Iron Films Research Articles

Area Selective Deposition of Metals from the Electrical Resistivity of the Substrate.

Area selective deposition (ASD) of films only on desired areas of the substrate opens for less complex fabrication of nanoscaled electronics. We show that a newly developed CVD method, where plasma electrons are used as the reducing agent in deposition of metallic thin films, is inherently area selective from the electrical resistivity of the substrate surface. When depositing iron with the new CVD method, no film is deposited on high-resistivity SiO2 surfaces whereas several hundred nanometers thick iron films are deposited on areas with low resistivity, obtained by adding a thin layer of silver on the SiO2 surface. On the basis of such a scheme, we show how to use the electric resistivity of the substrate surface as an extension of the ASD toolbox for metal-on-metal deposition.

Facile synthesis of N-doped lignin-based carbon nanofibers decorated with iron oxides for flexible supercapacitor electrodes

Flexible films of N-doped porous iron oxides/lignin-based carbon nanofibers (CNF@Fe-N) were fabricated and employed for high-performance supercapacitor electrode materials. The CNF@Fe-N films were synthesized through a simple and effective method, which was carried out by an electrospinning technique from lignin/Hemin mixed solution and followed by carbonization. In situ growth of iron oxides on the surface and interior of carbon nanofibers contribute to enhancing the capacitive performance through inducing pseudocapacitance. In the unique structure, the fibrous network structure with rich micropores provides plenty of channels for transportation and penetration of electrolyte ions. The obtained CNF@Fe-N binder-free electrode exhibits a high gravimetric capacitance of 148. 1 F g−1 and high energy density of 12.28 W h L-1 at 0.5 A g−1, as well as an excellent cycling stability with 92.8% capacitance retention after 5000 charge/discharge cycles. The material also presents an outstanding flexibility and folding resistance. The low-cost and renewable sources, easy preparation and remarkable supercapacitive property render CNF@Fe-N a promising candidate in energy storage applications.

Iron (III) doped titanium dioxide coated dimensionally stable graphite anode electrode for electro-chemical treatment of domestic wastewater

Availability of clean water is of concern due to pollution and diminishing supply pollution. However, purification is possible depending on the incorporated contaminants. Domestic wastewater contains dissolved organic matter and its remediation can be done by oxidation. The best oxidation can be achieved by electron transfer the same way metabolic processes occur. This study exploited the use of a film of iron (III) doped titanium dioxide applied on an electrode which was found to be effective. Natural light conditions generated electrons that migrated through the electrode leaving behind holes which oxidized the contaminants as the excess electrons were discharged at the cathode after passing through the casted proton exchange membrane (PEM) separating the two half cells of the prepared reactor. This electrochemical method has the advantage in that the organic pollutants are oxidized to carbon dioxide with no secondary pollutants and the inorganic pollutants into insoluble matter. The assembled cell was applied to purify both synthetic and real water samples of green leafy vegetable solution from the kitchen by clarification. The clarification process was monitored by UV-Vis using distilled water as a reference to compare the light that transmitted through a sample. It was observed that the electro-oxidation process took place showing a high potential 105 mV within the first 150 min followed by degradation at a high rate. The oxidation of the organic matter was confirmed by UV-Vis analysis as well as by cyclic voltametric analysis of iron released into the solution of the synthetic samples. The electro chemical treatment of the water was then applied to purify real water samples made from a sample of 4.5 g minced of green vegetables dispersed in one liter of water (4.5 g/l). The green leafy coloured solution was clarified after 154 h of continuous oxidation. The degradation process was confirmed to be independent of intermediates or other species present in solution as it was of first order reaction kinetics. The electrochemical oxidation of organic matter in water using iron (III) doped titanium dioxide coated graphite electrode has potential application on the purification of water.

