CEMS study of oxide layers formed on stainless steel (SUS304 and SUS316)

Stainless steel (SUS304 and SUS316) was chemically treated and heated at various temperatures, and the oxide films formed on the surface were analyzed by conversion electron Mössbauer spectrometry (CEMS). Three magnetic components of iron species were detected in the top oxide layers of stainless steels heated below 600°C and the fine particles of iron oxides were initially produced in the inner oxide layers of the samples heated at temperatures higher than 700°C. Only paramagnetic iron species were detected in the oxide layers of the stainless steels prepared by chemical treatment.     

Thermal oxidation behaviors and structures of Fe-9Cr-1Mo alloy

Isothermal oxidation behaviors of Fe-9Cr-1Mo alloy were investigated at 600, 700, 750 and 850 ^°C for 72 h in air atmosphere. The oxidation rates were measured using a thermogravimetric analyzer (TGA). The structure and composition of the oxide scale were characterized by X-ray diffraction (XRD), energy dispersive spectrometry (EDS) and conversion electron Mössbauer spectrometry (CEMS). In this study it was found that the oxide layers form duplex structures consisting of Fe and Cr oxides. CEMS spectra are composed of one doublet due to dispersed Fe ³⁺ in Cr₂O₃ oxidation layers produced at high temperatures and two magnetic components due to Fe-Cr-Mo alloy substrate and hematite (Fe, Cr)₂O₃ with lower hyperfine field than pure hematite (52 T). Fe rich oxides are formed at the surface by oxidation at relatively low temperatures of 600 ^°C and 700 ^°C, while Cr rich (Fe, Cr)-oxides are formed in the top surface layers by oxidation at higher than 750 ^°C.     

Onset of magnetization in monolayer films

Correlations between structural and magnetic properties for ultra-thin iron films are discussed. Some selected methods of structural and magnetic analysis are reviewed. The onset of magnetism for submonolayer Fe(110) film on W(110) is explained based on STM (scanning tunneling microscopy) imaging. Hyperfine magnetic fields in iron films sandwiched between Cr show unusual temperature behavior due to the influence of magnetic ordering in Cr. Magnetic properties of metastable iron phases on Cu and Ru are discussed, based on CEMS measurements.     

Mössbauer-Effect Study of Metastable c-FeSi Synthesized by Molecular Beam Epitaxy (MBE) and by Ion Implantation

Conversion electron Mössbauer spectroscopy (CEMS) has been applied to the study of the metastable c-FeSi phase (i.e. an iron silicide with CsCl lattice structure) that was synthesized by implantation of Si + ions of 50 keV in energy into f -Fe (95% 57 Fe) near room temperature with a nominal dose of 5 2 10 17 cm m 2 , and by molecular beam epitaxy (MBE). Iron silicide layers with different stoichiometry (FeSi 0.85 , FeSi, Fe 0.85 Si) were grown by codeposition of 57 Fe and Si onto an Fe buffer layer on MgO(100). For all FeSi layers the defective CsCl structure was observed after annealing at different temperatures. X-ray diffraction measurements were performed to determine the structure and epitaxial relationship of the c-FeSi films. The lattice parameter perpendicular to the film plane was found to be 2.77(5) Å. CEMS measurements revealed a lower than cubic site symmetry of the iron atoms for both the c-FeSi layers synthesized by ion implantation and by MBE. The formation of nearly undistorted c-FeSi after annealing is favored by excess Fe atoms in the deposited film.     

Preparation and characterisation of electrodeposited amorphous Sn-Co-Fe ternary alloys

Electrochemical deposition was investigated as a process to obtain alloys of Sn-Co-Fe, which to date have not been reported in the literature. A constant current technique was used to electrochemically deposit tin-cobalt-iron alloys from a gluconate electrolyte. The gluconate system was chosen as an electrolyte, which could potentially provide an environmentally safe process. The effect of plating parameters such as current density, deposition time, temperature and pH are discussed. Results are reported for current density and plating time using an electrolyte temperature of 20-60 °C and pH of 7.0 in relation to phase composition, crystal structure and magnetic anisotropy of the deposited alloys.Investigations were conducted using ⁵⁷Fe conversion electron Mössbauer spectroscopy (CEMS), ¹¹⁹Sn CEMS, transmission Mössbauer Spectroscopy and XRD. The ⁵⁷Fe and ¹¹⁹Sn CEMS spectra and XRD showed that the dominant phase in the deposits was amorphous Sn-Co-Fe. The relative area of the 2nd and 5th lines of the sextets representing the magnetic iron containing phases was found to decrease continuously with increasing current density while at the same time no significant changes in the magnetic anisotropy was found with plating time. Magnetically split ¹¹⁹Sn spectra reflecting a transferred hyperfine field were also observed.A range of good quality amorphous Sn-Co-Fe ternary alloys was obtained over a range of operating conditions from an environmentally acceptable gluconate electrolyte.     

