Soft Electron Research Articles

Event Studies of O+Density Variability Within Quiet‐Time Plasma Sheet

AbstractTo understand the variations of the O+ ions in the quiet‐time plasma sheet between the regions of cold‐dense plasma sheet (CDPS) and hot plasma sheet (HPS), we conduct three event studies. These studies investigate the O+ densities in the two regions and how they are correlated with the strength of two magnetospheric sources important to ion outflows: the soft electron flux and Poynting flux toward the ionosphere. The CDPS is characterized by two‐component ions (one hot component mixed with one cold component), while the HPS ions consist of only one single hot component. Comparing the O+ density between the CDPS and HPS of the same event, the average CDPS O+ density was higher by a factor of ~2–5. Compared to the HPS, the soft electron flux source within the CDPS was higher, consistent with the fact that the soft electron precipitation and O+ upward number fluxes observed in the ionosphere were also higher within the CDPS. In the plasma sheet, broadband ultralow‐frequency electric and magnetic field waves with the characteristics of kinetic Alfvén waves were often more intense within the CDPS, providing a stronger Poynting flux source. In addition, electron resonant interaction with kinetic Alfvén waves results in acceleration along the magnetic fields and, thus, may drive the observed soft electron precipitation. These correlations suggest that the higher soft electron precipitation and Poynting flux coming from the magnetospheric CDPS likely produce larger ionospheric O+ outflows back to the magnetosphere, thus resulting in the higher O+ density within the CDPS.

Development of readout electronics for bunch arrival-time monitor system at SXFEL

A bunch arrival-time monitor (BAM) system, based on electro-optical intensity modulation scheme, is under study at Shanghai Soft X-ray Free Electron Laser. The aim of the study is to achieve high-precision time measurement for minimizing bunch fluctuations. A readout electronics is developed to fulfill the requirements of the BAM system. The readout electronics is mainly composed of a signal conditioning circuit, field-programmable gate array (FPGA), mezzanine card (FMC150), and powerful FPGA carrier board. The signal conditioning circuit converts the laser pulses into electrical pulse signals using a photodiode. Thereafter, it performs splitting and low-noise amplification to achieve the best voltage sampling performance of the dual-channel analog-to-digital converter (ADC) in FMC150. The FMC150 ADC daughter card includes a 14-bit 250 Msps dual-channel high-speed ADC, a clock configuration, and a management module. The powerful FPGA carrier board is a commercial high-performance Xilinx Kintex-7 FPGA evaluation board. To achieve clock and data alignment for ADC data capture at a high sampling rate, we used ISERDES, IDELAY, and dedicated carry-in resources in the Kintex-7 FPGA. This paper presents a detailed development of the readout electronics in the BAM system and its performance.

Design, RF measurement, tuning, and high-power test of an X-band deflector for Soft X-ray Free Electron Lasers (SXFEL) at SINAP

Abstract An X-band transverse-deflecting structure is a crucial RF unit for bunch-length measurement conducted at the Shanghai Soft-X-ray Free Electron Laser Facility (SXFEL) at the Shanghai Institute of Applied Physics (SINAP), Chinese Academy of Sciences. The target of this prototype deflector is to operate at 30 MW to have a deflection of 10 MV/structure to realize 20-fs resolution in a full-size structure (0.6 meters long, used on user facility of SXFEL), which satisfies the requirement of the linac beam size measurement at 840 MeV. The program was started in 2010 focusing on X-band deflectors, including design, fabrication, and RF measurement. The electrical tuning of the deflector was successfully done using a unique “cage”-type bead. Recently, a high-power test was conducted at KEK on the first prototype deflector. The high-gradient features at the nominal gradient was proven, but the further increase of power and pulse width was limited at 45 MW with a 173-ns pulse width due to approaching the feasible limit of the modified pointing vector value 5 MW/mm2. In this final stage, frequent breakdowns near the badly brazed point occurred and further conditioning had to be suspended owing to limited available time.