Molecular Mechanism of Thermal Dry Etching of Iron in a Two-Step Atomic Layer Etching Process: Chlorination Followed by Exposure to Acetylacetone

Controlling thickness and morphology of transition-metal thin films used in magnetic random-access memory fabrication is a major challenge. Thermal dry etching has emerged as a method of choice for preparing the desired films; however, the mechanisms of the underlying surface processes are very difficult to assess. In this work, thermal dry etching of metallic iron by using sequential exposure to chlorine gas and 2,4-pentanedione (acetylacetone, acacH) was investigated. The mechanism of reacting acacH with chlorine-modified iron surface was studied by following the fragments desorbing from the surface in temperature-programmed desorption experiments in half-cycle processes that compared the chlorinated, oxidized, mixed (Cl and O), and clean (sputtered) iron films. In situ Auger electron spectroscopy and ex situ X-ray photoelectron spectroscopy of each sample after each etching step confirmed that the surface is activated by chlorine and then the chlorine-containing iron species are removed from the top layer of the sample, resulting in a metallic iron surface. No etching of clean (sputtered) surface was observed with acacH. The complete mechanism of acacH reaction with chlorinated iron samples is complicated, and etch products can contain both Fe2+ and Fe3+. However, a number of major conclusions, including the formation of surface intermediates and the final products of etching, primarily removal of Fe(acac)xCly, are inferred by comparing the results of these experiments with the computational investigation of selected surface processes using density functional theory calculations.

MULTIMODE WRINKLING PATTERNS OF IRON FILMS SPUTTER DEPOSITED ON FLEXIBLE SUBSTRATES WITH GRADIENT MODULUS

Wrinkling patterns are beneficial for a wide range of engineering applications including flexible electronics, tuned optics, sensoring, energy harvesting, surface wetting and biomedicine. Here we report on controllable multimode wrinkling patterns of metal (iron) films sputter deposited on flexible substrates with gradient modulus. It is found that disordered wrinkles (G1 wrinkling) form in the weakly crosslinking region at the early stage of film deposition. Disordered labyrinth wrinkles with larger wavelengths and ordered stripe wrinkles localized by cracks (both G2 wrinkling) appear in the strongly crosslinking region for the samples with small film thickness and large thickness, respectively. The coexistence of the labyrinth G1 wrinkling and labyrinth G2 wrinkling (or stripe G2 wrinkling) can be obtained by tuning the substrate modulus and film thickness. The morphologies, evolutions and mechanisms of such wrinkles are discussed in detail based on the stress theory. This study can promote better understanding of the substrate effect on the complex wrinkling patterns.

Microstructure heritance of metallographic feature in the anodization of carbon steels

The anodization of several carbon steels with typical metallographic structures were systematically investigated. It was shown that the anodized iron oxide films were inherited from the microstructural characteristics of the original metallographic structure by employing metallographic regulation. Different characteristics of the original metallographic structures could affect the rate of the anodization reaction and determine the thickness of the oxide layer on the substrate. Meanwhile, the connection of nanopore size with the original microstructure of the substrate was also revealed by the statistical analysis of pore size on the anodized iron films. The methodology and techniques could obtain tunable micro-nano structure and might be applicable in similar alloy systems.

Effect of thermal annealing on nitrogen implanted epitaxial Fe films

Nitridated iron is a promising material for potential applications in permanent magnets. Recent work on stabilization of nitridated iron in a foil form through nitrogen ion implantation and annealing motivates to study effect of thermal annealing on the surface of nitrogen-implanted iron. In this work, we show effect of annealing on chemical state and magnetism of nitrogen implanted epitaxial iron films. It is observed that nitrogen in the lattices only stays at the lower temperatures than 450 °C. In addition, significant reduction and lattice modification are taken placed, when the film is annealed at 450 °C. The increases of saturation magnetization and coercivity, where it is annealed at 450 °C, are likely to be triggered by reduction of oxygen contents at the surface and thinning of Fe2O3.

Comparing temperature convergence of shocked thin films of tin and iron to a bulk temperature source

An outstanding challenge in developing a complete equation of state for materials at elevated pressure and temperature is a robust method of determining the bulk temperature state under dynamic conditions. In metals, the determination of bulk temperature states by optical pyrometry is complicated by the small optical depth and thermal conduction effects. These effects lead to observed temperatures differing by 20% or more from the bulk temperature state. In this work, we show the presence of thermal conduction effects in temperature measurements of tin and iron coatings during dynamic compression experiments. We demonstrate that tin, in contrast to iron, coatings can fail to converge to a bulk temperature source over the time scale of the experiment, requiring the experimenter to modify assumptions, design, or analysis. This work bounds thermal transport at shocked conditions.

Корреляция электрических, гальваномагнитных и магнитных характеристик нанокристаллических пленок железа, полученных методом ионно-ассистированного осаждения

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 450 oC 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.

