Measurement of relative L X-ray intensity ratio following radioactive decay and photoionization

The measurements of the L   X-ray intensity ratio I(Lα)/I(Lβ)$I(L\alpha )/I(L\beta )$, I(Lα)/I(Lγ)$I(L\alpha )/I(L\gamma )$, I(Lα)/I(Lι)$I(L\alpha )/I(L\iota )$, I(Lβ)/I(Lγ)$I(L\beta )/I(L\gamma )$ and I(Lι)/I(Lγ)$I(L\iota )/I(L\gamma )$ for elements Dy, Ho, Yb, W, Hg, Tl and Pb were experimentally determined both by photon excitation, in which 59.5 keV γ-rays from a filtered radioisotope ²⁴¹Am was used, and by the radioactive decay of ¹⁶⁰Tb, ¹⁶⁰Er, ¹⁷³Lu, ¹⁸²Re, ²⁰¹Tl, ²⁰³Pb and ²⁰⁷Bi. L   X-rays emitted by samples were counted by a Si(Li) detector with resolution 160 eV at 5.9 keV. Obtained values were compared with the calculated theoretical values. Theoretical values of the I(Lα/Lβ)$I(L\alpha /L\beta )$, I(Lα/Lγ)$I(L\alpha /L\gamma )$, I(Lα/Lι)$I(L\alpha /L\iota )$, I(Lβ/Lγ)$I(L\beta /L\gamma )$ and I(Lι/Lγ)$I(L\iota /L\gamma )$ intensity ratios were calculated using theoretically tabulated values of subshell photoionization cross-section, fluorescence yield, fractional X-ray emission rates, Coster–Kronig transition probabilities. It was observed that present values agree with previous theoretical and other available experimental results.     

Energy-filtered XPEEM with NanoESCA using synchrotron and laboratory X-ray sources: Principles and first demonstrated results

The importance of energy filtering in PEEM-based imaging methods has been shown in recent years with the availability of powerful instruments. A new instrument, the NanoESCA, combines a fully electrostatic PEEM column and an aberration corrected double hemispherical analyser as energy filter. This paper reports on recently demonstrated XPEEM results using the first commercially available NanoESCA instrument operated with both synchrotron soft X-rays and monochromatic laboratory Al Kα radiation. The implementation of elemental and bonding-state specific imaging is shown with both excitation sources. The presently achieved (but not yet ultimate) lateral resolutions on energy filtered core-level images are 150 nm with a large synchrotron spot and below 1 μm with a focused laboratory source. To date this is the unique example of laboratory XPEEM core-level imaging.     

Spectroscopy of X2Y4 (D2h) molecules: tensorial formalism adapted to the O(3)⊃D2h chain, Hamiltonian and transition moment operators

A tensorial formalism adapted to the case of the X₂Y₄ molecules with D_2h symmetry has been developed in the same way as in the previous works on XY₄ (T_d) and XY₆ (O_h) spherical tops and XY₅Z (C_4v) symmetric tops. Here, we use the O(3)⊃D_2h group chain. All the coupling coefficients and formulas for the computation of matrix elements are given for this chain and used in the case of the Hamiltonian and transition moment operators.     

Electronic structure and surface structure of Cu2S nanorods from polarization dependent X-ray absorption spectroscopy

Highly aligned Cu₂S nanorods have been studied by polarization dependent X-ray absorption spectroscopy. In contrast to bulk Cu₂S, strong s, p, and d hybridization is found in the nanorods. The polarization dependence shows a predominant d_z2${\text{d}}_{z^2}$ character of Cu 3d states. Ab initio multiple-scattering calculations confirm the strong hybridization, and reveal that Cu₂S nanorods are grown along the z-axis of chalcocite structure with Cu₇ and Cu₁₀ sites being the main building blocks. The hybridized absorption peak in the nanorods is shifted towards lower energies for smaller diameter of nanorods, which is attributed to surface reconstruction due to strong Cu–Cu interactions on the Cu-rich surface of the nanorods.     

Formation of vinylidene and vinylene by selective reactivity of Si(1 0 0)2 × 1 towards iso, cis and trans isomers of dichloroethylene

The room temperature (RT) chemisorption of three (iso, cis and trans) isomers of dichloroethylene (DCE) on Si(1 0 0)2 × 1 have been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Unlike ethylene, the lack of molecular desorption features in the TPD data effectively rules out the cycloaddition adsorption mechanism for all three isomers. XPS spectra show that cis- and trans-DCE adsorb dissociatively on the 2 × 1 surface in equal proportion as mono-σ bonded 2-chlorovinyl and di-σ bonded vinylene adspecies, which could be produced by dechlorination mechanisms involving the proposed tri-atom π-complex and diradical intermediates, respectively. Acetylene (m/z 26) evolution from 2-chlorovinyl adspecies at 590 K and vinylene at 750 K are also observed for both cis- and trans-DCE, further confirming the common adsorption mechanisms for these geometrical isomers and the relative stabilities of the adspecies. In contrast, only vinylidene adspecies is found for iso-DCE, which indicates that the high ionicity of the CCl₂ group favours the diradical dechlorination mechanism. The single m/z 26 desorption peak for iso-DCE adspecies observed at a higher temperature (780 K) than cis and trans isomers is consistent with the higher adsorption energy of vinylidene than vinylene on Si(1 0 0) obtained in our ab initio calculations. The different relative locations of the Cl atoms in these isomers therefore play a crucial role in controlling the adsorption and thermal evolution on Si(1 0 0)2 × 1. The selective reactivity of the 2 × 1 surface towards these isomers can be used to generate vinylene or vinylidene templates from their corresponding adspecies.     

Electron energy-loss spectroscopy of LiMn2O4, LiMn1.6Ti0.4O4 and LiMn1.5Ni0.5O4

The dielectric properties of LiMn₂O₄, LiMn_1.6Ti_0.4O₄ and LiMn_1.5Ni_0.5O₄ powders, synthesized by sol-gel method, were determined by analyzing the low-loss region of the electron energy-loss spectroscopy (EELS) spectrum in a transmission electron microscope. From these data, the optical joint density of states (OJDS) was obtained by Kramers-Kronig analysis. Since maxima observed in the OJDS spectra are assigned to interband transitions above the Fermi level, these spectra can be interpreted on the basis of calculated density of states (DOS), carried out with the CASTEP code. Experimental and theoretical results are in good agreement.