In-beam implantation of iron into germanium,silicon and diamond studied by the Mössbauer effect

The Mössbauer effect of⁵⁷Fe implanted into diamond structure semiconductors, Ge, Si and C, has been studied by in-beam implantation of⁵⁷Fe ions, which were excited to the 14 keV state by a³⁵Cl beam from a tandem Van de Graaff accelerator. The time between the stopping of the⁵⁷Fe nucleus and the emission of the 14 keV -ray is determined by the lifetime (140 ns) of the 14 keV state. In each material the Mössbauer spectrum exhibits a doublet with velocity coordinates (in mm/s) at room temperature, relative to a sodium ferrocyanide absorber, as follows: diamond (–0.99, 1.10), silicon (–0.80, 0.21), and germanium (–0.88, –0.02). In silicon and germanium crystals the spectra were observed over the temperature range between 13 K and 870 K. The relative line intensities changed dramatically and the positions of the lines shifted systematically with temperature. In addition, channelling studies were made on iron that had been implanted into silicon.     

Weathering of Martian and Earth surface studied by Mössbauer spectroscopy

Martian regolith and Earth’s basaltoid samples have been investigated by means of Mössbauer spectroscopy. The identification of the same minerals: olivine, pyroxene, magnetite, hematite and confrontation of the Fe^3?+?/Fe^2?+?, Fe^3?+?/Fe_tot, Fe^2?+?/Fe_tot ratios are presented. Co-existence of olivine and hematite in Martian regolith, absent in presented by authors terrestrial samples has been tentatively explained.     

Formation of graphite encapsulated iron nanoparticles during mechanical activation and annealing analyzed by Mössbauer spectroscopy

The investigation performed by means of Mössbauer spectroscopy, X-ray diffraction and transmission electron microscopy demonstrated that the interaction in the system iron-amorphous carbon proceeds via the formation of nano-sized iron particles (10–40 nm) and the carbide nano- phases distributed over amorphous carbon matrix. The annealing of these samples causes a crystallization of the amorphous carbon, decomposition of nano-sized carbide phases and formation of iron nanoparticles (50–100 nm) encapsulated by graphite.     

Mössbauer and magnetization studies of iron oxide nanocrystals

Monodisperse iron oxide nanocrystals have been produced following non-hydrolytic, thermal decomposition routes. Spherically shaped particles with diameter of 4 and 12 nm and cubic shaped particles with an edge length of 9 nm have been studied. The particles have been shown to consist of mainly maghemite. A reduction of the saturation magnetic hyperfine field is observed for the 4 nm particles as compared to the corresponding bulk value. The anisotropy energy determined from the temperature variation of the magnetic hyperfine field was strongly enhanced for the 4 nm particles.     

Dynamics of iron in Fe-porphyrin aggregates studied by X-ray absorption and Mössbauer spectroscopy

The iron-porphyrin aggregates were studied by optical absorption and fluorescence method, infrared spectroscopy, X-ray absorption and Mössbauer spectroscopy. The aggregation of porphyrin molecules strengthens the Fe-ligands bonds and accelerates the spin-spin relaxations. A significant speeding-up of relaxation was observed with lowering the temperature down to 25 K. The comparison of the EXAFS (Extended X-ray Absorption Fine Structure) and Mössbauer spectroscopy results enabled some separation of the individual Fe vibration from its collective movement with ligands.     

Laser-produced iron nitrides seen by Mössbauer spectroscopy

Mössbauer spectroscopy is a very powerful tool to investigate technological processes performed mainly at the surface of materials. Nitriding of metals and steel is well established in surface engineering, and gas nitriding is used most frequently. Laser nitriding, i.e. the nitrogen take-up from the ambient gas upon irradiation of a steel surface with short laser pulses, is presented in its application to iron, stainless steel and plain carbon steels. It will be demonstrated how Mössbauer spectroscopy in combination with complementary methods (Rutherford backscattering spectroscopy, Resonant nuclear reaction analysis, Nanoindentation) can help to reveal basic mechanisms in these processes.     

Mössbauer study of the surface of core-shell type nanoparticles

The properties of the surface layer of core-shell nanoparticles incorporated into the matrix of macromolecules of 3,4-bis(decyloxybenzoyl) poly(propylene imine) derivative of the second generation are studied by Mössbauer spectroscopy at low temperatures. The spin states, the details of the phonon spectrum and the Debye temperature of surface layer atoms discussed.     

