An investigation of turbulent scatter from the mesosphere as observed by coherent-scatter radar

NASA Technical Reports Server (NTRS)

Gibbs, K. P.; Bowhill, S. A.

1983-01-01

Turbulent scatter from he mesosphere is observed using the Urbana coherent-scatter radar. The variation in signal-to-noise ratio as a function of time-of-day is examined. The origin of scattering regions is investigated by comparing the variations in scattered power and Doppler velocity. Nighttime echoes are shown for periods of enhanced electron concentration. The spectrum of the returned signal is studied with a resolution of ten seconds. Spectral information is used to increase altitude resolution and observe the motion of scatterers. The expected variation in signal-to-noise ratio with solar flux is observed. It is found that variations in the scattered power generally do not correspond to the gravity waves which are simultaneously observed. Turbulent layers are observed at altitudes with high shear in the horizontal velocity and at altitudes with low shear. The ten-second resolution is necessary to distinguish meteor echoes from echoes produced by the advection of a scattering layer through the radar beam.

Enhancing resolution in coherent x-ray diffraction imaging.

PubMed

Noh, Do Young; Kim, Chan; Kim, Yoonhee; Song, Changyong

2016-12-14

Achieving a resolution near 1 nm is a critical issue in coherent x-ray diffraction imaging (CDI) for applications in materials and biology. Albeit with various advantages of CDI based on synchrotrons and newly developed x-ray free electron lasers, its applications would be limited without improving resolution well below 10 nm. Here, we review the issues and efforts in improving CDI resolution including various methods for resolution determination. Enhancing diffraction signal at large diffraction angles, with the aid of interference between neighboring strong scatterers or templates, is reviewed and discussed in terms of increasing signal-to-noise ratio. In addition, we discuss errors in image reconstruction algorithms-caused by the discreteness of the Fourier transformations involved-which degrade the spatial resolution, and suggest ways to correct them. We expect this review to be useful for applications of CDI in imaging weakly scattering soft matters using coherent x-ray sources including x-ray free electron lasers.

Role of electron-electron interference in ultrafast time-resolved imaging of electronic wavepackets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dixit, Gopal; Santra, Robin; Department of Physics, University of Hamburg, D-20355 Hamburg

2013-04-07

Ultrafast time-resolved x-ray scattering is an emerging approach to image the dynamical evolution of the electronic charge distribution during complex chemical and biological processes in real-space and real-time. Recently, the differences between semiclassical and quantum-electrodynamical (QED) theory of light-matter interaction for scattering of ultrashort x-ray pulses from the electronic wavepacket were formally demonstrated and visually illustrated by scattering patterns calculated for an electronic wavepacket in atomic hydrogen [G. Dixit, O. Vendrell, and R. Santra, Proc. Natl. Acad. Sci. U.S.A. 109, 11636 (2012)]. In this work, we present a detailed analysis of time-resolved x-ray scattering from a sample containing a mixturemore » of non-stationary and stationary electrons within both the theories. In a many-electron system, the role of scattering interference between a non-stationary and several stationary electrons to the total scattering signal is investigated. In general, QED and semiclassical theory provide different results for the contribution from the scattering interference, which depends on the energy resolution of the detector and the x-ray pulse duration. The present findings are demonstrated by means of a numerical example of x-ray time-resolved imaging for an electronic wavepacket in helium. It is shown that the time-dependent scattering interference vanishes within semiclassical theory and the corresponding patterns are dominated by the scattering contribution from the time-independent interference, whereas the time-dependent scattering interference contribution do not vanish in the QED theory and the patterns are dominated by the scattering contribution from the non-stationary electron scattering.« less

Role of electron-electron interference in ultrafast time-resolved imaging of electronic wavepackets

NASA Astrophysics Data System (ADS)

Dixit, Gopal; Santra, Robin

2013-04-01

Ultrafast time-resolved x-ray scattering is an emerging approach to image the dynamical evolution of the electronic charge distribution during complex chemical and biological processes in real-space and real-time. Recently, the differences between semiclassical and quantum-electrodynamical (QED) theory of light-matter interaction for scattering of ultrashort x-ray pulses from the electronic wavepacket were formally demonstrated and visually illustrated by scattering patterns calculated for an electronic wavepacket in atomic hydrogen [G. Dixit, O. Vendrell, and R. Santra, Proc. Natl. Acad. Sci. U.S.A. 109, 11636 (2012)], 10.1073/pnas.1202226109. In this work, we present a detailed analysis of time-resolved x-ray scattering from a sample containing a mixture of non-stationary and stationary electrons within both the theories. In a many-electron system, the role of scattering interference between a non-stationary and several stationary electrons to the total scattering signal is investigated. In general, QED and semiclassical theory provide different results for the contribution from the scattering interference, which depends on the energy resolution of the detector and the x-ray pulse duration. The present findings are demonstrated by means of a numerical example of x-ray time-resolved imaging for an electronic wavepacket in helium. It is shown that the time-dependent scattering interference vanishes within semiclassical theory and the corresponding patterns are dominated by the scattering contribution from the time-independent interference, whereas the time-dependent scattering interference contribution do not vanish in the QED theory and the patterns are dominated by the scattering contribution from the non-stationary electron scattering.

Role of electron-electron interference in ultrafast time-resolved imaging of electronic wavepackets.

PubMed

Dixit, Gopal; Santra, Robin

2013-04-07

Ultrafast time-resolved x-ray scattering is an emerging approach to image the dynamical evolution of the electronic charge distribution during complex chemical and biological processes in real-space and real-time. Recently, the differences between semiclassical and quantum-electrodynamical (QED) theory of light-matter interaction for scattering of ultrashort x-ray pulses from the electronic wavepacket were formally demonstrated and visually illustrated by scattering patterns calculated for an electronic wavepacket in atomic hydrogen [G. Dixit, O. Vendrell, and R. Santra, Proc. Natl. Acad. Sci. U.S.A. 109, 11636 (2012)]. In this work, we present a detailed analysis of time-resolved x-ray scattering from a sample containing a mixture of non-stationary and stationary electrons within both the theories. In a many-electron system, the role of scattering interference between a non-stationary and several stationary electrons to the total scattering signal is investigated. In general, QED and semiclassical theory provide different results for the contribution from the scattering interference, which depends on the energy resolution of the detector and the x-ray pulse duration. The present findings are demonstrated by means of a numerical example of x-ray time-resolved imaging for an electronic wavepacket in helium. It is shown that the time-dependent scattering interference vanishes within semiclassical theory and the corresponding patterns are dominated by the scattering contribution from the time-independent interference, whereas the time-dependent scattering interference contribution do not vanish in the QED theory and the patterns are dominated by the scattering contribution from the non-stationary electron scattering.

Currents and Associated Electron Scattering and Bouncing Near the Diffusion Region at Earth's Magnetopause

NASA Technical Reports Server (NTRS)

Lavraud, B.; Zhang, Y. C.; Vernisse, Y.; Gershman, D. J.; Dorelli, J.; Cassak, P. A.; Dargent, J.; Pollock, C.; Giles, B.; Aunai, N.;

Is localized infrared spectroscopy now possible in the electron microscope?

PubMed

Rez, Peter

2014-06-01

The recently developed in-column monochromators make it possible to record energy-c spectra with resolutions better than 30 meV from nanometer-sized regions. It should therefore in principle be possible to detect localized vibrational excitations. The scattering geometry in the electron microscope means that bond stretching in the specimen plane or longitudinal optic phonons dominate the scattering. Most promising for initial studies are vibrations with energies between 300 and 400 meV from hydrogen bonded to other atoms. Estimates of the scattering cross-sections on the basis of a simple model show that they are about the same as inner shell scattering cross-sections. Cross-sections also increase with charge transfer between the atoms, and theory incorporating realistic charge distributions shows that signal/noise is the only limitation to high-resolution imaging. Given the magnitude of the scattering cross-sections, minimizing the tail of the zero-loss peak is just as important as achieving a small-width at half-maximum. Improvements in both resolution and controlling the zero-loss tail will be necessary before it is practical to detect optic phonons in solids between 40 and 60 meV.

Electron-Beam Mapping of Vibrational Modes with Nanometer Spatial Resolution.

PubMed

Dwyer, C; Aoki, T; Rez, P; Chang, S L Y; Lovejoy, T C; Krivanek, O L

2016-12-16

We demonstrate that a focused beam of high-energy electrons can be used to map the vibrational modes of a material with a spatial resolution of the order of one nanometer. Our demonstration is performed on boron nitride, a polar dielectric which gives rise to both localized and delocalized electron-vibrational scattering, either of which can be selected in our off-axial experimental geometry. Our experimental results are well supported by our calculations, and should reconcile current controversy regarding the spatial resolution achievable in vibrational mapping with focused electron beams.

Guiding the Design of Radiation Imagers with Experimentally Benchmarked Geant4 Simulations for Electron-Tracking Compton Imaging

NASA Astrophysics Data System (ADS)

Coffer, Amy Beth

Radiation imagers are import tools in the modern world for a wide range of applications. They span the use-cases of fundamental sciences, astrophysics, medical imaging, all the way to national security, nuclear safeguards, and non-proliferation verification. The type of radiation imagers studied in this thesis were gamma-ray imagers that detect emissions from radioactive materials. Gamma-ray imagers goal is to localize and map the distribution of radiation within their specific field-of-view despite the fact of complicating background radiation that can be terrestrial, astronomical, and temporal. Compton imaging systems are one type of gamma-ray imager that can map the radiation around the system without the use of collimation. Lack of collimation enables the imaging system to be able to detect radiation from all-directions, while at the same time, enables increased detection efficiency by not absorbing incident radiation in non-sensing materials. Each Compton-scatter events within an imaging system generated a possible cone-surface in space that the radiation could have originated from. Compton imaging is limited in its reconstructed image signal-to-background due to these source Compton-cones overlapping with background radiation Compton-cones. These overlapping cones limit Compton imaging's detection-sensitivity in image space. Electron-tracking Compton imaging (ETCI) can improve the detection-sensitivity by measuring the Compton-scattered electron's initial trajectory. With an estimate of the scattered electron's trajectory, one can reduce the Compton-back-projected cone to a cone-arc, thus enabling faster radiation source detection and localization. However, the ability to measure the Compton-scattered electron-trajectories adds another layer of complexity to an already complex methodology. For a real-world imaging applications, improvements are needed in electron-track detection efficiency and in electron-track reconstruction. One way of measuring Compton-scattered electron-trajectories is with high-resolution Charged-Coupled Devices (CCDs). The proof-of-principle CCD-based ETCI experiment demonstrated the CCDs' ability to measure the Compton-scattered electron-tracks as a 2-dimensional image. Electron-track-imaging algorithms using the electron-track-image are able to determine the 3-dimensional electron-track trajectory within +/- 20 degrees. The work presented here is the physics simulations developed along side the experimental proof-of-principle experiment. The development of accurate physics modeling for multiple-layer CCDs based ETCI systems allow for the accurate prediction of future ETCI system performance. The simulations also enable quick development insights for system design, and they guide the development of electron-track reconstruction methods. The physics simulation efforts for this project looked closely at the accuracy of the Geant4 Monte Carlo methods for medium energy electron transport. In older version of Geant4 there were some discrepancies between the electron-tracking experimental measurements and the simulation results. It was determined that when comparing the electron dynamics of electrons at very high resolutions, Geant4 simulations must be fine tuned with careful choices for physics production cuts and electron physics stepping sizes. One result of this work is a CCDs Monte Carlo model that has been benchmarked to experimental findings and fully characterized for both photon and electron transport. The CCDs physics model now match to within 1 percent error of experimental results for scattered-electron energies below 500 keV. Following the improvements of the CCDs simulations, the performance of a realistic two-layer CCD-stack system was characterized. The realistic CCD-stack system looked at the effect of thin passive-layers on the CCDs' front face and back-contact. The photon interaction efficiency was calculated for the two-layer CCD-stack, and we found that there is a 90 percent probability of scattered-electrons from a 662 keV source to stay within a single active layer. This demonstrates the improved detection efficiency, which is one of the strengths of the CCDs' implementation as a ETCI system. The CCD-stack simulations also established that electron-tracks scattering from one CCDs layer to another could be reconstructed. The passive-regions on the CCD-stack mean that these inter-layer scattered-electron-tracks will always loose both angular information and energy information. Looking at the angular changes of these electrons scattering between the CCDs layers showed us there is not a strong energy dependence on the angular changes due to the passive-regions of the CCDs. The angular changes of the electron track are, for the most part, a function of the thickness of the thin back-layer of the CCDs. Lastly, an approach using CCD-stack simulations was developed to reconstruct the energy transport across dead-layers and its feasibility was demonstrated. Adding back this lost energy will limit the loss of energy resolution of the scatter-interactions. Energy resolution losses would negatively impacted the achievable image resolution from image reconstruction algorithms. Returning some of the energy back to the reconstructed electron-track will help retain the expected performance of the electron-track trajectory determination algorithm.

Materials characterisation by angle-resolved scanning transmission electron microscopy.

PubMed

Müller-Caspary, Knut; Oppermann, Oliver; Grieb, Tim; Krause, Florian F; Rosenauer, Andreas; Schowalter, Marco; Mehrtens, Thorsten; Beyer, Andreas; Volz, Kerstin; Potapov, Pavel

2016-11-16

Solid-state properties such as strain or chemical composition often leave characteristic fingerprints in the angular dependence of electron scattering. Scanning transmission electron microscopy (STEM) is dedicated to probe scattered intensity with atomic resolution, but it drastically lacks angular resolution. Here we report both a setup to exploit the explicit angular dependence of scattered intensity and applications of angle-resolved STEM to semiconductor nanostructures. Our method is applied to measure nitrogen content and specimen thickness in a GaN x As 1-x layer independently at atomic resolution by evaluating two dedicated angular intervals. We demonstrate contrast formation due to strain and composition in a Si- based metal-oxide semiconductor field effect transistor (MOSFET) with Ge x Si 1-x stressors as a function of the angles used for imaging. To shed light on the validity of current theoretical approaches this data is compared with theory, namely the Rutherford approach and contemporary multislice simulations. Inconsistency is found for the Rutherford model in the whole angular range of 16-255 mrad. Contrary, the multislice simulations are applicable for angles larger than 35 mrad whereas a significant mismatch is observed at lower angles. This limitation of established simulations is discussed particularly on the basis of inelastic scattering.

Facing the phase problem in Coherent Diffractive Imaging via Memetic Algorithms.

PubMed

Colombo, Alessandro; Galli, Davide Emilio; De Caro, Liberato; Scattarella, Francesco; Carlino, Elvio

2017-02-09

Coherent Diffractive Imaging is a lensless technique that allows imaging of matter at a spatial resolution not limited by lens aberrations. This technique exploits the measured diffraction pattern of a coherent beam scattered by periodic and non-periodic objects to retrieve spatial information. The diffracted intensity, for weak-scattering objects, is proportional to the modulus of the Fourier Transform of the object scattering function. Any phase information, needed to retrieve its scattering function, has to be retrieved by means of suitable algorithms. Here we present a new approach, based on a memetic algorithm, i.e. a hybrid genetic algorithm, to face the phase problem, which exploits the synergy of deterministic and stochastic optimization methods. The new approach has been tested on simulated data and applied to the phasing of transmission electron microscopy coherent electron diffraction data of a SrTiO 3 sample. We have been able to quantitatively retrieve the projected atomic potential, and also image the oxygen columns, which are not directly visible in the relevant high-resolution transmission electron microscopy images. Our approach proves to be a new powerful tool for the study of matter at atomic resolution and opens new perspectives in those applications in which effective phase retrieval is necessary.

Analyzing indirect secondary electron contrast of unstained bacteriophage T4 based on SEM images and Monte Carlo simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ogura, Toshihiko, E-mail: t-ogura@aist.go.jp

2009-03-06

The indirect secondary electron contrast (ISEC) condition of the scanning electron microscopy (SEM) produces high contrast detection with minimal damage of unstained biological samples mounted under a thin carbon film. The high contrast image is created by a secondary electron signal produced under the carbon film by a low acceleration voltage. Here, we show that ISEC condition is clearly able to detect unstained bacteriophage T4 under a thin carbon film (10-15 nm) by using high-resolution field emission (FE) SEM. The results show that FE-SEM provides higher resolution than thermionic emission SEM. Furthermore, we investigated the scattered electron area within themore » carbon film under ISEC conditions using Monte Carlo simulation. The simulations indicated that the image resolution difference is related to the scattering width in the carbon film and the electron beam spot size. Using ISEC conditions on unstained virus samples would produce low electronic damage, because the electron beam does not directly irradiate the sample. In addition to the routine analysis, this method can be utilized for structural analysis of various biological samples like viruses, bacteria, and protein complexes.« less

On macromolecular refinement at subatomic resolution with interatomic scatterers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Afonine, Pavel V., E-mail: pafonine@lbl.gov; Grosse-Kunstleve, Ralf W.; Adams, Paul D.

2007-11-01

Modelling deformation electron density using interatomic scatters is simpler than multipolar methods, produces comparable results at subatomic resolution and can easily be applied to macromolecules. A study of the accurate electron-density distribution in molecular crystals at subatomic resolution (better than ∼1.0 Å) requires more detailed models than those based on independent spherical atoms. A tool that is conventionally used in small-molecule crystallography is the multipolar model. Even at upper resolution limits of 0.8–1.0 Å, the number of experimental data is insufficient for full multipolar model refinement. As an alternative, a simpler model composed of conventional independent spherical atoms augmented bymore » additional scatterers to model bonding effects has been proposed. Refinement of these mixed models for several benchmark data sets gave results that were comparable in quality with the results of multipolar refinement and superior to those for conventional models. Applications to several data sets of both small molecules and macromolecules are shown. These refinements were performed using the general-purpose macromolecular refinement module phenix.refine of the PHENIX package.« less

Resolution of ab initio shapes determined from small-angle scattering.

PubMed

Tuukkanen, Anne T; Kleywegt, Gerard J; Svergun, Dmitri I

2016-11-01

Spatial resolution is an important characteristic of structural models, and the authors of structures determined by X-ray crystallography or electron cryo-microscopy always provide the resolution upon publication and deposition. Small-angle scattering of X-rays or neutrons (SAS) has recently become a mainstream structural method providing the overall three-dimensional structures of proteins, nucleic acids and complexes in solution. However, no quantitative resolution measure is available for SAS-derived models, which significantly hampers their validation and further use. Here, a method is derived for resolution assessment for ab initio shape reconstruction from scattering data. The inherent variability of the ab initio shapes is utilized and it is demonstrated how their average Fourier shell correlation function is related to the model resolution. The method is validated against simulated data for proteins with known high-resolution structures and its efficiency is demonstrated in applications to experimental data. It is proposed that henceforth the resolution be reported in publications and depositions of ab initio SAS models.

Resolution of ab initio shapes determined from small-angle scattering

PubMed Central

Tuukkanen, Anne T.; Kleywegt, Gerard J.; Svergun, Dmitri I.

2016-01-01

Spatial resolution is an important characteristic of structural models, and the authors of structures determined by X-ray crystallography or electron cryo-microscopy always provide the resolution upon publication and deposition. Small-angle scattering of X-rays or neutrons (SAS) has recently become a mainstream structural method providing the overall three-dimensional structures of proteins, nucleic acids and complexes in solution. However, no quantitative resolution measure is available for SAS-derived models, which significantly hampers their validation and further use. Here, a method is derived for resolution assessment for ab initio shape reconstruction from scattering data. The inherent variability of the ab initio shapes is utilized and it is demonstrated how their average Fourier shell correlation function is related to the model resolution. The method is validated against simulated data for proteins with known high-resolution structures and its efficiency is demonstrated in applications to experimental data. It is proposed that henceforth the resolution be reported in publications and depositions of ab initio SAS models. PMID:27840683

Oxidation-state sensitive imaging of cerium dioxide by atomic-resolution low-angle annular dark field scanning transmission electron microscopy.

PubMed

Johnston-Peck, Aaron C; Winterstein, Jonathan P; Roberts, Alan D; DuChene, Joseph S; Qian, Kun; Sweeny, Brendan C; Wei, Wei David; Sharma, Renu; Stach, Eric A; Herzing, Andrew A

2016-03-01

Low-angle annular dark field (LAADF) scanning transmission electron microscopy (STEM) imaging is presented as a method that is sensitive to the oxidation state of cerium ions in CeO2 nanoparticles. This relationship was validated through electron energy loss spectroscopy (EELS), in situ measurements, as well as multislice image simulations. Static displacements caused by the increased ionic radius of Ce(3+) influence the electron channeling process and increase electron scattering to low angles while reducing scatter to high angles. This process manifests itself by reducing the high-angle annular dark field (HAADF) signal intensity while increasing the LAADF signal intensity in close proximity to Ce(3+) ions. This technique can supplement STEM-EELS and in so doing, relax the experimental challenges associated with acquiring oxidation state information at high spatial resolutions. Published by Elsevier B.V.

Probing mesoscopic crystals with electrons: One-step simultaneous inelastic and elastic scattering theory

NASA Astrophysics Data System (ADS)

Nazarov, Vladimir U.; Silkin, Vyacheslav M.; Krasovskii, Eugene E.

2017-12-01

Inelastic scattering of the medium-energy (˜10 -100 eV) electrons underlies the method of the high-resolution electron energy-loss spectroscopy (HREELS), which has been successfully used for decades to characterize pure and adsorbate-covered surfaces of solids. With the emergence of graphene and other quasi-two-dimensional (Q2D) crystals, HREELS could be expected to become the major experimental tool to study this class of materials. We, however, identify a critical flaw in the theoretical picture of the HREELS of Q2D crystals in the context of the inelastic scattering only ("energy-loss functions" formalism), in contrast to its justifiable use for bulk solids and surfaces. The shortcoming is the neglect of the elastic scattering, which we show is inseparable from the inelastic one, and which, affecting the spectra dramatically, must be taken into account for the meaningful interpretation of the experiment. With this motivation, using the time-dependent density functional theory for excitations, we build a theory of the simultaneous inelastic and elastic electron scattering at Q2D crystals. We apply this theory to HREELS of graphene, revealing an effect of the strongly coupled excitation of the π +σ plasmon and elastic diffraction resonances. Our results open a path to the theoretically interpretable study of the excitation processes in crystalline mesoscopic materials by means of HREELS, with its supreme resolution on the meV energy scale, which is far beyond the capacity of the now overwhelmingly used EELS in transmission electron microscopy.

Mapping atomic motions with ultrabright electrons: towards fundamental limits in space-time resolution.

PubMed

Manz, Stephanie; Casandruc, Albert; Zhang, Dongfang; Zhong, Yinpeng; Loch, Rolf A; Marx, Alexander; Hasegawa, Taisuke; Liu, Lai Chung; Bayesteh, Shima; Delsim-Hashemi, Hossein; Hoffmann, Matthias; Felber, Matthias; Hachmann, Max; Mayet, Frank; Hirscht, Julian; Keskin, Sercan; Hada, Masaki; Epp, Sascha W; Flöttmann, Klaus; Miller, R J Dwayne

2015-01-01

The long held objective of directly observing atomic motions during the defining moments of chemistry has been achieved based on ultrabright electron sources that have given rise to a new field of atomically resolved structural dynamics. This class of experiments requires not only simultaneous sub-atomic spatial resolution with temporal resolution on the 100 femtosecond time scale but also has brightness requirements approaching single shot atomic resolution conditions. The brightness condition is in recognition that chemistry leads generally to irreversible changes in structure during the experimental conditions and that the nanoscale thin samples needed for electron structural probes pose upper limits to the available sample or "film" for atomic movies. Even in the case of reversible systems, the degree of excitation and thermal effects require the brightest sources possible for a given space-time resolution to observe the structural changes above background. Further progress in the field, particularly to the study of biological systems and solution reaction chemistry, requires increased brightness and spatial coherence, as well as an ability to tune the electron scattering cross-section to meet sample constraints. The electron bunch density or intensity depends directly on the magnitude of the extraction field for photoemitted electron sources and electron energy distribution in the transverse and longitudinal planes of electron propagation. This work examines the fundamental limits to optimizing these parameters based on relativistic electron sources using re-bunching cavity concepts that are now capable of achieving 10 femtosecond time scale resolution to capture the fastest nuclear motions. This analysis is given for both diffraction and real space imaging of structural dynamics in which there are several orders of magnitude higher space-time resolution with diffraction methods. The first experimental results from the Relativistic Electron Gun for Atomic Exploration (REGAE) are given that show the significantly reduced multiple electron scattering problem in this regime, which opens up micron scale systems, notably solution phase chemistry, to atomically resolved structural dynamics.

Surface intervalley scattering on GaAs(110): Direct observation with picosecond laser photoemission

NASA Astrophysics Data System (ADS)

Haight, R.; Silberman, J. A.

1989-02-01

Angle-resolved laser photoemission investigations of the laser excited GaAs(110) surface have revealed a previously unobserved valley of the C3 unoccupied surface band whose minimum is at X¯ in the surface Brillouin zone. Electron population in this valley increases only as a result of scattering from the directly photoexcited valley at Γ¯. With high momentum resolution, we have isolated the dynamic electron population changes at both Γ¯ and X¯ and deduced the scattering time between the two valleys.

A study of optical scattering methods in laboratory plasma diagnosis

NASA Technical Reports Server (NTRS)

Phipps, C. R., Jr.

1972-01-01

Electron velocity distributions are deduced along axes parallel and perpendicular to the magnetic field in a pulsed, linear Penning discharge in hydrogen by means of a laser Thomson scattering experiment. Results obtained are numerical averages of many individual measurements made at specific space-time points in the plasma evolution. Because of the high resolution in k-space and the relatively low maximum electron density 2 x 10 to the 13th power/cu cm, special techniques were required to obtain measurable scattering signals. These techniques are discussed and experimental results are presented.

Future of Electron Scattering and Diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hall, Ernest; Stemmer, Susanne; Zheng, Haimei

2014-02-25

The ability to correlate the atomic- and nanoscale-structure of condensed matter with physical properties (e.g., mechanical, electrical, catalytic, and optical) and functionality forms the core of many disciplines. Directing and controlling materials at the quantum-, atomic-, and molecular-levels creates enormous challenges and opportunities across a wide spectrum of critical technologies, including those involving the generation and use of energy. The workshop identified next generation electron scattering and diffraction instruments that are uniquely positioned to address these grand challenges. The workshop participants identified four key areas where the next generation of such instrumentation would have major impact: A – Multidimensional Visualizationmore » of Real Materials B – Atomic-scale Molecular Processes C – Photonic Control of Emergence in Quantum Materials D – Evolving Interfaces, Nucleation, and Mass Transport Real materials are comprised of complex three-dimensional arrangements of atoms and defects that directly determine their potential for energy applications. Understanding real materials requires new capabilities for three-dimensional atomic scale tomography and spectroscopy of atomic and electronic structures with unprecedented sensitivity, and with simultaneous spatial and energy resolution. Many molecules are able to selectively and efficiently convert sunlight into other forms of energy, like heat and electric current, or store it in altered chemical bonds. Understanding and controlling such process at the atomic scale require unprecedented time resolution. One of the grand challenges in condensed matter physics is to understand, and ultimately control, emergent phenomena in novel quantum materials that necessitate developing a new generation of instruments that probe the interplay among spin, charge, orbital, and lattice degrees of freedom with intrinsic time- and length-scale resolutions. Molecules and soft matter require imaging and spectroscopy with high spatial resolution without damaging their structure. The strong interaction of electrons with matter allows high-energy electron pulses to gather structural information before a sample is damaged. Electron ScatteringImaging, diffraction, and spectroscopy are the fundamental capabilities of electron-scattering instruments. The DOE BES-funded TEAM (Transmission Electron Aberration-corrected Microscope) project achieved unprecedented sub-atomic spatial resolution in imaging through aberration-corrected transmission electron microscopy. To further advance electron scattering techniques that directly enable groundbreaking science, instrumentation must advance beyond traditional two-dimensional imaging. Advances in temporal resolution, recording the full phase and energy spaces, and improved spatial resolution constitute a new frontier in electron microscopy, and will directly address the BES Grand Challenges, such as to “control the emergent properties that arise from the complex correlations of atomic and electronic constituents” and the “hidden states” “very far away from equilibrium”. Ultrafast methods, such as the pump-probe approach, enable pathways toward understanding, and ultimately controlling, the chemical dynamics of molecular systems and the evolution of complexity in mesoscale and nanoscale systems. Central to understanding how to synthesize and exploit functional materials is having the ability to apply external stimuli (such as heat, light, a reactive flux, and an electrical bias) and to observe the resulting dynamic process in situ and in operando, and under the appropriate environment (e.g., not limited to UHV conditions). To enable revolutionary advances in electron scattering and science, the participants of the workshop recommended three major new instrumental developments: A. Atomic-Resolution Multi-Dimensional Transmission Electron Microscope: This instrument would provide quantitative information over the entire real space, momentum space, and energy space for visualizing dopants, interstitials, and light elements; for imaging localized vibrational modes and the motion of charged particles and vacancies; for correlating lattice, spin, orbital, and charge; and for determining the structure and molecular chemistry of organic and soft matter. The instrument will be uniquely suited to answer fundamental questions in condensed matter physics that require understanding the physical and electronic structure at the atomic scale. Key developments include stable cryogenic capabilities that will allow access to emergent electronic phases, as well as hard/soft interfaces and radiation- sensitive materials. B. Ultrafast Electron Diffraction and Microscopy Instrument: This instrument would be capable of nano-diffraction with 10 fs temporal resolution in stroboscopic mode, and better than 100 fs temporal resolution in single shot mode. The instrument would also achieve single- shot real-space imaging with a spatial/temporal resolution of 10 nm/10 ps, representing a thousand fold improvement over current microscopes. Such a capability would be complementary to x-ray free electron lasers due to the difference in the nature of electron and x-ray scattering, enabling space-time mapping of lattice vibrations and energy transport, facilitating the understanding of molecular dynamics of chemical reactions, the photonic control of emergence in quantum materials, and the dynamics of mesoscopic materials. C. Lab-In-Gap Dynamic Microscope: This instrument would enable quantitative measurements of materials structure, composition, and bonding evolution in technologically relevant environments, including liquids, gases and plasmas, thereby assuring the understanding of structure function relationship at the atomic scale with up to nanosecond temporal resolution. This instrument would employ a versatile, modular sample stage and holder geometry to allow the multi-modal (e.g., optical, thermal, mechanical, electrical, and electrochemical) probing of materials’ functionality in situ and in operando. The electron optics encompasses a pole piece that can accommodate the new stage, differential pumping, detectors, aberration correctors, and other electron optical elements for measurement of materials dynamics. To realize the proposed instruments in a timely fashion, BES should aggressively support research and development of complementary and enabling instruments, including new electron sources, advanced electron optics, new tunable specimen pumps and sample stages, and new detectors. The proposed instruments would have transformative impact on physics, chemistry, materials science, engineering« less

High Temporal and Spatial Resolution Global GPS TEC Observations of the 2015 St. Patrick Day Storm

NASA Astrophysics Data System (ADS)

Vierinen, J.

2015-12-01

High spatiotemperal resolution global GPS TEC measurements of the 2015 St. Patrick's day storm are presented. The high resolution data is useful, as it clearly shows the high latitude convection patterns, the equatorward progression of the auroral region, the tongue of ionization, as well as the increased electron density in the equatorial anomaly region. The measurements are compared with high power large aperture radar and passive radar measurements of coherent and incoherent scatter at Millstone Hill. Regions of fast convection identified in the GPS TEC data are found to coincide with coherent scatter in both radar data. Convection velocities determined from GPS TEC are compared with those obtained from incoherent scatter radar measurements.

Diffraction data of core-shell nanoparticles from an X-ray free electron laser

DOE PAGES

Li, Xuanxuan; Chiu, Chun -Ya; Wang, Hsiang -Ju; ...

2017-04-11

X-ray free-electron lasers provide novel opportunities to conduct single particle analysis on nanoscale particles. Coherent diffractive imaging experiments were performed at the Linac Coherent Light Source (LCLS), SLAC National Laboratory, exposing single inorganic core-shell nanoparticles to femtosecond hard-X-ray pulses. Each facetted nanoparticle consisted of a crystalline gold core and a differently shaped palladium shell. Scattered intensities were observed up to about 7 nm resolution. Analysis of the scattering patterns revealed the size distribution of the samples, which is consistent with that obtained from direct real-space imaging by electron microscopy. Furthermore, scattering patterns resulting from single particles were selected and compiledmore » into a dataset which can be valuable for algorithm developments in single particle scattering research.« less

Effects on electron scattering and resist characteristics using assisting underlayers for e-beam direct write lithography

NASA Astrophysics Data System (ADS)

Thrun, Xaver; Choi, Kang-Hoon; Hanisch, Norbert; Hohle, Christoph; Steidel, Katja; Guerrero, Douglas; Figueiro, Thiago; Bartha, Johann W.

2013-03-01

Resist processing for future technology nodes becomes more and more complex. The resist film thickness is getting thinner and hardmask concepts (trilayer) are needed for reproducible etch transfer into the stack. Additional layers between resist and substrate are influencing the electron scattering in e-beam lithography and may also improve sensitivity and resolution. In this study, bare silicon wafers with different assisting underlayers were processed in a 300 mm CMOS manufacturing environment and were exposed on a 50 keV VISTEC SB3050DW variable-shaped electron beam direct writer at Fraunhofer CNT. The underlayers are organic-inorganic hybrid coatings with different metal additives. The negative-tone resist was evaluated in terms of contrast, sensitivity, resolution and LWR/LER as a function of the stack. The interactions between resist and different assisting underlayers on e-beam direct writing will be investigated. These layers could be used to optimize the trade-off among resolution, LWR and sensitivity in future applications.

Optical Design and Performance of the Taiwan Inelastic X-Ray Scattering Beamline (BL12XU) at SPring-8

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, Y.Q.; Chow, P.; Chen, C.C.

2004-05-12

As part of the Taiwan x-ray facility at SPring-8, we have designed, constructed and commissioned a dedicated Inelastic X-ray Scattering (IXS) beamline (BL12XU) for both resonant and non-resonant experiments on electronic excitations in correlated electron systems with energy resolution from 10-1000 meV. At the Si(555) near-backscattering energy of 9.886 keV, a total energy resolution of 70 meV has been achieved with flux of 1.5x1011 phs/sec/50meV. The optical design and performance of the beamline are presented and discussed with selected results from recent commissioning experiments.

Extracting the redox orbitals in Li battery materials with high-resolution x-ray compton scattering spectroscopy.

PubMed

Suzuki, K; Barbiellini, B; Orikasa, Y; Go, N; Sakurai, H; Kaprzyk, S; Itou, M; Yamamoto, K; Uchimoto, Y; Wang, Yung Jui; Hafiz, H; Bansil, A; Sakurai, Y

2015-02-27

We present an incisive spectroscopic technique for directly probing redox orbitals based on bulk electron momentum density measurements via high-resolution x-ray Compton scattering. Application of our method to spinel Li_{x}Mn_{2}O_{4}, a lithium ion battery cathode material, is discussed. The orbital involved in the lithium insertion and extraction process is shown to mainly be the oxygen 2p orbital. Moreover, the manganese 3d states are shown to experience spatial delocalization involving 0.16±0.05 electrons per Mn site during the battery operation. Our analysis provides a clear understanding of the fundamental redox process involved in the working of a lithium ion battery.

Electron ptychographic phase imaging of light elements in crystalline materials using Wigner distribution deconvolution

DOE PAGES

Yang, Hao; MacLaren, Ian; Jones, Lewys; ...

2017-04-01

Recent development in fast pixelated detector technology has allowed a two dimensional diffraction pattern to be recorded at every probe position of a two dimensional raster scan in a scanning transmission electron microscope (STEM), forming an information-rich four dimensional (4D) dataset. Electron ptychography has been shown to enable efficient coherent phase imaging of weakly scattering objects from a 4D dataset recorded using a focused electron probe, which is optimised for simultaneous incoherent Z-contrast imaging and spectroscopy in STEM. Thus coherent phase contrast and incoherent Z-contrast imaging modes can be efficiently combined to provide a good sensitivity of both light andmore » heavy elements at atomic resolution. Here, we explore the application of electron ptychography for atomic resolution imaging of strongly scattering crystalline specimens, and present experiments on imaging crystalline specimens including samples containing defects, under dynamical channelling conditions using an aberration corrected microscope. A ptychographic reconstruction method called Wigner distribution deconvolution (WDD) was implemented. Our experimental results and simulation results suggest that ptychography provides a readily interpretable phase image and great sensitivity for imaging light elements at atomic resolution in relatively thin crystalline materials.« less

Source of coherent short wavelength radiation

DOEpatents

Villa, Francesco

1990-01-01

An apparatus for producing coherent radiation ranging from X-rays to the far ultraviolet (i.e., 1 Kev to 10 eV) utilizing the Compton scattering effect. A photon beam from a laser is scattered on a high energy electron bunch from a pulse power linac. The short wavelength radiation produced by such scattering has sufficient intensity and spatial coherence for use in high resolution applications such as microscopy.

Determination of scattering structures from spatial coherence measurements.

PubMed

Zarubin, A M

1996-03-01

A new method of structure determination and microscopic imaging with short-wavelength radiations (charged particles, X-rays, neutrons), based on measurements of the modulus and the phase of the degree of spatial coherence of the scattered radiation, is developed. The underlying principle of the method--transfer of structural information about the scattering potential via spatial coherence of the secondary (scattering) source of radiation formed by this potential--is expressed by the generalization of the van Cittert-Zernike theorem to wave and particle scattering [A.M. Zarubin, Opt. Commun. 100 (1993) 491; Opt. Commun. 102 (1993) 543]. Shearing interferometric techniques are proposed for implementing the above measurements; the limits of spatial resolution attainable by reconstruction of the absolute square of a 3D scattering potential and its 2D projections from the measurements are analyzed. It is shown theoretically that 3D imaging with atomic resolution can be realized in a "synthetic aperture" electron or ion microscope and that a 3D resolution of about 6 nm can be obtained with a "synthetic aperture" X-ray microscope. A proof-of-principle optical experiment is presented.

High-resolution quantitative determination of dielectric function by using scattering scanning near-field optical microscopy

PubMed Central

Tranca, D. E.; Stanciu, S. G.; Hristu, R.; Stoichita, C.; Tofail, S. A. M.; Stanciu, G. A.

2015-01-01

A new method for high-resolution quantitative measurement of the dielectric function by using scattering scanning near-field optical microscopy (s-SNOM) is presented. The method is based on a calibration procedure that uses the s-SNOM oscillating dipole model of the probe-sample interaction and quantitative s-SNOM measurements. The nanoscale capabilities of the method have the potential to enable novel applications in various fields such as nano-electronics, nano-photonics, biology or medicine. PMID:26138665

Alignment error envelopes for single particle analysis.

PubMed

Jensen, G J

2001-01-01

To determine the structure of a biological particle to high resolution by electron microscopy, image averaging is required to combine information from different views and to increase the signal-to-noise ratio. Starting from the number of noiseless views necessary to resolve features of a given size, four general factors are considered that increase the number of images actually needed: (1) the physics of electron scattering introduces shot noise, (2) thermal motion and particle inhomogeneity cause the scattered electrons to describe a mixture of structures, (3) the microscope system fails to usefully record all the information carried by the scattered electrons, and (4) image misalignment leads to information loss through incoherent averaging. The compound effect of factors 2-4 is approximated by the product of envelope functions. The problem of incoherent image averaging is developed in detail through derivation of five envelope functions that account for small errors in 11 "alignment" parameters describing particle location, orientation, defocus, magnification, and beam tilt. The analysis provides target error tolerances for single particle analysis to near-atomic (3.5 A) resolution, and this prospect is shown to depend critically on image quality, defocus determination, and microscope alignment. Copyright 2001 Academic Press.

Role of the kinematics of probing electrons in electron energy-loss spectroscopy of solid surfaces

NASA Astrophysics Data System (ADS)

Nazarov, V. U.; Silkin, V. M.; Krasovskii, E. E.

2016-01-01

Inelastic scattering of electrons incident on a solid surface is determined by two properties: (i) electronic response of the target system and (ii) the detailed quantum-mechanical motion of the projectile electron inside and in the vicinity of the target. We emphasize the equal importance of the second ingredient, pointing out the fundamental limitations of the conventionally used theoretical description of the electron energy-loss spectroscopy (EELS) in terms of the "energy-loss functions." Our approach encompasses the dipole and impact scattering as specific cases, with the emphasis on the quantum-mechanical treatment of the probe electron. Applied to the high-resolution EELS of Ag surface, our theory largely agrees with recent experiments, while some instructive exceptions are rationalized.

Prospects of high-resolution resonant X-ray inelastic scattering studies on solid materials, liquids and gases at diffraction-limited storage rings.

PubMed

Schmitt, Thorsten; de Groot, Frank M F; Rubensson, Jan Erik

2014-09-01

The spectroscopic technique of resonant inelastic X-ray scattering (RIXS) will particularly profit from immensely improved brilliance of diffraction-limited storage rings (DLSRs). In RIXS one measures the intensities of excitations as a function of energy and momentum transfer. DLSRs will allow for pushing the achievable energy resolution, signal intensity and the sampled spot size to new limits. With RIXS one nowadays probes a broad range of electronic systems reaching from simple molecules to complex materials displaying phenomena like peculiar magnetism, two-dimensional electron gases, superconductivity, photovoltaic energy conversion and heterogeneous catalysis. In this article the types of improved RIXS studies that will become possible with X-ray beams from DLSRs are envisioned.

Electron-excited energy dispersive x-ray spectrometry in the variable pressure scanning electron microscope (EDS/VPSEM): it's not microanalysis anymore!

NASA Astrophysics Data System (ADS)

Newbury, Dale E.; Ritchie, Nicholas W. M.

2015-10-01

X-ray spectra suffer significantly degraded spatial resolution when measured in the variable-pressure scanning electron microscope (VPSEM, chamber pressure 1 Pa to 2500 Pa) as compared to highvacuum SEM (operating pressure < 10 mPa). Depending on the gas path length, electrons that are scattered hundreds of micrometers outside the focused beam can contribute 90% or more of the measured spectrum. Monte Carlo electron trajectory simulation, available in NIST DTSA-II, models the gas scattering and simulates mixed composition targets, e.g., particle on substrate. The impact of gas scattering at the major (C > 0.1 mass fraction), minor (0.01 <= C <= 0.1), and trace (C < 0.01) constituent levels can be estimated. NIST DTSA-II for Java-platforms is available free at: http://www.cstl.nist.gov/div837/837.02/epq/dtsa2/index.html).

Magnetic effects in the paraxial regime of elastic electron scattering

NASA Astrophysics Data System (ADS)

Edström, Alexander; Lubk, Axel; Rusz, Ján

2016-11-01

Motivated by a recent claim [Phys. Rev. Lett. 116, 127203 (2016), 10.1103/PhysRevLett.116.127203] that electron vortex beams can be used to image magnetism at the nanoscale in elastic scattering experiments, using transmission electron microscopy, a comprehensive computational study is performed to study magnetic effects in the paraxial regime of elastic electron scattering in magnetic solids. Magnetic interactions from electron vortex beams, spin polarized electron beams, and beams with phase aberrations are considered, as they pass through ferromagnetic FePt or antiferromagnetic LaMnAsO. The magnetic signals are obtained by comparing the intensity over a disk in the diffraction plane for beams with opposite angular momentum or aberrations. The strongest magnetic signals are obtained from vortex beams with large orbital angular momentum, where relative magnetic signals above 10-3 are indicated for 10 ℏ orbital angular momentum, meaning that relative signals of one percent could be expected with the even larger orbital angular momenta, which have been produced in experimental setups. All results indicate that beams with low acceleration voltage and small convergence angles yield stronger magnetic signals, which is unfortunately problematic for the possibility of high spatial resolution imaging. Nevertheless, under atomic resolution conditions, relative magnetic signals in the order of 10-4 are demonstrated, corresponding to an increase with one order of magnitude compared to previous work.

Detecting non-maxwellian electron velocity distributions at JET by high resolution Thomson scattering.

PubMed

Beausang, K V; Prunty, S L; Scannell, R; Beurskens, M N; Walsh, M J; de la Luna, E

2011-03-01

The present work is motivated by a long standing discrepancy between the electron temperature measurements of Thomson scattering (TS) and electron cyclotron emission (ECE) diagnostics for plasmas with strong auxiliary heating observed at both JET and TFTR above 6–7 keV, where in some cases the ECE electron temperature measurements can be 15%–20% higher than the TS measurements. Recent analysis based on ECE results at JET has shown evidence of distortions to the Maxwellian electron velocity distribution and a correlation with the TS and ECE discrepancies has been suggested. In this paper, a technique to determine the presence of non-Maxwellian behavior using TS diagnostics is outlined. The difficulties and limitations of modern TS system designs to determine the electron velocity distribution are also discussed. It is demonstrated that small deviations such as those suggested by previous ECE analysis could be potentially detected, depending on the spectral layout of the TS polychromators. The spectral layout of the JET high resolution Thomson scattering system is such that it could be used to determine these deviations between 1 and 6 keV, and the results presented here indicate that no evidence of non-Maxwellian behavior is observed in this range. In this paper, a modification to the current polychromator design is proposed, allowing non-Maxwellian distortions to be detected up to at least 10 keV.

Hypernuclear Spectroscopy with Electron Beam at JLab Hall C

NASA Astrophysics Data System (ADS)

Fujii, Y.; Chiba, A.; Doi, D.; Gogami, T.; Hashimoto, O.; Kanda, H.; Kaneta, M.; Kawama, D.; Maeda, K.; Maruta, T.; Matsumura, A.; Nagao, S.; Nakamura, S. N.; Shichijo, A.; Tamura, H.; Taniya, N.; Yamamoto, T.; Yokota, K.; Kato, S.; Sato, Y.; Takahashi, T.; Noumi, H.; Motoba, T.; Hiyama, E.; Albayrak, I.; Ates, O.; Chen, C.; Christy, M.; Keppel, C.; Kohl, M.; Li, Y.; Liyanage, A.; Tang, L.; Walton, T.; Ye, Z.; Yuan, L.; Zhu, L.; Baturin, P.; Boeglin, W.; Dhamija, S.; Markowitz, P.; Raue, B.; Reinhold, J.; Hungerford, Ed. V.; Ent, R.; Fenker, H.; Gaskell, D.; Horn, T.; Jones, M.; Smith, G.; Vulcan, W.; Wood, S. A.; Johnston, C.; Simicevic, N.; Wells, S.; Samanta, C.; Hu, B.; Shen, J.; Wang, W.; Zhang, X.; Zhang, Y.; Feng, J.; Fu, Y.; Zhou, J.; Zhou, S.; Jiang, Y.; Lu, H.; Yan, X.; Ye, Y.; Gan, L.; Ahmidouch, A.; Danagoulian, S.; Gasparian, A.; Elaasar, M.; Wesselmann, F. R.; Asaturyan, A.; Margaryan, A.; Mkrtchyan, A.; Mkrtchyan, H.; Tadevosyan, V.; Androic, D.; Furic, M.; Petkovic, T.; Seva, T.; Niculescu, G.; Niculescu, I.; López, V. M. Rodríguez; Cisbani, E.; Cusanno, F.; Garibaldi, F.; Uuciuoli, G. M.; de Leo, R.; Maronne, S.

2010-10-01

Hypernuclear spectroscopy with electron beam at JLab Hall C has been studied since 2000. The first experiment, JLab E89-009, demonstrated the possibility of the (e,e'K+) reaction for hypernuclear spectroscopy by achieving an energy resolution of better than 1 MeV (FWHM). The second experiment, JLab E01-011 employed a newly constructed high resolution kaon spectrometer and introduced a vertically tilted electron arm setup to avoid electrons from bremsstrahlung and Moeller scattering. The setup allowed us to have 10 times yield rate and 4 times better signal to accidental ratio with expected energy resolution of 400 keV (FWHM). The third experiment, JLab E05-11B will be performed in 2009 with employing newly constructed high resolution electron spectrometer and a new charge-separation magnet. With the fully customized third generation experimental setup, we can study a variety of targets up to medium-heavy ones such as 52Cr.

Hypernuclear Spectroscopy with Electron Beam at JLab Hall C

NASA Astrophysics Data System (ADS)

Fujii, Y.; Chiba, A.; Doi, D.; Gogami, T.; Hashimoto, O.; Kanda, H.; Kaneta, M.; Kawama, D.; Maeda, K.; Maruta, T.; Matsumura, A.; Nagao, S.; Nakamura, S. N.; Shichijo, A.; Tamura, H.; Taniya, N.; Yamamoto, T.; Yokota, K.; Kato, S.; Sato, Y.; Takahashi, T.; Noumi, H.; Motoba, T.; Hiyama, E.; Albayrak, I.; Ates, O.; Chen, C.; Christy, M.; Keppel, C.; Kohl, M.; Li, Y.; Liyanage, A.; Tang, L.; Walton, T.; Ye, Z.; Yuan, L.; Zhu, L.; Baturin, P.; Boeglin, W.; Dhamija, S.; Markowitz, P.; Raue, B.; Reinhold, J.; Hungerford, Ed. V.; Ent, R.; Fenker, H.; Gaskell, D.; Horn, T.; Jones, M.; Smith, G.; Vulcan, W.; Wood, S. A.; Johnston, C.; Simicevic, N.; Wells, S.; Samanta, C.; Hu, B.; Shen, J.; Wang, W.; Zhang, X.; Zhang, Y.; Feng, J.; Fu, Y.; Zhou, J.; Zhou, S.; Jiang, Y.; Lu, H.; Yan, X.; Ye, Y.; Gan, L.; Ahmidouch, A.; Danagoulian, S.; Gasparian, A.; Elaasar, M.; Wesselmann, F. R.; Asaturyan, A.; Margaryan, A.; Mkrtchyan, A.; Mkrtchyan, H.; Tadevosyan, V.; Androic, D.; Furic, M.; Petkovic, T.; Seva, T.; Niculescu, G.; Niculescu, I.; Rodríguez López, V. M.; Cisbani, E.; Cusanno, F.; Garibaldi, F.; Uuciuoli, G. M.; de Leo, R.; Maronne, S.