ELECTROCHEMICAL SYNTHESIS OF IRON MONOSELENIDE THIN FILMS

In the presented research work, the kinetics and mechanism of the deposition process of thin iron, selenium and Fe-Se films have been studied by recording a cyclic and linear polarization curves by potentiodynamic method using Pt and Ni electrodes. Individual and co-deposition potential areas of the components of the electrolyte on the Pt electrode were determined. In order to determine the optimal electrolysis mode and electrolyte composition, the effect of various factors (concentration of initial components, temperature, etc.) on the co-electrodeposition process of Fe-Se was studied. In addition, Fe-Se samples deposited on the surface of Ni electrodes were thermally treated at 4500C and studied by SEM and X-ray phase analysis methods. Elemental analysis of the films shows that they contain 42.2% Fe and 57.8% Se.

Investigation of atomic mixing during adsorption of iron film on silver substrate

The results of calculations of the energy and magnetic characteristics of the activated adsorption of a monolayer ferromagnetic iron film on the silver surface are presented. The studies were carried out using two approaches: the variational method of the spin density functional taking into account temperature effects and inhomogeneous distribution of magnetization and the ab initio one, implemented using the VASP software package. Calculations were made of the total and interfacial energies, magnetic moment and adsorption energy of the Fe / Ag system, depending on the orientation of the substrate face, the coating parameter Θ and the fraction of adatoms in the film. The strong influence of mixing and the energetic advantage of the formation of a "sandwich" system have been revealed. A continuous Fe film will not form on the close-packed Ag face, which is confirmed by experimental studies.

Red‐coated rocks on the seashore: The esthetics and geology of prehistoric rock art in Alta, Arctic Norway

AbstractResearch suggests that the World Heritage rock engravings in Alta, Northern Norway, were made along the seashore over a period of 5000 years. The postglacial rebound and consequent land uplift have caused a continuous displacement of the shoreline, now situating the earliest rock art panels up to 26 m above sea level. By examining the rock surfaces at Hjemmeluft and other sites, using field observations and geological analyses, we found that the pronounced red bedrock surfaces in the current seashore zone are composed of inorganic iron films related to a high content of magnetite in the native sandstone. Coupled with an interpretation of regional environmental history, we also found that it is highly likely that the rock art was originally carved on rocks with red iron films, rocks that are now generally gray. Due to the land uplift and subsequent covering of the rock art with lichen, moss, and turf, the red color has waned at the rock art sites. This knowledge may renew interpretation and understanding of the location of rock art in Alta and may have implications for conservation and management.

Eutectic Mixture of Iron(III) Chloride and Acetamide — Physicochemical Properties, Chemical Speciation, and Electrodeposition of Iron

The electrodeposition of iron alloys is a significant research topic, owing to the potential applications such as corrosion/wear-resistant coatings1, magnetic thin films2, and catalyst electrodes3. Although aqueous electrolytes have been mostly used for electrodeposition, vigorous hydrogen evolution on the cathode can lead to hydrogen embrittlement and precipitation of metal hydroxides2. In addition, less noble elements such as aluminum and silicon cannot be co-deposited from aqueous electrolytes due to the limited electrochemical window.To overcome the limitations of aqueous solutions, non-aqueous systems such as molten salts and ionic liquids have gained significant research attention. The electrochemical behaviour of iron complexes in imidazolium- and pyrrolidinium-based ionic liquids, and electrodeposition of metallic Fe was demonstrated in some liquids4,5. Many ionic liquids are, however, not viable on a practical scale.In this study, we explored an alternative electrolyte to ionic liquids for electrodeposition of iron. A mixture of ferric chloride and acetamide is shown to give a liquid at ambient temperature. This eutectic mixture has a higher conductivity than comparable eutectics formed from either aluminium or zinc chloride. Ferric chloride disproportionates to form both anionic and cationic iron species identified using spectroscopic methods. The electrodeposition of dense metallic iron film was demonstrated. References N. Tsyntsaru et al., Surf. Eng. Appl. Electrochem., 48, 491–520 (2013)G. Panzeri et al., Electrochim. Acta, 271, 576–581 (2018)N.-C. Lo et al., J. Electrochem. Soc., 163, D9–D16 (2016).P. Giridhar, B. Weidenfeller, S. Z. El Abedin, and F. Endres, ChemPhysChem, 15, 3515–3522 (2014).Y. Zhu, Y. Katayama, and T. Miura, J. Electrochem. Soc., 159, D699–D704 (2012).

