Three-dimensional ultrafast charge-density-wave dynamics in CuTe.

Charge density waves (CDWs) involved with electronic and phononic subsystems simultaneously are a common quantum state in solid-state physics, especially in low-dimensional materials. However, CDW phase dynamics in various dimensions are yet to be studied, and their phase transition mechanism is currently moot. Here we show that using the distinct temperature evolution of orientation-dependent ultrafast electron and phonon dynamics, different dimensional CDW phases are verified in CuTe.

Dirac Nodal Line in Hourglass Semimetal NbSiTe.

Glide-mirror symmetry in nonsymmorphic crystals can foster the emergence of novel hourglass nodal loop states. Here, we present spectroscopic signatures from angle-resolved photoemission of a predicted topological hourglass semimetal phase in NbSiTe. Linear band crossings are observed at the zone boundary of NbSiTe, which could be the origin of the nontrivial Berry phase and are consistent with a predicted glide quantum spin Hall effect; such linear band crossings connect to form a nodal loop.

Hydrogen spillover in complex oxide multifunctional sites improves acidic hydrogen evolution electrocatalysis.

Improving the catalytic efficiency of platinum for the hydrogen evolution reaction is valuable for water splitting technologies. Hydrogen spillover has emerged as a new strategy in designing binary-component Pt/support electrocatalysts. However, such binary catalysts often suffer from a long reaction pathway, undesirable interfacial barrier, and complicated synthetic processes.

Formation of Co-O bonds and reversal of thermal annealing effects induced by X-ray irradiation in (Y, Co)-codoped CeO nanocrystals.

We report an unconventional effect of synchrotron X-ray irradiation in which Co-O bonds in thermally annealed (Y, Co)-codoped CeO nanocrystal samples were formed due to, instead of broken by, X-ray irradiation. Our experimental data indicate that escaping oxygen atoms from X-ray-broken Ce-O bonds may be captured by Co dopant atoms to form additional Co-O bonds. Consequently, the Co dopant atoms were pumped by X-rays from the energetically-favored thermally-stable Co-O4 square-planar structure to the metastable octahedral Co-O6 environment, practically a reversal of thermal annealing effects in (Y, Co)-codoped CeO nanocrystals.

Topological Proximity-Induced Dirac Fermion in Two-Dimensional Antimonene.

Antimonene is a promising two-dimensional (2D) material that is calculated to have a significant fundamental bandgap usable for advanced applications such as field-effect transistors, photoelectric devices, and the quantum-spin Hall (QSH) state. Herein, we demonstrate a phenomenon termed topological proximity effect, which occurs between a 2D material and a three-dimensional (3D) topological insulator (TI). We provide strong evidence derived from hydrogen etching on SbTe that large-area and well-ordered antimonene presents a 2D topological state.

The Observation of Interchain Motion in Self-Assembled Crystalline Platinum(II) Complexes: An Exquisite Case but By No Means the Only One in Molecular Solids.

In organic and organometallic solids, upon electronic excitation, most intermolecular structural relaxations follow a pathway along the π-π stacking direction or metal-metal bond with significant coupling strength. Differently, we discovered that the self-assembled platinum(II) complexes, , exhibit an unusual interchain contraction. The ground-state and excited-state multiple local minima were distinguished by temperature-dependent excitation/emission spectra, indicating the existence of multiple local minima.

Os Doping Suppressed Cu-Fe Charge Transfer and Induced Structural and Magnetic Phase Transitions in LaCuFeOsO ( = 1 and 2).

B-site Os-doped quadruple perovskite oxides LaCuFeOsO ( = 1 and 2) were prepared under high-pressure and high-temperature conditions. Although parent compound LaCuFeO experiences Cu-Fe intermetallic charge transfer that changes the Cu/Fe charge combination to Cu/Fe at 393 K, in the Os-doped samples, the Cu and Fe charge states are found to be constant 2+ and 3+, respectively, indicating the complete suppression of charge transfer. Correspondingly, Os and mixed Os valence states are determined by X-ray absorption spectroscopy for = 1 and = 2 compositions, respectively.

Reduction of dopant ions and enhancement of magnetic properties by UV irradiation in Ce-doped TiO.

We report the experimental observation of and theoretical explanation for the reduction of dopant ions and enhancement of magnetic properties in Ce-doped TiO diluted magnetic semiconductors from UV-light irradiation. Substantial increase in Ce concentration and creation of oxygen vacancy defects in the sample due to UV-light irradiation was observed by X-ray and optical methods. Magnetic measurements demonstrate a combination of paramagnetism and ferromagnetism up to room temperatures in all samples.

A combinatory ferroelectric compound bridging simple ABO and A-site-ordered quadruple perovskite.

The simple ABO and A-site-ordered AA'BO perovskites represent two types of classical perovskite functional materials. There are well-known simple perovskites with ferroelectric properties, while there is still no report of ferroelectricity due to symmetry breaking transition in A-site-ordered quadruple perovskites. Here we report the high pressure synthesis of an A-site-ordered perovskite PbHgTiO, the only known quadruple perovskite that transforms from high-temperature centrosymmetric paraelectric phase to low-temperature non-centrosymmetric ferroelectric phase.

Integrated optical chip for a high-resolution, single-resonance-mode x-ray monochromator system.