一种新型keV波段超高分辨光栅光谱仪设计

This paper presents a novel grating spectrometer design that combines a convexly cylindrical mirror with a concavely cylindrical varied line spacing grating to achieve an extreme resolving power of 33000-70000 in the photon energy range of 0.6-1.5 keV for a Gaussian light source with effective meridional size of 30 μm (root mean square) at an upstream initial object distance of 10 m. This type of spectrometer can be used to diagnose the radiation spectrum of a soft X-ray free electron laser and properly measure the spectral distribution and the detailed structure of the self-amplified spontaneous emission mode due to its extremely high resolving power. The overall optical aberrations of the system are well analyzed and compensated, providing an excellent flat field at the detector domain throughout the entire spectral range. A machine learning support vector machine algorithm is introduced into explore the optimal system to deliver the desired resolving performance. In addition, to enhance the spectral intensity and detection efficiency simultaneously, a sagittal confinement focusing mirror is introduced into the optical path of the spectrometer to reduce the astigmatism in spectral imaging. © 2019, Chinese Lasers Press. All right reserved.

Medroxyprogesterone effects on colony growth, autophagy and mitochondria of C6 glioma cells are augmented with tibolone and temozolomide: Cell kinetic and electron microscopical studies with a broad review of the literature

ObjectiveRisk of high grade gliomas is lower in young females and its incidence enhances after menopause suggesting likely protective roles of female hormones. Hormone replacement therapy (HRT) was widely employed to treat osteoporosis and some epidemiological studies showed that HRT regimes including progesterone analogs such as medroxyprogesterone acetate (MPA) decreased risk of glial tumors. Tibolone is a unique progesterone analog employed in HRT with tissue specific estrogenic effects and stimulates gene expressions very similar to those induced by MPA. Tibolone’s pro-estrogenic effects occur particularly in bone and brain and both MPA and tibolone inhibit AKR1C enzymes, which involve in temozolomide chemoresistance. Hence, we aimed to investigate interactions between MPA, tibolone and temozolomide in modification of glioma cell growth and fine structure. Patients and Methods: For our studies, we have particularly chosen C6 rat glioma cell line due to several reasons: i) We previously showed that MPA reduced growth and induced procarbazine-sensitization in C6 cells; ii) temozolomide has a triazene-type molecular structure like procarbazine; iii) other groups previously showed that C6 glioma cell line is more resistant to temozolomide than human glioma cells; hence it may provide a native model of chemoresistance. Monolayer plating efficacy, soft agar colony growth, 3D-spheroid S-phase (as determined by BrdU-labeling) and electron microscopical analyses were performed to assess mutual interactions between MPA, tibolone and temozolomide. Results: MPA inhibited clonogenic growth of C6 glioma and this effect is augmented by both tibolone and temozolomide. MPA and tibolone inhibited DNA synthesis in C6 glioma spheroids to similar levels which can be achieved with temozolomide. Electron microscopical analyses revealed synergisms between MPA, tibolone and temozolomide involved mitochondrial proliferation, condensation, mitophagy and autophagy. Conclusions: MPA and tibolone shall be studied in further experimental models of glioblastoma in vitro and in vivo.

Electron-Phonon Scattering in the Presence of Soft Modes and Electron Mobility in SrTiO_{3} Perovskite from First Principles.

Structural phase transitions and soft phonon modes pose a long-standing challenge to computing electron-phonon (e-ph) interactions in strongly anharmonic crystals. Here we develop a first-principles approach to compute e-ph scattering and charge transport in materials with anharmonic lattice dynamics. Our approach employs renormalized phonons to compute the temperature-dependent e-ph coupling for all phonon modes, including the soft modes associated with ferroelectricity and phase transitions. We show that the electron mobility in cubic SrTiO_{3} is controlled by scattering with longitudinal optical phonons at room temperature and with ferroelectric soft phonons below 200K. Our calculations can accurately predict the temperature dependence of the electron mobility in SrTiO_{3} between 150-300K, and reveal the microscopic origin of its roughly T^{-3} trend. Our approach enables first-principles calculations of e-ph interactions and charge transport in broad classes of crystals with phase transitions and strongly anharmonic phonons.

Stimulated CO Dissociation and Surface Graphitization by Microfocused X-ray and Electron Beams