Hypernuclear spectroscopy with electron beam at JLab Hall C has been studied since 2000. The first experiment, JLab E89-009, demonstrated the possibility of the (e, e‧ K+) reaction for hypernuclear spectroscopy by achieving an energy resolution of better than 1 MeV (FWHM). The second experiment, JLab E01-011 employed a newly constructed high resolution kaon spectrometer and introduced a vertically tilted electron arm setup to avoid electrons from bremsstrahlung and Moeller scattering. The setup allowed us to have 10 times yield rate and 4 times better signal to accidental ratio with expected energy resolution of 400 keV (FWHM). The third experiment, JLab E05-115 will be performed in 2009 with employing newly constructed high resolution electron spectrometer and a new charge-separation magnet. With the fully customized third generation experimental setup, we can study a variety of targets up to medium-heavy ones such as 52Cr.

Ultrafast electron-optical phonon scattering and quasiparticle lifetime in CVD-grown graphene.

PubMed

Shang, Jingzhi; Yu, Ting; Lin, Jianyi; Gurzadyan, Gagik G

2011-04-26

Ultrafast quasiparticle dynamics in graphene grown by chemical vapor deposition (CVD) has been studied by UV pump/white-light probe spectroscopy. Transient differential transmission spectra of monolayer graphene are observed in the visible probe range (400-650 nm). Kinetics of the quasiparticle (i.e., low-energy single-particle excitation with renormalized energy due to electron-electron Coulomb, electron-optical phonon (e-op), and optical phonon-acoustic phonon (op-ap) interactions) was monitored with 50 fs resolution. Extending the probe range to near-infrared, we find the evolution of quasiparticle relaxation channels from monoexponential e-op scattering to double exponential decay due to e-op and op-ap scattering. Moreover, quasiparticle lifetimes of mono- and randomly stacked graphene films are obtained for the probe photon energies continuously from 1.9 to 2.3 eV. Dependence of quasiparticle decay rate on the probe energy is linear for 10-layer stacked graphene films. This is due to the dominant e-op intervalley scattering and the linear density of states in the probed electronic band. A dimensionless coupling constant W is derived, which characterizes the scattering strength of quasiparticles by lattice points in graphene.

Limiting factors in atomic resolution cryo electron microscopy: No simple tricks

PubMed Central

Zhang, Xing; Zhou, Z. Hong

2013-01-01

To bring cryo electron microscopy (cryoEM) of large biological complexes to atomic resolution, several factors – in both cryoEM image acquisition and 3D reconstruction – that may be neglected at low resolution become significantly limiting. Here we present thorough analyses of four limiting factors: (a) electron-beam tilt, (b) inaccurate determination of defocus values, (c) focus gradient through particles, and (d) particularly for large particles, dynamic (multiple) scattering of electrons. We also propose strategies to cope with these factors: (a) the divergence and direction tilt components of electron-beam tilt could be reduced by maintaining parallel illumination and by using a coma-free alignment procedure, respectively. Moreover, the effect of all beam tilt components, including spiral tilt, could be eliminated by use of a spherical aberration corrector. (b) More accurate measurement of defocus value could be obtained by imaging areas adjacent to the target area at high electron dose and by measuring the image shift induced by tilting the electron beam. (c) Each known Fourier coefficient in the Fourier transform of a cryoEM image is the sum of two Fourier coefficients of the 3D structure, one on each of two curved ‘characteristic surfaces’ in 3D Fourier space. We describe a simple model-based iterative method that could recover these two Fourier coefficients on the two characteristic surfaces. (d) The effect of dynamic scattering could be corrected by deconvolution of a transfer function. These analyses and our proposed strategies offer useful guidance for future experimental designs targeting atomic resolution cryoEM reconstruction. PMID:21627992

Atomically Thin Graphene Windows That Enable High Contrast Electron Microscopy without a Specimen Vacuum Chamber.

PubMed

Han, Yimo; Nguyen, Kayla X; Ogawa, Yui; Park, Jiwoong; Muller, David A

2016-12-14

Scanning electron microscopes (SEMs) require a high vacuum environment to generate and shape an electron beam for imaging; however, the vacuum conditions greatly limit the nature of specimens that can be examined. From a purely scattering physics perspective, it is not necessary to place the specimen inside the vacuum chamber-the mean free paths (MFPs) for electron scattering in air at typical SEM beam voltages are 50-100 μm. This is the idea behind the airSEM, which removes the specimen vacuum chamber from the SEM and places the sample in air. The thickness of the gas layer is less than a MFP from an electron-transparent window to preserve the shape and resolution of the incident beam, resulting in comparable imaging quality to an all-vacuum SEM. Present silicon nitride windows scatter far more strongly than the air gap and are currently the contrast and resolution limiting factor in the airSEM. Graphene windows have been used previously to wrap or seal samples in vacuum for imaging. Here we demonstrate the use of a robust bilayer graphene window for sealing the electron optics from the room environment, providing an electron transparent window with only a 2% drop in contrast. There is a 5-fold-increase in signal/noise ratio for imaging compared to multi-MFP-thick silicon nitride windows, enabling high contrast in backscattered, transmission, and surface imaging modes for the new airSEM geometry.

Towards a Resolution of the Proton Form Factor Problem: New Electron and Positron Scattering Data

NASA Astrophysics Data System (ADS)

Adikaram, D.; Rimal, D.; Weinstein, L. B.; Raue, B.; Khetarpal, P.; Bennett, R. P.; Arrington, J.; Brooks, W. K.; Adhikari, K. P.; Afanasev, A. V.; Amaryan, M. J.; Anderson, M. D.; Anefalos Pereira, S.; Avakian, H.; Ball, J.; Battaglieri, M.; Bedlinskiy, I.; Biselli, A. S.; Bono, J.; Boiarinov, S.; Briscoe, W. J.; Burkert, V. D.; Carman, D. S.; Careccia, S.; Celentano, A.; Chandavar, S.; Charles, G.; Colaneri, L.; Cole, P. L.; Contalbrigo, M.; Crede, V.; D'Angelo, A.; Dashyan, N.; De Vita, R.; De Sanctis, E.; Deur, A.; Djalali, C.; Dodge, G. E.; Dupre, R.; Egiyan, H.; El Alaoui, A.; El Fassi, L.; Elouadrhiri, L.; Eugenio, P.; Fedotov, G.; Fegan, S.; Filippi, A.; Fleming, J. A.; Fradi, A.; Garillon, B.; Gilfoyle, G. P.; Giovanetti, K. L.; Girod, F. X.; Goetz, J. T.; Gohn, W.; Golovatch, E.; Gothe, R. W.; Griffioen, K. A.; Guegan, B.; Guidal, M.; Guo, L.; Hafidi, K.; Hakobyan, H.; Hanretty, C.; Harrison, N.; Hattawy, M.; Hicks, K.; Holtrop, M.; Hughes, S. M.; Hyde, C. E.; Ilieva, Y.; Ireland, D. G.; Ishkhanov, B. S.; Jenkins, D.; Jiang, H.; Jo, H. S.; Joo, K.; Joosten, S.; Kalantarians, N.; Keller, D.; Khandaker, M.; Kim, A.; Kim, W.; Klein, A.; Klein, F. J.; Koirala, S.; Kubarovsky, V.; Kuhn, S. E.; Livingston, K.; Lu, H. Y.; MacGregor, I. J. D.; Markov, N.; Mattione, P.; Mayer, M.; McKinnon, B.; Mestayer, M. D.; Meyer, C. A.; Mirazita, M.; Mokeev, V.; Montgomery, R. A.; Moody, C. I.; Moutarde, H.; Movsisyan, A.; Camacho, C. Munoz; Nadel-Turonski, P.; Niccolai, S.; Niculescu, G.; Osipenko, M.; Ostrovidov, A. I.; Park, K.; Pasyuk, E.; Peña, C.; Pisano, S.; Pogorelko, O.; Price, J. W.; Procureur, S.; Prok, Y.; Protopopescu, D.; Puckett, A. J. R.; Ripani, M.; Rizzo, A.; Rosner, G.; Rossi, P.; Roy, P.; Sabatié, F.; Salgado, C.; Schott, D.; Schumacher, R. A.; Seder, E.; Sharabian, Y. G.; Simonyan, A.; Skorodumina, I.; Smith, E. S.; Smith, G. D.; Sober, D. I.; Sokhan, D.; Sparveris, N.; Stepanyan, S.; Stoler, P.; Strauch, S.; Sytnik, V.; Taiuti, M.; Tian, Ye; Trivedi, A.; Ungaro, M.; Voskanyan, H.; Voutier, E.; Walford, N. K.; Watts, D. P.; Wei, X.; Wood, M. H.; Zachariou, N.; Zana, L.; Zhang, J.; Zhao, Z. W.; Zonta, I.; CLAS Collaboration

2015-02-01

There is a significant discrepancy between the values of the proton electric form factor, GEp, extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of GEp from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide range in virtual photon polarization (ɛ ) and momentum transfer (Q2) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing ɛ at Q2=1.45 GeV2 . This measurement is consistent with the size of the form factor discrepancy at Q2≈1.75 GeV2 and with hadronic calculations including nucleon and Δ intermediate states, which have been shown to resolve the discrepancy up to 2 - 3 GeV2 .

Quantum imaging with incoherently scattered light from a free-electron laser

NASA Astrophysics Data System (ADS)

Schneider, Raimund; Mehringer, Thomas; Mercurio, Giuseppe; Wenthaus, Lukas; Classen, Anton; Brenner, Günter; Gorobtsov, Oleg; Benz, Adrian; Bhatti, Daniel; Bocklage, Lars; Fischer, Birgit; Lazarev, Sergey; Obukhov, Yuri; Schlage, Kai; Skopintsev, Petr; Wagner, Jochen; Waldmann, Felix; Willing, Svenja; Zaluzhnyy, Ivan; Wurth, Wilfried; Vartanyants, Ivan A.; Röhlsberger, Ralf; von Zanthier, Joachim

2018-02-01

The advent of accelerator-driven free-electron lasers (FEL) has opened new avenues for high-resolution structure determination via diffraction methods that go far beyond conventional X-ray crystallography methods. These techniques rely on coherent scattering processes that require the maintenance of first-order coherence of the radiation field throughout the imaging procedure. Here we show that higher-order degrees of coherence, displayed in the intensity correlations of incoherently scattered X-rays from an FEL, can be used to image two-dimensional objects with a spatial resolution close to or even below the Abbe limit. This constitutes a new approach towards structure determination based on incoherent processes, including fluorescence emission or wavefront distortions, generally considered detrimental for imaging applications. Our method is an extension of the landmark intensity correlation measurements of Hanbury Brown and Twiss to higher than second order, paving the way towards determination of structure and dynamics of matter in regimes where coherent imaging methods have intrinsic limitations.

High time resolved electron temperature measurements by using the multi-pass Thomson scattering system in GAMMA 10/PDX.

PubMed

Yoshikawa, Masayuki; Yasuhara, Ryo; Ohta, Koichi; Chikatsu, Masayuki; Shima, Yoriko; Kohagura, Junko; Sakamoto, Mizuki; Nakashima, Yousuke; Imai, Tsuyoshi; Ichimura, Makoto; Yamada, Ichihiro; Funaba, Hisamichi; Minami, Takashi

2016-11-01

High time resolved electron temperature measurements are useful for fluctuation study. A multi-pass Thomson scattering (MPTS) system is proposed for the improvement of both increasing the TS signal intensity and time resolution. The MPTS system in GAMMA 10/PDX has been constructed for enhancing the Thomson scattered signals for the improvement of measurement accuracy. The MPTS system has a polarization-based configuration with an image relaying system. We optimized the image relaying optics for improving the multi-pass laser confinement and obtaining the stable MPTS signals over ten passing TS signals. The integrated MPTS signals increased about five times larger than that in the single pass system. Finally, time dependent electron temperatures were obtained in MHz sampling.

Whole-cell imaging of the budding yeast Saccharomyces cerevisiae by high-voltage scanning transmission electron tomography.

PubMed

Murata, Kazuyoshi; Esaki, Masatoshi; Ogura, Teru; Arai, Shigeo; Yamamoto, Yuta; Tanaka, Nobuo

2014-11-01

Electron tomography using a high-voltage electron microscope (HVEM) provides three-dimensional information about cellular components in sections thicker than 1 μm, although in bright-field mode image degradation caused by multiple inelastic scattering of transmitted electrons limit the attainable resolution. Scanning transmission electron microscopy (STEM) is believed to give enhanced contrast and resolution compared to conventional transmission electron microscopy (CTEM). Samples up to 1 μm in thickness have been analyzed with an intermediate-voltage electron microscope because inelastic scattering is not a critical limitation, and probe broadening can be minimized. Here, we employed STEM at 1 MeV high-voltage to extend the useful specimen thickness for electron tomography, which we demonstrate by a seamless tomographic reconstruction of a whole, budding Saccharomyces cerevisiae yeast cell, which is ~3 μm in thickness. High-voltage STEM tomography, especially in the bright-field mode, demonstrated sufficiently enhanced contrast and intensity, compared to CTEM tomography, to permit segmentation of major organelles in the whole cell. STEM imaging also reduced specimen shrinkage during tilt-series acquisition. The fidelity of structural preservation was limited by cytoplasmic extraction, and the spatial resolution was limited by the relatively large convergence angle of the scanning probe. However, the new technique has potential to solve longstanding problems of image blurring in biological specimens beyond 1 μm in thickness, and may facilitate new research in cellular structural biology. Copyright © 2014 Elsevier B.V. All rights reserved.

Monte Carlo simulation for scanning technique with scattering foil free electron beam: A proof of concept study

PubMed Central

Sung, Wonmo; Park, Jong In; Kim, Jung-in; Carlson, Joel; Ye, Sung-Joon

2017-01-01

This study investigated the potential of a newly proposed scattering foil free (SFF) electron beam scanning technique for the treatment of skin cancer on the irregular patient surfaces using Monte Carlo (MC) simulation. After benchmarking of the MC simulations, we removed the scattering foil to generate SFF electron beams. Cylindrical and spherical phantoms with 1 cm boluses were generated and the target volume was defined from the surface to 5 mm depth. The SFF scanning technique with 6 MeV electrons was simulated using those phantoms. For comparison, volumetric modulated arc therapy (VMAT) plans were also generated with two full arcs and 6 MV photon beams. When the scanning resolution resulted in a larger separation between beams than the field size, the plan qualities were worsened. In the cylindrical phantom with a radius of 10 cm, the conformity indices, homogeneity indices and body mean doses of the SFF plans (scanning resolution = 1°) vs. VMAT plans were 1.04 vs. 1.54, 1.10 vs. 1.12 and 5 Gy vs. 14 Gy, respectively. Those of the spherical phantom were 1.04 vs. 1.83, 1.08 vs. 1.09 and 7 Gy vs. 26 Gy, respectively. The proposed SFF plans showed superior dose distributions compared to the VMAT plans. PMID:28493940

Monte Carlo simulation for scanning technique with scattering foil free electron beam: A proof of concept study.

PubMed

Sung, Wonmo; Park, Jong In; Kim, Jung-In; Carlson, Joel; Ye, Sung-Joon; Park, Jong Min

2017-01-01

This study investigated the potential of a newly proposed scattering foil free (SFF) electron beam scanning technique for the treatment of skin cancer on the irregular patient surfaces using Monte Carlo (MC) simulation. After benchmarking of the MC simulations, we removed the scattering foil to generate SFF electron beams. Cylindrical and spherical phantoms with 1 cm boluses were generated and the target volume was defined from the surface to 5 mm depth. The SFF scanning technique with 6 MeV electrons was simulated using those phantoms. For comparison, volumetric modulated arc therapy (VMAT) plans were also generated with two full arcs and 6 MV photon beams. When the scanning resolution resulted in a larger separation between beams than the field size, the plan qualities were worsened. In the cylindrical phantom with a radius of 10 cm, the conformity indices, homogeneity indices and body mean doses of the SFF plans (scanning resolution = 1°) vs. VMAT plans were 1.04 vs. 1.54, 1.10 vs. 1.12 and 5 Gy vs. 14 Gy, respectively. Those of the spherical phantom were 1.04 vs. 1.83, 1.08 vs. 1.09 and 7 Gy vs. 26 Gy, respectively. The proposed SFF plans showed superior dose distributions compared to the VMAT plans.

Prospects of high-resolution resonant X-ray inelastic scattering studies on solid materials, liquids and gases at diffraction-limited storage rings

PubMed Central

Schmitt, Thorsten; de Groot, Frank M. F.; Rubensson, Jan-Erik

2014-01-01

The spectroscopic technique of resonant inelastic X-ray scattering (RIXS) will particularly profit from immensely improved brilliance of diffraction-limited storage rings (DLSRs). In RIXS one measures the intensities of excitations as a function of energy and momentum transfer. DLSRs will allow for pushing the achievable energy resolution, signal intensity and the sampled spot size to new limits. With RIXS one nowadays probes a broad range of electronic systems reaching from simple molecules to complex materials displaying phenomena like peculiar magnetism, two-dimensional electron gases, superconductivity, photovoltaic energy conversion and heterogeneous catalysis. In this article the types of improved RIXS studies that will become possible with X-ray beams from DLSRs are envisioned. PMID:25177995

Mapping momentum-dependent electron-phonon coupling and nonequilibrium phonon dynamics with ultrafast electron diffuse scattering

NASA Astrophysics Data System (ADS)

Stern, Mark J.; René de Cotret, Laurent P.; Otto, Martin R.; Chatelain, Robert P.; Boisvert, Jean-Philippe; Sutton, Mark; Siwick, Bradley J.

2018-04-01

Despite their fundamental role in determining material properties, detailed momentum-dependent information on the strength of electron-phonon and phonon-phonon coupling (EPC and PPC, respectively) across the entire Brillouin zone has remained elusive. Here we demonstrate that ultrafast electron diffuse scattering (UEDS) directly provides such information. By exploiting symmetry-based selection rules and time resolution, scattering from different phonon branches can be distinguished even without energy resolution. Using graphite as a model system, we show that UEDS patterns map the relative EPC and PPC strength through their profound sensitivity to photoinduced changes in phonon populations. We measure strong EPC to the K -point TO phonon of A1' symmetry (K -A1' ) and along the entire TO branch between Γ -K , not only to the Γ -E2 g phonon. We also determine that the subsequent phonon relaxation of these strongly coupled optical phonons involve three stages: decay via several identifiable channels to TA and LA phonons (1 -2 ps), intraband thermalization of the non-equilibrium TA/LA phonon populations (30 -40 ps) and interband relaxation of the TA/LA modes (115 ps). Combining UEDS with ultrafast angle-resolved photoelectron spectroscopy will yield a complete picture of the dynamics within and between electron and phonon subsystems, helping to unravel complex phases in which the intertwined nature of these systems has a strong influence on emergent properties.

High resolution Thomson scattering system for steady-state linear plasma sources

NASA Astrophysics Data System (ADS)

Lee, K. Y.; Lee, K. I.; Kim, J. H.; Lho, T.

2018-01-01

The high resolution Thomson scattering system with 63 points along a 25 mm line measures the radial electron temperature (Te) and its density (ne) in an argon plasma. By using a DC arc source with lanthanum hexaboride (LaB6) electrode, plasmas with electron temperature of over 5 eV and densities of 1.5 × 1019 m-3 have been measured. The system uses a frequency doubled (532 nm) Nd:YAG laser with 0.25 J/pulse at 20 Hz. The scattered light is collected and sent to a triple-grating spectrometer via optical-fibers, where images are recorded by an intensified charge coupled device (ICCD) camera. Although excellent in stray-light reduction, a disadvantage comes with its relatively low optical transmission and in sampling a tiny scattering volume. Thus requires accumulating multitude of images. In order to improve photon statistics, pixel binning in the ICCD camera as well as enlarging the intermediate slit-width inside the triple-grating spectrometer has been exploited. In addition, the ICCD camera capture images at 40 Hz while the laser is at 20 Hz. This operation mode allows us to alternate between background and scattering shot images. By image subtraction, influences from the plasma background are effectively taken out. Maximum likelihood estimation that uses a parameter sweep finds best fitting parameters Te and ne with the incoherent scattering spectrum.

High resolution Thomson scattering system for steady-state linear plasma sources.

PubMed

Lee, K Y; Lee, K I; Kim, J H; Lho, T

2018-01-01

The high resolution Thomson scattering system with 63 points along a 25 mm line measures the radial electron temperature (T e ) and its density (n e ) in an argon plasma. By using a DC arc source with lanthanum hexaboride (LaB 6 ) electrode, plasmas with electron temperature of over 5 eV and densities of 1.5 × 10 19 m -3 have been measured. The system uses a frequency doubled (532 nm) Nd:YAG laser with 0.25 J/pulse at 20 Hz. The scattered light is collected and sent to a triple-grating spectrometer via optical-fibers, where images are recorded by an intensified charge coupled device (ICCD) camera. Although excellent in stray-light reduction, a disadvantage comes with its relatively low optical transmission and in sampling a tiny scattering volume. Thus requires accumulating multitude of images. In order to improve photon statistics, pixel binning in the ICCD camera as well as enlarging the intermediate slit-width inside the triple-grating spectrometer has been exploited. In addition, the ICCD camera capture images at 40 Hz while the laser is at 20 Hz. This operation mode allows us to alternate between background and scattering shot images. By image subtraction, influences from the plasma background are effectively taken out. Maximum likelihood estimation that uses a parameter sweep finds best fitting parameters T e and n e with the incoherent scattering spectrum.

Acquisition parameters optimization of a transmission electron forward scatter diffraction system in a cold-field emission scanning electron microscope for nanomaterials characterization.

PubMed

Brodusch, Nicolas; Demers, Hendrix; Trudeau, Michel; Gauvin, Raynald

2013-01-01

Transmission electron forward scatter diffraction (t-EFSD) is a new technique providing crystallographic information with high resolution on thin specimens by using a conventional electron backscatter diffraction (EBSD) system in a scanning electron microscope. In this study, the impact of tilt angle, working distance, and detector distance on the Kikuchi pattern quality were investigated in a cold-field emission scanning electron microscope (CFE-SEM). We demonstrated that t-EFSD is applicable for tilt angles ranging from -20° to -40°. Working distance (WD) should be optimized for each material by choosing the WD for which the EBSD camera screen illumination is the highest, as the number of detected electrons on the screen is directly dependent on the scattering angle. To take advantage of the best performances of the CFE-SEM, the EBSD camera should be close to the sample and oriented towards the bottom to increase forward scattered electron collection efficiency. However, specimen chamber cluttering and beam/mechanical drift are important limitations in the CFE-SEM used in this work. Finally, the importance of t-EFSD in materials science characterization was illustrated through three examples of phase identification and orientation mapping. © Wiley Periodicals, Inc.

Comparative study of inelastic squared form factors of the vibronic states of B 1Σu+ , C 1Πu , and E F 1Σg+ for molecular hydrogen: Inelastic x-ray and electron scattering

NASA Astrophysics Data System (ADS)

Xu, Long-Quan; Kang, Xu; Peng, Yi-Geng; Xu, Xin; Liu, Ya-Wei; Wu, Yong; Yang, Ke; Hiraoka, Nozomu; Tsuei, Ku-Ding; Wang, Jian-Guo; Zhu, Lin-Fan

2018-03-01

A joint experimental and theoretical investigation of the valence-shell excitations of hydrogen has been performed by the high-resolution inelastic x-ray scattering and electron scattering as well as the multireference single- and double-excitation configuration-interaction method. Momentum-transfer-dependent inelastic squared form factors for the vibronic series belonging to the B 1Σu+ ,C 1Πu , and E F 1Σg+ electronic states of molecular hydrogen have been derived from the inelastic x-ray scattering method at an impact photon energy around 10 keV, and the electron energy-loss spectra measured at an incident electron energy of 1500 eV. It is found that both the present and the previous calculations cannot satisfactorily reproduce the inelastic squared form-factor profiles for the higher vibronic transitions of the B 1Σu+ state of molecular hydrogen, which may be due to the electronic-vibrational coupling for the higher vibronic states. For the C 1Πu state and some vibronic excitations of E F 1Σg+ state, the present experimental results are in good agreement with the present and previous calculations, while the slight differences between the inelastic x-ray scattering and electron energy-loss spectroscopy results in the larger squared momentum-transfer region may be attributed to the increasing role of the higher-order Born terms in the electron-scattering process.

Electron microscopy localization and characterization of functionalized composite organic-inorganic SERS nanoparticles on leukemia cells.

PubMed

Koh, Ai Leen; Shachaf, Catherine M; Elchuri, Sailaja; Nolan, Garry P; Sinclair, Robert

2008-12-01

We demonstrate the use of electron microscopy as a powerful characterization tool to identify and locate antibody-conjugated composite organic-inorganic nanoparticle (COINs) surface enhanced Raman scattering (SERS) nanoparticles on cells. U937 leukemia cells labeled with antibody CD54-conjugated COINs were characterized in their native, hydrated state using wet scanning electron microscopy (SEM) and in their dehydrated state using high-resolution SEM. In both cases, the backscattered electron (BSE) detector was used to detect and identify the silver constituents in COINs due to its high sensitivity to atomic number variations within a specimen. The imaging and analytical capabilities in the SEM were further complemented by higher resolution transmission electron microscopy (TEM) images and scanning Auger electron spectroscopy (AES) data to give reliable and high-resolution information about nanoparticles and their binding to cell surface antigens.

Electron Microscopy Localization and Characterization of Functionalized Composite Organic-Inorganic SERS Nanoparticles on Leukemia Cells

PubMed Central

Koh, Ai Leen; Shachaf, Catherine M.; Elchuri, Sailaja; Nolan, Garry P.; Sinclair, Robert

2008-01-01

We demonstrate the use of electron microscopy as a powerful characterization tool to identify and locate antibody-conjugated composite organic-inorganic (COINs) surface enhanced Raman scattering (SERS) nanoparticles on cells. U937 leukemia cells labeled with antibody CD54-conjugated COINs were characterized in their native, hydrated state using wet Scanning Electron Microscopy (SEM) and in their dehydrated state using high-resolution SEM. In both cases, the backscattered electron detector (BSE) was used to detect and identify the silver constituents in COINs due to its high sensitivity to atomic number variations within a specimen. The imaging and analytical capabilities in the SEM were further complemented by higher resolution Transmission Electron Microscope (TEM) images and Scanning Auger Electron Spectroscopy (AES) data to give reliable and high-resolution information about nanoparticles and their binding to cell surface antigens. PMID:18995965

Solar Wind Strahl Observations and Their Implication to the Core-Halo Formation due to Scattering

NASA Technical Reports Server (NTRS)

Vinas, Adolfo F.

2011-01-01

A study of the kinetic properties of the strahl electron velocity distribution functions (VDF?s) in the solar wind is presented. This study focuses on the mechanisms that control and regulate the electron VDF?s and the stability of the strahl electrons in the solar wind; mechanisms that are not yet well understood. Various parameters are investigated such as the strahl-electron density, temperature anisotropy, and electron heat-flux. These parameters are used to investigate the stability of the strahl population. The analysis check for whether the strahl electrons are constrained by some instability (e.g., the whistler or KAW instabilities), or are maintained by other types of processes. The electron heat-flux and temperature anisotropy are determined by modeling of the 3D-VDF?s from which the moments properties of the various populations are obtained. The results of this study have profound implication on the current hypothesis about the probable formation of the solar wind halo electrons produced from the scattering of the strahl population. This hypothesis is strengthened by direct observations of the strahl electrons being scattered into the core-halo in an isolated event. The observation implies that the scattering of the strahl is not a continuous process but occurs in bursts in regions where conditions for wave growth providing the scattering are optimum. Sometimes, observations indicate that the strahl component is anisotropic (Tper/Tpal approx. 2). This provides a possible free energy source for the excitation of whistler waves as a possible scattering mechanism, however this condition is not always observed. The study is based on high time resolution data from the Cluster/PEACE electron spectrometer.

EMRinger: side chain–directed model and map validation for 3D cryo-electron microscopy

DOE PAGES

Barad, Benjamin A.; Echols, Nathaniel; Wang, Ray Yu-Ruei; ...

2015-08-17

Advances in high-resolution cryo-electron microscopy (cryo-EM) require the development of validation metrics to independently assess map quality and model geometry. We report that EMRinger is a tool that assesses the precise fitting of an atomic model into the map during refinement and shows how radiation damage alters scattering from negatively charged amino acids. EMRinger (https://github.com/fraser-lab/EMRinger) will be useful for monitoring progress in resolving and modeling high-resolution features in cryo-EM.

Nonlinear X-Ray and Auger Spectroscopy at X-Ray Free-Electron Laser Sources

NASA Astrophysics Data System (ADS)

Rohringer, Nina

2015-05-01

X-ray free-electron lasers (XFELs) open the pathway to transfer non-linear spectroscopic techniques to the x-ray domain. A promising all x-ray pump probe technique is based on coherent stimulated electronic x-ray Raman scattering, which was recently demonstrated in atomic neon. By tuning the XFEL pulse to core-excited resonances, a few seed photons in the spectral tail of the XFEL pulse drive an avalanche of resonant inelastic x-ray scattering events, resulting in exponential amplification of the scattering signal by of 6-7 orders of magnitude. Analysis of the line profile of the emitted radiation permits to demonstrate the cross over from amplified spontaneous emission to coherent stimulated resonance scattering. In combination with statistical covariance mapping, a high-resolution spectrum of the resonant inelastic scattering process can be obtained, opening the path to coherent stimulated x-ray Raman spectroscopy. An extension of these ideas to molecules and a realistic feasibility study of stimulated electronic x-ray Raman scattering in CO will be presented. Challenges to realizing stimulated electronic x-ray Raman scattering at present-day XFEL sources will be discussed, corroborated by results of a recent experiment at the LCLS XFEL. Due to the small gain cross section in molecular targets, other nonlinear spectroscopic techniques such as nonlinear Auger spectroscopy could become a powerful alternative. Theory predictions of a novel pump probe technique based on resonant nonlinear Auger spectroscopic will be discussed and the method will be compared to stimulated x-ray Raman spectroscopy.

Fast imaging with inelastically scattered electrons by off-axis chromatic confocal electron microscopy.

PubMed

Zheng, Changlin; Zhu, Ye; Lazar, Sorin; Etheridge, Joanne

2014-04-25

We introduce off-axis chromatic scanning confocal electron microscopy, a technique for fast mapping of inelastically scattered electrons in a scanning transmission electron microscope without a spectrometer. The off-axis confocal mode enables the inelastically scattered electrons to be chromatically dispersed both parallel and perpendicular to the optic axis. This enables electrons with different energy losses to be separated and detected in the image plane, enabling efficient energy filtering in a confocal mode with an integrating detector. We describe the experimental configuration and demonstrate the method with nanoscale core-loss chemical mapping of silver (M4,5) in an aluminium-silver alloy and atomic scale imaging of the low intensity core-loss La (M4,5@840  eV) signal in LaB6. Scan rates up to 2 orders of magnitude faster than conventional methods were used, enabling a corresponding reduction in radiation dose and increase in the field of view. If coupled with the enhanced depth and lateral resolution of the incoherent confocal configuration, this offers an approach for nanoscale three-dimensional chemical mapping.

Characterization of conductive nanobiomaterials derived from viral assemblies by low-voltage STEM imaging and Raman scattering

NASA Astrophysics Data System (ADS)

Plascencia-Villa, Germán; Carreño-Fuentes, Liliana; Bahena, Daniel; José-Yacamán, Miguel; Palomares, Laura A.; Ramírez, Octavio T.

2014-09-01

New technologies require the development of novel nanomaterials that need to be fully characterized to achieve their potential. High-resolution low-voltage scanning transmission electron microscopy (STEM) has proven to be a very powerful technique in nanotechnology, but its use for the characterization of nanobiomaterials has been limited. Rotavirus VP6 self-assembles into nanotubular assemblies that possess an intrinsic affinity for Au ions. This property was exploited to produce hybrid nanobiomaterials by the in situ functionalization of recombinant VP6 nanotubes with gold nanoparticles. In this work, Raman spectroscopy and advanced analytical electron microscopy imaging with spherical aberration-corrected (Cs) STEM and nanodiffraction at low-voltage doses were employed to characterize nanobiomaterials. STEM imaging revealed the precise structure and arrangement of the protein templates, as well as the nanostructure and atomic arrangement of gold nanoparticles with high spatial sub-Angstrom resolution and avoided radiation damage. The imaging was coupled with backscattered electron imaging, ultra-high resolution scanning electron microscopy and x-ray spectroscopy. The hybrid nanobiomaterials that were obtained showed unique properties as bioelectronic conductive devices and showed enhanced Raman scattering by their precise arrangement into superlattices, displaying the utility of viral assemblies as functional integrative self-assembled nanomaterials for novel applications.

Coupling EELS/EFTEM Imaging with Environmental Fluid Cell Microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Unocic, Raymond R; Baggetto, Loic; Veith, Gabriel M

2012-01-01

Insight into dynamically evolving electrochemical reactions and mechanisms encountered in electrical energy storage (EES) and conversion technologies (batteries, fuel cells, and supercapacitors), materials science (corrosion and oxidation), and materials synthesis (electrodeposition) remains limited due to the present lack of in situ high-resolution characterization methodologies. Electrochemical fluid cell microscopy is an emerging in-situ method that allows for the direct, real-time imaging of electrochemical processes within a fluid environment. This technique is facilitated by the use of MEMS-based biasing microchip platforms that serve the purpose of sealing the highly volatile electrolyte between two electron transparent SiNx membranes and interfacing electrodes to anmore » external potentiostat for controlled nanoscale electrochemislly experiments [!]. In order to elucidate both stmctural and chemical changes during such in situ electrochemical experiments, it is impmtant to first improve upon the spatial resolution by utilizing energy-filtered transmission electron microscopy (EFTEM) (to minimize chromatic aben ation), then to detennine the chemical changes via electron energy loss spectroscopy (EELS). This presents a formidable challenge since the overall thickness through which electrons are scattered through the multiple layers of the cell can be on the order of hundreds of nanometers to microns, scattering through which has the deleterious effect of degrading image resolution and decreasing signal-to noise for spectroscopy [2].« less

Definition of the Spatial Resolution of X-Ray Microanalysis in Thin Foils

NASA Technical Reports Server (NTRS)

Williams, D. B.; Michael, J. R.; Goldstein, J. I.; Romig, A. D., Jr.

1992-01-01

The spatial resolution of X-ray microanalysis in thin foils is defined in terms of the incident electron beam diameter and the average beam broadening. The beam diameter is defined as the full width tenth maximum of a Gaussian intensity distribution. The spatial resolution is calculated by a convolution of the beam diameter and the average beam broadening. This definition of the spatial resolution can be related simply to experimental measurements of composition profiles across interphase interfaces. Monte Carlo calculations using a high-speed parallel supercomputer show good agreement with this definition of the spatial resolution and calculations based on this definition. The agreement is good over a range of specimen thicknesses and atomic number, but is poor when excessive beam tailing distorts the assumed Gaussian electron intensity distributions. Beam tailing occurs in low-Z materials because of fast secondary electrons and in high-Z materials because of plural scattering.

The Influence of Beam Broadening on the Spatial Resolution of Annular Dark Field Scanning Transmission Electron Microscopy.

PubMed

de Jonge, Niels; Verch, Andreas; Demers, Hendrix

2018-02-01

The spatial resolution of aberration-corrected annular dark field scanning transmission electron microscopy was studied as function of the vertical position z within a sample. The samples consisted of gold nanoparticles (AuNPs) positioned in different horizontal layers within aluminum matrices of 0.6 and 1.0 µm thickness. The highest resolution was achieved in the top layer, whereas the resolution was reduced by beam broadening for AuNPs deeper in the sample. To examine the influence of the beam broadening, the intensity profiles of line scans over nanoparticles at a certain vertical location were analyzed. The experimental data were compared with Monte Carlo simulations that accurately matched the data. The spatial resolution was also calculated using three different theoretical models of the beam blurring as function of the vertical position within the sample. One model considered beam blurring to occur as a single scattering event but was found to be inaccurate for larger depths of the AuNPs in the sample. Two models were adapted and evaluated that include estimates for multiple scattering, and these described the data with sufficient accuracy to be able to predict the resolution. The beam broadening depended on z 1.5 in all three models.

High quality single shot ultrafast MeV electron diffraction from a photocathode radio-frequency gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fu, Feichao; Liu, Shengguang; Zhu, Pengfei

2014-08-15

A compact ultrafast electron diffractometer, consisting of an s-band 1.6 cell photocathode radio-frequency gun, a multi-function changeable sample chamber, and a sensitive relativistic electron detector, was built at Shanghai Jiao Tong University. High-quality single-shot transmission electron diffraction patterns have been recorded by scattering 2.5 MeV electrons off single crystalline gold and polycrystalline aluminum samples. The high quality diffraction pattern indicates an excellent spatial resolution, with the ratio of the diffraction ring radius over the ring rms width beyond 10. The electron pulse width is estimated to be about 300 fs. The high temporal and spatial resolution may open new opportunities inmore » various areas of sciences.« less

High quality single shot ultrafast MeV electron diffraction from a photocathode radio-frequency gun.

PubMed

Fu, Feichao; Liu, Shengguang; Zhu, Pengfei; Xiang, Dao; Zhang, Jie; Cao, Jianming

2014-08-01

A compact ultrafast electron diffractometer, consisting of an s-band 1.6 cell photocathode radio-frequency gun, a multi-function changeable sample chamber, and a sensitive relativistic electron detector, was built at Shanghai Jiao Tong University. High-quality single-shot transmission electron diffraction patterns have been recorded by scattering 2.5 MeV electrons off single crystalline gold and polycrystalline aluminum samples. The high quality diffraction pattern indicates an excellent spatial resolution, with the ratio of the diffraction ring radius over the ring rms width beyond 10. The electron pulse width is estimated to be about 300 fs. The high temporal and spatial resolution may open new opportunities in various areas of sciences.

Spatial Resolution in Scanning Electron Microscopy and Scanning Transmission Electron Microscopy Without a Specimen Vacuum Chamber.

PubMed

Nguyen, Kayla X; Holtz, Megan E; Richmond-Decker, Justin; Muller, David A

2016-08-01

A long-standing goal of electron microscopy has been the high-resolution characterization of specimens in their native environment. However, electron optics require high vacuum to maintain an unscattered and focused probe, a challenge for specimens requiring atmospheric or liquid environments. Here, we use an electron-transparent window at the base of a scanning electron microscope's objective lens to separate column vacuum from the specimen, enabling imaging under ambient conditions, without a specimen vacuum chamber. We demonstrate in-air imaging of specimens at nanoscale resolution using backscattered scanning electron microscopy (airSEM) and scanning transmission electron microscopy. We explore resolution and contrast using Monte Carlo simulations and analytical models. We find that nanometer-scale resolution can be obtained at gas path lengths up to 400 μm, although contrast drops with increasing gas path length. As the electron-transparent window scatters considerably more than gas at our operating conditions, we observe that the densities and thicknesses of the electron-transparent window are the dominant limiting factors for image contrast at lower operating voltages. By enabling a variety of detector configurations, the airSEM is applicable to a wide range of environmental experiments including the imaging of hydrated biological specimens and in situ chemical and electrochemical processes.

Spatial Resolution in Scanning Electron Microscopy and Scanning Transmission Electron Microscopy Without a Specimen Vacuum Chamber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Kayla X.; Holtz, Megan E.; Richmond-Decker, Justin

2016-07-25

Abstract A long-standing goal of electron microscopy has been the high-resolution characterization of specimens in their native environment. However, electron optics require high vacuum to maintain an unscattered and focused probe, a challenge for specimens requiring atmospheric or liquid environments. Here, we use an electron-transparent window at the base of a scanning electron microscope’s objective lens to separate column vacuum from the specimen, enabling imaging under ambient conditions, without a specimen vacuum chamber. We demonstrate in-air imaging of specimens at nanoscale resolution using backscattered scanning electron microscopy (airSEM) and scanning transmission electron microscopy. We explore resolution and contrast using Montemore » Carlo simulations and analytical models. We find that nanometer-scale resolution can be obtained at gas path lengths up to 400μm, although contrast drops with increasing gas path length. As the electron-transparent window scatters considerably more than gas at our operating conditions, we observe that the densities and thicknesses of the electron-transparent window are the dominant limiting factors for image contrast at lower operating voltages. By enabling a variety of detector configurations, the airSEM is applicable to a wide range of environmental experiments including the imaging of hydrated biological specimens andin situchemical and electrochemical processes.« less

Electron Trajectory Reconstruction for Advanced Compton Imaging of Gamma Rays

NASA Astrophysics Data System (ADS)

Plimley, Brian Christopher

Gamma-ray imaging is useful for detecting, characterizing, and localizing sources in a variety of fields, including nuclear physics, security, nuclear accident response, nuclear medicine, and astronomy. Compton imaging in particular provides sensitivity to weak sources and good angular resolution in a large field of view. However, the photon origin in a single event sequence is normally only limited to the surface of a cone. If the initial direction of the Compton-scattered electron can be measured, the cone can be reduced to a cone segment with width depending on the uncertainty in the direction measurement, providing a corresponding increase in imaging sensitivity. Measurement of the electron's initial direction in an efficient detection material requires very fine position resolution due to the electron's short range and tortuous path. A thick (650 mum), fully-depleted charge-coupled device (CCD) developed for infrared astronomy has 10.5-mum position resolution in two dimensions, enabling the initial trajectory measurement of electrons of energy as low as 100 keV. This is the first time the initial trajectories of electrons of such low energies have been measured in a solid material. In this work, the CCD's efficacy as a gamma-ray detector is demonstrated experimentally, using a reconstruction algorithm to measure the initial electron direction from the CCD track image. In addition, models of fast electron interaction physics, charge transport and readout were used to generate modeled tracks with known initial direction. These modeled tracks allowed the development and refinement of the reconstruction algorithm. The angular sensitivity of the reconstruction algorithm is evaluated extensively with models for tracks below 480 keV, showing a FWHM as low as 20° in the pixel plane, and 30° RMS sensitivity to the magnitude of the out-of-plane angle. The measurement of the trajectories of electrons with energies as low as 100 keV have the potential to make electron track Compton imaging an effective means of reducing image background for photons of energy as low as 500 keV, or even less. The angular sensitivity of the reconstruction algorithm was also evaluated experimentally, by measuring electron tracks in the CCD in coincidence with the scattered photon in a germanium double-sided strip detector. By this method, electron tracks could be measured with the true initial direction known to within 3° FWHM, and the angular response of the algorithm compared to the known direction. The challenge of this experiment lay in the low geometric efficiency for photons scattering into the germanium, the poor time resolution in the current CCD implementation, and the resulting signal-to-background ratio of about 10--4 for photons scattered from the CCD into the germanium detector. Nonetheless, 87 events were measured in the FWHM of the total energy deposited and the angular resolution measure, with electron tracks between 160 keV and 360 keV in energy. The electron tracks from true coincident event sequences showed a FWHM in the pixel plane of 23°, and excellent agreement with the distribution calculated with models, with likelihood p-values of 0.44 and 0.73. Thus, the models used for the more thorough evaluation of angular sensitivities are shown to be consistent with the measured tracks from true coincident event sequences.

Real-space localization and quantification of hole distribution in chain-ladder Sr3Ca11Cu24O41 superconductor.

PubMed

Bugnet, Matthieu; Löffler, Stefan; Hawthorn, David; Dabkowska, Hanna A; Luke, Graeme M; Schattschneider, Peter; Sawatzky, George A; Radtke, Guillaume; Botton, Gianluigi A

2016-03-01

Understanding the physical properties of the chain-ladder Sr3Ca11Cu24O41 hole-doped superconductor has been precluded by the unknown hole distribution among chains and ladders. We use electron energy-loss spectrometry (EELS) in a scanning transmission electron microscope (STEM) at atomic resolution to directly separate the contributions of chains and ladders and to unravel the hole distribution from the atomic scale variations of the O-K near-edge structures. The experimental data unambiguously demonstrate that most of the holes lie within the chain layers. A quantitative interpretation supported by inelastic scattering calculations shows that about two holes are located in the ladders, and about four holes in the chains, shedding light on the electronic structure of Sr3Ca11Cu24O41. Combined atomic resolution STEM-EELS and inelastic scattering calculations is demonstrated as a powerful approach toward a quantitative understanding of the electronic structure of cuprate superconductors, offering new possibilities for elucidating their physical properties.

Real-space localization and quantification of hole distribution in chain-ladder Sr3Ca11Cu24O41 superconductor

PubMed Central

Bugnet, Matthieu; Löffler, Stefan; Hawthorn, David; Dabkowska, Hanna A.; Luke, Graeme M.; Schattschneider, Peter; Sawatzky, George A.; Radtke, Guillaume; Botton, Gianluigi A.

2016-01-01

Understanding the physical properties of the chain-ladder Sr3Ca11Cu24O41 hole-doped superconductor has been precluded by the unknown hole distribution among chains and ladders. We use electron energy-loss spectrometry (EELS) in a scanning transmission electron microscope (STEM) at atomic resolution to directly separate the contributions of chains and ladders and to unravel the hole distribution from the atomic scale variations of the O-K near-edge structures. The experimental data unambiguously demonstrate that most of the holes lie within the chain layers. A quantitative interpretation supported by inelastic scattering calculations shows that about two holes are located in the ladders, and about four holes in the chains, shedding light on the electronic structure of Sr3Ca11Cu24O41. Combined atomic resolution STEM-EELS and inelastic scattering calculations is demonstrated as a powerful approach toward a quantitative understanding of the electronic structure of cuprate superconductors, offering new possibilities for elucidating their physical properties. PMID:27051872

Towards a Resolution of the Proton Form Factor Problem: New Electron and Positron Scattering Data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adikaram, D.; Rimal, D.; Weinstein, L. B.

There is a significant discrepancy between the values of the proton electric form factor, GpE, extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of GpE from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide range in virtual photon polarization (epsilon) and momentummore » transfer (Q2) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing ε at Q2=1.45 GeV2. This measurement is consistent with the size of the form factor discrepancy at Q2≈1.75 GeV2 and with hadronic calculations including nucleon and Delta intermediate states, which have been shown to resolve the discrepancy up to 2-3 GeV2.« less

Towards a Resolution of the Proton Form Factor Problem: New Electron and Positron Scattering Data

DOE PAGES

Adikaram, D.; Rimal, D.; Weinstein, L. B.; ...

2015-02-10

There is a significant discrepancy between the values of the proton electric form factor, GpE, extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of GpE from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide range in virtual photon polarization (epsilon) and momentummore » transfer (Q2) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing ε at Q2=1.45 GeV2. This measurement is consistent with the size of the form factor discrepancy at Q2≈1.75 GeV2 and with hadronic calculations including nucleon and Delta intermediate states, which have been shown to resolve the discrepancy up to 2-3 GeV2.« less

Towards a resolution of the proton form factor problem: new electron and positron scattering data.

PubMed

Adikaram, D; Rimal, D; Weinstein, L B; Raue, B; Khetarpal, P; Bennett, R P; Arrington, J; Brooks, W K; Adhikari, K P; Afanasev, A V; Amaryan, M J; Anderson, M D; Anefalos Pereira, S; Avakian, H; Ball, J; Battaglieri, M; Bedlinskiy, I; Biselli, A S; Bono, J; Boiarinov, S; Briscoe, W J; Burkert, V D; Carman, D S; Careccia, S; Celentano, A; Chandavar, S; Charles, G; Colaneri, L; Cole, P L; Contalbrigo, M; Crede, V; D'Angelo, A; Dashyan, N; De Vita, R; De Sanctis, E; Deur, A; Djalali, C; Dodge, G E; Dupre, R; Egiyan, H; El Alaoui, A; El Fassi, L; Elouadrhiri, L; Eugenio, P; Fedotov, G; Fegan, S; Filippi, A; Fleming, J A; Fradi, A; Garillon, B; Gilfoyle, G P; Giovanetti, K L; Girod, F X; Goetz, J T; Gohn, W; Golovatch, E; Gothe, R W; Griffioen, K A; Guegan, B; Guidal, M; Guo, L; Hafidi, K; Hakobyan, H; Hanretty, C; Harrison, N; Hattawy, M; Hicks, K; Holtrop, M; Hughes, S M; Hyde, C E; Ilieva, Y; Ireland, D G; Ishkhanov, B S; Jenkins, D; Jiang, H; Jo, H S; Joo, K; Joosten, S; Kalantarians, N; Keller, D; Khandaker, M; Kim, A; Kim, W; Klein, A; Klein, F J; Koirala, S; Kubarovsky, V; Kuhn, S E; Livingston, K; Lu, H Y; MacGregor, I J D; Markov, N; Mattione, P; Mayer, M; McKinnon, B; Mestayer, M D; Meyer, C A; Mirazita, M; Mokeev, V; Montgomery, R A; Moody, C I; Moutarde, H; Movsisyan, A; Camacho, C Munoz; Nadel-Turonski, P; Niccolai, S; Niculescu, G; Osipenko, M; Ostrovidov, A I; Park, K; Pasyuk, E; Peña, C; Pisano, S; Pogorelko, O; Price, J W; Procureur, S; Prok, Y; Protopopescu, D; Puckett, A J R; Ripani, M; Rizzo, A; Rosner, G; Rossi, P; Roy, P; Sabatié, F; Salgado, C; Schott, D; Schumacher, R A; Seder, E; Sharabian, Y G; Simonyan, A; Skorodumina, I; Smith, E S; Smith, G D; Sober, D I; Sokhan, D; Sparveris, N; Stepanyan, S; Stoler, P; Strauch, S; Sytnik, V; Taiuti, M; Tian, Ye; Trivedi, A; Ungaro, M; Voskanyan, H; Voutier, E; Walford, N K; Watts, D P; Wei, X; Wood, M H; Zachariou, N; Zana, L; Zhang, J; Zhao, Z W; Zonta, I

2015-02-13

There is a significant discrepancy between the values of the proton electric form factor, G(E)(p), extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of G(E)(p) from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide range in virtual photon polarization (ϵ) and momentum transfer (Q(2)) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing ϵ at Q(2)=1.45  GeV(2). This measurement is consistent with the size of the form factor discrepancy at Q(2)≈1.75  GeV(2) and with hadronic calculations including nucleon and Δ intermediate states, which have been shown to resolve the discrepancy up to 2-3  GeV(2).

Ab initio structure determination from prion nanocrystals at atomic resolution by MicroED

PubMed Central

Sawaya, Michael R.; Rodriguez, Jose; Cascio, Duilio; Collazo, Michael J.; Shi, Dan; Reyes, Francis E.; Gonen, Tamir; Eisenberg, David S.

