Mutual optical intensity propagation through non-ideal two-dimensional mirrors.

The mutual optical intensity (MOI) model is a partially coherent radiation propagation tool that can sequentially simulate beamline optics and provide beam intensity, local degree of coherence and phase distribution at any location along a beamline. This paper extends the MOI model to non-ideal two-dimensional (2D) optical systems, such as ellipsoidal and toroidal mirrors with 2D figure errors. Simulation results show that one can tune the trade-off between calculation efficiency and accuracy by varying the number of wavefront elements. The focal spot size of an ellipsoidal mirror calculated with 100 × 100 elements gives less than 0.4% deviation from that with 250 × 250 elements, and the computation speed is nearly two orders of magnitude faster. Effects of figure errors on 2D focusing are also demonstrated for a non-ideal ellipsoidal mirror and by comparing the toroidal and ellipsoidal mirrors. Finally, the MOI model is benchmarked against the multi-electron Synchrotron Radiation Workshop (SRW) code showing the model's high accuracy.

Partially coherent light propagation through a kinoform lens.

Combining wave optics propagation and geometric ray tracing, the mutual optical intensity (MOI) model is extended to quantitatively simulate the propagation of partially coherent light through a kinoform lens at high speed. The MOI model can provide both a high accuracy and a high efficiency simulation. The intensity and coherence degree distributions at the focal plane are calculated using the MOI model. It is beneficial to improve the focusing capability of the kinoform lens by reducing the coherence or increasing the number of lens steps. In addition, increasing the number of steps is also beneficial to increase the photon flux and reduce the depth of focus.

X-ray propagation through a kinoform lens.

Combining geometric ray tracing and wave optics propagation, a new simulation model named LWF is established to calculate the full coherent X-ray propagation through a kinoform lens. The LWF model is used to analyze the X-ray propagation through long and short kinoform lenses and calculate the intensity distribution at the focal plane. When the aperture is large, the focal spot for the long kinoform lens is smaller than that for the short kinoform lens. Due to the use of the geometric ray-tracing method to calculate the beam propagation inside the kinoform lens, the LWF model takes a low number of transversal wavefront segments, i.e. a short time, to achieve high accuracy. The simulation times for the one-dimensional and two-dimensional LWF models are 0.025 s and 5.3 s, respectively, with a calculation error of less than 0.5%. The high efficiency and high accuracy make the LWF model a strong tool in designing kinoform lenses.

Phase analysis for partially coherent light propagating through an optimized aperture in a synchrotron beamline.

The mutual optical intensity propagation of partially coherent light through a beamline is calculated for different aperture sizes and positions. The coherence, intensity and phase distribution can be extracted from the mutual optical intensity. The phase distribution depends on the aperture size and position. The results show that the widest flat phase distribution is obtained at the optimized aperture size and position. The aperture plays a more important role for partially coherent light than for incoherent light. The influence of the aperture size and position on the intensity and spot size at the focal plane is also analyzed. A way to obtain a balance between the flat phase distribution area, spot size and intensity for partially coherent light in the beamline is demonstrated.

Study on the layering phenomenon of SiC porous layer fabricated by constant current electrochemical etching.

Electrochemical etching of silicon carbide (SiC) material has received increasing attention in recent years, due to its simple procedure, low cost and significance in the exploration of novel optoelectronic devices. In this paper, 4H-SiC substrates were electrochemically etched at a constant current density of 392.98 mA cm-2 in an electrolyte made up of hydrofluoric acid and deionized water. The layering of a SiC porous layer and periodic fluctuation of the voltage were witnessed for the first time, with the layering phenomenon corresponding well to the voltage period. However, no such phenomenon was observed when the SiC substrates were anodic etched under the same conditions with magnet stirring. As a result, the periodic variation of voltage was hypothesized to be the cause of regular layering during constant current electrochemical etching. Electrochemical etching in potentiostatic mode was thus performed at different voltages. We found that the diameter of the SiC nanopores increased while the thickness of the sidewall decreased with the increasing voltage. Based on the experimental findings, a model of mass transport was proposed. The mass transport process leads to periodic changes in resistance, hence the periodic change in voltage. This successfully explained the reason for the layering. Furthermore, SiC substrates were also electrochemically etched at high and low current densities, finding the existence of a threshold current density for the occurrence of the layering. Energy dispersive x-ray spectroscopy analysis showed that the composition of the SiC porous layer remained unchanged compared to the pure SiC wafer, implying that the peeling-off of the SiC porous layer obtained by electrochemical etching can be directly adopted for use on devices requiring a SiC porous structure.

Optimization of the design for beamline with fast polarization switching elliptically polarized undulators.

Fast switching of X-ray polarization with a lock-in amplifier is a good method for acquiring weak signals from background noise for X-ray magnetic circular dichroism (XMCD) experiments. The usual way to obtain a beam with fast polarization switching is to use two series of elliptically polarized undulators (tandem twin EPUs). The two EPUs generate two individual beams. Each beam has a different polarization and is fast switched into the beamline. It is very important to ensure that the energy resolution, the flux and the spot size at the sample of the two beams are equal in XMCD experiments. However, it is difficult in beamline design because the distances from the two EPUs to the beamline optics are different and the beamline is not switchable. In this work, a beamline design without an entrance slit for fast polarization switching EPUs is discussed. The energy resolution of the two beams can be tuned to be equal by minor rotation of the optics in the monochromator. The flux of the two beams can be balanced through separation blades X, Y in the exit slit, and by adjusting the position of the X blades along the beam. The spot size of the two beams can be adjusted to be equal by shifting the sample as well.

