Improvements in Depth Selective Electron Mössbauer Spectroscopy

The conditions for achievement of high resolving power of depth selective conversion electron Mössbauer spectroscopy method at a combined installation ‘electron spectrometer–nuclear gamma-resonance spectrometer’ have been obtained. There has been made a considerable step in development of the method at its realization at a magnetic sector electron spectrometer with double focusing, equipped with electron source (a sample under investigation) of large-area and position-sensitive detector. The paper presents a prospective symmetrical version of a magnetic sector electron spectrometer that allows realizing more completely possibilities of the method. It is noted that the proposed method is particularly valuable for investigations of nanosystems, nanostrutures that contain Mössbauer nuclei.     

Photon and Ion-Beam Induced Processes in Materials Studied by Hyperfine Interactions

Laser nitriding and laser cementation are investigated by Mössbauer spectroscopy and complementary methods. It is demonstrated how the backscattering versions of Conversion Electron and Conversion X-ray Mössbauer spectroscopy can contribute to the investigation of surface processes, like the laser-induced formation of nitrides and carbides. Additionally, the formation of semiconducting iron disilicide can be achieved by ion-beam mixing and pulsed laser irradiation of Fe/Si bilayers. The results of both processes are compared.

     

Degradation of the Giant Magnetoresistance in Fe/Cr Multilayers Due to Ar-Ion Beam Mixing

The influence of 200 keV Ar-ion irradiation on the interlayer coupling in the Fe/Cr multilayer system exhibiting the giant magnetoresistance effect (GMR) is studied by conversion electron Mössbauer spectroscopy (CEMS), VSM hysteresis loops, magnetoresistivity and electric resistivity measurements and supplemented by the small-angle X-ray diffraction (SAXRD). The increase of Ar ion dose causes an increase of interface roughness, as evidenced by the increase of the Fe step-sites detected by CEMS as a result of which the GMR gradually decreases and vanishes at doses exceeding 1×10¹⁴ Ar/cm². A degradation of GMR with increasing Ar-ion dose is related to the formation of pinholes between Fe layers and the decrease of the antiferromagnetically coupled fraction.

     

CEMS of nitride coatings in agressive environments

The corrosion properties of single layered TiN and CrN films have been compared to bi-layered and multi-layered Ti/TiN films. XPS has showed that in humid SO₂ atmosphere the best corrosion properties have been achieved by a multi-layered Ti/TiN coating. Cyclic voltammetry in acetate buffer has been applied to measure the porousity and corrosion resistance of coatings. The best results have been achieved by multi-layered Ti/TiN and CrN films. Conversion electron Mössbauer spectroscopy has been used to study the changes in the interface Fe/TiN during thermal treatment in UHV. It has been shown that the amount of iron nitrides in the interface increases with increasing temperature.     

Hematite thin films: growth and characterization

We have grown hematite (α–Fe ₂ O ₃) thin films on stainless steel and (001)-silicon single-crystal substrates by RF magnetron sputtering process in argon atmosphere at substrate temperatures from 400 to 800°C. Conversion Electron Mössbauer (CEM) spectra of the sample grown on stainless steel at 400°C exhibit values for hyperfine parameter characteristic of bulk hematite phase in the weak ferromagnetic state. Also, the relative line intensity ratio suggests that the magnetization vector of the polycrystalline film is aligned preferentially parallel to the surface. The X-ray diffraction (XRD) pattern of the polycrystalline thin film grown on steel substrates also corresponds to α–Fe ₂ O ₃. The samples were also analyzed by Atomic Force Microscopy (AFM), those grown on stainless steel reveal a morphology consisting of columnar grains with random orientation, given the inhomogeneity of the substrate surface.     

Study of Phase Formations in ε-FeSi Layers by Pulsed Laser Annealing

Pulsed laser annealing has been applied on ε-FeSi layers in order to study the formation of (meta)stable iron silicides. Laser shots of different energy density were applied and/or the number of laser shots was also varied. Characterisation was performed using Rutherford Backscattering Spectroscopy (RBS)/Channelling and Conversion Electron Mössbauer Spectroscopy (CEMS). The reaction mechanisms of the Fe/Si system as well as the stability of the phases are discussed.     

Vibrational dynamics of Fe in amorphous Fe–Sc and Fe–Al alloy thin films

The atomic vibrational dynamics of ⁵⁷Fe in 800-Å thick amorphous (a-) ⁵⁷Fe_0.25Sc_0.75, a-⁵⁷Fe_0.67Sc_0.33 and a-⁵⁷Fe_0.14Al_0.86 alloy thin films has been investigated at room temperature by nuclear resonant inelastic X-ray scattering (NRIXS) of synchrotron radiation. The amorphous phase has been successfully stabilized by codeposition of Fe and Sc or Al in ultrahigh vacuum onto substrates held at –140 °C during deposition. The amorphous structure of the samples was confirmed by X-ray diffraction and conversion electron Mössbauer spectroscopy. The ⁵⁷Fe-projected partial vibrational density of states, g(E), has been obtained from the measured NRIXS vibrational excitation probability, together with thermodynamic quantities such as the probability of recoilless absorption (f-factor), the average kinetic energy per Fe atom, the average force constant, and the vibrational entropy per Fe atom. A plot of the reduced density of states, g(E)/E², versus excitation energy E proves the existence of non-Debye-like vibrational modes (boson peak) with a peak energy, E _bp , in the range of 3–7 meV. Both, the boson peak height H _bp and E _bp were found to depend on the composition. Above the boson peak, g(E)/E² exhibits an exponential decrease. Our results demonstrates that the features of the boson peak depend on the amount and type of element M (M = Al, Si, Mg, Sc).     

