K. Lawniczak-Jablonska

Local atomic structure and magnetic ordering of iron in Fe-chitosan complexes.

The iron crosslinked chitosan (Ch-Fe-CL) and N-carboxylmethyl chitosan (N-CM-Ch-Fe) complexes were studied by complementary techniques: structurally sensitive Mössbauer and X-ray absorption methods, as well as static magnetic measurements. A detailed and consistent description of these complexes including, besides the overall magnetic behavior, the spin ordering and local atomic structure around Fe ions is presented. Fe atoms in the investigated samples are mostly penta-coordinated and appear in a high spin Fe (3+) ionic state. In Ch-Fe-CL, two kinds of Fe near neighbors are equally probable and several Fe atoms are situated in the second coordination sphere. The magnetic interactions between these Fe ions lead to a sperimagnetic-like ordering. In N-CM-Ch-Fe, only one Fe neighborhood was found. Other Fe atoms were identified neither in the first nor in the second coordination sphere, but the third coordination sphere indicates the presence of Fe atoms. The magnetic coupling between these atoms is antiferromagnetic, but the dominant part of Fe in this sample remains in a paramagnetic state.

Tetrahedral covalent radii of Mn, Fe, Co and Ni estimated from extended X-ray absorption fine structure studies

Abstract The bond radius of an atom in a solid is an important parameter since it remains simply correlated with the bond length in a local coordination of the particular crystal structure. The tetrahedral covalent radii of Mn, Fe, Co and Ni were estimated from the measurements of their K-edge extended X-ray absorption fine structure in Zn 1− x M x S (M=Mn, Fe, Co, Ni) alloys. Analysis of these data provided us with the bond lengths of both cationic species (Zn and M) with sulphur. The advantage of the common anion and the knowledge of the tetrahedral radius of Zn enabled us to derive the tetrahedral covalent radii of the transition metals studied.

Polarization dependent X-ray absorption studies of the chemical bonds anisotropy in wurtzite GaN grown at different conditions

Polarization-dependent X-ray absorption spectroscopy was used to examine the influence of crystal growth techniques and substrates type on the bond lengths and the bond structure of the single crystalline, wurtzite GaN in a form of bulk materials and epitaxial layers. The layers were grown by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) on different substrates such as SiC, sapphire and GaN. From the observed X-ray absorption near edge structure (XANES) of the Ga K-edges, it was found that MOCVD introduces a stronger disorder around Ga atoms than MBE. Comparing the Ga and N K-edges of the epilayers and the bulk crystal, we found a prevailing contribution of N-vacancies in the layers and dominance of Ga-vacancies in the bulk crystal. The bonds along the c-axis are less perfect than the bonds in the c-plane for all investigated epilayers. The performed standard extended X-ray absorption fine structure analysis (EXAFS) resulted in a direct estimate of the bond lengths in the c-plane and along the c-axis.

Understanding Chloroquine Action at the Molecular Level in Antimalarial Therapy: X-ray Absorption Studies in Dimethyl Sulfoxide Solution

X-ray absorption spectroscopy is used to determine the local atomic structure around the iron atom from a soluble synthetic analogue of malaria pigment (hemozoin), cf. ferrimesoporphyrin IX of mesohematin anhydride, in the absence or presence of chloroquine (CQ) in dimethyl sulfoxide (DMSO). Of particular note are the CQ-induced changes in the structure of mesohematin anhydride, which might confirm the formation of CQ-ferrimesoporphyrin IX complex. Examination of solutions of mesohematin anhydride dissolved in DMSO reveals preservation of the dimerlike structure with the central iron atoms of the ferric porphyrin IX reciprocally linked by propionate side chains, which is typical for hematin anhydride (β-hematin). In the presence of CQ, additional light atoms, such as nitrogen, carbon, and oxygen, were detected surrounding the iron in a distance ranging from 2.48 to 3.77 Å. The changes introduced by CQ in DMSO are different from that observed in the acetic acid solution.

Toward understanding the chloroquine action at the molecular level in antimalarial therapy--X-ray absorption studies in acetic acid solution.

The local atomic structure around the central iron of the synthetic soluble analog of malarial pigment in acetic acid solution and with addition of chloroquine as found by X-ray absorption spectroscopy is reported. The special interest was drawn to the axial linkage between the central iron atom of the ferriprotoporphyrin IX (FePPIX) coordinated axially to the propionate group of the adjacent FePPIX. This kind of bonding is typical for hematin anhydride. Detailed analysis revealed differences in oxygen coordination sphere (part of dimer linkage bond) between synthetic equivalent of hemozoin in the powder state and dissolved in acetic acid and water at different concentrations mimicking the physiological condition of the parasites food vacuole. The results of performed studies suggest that the molecular structure of synthetic analogue of hemozoin is no longer dimer-like in acidic solution. Further changes in atomic order around Fe are seen after addition of the antimalarial drug chloroquine.