2016-01-01

Electrons, because of their strong interaction with matter, produce high-resolution diffraction patterns from tiny 3D crystals only a few hundred nanometers thick in a frozen-hydrated state. This discovery offers the prospect of facile structure determination of complex biological macromolecules, which cannot be coaxed to form crystals large enough for conventional crystallography or cannot easily be produced in sufficient quantities. Two potential obstacles stand in the way. The first is a phenomenon known as dynamical scattering, in which multiple scattering events scramble the recorded electron diffraction intensities so that they are no longer informative of the crystallized molecule. The second obstacle is the lack of a proven means of de novo phase determination, as is required if the molecule crystallized is insufficiently similar to one that has been previously determined. We show with four structures of the amyloid core of the Sup35 prion protein that, if the diffraction resolution is high enough, sufficiently accurate phases can be obtained by direct methods with the cryo-EM method microelectron diffraction (MicroED), just as in X-ray diffraction. The success of these four experiments dispels the concern that dynamical scattering is an obstacle to ab initio phasing by MicroED and suggests that structures of novel macromolecules can also be determined by direct methods. PMID:27647903

Computer synthesis of high resolution electron micrographs

NASA Technical Reports Server (NTRS)

Nathan, R.

1976-01-01

Specimen damage, spherical aberration, low contrast and noisy sensors combine to prevent direct atomic viewing in a conventional electron microscope. The paper describes two methods for obtaining ultra-high resolution in biological specimens under the electron microscope. The first method assumes the physical limits of the electron objective lens and uses a series of dark field images of biological crystals to obtain direct information on the phases of the Fourier diffraction maxima; this information is used in an appropriate computer to synthesize a large aperture lens for a 1-A resolution. The second method assumes there is sufficient amplitude scatter from images recorded in focus which can be utilized with a sensitive densitometer and computer contrast stretching to yield fine structure image details. Cancer virus characterization is discussed as an illustrative example. Numerous photographs supplement the text.

Multipurpose end-station for coherent diffraction imaging and scattering at FERMI@Elettra free-electron laser facility.

PubMed

Capotondi, Flavio; Pedersoli, Emanuele; Bencivenga, Filippo; Manfredda, Michele; Mahne, Nicola; Raimondi, Lorenzo; Svetina, Cristian; Zangrando, Marco; Demidovich, Alexander; Nikolov, Ivaylo; Danailov, Miltcho; Masciovecchio, Claudio; Kiskinova, Maya

2015-05-01

The Diffraction and Projection Imaging (DiProI) beamline at FERMI, the Elettra free-electron laser (FEL), hosts a multi-purpose station that has been opened to users since the end of 2012. This paper describes the core capabilities of the station, designed to make use of the unique features of the FERMI-FEL for performing a wide range of static and dynamic scattering experiments. The various schemes for time-resolved experiments, employing both soft X-ray FEL and seed laser IR radiation are presented by using selected recent results. The ongoing upgrade is adding a reflection geometry setup for scattering experiments, expanding the application fields by providing both high lateral and depth resolution.

Multiplexed high resolution soft x-ray RIXS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chuang, Y.-D.; Voronov, D.; Warwick, T.

2016-07-27

High-resolution Resonance Inelastic X-ray Scattering (RIXS) is a technique that allows us to probe the electronic excitations of complex materials with unprecedented precision. However, the RIXS process has a low cross section, compounded by the fact that the optical spectrometers used to analyze the scattered photons can only collect a small solid angle and overall have a small efficiency. Here we present a method to significantly increase the throughput of RIXS systems, by energy multiplexing, so that a complete RIXS map of scattered intensity versus photon energy in and photon energy out can be recorded simultaneously{sup 1}. This parallel acquisitionmore » scheme should provide a gain in throughput of over 100.. A system based on this principle, QERLIN, is under construction at the Advanced Light Source (ALS).« less

Benefits and Limitations of Low-kV Macromolecular Imaging of Frozen-Hydrated Biological Samples

PubMed Central

Majorovits, Endre; Angert, Isabel; Kaiser, Ute; Schröder, Rasmus R.

2016-01-01

Object contrast is one of the most important parameters of macromolecular imaging. Low-voltage transmission electron microscopy has shown an increased atom contrast for carbon materials, indicating that amplitude contrast contributions increase at a higher rate than phase contrast and inelastic scattering. Here, we studied image contrast using ice-embedded tobacco mosaic virus particles as test samples at 20–80 keV electron energy. The particles showed the expected increase in contrast for lower energies, but at the same time the 2.3-nm-resolution measure decayed more rapidly. We found a pronounced signal loss below 60 keV, and therefore we conclude that increased inelastic scattering counteracts increased amplitude contrast. This model also implies that as long as the amplitude contrast does not increase with resolution, beam damage and multiple scattering will always win over increased contrast at the lowest energies. Therefore, we cannot expect that low-energy imaging of conventionally prepared samples would provide better data than state-of-the-art 200–300 keV imaging. PMID:26910420

Electron Identification and Energy Measurement with Emulsion Cloud Chamber

NASA Astrophysics Data System (ADS)

Kitagawa, Nobuko; Komatsu, Masahiro

Charged particles undergo the Multiple Coulomb Scattering (MCS) when passing through a material. Their momentum can be estimated from the distribution of the scattering angle directly. Angle of electrons (or positrons) largely changes because of the energy loss in bremsstrahlung, and they are distinguished from other charged particles by making use of its feature. Electron energy is generally measured by counting of electromagnetic shower (e.m. shower) tracks in Emulsion Cloud Chamber (ECC), so enough absorber material is needed to develop the shower. In the range from sub-GeV to a few GeV, electrons don't develop noticeable showers. In order to estimate the energy of electrons in this range with a limited material, we established the new method which is based on the scattering angle considering the energy loss in bremsstrahlung. From the Monte Carlo simulation (MC) data, which is generated by electron beam (0.5 GeV, 1 GeV, 2 GeV) exposure to ECC, we derived the correlation between energy and scattering angle in each emulsion layer. We fixed the function and some parameters which 1 GeV MC sample would return 1 GeV as the center value, and then applied to 0.5 GeV and 2 GeV sample and confirmed the energy resolution about 50% within two radiation length.

Active pixel sensor array as a detector for electron microscopy.

PubMed

Milazzo, Anna-Clare; Leblanc, Philippe; Duttweiler, Fred; Jin, Liang; Bouwer, James C; Peltier, Steve; Ellisman, Mark; Bieser, Fred; Matis, Howard S; Wieman, Howard; Denes, Peter; Kleinfelder, Stuart; Xuong, Nguyen-Huu

2005-09-01

A new high-resolution recording device for transmission electron microscopy (TEM) is urgently needed. Neither film nor CCD cameras are systems that allow for efficient 3-D high-resolution particle reconstruction. We tested an active pixel sensor (APS) array as a replacement device at 200, 300, and 400 keV using a JEOL JEM-2000 FX II and a JEM-4000 EX electron microscope. For this experiment, we used an APS prototype with an area of 64 x 64 pixels of 20 microm x 20 microm pixel pitch. Single-electron events were measured by using very low beam intensity. The histogram of the incident electron energy deposited in the sensor shows a Landau distribution at low energies, as well as unexpected events at higher absorbed energies. After careful study, we concluded that backscattering in the silicon substrate and re-entering the sensitive epitaxial layer a second time with much lower speed caused the unexpected events. Exhaustive simulation experiments confirmed the existence of these back-scattered electrons. For the APS to be usable, the back-scattered electron events must be eliminated, perhaps by thinning the substrate to less than 30 microm. By using experimental data taken with an APS chip with a standard silicon substrate (300 microm) and adjusting the results to take into account the effect of a thinned silicon substrate (30 microm), we found an estimate of the signal-to-noise ratio for a back-thinned detector in the energy range of 200-400 keV was about 10:1 and an estimate for the spatial resolution was about 10 microm.

A method to investigate the electron scattering characteristics of ultrathin metallic films by in situ electrical resistance measurements.

PubMed

Trindade, I G; Fermento, R; Leitão, D; Sousa, J B

2009-07-01

In this article, a method to measure the electrical resistivity/conductivity of metallic thin films during layer growth on specific underlayers is described. The in situ monitoring of an underlayer electrical resistance, its change upon the incoming of new material atoms/molecules, and the growth of a new layer are presented. The method is easy to implement and allows obtaining in situ experimental curves of electrical resistivity dependence upon film thickness with a subatomic resolution, providing insight in film growth microstructure characteristics, specular/diffuse electron scattering surfaces, and optimum film thicknesses.

Mega-electron-volt ultrafast electron diffraction at SLAC National Accelerator Laboratory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weathersby, S. P.; Brown, G.; Chase, T. F.

Ultrafast electron probes are powerful tools, complementary to x-ray free-electron lasers, used to study structural dynamics in material, chemical, and biological sciences. High brightness, relativistic electron beams with femtosecond pulse duration can resolve details of the dynamic processes on atomic time and length scales. SLAC National Accelerator Laboratory recently launched the Ultrafast Electron Diffraction (UED) and microscopy Initiative aiming at developing the next generation ultrafast electron scattering instruments. As the first stage of the Initiative, a mega-electron-volt (MeV) UED system has been constructed and commissioned to serve ultrafast science experiments and instrumentation development. The system operates at 120-Hz repetition ratemore » with outstanding performance. In this paper, we report on the SLAC MeV UED system and its performance, including the reciprocal space resolution, temporal resolution, and machine stability.« less

Mega-electron-volt ultrafast electron diffraction at SLAC National Accelerator Laboratory.

PubMed

Weathersby, S P; Brown, G; Centurion, M; Chase, T F; Coffee, R; Corbett, J; Eichner, J P; Frisch, J C; Fry, A R; Gühr, M; Hartmann, N; Hast, C; Hettel, R; Jobe, R K; Jongewaard, E N; Lewandowski, J R; Li, R K; Lindenberg, A M; Makasyuk, I; May, J E; McCormick, D; Nguyen, M N; Reid, A H; Shen, X; Sokolowski-Tinten, K; Vecchione, T; Vetter, S L; Wu, J; Yang, J; Dürr, H A; Wang, X J

2015-07-01

Ultrafast electron probes are powerful tools, complementary to x-ray free-electron lasers, used to study structural dynamics in material, chemical, and biological sciences. High brightness, relativistic electron beams with femtosecond pulse duration can resolve details of the dynamic processes on atomic time and length scales. SLAC National Accelerator Laboratory recently launched the Ultrafast Electron Diffraction (UED) and microscopy Initiative aiming at developing the next generation ultrafast electron scattering instruments. As the first stage of the Initiative, a mega-electron-volt (MeV) UED system has been constructed and commissioned to serve ultrafast science experiments and instrumentation development. The system operates at 120-Hz repetition rate with outstanding performance. In this paper, we report on the SLAC MeV UED system and its performance, including the reciprocal space resolution, temporal resolution, and machine stability.

Diffuse x-ray scattering and transmission electron microscopy study of defects in antimony-implanted silicon

NASA Astrophysics Data System (ADS)

Takamura, Y.; Marshall, A. F.; Mehta, A.; Arthur, J.; Griffin, P. B.; Plummer, J. D.; Patel, J. R.

2004-04-01

Ion implantation followed by laser annealing has been used to create supersaturated and electrically active concentrations of antimony in silicon. Upon subsequent thermal annealing, however, these metastable dopants deactivate towards the equilibrium solubility limit. In this work, the formation of inactive antimony structures has been studied with grazing incidence diffuse x-ray scattering, and transmission electron microscopy, and the results are correlated to previous high-resolution x-ray diffraction data. We find that at a concentration of 6.0×1020 cm-3, small, incoherent clusters of radius 3-4 Å form during annealing at 900 °C. At a higher concentration of 2.2×1021 cm-3, deactivation at 600 °C occurs through the formation of small, antimony aggregates and antimony precipitates. The size of these precipitates from diffuse x-ray scattering is roughly 15 Å in radius for anneal times from 15 to 180 seconds. This value is consistent with the features observed in high-resolution and mass contrast transmission electron microscopy images. The coherent nature of the aggregates and precipitates causes the expansion of the surrounding silicon matrix as the deactivation progresses. In addition, the sensitivity of the diffuse x-ray scattering technique has allowed us to detect the presence of small clusters of radius ˜2 Å in unprocessed Czochralski silicon wafers. These defects are not observed in floating zone silicon wafers, and are tentatively attributed to thermal donors.

Soft X-ray radiation damage in EM-CCDs used for Resonant Inelastic X-ray Scattering

NASA Astrophysics Data System (ADS)

Gopinath, D.; Soman, M.; Holland, A.; Keelan, J.; Hall, D.; Holland, K.; Colebrook, D.

2018-02-01

Advancement in synchrotron and free electron laser facilities means that X-ray beams with higher intensity than ever before are being created. The high brilliance of the X-ray beam, as well as the ability to use a range of X-ray energies, means that they can be used in a wide range of applications. One such application is Resonant Inelastic X-ray Scattering (RIXS). RIXS uses the intense and tuneable X-ray beams in order to investigate the electronic structure of materials. The photons are focused onto a sample material and the scattered X-ray beam is diffracted off a high resolution grating to disperse the X-ray energies onto a position sensitive detector. Whilst several factors affect the total system energy resolution, the performance of RIXS experiments can be limited by the spatial resolution of the detector used. Electron-Multiplying CCDs (EM-CCDs) at high gain in combination with centroiding of the photon charge cloud across several detector pixels can lead to sub-pixel spatial resolution of 2-3 μm. X-ray radiation can cause damage to CCDs through ionisation damage resulting in increases in dark current and/or a shift in flat band voltage. Understanding the effect of radiation damage on EM-CCDs is important in order to predict lifetime as well as the change in performance over time. Two CCD-97s were taken to PTB at BESSY II and irradiated with large doses of soft X-rays in order to probe the front and back surfaces of the device. The dark current was shown to decay over time with two different exponential components to it. This paper will discuss the use of EM-CCDs for readout of RIXS spectrometers, and limitations on spatial resolution, together with any limitations on instrument use which may arise from X-ray-induced radiation damage.

Conventions and workflows for using Situs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wriggers, Willy, E-mail: wriggers@biomachina.org

2012-04-01

Recent developments of the Situs software suite for multi-scale modeling are reviewed. Typical workflows and conventions encountered during processing of biophysical data from electron microscopy, tomography or small-angle X-ray scattering are described. Situs is a modular program package for the multi-scale modeling of atomic resolution structures and low-resolution biophysical data from electron microscopy, tomography or small-angle X-ray scattering. This article provides an overview of recent developments in the Situs package, with an emphasis on workflows and conventions that are important for practical applications. The modular design of the programs facilitates scripting in the bash shell that allows specific programs tomore » be combined in creative ways that go beyond the original intent of the developers. Several scripting-enabled functionalities, such as flexible transformations of data type, the use of symmetry constraints or the creation of two-dimensional projection images, are described. The processing of low-resolution biophysical maps in such workflows follows not only first principles but often relies on implicit conventions. Situs conventions related to map formats, resolution, correlation functions and feature detection are reviewed and summarized. The compatibility of the Situs workflow with CCP4 conventions and programs is discussed.« less

High Resolution UV Emission Spectroscopy of Molecules Excited by Electron Impact

NASA Technical Reports Server (NTRS)

James, G. K.; Ajello, J. M.; Beegle, L.; Ciocca, M.; Dziczek, D.; Kanik, I.; Noren, C.; Jonin, C.; Hansen, D.

1999-01-01

Photodissociation via discrete line absorption into predissociating Rydberg and valence states is the dominant destruction mechanism of CO and other molecules in the interstellar medium and molecular clouds. Accurate values for the rovibronic oscillator strengths of these transitions and predissociation yields of the excited states are required for input into the photochemical models that attempt to reproduce observed abundances. We report here on our latest experimental results of the electron collisional properties of CO and N2 obtained using the 3-meter high resolution single-scattering spectroscopic facility at JPL.

Biophysical interpretation and ex-vivo characterization of scattered light from tumor-associated breast stroma

NASA Astrophysics Data System (ADS)

Laughney, Ashley; Krishnaswamy, Venkat; Schwab, Mary; Wells, Wendy A.; Paulsen, Keith D.; Pogue, Brian W.

2009-02-01

The purpose of this study was to extract scatter parameters related to tissue ultra-structures from freshly excised breast tissue and to assess whether evident changes in scatter across diagnostic categories is primarily influenced by variation in the composition of each tissues subtypes or by physical remodeling of the extra-cellular environment. Pathologists easily distinguish between epithelium, stroma and adipose tissues, so this classification was adopted for macroscopic subtype classification. Micro-sampling reflectance spectroscopy was used to characterize single-backscattered photons from fresh, excised tumors and normal reduction specimens with sub-millimeter resolution. Phase contrast microscopy (sub-micron resolution) was used to characterize forward-scattered light through frozen tissue from the DHMC Tissue Bank, representing normal, benign and malignant breast tissue, sectioned at 10 microns. The packing density and orientation of collagen fibers in the extracellular matrix (ECM) associated with invasive, normal and benign epithelium was evaluated using transmission electron microscopy (TEM). Regions of interest (ROIs) in the H&E stained tissues were identified for analysis, as outlined by a pathologist as the gold standard. We conclude that the scatter parameters associated with tumor specimens (Npatients=6, Nspecimens=13) significantly differs from that of normal reductions (Npatients=6, Nspecimens=10). Further, tissue subtypes may be identified by their scatter spectra at sub-micron resolution. Stromal tissue scatters significantly more than the epithelial cells embedded in its ECM and adipose tissue scatters much less. However, the scatter signature of the stroma at the sub-micron level is not particularly differentiating in terms of a diagnosis.

Hollow Cone Electron Imaging for Single Particle 3D Reconstruction of Proteins

PubMed Central

Tsai, Chun-Ying; Chang, Yuan-Chih; Lobato, Ivan; Van Dyck, Dirk; Chen, Fu-Rong

2016-01-01

The main bottlenecks for high-resolution biological imaging in electron microscopy are radiation sensitivity and low contrast. The phase contrast at low spatial frequencies can be enhanced by using a large defocus but this strongly reduces the resolution. Recently, phase plates have been developed to enhance the contrast at small defocus but electrical charging remains a problem. Single particle cryo-electron microscopy is mostly used to minimize the radiation damage and to enhance the resolution of the 3D reconstructions but it requires averaging images of a massive number of individual particles. Here we present a new route to achieve the same goals by hollow cone dark field imaging using thermal diffuse scattered electrons giving about a 4 times contrast increase as compared to bright field imaging. We demonstrate the 3D reconstruction of a stained GroEL particle can yield about 13.5 Å resolution but using a strongly reduced number of images. PMID:27292544

Energy-weighted dynamical scattering simulations of electron diffraction modalities in the scanning electron microscope.

PubMed

Pascal, Elena; Singh, Saransh; Callahan, Patrick G; Hourahine, Ben; Trager-Cowan, Carol; Graef, Marc De

2018-04-01

Transmission Kikuchi diffraction (TKD) has been gaining momentum as a high resolution alternative to electron back-scattered diffraction (EBSD), adding to the existing electron diffraction modalities in the scanning electron microscope (SEM). The image simulation of any of these measurement techniques requires an energy dependent diffraction model for which, in turn, knowledge of electron energies and diffraction distances distributions is required. We identify the sample-detector geometry and the effect of inelastic events on the diffracting electron beam as the important factors to be considered when predicting these distributions. However, tractable models taking into account inelastic scattering explicitly are lacking. In this study, we expand the Monte Carlo (MC) energy-weighting dynamical simulations models used for EBSD [1] and ECP [2] to the TKD case. We show that the foil thickness in TKD can be used as a means of energy filtering and compare band sharpness in the different modalities. The current model is shown to correctly predict TKD patterns and, through the dictionary indexing approach, to produce higher quality indexed TKD maps than conventional Hough transform approach, especially close to grain boundaries. Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.

Resolution enhancement in coherent x-ray diffraction imaging by overcoming instrumental noise.

PubMed

Kim, Chan; Kim, Yoonhee; Song, Changyong; Kim, Sang Soo; Kim, Sunam; Kang, Hyon Chol; Hwu, Yeukuang; Tsuei, Ku-Ding; Liang, Keng San; Noh, Do Young

2014-11-17

We report that reference objects, strong scatterers neighboring weak phase objects, enhance the phase retrieval and spatial resolution in coherent x-ray diffraction imaging (CDI). A CDI experiment with Au nano-particles exhibited that the reference objects amplified the signal-to-noise ratio in the diffraction intensity at large diffraction angles, which significantly enhanced the image resolution. The interference between the diffracted x-ray from reference objects and a specimen also improved the retrieval of the phase of the diffraction signal. The enhancement was applied to image NiO nano-particles and a mitochondrion and confirmed in a simulation with a bacteria phantom. We expect that the proposed method will be of great help in imaging weakly scattering soft matters using coherent x-ray sources including x-ray free electron lasers.

Electric field imaging of single atoms

PubMed Central

Shibata, Naoya; Seki, Takehito; Sánchez-Santolino, Gabriel; Findlay, Scott D.; Kohno, Yuji; Matsumoto, Takao; Ishikawa, Ryo; Ikuhara, Yuichi

2017-01-01

In scanning transmission electron microscopy (STEM), single atoms can be imaged by detecting electrons scattered through high angles using post-specimen, annular-type detectors. Recently, it has been shown that the atomic-scale electric field of both the positive atomic nuclei and the surrounding negative electrons within crystalline materials can be probed by atomic-resolution differential phase contrast STEM. Here we demonstrate the real-space imaging of the (projected) atomic electric field distribution inside single Au atoms, using sub-Å spatial resolution STEM combined with a high-speed segmented detector. We directly visualize that the electric field distribution (blurred by the sub-Å size electron probe) drastically changes within the single Au atom in a shape that relates to the spatial variation of total charge density within the atom. Atomic-resolution electric field mapping with single-atom sensitivity enables us to examine their detailed internal and boundary structures. PMID:28555629

Non-destructive diagnostics of irradiated materials using neutron scattering from pulsed neutron sources

NASA Astrophysics Data System (ADS)

Korenev, Sergey; Sikolenko, Vadim

2004-09-01

The advantage of neutron-scattering studies as compared to the standard X-ray technique is the high penetration of neutrons that allow us to study volume effects. The high resolution of instrumentation on the basis neutron scattering allows measurement of the parameters of lattice structure with high precision. We suggest the use of neutron scattering from pulsed neutron sources for analysis of materials irradiated with pulsed high current electron and ion beams. The results of preliminary tests using this method for Ni foils that have been studied by neutron diffraction at the IBR-2 (Pulsed Fast Reactor at Joint Institute for Nuclear Research) are presented.

Vibrational spectroscopy in the electron microscope.

PubMed

Krivanek, Ondrej L; Lovejoy, Tracy C; Dellby, Niklas; Aoki, Toshihiro; Carpenter, R W; Rez, Peter; Soignard, Emmanuel; Zhu, Jiangtao; Batson, Philip E; Lagos, Maureen J; Egerton, Ray F; Crozier, Peter A

2014-10-09

Vibrational spectroscopies using infrared radiation, Raman scattering, neutrons, low-energy electrons and inelastic electron tunnelling are powerful techniques that can analyse bonding arrangements, identify chemical compounds and probe many other important properties of materials. The spatial resolution of these spectroscopies is typically one micrometre or more, although it can reach a few tens of nanometres or even a few ångströms when enhanced by the presence of a sharp metallic tip. If vibrational spectroscopy could be combined with the spatial resolution and flexibility of the transmission electron microscope, it would open up the study of vibrational modes in many different types of nanostructures. Unfortunately, the energy resolution of electron energy loss spectroscopy performed in the electron microscope has until now been too poor to allow such a combination. Recent developments that have improved the attainable energy resolution of electron energy loss spectroscopy in a scanning transmission electron microscope to around ten millielectronvolts now allow vibrational spectroscopy to be carried out in the electron microscope. Here we describe the innovations responsible for the progress, and present examples of applications in inorganic and organic materials, including the detection of hydrogen. We also demonstrate that the vibrational signal has both high- and low-spatial-resolution components, that the first component can be used to map vibrational features at nanometre-level resolution, and that the second component can be used for analysis carried out with the beam positioned just outside the sample--that is, for 'aloof' spectroscopy that largely avoids radiation damage.

Electron volt spectroscopy on a pulsed neutron source

NASA Astrophysics Data System (ADS)

Newport, R. J.; Penfold, J.; Williams, W. G.

1984-07-01

The principal design aspects of a pulsed source neutron spectrometer in which the scattered neutron energy is determined by a resonance absorption filter difference method are discussed. Calculations of the accessible dynamic range, resolution and spectrum simulations are given for the spectrometer on a high intensity pulsed neutron source, such as the spallation neutron source (SNS) now being constructed at the Rutherford Appleton Laboratory. Special emphasis is made of the advantage gained by placing coarse and fixed energy-sensitive filters before and after the scatterer; these enhance the inelastic/elastic descrimination of the method. A brief description is given of a double difference filter method which gives a superior difference peak shape, as well as a better energy transfer resolution. Finally, some first results of scattering from zirconium hydride, obtained on a test spectrometer, are presented.

Stochastic stimulated electronic x-ray Raman spectroscopy

PubMed Central

Kimberg, Victor; Rohringer, Nina

2016-01-01

Resonant inelastic x-ray scattering (RIXS) is a well-established tool for studying electronic, nuclear, and collective dynamics of excited atoms, molecules, and solids. An extension of this powerful method to a time-resolved probe technique at x-ray free electron lasers (XFELs) to ultimately unravel ultrafast chemical and structural changes on a femtosecond time scale is often challenging, due to the small signal rate in conventional implementations at XFELs that rely on the usage of a monochromator setup to select a small frequency band of the broadband, spectrally incoherent XFEL radiation. Here, we suggest an alternative approach, based on stochastic spectroscopy, which uses the full bandwidth of the incoming XFEL pulses. Our proposed method is relying on stimulated resonant inelastic x-ray scattering, where in addition to a pump pulse that resonantly excites the system a probe pulse on a specific electronic inelastic transition is provided, which serves as a seed in the stimulated scattering process. The limited spectral coherence of the XFEL radiation defines the energy resolution in this process and stimulated RIXS spectra of high resolution can be obtained by covariance analysis of the transmitted spectra. We present a detailed feasibility study and predict signal strengths for realistic XFEL parameters for the CO molecule resonantly pumped at the O1s→π* transition. Our theoretical model describes the evolution of the spectral and temporal characteristics of the transmitted x-ray radiation, by solving the equation of motion for the electronic and vibrational degrees of freedom of the system self consistently with the propagation by Maxwell equations. PMID:26958585

Influence of total beam current on HRTEM image resolution in differentially pumped ETEM with nitrogen gas.

PubMed

Bright, A N; Yoshida, K; Tanaka, N

2013-01-01

Environmental transmission electron microscopy (ETEM) enables the study of catalytic and other reaction processes as they occur with Angstrom-level resolution. The microscope used is a dedicated ETEM (Titan ETEM, FEI Company) with a differential pumping vacuum system and apertures, allowing aberration corrected high-resolution transmission electron microscopy (HRTEM) imaging to be performed with gas pressures up to 20 mbar in the sample area and with significant advantages over membrane-type E-cell holders. The effect on image resolution of varying the nitrogen gas pressure, electron beam current density and total beam current were measured using information limit (Young's fringes) on a standard cross grating sample and from silicon crystal lattice imaging. As expected, increasing gas pressure causes a decrease in HRTEM image resolution. However, the total electron beam current also causes big changes in the image resolution (lower beam current giving better resolution), whereas varying the beam current density has almost no effect on resolution, a result that has not been reported previously. This behavior is seen even with zero-loss filtered imaging, which we believe shows that the drop in resolution is caused by elastic scattering at gas ions created by the incident electron beam. Suitable conditions for acquiring high resolution images in a gas environment are discussed. Lattice images at nitrogen pressures up to 16 mbar are shown, with 0.12 nm information transfer at 4 mbar. Copyright © 2012 Elsevier B.V. All rights reserved.

Solar neutrino detection in a large volume double-phase liquid argon experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Franco, D.; Agnes, P.; Giganti, C.

2016-08-01

Precision measurements of solar neutrinos emitted by specific nuclear reaction chains in the Sun are of great interest for developing an improved understanding of star formation and evolution. Given the expected neutrino fluxes and known detection reactions, such measurements require detectors capable of collecting neutrino-electron scattering data in exposures on the order of 1 ktonne-yr, with good energy resolution and extremely low background. Two-phase liquid argon time projection chambers (LAr TPCs) are under development for direct Dark Matter WIMP searches, which possess very large sensitive mass, high scintillation light yield, good energy resolution, and good spatial resolution in all threemore » cartesian directions. While enabling Dark Matter searches with sensitivity extending to the ''neutrino floor'' (given by the rate of nuclear recoil events from solar neutrino coherent scattering), such detectors could also enable precision measurements of solar neutrino fluxes using the neutrino-electron elastic scattering events. Modeling results are presented for the cosmogenic and radiogenic backgrounds affecting solar neutrino detection in a 300 tonne (100 tonne fiducial) LAr TPC operating at LNGS depth (3,800 meters of water equivalent). The results show that such a detector could measure the CNO neutrino rate with ∼15% precision, and significantly improve the precision of the {sup 7}Be and pep neutrino rates compared to the currently available results from the Borexino organic liquid scintillator detector.« less

Ab initio structure determination from prion nanocrystals at atomic resolution by MicroED

DOE PAGES

Sawaya, Michael R.; Rodriguez, Jose; Cascio, Duilio; ...

2016-09-19

Electrons, because of their strong interaction with matter, produce high-resolution diffraction patterns from tiny 3D crystals only a few hundred nanometers thick in a frozen-hydrated state. This discovery offers the prospect of facile structure determination of complex biological macromolecules, which cannot be coaxed to form crystals large enough for conventional crystallography or cannot easily be produced in sufficient quantities. Two potential obstacles stand in the way. The first is a phenomenon known as dynamical scattering, in which multiple scattering events scramble the recorded electron diffraction intensities so that they are no longer informative of the crystallized molecule. The second obstaclemore » is the lack of a proven means of de novo phase determination, as is required if the molecule crystallized is insufficiently similar to one that has been previously determined.We showwith four structures of the amyloid core of the Sup35 prion protein that, if the diffraction resolution is high enough, sufficiently accurate phases can be obtained by direct methods with the cryo-EM method microelectron diffraction (MicroED), just as in X-ray diffraction. The success of these four experiments dispels the concern that dynamical scattering is an obstacle to ab initio phasing by MicroED and suggests that structures of novel macromolecules can also be determined by direct methods.« less

Ab initio structure determination from prion nanocrystals at atomic resolution by MicroED

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sawaya, Michael R.; Rodriguez, Jose; Cascio, Duilio

Electrons, because of their strong interaction with matter, produce high-resolution diffraction patterns from tiny 3D crystals only a few hundred nanometers thick in a frozen-hydrated state. This discovery offers the prospect of facile structure determination of complex biological macromolecules, which cannot be coaxed to form crystals large enough for conventional crystallography or cannot easily be produced in sufficient quantities. Two potential obstacles stand in the way. The first is a phenomenon known as dynamical scattering, in which multiple scattering events scramble the recorded electron diffraction intensities so that they are no longer informative of the crystallized molecule. The second obstaclemore » is the lack of a proven means of de novo phase determination, as is required if the molecule crystallized is insufficiently similar to one that has been previously determined.We showwith four structures of the amyloid core of the Sup35 prion protein that, if the diffraction resolution is high enough, sufficiently accurate phases can be obtained by direct methods with the cryo-EM method microelectron diffraction (MicroED), just as in X-ray diffraction. The success of these four experiments dispels the concern that dynamical scattering is an obstacle to ab initio phasing by MicroED and suggests that structures of novel macromolecules can also be determined by direct methods.« less

Joint small-angle X-ray and neutron scattering data analysis of asymmetric lipid vesicles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eicher, Barbara; Heberle, Frederick A.; Marquardt, Drew T.

2017-02-28

Low- and high-resolution models describing the internal transbilayer structure of asymmetric lipid vesicles have been developed. These models can be used for the joint analysis of small-angle neutron and X-ray scattering data. The models describe the underlying scattering length density/electron density profiles either in terms of slabs or through the so-called scattering density profile, previously applied to symmetric lipid vesicles. Both models yield structural details of asymmetric membranes, such as the individual area per lipid, and the hydrocarbon thickness of the inner and outer bilayer leaflets. The scattering density profile model, however, comes at a cost of increased computational effortmore » but results in greater structural resolution, showing a slightly lower packing of lipids in the outer bilayer leaflet of ~120 nm diameter palmitoyloleoyl phosphatidylcholine (POPC) vesicles, compared to the inner leaflet. Here, analysis of asymmetric dipalmitoyl phosphatidylcholine/POPC vesicles did not reveal evidence of transbilayer coupling between the inner and outer leaflets at 323 K, i.e.above the melting transition temperature of the two lipids.« less

Ponderomotive phase plate for transmission electron microscopes

DOEpatents

Reed, Bryan W [Livermore, CA

2012-07-10

A ponderomotive phase plate system and method for controllably producing highly tunable phase contrast transfer functions in a transmission electron microscope (TEM) for high resolution and biological phase contrast imaging. The system and method includes a laser source and a beam transport system to produce a focused laser crossover as a phase plate, so that a ponderomotive potential of the focused laser crossover produces a scattering-angle-dependent phase shift in the electrons of the post-sample electron beam corresponding to a desired phase contrast transfer function.

Feasibility of track-based multiple scattering tomography

NASA Astrophysics Data System (ADS)

Jansen, H.; Schütze, P.

2018-04-01

We present a tomographic technique making use of a gigaelectronvolt electron beam for the determination of the material budget distribution of centimeter-sized objects by means of simulations and measurements. In both cases, the trajectory of electrons traversing a sample under test is reconstructed using a pixel beam-telescope. The width of the deflection angle distribution of electrons undergoing multiple Coulomb scattering at the sample is estimated. Basing the sinogram on position-resolved estimators enables the reconstruction of the original sample using an inverse radon transform. We exemplify the feasibility of this tomographic technique via simulations of two structured cubes—made of aluminium and lead—and via an in-beam measured coaxial adapter. The simulations yield images with FWHM edge resolutions of (177 ± 13) μm and a contrast-to-noise ratio of 5.6 ± 0.2 (7.8 ± 0.3) for aluminium (lead) compared to air. The tomographic reconstruction of a coaxial adapter serves as experimental evidence of the technique and yields a contrast-to-noise ratio of 15.3 ± 1.0 and a FWHM edge resolution of (117 ± 4) μm.

Ultra-high resolution electron microscopy

DOE PAGES

Oxley, Mark P.; Lupini, Andrew R.; Pennycook, Stephen J.

2016-12-23

The last two decades have seen dramatic advances in the resolution of the electron microscope brought about by the successful correction of lens aberrations that previously limited resolution for most of its history. Here we briefly review these advances, the achievement of sub-Ångstrom resolution and the ability to identify individual atoms, their bonding configurations and even their dynamics and diffusion pathways. We then present a review of the basic physics of electron scattering, lens aberrations and their correction, and an approximate imaging theory for thin crystals which provides physical insight into the various different imaging modes. Then we proceed tomore » describe a more exact imaging theory starting from Yoshioka’s formulation and covering full image simulation methods using Bloch waves, the multislice formulation and the frozen phonon/quantum excitation of phonons models. Delocalization of inelastic scattering has become an important limiting factor at atomic resolution. We therefore discuss this issue extensively, showing how the full-width-half-maximum is the appropriate measure for predicting image contrast, but the diameter containing 50% of the excitation is an important measure of the range of the interaction. These two measures can differ by a factor of 5, are not a simple function of binding energy, and full image simulations are required to match to experiment. The Z-dependence of annular dark field images is also discussed extensively, both for single atoms and for crystals, and we show that temporal incoherence must be included accurately if atomic species are to be identified through matching experimental intensities to simulations. Finally we mention a few promising directions for future investigation.« less

Generation of Gigawatt Circularly Polarized Attosecond-Pulse Pairs

NASA Astrophysics Data System (ADS)

Hu, K.; Wu, H.-C.

2017-12-01

A novel scheme for generating a pair of gigawatt attosecond pulses by coherent Thomson scattering from relativistic electron sheets is proposed. With a circularly polarized relativistic laser pulse, the scattered x-ray signal can have a saddlelike temporal profile, where the lower electromagnetic frequencies are found mostly in the center region of this saddlelike profile. By filtering out the latter, we can obtain two few-attosecond pulses separated by a subfemtosecond interval, which is tunable by controlling the energy of the sheet electrons. Such a pulse pair can be useful for an attosecond pump probe at an unprecedented time resolution and for ultrafast chiral studies in molecules and materials.

Stimulated resonant x-ray Raman scattering with incoherent radiation

NASA Astrophysics Data System (ADS)

Weninger, Clemens; Rohringer, Nina

2013-11-01

We present a theoretical study on stimulated electronic Raman scattering in neon by resonant excitation with an x-ray free electron laser (XFEL). This study is in support of the recent experimental demonstration [C. Weninger , Phys. Rev. Lett. (to be published)] of stimulated x-ray Raman scattering. Focusing the broadband XFEL pulses into a cell of neon gas at atmospheric pressure a strong inelastic x-ray scattering signal in the forward direction was observed, as the x-ray energy was varied across the region of core-excited Rydberg states and the K edge. The broadband and intrinsically incoherent x-ray pulses from the XFEL lead to a rich, structured line shape of the scattered radiation. We present a generalized Maxwell-Liouville-von Neumann approach to self-consistently solve for the amplification of the scattered radiation along with the time evolution of the density matrix of the atomic and residual ionic system. An in-depth analysis of the evolution of the emission spectra as a function of the Raman gain is presented. Furthermore, we propose the use of statistical methods to obtain high-resolution scattering data beyond the lifetime broadening despite pumping with incoherent x-ray pulses.

Precision measurement of quasi-elastic transverse and longitudinal response functions in the range 0.55 GeV/c lte |q-right arrow| lte 1.0 GeV/c

DOE Office of Scientific and Technical Information (OSTI.GOV)

Atac, Hamza

The Coulomb Sum is defined by the quasi-elastic nucleon knock-out process and it is the integration of the longitudinal response function over the energy loss of the incident electron. The Coulomb sum goes to the total charge at large q. The existing measurements of the Coulomb Sum Rule show disagreement with the theoretical calculations for the medium and heavy nuclei. To find the reason behind the disagreement might answer the question of whether the properties of the nucleons are affected by the nuclear medium or not. In order to determine the Coulomb Sum in nuclei, a precision measurement of inclusivemore » electron scattering in the quasi-elastic region was performed at the Thomas Jefferson National Accelerator Facility. Incident electrons with energies ranging from 0.4 GeV to 4 GeV scattered off 4He,12C,56Fe and 208Pb nuclei at four scattering angles (15 deg.; 60 deg.; 90 deg.; 120 deg.) and scattered energies ranging from 0.1 GeV to 4 GeV. The Born cross sections were extracted for the Left High Resolution Spectrometer (LHRS) and the Right High Resolution Spectrometer 56Fe data. The Rosenbluth separation was performed to extract the transverse and longitudinal response functions at 650 MeV three-momentum transfer. The preliminary results of the longitudinal and transverse functions were extracted for 56Fe target at 650 MeV three-momentum transfer.« less

Quartz-based flat-crystal resonant inelastic x-ray scattering spectrometer with sub-10 meV energy resolution

DOE PAGES

Kim, Jungho; Casa, D.; Said, Ayman; ...

2018-01-31

Continued improvement of the energy resolution of resonant inelastic x-ray scattering (RIXS) spectrometers is crucial for fulfilling the potential of this technique in the study of electron dynamics in materials of fundamental and technological importance. In particular, RIXS is the only alternative tool to inelastic neutron scattering capable of providing fully momentum resolved information on dynamic spin structures of magnetic materials, but is limited to systems whose magnetic excitation energy scales are comparable to the energy resolution. The state-of-the-art spherical diced crystal analyzer optics provides energy resolution as good as 25 meV but has already reached its theoretical limit. Formore » this study, we demonstrate a novel sub-10 meV RIXS spectrometer based on flat-crystal optics at the Ir-L3 absorption edge (11.215 keV) that achieves an analyzer energy resolution of 3.9 meV, very close to the theoretical value of 3.7 meV. In addition, the new spectrometer allows efficient polarization analysis without loss of energy resolution. The performance of the instrument is emonstrated using longitudinal acoustical and optical phonons in diamond, and magnon in Sr 3Ir 2O 7. The novel sub-10 meV RIXS spectrometer thus provides a window into magnetic materials with small energy scales.« less

Quartz-based flat-crystal resonant inelastic x-ray scattering spectrometer with sub-10 meV energy resolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Jungho; Casa, D.; Said, Ayman

Continued improvement of the energy resolution of resonant inelastic x-ray scattering (RIXS) spectrometers is crucial for fulfilling the potential of this technique in the study of electron dynamics in materials of fundamental and technological importance. In particular, RIXS is the only alternative tool to inelastic neutron scattering capable of providing fully momentum resolved information on dynamic spin structures of magnetic materials, but is limited to systems whose magnetic excitation energy scales are comparable to the energy resolution. The state-of-the-art spherical diced crystal analyzer optics provides energy resolution as good as 25 meV but has already reached its theoretical limit. Formore » this study, we demonstrate a novel sub-10 meV RIXS spectrometer based on flat-crystal optics at the Ir-L3 absorption edge (11.215 keV) that achieves an analyzer energy resolution of 3.9 meV, very close to the theoretical value of 3.7 meV. In addition, the new spectrometer allows efficient polarization analysis without loss of energy resolution. The performance of the instrument is emonstrated using longitudinal acoustical and optical phonons in diamond, and magnon in Sr 3Ir 2O 7. The novel sub-10 meV RIXS spectrometer thus provides a window into magnetic materials with small energy scales.« less

Impact of metal gates on remote phonon scattering in titanium nitride/hafnium dioxide n-channel metal-oxide-semiconductor field effect transistors-low temperature electron mobility study

NASA Astrophysics Data System (ADS)

Maitra, Kingsuk; Frank, Martin M.; Narayanan, Vijay; Misra, Veena; Cartier, Eduard A.

2007-12-01

We report low temperature (40-300 K) electron mobility measurements on aggressively scaled [equivalent oxide thickness (EOT)=1 nm] n-channel metal-oxide-semiconductor field effect transistors (nMOSFETs) with HfO2 gate dielectrics and metal gate electrodes (TiN). A comparison is made with conventional nMOSFETs containing HfO2 with polycrystalline Si (poly-Si) gate electrodes. No substantial change in the temperature acceleration factor is observed when poly-Si is replaced with a metal gate, showing that soft optical phonons are not significantly screened by metal gates. A qualitative argument based on an analogy between remote phonon scattering and high-resolution electron energy-loss spectroscopy (HREELS) is provided to explain the underlying physics of the observed phenomenon. It is also shown that soft optical phonon scattering is strongly damped by thin SiO2 interface layers, such that room temperature electron mobility values at EOT=1 nm become competitive with values measured in nMOSFETs with SiON gate dielectrics used in current high performance processors.

Direct observation of electronic and nuclear ground state splitting in external magnetic field by inelastic neutron scattering on oxidized ferrocene and ferrocene containing polymers

NASA Astrophysics Data System (ADS)

Appel, Markus; Frick, Bernhard; Elbert, Johannes; Gallei, Markus; Stühn, Bernd

2015-01-01

The quantum mechanical splitting of states by interaction of a magnetic moment with an external magnetic field is well known, e.g., as Zeeman effect in optical transitions, and is also often seen in magnetic neutron scattering. We report excitations observed in inelastic neutron spectroscopy on the redox-responsive polymer poly(vinylferrocene). They are interpreted as splitting of the electronic ground state in the organometallic ferrocene units attached to the polymer chain where a magnetic moment is created by oxidation. In a second experiment using high resolution neutron backscattering spectroscopy we observe the hyperfine splitting, i.e., interaction of nuclear magnetic moments with external magnetic fields leading to sub-μeV excitations observable in incoherent neutron spin-flip scattering on hydrogen and vanadium nuclei.

Direct Imaging of Radionuclide-Produced Electrons and Positrons with an Ultrathin Phosphor

PubMed Central

Chen, Liying; Gobar, Lisa S.; Knowles, Negar G.; Liu, Zhonglin; Gmitro, Arthur F.; Barrett, Harrison H.

2008-01-01

Current electron detectors are either unable to image in vivo or lack sufficient spatial resolution because of electron scattering in thick detector materials. This study was aimed at developing a sensitive high-resolution system capable of detecting electron-emitting isotopes in vivo. Methods The system uses a lens-coupled charge-coupled-device camera to capture the scintillation light excited by an electron-emitting object near an ultrathin phosphor. The spatial resolution and sensitivity of the system were measured with a 3.7-kBq 90Y/90Sr β-source and a 70-µm resin bead labeled with 99mTc. Finally, we imaged the 99mTc-pertechnetate concentration in the mandibular gland of a mouse in vivo. Results Useful images were obtained with only a few hundred emitted β particles from the 90Y/90Sr source or conversion electrons from the 99mTc bead source. The in vivo image showed a clear profile of the mandibular gland and many fine details with exposures of as low as 30 s. All measurements were consistent with a spatial resolution of about 50 µm, corresponding to 2.5 detector pixels with the current camera. Conclusion Our new electron-imaging system can image electron-emitting isotope distributions at high resolution and sensitivity. The system is useful for in vivo imaging of small animals and small, exposed regions on humans. The ability to image β particles, positrons, and conversion electrons makes the system applicable to most isotopes. PMID:18552136

Collimator application for microchannel plate image intensifier resolution improvement

DOEpatents

Thomas, Stanley W.

1996-02-27

A collimator is included in a microchannel plate image intensifier (MCPI). Collimators can be useful in improving resolution of MCPIs by eliminating the scattered electron problem and by limiting the transverse energy of electrons reaching the screen. Due to its optical absorption, a collimator will also increase the extinction ratio of an intensifier by approximately an order of magnitude. Additionally, the smooth surface of the collimator will permit a higher focusing field to be employed in the MCP-to-collimator region than is currently permitted in the MCP-to-screen region by the relatively rough and fragile aluminum layer covering the screen. Coating the MCP and collimator surfaces with aluminum oxide appears to permit additional significant increases in the field strength, resulting in better resolution.

Demonstration of x-ray Thomson scattering using picosecond K-α x-ray sources in the characterization of dense heated matter

DOE PAGES

Kritcher, A. L.; Neumayer, P.; Lee, H. J.; ...

2008-10-31

Here, we present K-α x-ray Thomson scattering from shock compressed matter for use as a diagnostic in determining the temperature, density, and ionization state with picosecond resolution. The development of this source as a diagnostic as well as stringent requirements for successful K-α x-ray Thomson scattering are addressed. Here, the first elastic and inelastic scattering measurements on a medium size laser facility have been observed. We present scattering data from solid density carbon plasmas with >1X 10 5 photons in the elastic peak that validate the capability of single shot characterization of warm dense matter and the ability to usemore » this scattering source at future free electron lasers and for fusion experiments at the National Ignition Facility (NIF), LLNL.« less

Resonant nuclear scattering of synchrotron radiation: Detector development and specular scattering from a thin layer of {sup 57}Fe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baron, A.Q.R.

1995-04-01

This thesis explores resonant nudear scattering of synchrotron radiation. An introductory chapter describes some useful concepts, such as speedup and coherent enhancement, in the context of some basic physical principles. Methods of producing highly monochromatic synchrotron beams usmg either electronic or nuclear scattering are also discussed. The body of the thesis concentrates on detector development and specular scattering from iynthetic layered materials. A detector employing n-dcrochannel plate electron multipliers is shown to have good ({approximately}50%) effidency for detecting 14.4 key x-rays incident at small ({approximately}0.5 degree) grazing angles onto Au or CsI photocathodes. However, being complicated to use, it wasmore » replaced with a large area (>=lan2) avalanche photodiode (APD) detector. The APD`s are simpler to use and have comparable (30--70%) efficiencies at 14.4 key, subnanosecond time resolution, large dynan-dc range (usable at rates up to {approximately}10{sup 8} photons/second) and low (<{approximately}0.01 cts/sec) background rates. Maxwell`s equations are used to derive the specular x-ray reflectivity of layered materials with resonant transitions and complex polarization dependencies. The effects of interfadal roughness are treated with some care, and the distorted wave Born approximation (DWBA) used to describe electronic scattering is generalized to the nuclear case. The implications of the theory are discussed in the context of grazing incidence measurements with emphasis on the kinematic and dynamical aspects of the scattering.« less

A menu of electron probes for optimising information from scanning transmission electron microscopy.

PubMed

Nguyen, D T; Findlay, S D; Etheridge, J

2018-01-01

We assess a selection of electron probes in terms of the spatial resolution with which information can be derived about the structure of a specimen, as opposed to the nominal image resolution. Using Ge [001] as a study case, we investigate the scattering dynamics of these probes and determine their relative merits in terms of two qualitative criteria: interaction volume and interpretability. This analysis provides a 'menu of probes' from which an optimum probe for tackling a given materials science question can be selected. Hollow cone, vortex and spherical wave fronts are considered, from unit cell to Ångstrom size, and for different defocus and specimen orientations. Copyright © 2017 Elsevier B.V. All rights reserved.

From structure to structural dynamics: Ahmed Zewail's legacy.

PubMed

Chergui, Majed; Thomas, John Meurig

2017-07-01

In this brief tribute to Ahmed Zewail, we highlight and place in the historical context, several of the major achievements that he and his colleagues have made in Femtochemistry (of which he was the principal instigator) and his introduction of ultrafast electron scattering, diffraction, microscopy and spectroscopy. By achieving a sub-picosecond temporal resolution, coupled with a picometer spatial resolution, he revolutionised our understanding of the corpus of chemical, physical, biological and materials science systems.

On macromolecular refinement at subatomic resolution withinteratomic scatterers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Afonine, Pavel V.; Grosse-Kunstleve, Ralf W.; Adams, Paul D.

