Blue light emitting graphene-based materials and their use in generating white light

It has been demonstrated that acid-treated graphene samples as well as reduced graphene oxide show fairly intense blue emission centered around 440 nm. Reduction of graphene oxide can be carried out either chemically or by using different types of radiations. Blue emission from graphene-based materials can be combined with the yellow emission from materials like ZnO to produce white light sources.     

Fissile core and Tritium-Breeding Blanket: structural materials and their requirements

High radiation resistant structural materials for fusion and fission nuclear power plants are a key issue for the development of both types of reactors. Selection criteria, elements of metallurgy of the selected materials, and the major issues as they are revealed by the results of the present development programmes, are presented. At low temperature (300 °C) ferritic/martensitic steels are suffering from He-embrittlement, associated with possible hardening due to α/α^′ unmixing. The kinetics of hardening and embrittlement versus dose, especially saturation with dose, are still open key issues, difficult to settle on the basis of a purely experimental programme. Important progress is still to be made in mastering the initial microstructure, inclusion cleanness and joining techniques of oxide dispersion strengthened steels for higher heat resistance. Physics modeling as presented in this issue should promote guidance to the understanding of the mechanisms involved, provide solutions to master the initial microstructure and phase stability, and mitigate the in-service property degradation. To cite this article: J.-L. Boutard et al., C. R. Physique 9 (2008).     

紫外光诱导纳米颗粒胶体微射流碰撞特性(英)

采用流体力学模拟方法,建立了垂直非淹没射流的计算流体动力学模型,研究了在紫外光诱导纳米颗粒胶体射流中用直径D为500 m的微孔光-液耦合喷嘴进行抛光加工的冲击动力学,分析了非淹没射流条件下光-液耦合喷嘴内、外的流场分布情况及其对工件表面的喷射冲击特征,对紫外光诱导纳米颗粒胶体射流冲击动力学过程进行了理论描述。计算结果表明,在1 MPa入射压力时,微孔光-液耦合喷嘴口TiO2胶体的喷射速度约为30 m/s,其集束匀速喷射距离约为5 mm。在此喷射距离时进行垂直喷射,在胶束与工件表面的冲击射流作用区域,其射流静压最大值分布在射流冲击作用中心,但射流动压及射流合成速度在此区域的截面分布呈W形状,射流动压及速度最大值出现在胶体射流束的外环直径约2 mm处。     

紫外光诱导纳米颗粒胶体微射流碰撞特性（英文）北大核心CSCD

采用流体力学模拟方法,建立了垂直非淹没射流的计算流体动力学模型,研究了在紫外光诱导纳米颗粒胶体射流中用直径D为500μm的微孔光-液耦合喷嘴进行抛光加工的冲击动力学,分析了非淹没射流条件下光-液耦合喷嘴内、外的流场分布情况及其对工件表面的喷射冲击特征,对紫外光诱导纳米颗粒胶体射流冲击动力学过程进行了理论描述。计算结果表明,在1MPa入射压力时,微孔光-液耦合喷嘴口TiO2胶体的喷射速度约为30m/s,其集束匀速喷射距离约为5mm。在此喷射距离时进行垂直喷射,在胶束与工件表面的冲击射流作用区域,其射流静压最大值分布在射流冲击作用中心,但射流动压及射流合成速度在此区域的截面分布呈"W"形状,射流动压及速度最大值出现在胶体射流束的外环直径约2mm处。     

Exchange dynamics at the interface of nanoporous materials with their surroundings

The evolution of transient concentration profiles in nanoporous materials is shown to provide direct information about the rate of molecular exchange at the interface of these materials with the surrounding atmosphere. This includes the quantitation of a surface permeability and, related with each other, of the sticking factor, i.e., of the probability that a molecule colliding with the external surface from the outside atmosphere, will in fact enter the genuine pore system of the material under study. Owing to the recent introduction of interference microscopy to this type of systems, the relevant experimental evidence has become directly accessible and is applied to two model systems which are found to differ notably in their interface dynamics.     