Mössbauer spectroscopy studies of the magnetic properties of ferrite nanoparticles

Studies of the ferrite nanoparticles prepared by the chemical decomposition of iron chlorides with a various ratio ξ = Fe³⁺/Fe²⁺ are herein presented. The microstructure and the magnetic properties have been studied by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Mössbauer spectroscopy (MS). The TEM studies show that the nanoparticles have almost a spherical shape with the diameter of (12 ± 2) nm for all samples. The measured XRD pattern was mainly composed of lines which were indexed with a cubic spinel structure. The analysis of the Mössbauer data shows that the microstructure of the nanoparticles consists of the core formed by nonstoichiometric magnetite and maghemite shell. A small amount of hematite, probably on the surface of the nanoparticles with ξ = 1.75, 2.0, was detected. At temperatures T ≤ 150 K the spin canting of surface maghemite with ξ = 2.25 was observed while for the samples with ξ = 1.75, 2.0 such effect was suppressed by the presence of hematite on the surface of the nanoparticles. Infield Mössbauer spectra with ξ = 1.75, 2.0 show that magnetic moments of the magnetite/maghemite core are parallel while magnetic moments of the surface hematite are perpendicular to the direction of the external magnetic field.     

Mössbauer study of iron carbide nanoparticles produced by laser ablation in alcohols

Iron carbide nanoparticles were synthesized by laser ablation of iron in alcohols (methanol and ethanol). A new cell, designed to allow the ablation to be conducted in a flowing solvent, enabled separation and collection of the nanoparticles immediately after production, thus preventing further photochemical reactions of the colloids. The nanoparticles were investigated using Mössbauer spectroscopy, X-ray diffraction, and transmission electron microscopy. In methanol, they consisted of α-iron, γ-iron, iron carbide, and amorphous paramagnetic iron carbides, whereas in ethanol they consisted of iron carbides and amorphous paramagnetic iron carbides. The difference in products depending on the alcohol was attributed to the different carbon supplies for methanol and ethanol. For both solvents, the average particle size was found to be 16 nm, and the nanoparticles were dispersed in amorphous carbon. We also examined the effect of further laser irradiation of the colloids using stagnant solvent, and the particle size was found to increase and a very small amount of carbonization was observed.     

Mössbauer spectroscopy and proton relaxometry study of magnetite nanoparticles designed for preparing diagnostic contrast media

Mössbauer spectroscopy, proton relaxometry, and transmission electron microscopy are used to study magnetite nanoparticles designed for creating diagnostic contrast media. Superparamagnetic magnetite nanoparticles with a size of 5–7 nm and blocking temperature of T _b = 50 K are examined as a component of diagnostic contrast media with relaxation times T ₁ and T ₂ capable of circulating in the bloodstream for a long time. Larger ferrimagnetic nanoparticles (30–40 nm) can be concentrated in pathological tissues by applying an external magnetic field, thereby providing a means for hyperthermia.     

Investigation of constitutional and thermal defects in the ordered β-phases CoGa and NiGa alloys by Mössbauer spectroscopy

The constitutional and thermal defect formation in the Co_100-xGa_x alloys (42⩽x⩽53) and Ni_100-xGa_x alloys (47⩽x⩽52) was studied by Mössbauer spectroscopy. The formation of both constitutional and thermal defects in the CoGa alloys was observed by the appearance of resolved quadrupole split spectral components. The influence of these defects in the NiGa system was detected only by the broadening of the absorption line. The ⁵⁷Fe probe atoms were found to populate the Nisublattice in these alloys. The highest concentration of thermal defects was found in the equiatomic composition of the NiGa alloys.     

Kinetic study of the thermal transformation of limonite to hematite by X-ray diffraction, ��-Raman and M?ssbauer spectroscopy

A kinetic study about the phase limonite (FeO(OH)-nH₂O) was performed through X-ray diffraction, ??-Raman spectroscopy and Mössbauer spectroscopy. The oxide powder sample was extracted from Taraco district, Huancané province of Puno (Peru). X-ray diffraction identified the phase goethite as the main mineralogical component, and then the sample was subjected to in-situ heat treatment in the temperature range: 100 to 500°C in oxidizing (air) and inert (nitrogen) atmospheres. The goethite phase remains stable in this range: room temperature to 200°C. Between 200°C to 250°C there is a phase transition: ??-Fe^3?+?O(OH) ?? ??-Fe₂O₃, i.e., from goethite to hematite phase, taking as evidence the evolution of the diffraction profiles. At 200°C spectra shows the start of broadened magnetic component and it was adjusted through of a magnetic distribution giving a mean field of 38.6T and a relative area of 52.9%, which is a characteristic of goethite. Also, it is noticed the presence of a small amount of hematite with a mean field of 49.0T linked with a superparamagnetic broadened doublet of relative area of 47.1% where the domains of the particles have sizes smaller than 100 Å and it is evidence the superparamagnetic limit; i.e., the superparamagnetic effect tends toward a distribution of magnetic fields. Moreover, the Raman spectra of the in-situ thermal treatment, support the transition at 290°C through the transformation of characteristic bands of goethite to hematite phase at the frequency range from 200 to 1,800 cm^???1.     