Magnetic Anisotropy of Graphene-Coated Ultrathin Iron Layers on a Substrate of Hexagonal Boron Nitride Gr/Fe/h-BN

The theoretical results of the computer simulation of the magnetic properties of ultrathin iron films on a nonmagnetic substrate of hexagonal boron nitride Gr/Fe/h-BN have been obtained in terms of the spin density functional theory (SDFT). The main attention is focused on numerical studies of the magnetic anisotropy of iron films with the hexagonal structure similar to the crystal structure of intercalated iron films in the Gr/Fe/Ni(111) system. For this purpose, the total energies are calculated for ferromagnetic structures with different directions of the magnetic moments of iron atoms with respect to the film surface. The effect of graphene on the magnetic properties of the Gr/Fe/h-BN system is analyzed. The results of the theoretical simulation of Fe/h-BN and Gr/Fe/h-BN show that it is possible to obtain in this system quite “thick” iron films (dFe ≥ 10 A) that will have the perpendicular magnetic anisotropy.

Detection of femtosecond spin voltage pulses in a thin iron film.

We present experimental evidence of a spin voltage—a difference between the chemical potentials of the two spin directions—in a thin iron film based on spin- and time-resolved photoemission spectroscopy. This voltage is the driving force for a spin current during the ultrafast demagnetization of the sample. The observed magnitude is on the order of 50 mV, a value that is quite consistent with predictions based on particle conservation and persists for approximately 100 fs.

Looking at Electron Dynamics to Better Understand Photo-Active Materials

The generation of free and energetic electrons is the key to the next generation of photo-voltaic and photo-catalysts. In order to produce such electrons, the sunlight is so far the most promising sustainable source of energy. However, the conversion efficiency from light to the liberation of a functional electron depends on numerous factors and processes that are difficult to account for. One of the reasons is the difficulty of monitoring the early electron dynamics such as the charge separation event and the subsequent electronic relaxation and migration. Here, I propose the use of ultrafast transient absorption spectroscopy to watch these electronic events “live” in the femto- to nano-seconds (10-15-10-9 sec.) time scales. In this presentation, I will demonstrate this technique on iron and copper oxides thin films. In this study, we produce ultrashort laser pulses to mimic sunlight and trigger charge separations that ultimately lead to the generation of the reactive oxygen species that confer the films their antibacterial properties. With this technique, we are able to harvest information such as the charge separation efficiency, electron dynamics, excited state’s bandgap energy, and even material deformation upon photo-excitation, all of which are key to understand, control and enhance the conversion process.

Bis(terpyridine) Iron(II) Functionalized Vertically-Oriented Nanostructured Silica Films: Toward Electrochromic Materials.

Recent and potential applications of electrochromic materials include smart windows, optoelectronic devices, and energy conversion. In this study, we have incorporated bis(terpyridine) iron (II) complexes into vertically-oriented silica thin films deposited on indium-tin oxide (ITO) and their electrochromic behavior has been investigated. If 2,2′:6′,2″-terpyridine is commonly used as a ligand for forming metallo-supramolecular assemblies, with the objective to get metal-terpyridine complexes with multiple stable redox states, their simple and reliable arrangement into linear structures enabling effective electronic communication is however more challenging. We propose to overcome this difficulty by generating such complexes within vertical nanochannels on electrode. Terpyridine ligands were firstly immobilized by combining a click chemistry azide/alkyne approach with an electrochemically-assisted self-assembly (EASA) method used to grow an oriented mesoporous silica membrane bearing azide groups which were further derivatized with 4′-ethynyl-terpyridine ligands. The resulting terpyridine-functionalized films were consecutively dipped in an aqueous solution of Fe(BF4)2 and then in a solution of terpyridine in acetonitrile to form the bis(terpyridine) iron (II) complexes in situ. The electrochromic properties of the films functionalized at various levels were examined by monitoring the changes in their UV/Vis spectra upon electrochemical oxidation at controlled potential of +1.2 V vs. Ag/AgCl. Due to facile charge delocalization during the Fe2+ to Fe3+ redox process, the bis(terpyridine) iron (II) functionalized silica films exhibited electrochromic properties by changing from violet to non-colored using TBABF4 in acetonitrile as an electrolyte. The bis(terpyridine) iron(II) film experienced reversible electrochromic switching by applying +0.5 V in a reverse reduction electrochemical process. The Fe(tpy)2-functionalized silica thin films displayed a good contrast ratio (ΔT%) of 47% and relatively high coloration efficiency (CE) of about 245 cm2/C with a response time of coloring and bleaching of a few seconds (< 4 s).