The effect of peptone on the structure of electrodeposited Sn-Fe binary alloys

Sn-Fe thin films were electrodeposited by constant current deposition on copper substrates using an aqueous gluconate based electrolyte with varying concentrations of the organic additive peptone. Good quality metallic deposits were obtained with surface morphologies which varied with the concentration of peptone present in the electrolyte. The effect of peptone concentration on the deposition process was studied using electrochemical polarization curves and EDX analysis. The effect of peptone concentration on deposit structure and surface morphology was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and ⁵⁷Fe and ¹¹⁹Sn conversion electron Mössbauer spectroscopy (CEMS). It was concluded that the addition of small amounts of peptone to the electrolyte slightly increased the bath stability and led to changes in the alloy composition of the electrodeposits. It was found that increases in the peptone content increased the amount of the crystalline structure in the deposits with corresponding reductions in the amounts of amorphous structure present in the deposits.     

CEMS characterisation of Fe/high-κ oxide interfaces

The interfaces between Fe and different high-κ oxides are investigated by means of conversion electron Mössbauer spectroscopy (CEMS). Information on the magnetic ordering at the interface is obtained from the magnetic hyperfine splitting of the Mössbauer spectra. The reactivity of the Fe atoms at the interface (intermixing) is also estimated by CEMS. X-ray diffraction (XRD) and X-ray reflectivity (XRR) provide additional information on the intermixing and different phases present at the interface. CEM-spectra show the presence of both ferromagnetic and paramagnetic phases. CEMS and XRD results show that the Fe/HfO₂ and Fe/Al₂O₃ interfaces are the least reactive. The degree of intermixing between Fe and the high-κ oxide is determined by the oxide surface roughness.     

Characterization of oxide layers and interface layers of ferrite stainless steel (SUS430) by57Fe CEMS

The oxide layers on stainless steel formed by heating at various high temperatures and by dipping in LiF + BeF₂ molten (Flibe) bath at 600 °C were characterized by CEMS. Hematite was a major iron product at 600 °C and fine oxides with paramagnetic Fe(III) species were produced at the higher temperatures than 700 °C. The interface of stainless steel beneath oxide films was characterized as the hyperfine field distributions. Paramagnetic Fe(III) species were produced on Cr depleted layers in the Flibe bath. CEMS is effective for simultaneous characterization of both oxide surface and interface layers of the ferritic stainless steel.     

Structure of sputter-deposited Pt/Fe and Cr/Fe multilayers

Conversion electron Mössbauer spectroscopy (CEMS) and X-ray diffraction (XRD) have been used to investigate the structure of Pt/Fe and Cr/Fe multilayers deposited by magnetron sputtering. The Cr/Fe samples consisted of four samples prepared under Ar sputtering pressures of 1.3, 3.0, 5.0, and 10.0 mT, all with the same multilayer structure of 3.5 nm Cr/2.5 nm Fe, repeated 35 times onto c-Si wafer substrates. The quality of the interfaces between Cr and Fe is clearly degraded with increasing sputter pressure, as seen by changes in the relative intensities of four magnetic subspectra in the CEMS and the gradual appearance of a single-line resonance similar to Fe in solution in Cr. The low-angle XRD superlattice peaks also disappear with increasing sputter pressure, while the high-angle XRD shows a tendency for loss of the preferred (110) texture. Two films of Pt/Fe were deposited epitaxially onto MgO single crystals with bilayer periods of 1.3 nm and 2.6 nm and total thickness of 300 nm each. A transition from fcc-PtFe with near-perpendicular magnetic anisotropy to a bcc-Fe/fcc-PtFe mixture with in-plane magnetic texture is observed by CEMS for the factor of two increase in bilayer period.     