2007-11-09

A study of the accurate electron density distribution in molecular crystals at subatomic resolution, better than {approx} 1.0 {angstrom}, requires more detailed models than those based on independent spherical atoms. A tool conventionally used in small-molecule crystallography is the multipolar model. Even at upper resolution limits of 0.8-1.0 {angstrom}, the number of experimental data is insufficient for the full multipolar model refinement. As an alternative, a simpler model composed of conventional independent spherical atoms augmented by additional scatterers to model bonding effects has been proposed. Refinement of these mixed models for several benchmark datasets gave results comparable in quality withmore » results of multipolar refinement and superior of those for conventional models. Applications to several datasets of both small- and macro-molecules are shown. These refinements were performed using the general-purpose macromolecular refinement module phenix.refine of the PHENIX package.« less

On macromolecular refinement at subatomic resolution with interatomic scatterers

PubMed Central

Afonine, Pavel V.; Grosse-Kunstleve, Ralf W.; Adams, Paul D.; Lunin, Vladimir Y.; Urzhumtsev, Alexandre

2007-01-01

A study of the accurate electron-density distribution in molecular crystals at subatomic resolution (better than ∼1.0 Å) requires more detailed models than those based on independent spherical atoms. A tool that is conventionally used in small-molecule crystallography is the multipolar model. Even at upper resolution limits of 0.8–1.0 Å, the number of experimental data is insufficient for full multipolar model refinement. As an alternative, a simpler model composed of conventional independent spherical atoms augmented by additional scatterers to model bonding effects has been proposed. Refinement of these mixed models for several benchmark data sets gave results that were comparable in quality with the results of multipolar refinement and superior to those for conventional models. Applications to several data sets of both small molecules and macromolecules are shown. These refinements were performed using the general-purpose macromolecular refinement module phenix.refine of the PHENIX package. PMID:18007035

On macromolecular refinement at subatomic resolution with interatomic scatterers.

PubMed

Afonine, Pavel V; Grosse-Kunstleve, Ralf W; Adams, Paul D; Lunin, Vladimir Y; Urzhumtsev, Alexandre

2007-11-01

A study of the accurate electron-density distribution in molecular crystals at subatomic resolution (better than approximately 1.0 A) requires more detailed models than those based on independent spherical atoms. A tool that is conventionally used in small-molecule crystallography is the multipolar model. Even at upper resolution limits of 0.8-1.0 A, the number of experimental data is insufficient for full multipolar model refinement. As an alternative, a simpler model composed of conventional independent spherical atoms augmented by additional scatterers to model bonding effects has been proposed. Refinement of these mixed models for several benchmark data sets gave results that were comparable in quality with the results of multipolar refinement and superior to those for conventional models. Applications to several data sets of both small molecules and macromolecules are shown. These refinements were performed using the general-purpose macromolecular refinement module phenix.refine of the PHENIX package.

Long-range two-dimensional superstructure in the superconducting electron-doped cuprate Pr 0.88 LaCe 0.12 CuO 4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campbell, B. J.; Rosenkranz, S.; Kang, H. J.

2015-07-01

Utilizing single-crystal synchrotron x-ray scattering, we observe distorted CuO 2 planes in the electron- doped superconductor Pr 1-xLaCe xCuO 4+δ , x =0.12. Resolution-limited rods of scattering are indicative of a long-range two-dimensional 2√2 × 2√2 superstructure in the a-b plane, adhering to planar space-group symmetry p4gm, which is subject to stacking disorder perpendicular to the planes. This superstructure is present only in annealed, superconducting samples, but not in the as-grown, nonsuperconducting samples. These long-range distortions of the CuO 2 planes, which are generally considered to be detrimental to superconductivity, have avoided detection to date due to the challenges ofmore » observing and interpreting subtle diffuse-scattering features.« less

Topology of the electron density of d0 transition metal compounds at subatomic resolution.

PubMed

Batke, Kilian; Eickerling, Georg

2013-11-14

Accurate X-ray diffraction experiments allow for a reconstruction of the electron density distribution of solids and molecules in a crystal. The basis for the reconstruction of the electron density is in many cases a multipolar expansion of the X-ray scattering factors in terms of spherical harmonics, a so-called multipolar model. This commonly used ansatz splits the total electron density of each pseudoatom in the crystal into (i) a spherical core, (ii) a spherical valence, and (iii) a nonspherical valence contribution. Previous studies, for example, on diamond and α-silicon have already shown that this approximation is no longer valid when ultrahigh-resolution diffraction data is taken into account. We report here the results of an analysis of the calculated electron density distribution in the d(0) transition metal compounds [TMCH3](2+) (TM = Sc, Y, and La) at subatomic resolution. By a detailed molecular orbital analysis, it is demonstrated that due to the radial nodal structure of the 3d, 4d, and 5d orbitals involved in the TM-C bond formation a significant polarization of the electron density in the inner electronic shells of the TM atoms is observed. We further show that these polarizations have to be taken into account by an extended multipolar model in order to recover accurate electron density distributions from high-resolution structure factors calculated for the title compounds.

Synthesis and characterization of metal-dielectric composites with copper nanoparticles embedded in a glass matrix: A multitechnique approach

NASA Astrophysics Data System (ADS)

Lipinska-Kalita, Kristina E.; Krol, Denise M.; Hemley, Russell J.; Mariotto, Gino; Kalita, Patricia E.; Ohki, Yoshimichi

2005-09-01

The precipitation and growth of copper nanoparticles in an optically transparent aluminosilicate glass matrix was investigated. The size of particles in this heterophase glass-based composite was modified in a controlled manner by isothermal heat treatments. A multitechnique approach, consisting of Raman scattering spectroscopy, high-resolution transmission electron microscopy, x-ray diffraction technique, and optical absorption spectroscopy, has been used to study the nucleation and crystallization processes. Optical absorption spectroscopy revealed the presence of intense absorption bands attributed to oscillations of free electrons, known as the surface-plasmon resonance band of copper particles, and confirmed a gradual increase of the particles' mean size and density with annealing time. The Raman scattering on acoustical phonons from Cu quantum dots in the glass matrix measured for off-resonance conditions demonstrated the presence of intense, inhomogeneously broadened peaks that have been assigned to the confined acoustic eigenmodes of copper nanoparticles. The particle-size dependence of the acoustic peak energies and the relation between the size distribution and bandwidths of these peaks were derived. High-resolution transmission electron microscopy was used to monitor the nucleation of the nanoparticles and to estimate their mean size.

High-energy-resolution monochromator for nuclear resonant scattering of synchrotron radiation by Te-125 at 35.49 keV

NASA Astrophysics Data System (ADS)

Imai, Yasuhiko; Yoda, Yoshitaka; Kitao, Shinji; Masuda, Ryo; Higashitaniguchi, Satoshi; Inaba, Chika; Seto, Makoto

2007-09-01

We have developed a high-resolution monochromator (HRM) for the measurement of nuclear resonant scattering (NRS) of synchrotron radiation by Te-125 at 35.49 keV using the backscattering of sapphire (9 1 -10 68). HRMs for nuclei with excitation energies less than 30 keV have been successfully developed using high angle diffractions by silicon crystals. Nearly perfect silicon crystal, however, is not suitable for high efficient HRMs at higher energy regions because the symmetry of the crystal structure is high and the Debye-temperature is low. Therefore, we used high quality synthetic sapphire crystal, which has low symmetry of crystal structure and high Debye-temperature. The temperature of the crystal was precisely controlled around 218 K to diffract synchrotron radiation with a Bragg angle of π/2 - 0.52 mrad. Energy was tuned by changing the crystal temperature under the condition of constant diffraction angle. Energy resolution was measured by detecting nuclear forward scattering by Te-125 in enriched TeO II. The relative energy resolution of 2.1×10 -7 is achieved, that is 7.5 meV in energy bandwidth. This HRM opens studies on element-specific dynamics and electronic state of substances containing Te-125.

Method for improving the angular resolution of a neutron scatter camera

DOEpatents

Mascarenhas, Nicholas; Marleau, Peter; Gerling, Mark; Cooper, Robert Lee; Mrowka, Stanley; Brennan, James S.

2012-12-25

An instrument that will directly image the fast fission neutrons from a special nuclear material source wherein the neutron detection efficiency is increased has been described. Instead of the previous technique that uses a time-of-flight (TOF) between 2 widely spaced fixed planes of neutron detectors to measure scatter neutron kinetic energy, we now use the recoil proton energy deposited in the second of the 2 scatter planes which can now be repositioned either much closer together or further apart. However, by doubling the separation distance between the 2 planes from 20 cm to a distance of 40 cm we improved the angular resolution of the detector from about 12.degree. to about 10.degree.. A further doubling of the separation distance to 80 cm provided an addition improvement in angular resolution of the detector to about 6.degree. without adding additional detectors or ancillary electronics. The distance between planes also may be dynamically changed using a suitable common technique such as a gear- or motor-drive to toggle between the various positions. The angular resolution of this new configuration, therefore, is increased at the expanse of detection sensitivity. However, the diminished sensitivity may be acceptable for those applications where the detector is able to interrogate a particular site for an extended period.

Collimator application for microchannel plate image intensifier resolution improvement

DOEpatents

Thomas, S.W.

1996-02-27

A collimator is included in a microchannel plate image intensifier (MCPI). Collimators can be useful in improving resolution of MCPIs by eliminating the scattered electron problem and by limiting the transverse energy of electrons reaching the screen. Due to its optical absorption, a collimator will also increase the extinction ratio of an intensifier by approximately an order of magnitude. Additionally, the smooth surface of the collimator will permit a higher focusing field to be employed in the MCP-to-collimator region than is currently permitted in the MCP-to-screen region by the relatively rough and fragile aluminum layer covering the screen. Coating the MCP and collimator surfaces with aluminum oxide appears to permit additional significant increases in the field strength, resulting in better resolution. 2 figs.

Low-loss electron energy loss spectroscopy: An atomic-resolution complement to optical spectroscopies and application to graphene

DOE PAGES

Kapetanakis, Myron; Zhou, Wu; Oxley, Mark P.; ...

2015-09-25

Photon-based spectroscopies have played a central role in exploring the electronic properties of crystalline solids and thin films. They are a powerful tool for probing the electronic properties of nanostructures, but they are limited by lack of spatial resolution. On the other hand, electron-based spectroscopies, e.g., electron energy loss spectroscopy (EELS), are now capable of subangstrom spatial resolution. Core-loss EELS, a spatially resolved analog of x-ray absorption, has been used extensively in the study of inhomogeneous complex systems. In this paper, we demonstrate that low-loss EELS in an aberration-corrected scanning transmission electron microscope, which probes low-energy excitations, combined with amore » theoretical framework for simulating and analyzing the spectra, is a powerful tool to probe low-energy electron excitations with atomic-scale resolution. The theoretical component of the method combines density functional theory–based calculations of the excitations with dynamical scattering theory for the electron beam. We apply the method to monolayer graphene in order to demonstrate that atomic-scale contrast is inherent in low-loss EELS even in a perfectly periodic structure. The method is a complement to optical spectroscopy as it probes transitions entailing momentum transfer. The theoretical analysis identifies the spatial and orbital origins of excitations, holding the promise of ultimately becoming a powerful probe of the structure and electronic properties of individual point and extended defects in both crystals and inhomogeneous complex nanostructures. The method can be extended to probe magnetic and vibrational properties with atomic resolution.« less

Efficient linear phase contrast in scanning transmission electron microscopy with matched illumination and detector interferometry

DOE PAGES

Ophus, Colin; Ciston, Jim; Pierce, Jordan; ...

2016-02-29

The ability to image light elements in soft matter at atomic resolution enables unprecedented insight into the structure and properties of molecular heterostructures and beam-sensitive nanomaterials. In this study, we introduce a scanning transmission electron microscopy technique combining a pre-specimen phase plate designed to produce a probe with structured phase with a high-speed direct electron detector to generate nearly linear contrast images with high efficiency. We demonstrate this method by using both experiment and simulation to simultaneously image the atomic-scale structure of weakly scattering amorphous carbon and strongly scattering gold nanoparticles. Our method demonstrates strong contrast for both materials, makingmore » it a promising candidate for structural determination of heterogeneous soft/hard matter samples even at low electron doses comparable to traditional phase-contrast transmission electron microscopy. Ultimately, simulated images demonstrate the extension of this technique to the challenging problem of structural determination of biological material at the surface of inorganic crystals.« less

Efficient linear phase contrast in scanning transmission electron microscopy with matched illumination and detector interferometry.

PubMed

Ophus, Colin; Ciston, Jim; Pierce, Jordan; Harvey, Tyler R; Chess, Jordan; McMorran, Benjamin J; Czarnik, Cory; Rose, Harald H; Ercius, Peter

2016-02-29

The ability to image light elements in soft matter at atomic resolution enables unprecedented insight into the structure and properties of molecular heterostructures and beam-sensitive nanomaterials. In this study, we introduce a scanning transmission electron microscopy technique combining a pre-specimen phase plate designed to produce a probe with structured phase with a high-speed direct electron detector to generate nearly linear contrast images with high efficiency. We demonstrate this method by using both experiment and simulation to simultaneously image the atomic-scale structure of weakly scattering amorphous carbon and strongly scattering gold nanoparticles. Our method demonstrates strong contrast for both materials, making it a promising candidate for structural determination of heterogeneous soft/hard matter samples even at low electron doses comparable to traditional phase-contrast transmission electron microscopy. Simulated images demonstrate the extension of this technique to the challenging problem of structural determination of biological material at the surface of inorganic crystals.

Efficient linear phase contrast in scanning transmission electron microscopy with matched illumination and detector interferometry

PubMed Central

Ophus, Colin; Ciston, Jim; Pierce, Jordan; Harvey, Tyler R.; Chess, Jordan; McMorran, Benjamin J.; Czarnik, Cory; Rose, Harald H.; Ercius, Peter

2016-01-01

The ability to image light elements in soft matter at atomic resolution enables unprecedented insight into the structure and properties of molecular heterostructures and beam-sensitive nanomaterials. In this study, we introduce a scanning transmission electron microscopy technique combining a pre-specimen phase plate designed to produce a probe with structured phase with a high-speed direct electron detector to generate nearly linear contrast images with high efficiency. We demonstrate this method by using both experiment and simulation to simultaneously image the atomic-scale structure of weakly scattering amorphous carbon and strongly scattering gold nanoparticles. Our method demonstrates strong contrast for both materials, making it a promising candidate for structural determination of heterogeneous soft/hard matter samples even at low electron doses comparable to traditional phase-contrast transmission electron microscopy. Simulated images demonstrate the extension of this technique to the challenging problem of structural determination of biological material at the surface of inorganic crystals. PMID:26923483

In situ characterization of nanoparticles using Rayleigh scattering

DOE PAGES

Santra, Biswajit; Shneider, Mikhail N.; Car, Roberto

2017-01-10

Here, we report a theoretical analysis showing that Rayleigh scattering could be used to monitor the growth of nanoparticles under arc discharge conditions. We compute the Rayleigh scattering cross sections of the nanoparticles by combining light scattering theory for gas-particle mixtures with calculations of the dynamic electronic polarizability of the nanoparticles. We find that the resolution of the Rayleigh scattering probe is adequate to detect nanoparticles as small as C 60 at the expected concentrations of synthesis conditions in the arc periphery. Larger asymmetric nanoparticles would yield brighter signals, making possible to follow the evolution of the growing nanoparticle populationmore » from the evolution of the scattered intensity. Observable spectral features include characteristic resonant behaviour, shape-dependent depolarization ratio, and mass-dependent line shape. Direct observation of nanoparticles in the early stages of growth with unobtrusive laser probes should give insight on the particle formation mechanisms and may lead to better-controlled synthesis protocols.« less

In situ Characterization of Nanoparticles Using Rayleigh Scattering

PubMed Central

Santra, Biswajit; Shneider, Mikhail N.; Car, Roberto

2017-01-01

We report a theoretical analysis showing that Rayleigh scattering could be used to monitor the growth of nanoparticles under arc discharge conditions. We compute the Rayleigh scattering cross sections of the nanoparticles by combining light scattering theory for gas-particle mixtures with calculations of the dynamic electronic polarizability of the nanoparticles. We find that the resolution of the Rayleigh scattering probe is adequate to detect nanoparticles as small as C60 at the expected concentrations of synthesis conditions in the arc periphery. Larger asymmetric nanoparticles would yield brighter signals, making possible to follow the evolution of the growing nanoparticle population from the evolution of the scattered intensity. Observable spectral features include characteristic resonant behaviour, shape-dependent depolarization ratio, and mass-dependent line shape. Direct observation of nanoparticles in the early stages of growth with unobtrusive laser probes should give insight on the particle formation mechanisms and may lead to better-controlled synthesis protocols. PMID:28071715

In situ characterization of nanoparticles using Rayleigh scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Santra, Biswajit; Shneider, Mikhail N.; Car, Roberto

Here, we report a theoretical analysis showing that Rayleigh scattering could be used to monitor the growth of nanoparticles under arc discharge conditions. We compute the Rayleigh scattering cross sections of the nanoparticles by combining light scattering theory for gas-particle mixtures with calculations of the dynamic electronic polarizability of the nanoparticles. We find that the resolution of the Rayleigh scattering probe is adequate to detect nanoparticles as small as C 60 at the expected concentrations of synthesis conditions in the arc periphery. Larger asymmetric nanoparticles would yield brighter signals, making possible to follow the evolution of the growing nanoparticle populationmore » from the evolution of the scattered intensity. Observable spectral features include characteristic resonant behaviour, shape-dependent depolarization ratio, and mass-dependent line shape. Direct observation of nanoparticles in the early stages of growth with unobtrusive laser probes should give insight on the particle formation mechanisms and may lead to better-controlled synthesis protocols.« less

Mechanisms of decoherence in electron microscopy.

PubMed

Howie, A

2011-06-01

The understanding and where possible the minimisation of decoherence mechanisms in electron microscopy were first studied in plasmon loss, diffraction contrast images but are of even more acute relevance in high resolution TEM phase contrast imaging and electron holography. With the development of phase retrieval techniques they merit further attention particularly when their effect cannot be eliminated by currently available energy filters. The roles of electronic excitation, thermal diffuse scattering, transition radiation and bremsstrahlung are examined here not only in the specimen but also in the electron optical column. Terahertz-range aloof beam electronic excitation appears to account satisfactorily for recent observations of decoherence in electron holography. An apparent low frequency divergence can emerge for the calculated classical bremsstrahlung event probability but can be ignored for photon wavelengths exceeding the required coherence distance or path lengths in the equipment. Most bremsstrahlung event probabilities are negligibly important except possibly in large-angle bending magnets or mandolin systems. A more reliable procedure for subtracting thermal diffuse scattering from diffraction pattern intensities is proposed. Copyright © 2010 Elsevier B.V. All rights reserved.

Angle-resolved molecular beam scattering of NO at the gas-liquid interface.

PubMed

Zutz, Amelia; Nesbitt, David J

2017-08-07

This study presents first results on angle-resolved, inelastic collision dynamics of thermal and hyperthermal molecular beams of NO at gas-liquid interfaces. Specifically, a collimated incident beam of supersonically cooled NO ( 2 Π 1/2 , J = 0.5) is directed toward a series of low vapor pressure liquid surfaces ([bmim][Tf 2 N], squalane, and PFPE) at θ inc = 45(1)°, with the scattered molecules detected with quantum state resolution over a series of final angles (θ s = -60°, -30°, 0°, 30°, 45°, and 60°) via spatially filtered laser induced fluorescence. At low collision energies [E inc = 2.7(9) kcal/mol], the angle-resolved quantum state distributions reveal (i) cos(θ s ) probabilities for the scattered NO and (ii) electronic/rotational temperatures independent of final angle (θ s ), in support of a simple physical picture of angle independent sticking coefficients and all incident NO thermally accommodating on the surface. However, the observed electronic/rotational temperatures for NO scattering reveal cooling below the surface temperature (T elec < T rot < T S ) for all three liquids, indicating a significant dependence of the sticking coefficient on NO internal quantum state. Angle-resolved scattering at high collision energies [E inc = 20(2) kcal/mol] has also been explored, for which the NO scattering populations reveal angle-dependent dynamical branching between thermal desorption and impulsive scattering (IS) pathways that depend strongly on θ s . Characterization of the data in terms of the final angle, rotational state, spin-orbit electronic state, collision energy, and liquid permit new correlations to be revealed and investigated in detail. For example, the IS rotational distributions reveal an enhanced propensity for higher J/spin-orbit excited states scattered into near specular angles and thus hotter rotational/electronic distributions measured in the forward scattering direction. Even more surprisingly, the average NO scattering angle (⟨θ s ⟩) exhibits a remarkably strong correlation with final angular momentum, N, which implies a linear scaling between net forward scattering propensity and torque delivered to the NO projectile by the gas-liquid interface.

Angle-resolved molecular beam scattering of NO at the gas-liquid interface

NASA Astrophysics Data System (ADS)

Zutz, Amelia; Nesbitt, David J.

2017-08-01

This study presents first results on angle-resolved, inelastic collision dynamics of thermal and hyperthermal molecular beams of NO at gas-liquid interfaces. Specifically, a collimated incident beam of supersonically cooled NO (2 Π 1/2, J = 0.5) is directed toward a series of low vapor pressure liquid surfaces ([bmim][Tf2N], squalane, and PFPE) at θinc = 45(1)°, with the scattered molecules detected with quantum state resolution over a series of final angles (θs = -60°, -30°, 0°, 30°, 45°, and 60°) via spatially filtered laser induced fluorescence. At low collision energies [Einc = 2.7(9) kcal/mol], the angle-resolved quantum state distributions reveal (i) cos(θs) probabilities for the scattered NO and (ii) electronic/rotational temperatures independent of final angle (θs), in support of a simple physical picture of angle independent sticking coefficients and all incident NO thermally accommodating on the surface. However, the observed electronic/rotational temperatures for NO scattering reveal cooling below the surface temperature (Telec < Trot < TS) for all three liquids, indicating a significant dependence of the sticking coefficient on NO internal quantum state. Angle-resolved scattering at high collision energies [Einc = 20(2) kcal/mol] has also been explored, for which the NO scattering populations reveal angle-dependent dynamical branching between thermal desorption and impulsive scattering (IS) pathways that depend strongly on θs. Characterization of the data in terms of the final angle, rotational state, spin-orbit electronic state, collision energy, and liquid permit new correlations to be revealed and investigated in detail. For example, the IS rotational distributions reveal an enhanced propensity for higher J/spin-orbit excited states scattered into near specular angles and thus hotter rotational/electronic distributions measured in the forward scattering direction. Even more surprisingly, the average NO scattering angle (⟨θs⟩) exhibits a remarkably strong correlation with final angular momentum, N, which implies a linear scaling between net forward scattering propensity and torque delivered to the NO projectile by the gas-liquid interface.

Theory of the spatial resolution of (scanning) transmission electron microscopy in liquid water or ice layers.

PubMed

de Jonge, Niels

2018-04-01

The sample dependent spatial resolution was calculated for transmission electron microscopy (TEM) and scanning TEM (STEM) of objects (e.g., nanoparticles, proteins) embedded in a layer of liquid water or amorphous ice. The theoretical model includes elastic- and inelastic scattering, beam broadening, and chromatic aberration. Different contrast mechanisms were evaluated as function of the electron dose, the detection angle, and the sample configuration. It was found that the spatial resolution scales with the electron dose to the -1/4th power. Gold- and carbon nanoparticles were examined in the middle of water layers ranging from 0.01--10 µm thickness representing relevant classes of experiments in both materials science and biology. The optimal microscope settings differ between experimental configurations. STEM performs the best for gold nanoparticles for all layer thicknesses, while carbon is best imaged with phase-contrast TEM for thin layers but bright field STEM is preferred for thicker layers. The resolution was also calculated for a water layer enclosed between thin membranes. The influence of chromatic aberration correction for TEM was examined as well. The theory is broadly applicable to other types of materials and sample configurations. Copyright © 2018 Elsevier B.V. All rights reserved.

Water without windows: Evaluating the performance of open cell transmission electron microscopy under saturated water vapor conditions, and assessing its potential for microscopy of hydrated biological specimens.

PubMed

Cassidy, Cathal; Yamashita, Masao; Cheung, Martin; Kalale, Chola; Adaniya, Hidehito; Kuwahara, Ryusuke; Shintake, Tsumoru

2017-01-01

We have performed open cell transmission electron microscopy experiments through pure water vapor in the saturation pressure regime (>0.6 kPa), in a modern microscope capable of sub-Å resolution. We have systematically studied achievable pressure levels, stability and gas purity, effective thickness of the water vapor column and associated electron scattering processes, and the effect of gas pressure on electron optical resolution and image contrast. For example, for 1.3 kPa pure water vapor and 300kV electrons, we report pressure stability of ± 20 Pa over tens of minutes, effective thickness of 0.57 inelastic mean free paths, lattice resolution of 0.14 nm on a reference Au specimen, and no significant degradation in contrast or stability of a biological specimen (M13 virus, with 6 nm body diameter). We have also done some brief experiments to confirm feasibility of loading specimens into an in situ water vapor ambient without exposure to intermediate desiccating conditions. Finally, we have also checked if water experiments had any discernible impact on the microscope performance, and report pertinent vacuum and electron optical data, for reference purposes.

Direct observation and analysis of york-shell materials using low-voltage high-resolution scanning electron microscopy: Nanometal-particles encapsulated in metal-oxide, carbon, and polymer

NASA Astrophysics Data System (ADS)

Asahina, Shunsuke; Suga, Mitsuo; Takahashi, Hideyuki; Young Jeong, Hu; Galeano, Carolina; Schüth, Ferdi; Terasaki, Osamu

2014-11-01

Nanometal particles show characteristic features in chemical and physical properties depending on their sizes and shapes. For keeping and further enhancing their features, the particles should be protected from coalescence or degradation. One approach is to encapsulate the nanometal particles inside pores with chemically inert or functional materials, such as carbon, polymer, and metal oxides, which contain mesopores to allow permeation of only chemicals not the nanometal particles. Recently developed low-voltage high-resolution scanning electron microscopy was applied to the study of structural, chemical, and electron state of both nanometal particles and encapsulating materials in yolk-shell materials of Au@C, Ru/Pt@C, Au@TiO2, and Pt@Polymer. Progresses in the following categories were shown for the yolk-shell materials: (i) resolution of topographic image contrast by secondary electrons, of atomic-number contrast by back-scattered electrons, and of elemental mapping by X-ray energy dispersive spectroscopy; (ii) sample preparation for observing internal structures; and (iii) X-ray spectroscopy such as soft X-ray emission spectroscopy. Transmission electron microscopy was also used for characterization of Au@C.

First measurement of time evolution of electron temperature profiles with Nd:YAG Thomson scattering system on Heliotron J.

PubMed

Kenmochi, N; Minami, T; Takahashi, C; Tei, S; Mizuuchi, T; Kobayashi, S; Nagasaki, K; Nakamura, Y; Okada, H; Kado, S; Yamamoto, S; Ohshima, S; Konoshima, S; Shi, N; Zang, L; Ohtani, Y; Kasajima, K; Sano, F

2014-11-01

A Nd:YAG Thomson scattering system has been developed for Heliotron J. The system consists of two 550 mJ 50 Hz lasers, large collection optics, and 25 radial channel (∼1 cm spatial resolution) interference polychromators. This measurement system achieves a S/N ratio of ∼50 for low-density plasma (ne ∼ 0.5 × 10(19) m(-3)). A time evolution of electron temperature profiles was measured with this system for a high-intensity gas-puff (HIGP) fueling neutral-beam-injection plasma. The peripheral temperature of the higher-density phase after HIGP recovers to the low-density pre-HIGP level, suggesting that improving particle transport in the HIGP plasma may be possible.

The role of gas in determining image quality and resolution during in situ scanning transmission electron microscopy experiments

DOE PAGES

Zhu, Yuanyuan; Browning, Nigel D.

2017-05-24

As gas-solid heterogeneous catalytic reactions are molecular in nature, a full mechanistic understanding of the process requires atomic scale characterization under realistic operating conditions. While atomic resolution imaging has become a routine in modern high-vacuum (scanning) transmission electron microscopy ((S)TEM), both image quality and resolution nominally degrade when reaction gases are introduced. In this work, we systematically assess the effects of different gases at various pressures on the quality and resolution of images obtained at room temperature in the annular dark field STEM imaging mode using a differentially pumped (DP) gas cell. This imaging mode is largely free from inelasticmore » scattering effects induced by the presence of gases and retains good imaging properties over a wide range of gas mass/pressures. Furthermore, we demonstrate the application of the ESTEM with atomic resolution images of a complex oxide alkane oxidation catalyst MoVNbTeOx (M1) immersed in light and heavy gas environments.« less

A large area high resolution imaging detector for fast atom diffraction

NASA Astrophysics Data System (ADS)

Lupone, Sylvain; Soulisse, Pierre; Roncin, Philippe

2018-07-01

We describe a high resolution imaging detector based on a single 80 mm micro-channel-plate (MCP) and a phosphor screen mounted on a UHV flange of only 100 mm inner diameter. It relies on standard components and we describe its performance with one or two MCPs. A resolution of 80 μm rms is observed on the beam profile. At low count rate, individual impact can be pinpointed with few μm accuracy but the resolution is probably limited by the MCP channel diameter. The detector has been used to record the diffraction of fast atoms at grazing incidence on crystal surfaces (GIFAD), a technique probing the electronic density of the topmost layer only. The detector was also used to record the scattering profile during azimuthal scan of the crystal to produce triangulation curves revealing the surface crystallographic directions of molecular layers. It should also be compatible with reflection high energy electron (RHEED) experiment when fragile surfaces require a low exposure to the electron beam. The discussions on the mode of operation specific to diffraction experiments apply also to commercial detectors.

Electron-beam broadening in amorphous carbon films in low-energy scanning transmission electron microscopy.

PubMed

Drees, H; Müller, E; Dries, M; Gerthsen, D

2018-02-01

Resolution in scanning transmission electron microscopy (STEM) is ultimately limited by the diameter of the electron beam. The electron beam diameter is not only determined by the properties of the condenser lens system but also by electron scattering in the specimen which leads to electron-beam broadening and degradation of the resolution with increasing specimen thickness. In this work we introduce a new method to measure electron-beam broadening which is based on STEM imaging with a multi-segmented STEM detector. We focus on STEM at low electron energies between 10 and 30 keV and use an amorphous carbon film with known thickness as test object. The experimental results are compared with calculated beam diameters using different analytical models and Monte-Carlo simulations. We find excellent agreement of the experimental data with the recently published model by Gauvin and Rudinsky [1] for small t/λ el (thickness to elastic mean free path) values which are considered in our study. Copyright © 2017 Elsevier B.V. All rights reserved.

Electron-density-sensitive Line Ratios of Fe XIII– XVI from Laboratory Sources Compared to CHIANTI

NASA Astrophysics Data System (ADS)

Weller, M. E.; Beiersdorfer, P.; Soukhanovskii, V. A.; Scotti, F.; LeBlanc, B. P.

2018-02-01

We present electron-density-sensitive line ratios for Fe XIII– XVI measured in the spectral wavelength range of 200–440 Å and an electron density range of (1–4) × 1013 cm‑3. The results provide a test at the high-density limit of density-sensitive line ratios useful for astrophysical studies. The measurements were performed on the National Spherical Torus Experiment-Upgrade, where electron densities were measured independently by the laser Thomson scattering diagnostic. Spectra were collected with a flat-field grazing-incidence spectrometer, which provided a spectral resolution of up to 0.3 Å, i.e., high resolution across the broad wavelength range. The response of the instrument was relatively calibrated using spectroscopic techniques in order to improve accuracy. The line ratios are compared to other laboratory sources and the latest version of CHIANTI (8.0.2), and an agreement within 30% is found.

Elastic electron differential cross sections for argon atom in the intermediate energy range from 40 eV to 300 eV

NASA Astrophysics Data System (ADS)

Ranković, Miloš Lj.; Maljković, Jelena B.; Tökési, Károly; Marinković, Bratislav P.

2018-02-01

Measurements and calculations for electron elastic differential cross sections (DCS) of argon atom in the energy range from 40 to 300 eV are presented. DCS have been measured in the crossed beam arrangement of the electron spectrometer with an energy resolution of 0.5 eV and angular resolution of 1.5∘ in the range of scattering angles from 20∘ to 126∘. Both angular behaviour and energy dependence of DCS are obtained in a separate sets of experiments, while the absolute scale is achieved via relative flow method, using helium as a reference gas. All data is corrected for the energy transmission function, changes of primary electron beam current and target pressure, and effective path length (volume correction). DCSs are calculated in relativistic framework by expressing the Mott's cross sections in partial wave expansion. Our results are compared with other available data.

A threshold gas Cerenkov detector for the spin asymmetries of the nucleon experiment

DOE PAGES

Armstrong, Whitney R.; Choi, Seonho; Kaczanowicz, Ed; ...

2015-09-26

In this study, we report on the design, construction, commissioning, and performance of a threshold gas Cerenkov counter in an open configuration, which operates in a high luminosity environment and produces a high photo-electron yield. Part of a unique open geometry detector package known as the Big Electron Telescope Array, this Cerenkov counter served to identify scattered electrons and reject produced pions in an inclusive scattering experiment known as the Spin Asymmetries of the Nucleon Experiment E07-003 at the Thomas Jefferson National Accelerator Facility (TJNAF) also known as Jefferson Lab. The experiment consisted of a measurement of double spin asymmetriesmore » A || and A ⊥ of a polarized electron beam impinging on a polarized ammonia target. The Cerenkov counter's performance is characterised by a yield of about 20 photoelectrons per electron or positron track. Thanks to this large number of photoelectrons per track, the Cerenkov counter had enough resolution to identify electron-positron pairs from the conversion of photons resulting mainly from π 0 decays.« less

Conformational landscape of a virus by single-particle X-ray scattering

DOE PAGES

Hosseinizadeh, Ahmad; Mashayekhi, Ghoncheh; Copperman, Jeremy; ...

2017-08-14

Using a manifold-based analysis of experimental diffraction snapshots from an X-ray free electron laser, we determine the three-dimensional structure and conformational landscape of the PR772 virus to a detector-limited resolution of 9 nm. Our results indicate that a single conformational coordinate controls reorganization of the genome, growth of a tubular structure from a portal vertex and release of the genome. Furthermore, these results demonstrate that single-particle X-ray scattering has the potential to shed light on key biological processes.

Absorption band oscillator strengths of N2 transitions between 95.8 and 99.4 nm

NASA Technical Reports Server (NTRS)

Stark, G.; Smith, Peter L.; Huber, K. P.; Yoshino, K.; Stevens, M. H.; Ito, K.

1992-01-01

Molecular nitrogen plays a central role in the energetics of the earth's upper atmosphere and is the major constituent of the atmospheres of the planetary satellites Titan and Triton. This paper reports a new set of absorption oscillator strengths measured at higher resolution for seven bands in the 95.8-99.4 nm region. The results are compared with earlier, lower resolution absorption measurements, electron scattering measurements, and calculations based on a deperturbation analysis of the excited states.

Thermometry with Subnanometer Resolution in the Electron Microscope Using the Principle of Detailed Balancing.

PubMed

Lagos, Maureen J; Batson, Philip E

2018-06-13

We measure phonon energy gain and loss down to 20 meV in a single nanostructure using an atom-wide monochromatic electron beam. We show that the bulk and surface, energy loss and energy gain processes obey the principle of detailed balancing in nanostructured systems at thermal equilibrium. By plotting the logarithm of the ratio of the loss and gain bulk/surface scattering as a function of the excitation energy, we find a linear behavior, expected from detailed balance arguments. Since that universal linearity scales with the inverse of the nanosystem temperature only, we can measure the temperature of the probed object with precision down to about 1 K without reference to the nanomaterial. We also show that subnanometer spatial resolution (down to ∼2 Å) can be obtained using highly localized acoustic phonon scattering. The surface phonon polariton signal can also be used to measure the temperature near the nanostructure surfaces, but with unavoidable averaging over several nanometers. Comparison between transmission and aloof probe configurations suggests that our method exhibits noninvasive characteristics. Our work demonstrates the validity of the principle of detailed balancing within nanoscale materials at thermal equilibrium, and it describes a transparent method to measure nanoscale temperature, thus representing an advance in the development of a noninvasive method for measurements with angstrom resolution.

Extreme ultraviolet resonant inelastic X-ray scattering (RIXS) at a seeded free-electron laser

DOE PAGES

Dell’Angela, M.; Hieke, F.; Malvestuto, M.; ...

2016-12-12

In the past few years, we have been witnessing an increased interest for studying materials properties under non-equilibrium conditions. Several well established spectroscopies for experiments in the energy domain have been successfully adapted to the time domain with sub-picosecond time resolution. Here we show the realization of high resolution resonant inelastic X-ray scattering (RIXS) with a stable ultrashort X-ray source such as an externally seeded free electron laser (FEL). We have designed and constructed a RIXS experimental endstation that allowed us to successfully measure the d-d excitations in KCoF 3 single crystals at the cobalt M 2,3-edge at FERMI FELmore » (Elettra-Sincrotrone Trieste, Italy). The FEL-RIXS spectra show an excellent agreement with the ones obtained from the same samples at the MERIXS endstation of the MERLIN beamline at the Advanced Light Source storage ring (Berkeley, USA). We established experimental protocols for performing time resolved RIXS experiments at a FEL source to avoid X ray-induced sample damage, while retaining comparable acquisition time to the synchrotron based measurements. Finally, we measured and modelled the influence of the FEL mixed electromagnetic modes, also present in externally seeded FELs, and the beam transport with ~120 meV experimental resolution achieved in the presented RIXS setup.« less

Computed radiography imaging plates and associated methods of manufacture

DOEpatents

Henry, Nathaniel F.; Moses, Alex K.

2015-08-18

Computed radiography imaging plates incorporating an intensifying material that is coupled to or intermixed with the phosphor layer, allowing electrons and/or low energy x-rays to impart their energy on the phosphor layer, while decreasing internal scattering and increasing resolution. The radiation needed to perform radiography can also be reduced as a result.

Merging single-shot XFEL diffraction data from inorganic nanoparticles: a new approach to size and orientation determination

DOE PAGES

Li, Xuanxuan; Spence, John C. H.; Hogue, Brenda G.; ...

2017-09-22

X-ray free-electron lasers (XFELs) provide new opportunities for structure determination of biomolecules, viruses and nanomaterials. With unprecedented peak brilliance and ultra-short pulse duration, XFELs can tolerate higher X-ray doses by exploiting the femtosecond-scale exposure time, and can thus go beyond the resolution limits achieved with conventional X-ray diffraction imaging techniques. Using XFELs, it is possible to collect scattering information from single particles at high resolution, however particle heterogeneity and unknown orientations complicate data merging in three-dimensional space. Using the Linac Coherent Light Source (LCLS), synthetic inorganic nanocrystals with a core–shell architecture were used as a model system for proof-of-principle coherentmore » diffractive single-particle imaging experiments. To deal with the heterogeneity of the core–shell particles, new computational methods have been developed to extract the particle size and orientation from the scattering data to assist data merging. The size distribution agrees with that obtained by electron microscopy and the merged data support a model with a core–shell architecture.« less

Merging single-shot XFEL diffraction data from inorganic nanoparticles: a new approach to size and orientation determination

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xuanxuan; Spence, John C. H.; Hogue, Brenda G.

X-ray free-electron lasers (XFELs) provide new opportunities for structure determination of biomolecules, viruses and nanomaterials. With unprecedented peak brilliance and ultra-short pulse duration, XFELs can tolerate higher X-ray doses by exploiting the femtosecond-scale exposure time, and can thus go beyond the resolution limits achieved with conventional X-ray diffraction imaging techniques. Using XFELs, it is possible to collect scattering information from single particles at high resolution, however particle heterogeneity and unknown orientations complicate data merging in three-dimensional space. Using the Linac Coherent Light Source (LCLS), synthetic inorganic nanocrystals with a core–shell architecture were used as a model system for proof-of-principle coherentmore » diffractive single-particle imaging experiments. To deal with the heterogeneity of the core–shell particles, new computational methods have been developed to extract the particle size and orientation from the scattering data to assist data merging. The size distribution agrees with that obtained by electron microscopy and the merged data support a model with a core–shell architecture.« less

Holography and coherent diffraction with low-energy electrons: A route towards structural biology at the single molecule level.

PubMed

Latychevskaia, Tatiana; Longchamp, Jean-Nicolas; Escher, Conrad; Fink, Hans-Werner

2015-12-01

The current state of the art in structural biology is led by NMR, X-ray crystallography and TEM investigations. These powerful tools however all rely on averaging over a large ensemble of molecules. Here, we present an alternative concept aiming at structural analysis at the single molecule level. We show that by combining electron holography and coherent diffraction imaging estimations concerning the phase of the scattered wave become needless as the phase information is extracted from the data directly and unambiguously. Performed with low-energy electrons the resolution of this lens-less microscope is just limited by the De Broglie wavelength of the electron wave and the numerical aperture, given by detector geometry. In imaging freestanding graphene, a resolution of 2Å has been achieved revealing the 660.000 unit cells of the graphene sheet from a single data set. Once applied to individual biomolecules the method shall ultimately allow for non-destructive imaging and imports the potential to distinguish between different conformations of proteins with atomic resolution. Copyright © 2015. Published by Elsevier B.V.

Non-Proportionality of Electron Response and Energy Resolution of Compton Electrons in Scintillators

NASA Astrophysics Data System (ADS)

Swiderski, L.; Marcinkowski, R.; Szawlowski, M.; Moszynski, M.; Czarnacki, W.; Syntfeld-Kazuch, A.; Szczesniak, T.; Pausch, G.; Plettner, C.; Roemer, K.

2012-02-01

Non-proportionality of light yield and energy resolution of Compton electrons in three scintillators (LaBr3:Ce, LYSO:Ce and CsI:Tl) were studied in a wide energy range from 10 keV up to 1 MeV. The experimental setup was comprised of a High Purity Germanium detector and tested scintillators coupled to a photomultiplier. Probing the non-proportionality and energy resolution curves at different energies was obtained by changing the position of various radioactive sources with respect to both detectors. The distance between both detectors and source was kept small to make use of Wide Angle Compton Coincidence (WACC) technique, which allowed us to scan large range of scattering angles simultaneously and obtain relatively high coincidence rate of 100 cps using weak sources of about 10 μCi activity. The results are compared with those obtained by direct irradiation of the tested scintillators with gamma-ray sources and fitting the full-energy peaks.

Theoretical and experimental differential cross sections for electron impact excitation of the electronic bands of furfural

NASA Astrophysics Data System (ADS)

Jones, D. B.; Neves, R. F. C.; Lopes, M. C. A.; da Costa, R. F.; do N. Varella, M. T.; Bettega, M. H. F.; Lima, M. A. P.; García, G.; Limão-Vieira, P.; Brunger, M. J.

2016-03-01

We report results from a joint experimental and theoretical investigation into electron scattering from the important industrial species furfural (C5H4O2). Specifically, differential cross sections (DCSs) have been measured and calculated for the electron-impact excitation of the electronic states of C5H4O2. The measurements were carried out at energies in the range 20-40 eV, and for scattered-electron angles between 10° and 90°. The energy resolution of those experiments was typically ˜80 meV. Corresponding Schwinger multichannel method with pseudo-potential calculations, for energies between 6-50 eV and with and without Born-closure, were also performed for a sub-set of the excited electronic-states that were accessed in the measurements. Those calculations were undertaken at the static exchange plus polarisation-level using a minimum orbital basis for single configuration interaction (MOB-SCI) approach. Agreement between the measured and calculated DCSs was qualitatively quite good, although to obtain quantitative accord, the theory would need to incorporate even more channels into the MOB-SCI. The role of multichannel coupling on the computed electronic-state DCSs is also explored in some detail.

Chemical and morphological characterization of III-V strained layered heterostructures

NASA Astrophysics Data System (ADS)

Gray, Allen Lindsay

This dissertation describes investigations into the chemical and morphological characterization of III-V strained layered heterostructures by high-resolution x-ray diffraction. The purpose of this work is two-fold. The first was to use high-resolution x-ray diffraction coupled with transmission electron microscopy to characterize structurally a quaternary AlGaAsSb/InGaAsSb multiple quantum well heterostructure laser device. A method for uniquely determining the chemical composition of the strain quaternary quantum well, information previously thought to be unattainable using high resolution x-ray diffraction is thoroughly described. The misconception that high-resolution x-ray diffraction can separately find the well and barrier thickness of a multi-quantum well from the pendellosung fringe spacing is corrected, and thus the need for transmission electron microscopy is motivated. Computer simulations show that the key in finding the well composition is the intensity of the -3rd order satellite peaks in the diffraction pattern. The second part of this work addresses the evolution of strain relief in metastable multi-period InGaAs/GaAs multi-layered structures by high-resolution x-ray reciprocal space maps. Results are accompanied by transmission electron and differential contrast microscopy. The evolution of strain relief is tracked from a coherent "pseudomorphic" growth to a dislocated state as a function of period number by examining the x-ray diffuse scatter emanating from the average composition (zeroth-order) of the multi-layer. Relaxation is determined from the relative positions of the substrate with respect to the zeroth-order peak. For the low period number, the diffuse scatter from the multi-layer structure region arises from periodic, coherent crystallites. For the intermediate period number, the displacement fields around the multi-layer structure region transition to random coherent crystallites. At the higher period number, displacement fields of overlapping dislocations from relaxation of the random crystallites cause the initial stages of relaxation of the multi-layer structure. At the highest period number studied, relaxation of the multi-layer structure becomes bi-modal characterized by overlapping dislocations caused by mosaic block relaxation and periodically spaced misfit dislocations formed by 60°-type dislocations. The relaxation of the multi-layer structure has an exponential dependence on the diffuse scatter length-scale, which is shown to be a sensitive measure of the onset of relaxation.

Investigation into Cherenkov light scattering and refraction on aerogel surface

NASA Astrophysics Data System (ADS)

Barnyakov, A. Yu.; Barnyakov, M. Yu.; Bobrovnikov, V. S.; Buzykaev, A. R.; Danilyuk, A. F.; Katcin, A. A.; Kirilenko, P. S.; Kononov, S. A.; Korda, D. V.; Kravchenko, E. A.; Kudryavtsev, V. N.; Kuyanov, I. A.; Onuchin, A. P.; Ovtin, I. V.; Podgornov, N. A.; Predein, A. Yu.; Prisekin, V. G.; Protsenko, R. S.; Shekhtman, L. I.

2017-12-01

The work concerns the development of aerogel radiators for RICH detectors. Aerogel tiles with a refractive index of 1.05 were tested with a RICH prototype on the electron beam on the VEPP-4M collider. It has been shown that polishing with silk tissue yields good surface quality, the amount of light loss at this surface being about 5-7%. The Cherenkov angle resolution was measured for a tile in two conditions: with a clean exit face and with a polished exit face. The number of photons detected was 13.3 and 12.7 for the clean and polished surfaces, respectively. The Cherenkov angle resolution for the polished surface is 55% worse, which can be explained with the forward scattering on the polished surface. A tile with a crack inside was also tested. The experimental data show that the Cherenkov angle resolution is the same for tracks crossing the crack area and in a crack-free area.

Unusual inhomogeneous microstructures in charge glass state of PbCrO3

NASA Astrophysics Data System (ADS)

Kurushima, Kosuke; Tsukasaki, Hirofumi; Ogata, Takahiro; Sakai, Yuki; Azuma, Masaki; Ishii, Yui; Mori, Shigeo

2018-05-01

We investigated the microstructures and local structures of perovskite PbCrO3, which shows a metal-to-insulator transition and a 9.8% volume collapse, by electron diffraction, high-resolution transmission electron microscopy (TEM), and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). It is revealed that the charge glass state is characterized by the unique coexistence of the crystalline state with a cubic symmetry on average and the noncrystalline state. HAADF-STEM observation at atomic resolution revealed that Pb ions were displaced from the ideal A site position of the cubic perovskite structure, which gives rise to characteristic diffuse scatterings around the fundamental Bragg reflections. These structural inhomogeneities are crucial to the understanding of the unique physical properties in the charge glass state of PbCrO3.

Development of an integrated four-channel fast avalanche-photodiode detector system with nanosecond time resolution

NASA Astrophysics Data System (ADS)

Li, Zhenjie; Li, Qiuju; Chang, Jinfan; Ma, Yichao; Liu, Peng; Wang, Zheng; Hu, Michael Y.; Zhao, Jiyong; Alp, E. E.; Xu, Wei; Tao, Ye; Wu, Chaoqun; Zhou, Yangfan

2017-10-01

A four-channel nanosecond time-resolved avalanche-photodiode (APD) detector system is developed at Beijing Synchrotron Radiation. It uses a single module for signal processing and readout. This integrated system provides better reliability and flexibility for custom improvement. The detector system consists of three parts: (i) four APD sensors, (ii) four fast preamplifiers and (iii) a time-digital-converter (TDC) readout electronics. The C30703FH silicon APD chips fabricated by Excelitas are used as the sensors of the detectors. It has an effective light-sensitive area of 10 × 10 mm2 and an absorption layer thickness of 110 μm. A fast preamplifier with a gain of 59 dB and bandwidth of 2 GHz is designed to readout of the weak signal from the C30703FH APD. The TDC is realized by a Spartan-6 field-programmable-gate-array (FPGA) with multiphase method in a resolution of 1ns. The arrival time of all scattering events between two start triggers can be recorded by the TDC. The detector has been used for nuclear resonant scattering study at both Advanced Photon Source and also at Beijing Synchrotron Radiation Facility. For the X-ray energy of 14.4 keV, the time resolution, the full width of half maximum (FWHM) of the detector (APD sensor + fast amplifier) is 0.86 ns, and the whole detector system (APD sensors + fast amplifiers + TDC readout electronics) achieves a time resolution of 1.4 ns.

Design of a collective scattering system for small scale turbulence study in Korea Superconducting Tokamak Advanced Research

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, W., E-mail: woochanglee@unist.ac.kr; Lee, D. J.; Park, H. K.

The design characteristics of a multi-channel collective (or coherent) scattering system for small scale turbulence study in Korea Superconducting Tokamak Advanced Research (KSTAR), which is planned to be installed in 2017, are given in this paper. A few critical issues are discussed in depth such as the Faraday and Cotton-Mouton effects on the beam polarization, radial spatial resolution, probe beam frequency, polarization, and power. A proper and feasible optics with the 300 GHz probe beam, which was designed based on these issues, provides a simultaneous measurement of electron density fluctuations at four discrete poloidal wavenumbers up to 24 cm{sup −1}.more » The upper limit corresponds to the normalized wavenumber k{sub θ}ρ{sub e} of ∼0.15 in nominal KSTAR plasmas. To detect the scattered beam power and extract phase information, a quadrature detection system consisting of four-channel antenna/detector array and electronics will be employed.« less

Correction of the spectral calibration of the Joint European Torus core light detecting and ranging Thomson scattering diagnostic using ray tracing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hawke, J.; Scannell, R.; Maslov, M.

