CEMS/XPS study of iron stearate Langmuir-Blodgett layers

Summary Langmuir-Blodgett mono- and multilayers of ferric stearate have been formed on oxidized silicon wafers. Thermodesorption of these layers was investigated by conversion electron Mössbauer and photoelectron spectroscopy and some complementary methods. Heating of samples in air up to 523 K leads to a desorption of the fatty acid chains, while the ferric ions are left on the substrate surface. These ions do not cluster laterally like it was found for Cd ions. They form a rather homogeneous, closed oxidic layer. This well defined layer may be used afterwards for further studies of surface reactions as well as interface and intra-layer interactions. The surface iron ions were found to exhibit a reasonably high recoilless fraction. Therefore, Mössbauer spectroscopy allows to follow chemical, structural, and magnetic changes of the iron ions even if the surface is covered by less than one monolayer.     

Initial 119Sn Mössbauer Spectroscopy and X-ray Diffractometry Investigations of Electrodeposited Tin-Chromium and Tin-Zinc-Chromium Alloys

¹¹⁹Sn conversion electron Mössbauer spectroscopy, X-ray diffractometry and energy dispersive X-ray analysis (EDAX) were employed to investigate microstructure, composition and phases present in as-electroplated Sn-Cr and Sn-Cr-Zn alloys deposited on copper substrates. In the Sn-Cr deposits Cu, -Sn, Cr-Sn phases can be identified by X-ray diffractometry. The phase composition is significantly different between the samples prepared with relatively higher and lower current densities. In the diffractograms of Sn-Cr-Zn deposits Cu, -Sn, Zn phases can be well identified. A small intensity amorphous peak is also present, which can perhaps be associated with the presence of some amorphous Zn and Sn alloy. ¹¹⁹Sn Mössbauer spectra of Sn-Cr deposits exhibit an asymmetric broad main line centered near the isomer shift characteristic of -Sn as well as they contain a small component near the zero velocity which can be attributed to a SnO₂ phase based upon its characteristic. ¹¹⁹Sn Mössbauer spectra of Sn-Cr-Zn deposits are roughly similar to those of Sn-Cr deposits although the Mössbauer parameters of the third phase are different and vary with the Zn content. The presence of SnO₂ on the surface mainly in the Sn-Cr samples can be attributed to the corrosion process in the air.     

Development and application of parallel-plate avalanche counter for in-beam Mössbauer spectroscopy

For Mössbauer -rays in the in-beam Mössbauer experiments using various beams such as heavy ion, secondary short-lived isotope, and neutron beams, it is important to develop a detector. A parallel-plate avalanche counter (PPAC) is the most suitable gas counter for on-line measurements, because PPAC collects the internal conversion electrons emitted by the Mössbauer effect even under high -background. We evaluated the influences of the pressure and flow rate of the counter gas against the counting efficiency of PPAC, and determined the optimum conditions for use in the in-beam Mössbauer experiments.     

M?ssbauer spectroscopy and structural analysis of solids

Mössbauer spectroscopy is reviewed as a method of analysis of hyperfine interactions in the solid state. It is sensitive both to the atomic scale and to phase structures. It utilizes the interactions between the hyperfine fields and nuclei in solids measured by a nuclear technique. The importance of various Mössbauer isotopes is discussed, the ⁵⁷Fe being still the most important. Principles of the qualitative determination of the structure sites and/or phase attachment are explained on the basis of the measurement of hyperfine structure parameters (i.e. the isomer (chemical) shift, the quadrupole and magnetic splittings). The role of the hyperfine field distribution determination is stressed, especially the magnetic hyperfine induction distribution in magnetically ordered solids. Conditions are explained for the feasibility of quantitative estimations of site occupancy and phase abundance. With respect to the predominant role of the magnetic hyperfine structure predestinating Mössbauer spectroscopy to be considered simultaneously as a special magnetic measuring technique, examples are chosen from the field of new magnetic materials. For the substituted hexagonal (M-type) ferrites (aimed, e.g., for the perpendicular magnetic recording), Mössbauer determination of the cation site occupancy is discussed. Structural changes in ion implanted Fe-B-based amorphous alloys detected by the hyperfine field distribution are shown. For the magnetically extremely soft FeCuNbSiB alloys, produced by the controlled crystallization of an amorphous ribbon, the estimation of their rather complicated phase composition by the Mössbauer phase analysis is demonstrated.Common enterprise of the Department of Low Temperature Physics with the Institute of Physics and Institute of Inorganic Chemistry, Czech Academy of Sciences, Prague     