The irradiation with photons or electrons can dramatically influence the chemical stability of a molecule, either free or adsorbed on a surface, inducing its fragmentation or desorption. We revisit here the exostimulated dissociation of CO, a prototypical case, choosing hcp thin cobalt films as model support. Intense, microfocused soft X-rays or electron beams are used to locally stimulate CO dissociation. Fast-XPS gives direct access to the adsorbates’ chemical state and coverage during irradiation, enabling the kinetics of the process to be monitored in real time. The energy-dependent cross sections for photon and electron stimulated molecular dissociation and desorption are estimated for a fixed initial CO coverage of 1/3 ML. In the soft X-ray regime, the desorption channel always prevails over dissociation and is significantly enhanced above the O K edge. The relative dissociation probability increases steadily with increasing photon energy, reaching 30% at 780 eV. Furthermore, we show that low energy electrons in the range 50 to 200 eV dissociate CO more efficiently than X-rays. The prolonged irradiation of the Co surface in CO ambient is found to produce a continuous increase of the carbon coverage, initially promoting the formation of carbides and subsequently accumulating sp2 carbon on the surface. Far from being a detrimental effect, the CO stimulated dissociation can be exploited to lithographically graft carbon-rich microscopic patterns on Co, with resolution well into the nanometer scale. A brief thermal treatment following irradiation results in the formation of a graphitic carbon overlayer, which effectively protects Co from oxidation upon exposure to ambient conditions, preserving its out-of-plane magnetic anisotropy and domain configuration.

Impulsive UV-pump/X-ray probe study of vibrational dynamics in glycine

We report an ab-initio study of a pump-probe experiment on the amino-acid glycine. We consider an UV pump followed by an X-ray probe tuned to carbon K-edge and study the vibronic structure of the core transition. The simulated experiment is feasible using existing free electron laser or high harmonic generation sources and thanks to the localization of the core orbitals posseses chemical selectivity. The present theory applies to other experimental schemes, including the use of a THz probe, available with present soft X-ray free electron lasers and/or high harmonic generation sources.

Magnetic domain formation in ultrathin complex oxide ferromagnetic/antiferromagnetic bilayers

In this study, we report on the magnetic domain formation in ultrathin blanket films and patterned micro- and nanostructures of ferromagnetic (FM) La0.7Sr0.3MnO3 single-layers and antiferromagnetic (AF)/ferromagnetic LaFeO3/La0.7Sr0.3MnO3 bilayers, as investigated by soft x-ray photoemission electron microscopy. In single-layer La0.7Sr0.3MnO3, the domain size is significantly reduced compared to that found in thicker layers, and rectangular micromagnets display metastable multidomain states distinctly different from the flux-closure ground states commonly found in thicker elements. In the LaFeO3/La0.7Sr0.3MnO3 bilayers, complex multidomain patterns are observed for blanket films and patterned magnets with robust perpendicular (spin-flop) coupling between spins in the AF and FM layers. By thermal cycling of the sample through the La0.7Sr0.3MnO3 Curie temperature, we find that the native antiferromagnetic domain pattern of LaFeO3 pins the location of domain boundaries in the adjacent La0.7Sr0.3MnO3 layer.

Design a high power pulse transformer for c-band klystron modulator

Shanghai soft X-ray Free Electron Lasers (SXFEL) used C-band accelerator structure to accelerate electrons at SINAP (Shanghai Institute of Applied Physics). 50MW C-band klystron and 110MW modulator are used to provide power supply for accelerator structure. In order to meet the modulator-klystron demands, a reliable and stable high power pulse transformer is indispensable. In this paper, the key design points for the high voltage pulse transformer are presented. The methods of shortening rise time and diminishing flattop droop are highlighted.

Femtosecond resonant magneto-optical Kerr effect measurement on an ultrathin magnetic film in a soft X-ray free electron laser

Time-resolved magneto-optical Kerr effect (MOKE) measurement was demonstrated on a sample of the Au/Fe/Au heterostructure with the Fe layer of 0.35 nm thickness under Fe M-edge resonance condition. An ultrabrilliant free electron laser (FEL) in the soft X-ray range was facilitated for the detection of transient signals of resonant MOKE from the ultrathin Fe film. A variation in the Kerr rotation angle was successfully observed on the femtosecond timescale. This technique enables us to reveal the transient magnetization dynamics of such a-few-monolayer magnetic films, which promote the development of spintronic devices.

Soft X-ray harmonic lasing self-seeded free electron laser at Pohang Accelerator Laboratory X-ray free electron laser

The demonstration of a harmonic lasing self-seeded free-electron laser (HLSS FEL) scheme in the soft X-ray range at the Pohang Accelerator Laboratory X-ray Free Electron Laser is presented. We report the experimental results of HLSS FEL radiation with the shortest wavelength of 1 nm by using the optimized phase shift of 2/3π. The key feature of the HLSS scheme is that the mode number is decreased (the longitudinal coherence length is enhanced) which is directly observed using a single-shot spectrometer. The spectral brightness is enhanced by a factor of 1.7 compared to the self-amplified spontaneous emission FEL because of the narrowed bandwidth. Our results show a good agreement with the theoretical expectation and simulations. The HLSS mode is a promising standard operation mode to generate a stable and high-brightness X-ray FEL that will provide more benefits to users for various applications.