2013-10-15

This work isolated the cause of the observed discrepancy between the electron temperature (T{sub e}) measurements before and after the JET Core LIDAR Thomson Scattering (TS) diagnostic was upgraded. In the upgrade process, stray light filters positioned just before the detectors were removed from the system. Modelling showed that the shift imposed on the stray light filters transmission functions due to the variations in the incidence angles of the collected photons impacted plasma measurements. To correct for this identified source of error, correction factors were developed using ray tracing models for the calibration and operational states of the diagnostic. Themore » application of these correction factors resulted in an increase in the observed T{sub e}, resulting in the partial if not complete removal of the observed discrepancy in the measured T{sub e} between the JET core LIDAR TS diagnostic, High Resolution Thomson Scattering, and the Electron Cyclotron Emission diagnostics.« less

Microstructures and magnetic properties of Co-Al-O granular thin films

NASA Astrophysics Data System (ADS)

Ohnuma, M.; Hono, K.; Onodera, H.; Ohnuma, S.; Fujimori, H.; Pedersen, J. S.

2000-01-01

The microstructures of Co-Al-O thin films of wide varieties of compositions are studied by transmission electron microscopy and small angle x-ray scattering (SAXS). In the superparamagnetic specimens, high resolution electron microscope images reveal that isolated spherical Co particles are surrounded by an amorphous aluminum oxide matrix. However, in the soft ferromagnetic films, the shape of the Co particles is prolate ellipsoidal. SAXS intensities from the soft magnetic specimens decrease inversely with the wave vector, q, in a low wave-vector region, while an interparticle interference peak is observed for the superparamagnetic specimens. The scattering profiles of the soft magnetic films imply that the Co particles have a cylindrical shape and are randomly oriented. The correlation between the magnetic properties and the microstructures is discussed.

First measurement of time evolution of electron temperature profiles with Nd:YAG Thomson scattering system on Heliotron J

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kenmochi, N., E-mail: kemmchi.naoki.62r@st.kyoto-u.ac.jp; Tei, S.; Zang, L.

2014-11-15

A Nd:YAG Thomson scattering system has been developed for Heliotron J. The system consists of two 550 mJ 50 Hz lasers, large collection optics, and 25 radial channel (∼1 cm spatial resolution) interference polychromators. This measurement system achieves a S/N ratio of ∼50 for low-density plasma (n{sub e} ∼ 0.5 × 10{sup 19} m{sup −3}). A time evolution of electron temperature profiles was measured with this system for a high-intensity gas-puff (HIGP) fueling neutral-beam-injection plasma. The peripheral temperature of the higher-density phase after HIGP recovers to the low-density pre-HIGP level, suggesting that improving particle transport in the HIGP plasma maymore » be possible.« less

On the Progress of Scanning Transmission Electron Microscopy (STEM) Imaging in a Scanning Electron Microscope.

PubMed

Sun, Cheng; Müller, Erich; Meffert, Matthias; Gerthsen, Dagmar

2018-04-01

Transmission electron microscopy (TEM) with low-energy electrons has been recognized as an important addition to the family of electron microscopies as it may avoid knock-on damage and increase the contrast of weakly scattering objects. Scanning electron microscopes (SEMs) are well suited for low-energy electron microscopy with maximum electron energies of 30 keV, but they are mainly used for topography imaging of bulk samples. Implementation of a scanning transmission electron microscopy (STEM) detector and a charge-coupled-device camera for the acquisition of on-axis transmission electron diffraction (TED) patterns, in combination with recent resolution improvements, make SEMs highly interesting for structure analysis of some electron-transparent specimens which are traditionally investigated by TEM. A new aspect is correlative SEM, STEM, and TED imaging from the same specimen region in a SEM which leads to a wealth of information. Simultaneous image acquisition gives information on surface topography, inner structure including crystal defects and qualitative material contrast. Lattice-fringe resolution is obtained in bright-field STEM imaging. The benefits of correlative SEM/STEM/TED imaging in a SEM are exemplified by structure analyses from representative sample classes such as nanoparticulates and bulk materials.

Study of the spatial resolution of low-material GEM tracking detectors

NASA Astrophysics Data System (ADS)

Kudryavtsev, V. N.; Maltsev, T. V.; Shekhtman, L. I.

2018-02-01

The spatial resolution of GEM based tracking detectors has been simulated and measured. The simulation includes the GEANT4 based transport of high energy electrons with careful accounting for atomic relaxation processes including emission of fluorescent photons and Auger electrons and custom post-processing, including accounting for diffusion, gas amplification fluctuations, the distribution of signals on readout electrodes, electronics noise and a particular algorithm of the final coordinate calculation (center of gravity). The simulation demonstrates that a minimum of the spatial resolution of about 10 μm can be achieved with strip pitches from 250 μm to 300 μm. For larger pitches the resolution is quickly degrading reaching 80-100 μm at a pitch of 500 μm. The spatial resolution of low-material triple-GEM detectors for the DEUTRON facility at the VEPP-3 storage ring is measured at the extracted beam facility of the VEPP-4M collider. The amount of material in these detectors is reduced by etching the copper of the GEMs electrodes and using a readout structure on a thin kapton foil rather than on a glass fibre plate. The exact amount of material in one DEUTRON detector is measured by studying multiple scattering of 100 MeV electrons in it. The result of these measurements is X/X0 = 2.4×10-3 corresponding to a thickness of the copper layers of the GEM foils of 3 μm. The spatial resolution of one DEUTRON detector is measured with 500 MeV electrons and the measured value is equal to 35 ± 1 μm for orthogonal tracks.

Electron beam patterning for writing of positively charged gold colloidal nanoparticles

NASA Astrophysics Data System (ADS)

Zafri, Hadar; Azougi, Jonathan; Girshevitz, Olga; Zalevsky, Zeev; Zitoun, David

2018-02-01

Synthesis at the nanoscale has progressed at a very fast pace during the last decades. The main challenge today lies in precise localization to achieve efficient nanofabrication of devices. In the present work, we report on a novel method for the patterning of gold metallic nanoparticles into nanostructures on a silicon-on-insulator (SOI) wafer. The fabrication makes use of relatively accessible equipment, a scanning electron microscope (SEM), and wet chemical synthesis. The electron beam implants electrons into the insulating material, which further anchors the positively charged Au nanoparticles by electrostatic attraction. The novel fabrication method was applied to several substrates useful in microelectronics to add plasmonic particles. The resolution and surface density of the deposition were tuned, respectively, by the electron energy (acceleration voltage) and the dose of electronic irradiation. We easily achieved the smallest written feature of 68 ± 18 nm on SOI, and the technique can be extended to any positively charged nanoparticles, while the resolution is in principle limited by the particle size distribution and the scattering of the electrons in the substrate. [Figure not available: see fulltext.

Novel Crystalline SiO2 Nanoparticles via Annelids Bioprocessing of Agro-Industrial Wastes

PubMed Central

2010-01-01

The synthesis of nanoparticles silica oxide from rice husk, sugar cane bagasse and coffee husk, by employing vermicompost with annelids (Eisenia foetida) is reported. The product (humus) is calcinated and extracted to recover the crystalline nanoparticles. X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and dynamic light scattering (DLS) show that the biotransformation allows creating specific crystalline phases, since equivalent particles synthesized without biotransformation are bigger and with different crystalline structure. PMID:20802789

Nonlinear Whistler Wave Physics in the Radiation Belts

NASA Astrophysics Data System (ADS)

Crabtree, Chris

2016-10-01

Wave particle interactions between electrons and whistler waves are a dominant mechanism for controlling the dynamics of energetic electrons in the radiation belts. They are responsible for loss, via pitch-angle scattering of electrons into the loss cone, and energization to millions of electron volts. It has previously been theorized that large amplitude waves on the whistler branch may scatter their wave-vector nonlinearly via nonlinear Landau damping leading to important consequences for the global distribution of whistler wave energy density and hence the energetic electrons. It can dramatically reduce the lifetime of energetic electrons in the radiation belts by increasing the pitch angle scattering rate. The fundamental building block of this theory has now been confirmed through laboratory experiments. Here we report on in situ observations of wave electro-magnetic fields from the EMFISIS instrument on board NASA's Van Allen Probes that show the signatures of nonlinear scattering of whistler waves in the inner radiation belts. In the outer radiation belts, whistler mode chorus is believed to be responsible for the energization of electrons from 10s of Kev to MeV energies. Chorus is characterized by bursty large amplitude whistler mode waves with frequencies that change as a function of time on timescales corresponding to their growth. Theories explaining the chirping have been developed for decades based on electron trapping dynamics in a coherent wave. New high time resolution wave data from the Van Allen probes and advanced spectral techniques are revealing that the wave dynamics is highly structured, with sub-elements consisting of multiple chirping waves with discrete frequency hops between sub-elements. Laboratory experiments with energetic electron beams are currently reproducing the complex frequency vs time dynamics of whistler waves and in addition revealing signatures of wave-wave and beat-wave nonlinear wave-particle interactions. These new data suggest that these weak turbulence processes may be playing a role in saturating the nonlinear instability.

Experimental and theoretical studies of the He(2+)-He system - Differential cross sections for direct, single-, and double-charge-transfer scattering at keV energies

NASA Technical Reports Server (NTRS)

Gao, R. S.; Dutta, C. M.; Lane, N. F.; Smith, K. A.; Stebbings, R. F.; Kimura, M.

1992-01-01

Measurements and calculations of differential cross sections for direct scattering, single-charge transfer, and double-charge transfer in collisions of 1.5-, 2.0-, 6.0-, and 10.0-keV (He-3)2+ with an He-4 target are reported. The measurements cover laboratory scattering angles below 1.5 deg with an angular resolution of about 0.03 deg. A quantum-mechanical molecular-state representation is employed in the calculations; in the case of single-charge transfer a two-state close-coupling calculation is carried out taking into account electron-translation effects. The theoretical calculations agree well with the experimental results for direct scattering and double-charge transfer. The present calculation identifies the origins of oscillatory structures observed in the differential cross sections.

Small-angle x-ray scattering from lipid bilayers is well described by modified Caillé theory but not by paracrystalline theory.

PubMed Central

Zhang, R; Tristram-Nagle, S; Sun, W; Headrick, R L; Irving, T C; Suter, R M; Nagle, J F

1996-01-01

X-ray scattering data at high instrumental resolution are reported for multilamellar vesicles of L alpha phase lipid bilayers of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine at 50 degrees C under varying osmotic pressure. The data are fitted to two theories that account for noncrystalline disorder, paracrystalline theory (PT) and modified Caillé theory (MCT). The MCT provides good fits to the data, much better than the PT fits. The particularly important characteristic of MCT is the long power law tails in the scattering. PT fits (as well as ordinary integration with no attempt to account for the noncrystalline disorder) increasingly underestimate this scattering intensity as the order h increases, thereby underestimating the form factors used to obtain electron density profiles. Images FIGURE 4 PMID:8770211

High quality transmission Kikuchi diffraction analysis of deformed alloys - Case study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tokarski, Tomasz, E-mail: tokarski@agh.edu.pl

Modern scanning electron microscopes (SEM) equipped with thermally assisted field emission guns (Schottky FEG) are capable of imaging with a resolution in the range of several nanometers or better. Simultaneously, the high electron beam current can be used, which enables fast chemical and crystallographic analysis with a higher resolution than is normally offered by SEM with a tungsten cathode. The current resolution that limits the EDS and EBSD analysis is related to materials' physics, particularly to the electron-specimen interaction volume. The application of thin, electron-transparent specimens, instead of bulk samples, improves the resolution and allows for the detailed analysis ofmore » very fine microstructural features. Beside the typical imaging mode, it is possible to use a standard EBSD camera in such a configuration that only transmitted and scattered electrons are detected. This modern approach was successfully applied to various materials giving rise to significant resolution improvement, especially for the light element magnesium based alloys. This paper presents an insight into the application of the transmission Kikuchi diffraction (TKD) technique applied to the most troublesome, heavily-deformed materials. In particular, the values of the highest possible acquisition rates for high resolution and high quality mapping were estimated within typical imaging conditions of stainless steel and magnesium-yttrium alloy. - Highlights: •Monte Carlo simulations were used to simulate EBSD camera intensity for various measuring conditions. •Transmission Kikuchi diffraction parameters were evaluated for highly deformed, light and heavy elements based alloys. •High quality maps with 20 nm spatial resolution were acquired for Mg and Fe based alloys. •High speed TKD measurements were performed at acquisition rates comparable to the reflection EBSD.« less

Water without windows: Evaluating the performance of open cell transmission electron microscopy under saturated water vapor conditions, and assessing its potential for microscopy of hydrated biological specimens

PubMed Central

Yamashita, Masao; Cheung, Martin; Kalale, Chola; Adaniya, Hidehito; Kuwahara, Ryusuke; Shintake, Tsumoru

2017-01-01

We have performed open cell transmission electron microscopy experiments through pure water vapor in the saturation pressure regime (>0.6 kPa), in a modern microscope capable of sub-Å resolution. We have systematically studied achievable pressure levels, stability and gas purity, effective thickness of the water vapor column and associated electron scattering processes, and the effect of gas pressure on electron optical resolution and image contrast. For example, for 1.3 kPa pure water vapor and 300kV electrons, we report pressure stability of ± 20 Pa over tens of minutes, effective thickness of 0.57 inelastic mean free paths, lattice resolution of 0.14 nm on a reference Au specimen, and no significant degradation in contrast or stability of a biological specimen (M13 virus, with 6 nm body diameter). We have also done some brief experiments to confirm feasibility of loading specimens into an in situ water vapor ambient without exposure to intermediate desiccating conditions. Finally, we have also checked if water experiments had any discernible impact on the microscope performance, and report pertinent vacuum and electron optical data, for reference purposes. PMID:29099843

Raman Scattered He II 4332 and Photoionization Model in the Symbiotic Star V1016 Cygni

NASA Astrophysics Data System (ADS)

Lee, H.-W.; Heo, J.-E.; Lee, B.-C.

2014-08-01

Symbiotic stars are wide binary systems of a white dwarf and a mass losing giant. They exhibit unique Raman scattered features as a result of inelastic scattering of far UV line photons by atomic hydrogen. Co-existence of a far UV He II emission region and a thick H I region in symbiotic stars is necessary for the formation of Raman-scattered features blueward of hydrogen Balmer emission lines. Being a single electron atom, He II has the same atomic structure as the hydrogen atom and hence emits far UV emission lines that are slightly blueward of hydrogen Lyman lines. These far UV He II emission lines can be Raman scattered to appear blueward of hydrogen Balmer lines. In particular, the symbiotic star V1016 Cyg is found to exhibit Raman scattered He II 4332 feature in the BOES high resolution spectrum. Our profile fitting of Raman scattered He II 4332 is consistent with the mass loss geometry proposed by Jung & Lee (2004). We use the photoionization code ‘ CLOUDY' to estimate the far UV He II emission lines and make comparisons with the observed Raman scattered He II 4332 blueward of Hγ in the high resolution echelle V1016 Cyg. The emission nebula is assumed to be of uniform density of 108 cm-3 that is illuminated by a black body characterized by its temperature and total luminosity. With our comparisons we conclude that the Raman scattered He II features are consistent with the existence of a photoionized nebula by a hot black body source with temperature 7-8× 104 K with a luminosity 1038erg s-1.

A sensitive EUV Schwarzschild microscope for plasma studies with sub-micrometer resolution

DOE PAGES

Zastrau, U.; Rodel, C.; Nakatsutsumi, M.; ...

2018-02-05

We present an extreme ultraviolet (EUV) microscope using a Schwarzschild objective which is optimized for single-shot sub-micrometer imaging of laser-plasma targets. The microscope has been designed and constructed for imaging the scattering from an EUV-heated solid-density hydrogen jet. Here, imaging of a cryogenic hydrogen target was demonstrated using single pulses of the free-electron laser in Hamburg (FLASH) free-electron laser at a wavelength of 13.5 nm. In a single exposure, we observe a hydrogen jet with ice fragments with a spatial resolution in the sub-micrometer range. In situ EUV imaging is expected to enable novel experimental capabilities for warm dense mattermore » studies of micrometer-sized samples in laser-plasma experiments.« less

A sensitive EUV Schwarzschild microscope for plasma studies with sub-micrometer resolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zastrau, U.; Rodel, C.; Nakatsutsumi, M.

We present an extreme ultraviolet (EUV) microscope using a Schwarzschild objective which is optimized for single-shot sub-micrometer imaging of laser-plasma targets. The microscope has been designed and constructed for imaging the scattering from an EUV-heated solid-density hydrogen jet. Here, imaging of a cryogenic hydrogen target was demonstrated using single pulses of the free-electron laser in Hamburg (FLASH) free-electron laser at a wavelength of 13.5 nm. In a single exposure, we observe a hydrogen jet with ice fragments with a spatial resolution in the sub-micrometer range. In situ EUV imaging is expected to enable novel experimental capabilities for warm dense mattermore » studies of micrometer-sized samples in laser-plasma experiments.« less

Time-resolved scanning electron microscopy with polarization analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Frömter, Robert, E-mail: rfroemte@physik.uni-hamburg.de; Oepen, Hans Peter; The Hamburg Centre for Ultrafast Imaging, Luruper Chaussee 149, 22761 Hamburg

2016-04-04

We demonstrate the feasibility of investigating periodically driven magnetization dynamics in a scanning electron microscope with polarization analysis based on spin-polarized low-energy electron diffraction. With the present setup, analyzing the time structure of the scattering events, we obtain a temporal resolution of 700 ps, which is demonstrated by means of imaging the field-driven 100 MHz gyration of the vortex in a soft-magnetic FeCoSiB square. Owing to the efficient intrinsic timing scheme, high-quality movies, giving two components of the magnetization simultaneously, can be recorded on the time scale of hours.

Tunable all-optical quasimonochromatic thomson x-ray source in the nonlinear regime.

PubMed

Khrennikov, K; Wenz, J; Buck, A; Xu, J; Heigoldt, M; Veisz, L; Karsch, S

2015-05-15

We present an all-laser-driven, energy-tunable, and quasimonochromatic x-ray source based on Thomson scattering from laser-wakefield-accelerated electrons. One part of the laser beam was used to drive a few-fs bunch of quasimonoenergetic electrons, while the remainder was backscattered off the bunch at weakly relativistic intensity. When the electron energy was tuned from 17-50 MeV, narrow x-ray spectra peaking at 5-42 keV were recorded with high resolution, revealing nonlinear features. We present a large set of measurements showing the stability and practicality of our source.

Thorough small-angle X-ray scattering analysis of the instability of liquid micro-jets in air.

PubMed

Marmiroli, Benedetta; Cacho-Nerin, Fernando; Sartori, Barbara; Pérez, Javier; Amenitsch, Heinz

2014-01-01

Liquid jets are of interest, both for their industrial relevance and for scientific applications (more important, in particular for X-rays, after the advent of free-electron lasers that require liquid jets as sample carrier). Instability mechanisms have been described theoretically and by numerical simulation, but confirmed by few experimental techniques. In fact, these are mainly based on cameras, which is limited by the imaging resolution, and on light scattering, which is hindered by absorption, reflection, Mie scattering and multiple scattering due to complex air/liquid interfaces during jet break-up. In this communication it is demonstrated that synchrotron small-angle X-ray scattering (SAXS) can give quantitative information on liquid jet dynamics at the nanoscale, by detecting time-dependent morphology and break-up length. Jets ejected from circular tubes of different diameters (100-450 µm) and speeds (0.7-21 m s(-1)) have been explored to cover the Rayleigh and first wind-induced regimes. Various solvents (water, ethanol, 2-propanol) and their mixtures have been examined. The determination of the liquid jet behaviour becomes essential, as it provides background data in subsequent studies of chemical and biological reactions using SAXS or X-ray diffraction based on synchrotron radiation and free-electron lasers.

Spotting the differences in two-dimensional materials - the Raman scattering perspective.

PubMed

Zhang, Shishu; Zhang, Na; Zhao, Yan; Cheng, Ting; Li, Xiaobo; Feng, Rui; Xu, Hua; Liu, Zhirong; Zhang, Jin; Tong, Lianming

2018-05-08

Two-dimensional (2D) layered materials have attracted tremendous attention and led to a prosperous development in both fundamental investigation and device applications in various fields, such as nanoelectronics, flexible devices, sustainable energy and catalysts. The precise characterization of the structure and properties of 2D materials is in urgent need. Raman scattering spectroscopy is one of the most popular characterization tools that is convenient, rapid and non-invasive. It provides information on both the lattice structure from the frequency of phonon modes and the electronic band structure through the intensity due to electronic resonance Raman scattering. Although a few morphological characterization tools can image 2D materials with atomic resolution, Raman scattering measurements are more tolerant to the conditions of sample preparation such as the substrate and less technically demanding, and have been one of the routine tools for the characterization of 2D materials. In this review, we focus on the characterization of 2D materials using Raman scattering spectroscopy, in particular, the revealing of differences from primitive 2D materials, such as defects, doping effects, van der Waals heterostructures and the interaction with molecules. The characteristic Raman features of such differences and the corresponding interpretation will be discussed. We hope that this review will be useful for wide research communities of materials, physics, chemistry and engineering.

UV Resonant Raman Spectrometer with Multi-Line Laser Excitation

NASA Technical Reports Server (NTRS)

Lambert, James L.; Kohel, James M.; Kirby, James P.; Morookian, John Michael; Pelletier, Michael J.

2013-01-01

A Raman spectrometer employs two or more UV (ultraviolet) laser wavel engths to generate UV resonant Raman (UVRR) spectra in organic sampl es. Resonant Raman scattering results when the laser excitation is n ear an electronic transition of a molecule, and the enhancement of R aman signals can be several orders of magnitude. In addition, the Ra man cross-section is inversely proportional to the fourth power of t he wavelength, so the UV Raman emission is increased by another fact or of 16, or greater, over visible Raman emissions. The Raman-scatter ed light is collected using a high-resolution broadband spectrograph . Further suppression of the Rayleigh-scattered laser light is provi ded by custom UV notch filters.

GEM detector performance and efficiency in Proton Charge Radius (PRad) Experiment

NASA Astrophysics Data System (ADS)

Bai, Xinzhan; PRad Collaboration

2017-09-01

The PRad experiment (E12-11-106) was performed in 2016 at Jefferson Lab in Hall B. It aims to investigate the proton charge radius puzzle through electron proton elastic scattering process. The experiment used a non-magnetic spectrometer method, and reached a very small ep scattering angle and thus an unprecedented small four-momentum transfer squared region, Q2 from 2 ×10-4 to 0.06(GeV / c) 2 . PRad experiment was designed to measure the proton charge radius within a sub-percent precision. Gas Electron Multiplier (GEM) detectors have contributed to reach the experimental goal. A pair of large area GEM detectors, and a large acceptance, high resolution calorimeter(HyCal) were utilized in the experiment to detect the scattered electrons. The precision requirements of the experiment demands a highly accurate understanding of efficiency and stability of GEM detectors. In this talk, we will present the preliminary results on the performance and efficiency of GEM detectors. This work is supported in part by NSF MRI award PHY-1229153, the U.S. Department of Energy under Contract No. DE-FG02-07ER41528, No. DE-FG02-03ER41240 and Thomas Jefferson National Laboratory.

Edge Thomson scattering diagnostic on COMPASS tokamak: Installation, calibration, operation, improvements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bohm, P., E-mail: bohm@ipp.cas.cz; Bilkova, P.; Melich, R.

2014-11-15

The core Thomson scattering diagnostic (TS) on the COMPASS tokamak was put in operation and reported earlier. Implementation of edge TS, with spatial resolution along the laser beam up to ∼1/100 of the tokamak minor radius, is presented now. The procedure for spatial calibration and alignment of both core and edge systems is described. Several further upgrades of the TS system, like a triggering unit and piezo motor driven vacuum window shutter, are introduced as well. The edge TS system, together with the core TS, is now in routine operation and provides electron temperature and density profiles.

Electron radiography

DOEpatents

Merrill, Frank E.; Morris, Christopher

2005-05-17

A system capable of performing radiography using a beam of electrons. Diffuser means receive a beam of electrons and diffuse the electrons before they enter first matching quadrupoles where the diffused electrons are focused prior to the diffused electrons entering an object. First imaging quadrupoles receive the focused diffused electrons after the focused diffused electrons have been scattered by the object for focusing the scattered electrons. Collimator means receive the scattered electrons and remove scattered electrons that have scattered to large angles. Second imaging quadrupoles receive the collimated scattered electrons and refocus the collimated scattered electrons and map the focused collimated scattered electrons to transverse locations on an image plane representative of the electrons' positions in the object.

Determination of atomic-scale chemical composition at semiconductor heteroepitaxial interfaces by high-resolution transmission electron microscopy.

PubMed

Wen, C; Ma, Y J

2018-03-01

The determination of atomic structures and further quantitative information such as chemical compositions at atomic scale for semiconductor defects or heteroepitaxial interfaces can provide direct evidence to understand their formation, modification, and/or effects on the properties of semiconductor films. The commonly used method, high-resolution transmission electron microscopy (HRTEM), suffers from difficulty in acquiring images that correctly show the crystal structure at atomic resolution, because of the limitation in microscope resolution or deviation from the Scherzer-defocus conditions. In this study, an image processing method, image deconvolution, was used to achieve atomic-resolution (∼1.0 Å) structure images of small lattice-mismatch (∼1.0%) AlN/6H-SiC (0001) and large lattice-mismatch (∼8.5%) AlSb/GaAs (001) heteroepitaxial interfaces using simulated HRTEM images of a conventional 300-kV field-emission-gun transmission electron microscope under non-Scherzer-defocus conditions. Then, atomic-scale chemical compositions at the interface were determined for the atomic intermixing and Lomer dislocation with an atomic step by analyzing the deconvoluted image contrast. Furthermore, the effect of dynamical scattering on contrast analysis was also evaluated for differently weighted atomic columns in the compositions. Copyright © 2018 Elsevier Ltd. All rights reserved.

Improving spatial and spectral resolution of TCV Thomson scattering

NASA Astrophysics Data System (ADS)

Hawke, J.; Andrebe, Y.; Bertizzolo, R.; Blanchard, P.; Chavan, R.; Decker, J.; Duval, B.; Lavanchy, P.; Llobet, X.; Marlétaz, B.; Marmillod, P.; Pochon, G.; Toussaint, M.

2017-12-01

The recently completed MST2 upgrade to the Thomson scattering (TS) system on TCV (Tokamak à Configuration Variable) at the Swiss Plasma Center aims to provide an enhanced spatial and spectral resolution while maintaining the high level of diagnostic flexibility for the study of TCV plasmas. The MST2 (Medium Sized Tokamak) is a work program within the Eurofusion ITER physics department, aimed at exploiting Europe's medium sized tokamak programs for a better understanding of ITER physics. This upgrade to the TCV Thomson scattering system involved the installation of 40 new compact 5-channel spectrometers and modifications to the diagnostics fiber optic design. The complete redesign of the fiber optic backplane incorporates fewer larger diameter fibers, allowing for a higher resolution in both the core and edge of TCV plasmas along the laser line, with a slight decrease in the signal to noise ratio of Thomson measurements. The 40 new spectrometers added to the system are designed to cover the full range of temperatures expected in TCV, able to measure electron temperatures (Te) with high precision between (6 eV and 20 keV) . The design of these compact spectrometers stems originally from the design utilized in the MAST (Mega Amp Spherical Tokamak) TS system located in Oxfordshire, United Kingdom. This design was implemented on TCV with an overall layout of optical fibers and spectrometers to achieve an overall increase in the spatial resolution, specifically a resolution of approximately 1% of the minor radius within the plasma pedestal region. These spectrometers also enhance the diagnostic spectral resolution, especially within the plasma edge, due to the low Te measurement capabilities. These additional spectrometers allow for a much greater diagnostic flexibility, allowing for quality full Thomson profiles in 75% of TCV plasma configurations.

Analysis of the kinestatic charge detection system as a high detective quantum efficiency electronic portal imaging device.

PubMed

Samant, Sanjiv S; Gopal, Arun

2006-09-01

Megavoltage x-ray imaging suffers from reduced image quality due to low differential x-ray attenuation and large Compton scatter compared with kilovoltage imaging. Notwithstanding this, electronic portal imaging devices (EPIDs) are now widely used in portal verification in radiotherapy as they offer significant advantages over film, including immediate digital imaging and superior contrast range. However video-camera-based EPIDs (VEPIDs) are limited by problems of low light collection efficiency and significant light scatter, leading to reduced contrast and spatial resolution. Indirect and direct detection-based flat-panel EPIDs have been developed to overcome these limitations. While flat-panel image quality has been reported to exceed that achieved with portal film, these systems have detective quantum efficiency (DQE) limited by the thin detection medium and are sensitive to radiation damage to peripheral read-out electronics. An alternative technology for high-quality portal imaging is presented here: kinesatic charge detection (KCD). The KCD is a scanning tri-electrode ion-chamber containing high-pressure noble gas (xenon at 100 atm) used in conjunction with a strip-collimated photon beam. The chamber is scanned across the patient, and an external electric field is used to regulate the cation drift velocity. By matching the scanning velocity with that of the cation (i.e., ion) drift velocity, the cations remain static in the object frame of reference, allowing temporal integration of the signal. The KCD offers several advantages as a portal imaging system. It has a thick detector geometry with an active detection depth of 6.1 cm, compared to the sub-millimeter thickness of the phosphor layer in conventional phosphor screens, leading to an order of magnitude advantage in quantum efficiency (>0.3). The unique principle of and the use of the scanning strip-collimated x-ray beam provide further integration of charges in time, reduced scatter, and a significantly reduced imaging dose, enhancing the imaging signal-to-noise ratio (SNR) and leading to high DQE. While thick detectors usually suffer from reduced spatial resolution, the KCD provides good spatial resolution due to high gas pressure that limits the spread of scattered electrons, and a strip-collimated beam that significantly reduces the inclusion of scatter in the imaging signal. A 10 cm wide small-field-of-view (SFOV) prototype of the KCD is presented with a complete analysis of its imaging performance. Measurements of modulation transfer function (MTF), noise power spectrum (NPS), and DQE were in good agreement with Monte Carlo simulations. Imaging signal loss from recombination within the KCD chamber was measured at different gas pressures, ion drift velocities, and strip-collimation widths. Image quality for the prototype KCD was also observed with anthropomorphic phantom imaging in comparison with various commercial and research portal imaging systems, including VEPID, flat-panel imager, and conventional and high contrast film systems. KCD-based imaging provided very good contrast and good spatial resolution at very low imaging dose (0.1 cGy per image). For the prototype KCD, measurements yielded DQE(0)=0.19 and DQE(1 cy/mm)=0.004.

Imaging electronic motions by ultrafast electron diffraction

NASA Astrophysics Data System (ADS)

Shao, Hua-Chieh; Starace, Anthony F.

2017-08-01

Recently ultrafast electron diffraction and microscopy have reached unprecedented temporal resolution, and transient structures with atomic precision have been observed in various reactions. It is anticipated that these extraordinary advances will soon allow direct observation of electronic motions during chemical reactions. We therefore performed a series of theoretical investigations and simulations to investigate the imaging of electronic motions in atoms and molecules by ultrafast electron diffraction. Three prototypical electronic motions were considered for hydrogen atoms. For the case of a breathing mode, the electron density expands and contracts periodically, and we show that the time-resolved scattering intensities reflect such changes of the charge radius. For the case of a wiggling mode, the electron oscillates from one side of the nucleus to the other, and we show that the diffraction images exhibit asymmetric angular distributions. The last case is a hybrid mode that involves both breathing and wiggling motions. Owing to the demonstrated ability of ultrafast electrons to image these motions, we have proposed to image a coherent population transfer in lithium atoms using currently available femtosecond electron pulses. A frequency-swept laser pulse adiabatically drives the valence electron of a lithium atom from the 2s to 2p orbitals, and a time-delayed electron pulse maps such motion. Our simulations show that the diffraction images reflect this motion both in the scattering intensities and the angular distributions.

Design and Study of the Observation Optics for the Thomson Scattering Planned at Wendelstein 7-X

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cantarini, J.; Knauer, J. P.; Pasch, E.

2008-03-19

The main aim of the Thomson scattering system is the measurement of electron temperature and density profiles with high time and spatial resolution. To cover the whole laser beam line (1.6 m) through the plasma cross section, two ports are provided for the observation optics, which image the scattering volumes (each with 28 mm length and 9 mm diameter) onto fiber bundles. The observation optics are important components of the diagnostic set-up, because their imaging properties determine the spectral and spatial resolution of the whole system. Therefore the design of the optics must be optimized according to the geometrical constrainsmore » of the observation ports in terms of position and dimensions. To optimize this optical engineering, the commercial ZEMAX program is used. The composition of the optical system is elaborated to minimize losses of collected light with wavelength from 700 nm up to 1064 nm. Environmental criteria (e.g. neutrons, ECR plasma heating and temperature) will be considered choosing optical materials. First results of calculations will be presented.« less

Isotopic imaging via nuclear resonance fluorescence with laser-based Thomson radiation

DOEpatents

Barty, Christopher P. J. [Hayward, CA; Hartemann, Frederic V [San Ramon, CA; McNabb, Dennis P [Alameda, CA; Pruet, Jason A [Brentwood, CA

2009-07-21

The present invention utilizes novel laser-based, high-brightness, high-spatial-resolution, pencil-beam sources of spectrally pure hard x-ray and gamma-ray radiation to induce resonant scattering in specific nuclei, i.e., nuclear resonance fluorescence. By monitoring such fluorescence as a function of beam position, it is possible to image in either two dimensions or three dimensions, the position and concentration of individual isotopes in a specific material configuration. Such methods of the present invention material identification, spatial resolution of material location and ability to locate and identify materials shielded by other materials, such as, for example, behind a lead wall. The foundation of the present invention is the generation of quasimonochromatic high-energy x-ray (100's of keV) and gamma-ray (greater than about 1 MeV) radiation via the collision of intense laser pulses from relativistic electrons. Such a process as utilized herein, i.e., Thomson scattering or inverse-Compton scattering, produces beams having diameters from about 1 micron to about 100 microns of high-energy photons with a bandwidth of .DELTA.E/E of approximately 10E.sup.-3.

An experimental and theoretical investigation into the electronically excited states of para-benzoquinone

NASA Astrophysics Data System (ADS)

Jones, D. B.; Limão-Vieira, P.; Mendes, M.; Jones, N. C.; Hoffmann, S. V.; da Costa, R. F.; Varella, M. T. do N.; Bettega, M. H. F.; Blanco, F.; García, G.; Ingólfsson, O.; Lima, M. A. P.; Brunger, M. J.

2017-05-01

We report on a combination of experimental and theoretical investigations into the structure of electronically excited para-benzoquinone (pBQ). Here synchrotron photoabsorption measurements are reported over the 4.0-10.8 eV range. The higher resolution obtained reveals previously unresolved pBQ spectral features. Time-dependent density functional theory calculations are used to interpret the spectrum and resolve discrepancies relating to the interpretation of the Rydberg progressions. Electron-impact energy loss experiments are also reported. These are combined with elastic electron scattering cross section calculations performed within the framework of the independent atom model-screening corrected additivity rule plus interference (IAM-SCAR + I) method to derive differential cross sections for electronic excitation of key spectral bands. A generalized oscillator strength analysis is also performed, with the obtained results demonstrating that a cohesive and reliable quantum chemical structure and cross section framework has been established. Within this context, we also discuss some issues associated with the development of a minimal orbital basis for the single configuration interaction strategy to be used for our high-level low-energy electron scattering calculations that will be carried out as a subsequent step in this joint experimental and theoretical investigation.

Electron-density-sensitive Line Ratios of Fe xiii– xvi from Laboratory Sources Compared to CHIANTI

DOE PAGES

Weller, M. E.; Beiersdorfer, P.; Soukhanovskii, V. A.; ...

2018-02-15

We present electron-density-sensitive line ratios for Fe xiii– xvi measured in the spectral wavelength range of 200–440 Å and an electron density range of (1-4) × 10 13 cm -3. The results provide a test at the high-density limit of density-sensitive line ratios useful for astrophysical studies. The measurements were performed on the National Spherical Torus Experiment-Upgrade, where electron densities were measured independently by the laser Thomson scattering diagnostic. Spectra were collected with a flat-field grazing-incidence spectrometer, which provided a spectral resolution of up to 0.3 Å, i.e., high resolution across the broad wavelength range. The response of the instrumentmore » was relatively calibrated using spectroscopic techniques in order to improve accuracy. Lastly, the line ratios are compared to other laboratory sources and the latest version of CHIANTI (8.0.2), and an agreement within 30% is found.« less

Atomic scale imaging of magnetic circular dichroism by achromatic electron microscopy.

PubMed

Wang, Zechao; Tavabi, Amir H; Jin, Lei; Rusz, Ján; Tyutyunnikov, Dmitry; Jiang, Hanbo; Moritomo, Yutaka; Mayer, Joachim; Dunin-Borkowski, Rafal E; Yu, Rong; Zhu, Jing; Zhong, Xiaoyan

2018-03-01

In order to obtain a fundamental understanding of the interplay between charge, spin, orbital and lattice degrees of freedom in magnetic materials and to predict and control their physical properties 1-3 , experimental techniques are required that are capable of accessing local magnetic information with atomic-scale spatial resolution. Here, we show that a combination of electron energy-loss magnetic chiral dichroism 4 and chromatic-aberration-corrected transmission electron microscopy, which reduces the focal spread of inelastically scattered electrons by orders of magnitude when compared with the use of spherical aberration correction alone, can achieve atomic-scale imaging of magnetic circular dichroism and provide element-selective orbital and spin magnetic moments atomic plane by atomic plane. This unique capability, which we demonstrate for Sr 2 FeMoO 6 , opens the door to local atomic-level studies of spin configurations in a multitude of materials that exhibit different types of magnetic coupling, thereby contributing to a detailed understanding of the physical origins of magnetic properties of materials at the highest spatial resolution.

Atomic resolution of Lithium Ions in LiCoO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao-Horn, Yang; Croguennec, Laurence; Delmas, Claude

2003-03-18

LiCoO2 is the most common lithium storage material for lithium rechargeable batteries, used widely to power portable electronic devices such as laptop computers. Lithium arrangements in the CoO2 framework have a profound effect on the structural stability and electrochemical properties of LixCoO2 (0 < x < 1), however, probing lithium ions has been difficult using traditional X-ray and neutron diffraction techniques. Here we have succeeded in simultaneously resolving columns of cobalt, oxygen, and lithium atoms in layered LiCoO2 battery material using experimental focal series of LiCoO2 images obtained at sub-Angstrom resolution in a mid-voltage transmission electron microscope. Lithium atoms aremore » the smallest and lightest metal atoms, and scatter electrons only very weakly. We believe our observations of lithium to be the first by electron microscopy, and that they show promise to direct visualization of the ordering of lithium and vacancy in LixCoO2.« less

Electron-density-sensitive Line Ratios of Fe xiii– xvi from Laboratory Sources Compared to CHIANTI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weller, M. E.; Beiersdorfer, P.; Soukhanovskii, V. A.

We present electron-density-sensitive line ratios for Fe xiii– xvi measured in the spectral wavelength range of 200–440 Å and an electron density range of (1-4) × 10 13 cm -3. The results provide a test at the high-density limit of density-sensitive line ratios useful for astrophysical studies. The measurements were performed on the National Spherical Torus Experiment-Upgrade, where electron densities were measured independently by the laser Thomson scattering diagnostic. Spectra were collected with a flat-field grazing-incidence spectrometer, which provided a spectral resolution of up to 0.3 Å, i.e., high resolution across the broad wavelength range. The response of the instrumentmore » was relatively calibrated using spectroscopic techniques in order to improve accuracy. Lastly, the line ratios are compared to other laboratory sources and the latest version of CHIANTI (8.0.2), and an agreement within 30% is found.« less

StatSTEM: An efficient approach for accurate and precise model-based quantification of atomic resolution electron microscopy images.

PubMed

De Backer, A; van den Bos, K H W; Van den Broek, W; Sijbers, J; Van Aert, S

2016-12-01

An efficient model-based estimation algorithm is introduced to quantify the atomic column positions and intensities from atomic resolution (scanning) transmission electron microscopy ((S)TEM) images. This algorithm uses the least squares estimator on image segments containing individual columns fully accounting for overlap between neighbouring columns, enabling the analysis of a large field of view. For this algorithm, the accuracy and precision with which measurements for the atomic column positions and scattering cross-sections from annular dark field (ADF) STEM images can be estimated, has been investigated. The highest attainable precision is reached even for low dose images. Furthermore, the advantages of the model-based approach taking into account overlap between neighbouring columns are highlighted. This is done for the estimation of the distance between two neighbouring columns as a function of their distance and for the estimation of the scattering cross-section which is compared to the integrated intensity from a Voronoi cell. To provide end-users this well-established quantification method, a user friendly program, StatSTEM, is developed which is freely available under a GNU public license. Copyright © 2016 Elsevier B.V. All rights reserved.

High Resolution X-ray Scattering Studies of Structural Phase Transitions in BaFe2-x Cr x As 2

NASA Astrophysics Data System (ADS)

Gaulin, B. D.; Clancy, J. P.; Wagman, J. J.; Sefat, A. S.

2011-03-01

While the effects of electron-doping on the parent compounds of the 122 family of Fe-based superconductors have been extremely well-studied in recent years, far less is known about the influence of hole-doping in compounds such as BaFe 2-x Cr x As 2 . In contrast to the electron-doped 122 systems, the hole-doped compounds do not become superconducting. Furthermore, while the hole-doped compounds exhibit similar structural and magnetic phase transitions, they appear to be much less sensitive to dopant concentration. We have performed high resolution x-ray scattering and magnetic susceptibility measurements on single crystal samples of BaFe 2-x Cr x As 2 for Cr concentrations ranging from 0 <= x <= 0.67 . These measurements allow us to determine the magnetic and structural phase transitions for this series and map out the low temperature phase diagram as a function of doping. In particular, we have carried out detailed measurements of the tetragonal (I4/mmm) to orthorhombic (Fmmm) structural phase transition which reveal how the orthorhombicity of the system evolves with increasing Cr concentration and how this correlates with the values of Ts and Tm .

Speckle correlation resolution enhancement of wide-field fluorescence imaging (Conference Presentation)

NASA Astrophysics Data System (ADS)

Yilmaz, Hasan

2016-03-01

Structured illumination enables high-resolution fluorescence imaging of nanostructures [1]. We demonstrate a new high-resolution fluorescence imaging method that uses a scattering layer with a high-index substrate as a solid immersion lens [2]. Random scattering of coherent light enables a speckle pattern with a very fine structure that illuminates the fluorescent nanospheres on the back surface of the high-index substrate. The speckle pattern is raster-scanned over the fluorescent nanospheres using a speckle correlation effect known as the optical memory effect. A series of standard-resolution fluorescence images per each speckle pattern displacement are recorded by an electron-multiplying CCD camera using a commercial microscope objective. We have developed a new phase-retrieval algorithm to reconstruct a high-resolution, wide-field image from several standard-resolution wide-field images. We have introduced phase information of Fourier components of standard-resolution images as a new constraint in our algorithm which discards ambiguities therefore ensures convergence to a unique solution. We demonstrate two-dimensional fluorescence images of a collection of nanospheres with a deconvolved Abbe resolution of 116 nm and a field of view of 10 µm × 10 µm. Our method is robust against optical aberrations and stage drifts, therefore excellent for imaging nanostructures under ambient conditions. [1] M. G. L. Gustafsson, J. Microsc. 198, 82-87 (2000). [2] H. Yilmaz, E. G. van Putten, J. Bertolotti, A. Lagendijk, W. L. Vos, and A. P. Mosk, Optica 2, 424-429 (2015).

Nanometer-scale characterization of laser-driven compression, shocks, and phase transitions, by x-ray scattering using free electron lasers

DOE PAGES

Kluge, T.; Rödel, C.; Rödel, M.; ...

2017-10-23

In this paper, we study the feasibility of using small angle X-ray scattering (SAXS) as a new experimental diagnostic for intense laser-solid interactions. By using X-ray pulses from a hard X-ray free electron laser, we can simultaneously achieve nanometer and femtosecond resolution of laser-driven samples. This is an important new capability for the Helmholtz international beamline for extreme fields at the high energy density endstation currently built at the European X-ray free electron laser. We review the relevant SAXS theory and its application to transient processes in solid density plasmas and report on first experimental results that confirm the feasibilitymore » of the method. Finally, we present results of two test experiments where the first experiment employs ultra-short laser pulses for studying relativistic laser plasma interactions, and the second one focuses on shock compression studies with a nanosecond laser system.« less

Nanometer-scale characterization of laser-driven compression, shocks, and phase transitions, by x-ray scattering using free electron lasers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kluge, T.; Rödel, C.; Rödel, M.

In this paper, we study the feasibility of using small angle X-ray scattering (SAXS) as a new experimental diagnostic for intense laser-solid interactions. By using X-ray pulses from a hard X-ray free electron laser, we can simultaneously achieve nanometer and femtosecond resolution of laser-driven samples. This is an important new capability for the Helmholtz international beamline for extreme fields at the high energy density endstation currently built at the European X-ray free electron laser. We review the relevant SAXS theory and its application to transient processes in solid density plasmas and report on first experimental results that confirm the feasibilitymore » of the method. Finally, we present results of two test experiments where the first experiment employs ultra-short laser pulses for studying relativistic laser plasma interactions, and the second one focuses on shock compression studies with a nanosecond laser system.« less

Phosphorus detection in vitrified bacteria by cryo-STEM annular dark-field analysis.

PubMed

Wolf, Sharon Grayer; Rez, Peter; Elbaum, Michael

2015-11-01

Bacterial cells often contain dense granules. Among these, polyphosphate bodies (PPBs) store inorganic phosphate for a variety of essential functions. Identification of PPBs has until now been accomplished by analytical methods that required drying or chemically fixing the cells. These methods entail large electron doses that are incompatible with low-dose imaging of cryogenic specimens. We show here that Scanning Transmission Electron Microscopy (STEM) of fully hydrated, intact, vitrified bacteria provides a simple means for mapping of phosphorus-containing dense granules based on quantitative sensitivity of the electron scattering to atomic number. A coarse resolution of the scattering angles distinguishes phosphorus from the abundant lighter atoms: carbon, nitrogen and oxygen. The theoretical basis is similar to Z contrast of materials science. EDX provides a positive identification of phosphorus, but importantly, the method need not involve a more severe electron dose than that required for imaging. The approach should prove useful in general for mapping of heavy elements in cryopreserved specimens when the element identity is known from the biological context. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

High-resolution monochromated electron energy-loss spectroscopy of organic photovoltaic materials.

PubMed

Alexander, Jessica A; Scheltens, Frank J; Drummy, Lawrence F; Durstock, Michael F; Hage, Fredrik S; Ramasse, Quentin M; McComb, David W

2017-09-01

Advances in electron monochromator technology are providing opportunities for high energy resolution (10 - 200meV) electron energy-loss spectroscopy (EELS) to be performed in the scanning transmission electron microscope (STEM). The energy-loss near-edge structure in core-loss spectroscopy is often limited by core-hole lifetimes rather than the energy spread of the incident illumination. However, in the valence-loss region, the reduced width of the zero loss peak makes it possible to resolve clearly and unambiguously spectral features at very low energy-losses (<3eV). In this contribution, high-resolution EELS was used to investigate four materials commonly used in organic photovoltaics (OPVs): poly(3-hexlythiophene) (P3HT), [6,6] phenyl-C 61 butyric acid methyl ester (PCBM), copper phthalocyanine (CuPc), and fullerene (C 60 ). Data was collected on two different monochromated instruments - a Nion UltraSTEM 100 MC 'HERMES' and a FEI Titan 3 60-300 Image-Corrected S/TEM - using energy resolutions (as defined by the zero loss peak full-width at half-maximum) of 35meV and 175meV, respectively. The data was acquired to allow deconvolution of plural scattering, and Kramers-Kronig analysis was utilized to extract the complex dielectric functions. The real and imaginary parts of the complex dielectric functions obtained from the two instruments were compared to evaluate if the enhanced resolution in the Nion provides new opto-electronic information for these organic materials. The differences between the spectra are discussed, and the implications for STEM-EELS studies of advanced materials are considered. Copyright © 2017 Elsevier B.V. All rights reserved.

High quality single shot diffraction patterns using ultrashort megaelectron volt electron beams from a radio frequency photoinjector.

PubMed

Musumeci, P; Moody, J T; Scoby, C M; Gutierrez, M S; Bender, H A; Wilcox, N S

2010-01-01

Single shot diffraction patterns using a 250-fs-long electron beam have been obtained at the UCLA Pegasus laboratory. High quality images with spatial resolution sufficient to distinguish closely spaced peaks in the Debye-Scherrer ring pattern have been recorded by scattering the 1.6 pC 3.5 MeV electron beam generated in the rf photoinjector off a 100-nm-thick Au foil. Dark current and high emittance particles are removed from the beam before sending it onto the diffraction target using a 1 mm diameter collimating hole. These results open the door to the study of irreversible phase transformations by single shot MeV electron diffraction.

First Dark Matter Constraints from SuperCDMS Single-Charge Sensitive Detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agnese, R.; et al.

We present the first limits on inelastic electron-scattering dark matter and dark photon absorption using a prototype SuperCDMS detector having a charge resolution of 0.1 electron-hole pairs (CDMS HVeV, a 0.93 gram CDMS HV device). These electron-recoil limits significantly improve experimental constraints on dark matter particles with masses as low as 1 MeV/more » $$\\mathrm{c^2}$$. We demonstrate a sensitivity to dark photons competitive with other leading approaches but using substantially less exposure (0.49 gram days). These results demonstrate the scientific potential of phonon-mediated semiconductor detectors that are sensitive to single electronic excitations.« less

An iterative three-dimensional electron density imaging algorithm using uncollimated compton scattered x rays from a polyenergetic primary pencil beam.

PubMed

Van Uytven, Eric; Pistorius, Stephen; Gordon, Richard

2007-01-01

X-ray film-screen mammography is currently the gold standard for detecting breast cancer. However, one disadvantage is that it projects a three-dimensional (3D) object onto a two-dimensional (2D) image, reducing contrast between small lesions and layers of normal tissue. Another limitation is its reduced sensitivity in women with mammographically dense breasts. Computed tomography (CT) produces a 3D image yet has had a limited role in mammography due to its relatively high dose, low resolution, and low contrast. As a first step towards implementing quantitative 3D mammography, which may improve the ability to detect and specify breast tumors, we have developed an analytical technique that can use Compton scatter to obtain 3D information of an object from a single projection. Imaging material with a pencil beam of polychromatic x rays produces a characteristic scattered photon spectrum at each point on the detector plane. A comparable distribution may be calculated using a known incident x-ray energy spectrum, beam shape, and an initial estimate of the object's 3D mass attenuation and electron density. Our iterative minimization algorithm changes the initially arbitrary electron density voxel matrix to reduce regular differences between the analytically predicted and experimentally measured spectra at each point on the detector plane. The simulated electron density converges to that of the object as the differences are minimized. The reconstruction algorithm has been validated using simulated data produced by the EGSnrc Monte Carlo code system. We applied the imaging algorithm to a cylindrically symmetric breast tissue phantom containing multiple inhomogeneities. A preliminary ROC analysis scores greater than 0.96, which indicate that under the described simplifying conditions, this approach shows promise in identifying and localizing inhomogeneities which simulate 0.5 mm calcifications with an image voxel resolution of 0.25 cm and at a dose comparable to mammography.

