastic and Polymorphic Transformations in Iron Films Loaded by Ultrashort Laser Shock Waves

Iron carbide formation on thin iron films grown on Cu(1 0 0): FCC iron stabilized by a stable surface carbide

Thin iron films evaporated onto Cu(100) were carburized using ethylene to produce iron carbide surfaces for use as model systems in experimental research. XPS and AES confirm that ethylene dissociation produces a pure iron carbide. A maximum of 0.5 ML carbon can be deposited for film thicknesses below 12 ML where Fe grows as γ-iron (FCC). For thick, BCC-Fe(110) films, post-treatment with ethylene leads to carbon coverages beyond 0.5 ML where some carbon diffuses into the bulk. The film remains α-iron (BCC) and a different surface carbide with a (4 × 3) unit cell is found. On the thin FCC-Fe(100) films, carbon reconstructs the surface into a p4g(2 × 2)-Fe2C layer which has a special stability and acts as a carbon trap that prevents carbon diffusion into the bulk. Fe2C is thermally stable up to 700 K above which Fe diffuses into the copper substrate while leaving graphitic carbon behind. Carbon segregates to the surface during evaporation of iron on top of an Fe2C-covered FCC-Fe film and causes the film to retain the FCC structure up to a thickness of at least 30 ML, far beyond 12 ML where BCC-Fe forms on Cu(100) in absence of surface carbon.

Study of Substitutional Adsorption of an Iron Film on a Silver Surface

Study of Substitutional Adsorption of an Iron Film on a Silver Surface

Correlation between electrical, galvanomagnetic and magnetic properties of nanocrystalline iron films obtained by ion assisted deposition

Here we present the measurements of the temperature dependence of resistance, transverse and longitudinal magnetoresistance (MR) in nanocrystalline iron films in the temperature range 2-300 K and the sweep of the magnetic field up to 8 T. Thin nanocrystalline films of α-iron phase with 80 nm thickness were obtained by ion-beam assisted deposition on a silicon substrate. In addition to the shape anisotropy, the obtained iron films exhibited perpendicular magnetic anisotropy (PMA), which disappeared after annealing the films at a temperature of 450oC in a vacuum. The effect of PMA on the sign and magnitude of the MR of iron films, as well as on the magnetic field dependences of the magnetoresistive effect, recorded at different orientations of the external magnetic field with respect to the film plane and current direction, is experimentally shown. The results obtained are discussed in the framework of modern views on the processes of charge transfer in a weakly disordered ferromagnetic films with different magnetic anisotropy and domain structure when a weak (less than the saturation field of magnetization) or strong (higher than the saturation field) external magnetic field is applied. Keywords: nanocrystalline iron films, perpendicular magnetic anisotropy, magnetoresistance, anisotropic magnetoresistance, magnon magnetoresistance, percolation, weak localization.

Iron Carbide Formation on Thin Iron Films Grown on Cu(100): Fcc Iron Stabilized by a Stable Surface Carbide

Iron Carbide Formation on Thin Iron Films Grown on Cu(100): Fcc Iron Stabilized by a Stable Surface Carbide

Исследование эффектов релаксации и реконструкции при образовании пленки железа на поверхности серебра

The effects of relaxation and reconstruction during the formation of an iron film on a silver surface were studied using the USPEX and VASP software packages. The results of calculations are presented for a surface system with a single Fe layer (4 atoms per layer) on an Ag substrate with a (100) surface facet orientation and a thickness of 4 monolayer, 3 of which were not involved in the reconstruction. The most stable structure was chosen, which was obtained by the evolutionary algorithm presented in the USPEX software package. For two types of calculations, the energy efficiency of the “sandwich” type structure was revealed. Calculations taking into account the influence of magnetization for two types of effects showed the advantage of ferromagnetic ordering.

Elastoplastic and polymorphic transformations of iron at ultra-high strain rates in laser-driven shock waves

Elastoplastic and polymorphic α–ε transformations in iron films induced by ultra-short laser-driven shock waves are studied. Interpretation of time-resolved interferometric measurements is performed using an inverse analysis technique of experimental rear-side velocity profiles. The lasts are obtained by numerical differentiation of free surface displacements detected by probe laser pulses. The inverse analysis techniques are validated in consistent two-temperature hydrodynamics and molecular dynamics simulations of laser energy deposition and diffusion, generation, and propagation of shock waves in a polycrystalline iron sample. The stress–strain diagrams containing information about elastoplastic deformation and phase transformation are reconstructed by the inverse analysis. We found that the polymorphic transformation in iron under picosecond duration of loading requires much higher stress in contrast to that in microsecond-scale plate-impact experiments. Moreover, such transition may be accomplished partially even at very high stresses if an unloading tail after the shock front is too short.