Mössbauer and MCD spectroscopy of the Fe3S4 nanoparticles synthesized by the thermal decomposition method with two different surfactants

Greigite (Fe₃S₄) nanoparticles (NPs) were fabricated by the thermal decomposition method using two different surfactants: oleylamine (OLA) and 1-hexadecylamine (HDA). In both cases, the synthesized NPs were characterized as the Fe₃S₄ nanocrystals with minor inclusions of Fe₉S₁₁ phase. FT-IR spectroscopy and thermo-gravimetric analysis allow concluding about OLA or HDA shells covering magnetic core of NPs. Mössbauer spectra has revealed deviations of iron ions distribution among crystal positions from that presented in literature for pure greigite. In accordance with these deviations, the pronounce changes are observed in the magnetic circular dichroism (MCD) spectra which manifest themselves as the spectrum shift to higher energies of electromagnetic waves and redistribution of the MCD maximum intensities. These effects are associated with a change in the density of electronic states in the samples due to the redistribution of iron ions between octahedral and tetrahedral positions in nanocrystals under the influence of surfactants.     

Corrosion studies of iron and its alloys by means of57Fe Mössbauer spectroscopy

Some of the advantages and limitations of Mössbauer spectroscopy when used in corrosion research are shown by using three examples taken from the work of the authors on (i) the passive layer of iron, (ii) the corrosion of weathering steels by SO₂-polluted atmospheres and (iii) the performance of rust converters.     

Study of archaeological iron objects by PGAA,Mössbauer spectroscopy and X-ray diffraction

Archaeological iron objects often corrode rapidly after their excavation, even though they have survived long times of burial in the ground. Chlorine that accumulates during burial is thought to play a major role in this destructive post-excavation corrosion. It is therefore important for the conservation of such objects to determine the chlorine content in a non-destructive manner and, if necessary, to remove the chlorine from the artefacts by appropriate methods. Such methods are leaching in alkaline solutions or heating in a reducing atmosphere at temperatures up to 800 ^°C. We have studied the efficiency of the heating method using prompt gamma activation analysis (PGAA) for monitoring the Cl content and Mössbauer spectroscopy at room temperature (RT) and 4.2 K as well as X-ray diffraction to study the mineralogical transformations of the rust layers. The heat treatments were performed a N₂/H₂ (90/10) mixture at temperatures up to 750 ^°C. As test specimens sections of iron rods from the Celtic oppidum of Manching (Bavaria) were used. The initial Cl contents of the pieces varied in the range of several hundred ppm, referring to the iron mass. Annealing for 24 h at 350, 550 and 750 ^°C was found to reduce the Cl contents of the specimens, to about 70, 30 and 15 % of the original values, respectively. The rust consists mainly of goethite with admixtures of magnetite, lepidocrocite and akaganeite, which is thought to be a major carrier of chlorine, probably together with iron chlorides. Much of the goethite is so fine-grained that it does not split magnetically at RT. Annealing converts the rust mainly to maghemite at 350 ^°C, to magnetite at 550 ^°C and to wüstite plus magnetite and metallic iron at 750 ^°C. Pure akaganeite behaves in nearly the same manner.     

Observation of iron impurity diffusion in silicon under bending stress by Mössbauer spectroscopy

In the present work, the formation of the Al₇₀Cu₂₀Fe₁₀ icosahedral phase by mechanical alloying the elemental powders in a high-energy planetary mill was investigated by X-ray diffraction and Mössbauer spectroscopy. It was verified that the sample milled for 80 h produces an icosahedral phase besides Al(Cu, Fe) solid solution (β-phase) and Al₂Cu intermetallic phase. The Mössbauer spectrum for this sample was fitted with a distribution of quadrupole splitting, a doublet and a sextet, revealing the presence of the icosahedral phase, β-phase and α-Fe, respectively. This compound is not a good hydrogen storage. The results of the X-ray diffraction and Mössbauer spectroscopy of the sample milled for 40 h and annealed at 623°C for 16 h shows essentially single i-phase and tetragonal Al₇Cu₂ Fe phase.