Short-lived solar burst spectral component at f approximately 100 GHz

NASA Technical Reports Server (NTRS)

Kaufmann, P.; Correia, E.; Costa, J. E. R.; Vaz, A. M. Z.

1986-01-01

A new kind of burst emission component was discovered, exhibiting fast and distinct pulses (approx. 60 ms durations), with spectral peak emission at f approx. 100 GHz, and onset time coincident to hard X-rays to within approx. 128 ms. These features pose serious constraints for the interpretation using current models. One suggestion assumes the f approx. 100 GHz pulses emission by synchrotron mechanism of electrons accelerated to ultrarelativistic energies. The hard X-rays originate from inverse Compton scattering of the electrons on the synchrotron photons. Several crucial observational tests are needed for the understanding of the phenomenon, requiring high sensitivity and high time resolution (approx. 1 ms) simultaneous to high spatial resolution (0.1 arcsec) at f approx. 110 GHz and hard X-rays.

Observation of the Λ⁷He Hypernucleus by the (e, e'K⁺) Reaction

DOE PAGES

Nakamura, S. N.; Matsumura, A.; Okayasu, Y.; ...

2013-01-02

An experiment with a newly developed high-resolution kaon spectrometer and a scattered electron spectrometer with a novel configuration was performed in Hall C at Jefferson Lab. The ground state of a neutron-rich hypernucleus, He Λ⁷, was observed for the first time with the (e, e'K⁺) reaction with an energy resolution of ~0.6 MeV. This resolution is the best reported to date for hypernuclear reaction spectroscopy. The He Λ⁷ binding energy supplies the last missing information of the A=7, T=1 hypernuclear isotriplet, providing a new input for the charge symmetry breaking effect of the ΛN potential.

Programmable Multiple-Ramped-Voltage Power Supply

NASA Technical Reports Server (NTRS)

Ajello, Joseph M.; Howell, S. K.

1993-01-01

Ramp waveforms range up to 2,000 V. Laboratory high-voltage power-supply system puts out variety of stable voltages programmed to remain fixed with respect to ground or float with respect to ramp waveform. Measures voltages it produces with high resolution; automatically calibrates, zeroes, and configures itself; and produces variety of input/output signals for use with other instruments. Developed for use with ultraviolet spectrometer. Also applicable to control of electron guns in general and to operation of such diverse equipment used in measuring scattering cross sections of subatomic particles and in industrial electron-beam welders.

Development of inorganic resists for electron beam lithography: Novel materials and simulations

NASA Astrophysics Data System (ADS)

Jeyakumar, Augustin

Electron beam lithography is gaining widespread utilization as the semiconductor industry progresses towards both advanced optical and non-optical lithographic technologies for high resolution patterning. The current resist technologies are based on organic systems that are imaged most commonly through chain scission, networking, or a chemically amplified polarity change in the material. Alternative resists based on inorganic systems were developed and characterized in this research for high resolution electron beam lithography and their interactions with incident electrons were investigated using Monte Carlo simulations. A novel inorganic resist imaging scheme was developed using metal-organic precursors which decompose to form metal oxides upon electron beam irradiation that can serve as inorganic hard masks for hybrid bilayer inorganic-organic imaging systems and also as directly patternable high resolution metal oxide structures. The electron beam imaging properties of these metal-organic materials were correlated to the precursor structure by studying effects such as interactions between high atomic number species and the incident electrons. Optimal single and multicomponent precursors were designed for utilization as viable inorganic resist materials for sub-50nm patterning in electron beam lithography. The electron beam imaging characteristics of the most widely used inorganic resist material, hydrogen silsesquioxane (HSQ), was also enhanced using a dual processing imaging approach with thermal curing as well as a sensitizer catalyzed imaging approach. The interaction between incident electrons and the high atomic number species contained in these inorganic resists was also studied using Monte Carlo simulations. The resolution attainable using inorganic systems as compared to organic systems can be greater for accelerating voltages greater than 50 keV due to minimized lateral scattering in the high density inorganic systems. The effects of loading nanoparticles in an electron beam resist was also investigated using a newly developed hybrid Monte Carlo approach that accounts for multiple components in a solid film. The resolution of the nanocomposite resist process was found to degrade with increasing nanoparticle loading. Finally, the electron beam patterning of self-assembled monolayers, which were found to primarily utilize backscattered electrons from the high atomic number substrate materials to form images, was also investigated and characterized. It was found that backscattered electrons limit the resolution attainable at low incident electron energies.

High-resolution ab initio three-dimensional x-ray diffraction microscopy

DOE PAGES

Chapman, Henry N.; Barty, Anton; Marchesini, Stefano; ...

2006-01-01

Coherent x-ray diffraction microscopy is a method of imaging nonperiodic isolated objects at resolutions limited, in principle, by only the wavelength and largest scattering angles recorded. We demonstrate x-ray diffraction imaging with high resolution in all three dimensions, as determined by a quantitative analysis of the reconstructed volume images. These images are retrieved from the three-dimensional diffraction data using no a priori knowledge about the shape or composition of the object, which has never before been demonstrated on a nonperiodic object. We also construct two-dimensional images of thick objects with greatly increased depth of focus (without loss of transverse spatialmore » resolution). These methods can be used to image biological and materials science samples at high resolution with x-ray undulator radiation and establishes the techniques to be used in atomic-resolution ultrafast imaging at x-ray free-electron laser sources.« less

STM on Gate-Tunable Graphene

NASA Astrophysics Data System (ADS)

Zhang, Yuanbo

2009-03-01

We have successfully performed atomically-resolved scanning tunneling microscopy and spectroscopy (STS) on mechanically exfoliated graphene samples having tunable back-gates. We have discovered that the tunneling spectra of graphene flakes display an unexpected gap-like feature that is pinned to the Fermi level for different gate voltages, and which coexists with another depression in density-of-states that moves with gate voltage. Extensive tests and careful analysis show that the gap-feature is due to phonon-assisted inelastic tunneling, and the depression directly marks the location of the graphene Dirac point. Using tunneling spectroscopy as a new tool, we further probe the local energetic variations of the graphene charge neutral point (Dirac point) to map out spatial electron density inhomogeneities in graphene. Such measurements are two orders of magnitude higher in resolution than previous experiments, and they can be directly correlated with nanometer scale topographic features. Based on our observation of energy-dependent periodic electronic interference patterns, our measurements also reveal the nature of impurity scattering of Dirac fermions in graphene. These results are significant for understanding the sources of electron density inhomogeneity and electron scattering in graphene, and the microscopic causes of graphene electron mobility.

Angle selective backscattered electron contrast in the low-voltage scanning electron microscope: Simulation and experiment for polymers.

PubMed

Wan, Q; Masters, R C; Lidzey, D; Abrams, K J; Dapor, M; Plenderleith, R A; Rimmer, S; Claeyssens, F; Rodenburg, C

2016-12-01

Recently developed detectors can deliver high resolution and high contrast images of nanostructured carbon based materials in low voltage scanning electron microscopes (LVSEM) with beam deceleration. Monte Carlo Simulations are also used to predict under which exact imaging conditions purely compositional contrast can be obtained and optimised. This allows the prediction of the electron signal intensity in angle selective conditions for back-scattered electron (BSE) imaging in LVSEM and compares it to experimental signals. Angle selective detection with a concentric back scattered (CBS) detector is considered in the model in the absence and presence of a deceleration field, respectively. The validity of the model prediction for both cases was tested experimentally for amorphous C and Cu and applied to complex nanostructured carbon based materials, namely a Poly(N-isopropylacrylamide)/Poly(ethylene glycol) Diacrylate (PNIPAM/PEGDA) semi-interpenetration network (IPN) and a Poly(3-hexylthiophene-2,5-diyl) (P3HT) film, to map nano-scale composition and crystallinity distribution by avoiding experimental imaging conditions that lead to a mixed topographical and compositional contrast. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

Parameter dependence of the MCNP electron transport in determining dose distributions.

PubMed

Reynaert, N; Palmans, H; Thierens, H; Jeraj, R

2002-10-01

In this paper, a detailed study of the electron transport in MCNP is performed, separating the effects of the energy binning technique on the energy loss rate, the scattering angles, and the sub-step length as a function of energy. As this problem is already well known, in this paper we focus on the explanation as to why the default mode of MCNP can lead to large deviations. The resolution dependence was investigated as well. An error in the MCNP code in the energy binning technique in the default mode (DBCN 18 card = 0) was revealed, more specific in the updating of cross sections when a sub-step is performed corresponding to a high-energy loss. This updating error is not present in the ITS mode (DBCN 18 card = 1) and leads to a systematically lower dose deposition rate in the default mode. The effect is present for all energies studied (0.5-10 MeV) and depends on the geometrical resolution of the scoring regions and the energy grid resolution. The effect of the energy binning technique is of the same order of that of the updating error for energies below 2 MeV, and becomes less important for higher energies. For a 1 MeV point source surrounded by homogeneous water, the deviation of the default MCNP results at short distances attains 9% and remains approximately the same for all energies. This effect could be corrected by removing the completion of an energy step each time an electron changes from an energy bin during a sub-step. Another solution consists of performing all calculations in the ITS mode. Another problem is the resolution dependence, even in the ITS mode. The higher the resolution is chosen (the smaller the scoring regions) the faster the energy is deposited along the electron track. It is proven that this is caused by starting a new energy step when crossing a surface. The resolution effect should be investigated for every specific case when calculating dose distributions around beta sources. The resolution should not be higher than 0.85*(1-EFAC)*CSDA, where EFAC is the energy loss per energy step and CSDA a continuous slowing down approximation range. This effect could as well be removed by determining the cross sections for energy loss and multiple scattering at the average energy of an energy step and by sampling the cross sections for each sub-step. Overall, we conclude that MCNP cannot be used without a caution due to possible errors in the electron transport. When care is taken, it is possible to obtain correct results that are in agreement with other Monte Carlo codes.

Atomic-Scale Visualization of Quasiparticle Interference on a Type-II Weyl Semimetal Surface.

PubMed

Zheng, Hao; Bian, Guang; Chang, Guoqing; Lu, Hong; Xu, Su-Yang; Wang, Guangqiang; Chang, Tay-Rong; Zhang, Songtian; Belopolski, Ilya; Alidoust, Nasser; Sanchez, Daniel S; Song, Fengqi; Jeng, Horng-Tay; Yao, Nan; Bansil, Arun; Jia, Shuang; Lin, Hsin; Hasan, M Zahid

2016-12-23

We combine quasiparticle interference simulation (theory) and atomic resolution scanning tunneling spectromicroscopy (experiment) to visualize the interference patterns on a type-II Weyl semimetal Mo_{x}W_{1-x}Te_{2} for the first time. Our simulation based on first-principles band topology theoretically reveals the surface electron scattering behavior. We identify the topological Fermi arc states and reveal the scattering properties of the surface states in Mo_{0.66}W_{0.34}Te_{2}. In addition, our result reveals an experimental signature of the topology via the interconnectivity of bulk and surface states, which is essential for understanding the unusual nature of this material.

Fine-structure-resolution for Rovibrational Excitation of CN Due to H2

NASA Astrophysics Data System (ADS)

Byrd, Nat; Yang, Benhui H.; Stancil, Phillip C.

2018-06-01

Diatomic molecules can be readily excited in interstellar environments exposed to intense UV radiation, such as the inner rim of a protoplanetary disk. Non-thermal populations of excited rovibrational levels can result, for example, following decay from electronically excited states to the electronic ground state. Competition between radiative decay and collisional processes, mostly due to H2, determine the resulting rovibrational emission spectrum. For CN, and other open-shell molecules, the resulting spectrum will be complicated due to fine-structure splitting of the rotational levels. In some cases, fine-structure resolution has been previously computed for rotational transitions in atom- or diatom-diatom collisional processes. Here we present the first fine-structure resolution for vibrational deexcitation for CN colliding with H2. The collisional cross sections were computed using a 6D potential energy surface with a full close-coupling approach. Fine-structure resolution is obtained by adopting an angular momentum recoupling scheme to transform the scattering matrices to a recoupled basis. Here we present low-energy calculations for the v=1 to 0 transition.This work was supported by NASA Grant NNX16AF09G.

Single-pulse enhanced coherent diffraction imaging of bacteria with an X-ray free-electron laser

NASA Astrophysics Data System (ADS)

Fan, Jiadong; Sun, Zhibin; Wang, Yaling; Park, Jaehyun; Kim, Sunam; Gallagher-Jones, Marcus; Kim, Yoonhee; Song, Changyong; Yao, Shengkun; Zhang, Jian; Zhang, Jianhua; Duan, Xiulan; Tono, Kensuke; Yabashi, Makina; Ishikawa, Tetsuya; Fan, Chunhai; Zhao, Yuliang; Chai, Zhifang; Gao, Xueyun; Earnest, Thomas; Jiang, Huaidong

2016-09-01

High-resolution imaging offers one of the most promising approaches for exploring and understanding the structure and function of biomaterials and biological systems. X-ray free-electron lasers (XFELs) combined with coherent diffraction imaging can theoretically provide high-resolution spatial information regarding biological materials using a single XFEL pulse. Currently, the application of this method suffers from the low scattering cross-section of biomaterials and X-ray damage to the sample. However, XFELs can provide pulses of such short duration that the data can be collected using the “diffract and destroy” approach before the effects of radiation damage on the data become significant. These experiments combine the use of enhanced coherent diffraction imaging with single-shot XFEL radiation to investigate the cellular architecture of Staphylococcus aureus with and without labeling by gold (Au) nanoclusters. The resolution of the images reconstructed from these diffraction patterns were twice as high or more for gold-labeled samples, demonstrating that this enhancement method provides a promising approach for the high-resolution imaging of biomaterials and biological systems.

Single-pulse enhanced coherent diffraction imaging of bacteria with an X-ray free-electron laser

PubMed Central

Fan, Jiadong; Sun, Zhibin; Wang, Yaling; Park, Jaehyun; Kim, Sunam; Gallagher-Jones, Marcus; Kim, Yoonhee; Song, Changyong; Yao, Shengkun; Zhang, Jian; Zhang, Jianhua; Duan, Xiulan; Tono, Kensuke; Yabashi, Makina; Ishikawa, Tetsuya; Fan, Chunhai; Zhao, Yuliang; Chai, Zhifang; Gao, Xueyun; Earnest, Thomas; Jiang, Huaidong

2016-01-01

High-resolution imaging offers one of the most promising approaches for exploring and understanding the structure and function of biomaterials and biological systems. X-ray free-electron lasers (XFELs) combined with coherent diffraction imaging can theoretically provide high-resolution spatial information regarding biological materials using a single XFEL pulse. Currently, the application of this method suffers from the low scattering cross-section of biomaterials and X-ray damage to the sample. However, XFELs can provide pulses of such short duration that the data can be collected using the “diffract and destroy” approach before the effects of radiation damage on the data become significant. These experiments combine the use of enhanced coherent diffraction imaging with single-shot XFEL radiation to investigate the cellular architecture of Staphylococcus aureus with and without labeling by gold (Au) nanoclusters. The resolution of the images reconstructed from these diffraction patterns were twice as high or more for gold-labeled samples, demonstrating that this enhancement method provides a promising approach for the high-resolution imaging of biomaterials and biological systems. PMID:27659203

Single-pulse enhanced coherent diffraction imaging of bacteria with an X-ray free-electron laser.

PubMed

Fan, Jiadong; Sun, Zhibin; Wang, Yaling; Park, Jaehyun; Kim, Sunam; Gallagher-Jones, Marcus; Kim, Yoonhee; Song, Changyong; Yao, Shengkun; Zhang, Jian; Zhang, Jianhua; Duan, Xiulan; Tono, Kensuke; Yabashi, Makina; Ishikawa, Tetsuya; Fan, Chunhai; Zhao, Yuliang; Chai, Zhifang; Gao, Xueyun; Earnest, Thomas; Jiang, Huaidong

2016-09-23

High-resolution imaging offers one of the most promising approaches for exploring and understanding the structure and function of biomaterials and biological systems. X-ray free-electron lasers (XFELs) combined with coherent diffraction imaging can theoretically provide high-resolution spatial information regarding biological materials using a single XFEL pulse. Currently, the application of this method suffers from the low scattering cross-section of biomaterials and X-ray damage to the sample. However, XFELs can provide pulses of such short duration that the data can be collected using the "diffract and destroy" approach before the effects of radiation damage on the data become significant. These experiments combine the use of enhanced coherent diffraction imaging with single-shot XFEL radiation to investigate the cellular architecture of Staphylococcus aureus with and without labeling by gold (Au) nanoclusters. The resolution of the images reconstructed from these diffraction patterns were twice as high or more for gold-labeled samples, demonstrating that this enhancement method provides a promising approach for the high-resolution imaging of biomaterials and biological systems.

Progress on Thomson scattering in the Pegasus Toroidal Experiment

NASA Astrophysics Data System (ADS)

Schlossberg, D. J.; Bongard, M. W.; Fonck, R. J.; Schoenbeck, N. L.; Winz, G. R.

2013-11-01

A novel Thomson scattering system has been implemented on the Pegasus Toroidal Experiment where typical densities of 1019 m-3 and electron temperatures of 10 to 500 eV are expected. The system leverages technological advances in high-energy pulsed lasers, volume phase holographic (VPH) diffraction gratings, and gated image intensified (ICCD) cameras to provide a relatively low-maintenance, economical, robust diagnostic system. Scattering is induced by a frequency-doubled, Q-switched Nd:YAG laser (2 J at 532 nm, 7 ns FWHM pulse) directed to the plasma over a 7.7 m long beam path, and focused to < 3 mm throughout the collection region. Inter-shot beam alignment is adjustable with less than a 0.01 mm spatial resolution in the collection region. A custom lens system collects scattered photons at radii 15 cm to 85 cm from the machine's center, at ~ F/6 with 14 mm radial resolution. The initial configuration provides scattering measurements at 12 spatial locations and 12 simultaneous background measurements at adjacent locations. If plasma background subtraction proves to be insignificant, these background channels will be used as viewing channels. Each spectrometer supports 8 spatial channels and can provide 8 or more spectral bins each. The spectrometers use high-efficiency VPH transmission gratings (eff. > 80%) and fast-gated ICCDs (gate > 2 ns, Gen III intensifier) with high-throughput (F/1.8), achromatic lensing. A stray light mitigation facility has been implemented, consisting of a multi-aperture optical baffle system and a simple beam dump. Successful stray light reduction has enabled detection of scattered signal, and Rayleigh scattering has been used to provide a relative calibration. Initial temperature measurements have been made and data analysis algorithms are under development.

Elastic scattering and vibrational excitation for electron impact on para-benzoquinone

NASA Astrophysics Data System (ADS)

Jones, D. B.; Blanco, F.; García, G.; da Costa, R. F.; Kossoski, F.; Varella, M. T. do N.; Bettega, M. H. F.; Lima, M. A. P.; White, R. D.; Brunger, M. J.

2017-12-01

We report on theoretical elastic and experimental vibrational-excitation differential cross sections (DCSs) for electron scattering from para-benzoquinone (C6H4O2), in the intermediate energy range 15-50 eV. The calculations were conducted with two different theoretical methodologies, the Schwinger multichannel method with pseudopotentials (SMCPP) and the independent atom method with screening corrected additivity rule (IAM-SCAR) that also now incorporates a further interference (I) term. The SMCPP with N energetically open electronic states (Nopen) at the static-exchange-plus-polarisation (Nopench-SEP) level was used to calculate the scattering amplitudes using a channel coupling scheme that ranges from 1ch-SE up to the 89ch-SEP level of approximation. We found that in going from the 38ch-SEP to the 89ch-SEP, at all energies considered here, the elastic DCSs did not change significantly in terms of both their shapes and magnitudes. This is a good indication that our SMCPP 89ch-SEP elastic DCSs are converged with respect to the multichannel coupling effect for the investigated intermediate energies. While agreement between our IAM-SCAR+I and SMCPP 89ch-SEP computations improves as the incident electron energy increases from 15 eV, overall the level of accord is only marginal. This is particularly true at middle scattering angles, suggesting that our SCAR and interference corrections are failing somewhat for this molecule below 50 eV. We also report experimental DCS results, using a crossed-beam apparatus, for excitation of some of the unresolved ("hybrid") vibrational quanta (bands I-III) of para-benzoquinone. Those data were derived from electron energy loss spectra that were measured over a scattered electron angular range of 10°-90° and put on an absolute scale using our elastic SMCPP 89ch-SEP DCS results. The energy resolution of our measurements was ˜80 meV, which is why, at least in part, the observed vibrational features were only partially resolved. To the best of our knowledge, there are no other experimental or theoretical vibrational excitation results against which we might compare the present measurements.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akerib, DS; Alsum, S; Araújo, HM

The LUX experiment has performed searches for dark matter particles scattering elastically on xenon nuclei, leading to stringent upper limits on the nuclear scattering cross sections for dark matter. Here, for results derived frommore » $${1.4}\\times 10^{4}\\;\\mathrm{kg\\,days}$$ of target exposure in 2013, details of the calibration, event-reconstruction, modeling, and statistical tests that underlie the results are presented. Detector performance is characterized, including measured efficiencies, stability of response, position resolution, and discrimination between electron- and nuclear-recoil populations. Models are developed for the drift field, optical properties, background populations, the electron- and nuclear-recoil responses, and the absolute rate of low-energy background events. Innovations in the analysis include in situ measurement of the photomultipliers' response to xenon scintillation photons, verification of fiducial mass with a low-energy internal calibration source, and new empirical models for low-energy signal yield based on large-sample, in situ calibrations.« less

JLab Measurements of the He 3 Form Factors at Large Momentum Transfers

DOE PAGES

Camsonne, A.; Katramatou, A. T.; Olson, M.; ...

2017-10-19

The charge and magnetic form factors, F C and F M, respectively, of 3He are extracted in the kinematic range 25 fm –2 ≤ Q 2 ≤ 61 fm –2 from elastic electron scattering by detecting 3He recoil nuclei and scattered electrons in coincidence with the two High Resolution Spectrometers of the Hall A Facility at Jefferson Lab. The measurements find evidence for the existence of a second diffraction minimum for the magnetic form factor at Q 2 = 49.3 fm –2 and for the charge form factor at Q 2 = 62.0 fm –2. Both minima are predicted tomore » exist in the Q 2 range accessible by this Jefferson Lab experiment. Here, the data are in qualitative agreement with theoretical calculations based on realistic interactions and accurate methods to solve the three-body nuclear problem.« less

JLab Measurements of the He 3 Form Factors at Large Momentum Transfers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Camsonne, A.; Katramatou, A. T.; Olson, M.

The charge and magnetic form factors, F C and F M, respectively, of 3He are extracted in the kinematic range 25 fm –2 ≤ Q 2 ≤ 61 fm –2 from elastic electron scattering by detecting 3He recoil nuclei and scattered electrons in coincidence with the two High Resolution Spectrometers of the Hall A Facility at Jefferson Lab. The measurements find evidence for the existence of a second diffraction minimum for the magnetic form factor at Q 2 = 49.3 fm –2 and for the charge form factor at Q 2 = 62.0 fm –2. Both minima are predicted tomore » exist in the Q 2 range accessible by this Jefferson Lab experiment. Here, the data are in qualitative agreement with theoretical calculations based on realistic interactions and accurate methods to solve the three-body nuclear problem.« less

Ultrafast collinear scattering and carrier multiplication in graphene.

PubMed

Brida, D; Tomadin, A; Manzoni, C; Kim, Y J; Lombardo, A; Milana, S; Nair, R R; Novoselov, K S; Ferrari, A C; Cerullo, G; Polini, M

2013-01-01

Graphene is emerging as a viable alternative to conventional optoelectronic, plasmonic and nanophotonic materials. The interaction of light with charge carriers creates an out-of-equilibrium distribution, which relaxes on an ultrafast timescale to a hot Fermi-Dirac distribution, that subsequently cools emitting phonons. Although the slower relaxation mechanisms have been extensively investigated, the initial stages still pose a challenge. Experimentally, they defy the resolution of most pump-probe setups, due to the extremely fast sub-100 fs carrier dynamics. Theoretically, massless Dirac fermions represent a novel many-body problem, fundamentally different from Schrödinger fermions. Here we combine pump-probe spectroscopy with a microscopic theory to investigate electron-electron interactions during the early stages of relaxation. We identify the mechanisms controlling the ultrafast dynamics, in particular the role of collinear scattering. This gives rise to Auger processes, including charge multiplication, which is key in photovoltage generation and photodetectors.

Calibration, event reconstruction, data analysis, and limit calculation for the LUX dark matter experiment

NASA Astrophysics Data System (ADS)

Akerib, D. S.; Alsum, S.; Araújo, H. M.; Bai, X.; Bailey, A. J.; Balajthy, J.; Beltrame, P.; Bernard, E. P.; Bernstein, A.; Biesiadzinski, T. P.; Boulton, E. M.; Brás, P.; Byram, D.; Cahn, S. B.; Carmona-Benitez, M. C.; Chan, C.; Currie, A.; Cutter, J. E.; Davison, T. J. R.; Dobi, A.; Dobson, J. E. Y.; Druszkiewicz, E.; Edwards, B. N.; Faham, C. H.; Fallon, S. R.; Fan, A.; Fiorucci, S.; Gaitskell, R. J.; Gehman, V. M.; Genovesi, J.; Ghag, C.; Gilchriese, M. G. D.; Hall, C. R.; Hanhardt, M.; Haselschwardt, S. J.; Hertel, S. A.; Hogan, D. P.; Horn, M.; Huang, D. Q.; Ignarra, C. M.; Jacobsen, R. G.; Ji, W.; Kamdin, K.; Kazkaz, K.; Khaitan, D.; Knoche, R.; Larsen, N. A.; Lee, C.; Lenardo, B. G.; Lesko, K. T.; Lindote, A.; Lopes, M. I.; Manalaysay, A.; Mannino, R. L.; Marzioni, M. F.; McKinsey, D. N.; Mei, D.-M.; Mock, J.; Moongweluwan, M.; Morad, J. A.; Murphy, A. St. J.; Nehrkorn, C.; Nelson, H. N.; Neves, F.; O'Sullivan, K.; Oliver-Mallory, K. C.; Palladino, K. J.; Pease, E. K.; Reichhart, L.; Rhyne, C.; Shaw, S.; Shutt, T. A.; Silva, C.; Solmaz, M.; Solovov, V. N.; Sorensen, P.; Sumner, T. J.; Szydagis, M.; Taylor, D. J.; Taylor, W. C.; Tennyson, B. P.; Terman, P. A.; Tiedt, D. R.; To, W. H.; Tripathi, M.; Tvrznikova, L.; Uvarov, S.; Velan, V.; Verbus, J. R.; Webb, R. C.; White, J. T.; Whitis, T. J.; Witherell, M. S.; Wolfs, F. L. H.; Xu, J.; Yazdani, K.; Young, S. K.; Zhang, C.; LUX Collaboration

2018-05-01

The LUX experiment has performed searches for dark-matter particles scattering elastically on xenon nuclei, leading to stringent upper limits on the nuclear scattering cross sections for dark matter. Here, for results derived from 1.4 ×104 kg days of target exposure in 2013, details of the calibration, event-reconstruction, modeling, and statistical tests that underlie the results are presented. Detector performance is characterized, including measured efficiencies, stability of response, position resolution, and discrimination between electron- and nuclear-recoil populations. Models are developed for the drift field, optical properties, background populations, the electron- and nuclear-recoil responses, and the absolute rate of low-energy background events. Innovations in the analysis include in situ measurement of the photomultipliers' response to xenon scintillation photons, verification of fiducial mass with a low-energy internal calibration source, and new empirical models for low-energy signal yield based on large-sample, in situ calibrations.

Measurement of the neutron electric to magnetic form factor ratio at Q2=1.58  GeV2 using the reaction 3He[over →](e[over →],e'n)pp.

PubMed

Schlimme, B S; Achenbach, P; Ayerbe Gayoso, C A; Bernauer, J C; Böhm, R; Bosnar, D; Challand, Th; Distler, M O; Doria, L; Fellenberger, F; Fonvieille, H; Gómez Rodríguez, M; Grabmayr, P; Hehl, T; Heil, W; Kiselev, D; Krimmer, J; Makek, M; Merkel, H; Middleton, D G; Müller, U; Nungesser, L; Ott, B A; Pochodzalla, J; Potokar, M; Sánchez Majos, S; Sargsian, M M; Sick, I; Sirca, S; Weinriefer, M; Wendel, M; Yoon, C J

2013-09-27

A measurement of beam helicity asymmetries in the reaction 3He[over →](e[over →],e'n)pp is performed at the Mainz Microtron in quasielastic kinematics to determine the electric to magnetic form factor ratio of the neutron GEn/GMn at a four-momentum transfer Q2=1.58  GeV2. Longitudinally polarized electrons are scattered on a highly polarized 3He gas target. The scattered electrons are detected with a high-resolution magnetic spectrometer, and the ejected neutrons are detected with a dedicated neutron detector composed of scintillator bars. To reduce systematic errors, data are taken for four different target polarization orientations allowing the determination of GEn/GMn from a double ratio. We find μnGEn/GMn=0.250±0.058(stat)±0.017(syst).

Reflectometry diagnostics on TCV

NASA Astrophysics Data System (ADS)

Molina Cabrera, Pedro; Coda, Stefano; Porte, Laurie; Offeddu, Nicola; Tcv Team

2017-10-01

Both profile reflectometer and Doppler back-scattering (DBS) diagnostics are being developed for the TCV Tokamak using a steerable quasi-optical launcher and universal polarizers. First results will be presented. A pulse reflectometer is being developed to complement Thomson Scattering measurements of electron density, greatly increasing temporal resolution and also effectively enabling fluctuation measurements. Pulse reflectometry consists of sending short pulses of varying frequency and measuring the roundtrip group-delay with precise chronometers. A fast arbitrary waveform generator is used as a pulse source feeding frequency multipliers that bring the pulses to V-band. A DBS diagnostic is currently operational in TCV. DBS may be used to infer the perpendicular velocity and wave number spectrum of electron density fluctuations in the 3-15 cm-1 wave-number range. Off-the-shelf transceiver modules, originally used for VNA measurements, are being used in a Doppler radar configuration. See author list of S. Coda et al., 2017 Nucl. Fusion 57 102011.

Electron Microscope Studies of Cadmium Mercury Telluride

NASA Astrophysics Data System (ADS)

Lyster, Martin

Available from UMI in association with The British Library. Requires signed TDF. Epitaxial layers of Cd_{x }Hg_{(1-x)}Te grown on various substrates by liquid phase epitaxy and metallo-organic vapour phase epitaxy have been studied using transmission and scanning electron microscopy, in a variety of contrast modes. Wavelength-dispersive X-ray microanalysis has been used to study interfaces in epitaxial specimens, and the results are used to derive diffusion coefficients for a range of values of x in Cd_ {x}Hg_{(1-x)} Te. Extensive use has been made of back-scattered electron contrast in the SEM as a means of compositional mapping, and defect structures are imaged by this technique. The back-scattered electron contrast at interfaces has been studied in detail and is modelled using the Monte Carlo approach. The modelling is combined with calculations and practical measurements of the probe size in the SEM instrument used in the work, to arrive at a quantitative explanation of this contrast. The SEM and scintillator detector used allow a spatial resolution of better than 1000A, but it is shown that improvements in this are possible with present technology. Scanning infra-red microscopy (SIRM) and high -resolution transmission electron microscopy (HREM) have been applied to the study of CdTe. SIRM images reveal information about Te precipitation, including particle size and density. HREM images provide results concerning dislocation structures in CdTe. Selected-area diffraction contrast TEM results are presented which illustrate the microstructure of LPE and MOVPE material; and TEM foil preparation techniques are discussed, including the choice of ion species for milling cross-sectional specimens. In view of the results obtained, suggestions are made for future work in this field.

The architecture of amyloid-like peptide fibrils revealed by X-ray scattering, diffraction and electron microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Langkilde, Annette E., E-mail: annette.langkilde@sund.ku.dk; Morris, Kyle L.; Serpell, Louise C.

The aggregation process and the fibril state of an amyloidogenic peptide suggest monomer addition to be the prevailing mechanism of elongation and a model of the peptide packing in the fibrils has been obtained. Structural analysis of protein fibrillation is inherently challenging. Given the crucial role of fibrils in amyloid diseases, method advancement is urgently needed. A hybrid modelling approach is presented enabling detailed analysis of a highly ordered and hierarchically organized fibril of the GNNQQNY peptide fragment of a yeast prion protein. Data from small-angle X-ray solution scattering, fibre diffraction and electron microscopy are combined with existing high-resolution X-raymore » crystallographic structures to investigate the fibrillation process and the hierarchical fibril structure of the peptide fragment. The elongation of these fibrils proceeds without the accumulation of any detectable amount of intermediate oligomeric species, as is otherwise reported for, for example, glucagon, insulin and α-synuclein. Ribbons constituted of linearly arranged protofilaments are formed. An additional hierarchical layer is generated via the pairing of ribbons during fibril maturation. Based on the complementary data, a quasi-atomic resolution model of the protofilament peptide arrangement is suggested. The peptide structure appears in a β-sheet arrangement reminiscent of the β-zipper structures evident from high-resolution crystal structures, with specific differences in the relative peptide orientation. The complexity of protein fibrillation and structure emphasizes the need to use multiple complementary methods.« less

Protein crystal structure obtained at 2.9 Å resolution from injecting bacterial cells into an X-ray free-electron laser beam

PubMed Central

Sawaya, Michael R.; Cascio, Duilio; Gingery, Mari; Rodriguez, Jose; Goldschmidt, Lukasz; Colletier, Jacques-Philippe; Messerschmidt, Marc M.; Boutet, Sébastien; Koglin, Jason E.; Williams, Garth J.; Brewster, Aaron S.; Nass, Karol; Hattne, Johan; Botha, Sabine; Doak, R. Bruce; Shoeman, Robert L.; DePonte, Daniel P.; Park, Hyun-Woo; Federici, Brian A.; Sauter, Nicholas K.; Schlichting, Ilme; Eisenberg, David S.

2014-01-01

It has long been known that toxins produced by Bacillus thuringiensis (Bt) are stored in the bacterial cells in crystalline form. Here we describe the structure determination of the Cry3A toxin found naturally crystallized within Bt cells. When whole Bt cells were streamed into an X-ray free-electron laser beam we found that scattering from other cell components did not obscure diffraction from the crystals. The resolution limits of the best diffraction images collected from cells were the same as from isolated crystals. The integrity of the cells at the moment of diffraction is unclear; however, given the short time (∼5 µs) between exiting the injector to intersecting with the X-ray beam, our result is a 2.9-Å-resolution structure of a crystalline protein as it exists in a living cell. The study suggests that authentic in vivo diffraction studies can produce atomic-level structural information. PMID:25136092

Modern Material Analysis Instruments Add a New Dimension to Materials Characterization and Failure Analysis

NASA Technical Reports Server (NTRS)

Panda, Binayak

2009-01-01

Modern analytical tools can yield invaluable results during materials characterization and failure analysis. Scanning electron microscopes (SEMs) provide significant analytical capabilities, including angstrom-level resolution. These systems can be equipped with a silicon drift detector (SDD) for very fast yet precise analytical mapping of phases, as well as electron back-scattered diffraction (EBSD) units to map grain orientations, chambers that admit large samples, variable pressure for wet samples, and quantitative analysis software to examine phases. Advanced solid-state electronics have also improved surface and bulk analysis instruments: Secondary ion mass spectroscopy (SIMS) can quantitatively determine and map light elements such as hydrogen, lithium, and boron - with their isotopes. Its high sensitivity detects impurities at parts per billion (ppb) levels. X-ray photo-electron spectroscopy (XPS) can determine oxidation states of elements, as well as identifying polymers and measuring film thicknesses on coated composites. This technique is also known as electron spectroscopy for chemical analysis (ESCA). Scanning Auger electron spectroscopy (SAM) combines surface sensitivity, spatial lateral resolution (10 nm), and depth profiling capabilities to describe elemental compositions of near and below surface regions down to the chemical state of an atom.

Electron-beam-driven RI separator for SCRIT (ERIS) at RIKEN RI beam factory

NASA Astrophysics Data System (ADS)

Ohnishi, T.; Ichikawa, S.; Koizumi, K.; Kurita, K.; Miyashita, Y.; Ogawara, R.; Tamaki, S.; Togasaki, M.; Wakasugi, M.

2013-12-01

We constructed a radioactive isotope (RI) separator named ERIS (electron-beam-driven RI separator for SCRIT) for the SCRIT (Self-Confinement RI Target) electron scattering facility at RIKEN RI Beam Factory (RIBF). In ERIS, production rate of fission products in the photofission of uranium is estimated to be 2.2 ×1011 fissions/s with 30 g of uranium and a 1-kW electron beam. During the commissioning of ERIS, the mass resolution and overall efficiency, including ionization, extraction, and transmission, were found to be 1660 and 21%, respectively, using natural xenon gas. The preparation of uranium carbide (UC2) RI production targets is described from which a 132Sn beam was successfully separated in our first attempt at RI production.

High resolution spectroscopy of the 12Lambda B hypernucleus produced by the (e,e'K+) reaction.

PubMed

Miyoshi, T; Sarsour, M; Yuan, L; Zhu, X; Ahmidouch, A; Ambrozewicz, P; Androic, D; Angelescu, T; Asaturyan, R; Avery, S; Baker, O K; Bertovic, I; Breuer, H; Carlini, R; Cha, J; Chrien, R; Christy, M; Cole, L; Danagoulian, S; Dehnhard, D; Elaasar, M; Empl, A; Ent, R; Fenker, H; Fujii, Y; Furic, M; Gan, L; Garrow, K; Gasparian, A; Gueye, P; Harvey, M; Hashimoto, O; Hinton, W; Hu, B; Hungerford, E; Jackson, C; Johnston, K; Juengst, H; Keppel, C; Lan, K; Liang, Y; Likhachev, V P; Liu, J H; Mack, D; Margaryan, A; Markowitz, P; Martoff, J; Mkrtchyan, H; Nakamura, S N; Petkovic, T; Reinhold, J; Roche, J; Sato, Y; Sawafta, R; Simicevic, N; Smith, G; Stepanyan, S; Tadevosyan, V; Takahashi, T; Tanida, K; Tang, L; Ukai, M; Uzzle, A; Vulcan, W; Wells, S; Wood, S; Xu, G; Yamaguchi, H; Yan, C

2003-06-13

High-energy, cw electron beams at new accelerator facilities allow electromagnetic production and precision study of hypernuclear structure, and we report here on the first experiment demonstrating the potential of the (e,e'K+) reaction for hypernuclear spectroscopy. This experiment is also the first to take advantage of the enhanced virtual photon flux available when electrons are scattered at approximately zero degrees. The observed energy resolution was found to be approximately 900 keV for the (12)(Lambda)B spectrum, and is substantially better than any previous hypernuclear experiment using magnetic spectrometers. The positions of the major excitations are found to be in agreement with a theoretical prediction and with a previous binding energy measurement, but additional structure is also observed in the core excited region, underlining the future promise of this technique.

State-to-state time-of-flight measurements of NO scattering from Au(111): direct observation of translation-to-vibration coupling in electronically nonadiabatic energy transfer.

PubMed

Golibrzuch, Kai; Shirhatti, Pranav R; Altschäffel, Jan; Rahinov, Igor; Auerbach, Daniel J; Wodtke, Alec M; Bartels, Christof

2013-09-12

Translational motion is believed to be a spectator degree of freedom in electronically nonadiabatic vibrational energy transfer between molecules and metal surfaces, but the experimental evidence available to support this view is limited. In this work, we have experimentally determined the translational inelasticity in collisions of NO molecules with a single-crystal Au(111) surface-a system with strong electronic nonadiabaticity. State-to-state molecular beam surface scattering was combined with an IR-UV double resonance scheme to obtain high-resolution time-of-flight data. The measurements include vibrationally elastic collisions (v = 3→3, 2→2) as well as collisions where one or two quanta of molecular vibration are excited (2→3, 2→4) or de-excited (2→1, 3→2, 3→1). In addition, we have carried out comprehensive measurements of the effects of rotational excitation on the translational energy of the scattered molecules. We find that under all conditions of this work, the NO molecules lose a large fraction (∼0.45) of their incidence translational energy to the surface. Those molecules that undergo vibrational excitation (relaxation) during the collision recoil slightly slower (faster) than vibrationally elastically scattered molecules. The amount of translational energy change depends on the surface temperature. The translation-to-rotation coupling, which is well-known for v = 0→0 collisions, is found to be significantly weaker for vibrationally inelastic than elastic channels. Our results clearly show that the spectator view of the translational motion in electronically nonadiabatic vibrational energy transfer between NO and Au(111) is only approximately correct.

The Gamma-Ray Imager/Polarimeter for Solar Flares (GRIPS)

NASA Technical Reports Server (NTRS)

Shih, Albert Y.; Lin, Robert P.; Hurford, Gordon J.; Duncan, Nicole A.; Saint-Hilaire, Pascal; Bain, Hazel M.; Boggs, Steven E.; Zoglauer, Andreas C.; Smith, David M.; Tajima, Hiroyasu;

Preliminary neutron and X-ray crystallographic studies of equine cyanomethemoglobin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kovalevsky, A.Y.; Fisher, S.Z.; Seaver, S.

2010-08-18

Room-temperature and 100 K X-ray and room-temperature neutron diffraction data have been measured from equine cyanomethemoglobin to 1.7 {angstrom} resolution using a home source, to 1.6 {angstrom} resolution on NE-CAT at the Advanced Photon Source and to 2.0 {angstrom} resolution on the PCS at Los Alamos Neutron Science Center, respectively. The cyanomethemoglobin is in the R state and preliminary room-temperature electron and neutron scattering density maps clearly show the protonation states of potential Bohr groups. Interestingly, a water molecule that is in the vicinity of the heme group and coordinated to the distal histidine appears to be expelled from thismore » site in the low-temperature structure.« less

Challenges in quantitative crystallographic characterization of 3D thin films by ACOM-TEM.

PubMed

Kobler, A; Kübel, C

2017-02-01

Automated crystal orientation mapping for transmission electron microscopy (ACOM-TEM) has become an easy to use method for the investigation of crystalline materials and complements other TEM methods by adding local crystallographic information over large areas. It fills the gap between high resolution electron microscopy and electron back scatter diffraction in terms of spatial resolution. Recent investigations showed that spot diffraction ACOM-TEM is a quantitative method with respect to sample parameters like grain size, twin density, orientation density and others. It can even be used in combination with in-situ tensile or thermal testing. However, there are limitations of the current method. In this paper we discuss some of the challenges and discuss solutions, e.g. we present an ambiguity filter that reduces the number of pixels with a '180° ambiguity problem'. For that an ACOM-TEM tilt series of nanocrystalline Pd thin films with overlapping crystallites was acquired and analyzed. Copyright © 2017. Published by Elsevier B.V.

Anharmonic Thermal Oscillations of the Electron Momentum Distribution in Lithium Fluoride

NASA Astrophysics Data System (ADS)

Erba, A.; Maul, J.; Itou, M.; Dovesi, R.; Sakurai, Y.

2015-09-01

Anharmonic thermal effects on the electron momentum distribution of a lithium fluoride single crystal are experimentally measured through high-resolution Compton scattering and theoretically modeled with ab initio simulations, beyond the harmonic approximation to the lattice potential, explicitly accounting for thermal expansion. Directional Compton profiles are measured at two different temperatures, 10 and 300 K, with a high momentum space resolution (0.10 a.u. in full width at half maximum), using synchrotron radiation. The effect of temperature on measured directional Compton profiles is clearly revealed by oscillations extending almost up to |p |=4 a .u . , which perfectly match those predicted from quantum-mechanical simulations. The wave-function-based Hartree-Fock method and three classes of the Kohn-Sham density functional theory (local-density, generalized-gradient, and hybrid approximations) are adopted. The lattice thermal expansion, as described with the quasiharmonic approach, is found to entirely account for the effect of temperature on the electron momentum density within the experimental accuracy.

Quantitative Imaging of Single Unstained Magnetotactic Bacteria by Coherent X-ray Diffraction Microscopy.

PubMed

Fan, Jiadong; Sun, Zhibin; Zhang, Jian; Huang, Qingjie; Yao, Shengkun; Zong, Yunbing; Kohmura, Yoshiki; Ishikawa, Tetsuya; Liu, Hong; Jiang, Huaidong

2015-06-16

Novel coherent diffraction microscopy provides a powerful lensless imaging method to obtain a better understanding of the microorganism at the nanoscale. Here we demonstrated quantitative imaging of intact unstained magnetotactic bacteria using coherent X-ray diffraction microscopy combined with an iterative phase retrieval algorithm. Although the signal-to-noise ratio of the X-ray diffraction pattern from single magnetotactic bacterium is weak due to low-scattering ability of biomaterials, an 18.6 nm half-period resolution of reconstructed image was achieved by using a hybrid input-output phase retrieval algorithm. On the basis of the quantitative reconstructed images, the morphology and some intracellular structures, such as nucleoid, polyβ-hydroxybutyrate granules, and magnetosomes, were identified, which were also confirmed by scanning electron microscopy and energy dispersive spectroscopy. With the benefit from the quantifiability of coherent diffraction imaging, for the first time to our knowledge, an average density of magnetotactic bacteria was calculated to be ∼1.19 g/cm(3). This technique has a wide range of applications, especially in quantitative imaging of low-scattering biomaterials and multicomponent materials at nanoscale resolution. Combined with the cryogenic technique or X-ray free electron lasers, the method could image cells in a hydrated condition, which helps to maintain their natural structure.

Atomic resolution chemical bond analysis of oxygen in La2CuO4

NASA Astrophysics Data System (ADS)

Haruta, M.; Nagai, T.; Lugg, N. R.; Neish, M. J.; Nagao, M.; Kurashima, K.; Allen, L. J.; Mizoguchi, T.; Kimoto, K.

2013-08-01

The distorted CuO6 octahedron in La2CuO4 was studied using aberration-corrected scanning transmission electron microscopy at atomic resolution. The near-edge structure in the oxygen K-edge electron energy-loss spectrum was recorded as a function of the position of the electron probe. After background subtraction, the measured spectrum image was processed using a recently developed inversion process to remove the mixing of signals on the atomic columns due to elastic and thermal scattering. The spectra were then compared with first-principles band structure calculations based on the local-density approximation plus on-site Coulomb repulsion (LDA + U) approach. In this article, we describe in detail not only anisotropic chemical bonding of the oxygen 2p state with the Cu 3d state but also with the Cu 4p and La 5d/4f states. Furthermore, it was found that buckling of the CuO2 plane was also detectable at the atomic resolution oxygen K-edge. Lastly, it was found that the effects of core-hole in the O K-edge were strongly dependent on the nature of the local chemical bonding, in particular, whether it is ionic or covalent.

Exploring transmission Kikuchi diffraction using a Timepix detector

NASA Astrophysics Data System (ADS)

Vespucci, S.; Winkelmann, A.; Mingard, K.; Maneuski, D.; O'Shea, V.; Trager-Cowan, C.

2017-02-01

Electron backscatter diffraction (EBSD) is a well-established scanning electron microscope (SEM)-based technique [1]. It allows the non-destructive mapping of the crystal structure, texture, crystal phase and strain with a spatial resolution of tens of nanometers. Conventionally this is performed by placing an electron sensitive screen, typically consisting of a phosphor screen combined with a charge coupled device (CCD) camera, in front of a specimen, usually tilted 70° to the normal of the exciting electron beam. Recently, a number of authors have shown that a significant increase in spatial resolution is achievable when Kikuchi diffraction patterns are acquired in transmission geometry; that is when diffraction patterns are generated by electrons transmitted through an electron-transparent, usually thinned, specimen. The resolution of this technique, called transmission Kikuchi diffraction (TKD), has been demonstrated to be better than 10 nm [2,3]. We have recently demonstrated the advantages of a direct electron detector, Timepix [4,5], for the acquisition of standard EBSD patterns [5]. In this article we will discuss the advantages of Timepix to perform TKD and for acquiring spot diffraction patterns and more generally for acquiring scanning transmission electron microscopy micrographs in the SEM. Particularly relevant for TKD, is its very compact size, which allows much more flexibility in the positioning of the detector in the SEM chamber. We will furthermore show recent results using Timepix as a virtual forward scatter detector, and will illustrate the information derivable on producing images through processing of data acquired from different areas of the detector. We will show results from samples ranging from gold nanoparticles to nitride semiconductor nanorods.

Absolute vibrational excitation cross sections for 1-18 eV electron scattering from condensed dimethyl phosphate (DMP)

NASA Astrophysics Data System (ADS)

Lemelin, V.; Bass, A. D.; Wagner, J. R.; Sanche, L.

2017-12-01

Absolute cross sections (CSs) for vibrational excitation by 1-18 eV electrons incident on condensed dimethyl phosphate (DMP) were measured with a high-resolution electron energy loss (EEL) spectrometer. Absolute CSs were extracted from EEL spectra of DMP condensed on multilayer film of Ar held at about 20 K under ultra-high vacuum (˜1 × 10-11 Torr). Structures observed in the energy dependence of the CSs around 2, 4, 7, and 12 eV were compared with previous results of gas- and solid-phase experiments and with theoretical studies on dimethyl phosphate and related molecules. These structures were attributed to the formation of shape resonances.

Electron scattering by molecules. II - Experimental methods and data

NASA Technical Reports Server (NTRS)

Trajmar, S.; Chutjian, A.; Register, D. F.

1983-01-01

Experimental techniques for measuring electron-molecule collision cross sections are briefly summarized. A survey of the available experimental cross section data is presented. The emphasis here is on elastic scattering, rotational, vibrational and electronic excitations, total electron scattering, and momentum transfer in the few eV to few hundred eV impact energy range. Reference is made to works concerned with high energy electron scattering, innershell and multi-electron excitations, conicidence methods and electron scattering in laser fields.