Synthesis of magneto-dielectric coatings in electron-beam produced plasma in medium vacuum

Using sequential electron-beam evaporation of high-temperature dielectric (alumina ceramic) and magnetic (iron) targets in various gas atmospheres (helium, air, and oxygen) in medium vacuum (5–8 Pa), magneto-dielectric coatings with thickness of around 2 μm were deposited from a multicomponent beam plasma at a deposition rate of 0.2–0.3 μm/min. The coating magnetic properties were explored by the ferromagnetic resonance technique, revealing that their effective magnetization depends on the type of operating gas and varied from 4.2 to 6.8 kGs (for deposition in helium) to 0.3 kGs (in oxygen), which is characteristic of oxide ferromagnetic materials and is considerably lower than the corresponding value (∼22 kGs) for thin iron films formed by vacuum arc deposition in high vacuum. X-ray structural analysis of coatings deposited in medium vacuum in helium showed that the magnetic layer has a magnetite (Fe3O4) structure. The alumina ceramic layer provides the dielectric properties of the magneto-dielectric coating; a relative dielectric constant of 6.0 and a conductivity of 8.4 mS/m were achieved.

Structure of mono- and bilayer FeO on Ru(0001): STM and DFT study

Scanning tunneling microscopy (STM) and density functional theory (DFT) are used to determine the structure of mono- and bilayer iron monoxide (FeO) islands and films grown on Ru(0001). The experimental results provide information on the atomic and Moiré periodicities, the height of mono- and bilayer structures, the mutual shift of their crystalline lattices and the rotation with respect to the underlying single-crystal support. Based on the determined parameters, structural models are proposed. The calculations reveal the preferred stacking configurations of Fe and O layers in both structures, their stability within different high-symmetry regions of the Moiré supercell (top, fcc, hcp), the interlayer spacings and the possible magnetic configurations.

Pinpointing active sites for water splitting

Microscopic defects on a catalyst made of carbon and iron actively drive the hydrogen evolution reaction, one of the key steps in liberating hydrogen from water, according to a study that combines electrochemical analysis with atomic resolution microscopy ( Nat. Catal. 2021, DOI: 10.1038/s41929-021-00682-2 ). If scientists can find catalysts that efficiently split water into hydrogen and oxygen , then the oceans could serve as a nearly limitless supply of clean-burning, carbon-free hydrogen fuel for transportation and other uses. Precious metals work well as catalysts, but they’re expensive. So a team led by Stefano Agnoli and Gaetano Granozzi of the University of Padua examined inexpensive model catalysts consisting of thin films of graphene and iron. Sandwiches made from those films can be highly active electrocatalysts for hydrogen evolution, but how they work is unclear. The researchers used electrochemical scanning tunneling microscopy to examine the films while they mediated the catalytic

Soils of the Darkhitui catena in the southern Vitim Plateau and their micromorphological features

Soils of the Darkhitui catena in the south of the Vitim Plateau on a northern slope and the foothill plain were studied. Skeletic Folic Cryosols (Nechic) are formed on watersheds under larch forests on eluvium of mafic rocks. Soils have high humus content in a thin humus horizon and a significant content of clay. Folic Phaeozems (Colluvic, Tonguic) are developed on a gentle slope under a forb-birch forest on colluvium. The most prominent features of these soils are as follows: high content of humus and fine material, impregnation by carbonates, and iron films on ped faces. Luvic Chernozems (Tonguic) are developed in the foothills under steppe meadows on lacustrine sediments. These soils are characterized by redistribution of fine fractions along the profile and significant humus accumulation favored by permafrost moisture content.

Single stage synthesis of amorphous carbon covered nanotubes arrays

Structural features of carbon nanotubes make them highly promising for nanoelectronics, nanosensors, electrodes for energy storage and harvesting devices, composites, and weaving yarns. Carbon nanotubes covered with amorphous carbon can be efficiently applied as field emitters with higher brightness and stability compared to the metal ones. Vertically aligned arrays of the CNTs covered with amorphous carbon were synthesized by modified CVD method in the tube flow reactor via catalytic pyrolysis of acetylene. Stepwise films of iron on single crystal silicon substrate (100) obtained by the pulsed laser deposition (PLD) method were used as catalyst for their growth. The height of the CNT arrays was found to be dependent on the thickness of iron films. The obtained arrays were formed by multiwalled carbon nanotubes covered with the amorphous carbon. Low thermal stability of acetylene and insufficient activity of iron catalysts at the reaction temperature enable the reproducible formation of vertically aligned amorphous carbon covered CNT arrays promising for electronic applications and carbon textile preparation.

Rigorous signal reconstruction in terahertz emission spectroscopy.

Terahertz (THz) emission spectroscopy is a powerful method that allows one to measure the ultrafast dynamics of polarization, current, or magnetization in a material based on THz emission from the material. However, the practical implementation of this method can be challenging, and can result in significant errors in the reconstruction of the quantity of interest. Here, we experimentally and theoretically demonstrate a rigorous method of signal reconstruction in THz emission spectroscopy, and describe the main experimental and theoretical sources of reconstruction error. We identify the linear line-of-sight geometry of the THz emission spectrometer as the optimal configuration for accurate, fully calibrated THz signal reconstruction. As an example, we apply our reconstruction method to ultrafast THz magnetometry experiment, where we recover the ultrafast magnetization dynamics in a photoexcited iron film, including both its temporal shape and absolute magnitude.