X-ray absorption studies of phase formation in a Ti/TiN coating on cubic boron nitride

Abstract We report on the use of X-ray absorption spectroscopy as a tool for the identification of the phases formed in the technological process of composite preparation. A composite is a mixture of several compounds and, in many cases, the use of traditional X-ray diffraction to determine the phases can be difficult because of the small amount of phases present. X-ray absorption studies (XANES and EXAFS) of the c-BN Ti/TiN layered system are presented. These materials are models of the powdered composites used in industry for tool production. XANES and EXAFS analyses showed that, after annealing up to 1300 °C, a TiB 2 phase is formed, but the chemical bonding of the Ti atoms differs slightly from that of standard TiB 2 powder, showing the presence of defects in site occupancy. Assuming that the X-ray absorption spectral shape is a linear combination of the spectra of all the components, we estimated the kind and limits of other phase inclusions.

Mn-Te bond in the rocksalt Sn1-xMnxTe alloys and octahedral radius of Mn : X-ray absorption- and diffraction study

The studies of local atomic structure in Sn 1-x Mn x Te (x < 0.07) alloys, with an attention to the nature of Mn-Te bond, were performed for the first time with use of extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD) techniques, supplemented by photoelectron measurements. XRD unanimously indicated a single phase NaCI-type structure of these compounds. Analysis of Mn K-edge EXAFS data provided us with the bond length and Debye-Waller (DW) factor for Mn-Te bond in octahedral coordination of rocksalt Sn 1-x Mn x Te. The magnitude of DW factor suggested a moderate ionicity of Mn-Te bond (in the host SnTe matrix) indicative of its mixed covalent-ionic character. The determined value of Mn-Te bond length in Sn 1-x Mn x Te enabled us to estimate the octahedral covalent radius of Mn.

X-ray techniques for innovation in industry

Are synchrotrons needed for innovation in industry? What can scientists at large-scale facilities offer for R&D in industry? Is the comfort of life profiting from research?

Magnetic properties of MnSb inclusions formed in GaSb matrix directly during molecular beam epitaxial growth

Despite of intensive search for the proper semiconductor base materials for spintronic devices working at room temperature no appropriate material based on ferromagnetic semiconductors has been found so far. We demonstrate that the phase segregated system with MnSb hexagonal inclusions inside the GaSb matrix, formed directly during the molecular beam epitaxial growth reveals the ferromagnetic properties at room temperature and is a good candidate for exploitation in spintronics. Furthermore, the MnSb inclusions with only one crystalline structure were identified in this GaMn:MnSb granular material. The SQUID magnetometry confirmed that this material exhibits ferromagnetic like behavior starting from helium up to room temperature. Moreover, the magnetic anisotropy was found which was present also at room temperature, and it was proved that by choosing a proper substrate it is possible to control the direction of easy axis of inclusions’ magnetization moment between in-plane and out-of-plane; the latter is ...

Structural and magnetic properties of the molecular beam epitaxy grown MnSb layers on GaAs substrates

The structural and magnetic properties of MnSb layers grown on two differently oriented GaAs substrates are reported. The MnSb compounds grow nonhomogenously both on GaAs (111) B and on GaAs (100) substrates. In x-ray diffraction studies the formation of two epitaxial domains is observed depending on the crystallographic orientation of the substrate. The observed diffusion of Ga atoms from the substrate to the layers results in the formation of an additional Mn-rich cubic phase of GaMnSb. In the case of the (100) oriented substrate, the diffusion of Mn into the substrate was additionally found. Traces of other phases were also noticed. The complex morphology of the layers is found to influence their magnetic properties. Magnetic force microscopy images revealed an inhomogenous distribution of the magnetic force gradient on the surface and the formation of magnetic domains in the samples. X-ray absorption studies of the chemical bonding and local atomic structure around Mn atoms confirmed high structural and chemical disorder in the samples. The chemical bonding of the dominating fraction of Mn atoms is found, however, similar to that in the reference MnSb powder. The x-ray magnetic circular dichroism measurements reveal an enhanced orbital moment and a reduced spin moment, which is most likely caused by the presence of different phases and a Mn-rich surface in the investigated samples