Absorption-enhanced imaging through scattering media using carbon black nano-particles: from visible to near infrared wavelengths

NASA Astrophysics Data System (ADS)

Tanzid, Mehbuba; Hogan, Nathaniel J.; Robatjazi, Hossein; Veeraraghavan, Ashok; Halas, Naomi J.

2018-05-01

Imaging through scattering media can be improved with the addition of absorbers, since multiply-scattered photons, with their longer path length, are absorbed with a higher probability than ballistic photons. The image resolution enhancement is substantially greater when imaging through isotropic scatterers than when imaging through an ensemble of strongly forward-scattering particles. However, since the angular scattering distribution is determined by the size of the scatterers with respect to the wavelength of incident light, particles that are forward scatterers at visible wavelengths can be isotropic scatterers at infrared (IR) wavelengths. Here, we show that substantial image resolution enhancement can be achieved in the near-infrared wavelength regime for particles that are forward scattering at visible wavelengths using carbon black nanoparticles as a broadband absorber. This observation provides a new strategy for image enhancement through scattering media: by selecting the appropriate wavelength range for imaging, in this case the near-IR, the addition of absorbers more effectively enhances the image resolution.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, Brian B.; Kirkegaard, Marie C.; Miskowiec, Andrew J.

Uranyl fluoride (UO 2F 2) is a hygroscopic powder with two main structural phases: an anhydrous crystal and a partially hydrated crystal of the same R¯3m symmetry. The formally closed-shell electron structure of anhydrous UO 2F 2 is amenable to density functional theory calculations. We use density functional perturbation theory (DFPT) to calculate the vibrational frequencies of the anhydrous crystal structure and employ complementary inelastic neutron scattering and temperature-dependent Raman scattering to validate those frequencies. As a model closed-shell actinide, we investigated the effect of LDA, GGA, and non-local vdW functionals as well as the spherically-averaged Hubbard +U correction onmore » vibrational frequencies, electronic structure, and geometry of anhydrous UO 2F 2. A particular choice of U eff = 5.5 eV yields the correct U Oyl bond distance and vibrational frequencies for the characteristic Eg and A1g modes that are within the resolution of experiment. Inelastic neutron scattering and Raman scattering suggest a degree of water coupling to the lattice vibrations in the more experimentally accessible partially hydrated UO 2F 2 system, with the symmetric O-U-O stretching vibration shifted approximately 47 cm -1 lower in energy compared to the anhydrous structure. Evidence of water interaction with the uranyl ion is present from a two-peak decomposition of the uranyl stretching vibration in the Raman spectra and anion hydrogen stretching vibrations in the inelastic neutron scattering spectra. A first-order dehydration phase transition temperature is definitively identified to be 125 °C using temperature-dependent Raman scattering.« less

Vibrational Properties of Anhydrous and Partially Hydrated Uranyl Fluoride

DOE PAGES

Anderson, Brian B.; Kirkegaard, Marie C.; Miskowiec, Andrew J.; ...

2017-01-01

Uranyl fluoride (UO 2F 2) is a hygroscopic powder with two main structural phases: an anhydrous crystal and a partially hydrated crystal of the same R¯3m symmetry. The formally closed-shell electron structure of anhydrous UO 2F 2 is amenable to density functional theory calculations. We use density functional perturbation theory (DFPT) to calculate the vibrational frequencies of the anhydrous crystal structure and employ complementary inelastic neutron scattering and temperature-dependent Raman scattering to validate those frequencies. As a model closed-shell actinide, we investigated the effect of LDA, GGA, and non-local vdW functionals as well as the spherically-averaged Hubbard +U correction onmore » vibrational frequencies, electronic structure, and geometry of anhydrous UO 2F 2. A particular choice of U eff = 5.5 eV yields the correct U Oyl bond distance and vibrational frequencies for the characteristic Eg and A1g modes that are within the resolution of experiment. Inelastic neutron scattering and Raman scattering suggest a degree of water coupling to the lattice vibrations in the more experimentally accessible partially hydrated UO 2F 2 system, with the symmetric O-U-O stretching vibration shifted approximately 47 cm -1 lower in energy compared to the anhydrous structure. Evidence of water interaction with the uranyl ion is present from a two-peak decomposition of the uranyl stretching vibration in the Raman spectra and anion hydrogen stretching vibrations in the inelastic neutron scattering spectra. A first-order dehydration phase transition temperature is definitively identified to be 125 °C using temperature-dependent Raman scattering.« less

Resonant inelastic x-ray scattering and photoemission measurement of O2: Direct evidence for dependence of Rydberg-valence mixing on vibrational states in O 1s → Rydberg states

NASA Astrophysics Data System (ADS)

Gejo, T.; Oura, M.; Tokushima, T.; Horikawa, Y.; Arai, H.; Shin, S.; Kimberg, V.; Kosugi, N.

2017-07-01

High-resolution resonant inelastic x-ray scattering (RIXS) and low-energy photoemission spectra of oxygen molecules have been measured for investigating the electronic structure of Rydberg states in the O 1s → σ* energy region. The electronic characteristics of each Rydberg state have been successfully observed, and new assignments are made for several states. The RIXS spectra clearly show that vibrational excitation is very sensitive to the electronic characteristics because of Rydberg-valence mixing and vibronic coupling in O2. This observation constitutes direct experimental evidence that the Rydberg-valence mixing characteristic depends on the vibrational excitation near the avoided crossing of potential surfaces. We also measured the photoemission spectra of metastable oxygen atoms (O*) from O2 excited to 1s → Rydberg states. The broadening of the 4p Rydberg states of O* has been found with isotropic behavior, implying that excited oxygen molecules undergo dissociation with a lifetime of the order of 10 fs in 1s → Rydberg states.

Low Energy Positron Scattering, Transport, and Applications

NASA Astrophysics Data System (ADS)

Buckman, Stephen

2017-04-01

Relatively intense, high energy-resolution beams of low-energy positrons are now available through the use of buffer-gas (Surko) traps. These have led to measurements of interaction cross sections for a broad range of atoms and molecules, including molecules of biological interest. The increased energy resolution, and experimental techniques developed for scattering in strong magnetic fields has also enabled highly accurate measurements of discrete excitation processes such as electronic and vibrational excitation, positronium formation and ionization in a range of atomic and molecular species. This talk will review some of these measurements and discuss their application in new and sophisticated models of positron transport which aim, for example, to provide a better understanding of the atomic and molecular processes which occur when positrons are emitted in the body during a Positron Emission Tomography scan. This work is part of a broad collaboration between the ANU (James Sullivan, Joshua Machacek), Flinders University (Michael Brunger), James Cook University (Ronald White and co-workers) CSIC Madrid (Gustavo Garcia) and the Institute of Physics, Belgrade (Zoran Petrovic and colleagues).

Theory and Application of Auger and Photoelectron Diffraction and Holography

NASA Astrophysics Data System (ADS)

Chen, Xiang

This dissertation addresses the theories and applications of three important surface analysis techniques: Auger electron diffraction (AED), x-ray photoelectron diffraction (XPD), and Auger and photoelectron holography. A full multiple-scattering scheme for the calculations of XPD, AED, and Kikuchi electron diffraction pattern from a surface cluster is described. It is used to simulate 64 eV M_{2,3}VV and 913 eV L_3VV AED patterns from Cu(001) surfaces, in order to test assertions in the literature that they are explicable by a classical "blocking" and channeling model. We find that this contention is not valid, and that only a quantum mechanical multiple-scattering calculation is able to simulate these patterns well. The same multiple scattering simulation scheme is also used to investigate the anomalous phenomena of peak shifts off the forward-scattering directions in photo -electron diffraction patterns of Mg KLL (1180 eV) and O 1s (955 eV) from MgO(001) surfaces. These shifts are explained by calculations assuming a short electron mean free path. Similar simulations of XPD from a CoSi_2(111) surface for Co-3p and Si-2p normal emission agree well with experimental diffraction patterns. A filtering process aimed at eliminating the self -interference effect in photoelectron holography is developed. A better reconstructed image from Si-2p XPD from a Si(001) (2 times 1) surface is seen at atomic resolution. A reconstruction algorithm which corrects for the anisotropic emitter waves as well as the anisotropic atomic scattering factors is used for holographic reconstruction from a Co-3p XPD pattern from a CoSi_2 surface. This new algorithm considerably improves the reconstructed image. Finally, a new reconstruction algorithm called "atomic position recovery by iterative optimization of reconstructed intensities" (APRIORI), which takes account of the self-interference terms omitted by the other holographic algorithms, is developed. Tests on a Ni-C-O chain and Si(111)(sqrt{3} times sqrt{3})B surface suggest that this new method may overcome the twin image problem in the traditional holographic methods, reduce the artifacts in real space, and even separately identify the chemical species of the scatterers.

Electron tomography of HEK293T cells using scanning electron microscope-based scanning transmission electron microscopy.

PubMed

You, Yun-Wen; Chang, Hsun-Yun; Liao, Hua-Yang; Kao, Wei-Lun; Yen, Guo-Ji; Chang, Chi-Jen; Tsai, Meng-Hung; Shyue, Jing-Jong

2012-10-01

Based on a scanning electron microscope operated at 30 kV with a homemade specimen holder and a multiangle solid-state detector behind the sample, low-kV scanning transmission electron microscopy (STEM) is presented with subsequent electron tomography for three-dimensional (3D) volume structure. Because of the low acceleration voltage, the stronger electron-atom scattering leads to a stronger contrast in the resulting image than standard TEM, especially for light elements. Furthermore, the low-kV STEM yields less radiation damage to the specimen, hence the structure can be preserved. In this work, two-dimensional STEM images of a 1-μm-thick cell section with projection angles between ±50° were collected, and the 3D volume structure was reconstructed using the simultaneous iterative reconstructive technique algorithm with the TomoJ plugin for ImageJ, which are both public domain software. Furthermore, the cross-sectional structure was obtained with the Volume Viewer plugin in ImageJ. Although the tilting angle is constrained and limits the resulting structural resolution, slicing the reconstructed volume generated the depth profile of the thick specimen with sufficient resolution to examine cellular uptake of Au nanoparticles, and the final position of these nanoparticles inside the cell was imaged.

Imaging ultrafast dynamics of molecules with laser-induced electron diffraction.

PubMed

Lin, C D; Xu, Junliang

2012-10-14

We introduce a laser-induced electron diffraction method (LIED) for imaging ultrafast dynamics of small molecules with femtosecond mid-infrared lasers. When molecules are placed in an intense laser field, both low- and high-energy photoelectrons are generated. According to quantitative rescattering (QRS) theory, high-energy electrons are produced by a rescattering process where electrons born at the early phase of the laser pulse are driven back to rescatter with the parent ion. From the high-energy electron momentum spectra, field-free elastic electron-ion scattering differential cross sections (DCS), or diffraction images, can be extracted. With mid-infrared lasers as the driving pulses, it is further shown that the DCS can be used to extract atomic positions in a molecule with sub-angstrom spatial resolution, in close analogy to the standard electron diffraction method. Since infrared lasers with pulse duration of a few to several tens of femtoseconds are already available, LIED can be used for imaging dynamics of molecules with sub-angstrom spatial and a few-femtosecond temporal resolution. The first experiment with LIED has shown that the bond length of oxygen molecules shortens by 0.1 Å in five femtoseconds after single ionization. The principle behind LIED and its future outlook as a tool for dynamic imaging of molecules are presented.

Cluster/Peace Electrons Velocity Distribution Function: Modeling the Strahl in the Solar Wind

NASA Technical Reports Server (NTRS)

Figueroa-Vinas, Adolfo; Gurgiolo, Chris; Goldstein, Melvyn L.

2008-01-01

We present a study of kinetic properties of the strahl electron velocity distribution functions (VDF's) in the solar wind. These are used to investigate the pitch-angle scattering and stability of the population to interactions with electromagnetic (whistler) fluctuations. The study is based on high time resolution data from the Cluster/PEACE electron spectrometer. Our study focuses on the mechanisms that control and regulate the pitch-angle and stability of strahl electrons in the solar wind; mechanisms that are not yet well understood. Various parameters are investigated such as the electron heat-flux and temperature anisotropy. The goal is to check whether the strahl electrons are constrained by some instability (e.g., the whistler instability), or are maintained by other types of processes. The electron heat-flux and temperature anisotropy are determined by fitting the VDF's to a spectral spherical harmonic model from which the moments are derived directly from the model coefficients.

Profiling of back-scattered electrons in opposed magnetic field of a Twin Electron Beam Gun

NASA Astrophysics Data System (ADS)

Sethi, S.; Gupta, Anchal; Dileep Kumar, V.; Mukherjee, Jaya; Gantayet, L. M.

2012-11-01

Electron gun is extensively used in material processing, physical vapour deposition and atomic vapour based laser processes. In these processes where the electron beam is incident on the substrate, a significant fraction of electron beam gets back-scattered from the target surface. The trajectory of this back scattered electron beam depends on the magnetic field in the vicinity. The fraction of back-scattered depends on the atomic number of the target metal and can be as high as ~40% of the incident beam current. These back-scattered electrons can cause undesired hot spots and also affect the overall process. Hence, the study of the trajectory of these back-scattered electrons is important. This paper provides the details of experimentally mapped back-scattered electrons of a 2×20kW Twin Electron Beam Gun (TEBG) in opposed magnetic field i.e. with these guns placed at 180° to each other.

Atomic scale structure and chemistry of interfaces by Z-contrast imaging and electron energy loss spectroscopy in the stem

DOE Office of Scientific and Technical Information (OSTI.GOV)

McGibbon, M.M.; Browning, N.D.; Chisholm, M.F.

The macroscopic properties of many materials are controlled by the structure and chemistry at grain boundaries. A basic understanding of the structure-property relationship requires a technique which probes both composition and chemical bonding on an atomic scale. High-resolution Z-contrast imaging in the scanning transmission electron microscope (STEM) forms an incoherent image in which changes in atomic structure and composition across an interface can be interpreted directly without the need for preconceived atomic structure models. Since the Z-contrast image is formed by electrons scattered through high angles, parallel detection electron energy loss spectroscopy (PEELS) can be used simultaneously to provide complementarymore » chemical information on an atomic scale. The fine structure in the PEEL spectra can be used to investigate the local electronic structure and the nature of the bonding across the interface. In this paper we use the complimentary techniques of high resolution Z-contrast imaging and PEELS to investigate the atomic structure and chemistry of a 25{degree} symmetric tilt boundary in a bicrystal of the electroceramic SrTiO{sub 3}.« less

Inelastic Tunneling Spectroscopy of Alkanethiol Molecules: High-Resolution Spectroscopy and Theoretical Simulations

NASA Astrophysics Data System (ADS)

Okabayashi, Norio; Paulsson, Magnus; Ueba, Hiromu; Konda, Youhei; Komeda, Tadahiro

2010-02-01

We investigate inelastic electron tunneling spectroscopy (IETS) for alkanethiol self-assembled monolayers (SAM) with a scanning tunneling microscope and compare it to first-principles calculations. Using a combination of partial deuteration of the molecule and high-resolution measurements, we identify and differentiate between methyl (CH3) and methylene (CH2) groups and their symmetric and asymmetric C-H stretch modes. The calculations agree quantitatively with the measured IETS in producing the weight of the symmetric and asymmetric C-H stretch modes while the methylene stretch mode is largely underestimated. We further show that inelastic intermolecular scattering is important in the SAM by plotting the theoretical current densities.

Serial femtosecond X-ray diffraction of enveloped virus microcrystals

DOE PAGES

Lawrence, Robert M.; Conrad, Chelsie E.; Zatsepin, Nadia A.; ...

2015-08-20

Serial femtosecond crystallography (SFX) using X-ray free-electron lasers has produced high-resolution, room temperature, time-resolved protein structures. We report preliminary SFX of Sindbis virus, an enveloped icosahedral RNA virus with ~700 Å diameter. Microcrystals delivered in viscous agarose medium diffracted to ~40 Å resolution. Small-angle diffuse X-ray scattering overlaid Bragg peaks and analysis suggests this results from molecular transforms of individual particles. Viral proteins undergo structural changes during entry and infection, which could, in principle, be studied with SFX. This is a pertinent step toward determining room temperature structures from virus microcrystals that may enable time-resolved studies of enveloped viruses.

Space-resolved measurements of neutrons and ions emitted by a plasma focus

NASA Astrophysics Data System (ADS)

Jaeger, U.

1980-05-01

Space-resolved measurements of neutrons and of accelerated charged particles emitted by a plasma focus device are presented. The neutron source was measured with one and two dimensional paraffin collimators. The spatial resolution is 5 mn along the axis and the radius, with a time resolution of 10 ns. In order to make quantitative statements about the neutron yield, neutron scattering, absorption, and nuclear reactions were taken into account. Part of the neutron measurement was carried out together with time and space resolved measurements of the electron density to study possible correlations between n sub e and y sub n.

In situ data collection and structure refinement from microcapillary protein crystallization

PubMed Central

Yadav, Maneesh K.; Gerdts, Cory J.; Sanishvili, Ruslan; Smith, Ward W.; Roach, L. Spencer; Ismagilov, Rustem F.; Kuhn, Peter; Stevens, Raymond C.

2007-01-01

In situ X-ray data collection has the potential to eliminate the challenging task of mounting and cryocooling often fragile protein crystals, reducing a major bottleneck in the structure determination process. An apparatus used to grow protein crystals in capillaries and to compare the background X-ray scattering of the components, including thin-walled glass capillaries against Teflon, and various fluorocarbon oils against each other, is described. Using thaumatin as a test case at 1.8 Å resolution, this study demonstrates that high-resolution electron density maps and refined models can be obtained from in situ diffraction of crystals grown in microcapillaries. PMID:17468785

Muon energy estimate through multiple scattering with the MACRO detector

NASA Astrophysics Data System (ADS)

Ambrosio, M.; Antolini, R.; Auriemma, G.; Bakari, D.; Baldini, A.; Barbarino, G. C.; Barish, B. C.; Battistoni, G.; Becherini, Y.; Bellotti, R.; Bemporad, C.; Bernardini, P.; Bilokon, H.; Bloise, C.; Bower, C.; Brigida, M.; Bussino, S.; Cafagna, F.; Calicchio, M.; Campana, D.; Candela, A.; Carboni, M.; Caruso, R.; Cassese, F.; Cecchini, S.; Cei, F.; Chiarella, V.; Choudhary, B. C.; Coutu, S.; Cozzi, M.; de Cataldo, G.; de Deo, M.; Dekhissi, H.; de Marzo, C.; de Mitri, I.; Derkaoui, J.; de Vincenzi, M.; di Credico, A.; Dincecco, M.; Erriquez, O.; Favuzzi, C.; Forti, C.; Fusco, P.; Giacomelli, G.; Giannini, G.; Giglietto, N.; Giorgini, M.; Grassi, M.; Gray, L.; Grillo, A.; Guarino, F.; Gustavino, C.; Habig, A.; Hanson, K.; Heinz, R.; Iarocci, E.; Katsavounidis, E.; Katsavounidis, I.; Kearns, E.; Kim, H.; Kyriazopoulou, S.; Lamanna, E.; Lane, C.; Levin, D. S.; Lindozzi, M.; Lipari, P.; Longley, N. P.; Longo, M. J.; Loparco, F.; Maaroufi, F.; Mancarella, G.; Mandrioli, G.; Margiotta, A.; Marini, A.; Martello, D.; Marzari-Chiesa, A.; Mazziotta, M. N.; Michael, D. G.; Monacelli, P.; Montaruli, T.; Monteno, M.; Mufson, S.; Musser, J.; Nicolo, D.; Nolty, R.; Orth, C.; Osteria, G.; Palamara, O.; Patera, V.; Patrizii, L.; Pazzi, R.; Peck, C. W.; Perrone, L.; Petrera, S.; Pistilli, P.; Popa, V.; Raino, A.; Reynoldson, J.; Ronga, F.; Rrhioua, A.; Satriano, C.; Scapparone, E.; Scholberg, K.; Sciubba, A.; Serra, P.; Sioli, M.; Sirri, G.; Sitta, M.; Spinelli, P.; Spinetti, M.; Spurio, M.; Steinberg, R.; Stone, J. L.; Sulak, L. R.; Surdo, A.; Tarle, G.; Tatananni, E.; Togo, V.; Vakili, M.; Walter, C. W.; Webb, R.; MACRO Collaboration

2002-10-01

Muon energy measurement represents an important issue for any experiment addressing neutrino-induced up-going muon studies. Since the neutrino oscillation probability depends on the neutrino energy, a measurement of the muon energy adds an important piece of information concerning the neutrino system. We show in this paper how the MACRO limited streamer tube system can be operated in drift mode by using the TDCs included in the QTPs, an electronics designed for magnetic monopole search. An improvement of the space resolution is obtained, through an analysis of the multiple scattering of muon tracks as they pass through our detector. This information can be used further to obtain an estimate of the energy of muons crossing the detector. Here we present the results of two dedicated tests, performed at CERN PS-T9 and SPS-X7 beam lines, to provide a full check of the electronics and to exploit the feasibility of such a multiple scattering analysis. We show that by using a neural network approach, we are able to reconstruct the muon energy for E μ<40 GeV. The test beam data provide an absolute energy calibration, which allows us to apply this method to MACRO data.

Visualizing redox orbitals and their potentials in advanced lithium-ion battery materials using high-resolution x-ray Compton scattering

PubMed Central

Hafiz, Hasnain; Suzuki, Kosuke; Barbiellini, Bernardo; Orikasa, Yuki; Callewaert, Vincent; Kaprzyk, Staszek; Itou, Masayoshi; Yamamoto, Kentaro; Yamada, Ryota; Uchimoto, Yoshiharu; Sakurai, Yoshiharu; Sakurai, Hiroshi; Bansil, Arun

2017-01-01

Reduction-oxidation (redox) reactions are the key processes that underlie the batteries powering smartphones, laptops, and electric cars. A redox process involves transfer of electrons between two species. For example, in a lithium-ion battery, current is generated when conduction electrons from the lithium anode are transferred to the redox orbitals of the cathode material. The ability to visualize or image the redox orbitals and how these orbitals evolve under lithiation and delithiation processes is thus of great fundamental and practical interest for understanding the workings of battery materials. We show that inelastic scattering spectroscopy using high-energy x-ray photons (Compton scattering) can yield faithful momentum space images of the redox orbitals by considering lithium iron phosphate (LiFePO4 or LFP) as an exemplar cathode battery material. Our analysis reveals a new link between voltage and the localization of transition metal 3d orbitals and provides insight into the puzzling mechanism of potential shift and how it is connected to the modification of the bond between the transition metal and oxygen atoms. Our study thus opens a novel spectroscopic pathway for improving the performance of battery materials. PMID:28845452

Visualizing redox orbitals and their potentials in advanced lithium-ion battery materials using high-resolution x-ray Compton scattering.

PubMed

Hafiz, Hasnain; Suzuki, Kosuke; Barbiellini, Bernardo; Orikasa, Yuki; Callewaert, Vincent; Kaprzyk, Staszek; Itou, Masayoshi; Yamamoto, Kentaro; Yamada, Ryota; Uchimoto, Yoshiharu; Sakurai, Yoshiharu; Sakurai, Hiroshi; Bansil, Arun

2017-08-01

Reduction-oxidation (redox) reactions are the key processes that underlie the batteries powering smartphones, laptops, and electric cars. A redox process involves transfer of electrons between two species. For example, in a lithium-ion battery, current is generated when conduction electrons from the lithium anode are transferred to the redox orbitals of the cathode material. The ability to visualize or image the redox orbitals and how these orbitals evolve under lithiation and delithiation processes is thus of great fundamental and practical interest for understanding the workings of battery materials. We show that inelastic scattering spectroscopy using high-energy x-ray photons (Compton scattering) can yield faithful momentum space images of the redox orbitals by considering lithium iron phosphate (LiFePO 4 or LFP) as an exemplar cathode battery material. Our analysis reveals a new link between voltage and the localization of transition metal 3d orbitals and provides insight into the puzzling mechanism of potential shift and how it is connected to the modification of the bond between the transition metal and oxygen atoms. Our study thus opens a novel spectroscopic pathway for improving the performance of battery materials.

Comparative analysis of characteristic electron energy loss spectra and inelastic scattering cross-section spectra of Fe

NASA Astrophysics Data System (ADS)

Parshin, A. S.; Igumenov, A. Yu.; Mikhlin, Yu. L.; Pchelyakov, O. P.; Zhigalov, V. S.

2016-05-01

The inelastic electron scattering cross section spectra of Fe have been calculated based on experimental spectra of characteristic reflection electron energy loss as dependences of the product of the inelastic mean free path by the differential inelastic electron scattering cross section on the electron energy loss. It has been shown that the inelastic electron scattering cross-section spectra have certain advantages over the electron energy loss spectra in the analysis of the interaction of electrons with substance. The peaks of energy loss in the spectra of characteristic electron energy loss and inelastic electron scattering cross sections have been determined from the integral and differential spectra. It has been shown that the energy of the bulk plasmon is practically independent of the energy of primary electrons in the characteristic electron energy loss spectra and monotonically increases with increasing energy of primary electrons in the inelastic electron scattering cross-section spectra. The variation in the maximum energy of the inelastic electron scattering cross-section spectra is caused by the redistribution of intensities over the peaks of losses due to various excitations. The inelastic electron scattering cross-section spectra have been analyzed using the decomposition of the spectra into peaks of the energy loss. This method has been used for the quantitative estimation of the contributions from different energy loss processes to the inelastic electron scattering cross-section spectra of Fe and for the determination of the nature of the energy loss peaks.

Analysis of improvement in performance and design parameters for enhancing resolution in an atmospheric scanning electron microscope.

PubMed

Yoon, Yeo Hun; Kim, Seung Jae; Kim, Dong Hwan

2015-12-01

The scanning electron microscope is used in various fields to go beyond diffraction limits of the optical microscope. However, the electron pathway should be conducted in a vacuum so as not to scatter electrons. The pretreatment of the sample is needed for use in the vacuum. To directly observe large and fully hydrophilic samples without pretreatment, the atmospheric scanning electron microscope (ASEM) is needed. We developed an electron filter unit and an electron detector unit for implementation of the ASEM. The key of the electron filter unit is that electrons are transmitted while air molecules remain untransmitted through the unit. The electron detector unit collected the backscattered electrons. We conducted experiments using the selected materials with Havar foil, carbon film and SiN film. © The Author 2015. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Electron-molecule scattering in a strong laser field: Two-center interference effects

NASA Astrophysics Data System (ADS)

Dakić, J.; Habibović, D.; Čerkić, A.; Busuladžić, M.; Milošević, D. B.

2017-10-01

Laser-assisted scattering of electrons on diatomic molecules is considered using the S -matrix theory within the second Born approximation. The first term of the expansion in powers of the scattering potential corresponds to the direct or single laser-assisted scattering of electrons on molecular targets, while the second term of this expansion corresponds to the laser-assisted rescattering or double scattering. The rescattered electrons may have considerably higher energies in the final state than those that scattered only once. For multicenter polyatomic molecules scattering and rescattering may happen at any center and in any order. All these cases contribute to the scattering amplitude and the interference of different contributions leads to an increase or a decrease of the differential cross section in particular electron energy regions. For diatomic molecules there are two such contributions for single scattering and four contributions for double scattering. Analyzing the spectra of the scattered electrons, we find two interesting effects. For certain molecular orientations, the plateaus in the electron energy spectrum, characteristic of laser-assisted electron-atom scattering, are replaced by a sequence of gradually declining maxima, caused by the two-center interference effects. The second effect is the appearance of symmetric U -shaped structures in the angle-resolved energy spectra, which are described very well by the analytical formulas we provide.

Non-resonant inelastic x-ray scattering spectra of lithiated titanium oxides for battery applications

NASA Astrophysics Data System (ADS)

Nagle, Kenneth; Balasubramanian, Mali; Johnson, Christopher; Seidler, Gerald; Belharouak, Ilias

2008-03-01

Although lithium-ion batteries now see widespread use, there remain considerable questions concerning the basic solid state chemistry of both electrodes. Improved understanding of the local electronic structure, particularly the mechanism of charge transfer upon insertion and removal of lithium, could lead to innovation in battery design and improved performance. We present non-resonant inelastic x-ray scattering (NRIXS) spectra from 2p initial states in titanium; these spectra are among the first recorded for such states in a transition metal. These spectra were obtained using the lower energy resolution inelastic x-ray scattering (LERIX) spectrometer, which is capable of making simultaneous measurements at nineteen values of momentum transfer. We demonstrate the ability to obtain soft x-ray absorption-like information using a bulk-sensitive, hard x-ray technique. In addition, at high momentum transfer NRIXS provides information about non-dipole transitions that are inaccessible by soft x-ray spectroscopic methods.

Dynamic Positron Emission Tomography [PET] in Man Using Small Bismuth Germanate Crystals

DOE R&D Accomplishments Database

Derenzo, S. E.; Budinger, T. F.; Huesman, R. H.; Cahoon, J. L.

1982-04-01

Primary considerations for the design of positron emission tomographs for medical studies in humans are the need for high imaging sensitivity, whole organ coverage, good spatial resolution, high maximum data rates, adequate spatial sampling with minimum mechanical motion, shielding against out of plane activity, pulse height discrimination against scattered photons, and timing discrimination against accidental coincidences. We discuss the choice of detectors, sampling motion, shielding, and electronics to meet these objectives.

Phonon spectrum of single-crystalline FeSe probed by high-resolution electron energy-loss spectroscopy

NASA Astrophysics Data System (ADS)

Zakeri, Khalil; Engelhardt, Tobias; Le Tacon, Matthieu; Wolf, Thomas

2018-06-01

Utilizing high-resolution electron energy-loss spectroscopy (HREELS) we measure the phonon frequencies of β-FeSe(001), cleaved under ultra-high vacuum conditions. At the zone center (Γ bar-point) three prominent loss features are observed at loss energies of about ≃ 20.5 and 25.6 and 40 meV. Based on the scattering selection rules we assign the observed loss features to the A1g, B1g, and A2u phonon modes of β-FeSe(001). The experimentally measured phonon frequencies do not agree with the results of density functional based calculations in which a nonmagnetic, a checkerboard or a strip antiferromagnetic order is assumed for β-FeSe(001). Our measurements suggest that, similar to the other Fe-based materials, magnetism has a profound impact on the lattice dynamics of β-FeSe(001).

Crystallization and preliminary X-ray analysis of the inducible lysine decarboxylase from Escherichia coli

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alexopoulos, E.; Kanjee, U.; Snider, J.

2010-02-11

The decameric inducible lysine decarboxylase (LdcI) from Escherichia coli has been crystallized in space groups C2 and C222{sub 1}; the Ta{sub 6}Br{sub 12}{sup 2+} cluster was used to derivatize the C2 crystals. The method of single isomorphous replacement with anomalous scattering (SIRAS) as implemented in SHELXD was used to solve the Ta{sub 6}Br{sub 12}{sup 2+}-derivatized structure to 5 {angstrom} resolution. Many of the Ta{sub 6}Br{sub 12}{sup 2+}-binding sites had twofold and fivefold noncrystallographic symmetry. Taking advantage of this feature, phase modification was performed in DM. The electron-density map of LdcI displays many features in agreement with the low-resolution negative-stain electron-densitymore » map [Snider et al. (2006), J. Biol. Chem. 281, 1532-1546].« less

Poster — Thur Eve — 01: The effect of the number of projections on MTF and CNR in Compton scatter tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chighvinadze, T; Pistorius, S; CancerCare Manitoba, Winnipeg, MB

2014-08-15

Purpose: To investigate the dependence of the reconstructed image quality on the number of projections in multi-projection Compton scatter tomography (MPCST). The conventional relationship between the projection number used for reconstruction and reconstructed image quality pertained to CT does not necessarily apply to MPCST, which can produce images from a single projection if the detectors have sufficiently high energy and spatial resolution. Methods: The electron density image was obtained using filtered-backprojection of the scatter signal over circular arcs formed using Compton equation. The behavior of the reconstructed image quality as a function of the projection number was evaluated through analyticalmore » simulations and characterized by CNR and MTF. Results: The increase of the projection number improves the contrast with this dependence being a function of fluence. The number of projections required to approach the asymptotic maximum contrast decreases as the fluence increases. Increasing projection number increases the CNR but not spatial resolution. Conclusions: For MPCST using a 500eV energy resolution and a 2×2mm{sup 2} size detector, an adequate image quality can be obtained with a small number of projections provided the incident fluence is high enough. This is conceptually different from conventional CT where a minimum number of projections is required to obtain an adequate image quality. While increasing projection number, even for the lowest dose value, the CNR increases even though the number of photons per projection decreases. The spatial resolution of the image is improved by increasing the sampling within a projection rather than by increasing the number of projections.« less

Z-pinch Plasma Temperature and Implosion Velocity from Laboratory Plasma Jets using Thomson Scattering

NASA Astrophysics Data System (ADS)

Banasek, Jacob; Byvank, Tom; Kusse, Bruce; Hammer, David

2016-10-01

We discuss the use of collective Thomson scattering to determine the implosion velocity and other properties of laboratory plasma jets. The plasma jet is created using a 1 MA pulsed power machine with a 15 μm Al radial foil load. The Thomson scattering laser has a maximum energy of 10 J at 526.5 nm with a pulse duration of 3 ns. Using a time gated ICCD camera and spectrometer system we are able to record the scattered spectrum from 9 or 18 regions along the laser path with sub-mm spatial resolution. Collecting scattered radiation from the same area at two different angles simultaneously enables determination of both the radial and azimuthal velocities. The scattered spectrum for non-magnetized jets indicates a radial implosion velocity of 27 km/s into the jets. A determination of ion and electron temperatures from the scattered spectrum is in progress. Comparing results using a laser energy of 10 J and 1 J shows noticeable effects on plasma jet properties when using 10 J. Therefore the lower laser energy must be used to determine the plasma properties. This research is supported by the NNSA Stewardship Sciences Academic Programs under DOE Cooperative Agreement DE-NA0001836.

Large-scale atomistic calculations of clusters in intense x-ray pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ho, Phay J.; Knight, Chris

Here, we present the methodology of our recently developed Monte-Carlo/ Molecular-Dynamics method for studying the fundamental ultrafast dynamics induced by high-fluence, high-intensity x-ray free electron laser (XFEL) pulses in clusters. The quantum nature of the initiating ionization process is accounted for by a Monte Carlo method to calculate probabilities of electronic transitions, including photo absorption, inner-shell relaxation, photon scattering, electron collision and recombination dynamics, and thus track the transient electronic configurations explicitly. The freed electrons and ions are followed by classical particle trajectories using a molecular dynamics algorithm. These calculations reveal the surprising role of electron-ion recombination processes that leadmore » to the development of nonuniform spatial charge density profiles in x-ray excited clusters over femtosecond timescales. In the high-intensity limit, it is important to include the recombination dynamics in the calculated scattering response even for a 2- fs pulse. We also demonstrate that our numerical codes and algorithms can make e!cient use of the computational power of massively parallel supercomputers to investigate the intense-field dynamics in systems with increasing complexity and size at the ultrafast timescale and in non-linear x-ray interaction regimes. In particular, picosecond trajectories of XFEL clusters with attosecond time resolution containing millions of particles can be e!ciently computed on upwards of 262,144 processes.« less

Pulsating aurora from electron scattering by chorus waves

NASA Astrophysics Data System (ADS)

Kasahara, S.; Miyoshi, Y.; Yokota, S.; Mitani, T.; Kasahara, Y.; Matsuda, S.; Kumamoto, A.; Matsuoka, A.; Kazama, Y.; Frey, H. U.; Angelopoulos, V.; Kurita, S.; Keika, K.; Seki, K.; Shinohara, I.

2018-02-01

Auroral substorms, dynamic phenomena that occur in the upper atmosphere at night, are caused by global reconfiguration of the magnetosphere, which releases stored solar wind energy. These storms are characterized by auroral brightening from dusk to midnight, followed by violent motions of distinct auroral arcs that suddenly break up, and the subsequent emergence of diffuse, pulsating auroral patches at dawn. Pulsating aurorae, which are quasiperiodic, blinking patches of light tens to hundreds of kilometres across, appear at altitudes of about 100 kilometres in the high-latitude regions of both hemispheres, and multiple patches often cover the entire sky. This auroral pulsation, with periods of several to tens of seconds, is generated by the intermittent precipitation of energetic electrons (several to tens of kiloelectronvolts) arriving from the magnetosphere and colliding with the atoms and molecules of the upper atmosphere. A possible cause of this precipitation is the interaction between magnetospheric electrons and electromagnetic waves called whistler-mode chorus waves. However, no direct observational evidence of this interaction has been obtained so far. Here we report that energetic electrons are scattered by chorus waves, resulting in their precipitation. Our observations were made in March 2017 with a magnetospheric spacecraft equipped with a high-angular-resolution electron sensor and electromagnetic field instruments. The measured quasiperiodic precipitating electron flux was sufficiently intense to generate a pulsating aurora, which was indeed simultaneously observed by a ground auroral imager.

Large-scale atomistic calculations of clusters in intense x-ray pulses

DOE PAGES

Ho, Phay J.; Knight, Chris

2017-04-28

Here, we present the methodology of our recently developed Monte-Carlo/ Molecular-Dynamics method for studying the fundamental ultrafast dynamics induced by high-fluence, high-intensity x-ray free electron laser (XFEL) pulses in clusters. The quantum nature of the initiating ionization process is accounted for by a Monte Carlo method to calculate probabilities of electronic transitions, including photo absorption, inner-shell relaxation, photon scattering, electron collision and recombination dynamics, and thus track the transient electronic configurations explicitly. The freed electrons and ions are followed by classical particle trajectories using a molecular dynamics algorithm. These calculations reveal the surprising role of electron-ion recombination processes that leadmore » to the development of nonuniform spatial charge density profiles in x-ray excited clusters over femtosecond timescales. In the high-intensity limit, it is important to include the recombination dynamics in the calculated scattering response even for a 2- fs pulse. We also demonstrate that our numerical codes and algorithms can make e!cient use of the computational power of massively parallel supercomputers to investigate the intense-field dynamics in systems with increasing complexity and size at the ultrafast timescale and in non-linear x-ray interaction regimes. In particular, picosecond trajectories of XFEL clusters with attosecond time resolution containing millions of particles can be e!ciently computed on upwards of 262,144 processes.« less

The spatial coherence function in scanning transmission electron microscopy and spectroscopy.

PubMed

Nguyen, D T; Findlay, S D; Etheridge, J

2014-11-01

We investigate the implications of the form of the spatial coherence function, also referred to as the effective source distribution, for quantitative analysis in scanning transmission electron microscopy, and in particular for interpreting the spatial origin of imaging and spectroscopy signals. These questions are explored using three different source distribution models applied to a GaAs crystal case study. The shape of the effective source distribution was found to have a strong influence not only on the scanning transmission electron microscopy (STEM) image contrast, but also on the distribution of the scattered electron wavefield and hence on the spatial origin of the detected electron intensities. The implications this has for measuring structure, composition and bonding at atomic resolution via annular dark field, X-ray and electron energy loss STEM imaging are discussed. Copyright © 2014 Elsevier B.V. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mikheev, Evgeny; Himmetoglu, Burak; Kajdos, Adam P.

We analyze and compare the temperature dependence of the electron mobility of two- and three-dimensional electron liquids in SrTiO{sub 3}. The contributions of electron-electron scattering must be taken into account to accurately describe the mobility in both cases. For uniformly doped, three-dimensional electron liquids, the room temperature mobility crosses over from longitudinal optical (LO) phonon-scattering-limited to electron-electron-scattering-limited as a function of carrier density. In high-density, two-dimensional electron liquids, LO phonon scattering is completely screened and the mobility is dominated by electron-electron scattering up to room temperature. The possible origins of the observed behavior and the consequences for approaches to improvemore » the mobility are discussed.« less

Ion formation upon electron collisions with valine embedded in helium nanodroplets

NASA Astrophysics Data System (ADS)

Weinberger, Nikolaus; Ralser, Stefan; Renzler, Michael; Harnisch, Martina; Kaiser, Alexander; Denifl, Stefan; Böhme, Diethard K.; Scheier, Paul

2016-04-01

We report here experimental results for the electron ionization of large superfluid helium nanodroplets with sizes of about 105 atoms that are doped with valine and clusters of valine. Spectra of both cations and anions were monitored with high-resolution time-of-flight mass spectrometry (mass resolution >4000). Clear series of peaks with valine cluster sizes up to at least 40 and spaced by the mass of a valine molecule are visible in both the cation and anion spectra. Ion efficiency curves are presented for selected cations and anions at electron energies up to about 40 eV and these provide insight into the mode of ion formation. The measured onset of 24.59 eV for cations is indicative of valine ionization by He+ whereas broad resonances at 2, 10 and 22 eV (and beyond) in the formation of anions speak to the occurrence of various modes of dissociative electron attachment by collisions with electrons or He*- and the influence of droplet size on the relative importance of these processes. Comparisons are also made with gas phase results and these provide insight into a matrix effect within the superfluid helium nanodroplet. Contribution to the Topical Issue "Advances in Positron and Electron Scattering", edited by Paulo Limao-Vieira, Gustavo Garcia, E. Krishnakumar, James Sullivan, Hajime Tanuma and Zoran Petrovic.

Relationship between large horizontal electric fields and auroral arc elements

NASA Astrophysics Data System (ADS)

Lanchester, B. S.; Kailá, K.; McCrea, I. W.

1996-03-01

High time resolution optical measurements in the magnetic zenith are compared with European Incoherent Scatter (EISCAT) field-aligned measurements of electron density at 0.2-s resolution and with horizontal electric field measurements made at 278 km with resolution of 9 s. In one event, 20 min after a spectacular auroral breakup, a system of narrow and active arc elements moved southward into the magnetic zenith, where it remained for several minutes. During a 30-s interval of activity in a narrow arc element very close to the radar beam, the electric field vectors at 3-s resolution were found to be extremely large (up to 400 mVm-1) and to point toward the bright optical features in the arc, which moved along its length. It is proposed that the large electric fields are short-lived and are directly associated with the particle precipitation that causes the bright features in auroral arc elements.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Yuanyuan; Browning, Nigel D.

As gas-solid heterogeneous catalytic reactions are molecular in nature, a full mechanistic understanding of the process requires atomic scale characterization under realistic operating conditions. While atomic resolution imaging has become a routine in modern high-vacuum (scanning) transmission electron microscopy ((S)TEM), both image quality and resolution nominally degrade when reaction gases are introduced. In this work, we systematically assess the effects of different gases at various pressures on the quality and resolution of images obtained at room temperature in the annular dark field STEM imaging mode using a differentially pumped (DP) gas cell. This imaging mode is largely free from inelasticmore » scattering effects induced by the presence of gases and retains good imaging properties over a wide range of gas mass/pressures. We demonstrate the application of the ESTEM with atomic resolution images of a complex oxide alkane oxidation catalyst MoVNbTeOx (M1) immersed in light and heavy gas environments.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Yuanyuan; Browning, Nigel D.

As gas-solid heterogeneous catalytic reactions are molecular in nature, a full mechanistic understanding of the process requires atomic scale characterization under realistic operating conditions. While atomic resolution imaging has become a routine in modern high-vacuum (scanning) transmission electron microscopy ((S)TEM), both image quality and resolution nominally degrade when reaction gases are introduced. In this work, we systematically assess the effects of different gases at various pressures on the quality and resolution of images obtained at room temperature in the annular dark field STEM imaging mode using a differentially pumped (DP) gas cell. This imaging mode is largely free from inelasticmore » scattering effects induced by the presence of gases and retains good imaging properties over a wide range of gas mass/pressures. Furthermore, we demonstrate the application of the ESTEM with atomic resolution images of a complex oxide alkane oxidation catalyst MoVNbTeOx (M1) immersed in light and heavy gas environments.« less

Non-proportionality study of CaMoO4 and GAGG:Ce scintillation crystals using Compton coincidence technique.

PubMed

Kaewkhao, J; Limkitjaroenporn, P; Chaiphaksa, W; Kim, H J

2016-09-01

In this study, the CCT technique and nuclear instrument module (NIM) setup for the measurements of coincidence electron energy spectra of calcium molybdate (CaMoO4) and cerium doped gadolinium aluminium gallium garnet (Gd3Al2Ga3O12:Ce or GAGG:Ce) scintillation crystals were carried out. The (137)Cs irradiated gamma rays with an energy (Eγ) of 662keV was used as a radioactive source. The coincidence electron energy spectra were recorded at seven scattering angles of 30°-120°. It was found that seven corresponding electron energies were in the range of 100.5-435.4keV. The results show that, for all electron energies, the electron energy peaks of CaMoO4 crystal yielded higher number of counts than those of GAGG:Ce crystal. The electron energy resolution, the light yield and non-proportionality were also determined. It was found that the energy resolutions are inverse proportional to the square root of electron energy for both crystals. Furthermore, the results show that the light yield of GAGG:Ce crystal is much higher than that of CaMoO4 crystal. It was also found that both CaMoO4 and GAGG:Ce crystals demonstrated good proportional property in the electron energy range of 260-435.4keV. Copyright © 2016 Elsevier Ltd. All rights reserved.

Quantifying the Precipitation Loss of Radiation Belt Electrons During a Rapid Dropout Event

NASA Astrophysics Data System (ADS)

Pham, K. H.; Tu, W.; Xiang, Z.

2017-10-01

Relativistic electron flux in the radiation belt can drop by orders of magnitude within the timespan of hours. In this study, we used the drift-diffusion model that includes azimuthal drift and pitch angle diffusion of electrons to simulate low-altitude electron distribution observed by POES/MetOp satellites for rapid radiation belt electron dropout event occurring on 1 May 2013. The event shows fast dropout of MeV energy electrons at L > 4 over a few hours, observed by the Van Allen Probes mission. By simulating the electron distributions observed by multiple POES satellites, we resolve the precipitation loss with both high spatial and temporal resolutions and a range of energies. We estimate the pitch angle diffusion coefficients as a function of energy, pitch angle, and L-shell and calculate corresponding electron lifetimes during the event. The simulation results show fast electron precipitation loss at L > 4 during the electron dropout, with estimated electron lifetimes on the order of half an hour for MeV energies. The electron loss rate shows strong energy dependence with faster loss at higher energies, which suggest that this dropout event is dominated by quick and localized scattering process that prefers higher energy electrons. The improved temporal and spatial resolutions of electron precipitation rates provided by multiple low-altitude observations can resolve fast-varying electron loss during rapid electron dropouts (over a few hours), which occur too fast for a single low-altitude satellite. The capability of estimating the fast-varying electron lifetimes during rapid dropout events is an important step in improving radiation belt model accuracy.

Experimental Investigation of Ultrafast Hydration Structure and Dynamics at Sub-Angstrom Lengthscales

ERIC Educational Resources Information Center

Coridan, Robert Henry

2009-01-01

This thesis outlines how meV-resolution inelastic x-ray scattering and causality-enforcing mathematics can be used to measure the dynamical density-density linear response function for liquid water with Angstrom spatial resolution and 50fs temporal resolution. The results are compared to high-resolution spectroscopic and scattering experiments and…

Measurement of Coherence Decay in GaMnAs Using Femtosecond Four-wave Mixing

PubMed Central

Webber, Daniel; de Boer, Tristan; Yildirim, Murat; March, Sam; Mathew, Reuble; Gamouras, Angela; Liu, Xinyu; Dobrowolska, Margaret; Furdyna, Jacek; Hall, Kimberley

2013-01-01

The application of femtosecond four-wave mixing to the study of fundamental properties of diluted magnetic semiconductors ((s,p)-d hybridization, spin-flip scattering) is described, using experiments on GaMnAs as a prototype III-Mn-V system.  Spectrally-resolved and time-resolved experimental configurations are described, including the use of zero-background autocorrelation techniques for pulse optimization.  The etching process used to prepare GaMnAs samples for four-wave mixing experiments is also highlighted.  The high temporal resolution of this technique, afforded by the use of short (20 fsec) optical pulses, permits the rapid spin-flip scattering process in this system to be studied directly in the time domain, providing new insight into the strong exchange coupling responsible for carrier-mediated ferromagnetism.  We also show that spectral resolution of the four-wave mixing signal allows one to extract clear signatures of (s,p)-d hybridization in this system, unlike linear spectroscopy techniques.   This increased sensitivity is due to the nonlinearity of the technique, which suppresses defect-related contributions to the optical response. This method may be used to measure the time scale for coherence decay (tied to the fastest scattering processes) in a wide variety of semiconductor systems of interest for next generation electronics and optoelectronics. PMID:24326982

Implementation of a multichannel soft x-ray diagnostic for electron temperature measurements in TJ-II high-density plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baiao, D.; Varandas, C.; Medina, F.

2012-10-15

Based on the multi-foil technique, a multichannel soft x-ray diagnostic for electron temperature measurements has been recently implemented in the TJ-II stellarator. The diagnostic system is composed by four photodiodes arrays with beryllium filters of different thickness. An in-vacuum amplifier board is coupled to each array, aiming at preventing induced noise currents. The Thomson scattering and the vacuum ultraviolet survey diagnostics are used for assessing plasma profiles and composition, being the analysis carried out with the radiation code IONEQ. The electron temperature is determined through the different signal-pair ratios with temporal and spatial resolution. The design and preliminary results frommore » the diagnostic are presented.« less

Calibration, event reconstruction, data analysis and limits calculation for the LUX dark matter experiment

DOE PAGES

Akerib, DS; Alsum, S; Araújo, HM; ...