The Effects of Fe Film Thickness and the H₂ Annealing Time on the Spin-Capability of Carbon Nanotube Forest with Chemical Vapor Deposition Method.

The effects of as-deposited iron (Fe) film thickness and the hydrogen (H₂) annealing time on the spin-capability of carbon nanotube (CNT) forest have been studied. Both, the as-deposited Fe film thickness and the H₂ annealing time significantly changed the morphology of Fe nanoparticles (NPs) after annealing process during the synthesis step of spin-capable carbon nanotube (SCNT) forest. The spin capability of CNT forests depended heavily on the different thicknesses of Fe films and the H₂ annealing time. In conclusion, the spin-capability of CNT forest can be achieved by controlling the initial Fe film thickness and/or the H₂ annealing time.

Stable and efficient sulfamethoxazole and phosphorus removal by an electrolysis-integrated bio-rack constructed wetland system

Pollution of sulfamethoxazole (SMX) in rural domestic sewage are a great challenge for ecological security because of limited treatment. In this study, an electrolysis-integrated bio-rack constructed wetland system (EC-CW-P) without substrates was developed for enhancing SMX removal in rural domestic sewage. The dynamic performance and mechanism of SMX (1 mg L-1) removal, occurrence of antibiotic resistance genes (ARGs) and microbial community composition at 4 ~ 24℃ were assessed. Meanwhile, the simultaneous removal performance of phosphorus in EC-CW-P was also analyzed due to key role of substrate adsorption and iron flocculation. The results revealed that the removal efficiency of SMX could reach 97.13% at 4 ~ 24℃ in the EC-CW-P by the electrocatalysis and adsorption of a ferric iron coagulant and biodegradation. Moreover, efficient removal of 74.12%~99.52% total phosphorus (TP) was obtained through electrocoagulation because of the formation of ferric ions. The occurrence of SMX had no effect on TP removal because of the different removal pathway. Itshouldbeemphasizedthat the removal efficiency of SMX owing to high microbial and plant activity which may be due to the formation of iron film and micro current stimulation and TP owing to adsorption of iron mud remained high (>80%) when the electrode was gradually passivated. Overall, the performance of bio-rack CW system was intensified by electrolysis (iron electrode) with higher bacterial abundance and plant activity in the EC-CW-P. However, the high relative abundance of sul ARGs (from 2.15 × 10-1 to 2.41 × 101 copies 16S rRNA-1) in the influent of the EC-CW-P may pose a severe threat to ecosystem. These results provide a novel perspective for enhancing SMX and phosphorus removal by bio-rack constructed wetland system.

Passive Surface Acoustic Wave Sensors for Early Corrosion Onset Detection

Corrosion creates serious safety concerns and economic burden in fuel processing and transportation. Being able to monitor the infrastructures in real time and detect corrosion onset may prevent potential consequences resulting from their failure. Passive wireless surface acoustic wave (SAW) devices are promising passive devices to detect the presence of water and corrosion onset amongst other parameters in natural gas pipelines and wellbore tubes. Here, we present on the possibility of using shear horizontal (SH-) SAW devices for monitoring metal film dissolution in hydrochloric acid of varied pH. 520 MHz SH-SAW reflective delay lines with two reflectors were fabricated on 36°Y-X LiTaO3, of which a channel was coated with 60 nm thick iron film by magnetron sputtering. With the film, the sensor had a center frequency of 529.8 MHz when measured in air. The sensor showed a slight attenuation and small frequency shift in DI water. In HCl solution with pH 2.01, the sensor’s center frequency first decreased with time for the first six minutes to reach down to 521 MHz and then remained almost unchanged. The S11 magnitude also showed similar behavior. After ten minutes immersion into the corrosive solution, no iron film was left under a visual inspection. The decrease in the frequency and attenuation is probably due to the changes in the mass and elasticity and the film surface roughening, respectively. Observed initial results are promising towards the implementation of SAW devices for monitoring corrosion in metallic structures in real time.

Area selective deposition of iron films using temperature sensitive masking materials and plasma electrons as reducing agents

The potential of area-selective deposition (ASD) with a newly developed chemical vapor deposition (CVD) method, which utilizes plasma electrons as reducing agents for deposition of metal-containing films, is demonstrated using temperature sensitive polymer-based masking materials. The masking materials tested were polydimethylsiloxane, polymethylmethacrylate, polystyrene, parafilm, Kapton tape, Scotch tape, and office paper. The masking materials were all shown to prevent film growth on the masked area of the substrate without being affected by the film deposition process. X-ray photoelectron spectroscopy analysis confirms that the films deposited consist mainly of iron, whereas no film material is found on the masked areas after mask removal. Scanning electron microscopy analysis of films deposited with nonadhesive masking materials show that film growth extended for a small distance underneath the masking material, indicating that the CVD process with plasma electrons as reducing agents is not a line-of-sight deposition technique. The reported methodology introduces an inexpensive and straightforward approach for ASD that opens for exciting new possibilities for robust and less complex area-selective metal-on-metal deposition.