Hysteresis in structural dynamics

In this paper the Preisach hysteresis model is applied to determine the dynamic behavior of a steel column with mass on the top and loaded by an impulse force. The column is considered as a rigid element, while the fixed end of the column is modeled with a rotational spring of hysterestic characteristic. In the solution of the non-linear dynamical equation of motion the fix-point technique is inserted to the time marching iteration. In the investigation the non-linearity of the rotation spring is modeled with the Preisach hysteresis model. The variation of amplitude and the action time interval of force are changing. The results are plotted in figures.     

Ultrafast structural dynamics studied by kilohertz time-resolved x-ray diffraction

Ultrashort multi-ke V x-ray pulses are generated by electron plasma produced by the irradiation of femtosecond pulses on metals. These sub-picosecond x-ray pulses have extended the field of x-ray spectroscopy into the femtosecond time domain. However, pulse-to-pulse instability and long data acquisition time restrict the application of ultrashort x-ray systems operating at low repetition rates. Here we report on the performance of a femtosecond laser plasma-induced hard x-ray source that operates at 1-k Hz repetition rate, and provides a flux of 2.0 × 1010 photons/s of Cu Kαradiation. Using this system for time-resolved x-ray diffraction experiments, we record in real time, the transient processes and structural changes induced by the interaction of 400-nm femtosecond pulse with the surface of a 200-nm thick Au(111) single crystal.     

Lattice dynamics and structural phase transitions

Results of lattice dynamics, or atomic motions in a solid, explain many of the thermodynamic properties of solids. Inelastic neutron scattering conveniently explores the atomic motions, quantized as phonons. Of particular interest are materials that undergo structural phase transitions. The soft mode theory has been successful in relating anomalous phonon behavior to structural changes in solids. One such example is the ferromagnetic shape memory alloy, Ni₂MnGa, which undergoes a sequence of phase transitions leading to a magnetic, incommensurate modulated, tetragonal phase as the ground state. The experiments, coupled with first principles calculations, provide evidence that strong electron–phonon coupling is the driving mechanism of the phase transformation.     

Magnetic microstructures and their dynamics studied by X-ray microscopy

Full-field soft X-ray microscopy in combination with X-ray magnetic circular dichroism as contrast mechanism is a powerful technique to image with elemental specificity magnetic nanostructures and multilayered thin films at high lateral resolution down to 15nm by using Fresnel zone plates as X-ray optical elements. Magnetization reversal phenomena on a microscopic level are studied by recording the images in varying external magnetic fields. Local spin dynamics at a time resolution below 100ps can be addressed by engaging a stroboscopic pump-and-probe scheme taking into account the time pattern of synchrotron storage rings. Characteristic features of magnetic soft X-ray microscopy are reviewed and an outlook into future perspectives with regard to increased lateral and temporal resolution is given.     

Structure and dynamics in nanoionic materials

Nanomaterials, materials with particle dimensions less than 100 nm, show a range of unusual properties when compared with their bulk counterparts. Atomic transport is one of these properties and nanomaterials have been reported as having exceptionally high diffusion coefficients. In the case of ionic materials the atomic transport is important in a number of technological applications where they are used as solid electrolytes, for example in sensors, batteries and fuel cells. Hence ionic nanomaterials often referred to as nanoionics, can offer the means of producing electrolytes with improved performance. This contribution will examine the mechanisms of atomic transport in nanoionics in two model materials, zirconia and lithium niobate. Since an understanding of these mechanisms is dependent on knowledge of the microstructure of the materials consideration will also be given to the structural characterisation of the materials, with a focus on X-ray absorption spectroscopy. The use of this technique to characterise mesoporous a-Fe₂O₃ is also discussed.     

Protein structural dynamics as determined by Mössbauer spectroscopy

Mössbauer spectroscopy on⁵⁷Fe allows the study of dynamics with a characteristic time faster 100 ns. For myoglobin a detailed physical picture of protein dynamics has been obtained. A myoglobin molecule has no well defined energy minimum. X-ray structure analysis yields only an average conformation. At low temperatures the molecules are trapped in slightly different structures called conformational substates. At higher temperatures a Brownian type of oscillation of molecular segments in restricted space occurs. RSMR technique allows an estimation of the characteristic size of these segments which are in myoglobin well below 30 A and larger than 6 A. A determination of the quasielastic absorption with high accuracy yields the energy distribution of the conformational substates. As further examples bacteriorhodopsin and a model compound for membranes are discussed.     

