Velocity scaling of ion neutralization in low energy ion scattering

The ion fraction P+ is measured for He+ ions scattered by 129 degrees from a Cu surface. Both the primary energy and the angles of incidence and of exit are varied. From our results we conclude the following: along the incoming and outgoing trajectories, neutralization is due to Auger processes and depends on the normal velocity component v( perpendicular ) only. At higher energies, additional charge exchange is due to collision induced neutralization and reionization, both depending on the total ion energy only. Also in this regime P+ depends on v( perpendicular ), but via a two-valued function of the scattering geometry at fixed energy.     

Electronic excitation functions by low-energy electron-impact spectroscopy. Restrictions to the trapped-electron methods

Structures, at 0–2 eV above threshold, have been reported in electronic excitation functions, measured by means of a modification of the trapped-electron method (DRPD/TWM). These structures have often been classified as newly discovered resonances. In this paper it is shown that they are sometimes the result of the intrinsic properties of the method.     

Magnetic behavior of the oxide spinels: Li0.5Fe2.5−2x Al x Cr x O4

In order to study the effect of substitution of Fe³⁺ by Al³⁺ and Cr³⁺ in Li_0.5Fe_2.5O₄ on its structural and magnetic properties, the spinel system Li_0.5Al _x Cr _x Fe_2.5?2x O₄ (x=0.0, 0.2, 0.4, 0.5, 0.6 and 0.8) has been characterized by X-ray diffraction, high field magnetization, low field ac susceptibility and ⁵⁷Fe Mossbauer spectroscopy. Contrary to the earlier reports, about 50% of Al³⁺ is found to occupy the tetrahedral sites. The system exhibits canted spin structure and a central paramagnetic doublet was found superimposed on magnetic sextet in the Mössbauer spectra (x>0.5).     

Molecular orientation and morphology of contact printed α-quaterthiophene films on gold

We present contact printing as a technique to deposit α-quaterthiophene (α-4T) films from the solid phase onto gold. The molecular orientation and morphology of both the printed film and the original polycrystalline α-4T film on silica were investigated with low energy ion scattering (LEIS), atomic force microscopy (AFM), X-ray diffraction (XRD) and optical microscopy. We show that the strong interaction between clean gold and α-4T induces a drastic change in the molecular orientation and morphology of a 380 nm thick α-4T film. On gold the α-4T molecules are orientated with the thiophene rings parallel to the substrate and form rod-like crystallites (typically 13×1.3 μm²), whereas on silica α-4T molecules stand almost upright and form large cobblestone-like crystallites (typical diameter 10 μm). Exposure of α-4T to a low energy ion beam (dose <1×10¹⁴ 3 keV ³He⁺ ions/cm²) prior to printing causes polymerisation, which decreases the ability to print and alters the morphology of the printed film.     

Absolute emission cross sections for the calibration of optical detection systems in the 120–250 nm range

Absolute emission cross sections have been determined for electron impact on CO, NO and N₂. For the CO(A ¹ΠX ¹Σ⁺) and N₂(a ¹ΠX ¹Σ_g) radiation our data is in good agreement with that of other groups. For CO⁺ (B²Σ⁺X²Σ⁺) the values of the emission cross sections are different from those measured previously. This discrepancy is explained in terms of an inadequate straylight correction in the former experiments. For the NO(A²Σ⁺X²Π) emission no previous σ_em values are known to the authors. Furthermore the electronic transition moments of the NO(A²Σ⁺X²Π) and CO⁺(B²ΣX²Σ⁺) systems have been measured and are found to be independent of the internuclear distance.     

联苯胺分光光度法测定食盐中碘含量

基于在盐酸介质中,碘酸钾氧化联苯胺使其显色,提出了光度法测定食盐中微量碘的方法。在40℃的水浴中,当2 mol.L-1盐酸溶液用量为1.00 mL0、.42 g.L-1联苯胺溶液用量为0.80 mL时,方法的线性范围为100~1 400μg.L-1,最大吸收波长在425 nm处,表观摩尔吸光率为1.4×105L.mol-1.cm-1。用于测定加碘食盐中碘含量的测定,回收率在97.5%~101.2%之间,相对标准偏差(n=7)在0.9%~1.9%之间。     

Silica poisoning of oxygen membranes

Perovskite oxide membranes (La_0.6Sr_0.4Co_0.2Fe_0.8O₃) are used for the separation of oxygen from air. In oxygen permeation experiments these membranes showed a peculiar behavior. Besides poor performance, a characteristic coloring also appeared on the surface of the membranes. In order to understand what was happening to the surface of the membranes, they were analysed with Low-Energy Ion Spectroscopy (LEIS) and X-ray Photoelectron Spectroscopy (XPS). The analyses showed that the surface of the LSCF membrane was covered with a SiO₂ layer, which obviously reduced the performance and caused the coloring. It was established that the source of the silicon was siloxane containing grease that was used in the manual valves of the setup. In a new improved permeation setup, where grease-free valves were used, the LSCF membranes showed remarkably better performance. The LEIS measurements showed also that the permeation experiment of 300 h did not affect the surface composition of the membranes. The contamination-free LSCF membranes only showed the presence of La, Sr and O in the outermost atomic layer. The observed absence of Co and Fe suggests that further improvement of the membrane performance is possible.