Studying surfaces and thin films using Mössbauer spectroscopy

Using a series of bi-layer samples, we show how Conversion Electron Mössbauer Spectroscopy (CEMS) and X-ray Backscatter Mössbauer Spectroscopy (XBS) can be done with the same experimental set up. The penetration depths of the K and L conversion electrons are measured as 51(6) and 330(240) nm, respectively, with relative contributions of 88(9) and 12(9)%. The penetration depth of the Fe-K _α X-ray signal is determined to be 3.6(2) μm. As a demonstration we show data on surface damage effects in electropolished TRIP steels, and by comparing CEMS and XBS Mössbauer patterns we estimate the thickness of a damaged layer (created by sanding) to be 550(50) nm.     

中国山东方山与缅甸抹谷Le-shuza-kone矿区暗蓝色刚玉的谱学特征

为对比研究中国山东昌乐方山矿区与缅甸抹谷Le-shuza-kone矿区所产暗蓝色刚玉的光谱学特征,并确定方山矿区和Le-shuza-kone矿区刚玉中铁元素的价态及致色机理,采用X射线粉晶衍射（XRD）、显微拉曼光谱（RAMAN）、显微傅里叶红外光谱（FTIR）测试、电子探针（EPMA）及穆斯堡尔谱（CEMS）等方法,对产于方山矿区和Le-shuza-kone矿区暗蓝色刚玉的物相、光谱学特征及成分开展深入研究。X射线衍射结果表明,两个矿区所产的刚玉在2θ=25°～45°之间以3.408 8 Å（012）,2.551 8 Å（104）, 2.380 7 Å（110）和2.085 0 Å（113）四个衍射峰为特征。缅甸抹谷Le-shuza-kone矿区刚玉在2θ=22°～23°之间有3.981 5 Å（110）的弱衍射峰,在2θ=38°～40°之间有2.314 9 Å（111）的弱衍射峰,分别为硬水铝石和勃姆矿（一水软铝石）的特征。拉曼光谱散射峰主要分布于350～450和550～850 cm-1两个区间。416和378 cm-1为刚玉的特征峰,测试结果中415和377 cm-1的强峰属于内部结构变形导致的拉曼位移,749 cm-1处的拉曼散射峰归属于Al-O伸缩振动。方山矿区刚玉的793和811 cm-1拉曼峰和Le-shuza-kone矿区刚玉707, 793, 1 239和1 247 cm-1拉曼峰可作为区分产地的依据。红外光谱表现为两个矿区样品共有指纹区451,603,640, 779和1 088 cm-1的吸收峰,缅甸抹谷Le-shuza-kone矿区刚玉在官能团区有结构水（-OH）1 981, 2 110和3 311 cm-1的吸收峰,可作为特征峰与中国山东昌乐方山矿区刚玉相区别。缅甸抹谷Le-shuza-kone矿区暗蓝色刚玉含结构水,其形成过程中有水的参与,而山东昌乐方山矿区的刚玉中没有结构水。经电子探针测试和电价差法计算,中国山东昌乐方山矿区刚玉中铁元素的存在形式为Fe2+,Fe3+的含量为0,Le-shuza-kone矿区刚玉中Fe2+占Fe总量的91.9%,Fe3+占Fe总量的8.1%。创新性的在刚玉中铁元素的研究中引入了穆斯堡尔谱仪测试测得中国山东昌乐方山矿区刚玉内铁的赋存形式为Fe2+,而非Fe2++Fe3+,其深蓝色的体色是由Fe2+致色的,而非前人推测的Fe2++Fe3+或Fe2++Ti4+价间电荷转移致色。     

Laser Nitriding of Iron,Stainless Steel,and Plain Carbon Steel Investigated by Mössbauer Spectroscopy

Nitriding is a common method for improving the hardness, mechanical properties, wear and corrosion resistance of metals. Laser nitriding of metals is an efficient process, where the irradiation of surfaces in air or nitrogen atmospheres with short laser pulses leads to a fast take-up of nitrogen into the irradiated surfaces. This process has been extensively investigated for pure iron, but usually, no tools or functional parts are made of pure iron. Mainly steel or cast iron is used as a base material. Therefore, when looking for technical applicability, also the influence of alloying elements on the laser nitriding process is of great interest. Besides the pure iron various carbon steels and an austenitic stainless steel were studied in laser nitriding experiments in order to investigate the influence of the material itself. Here, the process is investigated via Conversion Electron and X-ray Mössbauer Spectroscopy (CEMS and CXMS), Resonant Nuclear Reaction Analysis (RNRA), and X-Ray Diffraction (XRD). It appears that carbon steels are even better suited for the laser nitriding process than pure iron, and the laser nitriding also works efficiently for the stainless steel which is normally difficult to be nitrided.