摘要:

We report on Mn K‐edge X‐ray absorption study, in plane and out of plane, of La0.7Sr0.3MnO3films, epitaxially grown on a tensile substrate SrTiO3by laser ablation. From Extended X‐ray Absorption Fine Structure in the film plane we observe a small increase of Mn‐Mn distances with respect to relaxed film. In addition, a small distortion of the MnO6octahedron is evidenced from Extended and Near Edge Absorption measurements. The respective amplitudes found for these two effects are on the same order, so that no modification of the Mn‐O‐Mn angle is evidenced. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536406

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Local lattice displacements in the copper oxide superconductors are determined by polarized Cu K‐edge extended x‐ray absorption fine structure (EXAFS) measurements. Temperature dependent local atomic displacements show anomalies, at the Tcand a temperature Tswhere the charge inhomogeneous state appears, as revealed by a change in the correlated Debye‐Waller factor (DWF) of the Cu&sngbnd;O bonds. While the DWF shows a clear drop at the Tc, an order parameter like up‐turn appears at the Ts. The anomalies shows‐up with different amplitude, depending on the superconducting transition temperature of the system and the micro‐strain in the electronically active CuO2plane. The measured Cu&sngbnd;O displacements appear to be closely related to the kink structure in the angle resolved photoemission experiments. The results are discussed to find some correlation between electron‐lattice coupling, inhomogeneous charge state and superconductivity in the copper oxides. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536407

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Increasing the speed and complexity of semiconductor integrated circuits requires advanced processes that put extreme constraints on the level of metal contamination allowed on the surfaces of silicon wafers. Such contamination degrades the performance of the ultrathin SiO2gate dielectrics that form the heart of the individual transistors. Ultimately, reliability and yield are reduced to levels that must be improved before new processes can be put into production. It should be noted that much of this metal contamination occurs during the wet chemical etching and rinsing steps required for the manufacture of integrated circuits and industry is actively developing new processes that have already brought the metal contamination to levels beyond the measurement capabilities of conventional analytical techniques. The measurement of these extremely low contamination levels has required the use of synchrotron radiation total reflection x‐ray fluorescence (SR‐TXRF) where sensitivities 100 times better than conventional techniques have been achieved. This has resulted in minimum detection limits for transition metals of 8×107atoms/cm2. SR‐TXRF studies of the amount of metal contamination deposited on a silicon surface as a function of pH and oxygen content of the etching solutions have provided insights into the mechanisms of metal deposition from solutions containing trace amounts of metals ranging from parts per trillion to parts per billion. Furthermore, by using XANES to understand the chemical state of the metal atoms after deposition, it has been possible to develop chemical models for the deposition processes. Examples will be provided for copper deposition from ultra pure water and acidic solutions. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536408

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

In this work we analyse the polarized Mg and FeK‐edge XANES spectra obtained on single crystals of phlogopite, (sample from Franklin, New Jersey), and of tetra‐ferriphlogopite (sample from Tapira, Alto Paranai´ba, Brazil). These crystals show composition close to the end‐members, thus they present similar chemical composition in octahedral and interlayer position, but they differ for tetrahedral substitutions. Our aim is thus to discover the influence of the different chemical composition of the T sheet on the M sheet topology. To reach this goal, as the differences observed in the XANES spectra when changing the beam incidence angle are associated with the different contributions of the photoelectron pathways involving the absorber atom and its near and next‐near‐shell neighbours in the direction of the electric field vector, we investigated the angular dependence of the spectral XANES features at the Mg and Fe K edges. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536409

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Electron momentum spectroscopy measurements of graphite single‐crystals are presented. Data were taken for incoming electrons with an energy of 50 keV, and both outgoing electrons with an energy near 25 keV. Spectra are presented for the major symmetry directions of graphite. To remove the effect of inelastic multiple scattering we use in all cases an identical deconvolution procedure, which consistently removed all intensity at high energy loss values. However the intensity becomes vanishing small only for binding energies of about twice the bandwidth. The shape of the observed spectra compare well with many‐body calculations based on the cumulant expansion scheme but the intensity at high momentum is less than predicted by this theory. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536410