Advanced characterization and in-situ growth monitoring of Cu(In,Ga)Se2 thin films and solar cells

The continuous improvement of Cu(In,Ga)Se2 (CIGSe) solar cells relies considerably on advanced characterization of individual layers in the solar-cell stacks as well as of completed CIGSe devices. The present contribution provides an overview of corresponding efforts performed by various research groups at Helmholtz-Zentrum Berlin für Materialien und Energie GmbH. In-situ growth monitoring of CIGSe absorber layers by means of energy-dispersive X-ray spectrometry and light scattering is described, as well as structural analyses by means of X-ray and neutron diffraction. In addition, the characterization of surfaces and interfaces by soft X-ray and electron spectroscopy, the microscopic analysis by means of correlative electron microscopy, and optoelectronic characterization by optical spectroscopy are highlighted. The present contribution shows which substantial efforts in a research network are necessary in order to obtain deeper insight into materials properties and potentially limiting factors for the device performance, as well as to be able to control these factors during the solar-cell production.

Two-photon absorption of soft X-ray free electron laser radiation by graphite near the carbon K-absorption edge

We have examined the transmission of soft X-ray pulses from the FERMI free electron laser through carbon films of varying thickness, quantifying nonlinear effects of pulses above and below the carbon K-edge. At typical of soft X-ray free electron laser intensities, pulses exhibit linear absorption at photon energies above and below the K-edge, ∼308 and ∼260 eV, respectively; whereas two-photon absorption becomes significant slightly below the K-edge, ∼284.2 eV. The measured two-photon absorption cross section at 284.18 eV (∼6 × 10−48 cm4 s) is 7 orders of magnitude above what is expected from a simple theory based on hydrogen-like atoms – a result of resonance effects.

Graphene liquid cells for multi-technique analysis of biological cells in water environment

In-cell exploration of biomolecular constituents is the new frontier of cellular biology that will allow full access to structure-activity correlation of biomolecules, overcoming the limitations imposed by dissecting the cellular milieu. However, the presence of water, which is a very strong IR absorber and incompatible with the vacuum working conditions of all analytical methods using soft x-rays and electrons, poses severe constraint to perform important imaging and spectroscopic analyses under physiological conditions. Recent advances to separate the sample compartment in liquid cell are based on electron and photon transparent but molecular-impermeable graphene membranes. This strategy has opened a unique opportunity to explore technological materials under realistic operation conditions using various types of electron microscopy. However, the widespread of the graphene liquid cell applications is still impeded by the lack of well-established approaches for their massive production. We report on the first preliminary results for the fabrication of reproducible graphene liquid cells appropriate for the analysis of biological specimens in their natural hydrated environment with several crucial analytical techniques, namely FTIR microscopy, Raman spectroscopy, AFM, SEM and TEM.

Impact of UV Pulsed Laser Radiation and of the Electron Flow on Dielectric States of Polymer Composite Nanomaterial Based on LDPE Matrix

The influence of the soft electron flow and irradiating pulsed UV laser on dielectric states of polymer composite nanomaterial based on LDPE matrix is experimentally studied. It was shown that irradiation of the samples LDPE–ZnO by electron beam (10 keV) for 10–15 minutes gives rise the appearance of the horizontal portion of the temperature dependence of capacitance (permittivity) and to memory effect (slow relaxation of dielectric situation within a few days). Irradiation with pulsed UV laser of the LDPE–CdS sample allows you to switch into a conducting state and return it to their original state upon application of a weak electric field. The observed phenomena may find practical applications for the polymer electronic memories and switching devices.