Mössbauer and XRD study of novel quaternary Sn-Fe-Co-Ni electroplated alloy

Constant current electrochemical deposition technique was used to obtain quaternary alloys of Sn-Fe-Co-Ni from a gluconate electrolyte, which to date have not been reported in the literature. For the characterization of electroplated alloys, ⁵⁷Fe and ¹¹⁹Sn Conversion Electron Mössbauer Spectroscopy (CEMS), XRD and SEM/EDAX were used. XRD revealed the amorphous character of the novel Sn-Fe-Co-Ni electrodeposited alloys. ⁵⁷Fe Mössbauer spectrum of quaternary deposit with composition of 37.0 at% Sn, 38.8 at% Fe, 16.8 at% Co and 7.4 at% Ni displayed a magnetically split sextet (B = 28.9T) with broad lines typical of iron bearing ferromagnetic amorphous alloys. Magnetically split ¹¹⁹Sn spectra reflecting a transferred hyperfine field (B = 2.3T) were also observed. New quaternary Sn-Fe-Co-Ni alloys were successfully prepared.     

Is a coating part of the substrate? The case of vanadium carbide on steel

Metallic surfaces, especially that of steel, are generally protected by various types of coatings. This paper presents some of the results of CEMS studies currently being made on mild steel substrate coated with a thin layer of vanadium carbide (VC). CEMS studies were done before and after coating. The internal magnetic field was found to be oriented at an angle of 48 degrees with respect to the transverse surface of the steel sample. After coating with VC at 950 °C, this value was reduced to 39 degrees. Molecular orbital calculations indicated that the electron density along the surface of the steel is significantly changed when the VC layer is formed, which leads to the changes in the magnetic field directions that are observed. The experimental data therefore reveal that vanadium from the coating diffuses into the iron substrate.     

Icems and dcems study of Fe layers evaporated onto Al and Si

Thin layers of⁵⁷Fe (2.5 nm, 10 nm and 70 nm thickness), vacuum evaporated onto Al and Si plates, have been investigated by conversion electron Mössbauer spectroscopy (CEMS). The measurements were performed employing both a proportional counter and a channeltron for conventional and ultrahigh-vacuum integral CEMS (UHV-ICEMS) studies, respectively, and a channeltron for depth-selective CEMS (DCEMS). The phase analysis of the layers on base of experimental results has indicated the presence of metallic iron and one or two iron compounds, ascribed to iron reaction products formed with the residual gas during evaporation. These products are most likely rather stable iron nitrides, are more or less clustered and are distributed throughout the whole layer.     

Mössbauer and XRD study of hot dip galvanized alloy

Mössbauer spectroscopy has been used to investigate the nature of the Zinc-Iron alloys present within the Hot Dip Galvanized (HDG) layers of steel with a silicon content of 0.35 %. The investigation also studied the impact of the powder coating pretreatment on the nature of the alloy layers. The acid etching process within the pretreatment process in particular would be expected to have a significant impact on the HDG layer. This study utilized ⁵⁷Fe Mössbauer spectroscopy to examine identically processed samples prior to and post pre treatment. XRD and ⁵⁷Fe CEMS measurements were performed on hot galvanized S355J2 + N samples, forming sandwiched structure. Both XRD and CEMS reveal the presence of dominant steel phase in accordance with its estimated occurrence on the surface of the sandwiched samples. Minor Γ-Fe3Zn10, ζ-FeZn15 and solid solution Fe-Zn as well as minor Fe-Si phases could also be identified.     

CEMS study of silicon implanted iron

Thin layers of iron-rich Fe-Si alloys were formed by silicon implantation into iron at room temperature with different energies (100, 200, and 300 keV) and ion doses (2 × 10¹⁷ to 1×10¹⁸ cm^–2). The produced layers were investigated by⁵⁷Fe conversion electron Mössbauer spectroscopy (CEMS) to identify the phases formed by the ion implantation. Auger electron spectroscopy (AES) was used to measure the concentration depth profiles of the implanted silicon. Depending on the implantation parameters different disordered Fe-Si structures were detected. At low doses only magnetic phases were formed while at high doses a non-magnetic phase with a hitherto unknown structure appeared. Annealing of the samples resulted first in the formation of a D0₃-like short-range order and a slow decrease of the non-magnetic phase, and subsequently in the migration of Si out of the investigated depth range.     

Growth of iron films on MgO(100) substrates at 560-600 K

The growth mechanism of heteroepitaxial thin iron films, deposited on MgO(100) substrates at 560-600 K, was investigated by means of tunnelling electron microscopy and spectroscopy. Scanning tunnelling microscopy (STM) analysis of the surface indicates the formation of long flat (about 10-20 nm) terraces for thicknesses greater than 3-4 nm. The fine structure of those samples contains sets of interpenetrating screw and helical dislocations. The onset of the formation of islands on these terraces and also their sizes were a result of stress relaxation in these films and this was supported by the Monte Carlo simulations. The resulting critical number of island layers needed to build up the gain in energy in a relaxed volume (compensating the misfit losses on its boundary) perfectly correlates with the observed STM pattern. At even larger thicknesses (greater than 9-10 nm) the surface becomes uniformly flat with a large number of mosaic voids. The differential conductivity spectra show the distinct surface peak of iron, positioned between the values for the iron crystal surface and the atomic limit. Manipulation of iron nanoparticles from the tip to the surface and back is demonstrated.     