Spin dynamics in magnetic materials investigated by muon spin relaxation

We present a quantitative analysis of the temperature dependence of the muon spin relaxation rate measured in simple magnets. We consider the low temperature, critical and high temperature regimes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mechanical properties of thin films of graphene materials: A study on their structural quality and functionalities

Several studies have been done on physiochemical properties of thin films of graphene materials, but less on their mechanical properties. The mechanical properties such as tensile and storage modulus of films of graphene oxide (GO), different reduced graphene oxides (rGO), functionalised reduced graphene oxide (frGO) and a few layers graphene (graphene) were analysed in this study. During syntheses processes, a range of variations occurs due to different reducing agents and functionalising components used; this affects or changes the mechanical properties of the materials. In addition, it has become vital to comprehend the mechanical properties of these films as the potential applications such as sensor and electrodes demand extended life cycles or lifetime. It has been found that the ultimate tensile strength (UTS), tensile modulus, and storage modulus vary across all the samples that highly depend on nature/efficiency of reducing agent used, amount of impurities such as oxygen functional groups and defect density such as discrepancies/holes in the aromatic structure. The highest UTS and modulus have been identified with a few layers graphene and with hydroiodic acid reduced GO among the rGOs. The frGO shows almost similar properties to that of graphene.     

Electrically controlled reflection and transmission of obliquely incident light by structurally chiral materials

The solution of a boundary-value problem for the reflection and transmission of obliquely incident plane waves due to a slab of a structurally chiral material (SCM) displaying the Pockels effect with a point group symmetry indicates the enhancement of circular Bragg phenomenon by the application of a dc voltage. The enhancement suggests that thinner SCMs can be used as devices such as polarization-rejection filters if the Pockels effect is exploited, for both normally and obliquely incident light.     

Synthesis of nano-structured materials by laser-ablation and their application to sensors

We describe the synthesis of nano-structured materials of ZnO and Pd by laser ablation and their applications to sensors. The synthesis of ZnO nano-wires was performed by nano-particle assisted deposition (NPAD) where nano-crystals were grown with nano-particles generated by laser-ablating a ZnO sintered target in an Ar background gas. The synthesized ZnO nano-wires were characterized with a scanning electron microscopy and the photoluminescent characteristics were examined under an excitation with the third harmonics of a Nd:YAG laser. The nano-wires with a diameter in the range from 50 to 150 nm and a length of up to 5 μm were taken out of the substrate by laser blow-off technique and/or sonication. It was confirmed that the nano-wires showed the stimulated emission under optical pumping, indicating a high quality of the crystalinity. Pd nano-particles were generated by laser-ablating a Pd plate in pure water. The transmission electron microscope observation revealed that Pd nano-particles with a diameter in the range from 3 nm to several tens of nanometers were produced. Using these nano-structured materials, we successfully fabricated sensors by the dielectrophoresis techniques. In the case of the ultraviolet photosensor, a detection sensitivity of 10 nW/cm² was achieved and in the case of hydrogen sensing, the response time of less than 10 s has been demonstrated with Pd nano-particles.     

Ultrafast structural dynamics of perovskite superlattices

Femtosecond x-ray diffraction provides direct insight into the ultrafast reversible lattice dynamics of materials with a perovskite structure. Superlattice (SL) structures consisting of a sequence of nanometer-thick layer pairs allow for optically inducing a tailored stress profile that drives the lattice motions and for limiting the influence of strain propagation on the observed dynamics. We demonstrate this concept in a series of diffraction experiments with femtosecond time resolution, giving detailed information on the ultrafast lattice dynamics of ferroelectric and ferromagnetic superlattices. Anharmonically coupled lattice motions in a SrRuO₃/PbZr_0.2Ti_0.8O₃ (SRO/PZT) SL lead to a switch-off of the electric polarizations on a time scale of the order of 1 ps. Ultrafast magnetostriction of photoexcited SRO layers is demonstrated in a SRO/SrTiO₃ (STO) SL.