Dosimetric Impact of Metal Artifacts From Dental Implants and Clinical Implications for Head And Neck IMRT Treatment Planning

Dental implants are increasingly prevalent in the head and neck cancer patient population and result in the creation of artifacts on CT imaging for treatment planning. In our practice, we have noticed more mucosal toxicity adjacent to dental implants and hypothesized that this observation may be due to errors in dose calculation. The purpose of this study was to retrospectively evaluate dosimetric differences in target coverage and organ at risk (OAR) sparing when adjusting for spurious CT measurements attributed to dental metal artifact. Nine patients with dental implants who were previously treated at our institution with definitive radiation for oropharyngeal cancer were selected for this retrospective study. All patients were treated with 6 MV photons using intensity modulated radiation therapy (IMRT). Dose calculation was performed using an algorithm with heterogeneity corrections. Dental implant and streak artifact volumes were contoured and new IMRT plans were generated with identical beam geometry and monitor units using the uncorrected reference CT data set and a corrected CT data set. Artifacts were assigned a soft tissue electron density value with a Hounsfield unit (HU) of zero. Using descriptive statistics, target volumes and OAR dosimetry were reported and compared between the clinical treatment plans and re-calculated plans. Target volumes analyzed were GTV (D95, D98, D99), intermediate-risk PTV (D95, D98, D99), and high-risk PTV (D95, D98, D99, D2cc). The maximum dose, Dmax, was also collected for each plan. OARs analyzed included the bilateral parotids (mean), oral uninvolved (mean), OAR pharynx (mean), mandible (max), and cord (max). The median artifact volume was 41.6 cc (range, 22.5 to 56.8 cc). When accounting for artifact error, there were small but statistically significant relative increases in Dmax (0.24%, P=.0273), mean oral uninvolved dose (0.24%, P=.0234), and mean left parotid dose (0.20%, P=.0469). On average, the hot spot (Dmax) increased by 181 cGy when accounting for artifact. There were no significant dosimetric differences between plans in terms of GTV, intermediate-risk PTV, and high-risk PTV coverage. There were no significant differences for the mandible max dose, cord max dose, OAR pharynx mean dose, or the right parotid mean dose. In this retrospective study, there was minimal dose variation to target volumes and OAR structures when substituting artifact with soft tissue density HUs. There were significant differences in terms of maximum dose and dose to the uninvolved oral cavity, which suggests that ignoring artifacts in CT images during planning may result in greater hot spots. While small, these differences are worthy of further study as they may at least partially contribute to increased rates of empirically observed mucosal toxicity in the vicinity of dental artifacts.

EuPRAXIA@SPARC_LAB Design study towards a compact FEL facility at LNF

On the wake of the results obtained so far at the SPARC_LAB test-facility at the Laboratori Nazionali di Frascati (Italy), we are currently investigating the possibility to design and build a new multi-disciplinary user-facility, equipped with a soft X-ray Free Electron Laser (FEL) driven by a ∼1 GeV high brightness linac based on plasma accelerator modules. This design study is performed in synergy with the EuPRAXIA design study. In this paper we report about the recent progresses in the on going design study of the new facility.

Bimetallic zeolite imidazolate framework for enhanced lithium storage boosted by the redox participation of nitrogen atoms

In this work, a bimetallic zeolitic imidazolate framework (ZIF) CoZn-ZIF was synthesized via a facile solvothermal approach and applied in lithium-ion batteries. The as-prepared CoZn-ZIF shows a high reversible capacity of 605.8 mA h g−1 at a current density of 100 mA g−1, far beyond the performance of the corresponding monometallic Co-ZIF-67 and Zn-ZIF-8. Ex-situ synchrotron soft X-ray absorption spectroscopy, X-ray diffraction, and electron paramagnetic resonance techniques were employed to explore the Li-storage mechanism. The superior performance of CoZn-ZIF over Co-ZIF-67 and Zn-ZIF-8 could be mainly attributed to lithiation and delithiation of nitrogen atoms, accompanied by the breakage and recoordination of metal nitrogen bond. Morever, a few metal nitrogen bonds without recoordination will lead to the amorphization of CoZn-ZIF and the formation of few nitrogen radicals.

Interplay between bulk and edge-bound topological defects in a square micromagnet

A field-driven transformation of a domain pattern in a square micromagnet, defined in a thin film of La0.7Sr0.3MnO3, is discussed in terms of creation and annihilation of bulk vortices and edge-bound topological defects with half-integer winding numbers. The evolution of the domain pattern was mapped with soft x-ray photoemission electron microscopy and magnetic force microscopy. Micromagnetic modeling, permitting detailed analysis of the spin texture, accurately reproduces the measured domain state transformation. The simulations also helped stipulate the energy barriers associated with the creation and annihilation of the topological charges and thus to assess the stability of the domain states in this magnetic microstructure.