Mössbauer and X-ray Investigation of Clay Minerals Originated from Libya

⁵⁷Fe transmission Mössbauer spectroscopy and X-ray diffractometry were used to study clay mineral samples originated from two different regions (Um-arrazm and Alkawasim) of Libya in order to get information about their mineralogical composition to assess their potential for use in the Libyan oil industry. In the samples originated from Um-arrazm calcite, akaganeite and nontronite while in the samples originated from Alkawasim quartz, akaganeite, montmorillonite, kaolinite, illite, mica and hematite were identified with different ratios by using diffraction method. The differences in the phase composition of iron-containing phases of samples from different localities have reflected in the complex Mössbauer spectra at both 300 K and 80 K. For the samples originated from Um-arrazm the Mössbauer parameters of subspectra were identified as nontronite and akaganeite.     

Mössbauer Spectroscopy and Preparation of Hg-1223, Tl-1223 and Tl-1212 Superconductors

Introduction of the Mössbauer nuclei ⁵⁷Fe into Hg-1223 phase and that of ⁵⁷Fe and ¹⁵¹Eu into Tl-1212 and Tl-1223 superconductors were investigated. Samples of high phase purity were obtained. Scanning electron microscopy and optical microscopy in normal and polarized light were employed to study the microstructure of the specimens. Energy dispersive X-ray analysis showed that ⁵⁷Fe in the Hg-based samples and ⁵⁷Fe as well as ¹⁵¹Eu in the Tl-based compounds, entered superconducting phases. Incorporation of Eu³⁺ into the superconducting phase favored the formation of the Tl-1212 phase. Mössbauer spectroscopy showed that Eu³⁺ entered the Ca-site. Two doublets found in the ⁵⁷Fe Mössbauer spectra in both the Hg-1223 and the Tl-1223 phase referred to two different micro-environments of Fe³⁺. The assignment of the ⁵⁷Fe Mössbauer spectra was made under the assumption that Fe favored the 1223 phase. Fe³⁺ may replace Cu in both the square pyramidal, five-fold oxygen coordinated Cu sites between the Ca and Ba-(Sr)-O layers, and in the square planar, four-fold oxygen coordinated Cu sites the Ca layers in the superconducting phases in both the Hg- and the Tl-based materials. From the relative areas of the two doublets, we concluded that the Fe³⁺ preferred the square planar Cu site.     

Mössbauer and X-ray analysis of corrosion products from surface equipment of oil production well

Wellhead equipment corrosion samples including internal surface of choke were analyzed by means of Mössbauer spectroscopy and X-ray diffractometry. The samples include some impurities of quartz, dolomite and calcite. The resulted analysis shows some iron oxides and oxyhydroxides as surface equipment corrosion products.     

Conversion electron Mössbauer study of short range ordering in electrochemically deposited Fe−Ni−Cr alloys

⁵⁷Fe Conversion electron Mössbauer spectroscopy, X-ray diffractometry and electron microprobe measurements were performed on Fe–Ni–Cr alloys coatings electrochemically deposited at different times (from 1 to 29 minutes). Significant differences have been found among the Mössbauer spectra of samples examined. The changes are also reflected by the hyperfine field distribution derived from the spectra. The observed changes can be associated with changes in the magnetic anisotropy and in the short range ordering in correlated to the duration of electrochemical deposition.     

Mössbauer effect study of liver tissues

Human liver samples were studied with the transmission Mössbauer effect technique. The samples were taken from patients with healthy livers during operation or by dissection. One sample was obtain by dissection from a patient who died of amyloidosis. The comparison of the fresh normal liver sample Mössbauer spectrum to the liophylizated one shows no other visible difference. The Mössbauer effect parameters of amyloidosis liver showed a change of ferritin into hemosiderin and a simultaneous decrease of Fe amont in the liver.