Tris‐amidoximate uranyl complexes via η2 binding mode coordinated in aqueous solution shown by X‐ray absorption spectroscopy and density functional theory methods

The present study sheds some light on the long‐standing debate concerning the coordination properties between uranyl ions and the amidoxime ligand, which is a key ingredient for achieving efficient extraction of uranium. Using X‐ray absorption fine structure combined with theoretical simulation methods, the binding mode and bonding nature of a uranyl–amidoxime complex in aqueous solution were determined for the first time. The results show that in a highly concentrated amidoxime solution the preferred binding mode between UO₂²⁺ and the amidoxime ligand is η² coordination with tris‐amidoximate species. In such a uranyl–amidoximate complex with η² binding motif, strong covalent interaction and orbital hybridization between U 5f/6d and (N, O) 2p should be responsible for the excellent binding ability of the amidoximate ligand to uranyl. The study was performed directly in aqueous solution to avoid the possible binding mode differences caused by crystallization of a single‐crystal sample. This work also is an example of the simultaneous study of local structure and electronic structure in solution systems using combined diagnostic tools.     

Simulations of X‐ray diffraction of shock‐compressed single‐crystal tantalum with synchrotron undulator sources

Polychromatic synchrotron undulator X‐ray sources are useful for ultrafast single‐crystal diffraction under shock compression. Here, simulations of X‐ray diffraction of shock‐compressed single‐crystal tantalum with realistic undulator sources are reported, based on large‐scale molecular dynamics simulations. Purely elastic deformation, elastic–plastic two‐wave structure, and severe plastic deformation under different impact velocities are explored, as well as an edge release case. Transmission‐mode diffraction simulations consider crystallographic orientation, loading direction, incident beam direction, X‐ray spectrum bandwidth and realistic detector size. Diffraction patterns and reciprocal space nodes are obtained from atomic configurations for different loading (elastic and plastic) and detection conditions, and interpretation of the diffraction patterns is discussed.     

Angular momenta and eigenvectors of the weakly coupled T ⊗ t Jahn‐Teller system

The eigenvalues of the weakly coupled T ? t Jahn‐Teller problem are known for several decades, and the same holds also true for the eigenstates. These, however, are only given in the traditional position representation, which proves inconvenient if one attempts to extend the weak‐coupling treatment into the region of stronger coupling. Here the solution of the T ? t eigenvalue problem at weak coupling is derived in terms of creation and annihilation operators. This reformulation of the problem is nontrivial, since the algebraic form of the oscillator eigenvectors, being simultaneous angular‐momentum eigenstates, has been worked out only recently and is probably still widely unknown. The electronic and oscillator eigenstates are then coupled to form eigenvectors of the total angular momentum. Finally, in preparation for an extension of the weak‐coupling treatment, the action of the boson creation and annihilation operators on the oscillator eigenvectors is calculated, thus completing the algebraic approach to the weakly coupled T ? t system.     

基于MOS-NDR负阻器件的D触发器设计

负阻器件由于在电流 电压特性曲线中表现出独特的负微分电阻特性,从而大大增加了单个器件所能实现的逻辑功能.如果将其用于数字逻辑电路设计,尤其是触发器的设计,可有效减少器件的数目.通过分析CMOS工艺负阻器件MOS-NDR及单双稳态转换逻辑单元MOBILE的工作特性,设计了一个时钟上升沿触发的D触发器.采用TSMC 0.18 μm工艺对所设计的电路进行HSPICE仿真,仿真结果表明所设计的电路具有正确的逻辑功能.与基于MOS-NDR负阻器件的同类触发器相比,新设计的D触发器具有更稳健的输出和较强的抗干扰能力     

A flexible block classical Gram–Schmidt skeleton with reorthogonalization

We investigate a variant of the reorthogonalized block classical Gram–Schmidt method for computing the QR factorization of a full column rank matrix. Our aim is to bound the loss of orthogonality even when the first local QR algorithm is only conditionally stable. In particular, this allows the use of modified Gram–Schmidt instead of Householder transformations as the first local QR algorithm. Numerical experiments confirm the stable behavior of the new variant. We also examine the use of non-QR local factorization and show by example that the resulting variants, although less stable, may also be applied to ill-conditioned problems.     

