Messungen zum lateralen Auflösungsvermögen für Röntgenquanten bei der Elektronenstrahl-Mikroanalyse

Zusammenfassung Die experimentelle Bestimmung der lateralen Ausdehnung des Röntgenemissionsvolumens gelingt aus Intensitätsmessungen an Schichten, deren Dicken in der Größenordnung der lateralen Ausdehnung liegen. Die Schichtsysteme werden dabei mit definierter Geschwindigkeit unter dem Elektronenstrahl hinweg bewegt, was einem Wandern des Röntgenemissionsvolumens durch das Schichtsystem gleichkommt. Von einer Schicht, deren Röntgenintensität gerade das Maximum eines Reinelement-Massivstandards erreicht, kann angenommen werden, daß ihre Dicke der lateralen Ausdehnung entspricht. Zur Messung der Schichtdicken wurden in erster Linie Liniendiagramme herangezogen; die Überprüfung erfolgte aus Röntgenrasterbildern der Elementverteilung.Die geeignete Auswahl der Proben, die aus Schichten leichter (Kohlenstoff), mittlerer (Kupfer) und schwerer (Gold) Elemente bestehen, gestattete die Interpolation der Ergebnisse auf Elemente beliebiger Ordnungszahl. Die Messung der Röntgenintensitäten bei verschiedener Anregungsenergie des Elektronenstrahls ergibt die Abhängigkeit der lateralen Ausdehnung von der Beschleunigungs-spannung.

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Measurements of the lateral resolution of X-ray emission by means of electron microprobe analysis

Summary The experimental determination of the diameter of the X-ray emission volume is obtained from intensity measurements on layers whose thickness lie in the range of this emission volume. The vertically orientated sandwich layers were moved with a definite velocity under the electron probe which amounts to a wandering of the X-ray emission volume through this system of layers. From a layer whose X-ray intensity is equivalent to maximum intensity of a bulk standard of the same material as the layer, one can assume that the diameter of the X-ray emission volume corresponds to the thickness of the layer. To measure the layer thickness, mostly linescans were used, followed by X-ray scan pictures of the element distribution to verify the same.A suitable choice of samples representing light (carbon), medium (copper) and heavy (gold) elements enables to interpolate the results on elements of any other mass number. The measurement of the X-ray intensity under varying electron energies shows the dependance of the diameter of the X-ray emission volume on accelerating voltage.

     

Coverage-dependent kinetics and thermodynamics of carbon monoxide adsorption on a ternary copper catalyst derived from static adsorption microcalorimetry

A reliable method for adsorption systems in equilibrium is established to derive coverage-dependent kinetics and thermodynamics from the volumetric data obtained during the static microcalorimetric measurement of heats of adsorption. The Wigner-Polanyi equation is applied to analyze the pressure change as a function of time during stepwise dosing of the adsorptive until thermodynamic adsorption-desorption equilibrium is established. For carbon monoxide adsorption on a hydrogen-reduced Cu/ZnO/Al2O3 catalyst, the adsorption rate constant (ka) is found to be in the range from 10(-6) to 10(-4) Pa(-1) s(-1), and the desorption rate constant (kd) from 10(-4) to 10(-2) s(-1), both increasing with fractional coverage theta. The kinetically derived equilibrium constant Ktheta is in good agreement with Ktheta obtained from the adsorption isotherm. RT ln(Kp0) and the differential heat of adsorption (qdiff) were found to decrease in parallel, reflecting a normal Temkin-type heterogeneity.     

Study of spectator tagging in the reaction np → ppπwith a deuteron beam

The reaction has been studied in a kinematically complete experiment at a single beam momentum GeV/c (T = 759MeV). All four ejectiles have been detected in the large-acceptance time-of-flight spectrometer COSY-TOF. We analyzed the data along the lines of the spectator model as a means to isolate the quasi-free reaction. The spectator proton was identified by its momentum and flight direction thus yielding access to the associated Fermi motion of the bound neutron. A comparison is carried out with Monte Carlo simulations based on two different parameterizations of the deuteron wave function. Up to a Fermi momentum of roughly 150MeV/c no significant deviations between experimental and simulated data of various observables were found from which we conclude that the deuteron can indeed be taken as a valid substitute for the neutron.     

Defect corrected averaging for parabolic PDEs

We consider parabolic partial differential equations with highly oscillatory source terms. The timescale of the problem is assumed to be much larger than the timescale of the oscillation. Resolution of the smallest timescale constitutes a strong restriction on the stepsize of time integration method. Averaging techniques like stroboscopic averaging have been developed to overcome this restriction. In case of parabolic equations these techniques are of limited advantage. We have developed defect corrected averaging techniques that allow timesteps taylored to the timescale of diffusion. They are based on Krylov subspace iterations for the abstract solution operator of the system. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Lewis Pair Polymerization of Epoxides via Zwitterionic Species as a Route to High‐Molar‐Mass Polyethers

A dual catalytic setup based on N‐heterocyclic olefins (NHOs) and magnesium bis(hexamethyldisilazide) (Mg(HMDS)₂) was used to prepare poly(propylene oxide) with a molar mass (M_n) >500 000 g mol^?1, in some cases even >10⁶ g mol^?1, as determined by GPC/light scattering. This is achieved by combining the rapid polymerization characteristics of a zwitterionic, Lewis pair type mechanism with the efficient epoxide activation by the Mg^II species. Transfer‐to‐monomer, traditionally frustrating attempts at synthesizing polyethers with a high degree of polymerization, is practically removed as a limiting factor by this approach. NMR and MALDI‐ToF MS experiments reveal key aspects of the proposed mechanism, whereby the polymerization is initiated via nucleophilic attack by the NHO on the activated monomer, generating a zwitterionic species. This strategy can also be extended to other epoxides, including functionalized monomers.     

A structure-based design approach to advance the allyltyrosine-based series of HIV integrase inhibitors

As of mid-2017, only one structure of the human immunodeficiency virus (HIV) integrase core domain co-crystallised with an active site inhibitor was reported. In this structure (1QS4), integrase is complexed with a diketo-acid based strand-transfer inhibitor (INSTI). This structure has been a preferred platform for the structure-based design of INSTIs despite concerns relating to structural irregularities arising from crystallographic packing effects. A survey of the current pool of 297 reported integrase catalytic core structures indicated that the anatomy of the active site in the complex structure 1QS4 exhibits subtle variations relative to all other structures examined. Consequently, the 1QS4 structure was employed for docking studies. From the docking of twenty-seven allyltyrosine analogues, a 3-point inhibitor binding motif required for activity was established and successfully utilised in the development of a tripeptide displaying an EC₅₀ value of 10 ± 5 μM in HIV infected human T-cells. Additional docking of “in-house” compound libraries unearthed a methyl ester based nitrile derivative displaying an IC₅₀ value of 0.5 μM in a combined 3′-processing and strand-transfer assay.