Soft X‐ray absorption spectroscopy and resonant inelastic X‐ray scattering spectroscopy below 100 eV: probing first‐row transition‐metal M‐edges in chemical complexes

X‐ray absorption and scattering spectroscopies involving the 3d transition‐metal K‐ and L‐edges have a long history in studying inorganic and bioinorganic molecules. However, there have been very few studies using the M‐edges, which are below 100 eV. Synchrotron‐based X‐ray sources can have higher energy resolution at M‐edges. M‐edge X‐ray absorption spectroscopy (XAS) and resonant inelastic X‐ray scattering (RIXS) could therefore provide complementary information to K‐ and L‐edge spectroscopies. In this study, M_2,3‐edge XAS on several Co, Ni and Cu complexes are measured and their spectral information, such as chemical shifts and covalency effects, are analyzed and discussed. In addition, M_2,3‐edge RIXS on NiO, NiF₂ and two other covalent complexes have been performed and different d–d transition patterns have been observed. Although still preliminary, this work on 3d metal complexes demonstrates the potential to use M‐edge XAS and RIXS on more complicated 3d metal complexes in the future. The potential for using high‐sensitivity and high‐resolution superconducting tunnel junction X‐ray detectors below 100 eV is also illustrated and discussed.     

Magnesium K‐edge XANES spectroscopy of geological standards

Magnesium K‐edge X‐ray absorption near‐edge structure (XANES) spectra have been investigated to develop a systematic understanding of a suite of Mg‐bearing geological materials such as silicate and carbonate minerals, sediments, rocks and chemical reagents. For the model compounds the Mg XANES was found to vary widely between compounds and to provide a fingerprint for the form of Mg involved in geologic materials. The energy positions and resonance features obtained from these spectra can be used to specify the dominant molecular host site of Mg, thus shedding light on Mg partitioning and isotope fractionation in geologic materials and providing a valuable complement to existing knowledge of Mg geochemistry.     

Investigations of the optical spectra and spin-Hamiltonian parameters for the rhombic Yb centers in garnets

Two complete diagonalization (of energy matrix) methods (CDM-I and CDM-II) are used to calculate the six optical spectral band positions and nine spin-Hamiltonian (SH) parameters (g factors g_i and hyperfine structure constants ¹⁷¹A_i, ¹⁷³A_i, where i=x, y, z) for Yb³⁺ ions in the rhombic dodecahedral sites of garnets Y₃Al₅O₁₂, Lu₃Al₅O₁₂ and Y₃Ga₅O₁₂. In CDM-I, the Hamiltonian concerning energy matrix does not contain the Zeeman and hyperfine interaction terms, whereas in CDM-II, it does. So, in CDM-I, the SH parameters are obtained by first-order perturbation method or the equivalence between SH and Zeeman term (or hyperfine interaction term) and in CDM-II, the SH parameters and optical spectral band positions are calculated together. The results obtained from both methods are not only close to each other, but also in reasonable agreement with the observed values. So the second-order perturbation formulas of SH parameters developed recently are incorrect and unnecessary.     

Elimination of GeO2 and Ge3N4 interfacial transition regions and defects at n-type Ge interfaces: A pathway for formation of n-MOS devices on Ge substrates

The contribution from relatively low-K SiON interfacial transition regions (ITRs) between Si and transition metal (TM) gate dielectrics places a significant limitation on equivalent oxide thickness (EOT) scaling for Si complementary metal-oxide-semiconductor (CMOS) devices. This limitation is equally significant and limiting for Ge CMOS devices. Low-K Ge-based ITRs in Ge devices have also been shown to limit performance and reliability, particular for n-MOS field effect transistors. This article identifies the source of significant electron trapping at interfaces between n-Ge or inverted p-Ge, and Ge oxide, nitride and oxynitride ITRs. This is shown to be an interfacial band alignment issue in which native Ge ITRs have conduction band offset energies smaller than those of TM dielectrics, and trap electrons for negative Ge substrate bias. This article also describes a novel remote plasma processing approach for effectively eliminating any significant native Ge ITRs and using a plasma-processing/annealing process sequence for bonding TM gate dielectrics directly to the Ge substrate surface.     

Empirical dead‐time corrections for synchrotron sources

An experimental comparison of models for performing dead‐time corrections of photon‐counting detectors at synchrotron sources is presented. The performance of several detectors in the three operating modes of the Advanced Photon Source is systematically compared, with particular emphasis on asymmetric fill patterns. Several simple and well known correction formulas are evaluated. The results demonstrate the critical importance of detector speed and synchrotron fill pattern in selecting the proper dead‐time correction.     

Properties of proton-rich nuclei in a three-body model

Using a three-body model and realistic two-body potentials, we investigate the properties of the nuclei ¹⁸Ne and ²⁸S near the proton dripline. We figure out the two-proton separation energies, occupation of the valence protons, root-mean-square radii of matter and the valence protons. Besides, the spatial correlation densities are displayed to reflect the correlation between the two valence protons. The first excited 0⁺ state of ¹⁸Ne is most likely to be a halo state according to our calculation. Turning off the Coulomb interactions among the three-body systems, we get the two-neutron separation energies and configuration of the valence neutrons of their corresponding mirror nuclei. The results indicate that the three-body model is proper to describe some proton-rich nuclei and can be used to deduce reliable information.     

A version of Stöber synthesis enabling the facile prediction of silica nanospheres size for the fabrication of opal photonic crystals

A sol-gel synthesis procedure based on the method proposed by Stöber et al. (J Colloid Interface Sci 26:302–315, 1968) has been adopted for the one-step preparation of mono-dispersed silica nanospheres. An excellent control of the particle diameter over a wide range is obtained by varying the amount of silicon alkoxide only, while the concentration of all other components is kept fixed: this allows the fabrication of artificial opals with a finely tuned and precisely predictable lattice parameter.     

Study on the binding of 2,3-diazabicyclo[2.2.2]oct-2-ene with bovine serum albumin by fluorescence spectroscopy

The interaction of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) with bovine serum albumin (BSA) has been studied using absorption and steady state fluorescence techniques. Fluorescence spectrum of BSA (λ_exi=280 nm) in the presence of DBO clearly shows that DBO acts as a quencher. The number of binding sites ‘n’ and apparent binding constant ‘K’ were measured by Stern-Volmer equation. Synchronous fluorescence and absorption spectra were used to study protein conformation. The interaction between DBO and BSA is consistent with static quenching and the conformational changes of BSA observed.     

Temperature dependent photoluminescence down to 4.2 K in EuTFC

The temperature dependence of photoluminescence in Europium tris[3-(trifluoro-methylhydroxymethylene)-(+)-camphorate] (EuTFC) embedded in polymer films has been examined from 40 K down to 4.2 K with the goal of preparing sensor films for low-temperature thermal imaging. The behavior of EuTFC showed significant difference when based on polystyrene compared to poly(n-alkyl methacrylate)s. In poly(n-alkyl methacrylate)s prepared by standard methods for imaging applications, the photoluminescence is fully saturated below 30 K, whereas in polystyrene films there is a strong temperature dependence even down to 4.2 K. By optimizing the preparation procedure for films made of poly(butyl methacrylate) (PBMA) and poly(methyl methacrylate), also these polymers became very sensitive down to liquid helium temperature. The maximum temperature sensitivity of EuTFC in PBMA is found to be 1.0%/K at 4.2 K. The problem of delamination and cracking of the polymer film at cryogenic temperature is also avoided by the special preparation method.