Magnetisation and magnetic anisotropy of ion beam synthesised iron nitride

We report the effects of implantation-induced-sputtering in determining the true magnetisation of iron nitrides formed by nitrogen implantation into iron films and the changes subsequently observed in their magnetic anisotropy. Iron thin films (40 nm) capped with gold layers were synthesized by ion beam sputtering. Nitrogen was implanted onto the thin film to a dose of 7 × 1016 cm−2. Dynamic ion–solid interaction simulations calculate the average nitrogen concentration within the iron thin films to be 13 at.%. Ion beam analysis was used to evaluate the composition and depth profile of the thin films before and after implantation. Cross-sectional transmission electron microscopy helped in identifying the implantation induced effects at the surface and interface of the thin film structure. Magnetisation measurements show that nitrogen implantation enhances the magnetisation of thin films and reduces their in-plane magnetic anisotropy. High resolution TEM and magnetisation results suggest formation of α’/α”-Fe16N2 with large magnetic moments and perpendicular magnetic anisotropy. The enhancement in magnetisation of the thin film with and without considering the sputtering losses is determined to be 15% and 5%, respectively. Our review of literature shows that underestimating the sputtering losses from implantation leads to reporting of inconsistent and reduced magnetic moments for Fe16N2.

The Effect of Laser Re-Solidification on Microstructure and Photo-Electrochemical Properties of Fe-Decorated TiO2 Nanotubes.

Fossil fuels became increasingly unpleasant energy source due to their negative impact on the environment; thus, attractiveness of renewable, and especially solar energy, is growing worldwide. Among others, the research is focused on smart combination of simple compounds towards formation of the photoactive materials. Following that, our work concerns the optimized manipulation of laser light coupled with the iron sputtering to transform titania that is mostly UV-active, as well as exhibiting poor oxygen evolution reaction to the material responding to solar light, and that can be further used in water splitting process. The preparation route of the material was based on anodization providing well organized system of nanotubes, while magnetron sputtering ensures formation of thin iron films. The last step covering pulsed laser treatment of 355 nm wavelength significantly changes the material morphology and structure, inducing partial melting and formation of oxygen vacancies in the elementary cell. Depending on the applied fluence, anatase, rutile, and hematite phases were recognized in the final product. The formation of a re-solidified layer on the surface of the nanotubes, in which thickness depends on the laser fluence, was shown by microstructure studies. Although a drastic decrement of light absorption was recorded especially in UV range, laser-annealed samples have shown activity under visible light even 20 times higher than bare titania. Electrochemical analysis has shown that the improvement of photoresponse originates mainly from over an order of magnitude higher charge carrier density as revealed by Mott-Schottky analysis. The results show that intense laser light can modulate the semiconductor properties significantly and can be considered as a promising tool towards activation of initially inactive material for the visible light harvesting.

Ultrafast terahertz magnetometry

A material’s magnetic state and its dynamics are of great fundamental research interest and are also at the core of a wide plethora of modern technologies. However, reliable access to magnetization dynamics in materials and devices on the technologically relevant ultrafast timescale, and under realistic device-operation conditions, remains a challenge. Here, we demonstrate a method of ultrafast terahertz (THz) magnetometry, which gives direct access to the (sub-)picosecond magnetization dynamics even in encapsulated materials or devices in a contact-free fashion, in a fully calibrated manner, and under ambient conditions. As a showcase for this powerful method, we measure the ultrafast magnetization dynamics in a laser-excited encapsulated iron film. Our measurements reveal and disentangle distinct contributions originating from (i) incoherent hot-magnon-driven magnetization quenching and (ii) coherent acoustically-driven modulation of the exchange interaction in iron, paving the way to technologies utilizing ultrafast heat-free control of magnetism. High sensitivity and relative ease of experimental arrangement highlight the promise of ultrafast THz magnetometry for both fundamental studies and the technological applications of magnetism.