A von Hamos full-cylindrical spectrometer based on striped Si/Ge crystal for advanced x-ray spectroscopy.

High-energy resolution core-level spectroscopies, including a group of different techniques to obtain element-specific information of the electronic structure around an absorption site, have become powerful tools for studying the chemical state, local geometric structure, and the nature of chemical bonding. High-resolution x-ray absorption and x-ray emission spectroscopies are well-established experimental techniques but have always been limited by the number of emitted photons and the limited acceptance of solid angles, as well as requiring high energy stability and repeatability for the whole experimental setup. A full-cylindrical x-ray spectrometer based on flexible HAPG (highly annealed pyrolitic graphite) mosaic crystals is an effective solution for the above issues.

Finite-element simulation for X-ray volume diffractive optics based on the wave optical theory.

We developed a novel numerical simulation method for volume diffractive optics based on the Takagi-Taupin (TT) dynamical theory of diffraction. A general integral system of equations with a powerful and convenient distortion function was developed for finite-element analysis (FEA). The proposed framework is promising with regard to flexibility, robustness, and stability and has potential for solving dynamical X-ray diffraction problems related to diffractive optical elements of arbitrary shape and deformation.

GeSi virtual-layer enhanced ferromagnetism in self-assembled MnGe quantum dots grown on Si wafers by molecular beam epitaxy.

Self-assembled MnGe quantum dots (QDs) on a Si substrate or GeSi virtual substrate (VS) were grown by molecular beam epitaxy. The GeSi VS of different thicknesses and Ge compositions x were utilized to modulate the ferromagnetic properties of the above QDs. The MnGe QDs on GeSi VS show a significantly enhanced ferromagnetism with a Curie temperature above 220 K.

Pressure-induced phase transitions and structural evolution across the insulator-metal transition in bulk and nanoscale BiFeO.

The pressure-induced phase-transition sequences and structural evolution across the insulator-metal transition (IMT) in multiferroic BiFeO still remain unclear. Here we use a combination of high-pressure XRD, XAFS experiment and first principle calculation to investigate the pressure-derived structural transformations and structure-related properties in bulk and nanoscale BiFeO up to 55 GPa. A new Imma structure of BiFeO has been discovered in the pressure range of 48-52 GPa, which presents ferromagnetic (FM) metallic properties and therefore plays a key role in the IMT.

Local insight into the La-induced structural phase transition in multiferroic BiFeO ceramics by x-ray absorption fine structure spectroscopy.

Substitution of bismuth by rare earth (RE) ions is of great technological importance to develop room-temperature BiFeO-based multiferroic materials. Despite this interest, many fundamental properties and the structure-property correlations of RE-doped BiFeO remain poorly understood. Here we report a systematical experimental and theoretical exploration on the structural phase transition in Bi La FeO (0  ⩽  x  ⩽  0.

Revisiting local structural changes in GeO glass at high pressure.

Despite the great importance in fundamental and industrial fields, understanding structural changes for pressure-induced polyamorphism in network-forming glasses remains a formidable challenge. Here, we revisited the local structural transformations in GeO glass up to 54 GPa using x-ray absorption fine structure (XAFS) spectroscopy via a combination diamond anvil cell and polycapillary half-lens. Three polyamorphic transitions can be clearly identified by XAFS structure refinement.

Fabrication and ferromagnetism of Si-SiGe/MnGe core-shell nanopillars.

Si-Si0.5Ge0.5/Mn0.

Improvement of depth resolution in depth-resolved wavenumber-scanning interferometry using wavenumber-domain least-squares algorithm: comparison and experiment.

It is important to improve the depth resolution in depth-resolved wavenumber-scanning interferometry (DRWSI) owing to the limited range of wavenumber scanning. In this work, a new nonlinear iterative least-squares algorithm called the wavenumber-domain least-squares algorithm (WLSA) is proposed for evaluating the phase of DRWSI. The simulated and experimental results of the Fourier transform (FT), complex-number least-squares algorithm (CNLSA), eigenvalue-decomposition and least-squares algorithm (EDLSA), and WLSA were compared and analyzed.

Nuclear resonant inelastic X-ray scattering at high pressure and low temperature.

A new synchrotron radiation experimental capability of coupling nuclear resonant inelastic X-ray scattering with the cryogenically cooled high-pressure diamond anvil cell technique is presented. The new technique permits measurements of phonon density of states at low temperature and high pressure simultaneously, and can be applied to studies of phonon contribution to pressure- and temperature-induced magnetic, superconducting and metal-insulator transitions in resonant isotope-bearing materials. In this report, a pnictide sample, EuFe2As2, is used as an example to demonstrate this new capability at beamline 3-ID of the Advanced Photon Source, Argonne National Laboratory.

1,8-Diiodooctane as the processing additive to improve the efficiency of P3HT:PC61BM solar cells.

Controlling the blend morphology is critical for achieving high power conversion efficiency in polymer/fullerene bulk heterojunction (BHJ) photovoltaic devices. As a simple and effective method to control morphology, adding processing additives has been widely applied in the organic BHJ solar cells. In this paper, we demonstrate that adding 1,8-diiodooctane as a processing additives is an effective method to improve the morphology and the efficiency of bulk heterojunctions (BHJ) solar cells based on the regioregular poly(3-hexylthiophene) (P3HT) and a soluble fullerene derivative ([6,6]-phenyl C61-butyric acid methyl ester, PC61BM).

Enhanced performance of inverted organic photovoltaic cells using CNTs-TiO(X) nanocomposites as electron injection layer.

In this study, we fabricated inverted organic photovoltaic cells with the structure ITO/carbon nanotubes (CNTs)-TiO(X)/P3HT:PCBM/MoO₃/Al by spin casting CNTs-TiO(X) nanocomposite (CNTs-TiO(X)) as the electron injection layer onto ITO/glass substrates. The power conversion efficiency (PCE) of the 0.1 wt% single-walled nanotubes (SWNTs)-TiO(X) nanocomposite device was almost doubled compared with the TiO(X) device, but with increasing concentration of the incorporated SWNTs in the TiO(X) film, the performance of the devices appeared to decrease rapidly.

[Research on AlInGaN quaternary alloys as MQW barriers in GaN-based laser diodes].

InGaN/GaN, InGaN/InGaN and InGaN/AlInGaN multi-quantum-well (MQW) laser diodes (LDs) were grown on (0001) sapphire substrate by metalorganic chemical vapor deposition (MOCVD). The GaN (0002) synchrotron X-ray diffraction (XRD), electroluminescence (EL) and optical power-current (L-I) measurement reveal that AlInGaN quaternary alloys as barriers in MQWs can improve the crystal quality, optical emission performance, threshold current and slope efficiency of the laser diode structure to a large extent compared with other barriers. The relevant mechanisms are that: 1.

Focusing synchrotron radiation using a polycapillary half-focusing X-ray lens for imaging.

An imaging system based on a polycapillary half-focusing X-ray lens (PHFXRL) and synchrotron radiation source has been designed. The focal spot size and the gain in power density of the PHFXRL were 22 microm (FWHM) and 4648, respectively, at 14.0 keV.

Temperature dependence of interfacial fluctuations of polymerized fatty acid salt multilayers.

X-ray scattering was used to study the temperature dependence of the profile structure of polymerized 10,12-tricosadiynoic acid salt multilayers. The stacking periodicity of the multilayers was found to decrease with increasing temperature due to the conformational changes of the alkyl chains. When the samples were fully hydrated in water, the reflectivity measurement showed that the thermal fluctuations of the interfaces are enhanced with temperature, resulting in reduced ordering.