An integrated optical chip that minimizes the size of the energy-tuning single-resonance-mode x-ray monochromator system into a 3×5 silicon wafer is proposed. A Fabry-Perot x-ray resonator and two back-reflecting Si mirrors are employed on the wafer as the optical components, where Si(12 4 0) back reflection is used for both Fabry-Perot resonance and re-diffraction of the x-ray beams from the resonator in the incident direction. We can achieve an energy bandwidth of 3.

Near-Room-Temperature Ferrimagnetic Ordering in a B-Site-Disordered 3d-5d-Hybridized Quadruple Perovskite Oxide, CaCuMnOsO.

A new 3d-5d hybridization oxide, CaCuMnOsO (CCMOO), was prepared by high-pressure and high-temperature synthesis methods. The compound crystallizes to an A-site-ordered but B-site-disordered quadruple perovskite structure with a space group of 3̅ (No. 204).

High-pressure synthesis and spin glass behavior of a Mn/Ir disordered quadruple perovskite CaCuMnIrO.

A new 3d-5d hybridized quadruple perovskite oxide, CaCuMnIrO, was synthesized by high-pressure and high-temperature methods. The Rietveld structure analysis reveals that the compound crystallizes in an [Formula: see text]-type perovskite structure with space group Im-3, where the Ca and Cu are 1:3 ordered at fixed atomic positions. At the B site the 3d Mn and the 5d Ir ions are disorderly distributed due to the rare equal  +4 charge states for both of them as determined by x-ray absorption spectroscopy.

Enhancement of catalytic activity by UV-light irradiation in CeO nanocrystals.

Ultraviolet (UV) light irradiation on CeO nanocrystals catalysts has been observed to largely increase the material's catalytic activity and reactive surface area. As revealed by x-ray absorption near edge structure (XANES) analysis, the concentration of subvalent Ce ions in the irradiated ceria samples progressively increases with the UV-light exposure time. The increase of Ce concentration as a result of UV irradiation was also confirmed by the UV-vis diffuse reflectance and photoluminescence spectra that indicate substantially increased concentration of oxygen vacancy defects in irradiated samples.

Time-resolved X-ray reflection phases of the nearly forbidden Si(222) reflection under laser excitation.

The covalent electron density, which makes Si(222) measurable, is subject to laser excitation. The three-wave Si(222)/(13 {\overline 1}) diffraction at 7.82 keV is used for phase measurements.

Defect engineering by synchrotron radiation X-rays in CeO nanocrystals.

This work reports an unconventional defect engineering approach using synchrotron-radiation-based X-rays on ceria nanocrystal catalysts of particle sizes 4.4-10.6 nm.

Directed Vertical Diffusion of Photovoltaic Active Layer Components into Porous ZnO-Based Cathode Buffer Layers.

Cathode buffer layers (CBLs) can effectively further the efficiency of polymer solar cells (PSCs), after optimization of the active layer. Hidden between the active layer and cathode of the inverted PSC device configuration is the critical yet often unattended vertical diffusion of the active layer components across CBL. Here, a novel methodology of contrast variation with neutron and anomalous X-ray reflectivity to map the multicomponent depth compositions of inverted PSCs, covering from the active layer surface down to the bottom of the ZnO-based CBL, is developed.

Critical Intermediate Structure That Directs the Crystalline Texture and Surface Morphology of Organo-Lead Trihalide Perovskite.

We have identified an often observed yet unresolved intermediate structure in a popular processing with dimethylformamide solutions of lead chloride and methylammonium iodide for perovskite solar cells. With subsecond time-resolved grazing-incidence X-ray scattering and X-ray photoemission spectroscopy, supplemental with ab initio calculation, the resolved intermediate structure (CHNH)PbICl·CHNHI features two-dimensional (2D) perovskite bilayers of zigzagged lead-halide octahedra and sandwiched CHNHI layers. Such intermediate structure reveals a hidden correlation between the intermediate phase and the composition of the processing solution.

Robustness of a Topologically Protected Surface State in a SbTeSe Single Crystal.

A topological insulator (TI) is a quantum material in a new class with attractive properties for physical and technological applications. Here we derive the electronic structure of highly crystalline SbTeSe single crystals studied with angle-resolved photoemission spectra. The result of band mapping reveals that the SbTeSe compound behaves as a p-type semiconductor and has an isolated Dirac cone of a topological surface state, which is highly favored for spintronic and thermoelectric devices because of the dissipation-less surface state and the decreased scattering from bulk bands.

Direct observation of charge ordering in magnetite using resonant multiwave x-ray diffraction.

Charge disproportion at octahedral Fe sites in magnetite was observed at low temperature using two inversion-symmetry related three-wave resonant x-ray diffraction, 022-311 and 002-̅3̅1, near the iron K edge. Both of the three-wave cases involve the (002) forbidden-weak reflection. The self-normalized three-wave to two-wave (002) diffraction intensity ratio automatically cancels the self-absorption effect and leads to direct determination of charge disproportion for magnetite below 120 K.

Multiple wave diffraction anomalous fine structure.

A new method, multiple-wave diffraction anomalous fine structure, combining the x-ray multiple-wave diffraction and diffraction anomalous fine structure techniques, is proposed. The real part of dispersion correction Deltaf' and fine structure chi function can be obtained directly by multiple diffraction analysis without using Kramers-Krönig relations and kinematical fitting of diffracted intensity. Better wave vector sensitivity of the fine structure is expected.