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Here we discuss origin of pre‐edge features in the K‐edge absorption spectra of transition metal atoms in octahedral coordination, in oxides and sulphides. We provide a unifying interpretation on the basis of multiple scattering simulations performed with different cluster models. We find that the pre‐edge features arise due to hybridisation of the orbitals belonging to the central atom with the higher‐shell metal orbitals. The results are obtained by performing multiple scattering simulations with cluster of size equal to the cation‐cation plus the cation‐anion bond lengths in order to ensure that the higher‐shell metal atoms remain in the octahedral coordination. Within this framework, we are able to identify the electronic structure of the metal atoms and the ligand‐field characters looking at position, shape and intensity of the different features observed in the XANES spectra. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536411

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The reflection of X‐rays from a semi‐infinite water target, for energies used in X‐ray diagnostics, is treated by the analog Monte Carlo simulation. In the developed procedure it was possible to calculate separately contributions of photons scattered, before reflection, fixed number of times with target electrons. It turned out that multiple collision type of reflection dominates at all energies investigated, whenever the absorption is small. The same process was also treated analytically as the classical albedo problem for isotropic scattering without energy loss. Very good agreement of results of the two approaches is obtained. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536412

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Synchrotron Radiation micro X‐Ray Fluorescence (SR &mgr;‐XRF) was applied for the first time to map the trace element content on Multicellular Tumor Spheroids (MTS), i.e. human cell clusters used as anin vitromodel for testing micrometastases responses to antitumoral drugs. In particular, immunotoxin molecules composed of a carrier protein (Transferrin) bound to a powerful cytotoxin (Ricin A), were here considered as representatives of a class of therapheutic macromolecules used in cancer theraphy. Spheroids included in polyacrylamide gel and placed inside quartz capillaries were studied at the ESRF ID22 beamline using a 15 keV monochromatic photon microbeam. Elemental maps (of Fe, Cu, Zn and Pb) on four groups of spheroids grown under different conditions were studied: untreated, treated only with the carrier molecule or with the toxin alone, and with the complete immunotoxin molecule (carrier+toxin). The results indicate that the distribution of Zn and, to some extent, Cu in the spheroid cells is homogeneous and independent of the treatment type. Total Reflection X‐Ray Fluorescence (TR‐XRF) was also applied to quantify the average trace element content in the spheroids. Future developments of the technique are finally outlined on the basis of these preliminary results. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536413

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

This work is an application of synchrotron microprobe X‐ Ray fluorescence in order to study elemental distribution along human hair samples of contemporary citizens. Furthermore, X‐Ray fluorescence spectrometry is also used to analyse human bones of different historical periods: Neolithic and contemporary subjects. The elemental content in the bones allowed us to conclude about environmental contamination, dietary habits and health status influence in the corresponding citizens. All samples were collectedpost‐mortem. Quantitative analysis was performed for Mn, Fe, Co, Ni, Cu, Zn, Br, Rb, Sr and Pb. Mn and Fe concentration were much higher in bones from pre‐historic periods. On the contrary, Pb bone concentrations of contemporary subjects are much higher than in pre‐historical ones, reaching 100 &mgr;g g‐1, in some cases. Very low concentrations for Co, Ni, Br and Rb were found in all the analysed samples. Cu concentrations, allows to distinguish Chalcolithic bones from the Neolithic ones. The distribution of trace elements along human hair was studied for Pb and the obtained pattern was consistent with the theoretical model, based on the diffusion of this element from the root and along the hair. Therefore, the higher concentrations in hair for Pb of contemporary individuals were also observed in the bones of citizens of the same sampling sites. All samples were analysed directly without any chemical treatment. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1536414

出版商:AIP    

年代:1903

数据来源: AIP