High‐resolution stimulated Raman spectroscopy and analysis of the ν1, 2ν1–ν1, ν2, 2ν2, and 3ν2–ν2 bands of CF4

The spectra of the ν₁, 2ν₁–ν₁, ν₂, 2ν₂, and 3ν₂–ν₂ bands of CF₄ were obtained with a quasi‐continuous wave stimulated Raman spectrometer. These five bands were studied at a temperature of 135 and 300 K (for the hot bands). The spectrum of ν₁ was obtained at a sample pressure of 2 mbar. For the spectra of the other regions, which are much weaker, higher pressures were used. The analysis has been performed thanks to the xtds and spview softwares developed in Dijon for such highly symmetric molecules. Combining the present results with a previous infrared study, we could determine a very accurate value for the C–F equilibrium bond length, i.e. r_e = 1.31588(6) Å. Copyright © 2013 John Wiley & Sons, Ltd.     

Study of carrier concentration profiles in Al‐implanted Ge by micro‐Raman spectroscopy under different excitation wavelengths

The distribution profile of Al implanted in crystalline Ge has been investigated by micro‐Raman spectroscopy. Using different excitation laser lines, corresponding to different optical penetration depths, the Al concentration at different depths beneath the sample surface has been studied. We have found a strong correlation between the intensity of the Al–Ge Raman peak at ~370 cm⁻¹, which is due to the local vibrational mode of substitutional Al atoms, and the carrier concentration profile, obtained by the spreading resistance profiling analysis. A similar connection has been also observed for both shape and position of the Ge–Ge Raman peak at ~300 cm⁻¹. According to these experimental findings, we propose here a fast and nondestructive method, based on micro‐Raman spectroscopy under different excitation wavelengths, to estimate the carrier concentration profiles in Al‐implanted Ge. Copyright © 2013 John Wiley & Sons, Ltd.     

Raman spectroscopy of very small Cd1−xCoxS quantum dots grown by a novel protocol: direct observation of acoustic‐optical phonon coupling

Glass‐embedded Cd_1−xCo_xS quantum dots (QDs) with mean radius of R ≈ 1.70 nm were successfully synthesized by a novel protocol on the basis of the melting‐nucleation synthesis route and herein investigated by several experimental techniques. Incorporation of Co²⁺ ions into the QD lattice was evidenced by X‐ray diffraction and magnetic force microscopy results. Optical absorption features with irregular spacing in the ligand field region confirmed that the majority of the incorporated Co²⁺ ions are under influence of a low‐symmetry crystal field located near to the Cd_1−xCo_xS QD surface. Electron paramagnetic resonance data confirmed the presence of Co²⁺ ions in a highly inhomogeneous crystal field environment identified at the interface between the hosting glass matrix (amorphous) and the crystalline QD. The acoustic‐optical phonon coupling in the Cd_1−xCo_xS QDs (x ≠ 0.000) was directly observed by Raman measurements, which have shown a high‐frequency shoulder of the longitudinal optical phonon peak. This effect is tuned by the size‐dependent sp‐d exchange interaction due to the magnetic doping, causing variations in the coupling between electrons and longitudinal optical phonon. Copyright © 2013 John Wiley & Sons, Ltd.     

Revised Assignment of the Raman Active Fundamental Vibrations of Tetracyanoethylene

We present a revised assignment of the Raman active fundamental vibrations of TCNE which utilizes new information obtained from Raman studies of electron donor/acceptor complexes of TCNE. This new assignment is consistent with and supported by all available evidence from previous studies.