Realizing Room-Temperature Ferromagnetism in Molecular-Intercalated Antiferromagnet VOCl.

2D van der Waals (vdW) magnets are gaining attention in fundamental physics and advanced spintronics, due to their unique dimension-dependent magnetism and potential for ultra-compact integration. However, achieving intrinsic ferromagnetism with high Curie temperature (TC) remains a technical challenge, including preparation and stability issues. Herein, an applicable electrochemical intercalation strategy to decouple interlayer interaction and guide charge doping in antiferromagnet VOCl, thereby inducing robust room-temperature ferromagnetism, is developed. The expanded vdW gap isolates the neighboring layers and shrinks the distance between the V-V bond, favoring the generation of ferromagnetic (FM) coupling with perpendicular magnetic anisotropy. Element-specific X-ray magnetic circular dichroism (XMCD) directly proves the source of the ferromagnetism. Detailed experimental results and density functional theory (DFT) calculations indicate that the charge doping enhances the FM interaction by promoting the orbital hybridization between t2 g and eg. This work sheds new light on a promising way to achieve room-temperature ferromagnetism in antiferromagnets, thus addressing the critical materials demand for designing spintronic devices.

Antiferromagnetism in Ni-Based Superconductors.

Due to the lack of any magnetic order down to 1.7 K in the parent bulk compound NdNiO2 , the recently discovered 9-15 K superconductivity in the infinite-layer Nd0.8 Sr0.2 NiO2 thin films has provided an exciting playground for unearthing new superconductivity mechanisms. Herein, the successful synthesis of a series of superconducting Nd0.8 Sr0.2 NiO2 thin films ranging from 8 to 40 nm is reported. The large exchange bias effect is observed between the superconducting Nd0.8 Sr0.2 NiO2 films and a thin ferromagnetic layer, which suggests the existence of the antiferromagnetic order. Furthermore, the existence of the antiferromagnetic order is evidenced by X-ray magnetic linear dichroism measurements. These experimental results are fundamentally critical for the current field.

A portable data-collection system for soft x-ray absorption spectroscopy in the Shanghai Synchrotron Radiation Facility.

Based on the Experimental Physics and Industrial Control System, a portable data-collection system for soft x-ray absorption spectroscopy has been developed at the BL02B and BL08U beamlines of the Shanghai Synchrotron Radiation Facility. The data-collection system can be used to carry out total electron yield (TEY) and total fluorescence yield (TFY) experiments simultaneously. The hardware consists of current preamplifiers, voltage-to-frequency converters, and a multi-channel counter, which are aimed at improving the signal-to-noise ratio. The control logic is developed using Python and Java. The novelty of this control system is its designed portability while being extensible and readable and having low noise and high real-time capabilities. The oxygen K-edge absorption spectra of SrTiO3 were obtained using the TEY and TFY technology at the BL02B beamline. Furthermore, the TEY and TFY spectra of the relaxor ferroelectric single-crystal of lead magnesium niobate-lead titanate measured by the present data-collection system have lower peak-to-peak noise amplitude than the ones measured by using a picoammeter. The experimental results show that the spectral signal-to-noise ratio recorded by the present system is 5.7-12.4 dB higher than that with the picoammeter detector.

Soft x-ray spectroscopic endstation at beamline 08U1A of Shanghai Synchrotron Radiation Facility.

A spectroscopic endstation with magnetic field, voltage, and low temperature control has been installed and commissioned at the soft X-ray beamline 08U1A of Shanghai Synchrotron Radiation Facility, which can obtain a magnetic field up to ±0.53 T, applied current and bias voltage, and cryogenic temperatures down to 14 K with a Gifford-McMahon cycle cryocooler. The endstation can perform soft X-ray absorption spectroscopy methods including total electron yield, fluorescence yield, and X-ray excited optical luminance. Combined with an elliptically polarized undulator and the in situ conditions, the endstation can effectively perform X-ray magnetic circular and linear dichroism experiments in the soft X-ray range between photon energies of 250 and 2000 eV.

Applicability study of the structure-factor phase method for determining the polarity of binary semiconductors.

The structure-factor phase method of convergent-beam electron diffraction (CBED) has been widely applied as an effective tool in determining the polarity of binary compound materials, for example, the typical sphalerite material, GaAs. However, its validity on other polar materials is still unknown. In this paper we extensively investigated its potential applicability onto 11 AB-type semiconductors by dynamical simulations of CBED. Two key factors during the simulation, the difference between A and B atomic numbers and the sample thickness, are discussed in detail. It was found that this method is efficient to determine the polarity for a sphalerite structure under certain conditions, and, reversely, limited to determine the polarity for a wurtzite structure even though it is very similar to the sphalerite structure.