Mössbauer Investigation of Electrodeposited Sn–Zn,Sn–Cr,Sn–Cr–Zn and Fe–Ni–Cr Coatings

⁵⁷Fe and ¹¹⁹Sn CEMS, XRD and electrochemical measurements were used to investigate the effect of the preparation parameters and the components on the structure and phase composition of electrodeposited Fe-Ni-Cr alloys in connection with their corrosion behavior. XRD of the electrodeposits reflect an amorphous-like character. ⁵⁷Fe CEM spectra of Fe-Ni-Cr electrodeposited samples, prepared in a continuous flow plating plastic circulation cell with variation of current density, electrolyte velocity and temperature, can be evaluated as a doublet associated with a highly disordered paramagnetic solid solution phase. This phase was identified earlier in Fe-Ni-Cr electrodeposits that were prepared by another plating method and contained both ferromagnetic and paramagnetic metastable phases [1]. This is the first time that we have succeeded to prepare Fe-Ni-Cr alloys containing only the metastable paramagnetic phase. The effect of the plating parameters on the structure is also analysed by the quadrupole splitting distribution method. ¹¹⁹Sn CEM spectra of all Sn-containing plated alloys show a broad line envelop which can be decomposed at least into two components. One can be associated with β-tin. The other one can be assigned to an alloy phase. The structure and distribution of microenvironments of these phases depends on the plating parameters especially on the parameters of the reverse pulse applied. This revised version was published online in August 2006 with corrections to the Cover Date.     

The porous silicon morphology effect on the growth of electrodeposited FeNi alloy

In this work, we report on cathodic deposition of FeNi thin films into porous silicon (PS) formed on n-type Si. Macroporous and mesoporous silicon layers were formed at constant potential or current density. The electrodeposited thin films were characterized by Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD). The magnetic properties of the FeNi layers were investigated by hysteresis loops measurements. SEM images of the FeNi films indicate that tubular and granular forms were obtained depending on the porous silicon surface morphology. Moreover, the FeNi films compositions are found to depend on the porous silicon microstructure. Finally, the XRD spectra of the deposited films show the presence of FeNi (111) and FeNi (220) peaks. The FeNi (111) peak has been shown for all polarization potentials, in agreement with results reported in the literature.     

Effect of organic additives on characterization of electrodeposited Co-W thin films

Co-W thin films were electrodeposited from aqueous bath with different organic additives. Electrochemical analysis showed that the transient state was limited and polarization behaviors were more evident during Co-W electrodeposition in the presence of organic additives. SEM measurement indicated that the surface morphology was affected by the nature of the organic additives to a large extent. Homogeneous Co-W thin films were obtained from the solutions containing ethyl methacrylate. Moreover, it was obvious that the presence of organic additives, in the electroplating bath, modified the structure and magnetic properties of the Co-W thin films according to the XRD and VSM measurements.     

Electrodeposition of nanostructured Ni(1−x)Mnx alloys films from chloride bath

NiMn alloys were electrodeposited from chloride bath with various Mn content up to 10 at.%. The effect of bath composition and current density on Mn content of electrodeposited thin films was explored. A maximum of 9.8 at.% Mn content in deposited films was obtained at optimized current density of 40 mA/cm² and MnCl₂/NiCl₂ concentration ratio of 2.5 in the bath. The morphology and crystal structure of deposits were evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The constituents in the films were determined by energy dispersive X-ray spectroscopy (EDS). It was revealed that the structure of NiMn coatings had an average grain size of about 17 nm. It was found that the deposits exhibited FCC structure with prefer orientation of <111>. The soft magnetic properties of electrodeposited films were measured by vibrating sample magnetometer (VSM). It was observed that the magnetic parameters such as coercivity and saturation magnetization were decreased with increasing of Mn in the deposits.     

Titanium and carbon implantation of iron

Pure iron foils have been implanted with Ti and with Ti plus C and characterized by conversion electron Mössbauer spectroscopy (CEMS) and Auger electron spectroscopy (AES). Both paramagnetic and magnetic phases are observed and attributed to amorphous Fe?Ti?C alloys of differing Ti and C contents. Estimates of the thicknesses of the amorphous layers based on the CEMS data are in good agreement with the AES concentration depth profiles.