2018-01-05

The LUX experiment has performed searches for dark matter particles scattering elastically on xenon nuclei, leading to stringent upper limits on the nuclear scattering cross sections for dark matter. Here, for results derived frommore » $${1.4}\\times 10^{4}\\;\\mathrm{kg\\,days}$$ of target exposure in 2013, details of the calibration, event-reconstruction, modeling, and statistical tests that underlie the results are presented. Detector performance is characterized, including measured efficiencies, stability of response, position resolution, and discrimination between electron- and nuclear-recoil populations. Models are developed for the drift field, optical properties, background populations, the electron- and nuclear-recoil responses, and the absolute rate of low-energy background events. Innovations in the analysis include in situ measurement of the photomultipliers' response to xenon scintillation photons, verification of fiducial mass with a low-energy internal calibration source, and new empirical models for low-energy signal yield based on large-sample, in situ calibrations.« less

Atomically resolved structural determination of graphene and its point defects via extrapolation assisted phase retrieval

DOE Office of Scientific and Technical Information (OSTI.GOV)

Latychevskaia, Tatiana; Fink, Hans-Werner

Previously reported crystalline structures obtained by an iterative phase retrieval reconstruction of their diffraction patterns seem to be free from displaying any irregularities or defects in the lattice, which appears to be unrealistic. We demonstrate here that the structure of a nanocrystal including its atomic defects can unambiguously be recovered from its diffraction pattern alone by applying a direct phase retrieval procedure not relying on prior information of the object shape. Individual point defects in the atomic lattice are clearly apparent. Conventional phase retrieval routines assume isotropic scattering. We show that when dealing with electrons, the quantitatively correct transmission functionmore » of the sample cannot be retrieved due to anisotropic, strong forward scattering specific to electrons. We summarize the conditions for this phase retrieval method and show that the diffraction pattern can be extrapolated beyond the original record to even reveal formerly not visible Bragg peaks. Such extrapolated wave field pattern leads to enhanced spatial resolution in the reconstruction.« less

Experimental status DVCS e p ---> e p gamma and e n ---> e n gamma at Jefferson Lab-Hall A

DOE Office of Scientific and Technical Information (OSTI.GOV)

C. Ferdi

2004-06-02

The experiments E00-110 and E03-106 [1] propose to measure the Deep Virtual Compton Scattering process (DVCS) ep --> ep{gamma} and en --> en{gamma} in Hall A at Jefferson Lab with a 5.75 GeV longitudinally polarized electron beam. The exclusivity requires the High Resolution Spectrometer of the Hall A for the detection of the scattered electron ({Delta}p/p = 10^-4), an electromagnetic calorimeter for the detection of the real photon ({sigma}/E<5%) and a scintillator array for the detection of the third particle. A 1 GHz sampling system allows one to deal with pile-up as expected from running detectors at small angles andmore » high luminosity L = 10^37 cm^-2 s^-1. We will describe the apparatus and will explain the method to extract GPDs and evaluate the contributions from higher twists from the measurement of the cross-section difference.« less

Calibration, event reconstruction, data analysis, and limit calculation for the LUX dark matter experiment

DOE PAGES

Akerib, D. S.; Alsum, S.; Araújo, H. M.; ...

2018-05-31

Here, the LUX experiment has performed searches for dark matter particles scattering elastically on xenon nuclei, leading to stringent upper limits on the nuclear scattering cross sections for dark matter. Here, for results derived frommore » $${1.4}\\times 10^{4}\\;\\mathrm{kg\\,days}$$ of target exposure in 2013, details of the calibration, event-reconstruction, modeling, and statistical tests that underlie the results are presented. Detector performance is characterized, including measured efficiencies, stability of response, position resolution, and discrimination between electron- and nuclear-recoil populations. Models are developed for the drift field, optical properties, background populations, the electron- and nuclear-recoil responses, and the absolute rate of low-energy background events. Innovations in the analysis include in situ measurement of the photomultipliers' response to xenon scintillation photons, verification of fiducial mass with a low-energy internal calibration source, and new empirical models for low-energy signal yield based on large-sample, in situ calibrations.« less

Characterization of core/shell structures based on CdTe and GaAs nanocrystalline layers deposited on SnO2 microwires

NASA Astrophysics Data System (ADS)

Ghimpu, L.; Ursaki, V. V.; Pantazi, A.; Mesterca, R.; Brâncoveanu, O.; Shree, Sindu; Adelung, R.; Tiginyanu, I. M.; Enachescu, M.

2018-04-01

We report the fabrication and characterization of SnO2/CdTe and SnO2/GaAs core/shell microstructures. CdTe or GaAs shell layers were deposited by radio-frequency (RF) magnetron sputtering on core SnO2 microwires synthesized by a flame-based thermal oxidation method. The produced structures were characterized by scanning electron microscopy (SEM), high-resolution scanning transmission electron microscope (HR-STEM), X-ray diffraction (XRD), Raman scattering and FTIR spectroscopy. It was found that the SnO2 core is of the rutile type, while the shells are composed of CdTe or GaAs nanocrystallites of zincblende structure with the dimensions of crystallites in the range of 10-20 nm. The Raman scattering investigations demonstrated that the quality of the porous nanostructured shell is improved by annealing at temperatures of 420-450 °C. The prospects of implementing these microstructures in intrinsic type fiber optic sensors are discussed.

Direct observation of low energy nuclear spin excitations in HoCrO3 by high resolution neutron spectroscopy.

PubMed

Chatterji, T; Jalarvo, N; Kumar, C M N; Xiao, Y; Brückel, Th

2013-07-17

We have investigated low energy nuclear spin excitations in the strongly correlated electron compound HoCrO3. We observe clear inelastic peaks at E = 22.18 ± 0.04 μeV in both energy loss and gain sides. The energy of the inelastic peaks remains constant in the temperature range 1.5-40 K at which they are observed. The intensity of the inelastic peak increases at first with increasing temperature and then decreases at higher temperatures. The temperature dependence of the energy and intensity of the inelastic peaks is very unusual compared to that observed in other Nd, Co, V and also simple Ho compounds. Huge quasielastic scattering appears at higher temperatures presumably due to the fluctuating electronic moments of the Ho ions that get increasingly disordered at higher temperatures. The strong quasielastic scattering may also originate in the first Ho crystal-field excitations at about 1.5 meV.

Calibration, event reconstruction, data analysis, and limit calculation for the LUX dark matter experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akerib, D. S.; Alsum, S.; Araújo, H. M.

Here, the LUX experiment has performed searches for dark matter particles scattering elastically on xenon nuclei, leading to stringent upper limits on the nuclear scattering cross sections for dark matter. Here, for results derived frommore » $${1.4}\\times 10^{4}\\;\\mathrm{kg\\,days}$$ of target exposure in 2013, details of the calibration, event-reconstruction, modeling, and statistical tests that underlie the results are presented. Detector performance is characterized, including measured efficiencies, stability of response, position resolution, and discrimination between electron- and nuclear-recoil populations. Models are developed for the drift field, optical properties, background populations, the electron- and nuclear-recoil responses, and the absolute rate of low-energy background events. Innovations in the analysis include in situ measurement of the photomultipliers' response to xenon scintillation photons, verification of fiducial mass with a low-energy internal calibration source, and new empirical models for low-energy signal yield based on large-sample, in situ calibrations.« less

Strategies for Analyzing Sub-Micrometer Features with the FE-EPMA

NASA Astrophysics Data System (ADS)

McSwiggen, P.; Armstrong, J. T.; Nielsen, C.

2013-12-01

Changes in column design and electronics, as well as new types of spectrometers and analyzing crystals, have significantly advanced electron microprobes, in terms of stability, reproducibility and detection limits. A major advance in spatial resolution has occurred through the use of the field emission electron gun. The spatial resolution of an analysis is controlled by the diameter of the electron beam and the amount of scatter that takes place within the sample. The beam diameter is controlled by the column and type of electron gun being used. The accelerating voltage and the average atomic number/density of the sample control the amount of electron scatter within the sample. However a large electron interaction volume does not necessarily mean a large analytical volume. The beam electrons may spread out within a large volume, but if the electrons lack sufficient energy to produce the X-ray of interest, the analytical volume could be significantly smaller. Therefore there are two competing strategies for creating the smallest analytical volumes. The first strategy is to reduce the accelerating voltage to produce the smallest electron interaction volume. This low kV analytical approach is ultimately limited by the size of the electron beam itself. With a field emission gun, normally the smallest analytical area is achieved at around 5-7 kV. At lower accelerating voltages, the increase in the beam diameter begins to overshadow the reduction in internal scattering. For tungsten filament guns, the smallest analytical volume is reached at higher accelerating voltages. The second strategy is to minimize the overvoltage during the analysis. If the accelerating voltage is only 1-3 kV greater than the critical ionization energy for the X-ray line of interest, then even if the overall electron interaction volume is large, those electrons quickly loose sufficient energy to produce the desired X-rays. The portion of the interaction volume in which the desired X-rays will be produce will be very small and very near the surface. Both strategies have advantages and disadvantages depending on the ultimate goal of the analysis and the elements involved. This work will examine a number of considerations when attempting to decide which approach is best for a given analytical situation. These include: (1) the size of the analytical volumes, (2) minimum detection limits, (3) quality of the matrix corrections, (4) secondary fluorescence, (5) effects of surface contamination, oxide layers, and carbon coatings. This work is based on results largely from the Fe-Ni binary. A simple conclusion cannot be draw as to which strategy is better overall. The determination is highly system dependent. For many mineral systems, both strategies used in combination will produce the best results. Using multiple accelerating voltages to preform a single analysis allows the analyst to optimize their analytical conditions for each element individually.

Experimental Retrieval of Target Structure Information from Laser-Induced Rescattered Photoelectron Momentum Distributions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Okunishi, M.; Pruemper, G.; Shimada, K.

We have measured two-dimensional photoelectron momentum spectra of Ne, Ar, and Xe generated by 800-nm, 100-fs laser pulses and succeeded in identifying the spectral ridge region (back-rescattered ridges) which marks the location of the returning electrons that have been backscattered at their maximum kinetic energies. We demonstrate that the structural information, in particular the differential elastic scattering cross sections of the target ion by free electrons, can be accurately extracted from the intensity distributions of photoelectrons on the ridges, thus effecting a first step toward laser-induced self-imaging of the target, with unprecedented spatial and temporal resolutions.

Comparison of energy flows in deep inelastic scattering events with and without a large rapidity gap

NASA Astrophysics Data System (ADS)

Derrick, M.; Krakauer, D.; Magill, S.; Musgrave, B.; Repond, J.; Schlereth, J.; Stanek, R.; Talaga, R. L.; Thron, J.; Arzarello, F.; Ayad, R.; Bari, G.; Basile, M.; Bellagamba, L.; Boscherini, D.; Bruni, A.; Bruni, G.; Bruni, P.; Romeo, G. Cara; Castellini, G.; Chiarini, M.; Cifarelli, L.; Cindolo, F.; Ciralli, F.; Contin, A.; D'Auria, S.; Del Papa, C.; Frasconi, F.; Giusti, P.; Iacobucci, G.; Laurenti, G.; Levi, G.; Maccarrone, G.; Margotti, A.; Massam, T.; Nania, R.; Nemoz, C.; Palmonari, F.; Polini, A.; Sartorelli, G.; Timellini, R.; Garcia, Y. Zamora; Zichichi, A.; Bargende, A.; Crittenden, J.; Desch, K.; Diekmann, B.; Doeker, T.; Feld, L.; Frey, A.; Geerts, M.; Geitz, G.; Grothe, M.; Hartmann, H.; Haun, D.; Heinloth, K.; Hilger, E.; Jakob, H.-P.; Katz, U. F.; Mari, S. M.; Mass, A.; Mengel, S.; Mollen, J.; Paul, E.; Rembser, Ch.; Schattevoy, R.; Schneider, J.-L.; Schramm, D.; Stamm, J.; Wedemeyer, R.; Campbell-Robson, S.; Cassidy, A.; Dyce, N.; Foster, B.; George, S.; Gilmore, R.; Heath, G. P.; Heath, H. F.; Llewellyn, T. J.; Morgado, C. J. S.; Norman, D. J. P.; O'Mara, J. A.; Tapper, R. J.; Wilson, S. S.; Yoshida, R.; Rau, R. R.; Arneodo, M.; Iannotti, L.; Schioppa, M.; Susinno, G.; Bernstein, A.; Caldwell, A.; Gialas, I.; Parsons, J. A.; Ritz, S.; Sciulli, F.; Straub, P. B.; Wai, L.; Yang, S.; Borzemski, P.; Chwastowski, J.; Eskreys, A.; Piotrzkowski, K.; Zachara, M.; Zawiejski, L.; Adamczyk, L.; Bednarek, B.; Eskreys, K.; Jeleń, K.; Kisielewska, D.; Kowalski, T.; Rulikowska-Zarȩbska, E.; Suszycki, L.; Zajaç, J.; Kȩdzierski, T.; Kotański, A.; Przybycień, M.; Bauerdick, L. A. T.; Behrens, U.; Bienlein, J. K.; Böttcher, S.; Coldewey, C.; Drews, G.; Flasiński, M.; Gilkinson, D. J.; Göttlicher, P.; Gutjahr, B.; Haas, T.; Hagge, L.; Hain, W.; Hasell, D.; Heßling, H.; Hultschig, H.; Iga, Y.; Joos, P.; Kasemann, M.; Klanner, R.; Koch, W.; Köpke, L.; Kötz, U.; Kowalski, H.; Kröger, W.; Krüger, J.; Labs, J.; Ladage, A.; Löhr, B.; Löwe, M.; Lüke, D.; Mainusch, J.; Mańczak, O.; Ng, J. S. T.; Nickel, S.; Notz, D.; Ohrenberg, K.; Roco, M.; Rohde, M.; Roldán, J.; Schneekloth, U.; Schroeder, J.; Schulz, W.; Selonke, F.; Stiliaris, E.; Voß, T.; Westphal, D.; Wolf, G.; Youngman, C.; Grabosch, H. J.; Leich, A.; Meyer, A.; Rethfeldt, C.; Schlenstedt, S.; Barbagli, G.; Pelfer, P.; Anzivino, G.; De Pasquale, S.; Qian, S.; Votano, L.; Bamberger, A.; Freidhof, A.; Poser, T.; Söldner-Rembold, S.; Theisen, G.; Trefzger, T.; Brook, N. H.; Bussey, P. J.; Doyle, A. T.; Fleck, I.; Forbes, J. R.; Jamieson, V. A.; Raine, C.; Saxon, D. H.; Stavrianakou, M.; Wilson, A. S.; Dannemann, A.; Holm, U.; Horstmann, D.; Kammerlocher, H.; Krebs, B.; Neumann, T.; Sinkus, R.; Wick, K.; Badura, E.; Burow, B. D.; Fürtjes, A.; Lohrmann, E.; Milewski, J.; Nakahata, M.; Pavel, N.; Poelz, G.; Schott, W.; Terron, J.; Zetsche, F.; Bacon, T. C.; Beuselinck, R.; Butterworth, I.; Gallo, E.; Harris, V. L.; Hung, B. H.; Long, K. R.; Miller, D. B.; Morawitz, P. P. O.; Prinias, A.; Sedgbeer, J. K.; Whitfield, A. F.; Mallik, U.; McCliment, E.; Wang, M. Z.; Zhang, Y.; Cloth, P.; Filges, D.; An, S. H.; Hong, S. M.; Kim, C. O.; Kim, T. Y.; Nam, S. W.; Park, S. K.; Suh, M. H.; Yon, S. H.; Imlay, R.; Kartik, S.; Kim, H.-J.; McNeil, R. R.; Metcalf, W.; Nadendla, V. K.; Barreiro, F.; Cases, G.; Graciani, R.; Hernández, J. M.; Hervás, L.; Labarga, L.; del Peso, J.; Puga, J.; de Trocóniz, J. F.; Ikraiam, F.; Mayer, J. K.; Smith, G. R.; Corriveau, F.; Hanna, D. S.; Hartmann, J.; Hung, L. W.; Lim, J. N.; Matthews, C. G.; Mitchell, J. W.; Patel, P. M.; Sinclair, L. E.; Stairs, D. G.; Laurent, M. St.; Ullmann, R.; Bashkirov, V.; Dolgoshein, B. A.; Stifutkin, A.; Bashindzhagyan, G. L.; Ermolov, P. F.; Gladilin, L. K.; Golubkov, Y. A.; Kobrin, V. D.; Kuzmin, V. A.; Proskuryakov, A. S.; Savin, A. A.; Shcheglova, L. M.; Solomin, A. N.; Zotov, N. P.; Bentvelsen, S.; Botje, M.; Chlebana, F.; Dake, A.; Engelen, J.; de Jong, P.; de Kamps, M.; Kooijman, P.; Kruse, A.; O'Dell, V.; Tenner, A.; Tiecke, H.; Verkerke, W.; Vreeswijk, M.; Wiggers, L.; de Wolf, E.; van Woudenberg, R.; Acosta, D.; Bylsma, B.; Durkin, L. S.; Honscheid, K.; Li, C.; Ling, T. Y.; McLean, K. W.; Murray, W. N.; Park, I. H.; Romanowski, T. A.; Seidlein, R.; Bailey, D. S.; Blair, G. A.; Byrne, A.; Cashmore, R. J.; Cooper-Sarkar, A. M.; Daniels, D.; Devenish, R. C. E.; Harnew, N.; Lancaster, M.; Luffman, P. E.; McFall, J.; Nath, C.; Quadt, A.; Uijterwaal, H.; Walczak, R.; Wilson, F. F.; Yip, T.; Abbiendi, G.; Bertolin, A.; Brugnera, R.; Carlin, R.; Dal Corso, F.; De Giorgi, M.; Dosselli, U.; Gasparini, F.; Limentani, S.; Morandin, M.; Posocco, M.; Stanco, L.; Stroili, R.; Voci, C.; Bulmahn, J.; Butterworth, J. M.; Feild, R. G.; Oh, B. Y.; Whitmore, J. J.; D'Agostini, G.; Iori, M.; Marini, G.; Mattioli, M.; Nigro, A.; Hart, J. C.; McCubbin, N. A.; Prytz, K.; Shah, T. P.; Short, T. L.; Barberis, E.; Cartiglia, N.; Dubbs, T.; Heusch, C.; Van Hook, M.; Hubbard, B.; Lockman, W.; Sadrozinski, H. F.-W.; Seiden, A.; Biltzinger, J.; Seifert, R. J.; Walenta, A. H.; Zech, G.; Abramowicz, H.; Dagan, S.; Levy, A.; Hasegawa, T.; Hazumi, M.; Ishii, T.; Kuze, M.; Mine, S.; Nagasawa, Y.; Nagira, T.; Nakao, M.; Suzuki, I.; Tokushuku, K.; Yamada, S.; Yamazaki, Y.; Chiba, M.; Hamatsu, R.; Hirose, T.; Homma, K.; Kitamura, S.; Nagayama, S.; Nakamitsu, Y.; Cirio, R.; Costa, M.; Ferrero, M. I.; Lamberti, L.; Maselli, S.; Peroni, C.; Sacchi, R.; Solano, A.; Staiano, A.; Dardo, M.; Bailey, D. C.; Bandyopadhyay, D.; Benard, F.; Brkic, M.; Crombie, M. B.; Gingrich, D. M.; Hartner, G. F.; Joo, K. K.; Levman, G. M.; Martin, J. F.; Orr, R. S.; Sampson, C. R.; Teuscher, R. J.; Catterall, C. D.; Jones, T. W.; Kaziewicz, P. B.; Lane, J. B.; Saunders, R. S.; Shulman, J.; Blankenship, K.; Kochocki, J.; Lu, B.; Mo, L. W.; Bogusz, W.; Charchuła, K.; Ciborowski, J.; Gajewski, J.; Grzelak, G.; Kasprzak, M.; Krzyżanowski, M.; Muchorowski, K.; Nowak, R. J.; Pawlak, J. M.; Tymieniecka, T.; Wróblewski, A. K.; Zakrzewski, J. A.; Żarnecki, A. F.; Adamus, M.; Eisenberg, Y.; Glasman, C.; Karshon, U.; Revel, D.; Shapira, A.; Ali, I.; Behrens, B.; Dasu, S.; Fordham, C.; Foudas, C.; Goussiou, A.; Loveless, R. J.; Reeder, D. D.; Silverstein, S.; Smith, W. H.; Tsurugai, T.; Bhadra, S.; Frisken, W. R.; Furutani, K. M.; ZEUS Collaboration

1994-11-01

Energy flows in deep inelastic electron-proton scattering are investigated at a centre-of-mass energy of 269 GeV for the range Q2 ≥ 10 GeV 2 using the ZEUS detector. A comparison is made between events with and without a large rapidity gap between the hadronic system and the proton direction. The energy flows, corrected for detector acceptance and resolution, are shown for these two classes of events in both the HERA laboratory frame and the Breit frame. From the differences in the shapes of these energy flows we conclude that QCD radiation is suppressed in the large-rapidity-gap eents compared to the events without a large rapidity gap.

Three-dimensional structure determination protocol for noncrystalline biomolecules using x-ray free-electron laser diffraction imaging.

PubMed

Oroguchi, Tomotaka; Nakasako, Masayoshi

2013-02-01

Coherent and intense x-ray pulses generated by x-ray free-electron laser (XFEL) sources are paving the way for structural determination of noncrystalline biomolecules. However, due to the small scattering cross section of electrons for x rays, the available incident x-ray intensity of XFEL sources, which is currently in the range of 10(12)-10(13) photons/μm(2)/pulse, is lower than that necessary to perform single-molecule diffraction experiments for noncrystalline biomolecules even with the molecular masses of megadalton and submicrometer dimensions. Here, we propose an experimental protocol and analysis method for visualizing the structure of those biomolecules by the combined application of coherent x-ray diffraction imaging and three-dimensional reconstruction methods. To compensate the small scattering cross section of biomolecules, in our protocol, a thin vitreous ice plate containing several hundred biomolecules/μm(2) is used as sample, a setup similar to that utilized by single-molecule cryoelectron microscopy. The scattering cross section of such an ice plate is far larger than that of a single particle. The images of biomolecules contained within irradiated areas are then retrieved from each diffraction pattern, and finally provide the three-dimensional electron density model. A realistic atomic simulation using large-scale computations proposed that the three-dimensional structure determination of the 50S ribosomal subunit embedded in a vitreous ice plate is possible at a resolution of 0.8 nm when an x-ray beam of 10(16) photons/500×500 nm(2)/pulse is available.

X-ray scattering study of pyrochlore iridates: Crystal structure, electronic, and magnetic excitations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clancy, J. P.; Gretarsson, H.; Lee, E. K. H.

2016-07-06

We have investigated the structural, electronic, and magnetic properties of the pyrochlore iridates Eu 2Ir 2O 7 and Pr 2Ir 2O 7 using a combination of resonant elastic x-ray scattering, x-ray powder diffraction, and resonant inelastic x-ray scattering (RIXS). The structural parameters of Eu 2Ir 2O 7 have been examined as a function of temperature and applied pressure, with a particular emphasis on regions of the phase diagram where electronic and magnetic phase transitions have been reported. We find no evidence of crystal symmetry change over the range of temperatures (~6 to 300 K) and pressures (~0.1 to 17 GPa)more » studied. We have also investigated the electronic and magnetic excitations in single-crystal samples of Eu 2Ir 2O 7 and Pr 2Ir 2O 7 using high-resolution Ir L- 3-edge RIXS. In spite of very different ground state properties, we find that these materials exhibit qualitatively similar excitation spectra, with crystal field excitations at ~3-5 eV, spin-orbit excitations at ~ 0.5-1 eV, and broad low-lying excitations below ~0.15 eV. In single-crystal samples of "Eu-rich" Eu 2Ir 2O 7 (found to possess an actual stoichiometry of Eu 2.18Ir 1.82O 7.06) we observe highly damped magnetic excitations at ~45 meV, which display significant momentum dependence. Here, we compare these results with recent dynamical structure factor calculations« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hosseinizadeh, Ahmad; Mashayekhi, Ghoncheh; Copperman, Jeremy

Using a manifold-based analysis of experimental diffraction snapshots from an X-ray free electron laser, we determine the three-dimensional structure and conformational landscape of the PR772 virus to a detector-limited resolution of 9 nm. Our results indicate that a single conformational coordinate controls reorganization of the genome, growth of a tubular structure from a portal vertex and release of the genome. Furthermore, these results demonstrate that single-particle X-ray scattering has the potential to shed light on key biological processes.

Imaging secondary structure of individual amyloid fibrils of a β2-microglobulin fragment using near-field infrared spectroscopy.

PubMed

Paulite, Melissa; Fakhraai, Zahra; Li, Isaac T S; Gunari, Nikhil; Tanur, Adrienne E; Walker, Gilbert C

2011-05-18

Amyloid fibril diseases are characterized by the abnormal production of aggregated proteins and are associated with many types of neuro- and physically degenerative diseases. X-ray diffraction techniques, solid-state magic-angle spinning NMR spectroscopy, circular dichroism (CD) spectroscopy, and transmission electron microscopy studies have been utilized to detect and examine the chemical, electronic, material, and structural properties of amyloid fibrils at up to angstrom spatial resolution. However, X-ray diffraction studies require crystals of the fibril to be analyzed, while other techniques can only probe the bulk solution or solid samples. In the work reported here, apertureless near-field scanning infrared microscopy (ANSIM) was used to probe the secondary structure of individual amyloid fibrils made from an in vitro solution. Simultaneous topographic and infrared images of individual amyloid fibrils synthesized from the #21-31 peptide fragment of β(2)-microglobulin were acquired. Using this technique, IR spectra of the amyloid fibrils were obtained with a spatial resolution of less than 30 nm. It is observed that the experimental scattered field spectrum correlates strongly with that calculated using the far-field absorption spectrum. The near-field images of the amyloid fibrils exhibit much lower scattering of the IR radiation at approximately 1630 cm(-1). In addition, the near-field images also indicate that composition and/or structural variations among individual amyloid fibrils were present. © 2011 American Chemical Society

Layout and results from the initial operation of the high-resolution x-ray imaging crystal spectrometer on the Large Helical Device.

PubMed

Pablant, N A; Bitter, M; Delgado-Aparicio, L; Goto, M; Hill, K W; Lazerson, S; Morita, S; Roquemore, A L; Gates, D; Monticello, D; Nielson, H; Reiman, A; Reinke, M; Rice, J E; Yamada, H

2012-08-01

First results of ion and electron temperature profile measurements from the x-ray imaging crystal spectrometer (XICS) diagnostic on the Large Helical Device (LHD) are presented. This diagnostic system has been operational since the beginning of the 2011 LHD experimental campaign and is the first application of the XICS diagnostic technique to helical plasma geometry. The XICS diagnostic provides measurements of ion and electron temperature profiles in LHD with a spatial resolution of 2 cm and a maximum time resolution of 5 ms (typically 20 ms). Ion temperature profiles from the XICS diagnostic are possible under conditions where charge exchange recombination spectroscopy (CXRS) is not possible (high density) or is perturbative to the plasma (low density or radio frequency heated plasmas). Measurements are made by using a spherically bent crystal to provide a spectrally resolved 1D image of the plasma from line integrated emission of helium-like Ar(16 +). The final hardware design and configuration are detailed along with the calibration procedures. Line-integrated ion and electron temperature measurements are presented, and the measurement accuracy is discussed. Finally central temperature measurements from the XICS system are compared to measurements from the Thomson scattering and CXRS systems, showing excellent agreement.

HREELS to identify electronic structures of organic thin films.

PubMed

Oeter, D; Ziegler, C; Göpel, W

1995-10-01

The electronic structure of alpha-oligothiophene (alphanT) thin films has been investigated for increasing chain lengths of n= 4-8 thiophene units with high resolution electron energy loss spectroscopy (HREELS) in the specular reflection geometry at a primary energy of 15 eV. The great advantage of this technique in contrast to UV/VIS absorption spectroscopy results from the fact, that the impact scattering mechanism of HREELS makes it possible to also detect optically forbidden electronic transitions. On the other hand, the electrons used as probes in HREELS have a wavelength which is two orders of magnitudes smaller if compared to those of photons used in UV/VIS absorption spectroscopy. Therefore individual molecules are excited by HREELS independent from each other and hence the excitation of collective excitons is not possible. As a result, information about the orientation of the molecules cannot be achieved with HREELS, which, however, is possible in polarization-dependent UV/VIS spectroscopy.

Macromolecular refinement by model morphing using non-atomic parameterizations.

PubMed

Cowtan, Kevin; Agirre, Jon

2018-02-01

Refinement is a critical step in the determination of a model which explains the crystallographic observations and thus best accounts for the missing phase components. The scattering density is usually described in terms of atomic parameters; however, in macromolecular crystallography the resolution of the data is generally insufficient to determine the values of these parameters for individual atoms. Stereochemical and geometric restraints are used to provide additional information, but produce interrelationships between parameters which slow convergence, resulting in longer refinement times. An alternative approach is proposed in which parameters are not attached to atoms, but to regions of the electron-density map. These parameters can move the density or change the local temperature factor to better explain the structure factors. Varying the size of the region which determines the parameters at a particular position in the map allows the method to be applied at different resolutions without the use of restraints. Potential applications include initial refinement of molecular-replacement models with domain motions, and potentially the use of electron density from other sources such as electron cryo-microscopy (cryo-EM) as the refinement model.

Rocket measurements of electron density irregularities during MAC/SINE

NASA Technical Reports Server (NTRS)

Ulwick, J. C.

1989-01-01

Four Super Arcas rockets were launched at the Andoya Rocket Range, Norway, as part of the MAC/SINE campaign to measure electron density irregularities with high spatial resolution in the cold summer polar mesosphere. They were launched as part of two salvos: the turbulent/gravity wave salvo (3 rockets) and the EISCAT/SOUSY radar salvo (one rocket). In both salvos meteorological rockets, measuring temperature and winds, were also launched and the SOUSY radar, located near the launch site, measured mesospheric turbulence. Electron density irregularities and strong gradients were measured by the rocket probes in the region of most intense backscatter observed by the radar. The electron density profiles (8 to 4 on ascent and 4 on descent) show very different characteristics in the peak scattering region and show marked spatial and temporal variability. These data are intercompared and discussed.

Ballistic Imaging and Scattering Measurements for Diesel Spray Combustion: Optical Development and Phenomenological Studies

DTIC Science & Technology

2016-04-01

polystyrene spheres in a water suspension. The impact of spatial filtering , temporal filtering , and scattering path length on image resolution are...The impact of spatial filtering , temporal filtering , and scattering path length on image resolution are reported. The technique is demonstrated...cell filled with polystyrene spheres in a water suspension. The impact of spatial filtering , temporal filtering , and scattering path length on image

Test Particle Simulations of Electron Injection by the Bursty Bulk Flows (BBFs) using High Resolution Lyon-Feddor-Mobarry (LFM) Code

NASA Astrophysics Data System (ADS)

Eshetu, W. W.; Lyon, J.; Wiltberger, M. J.; Hudson, M. K.

2017-12-01

Test particle simulations of electron injection by the bursty bulk flows (BBFs) have been done using a test particle tracer code [1], and the output fields of the Lyon-Feddor-Mobarry global magnetohydro- dynamics (MHD) code[2]. The MHD code was run with high resolu- tion (oct resolution), and with specified solar wind conditions so as to reproduce the observed qualitative picture of the BBFs [3]. Test par- ticles were injected so that they interact with earthward propagating BBFs. The result of the simulation shows that electrons are pushed ahead of the BBFs and accelerated into the inner magnetosphere. Once electrons are in the inner magnetosphere they are further energized by drift resonance with the azimuthal electric field. In addition pitch angle scattering of electrons resulting in the violation conservation of the first adiabatic invariant has been observed. The violation of the first adiabatic invariant occurs as electrons cross a weak magnetic field region with a strong gradient of the field perturbed by the BBFs. References 1. Kress, B. T., Hudson,M. K., Looper, M. D. , Albert, J., Lyon, J. G., and Goodrich, C. C. (2007), Global MHD test particle simulations of ¿ 10 MeV radiation belt electrons during storm sudden commencement, J. Geophys. Res., 112, A09215, doi:10.1029/2006JA012218. Lyon,J. G., Fedder, J. A., and Mobarry, C.M., The Lyon- Fedder-Mobarry (LFM) Global MHD Magnetospheric Simulation Code (2004), J. Atm. And Solar-Terrestrial Phys., 66, Issue 15-16, 1333- 1350,doi:10.1016/j.jastp. Wiltberger, Merkin, M., Lyon, J. G., and Ohtani, S. (2015), High-resolution global magnetohydrodynamic simulation of bursty bulk flows, J. Geophys. Res. Space Physics, 120, 45554566, doi:10.1002/2015JA021080.

Kinetics of Electrons from Plasma Discharge in a Latent Track Region Induced by Swift Heavy ION Irradiation

NASA Astrophysics Data System (ADS)

Minárik, Stanislav

2015-08-01

While passing swift heavy ion through a material structure, it produces a region of radiation affected material which is known as a "latent track". Scattering motions of electrons interacting with a swift heavy ion are dominant in the latent track region. These phenomena include the electron impurity and phonon scattering processes modified by the interaction with the ion projectile as well as the Coulomb scattering between two electrons. In this paper, we provide detailed derivation of a 3D Boltzmann scattering equation for the description of the relative scattering motion of such electrons. Phase-space distribution function for this non-equilibrioum system of scattering electrons can be found by the solution of mentioned equation.

Büttiker probes for dissipative phonon quantum transport in semiconductor nanostructures

NASA Astrophysics Data System (ADS)

Miao, K.; Sadasivam, S.; Charles, J.; Klimeck, G.; Fisher, T. S.; Kubis, T.

2016-03-01

Theoretical prediction of phonon transport in modern semiconductor nanodevices requires atomic resolution of device features and quantum transport models covering coherent and incoherent effects. The nonequilibrium Green's function method is known to serve this purpose well but is numerically expensive in simulating incoherent scattering processes. This work extends the efficient Büttiker probe approach widely used in electron transport to phonons and considers salient implications of the method. Different scattering mechanisms such as impurity, boundary, and Umklapp scattering are included, and the method is shown to reproduce the experimental thermal conductivity of bulk Si and Ge over a wide temperature range. Temperature jumps at the lead/device interface are captured in the quasi-ballistic transport regime consistent with results from the Boltzmann transport equation. Results of this method in Si/Ge heterojunctions illustrate the impact of atomic relaxation on the thermal interface conductance and the importance of inelastic scattering to activate high-energy channels for phonon transport. The resultant phonon transport model is capable of predicting the thermal performance in the heterostructure efficiently.

Ab initio molecular dynamics calculations on scattering of hyperthermal H atoms from Cu(111) and Au(111).

PubMed

Kroes, Geert-Jan; Pavanello, Michele; Blanco-Rey, María; Alducin, Maite; Auerbach, Daniel J

2014-08-07

Energy loss from the translational motion of an atom or molecule impinging on a metal surface to the surface may determine whether the incident particle can trap on the surface, and whether it has enough energy left to react with another molecule present at the surface. Although this is relevant to heterogeneous catalysis, the relative extent to which energy loss of hot atoms takes place to phonons or electron-hole pair (ehp) excitation, and its dependence on the system's parameters, remain largely unknown. We address these questions for two systems that present an extreme case of the mass ratio of the incident atom to the surface atom, i.e., H + Cu(111) and H + Au(111), by presenting adiabatic ab initio molecular dynamics (AIMD) predictions of the energy loss and angular distributions for an incidence energy of 5 eV. The results are compared to the results of AIMDEFp calculations modeling energy loss to ehp excitation using an electronic friction ("EF") model applied to the AIMD trajectories, so that the energy loss to the electrons is calculated "post" ("p") the computation of the AIMD trajectory. The AIMD calculations predict average energy losses of 0.38 eV for Cu(111) and 0.13-0.14 eV for Au(111) for H-atoms that scatter from these surfaces without penetrating the surface. These energies closely correspond with energy losses predicted with Baule models, which is suggestive of structure scattering. The predicted adiabatic integral energy loss spectra (integrated over all final scattering angles) all display a lowest energy peak at an energy corresponding to approximately 80% of the average adiabatic energy loss for non-penetrative scattering. In the adiabatic limit, this suggests a way of determining the approximate average energy loss of non-penetratively scattered H-atoms from the integral energy loss spectrum of all scattered H-atoms. The AIMDEFp calculations predict that in each case the lowest energy loss peak should show additional energy loss in the range 0.2-0.3 eV due to ehp excitation, which should be possible to observe. The average non-adiabatic energy losses for non-penetrative scattering exceed the adiabatic losses to phonons by 0.9-1.0 eV. This suggests that for scattering of hyperthermal H-atoms from coinage metals the dominant energy dissipation channel should be to ehp excitation. These predictions can be tested by experiments that combine techniques for generating H-atom beams that are well resolved in translational energy and for detecting the scattered atoms with high energy-resolution.

Compton scatter tomography in TOF-PET

NASA Astrophysics Data System (ADS)

Hemmati, Hamidreza; Kamali-Asl, Alireza; Ay, Mohammadreza; Ghafarian, Pardis

2017-10-01

Scatter coincidences contain hidden information about the activity distribution on the positron emission tomography (PET) imaging system. However, in conventional reconstruction, the scattered data cause the blurring of images and thus are estimated and subtracted from detected coincidences. List mode format provides a new aspect to use time of flight (TOF) and energy information of each coincidence in the reconstruction process. In this study, a novel approach is proposed to reconstruct activity distribution using the scattered data in the PET system. For each single scattering coincidence, a scattering angle can be determined by the recorded energy of the detected photons, and then possible locations of scattering can be calculated based on the scattering angle. Geometry equations show that these sites lie on two arcs in 2D mode or the surface of a prolate spheroid in 3D mode, passing through the pair of detector elements. The proposed method uses a novel and flexible technique to estimate source origin locations from the possible scattering locations, using the TOF information. Evaluations were based on a Monte-Carlo simulation of uniform and non-uniform phantoms at different resolutions of time and detector energy. The results show that although the energy uncertainties deteriorate the image spatial resolution in the proposed method, the time resolution has more impact on image quality than the energy resolution. With progress of the TOF system, the reconstruction using the scattered data can be used in a complementary manner, or to improve image quality in the next generation of PET systems.

SU-E-T-489: Quantum versus Classical Trajectory Monte Carlo Simulations of Low Energy Electron Transport.

PubMed

Thomson, R; Kawrakow, I

2012-06-01

Widely-used classical trajectory Monte Carlo simulations of low energy electron transport neglect the quantum nature of electrons; however, at sub-1 keV energies quantum effects have the potential to become significant. This work compares quantum and classical simulations within a simplified model of electron transport in water. Electron transport is modeled in water droplets using quantum mechanical (QM) and classical trajectory Monte Carlo (MC) methods. Water droplets are modeled as collections of point scatterers representing water molecules from which electrons may be isotropically scattered. The role of inelastic scattering is investigated by introducing absorption. QM calculations involve numerically solving a system of coupled equations for the electron wavefield incident on each scatterer. A minimum distance between scatterers is introduced to approximate structured water. The average QM water droplet incoherent cross section is compared with the MC cross section; a relative error (RE) on the MC results is computed. RE varies with electron energy, average and minimum distances between scatterers, and scattering amplitude. The mean free path is generally the relevant length scale for estimating RE. The introduction of a minimum distance between scatterers increases RE substantially (factors of 5 to 10), suggesting that the structure of water must be modeled for accurate simulations. Inelastic scattering does not improve agreement between QM and MC simulations: for the same magnitude of elastic scattering, the introduction of inelastic scattering increases RE. Droplet cross sections are sensitive to droplet size and shape; considerable variations in RE are observed with changing droplet size and shape. At sub-1 keV energies, quantum effects may become non-negligible for electron transport in condensed media. Electron transport is strongly affected by the structure of the medium. Inelastic scatter does not improve agreement between QM and MC simulations of low energy electron transport in condensed media. © 2012 American Association of Physicists in Medicine.

Ultra-high-resolution inelastic X-ray scattering at high-repetition-rate self-seeded X-ray free-electron lasers

PubMed Central

Chubar, Oleg; Geloni, Gianluca; Kocharyan, Vitali; Madsen, Anders; Saldin, Evgeni; Serkez, Svitozar; Shvyd’ko, Yuri; Sutter, John

2016-01-01

Inelastic X-ray scattering (IXS) is an important tool for studies of equilibrium dynamics in condensed matter. A new spectrometer recently proposed for ultra-high-resolution IXS (UHRIX) has achieved 0.6 meV and 0.25 nm−1 spectral and momentum-transfer resolutions, respectively. However, further improvements down to 0.1 meV and 0.02 nm−1 are required to close the gap in energy–momentum space between high- and low-frequency probes. It is shown that this goal can be achieved by further optimizing the X-ray optics and by increasing the spectral flux of the incident X-ray pulses. UHRIX performs best at energies from 5 to 10 keV, where a combination of self-seeding and undulator tapering at the SASE-2 beamline of the European XFEL promises up to a 100-fold increase in average spectral flux compared with nominal SASE pulses at saturation, or three orders of magnitude more than what is possible with storage-ring-based radiation sources. Wave-optics calculations show that about 7 × 1012 photons s−1 in a 90 µeV bandwidth can be achieved on the sample. This will provide unique new possibilities for dynamics studies by IXS. PMID:26917127

Using triple gamma coincidences with a pixelated semiconductor Compton-PET scanner: a simulation study

NASA Astrophysics Data System (ADS)

Kolstein, M.; Chmeissani, M.

2016-01-01

The Voxel Imaging PET (VIP) Pathfinder project presents a novel design using pixelated semiconductor detectors for nuclear medicine applications to achieve the intrinsic image quality limits set by physics. The conceptual design can be extended to a Compton gamma camera. The use of a pixelated CdTe detector with voxel sizes of 1 × 1 × 2 mm3 guarantees optimal energy and spatial resolution. However, the limited time resolution of semiconductor detectors makes it impossible to use Time Of Flight (TOF) with VIP PET. TOF is used in order to improve the signal to noise ratio (SNR) by using only the most probable portion of the Line-Of-Response (LOR) instead of its entire length. To overcome the limitation of CdTe time resolution, we present in this article a simulation study using β+-γ emitting isotopes with a Compton-PET scanner. When the β+ annihilates with an electron it produces two gammas which produce a LOR in the PET scanner, while the additional gamma, when scattered in the scatter detector, provides a Compton cone that intersects with the aforementioned LOR. The intersection indicates, within a few mm of uncertainty along the LOR, the origin of the beta-gamma decay. Hence, one can limit the part of the LOR used by the image reconstruction algorithm.

Ultra-high-resolution inelastic X-ray scattering at high-repetition-rate self-seeded X-ray free-electron lasers

DOE PAGES

Chubar, Oleg; Geloni, Gianluca; Kocharyan, Vitali; ...

2016-03-01

Inelastic X-ray scattering (IXS) is an important tool for studies of equilibrium dynamics in condensed matter. A new spectrometer recently proposed for ultra-high-resolution IXS (UHRIX) has achieved 0.6 meV and 0.25 nm ₋1spectral and momentum-transfer resolutions, respectively. However, further improvements down to 0.1 meV and 0.02 nm ₋1are required to close the gap in energy–momentum space between high- and low-frequency probes. It is shown that this goal can be achieved by further optimizing the X-ray optics and by increasing the spectral flux of the incident X-ray pulses. UHRIX performs best at energies from 5 to 10 keV, where a combinationmore » of self-seeding and undulator tapering at the SASE-2 beamline of the European XFEL promises up to a 100-fold increase in average spectral flux compared with nominal SASE pulses at saturation, or three orders of magnitude more than what is possible with storage-ring-based radiation sources. Wave-optics calculations show that about 7 × 10 12 photons s ₋1in a 90 µeV bandwidth can be achieved on the sample. Ultimately, this will provide unique new possibilities for dynamics studies by IXS.« less

Effect of electron-electron scattering on the conductance of a quantum wire studied with the Boltzman transport equation

NASA Astrophysics Data System (ADS)

Lyo, S. K.; Huang, Danhong

2006-05-01

Electron-electron scattering conserves total momentum and does not dissipate momentum directly in a low-density system where the umklapp process is forbidden. However, it can still affect the conductance through the energy relaxation of the electrons. We show here that this effect can be studied with arbitrary accuracy in a multisublevel one-dimensional (1D) single quantum wire system in the presence of roughness and phonon scattering using a formally exact solution of the Boltzmann transport equation. The intrasubband electron-electron scattering is found to yield no net effect on the transport of electrons in 1D with only one sublevel occupied. For a system with a multilevel occupation, however, we find a significant effect of intersublevel electron-electron scattering on the temperature and density dependence of the resistance at low temperatures.

Polarizable atomic multipole X-ray refinement: application to peptide crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schnieders, Michael J.; Fenn, Timothy D.; Howard Hughes Medical Institute

2009-09-01

A method to accelerate the computation of structure factors from an electron density described by anisotropic and aspherical atomic form factors via fast Fourier transformation is described for the first time. Recent advances in computational chemistry have produced force fields based on a polarizable atomic multipole description of biomolecular electrostatics. In this work, the Atomic Multipole Optimized Energetics for Biomolecular Applications (AMOEBA) force field is applied to restrained refinement of molecular models against X-ray diffraction data from peptide crystals. A new formalism is also developed to compute anisotropic and aspherical structure factors using fast Fourier transformation (FFT) of Cartesian Gaussianmore » multipoles. Relative to direct summation, the FFT approach can give a speedup of more than an order of magnitude for aspherical refinement of ultrahigh-resolution data sets. Use of a sublattice formalism makes the method highly parallelizable. Application of the Cartesian Gaussian multipole scattering model to a series of four peptide crystals using multipole coefficients from the AMOEBA force field demonstrates that AMOEBA systematically underestimates electron density at bond centers. For the trigonal and tetrahedral bonding geometries common in organic chemistry, an atomic multipole expansion through hexadecapole order is required to explain bond electron density. Alternatively, the addition of interatomic scattering (IAS) sites to the AMOEBA-based density captured bonding effects with fewer parameters. For a series of four peptide crystals, the AMOEBA–IAS model lowered R{sub free} by 20–40% relative to the original spherically symmetric scattering model.« less

Modeling silicon diode energy response factors for use in therapeutic photon beams.

PubMed

Eklund, Karin; Ahnesjö, Anders

2009-10-21

Silicon diodes have good spatial resolution, which makes them advantageous over ionization chambers for dosimetry in fields with high dose gradients. However, silicon diodes overrespond to low-energy photons, that are more abundant in scatter which increase with large fields and larger depths. We present a cavity-theory-based model for a general response function for silicon detectors at arbitrary positions within photon fields. The model uses photon and electron spectra calculated from fluence pencil kernels. The incident photons are treated according to their energy through a bipartition of the primary beam photon spectrum into low- and high-energy components. Primary electrons from the high-energy component are treated according to Spencer-Attix cavity theory. Low-energy primary photons together with all scattered photons are treated according to large cavity theory supplemented with an energy-dependent factor K(E) to compensate for energy variations in the electron equilibrium. The depth variation of the response for an unshielded silicon detector has been calculated for 5 x 5 cm(2), 10 x 10 cm(2) and 20 x 20 cm(2) fields in 6 and 15 MV beams and compared with measurements showing that our model calculates response factors with deviations less than 0.6%. An alternative method is also proposed, where we show that one can use a correlation with the scatter factor to determine the detector response of silicon diodes with an error of less than 3% in 6 MV and 15 MV photon beams.

Rapid automated superposition of shapes and macromolecular models using spherical harmonics.

PubMed

Konarev, Petr V; Petoukhov, Maxim V; Svergun, Dmitri I

2016-06-01

A rapid algorithm to superimpose macromolecular models in Fourier space is proposed and implemented ( SUPALM ). The method uses a normalized integrated cross-term of the scattering amplitudes as a proximity measure between two three-dimensional objects. The reciprocal-space algorithm allows for direct matching of heterogeneous objects including high- and low-resolution models represented by atomic coordinates, beads or dummy residue chains as well as electron microscopy density maps and inhomogeneous multi-phase models ( e.g. of protein-nucleic acid complexes). Using spherical harmonics for the computation of the amplitudes, the method is up to an order of magnitude faster than the real-space algorithm implemented in SUPCOMB by Kozin & Svergun [ J. Appl. Cryst. (2001 ▸), 34 , 33-41]. The utility of the new method is demonstrated in a number of test cases and compared with the results of SUPCOMB . The spherical harmonics algorithm is best suited for low-resolution shape models, e.g . those provided by solution scattering experiments, but also facilitates a rapid cross-validation against structural models obtained by other methods.

Nano-structure of the laminin γ-1 short arm reveals an extended and curved multidomain assembly.

PubMed

Patel, Trushar R; Morris, Gordon A; Zwolanek, Daniela; Keene, Douglas R; Li, Jianhua; Harding, Stephen E; Koch, Manuel; Stetefeld, Jörg

2010-09-01

Laminins are multidomain glycoproteins that play important roles in development and maintenance of the extracellular matrix via their numerous interactions with other proteins. Several receptors for the laminin short arms revealed their importance in network formation and intercellular signaling. However, both the detailed structure of the laminin γ-1 short arm and its organization within the complexes is poorly understood due to the complexity of the molecule and the lack of a high-resolution structure. The presented data provide the first subatomic resolution structure for the laminin γ-1 short arm in solution. This was achieved using an integrated approach that combined a number of complementary biophysical techniques such as small angle X-ray scattering (SAXS), analytical ultracentrifugation, dynamic light scattering and electron microscopy. As a result of this study, we have obtained a significantly improved model for the laminin γ-1 short arm that represents a major step forward in molecular understanding of laminin-mediated complex formations. Crown Copyright © 2010. Published by Elsevier B.V. All rights reserved.

Visualizing redox orbitals and their potentials in advanced lithium-ion battery materials using high-resolution x-ray Compton scattering

DOE PAGES

Hafiz, Hasnain; Suzuki, Kosuke; Barbiellini, Bernardo; ...

2017-08-02

Reduction-oxidation (redox) reactions are the key processes that underlie the batteries powering smartphones, laptops, and electric cars. A redox process involves transfer of electrons between two species. For example, in a lithium-ion battery, current is generated when conduction electrons from the lithium anode are transferred to the redox orbitals of the cathode material. The ability to visualize or image the redox orbitals and how these orbitals evolve under lithiation and delithiation processes is thus of great fundamental and practical interest for understanding the workings of battery materials. In this study, we show that inelastic scattering spectroscopy using high-energy x-ray photonsmore » (Compton scattering) can yield faithful momentum space images of the redox orbitals by considering lithium iron phosphate (LiFePO 4 or LFP) as an exemplar cathode battery material. Our analysis reveals a new link between voltage and the localization of transition metal 3d orbitals and provides insight into the puzzling mechanism of potential shift and how it is connected to the modification of the bond between the transition metal and oxygen atoms. Our study thus opens a novel spectroscopic pathway for improving the performance of battery materials.« less

Visualizing redox orbitals and their potentials in advanced lithium-ion battery materials using high-resolution x-ray Compton scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hafiz, Hasnain; Suzuki, Kosuke; Barbiellini, Bernardo

Reduction-oxidation (redox) reactions are the key processes that underlie the batteries powering smartphones, laptops, and electric cars. A redox process involves transfer of electrons between two species. For example, in a lithium-ion battery, current is generated when conduction electrons from the lithium anode are transferred to the redox orbitals of the cathode material. The ability to visualize or image the redox orbitals and how these orbitals evolve under lithiation and delithiation processes is thus of great fundamental and practical interest for understanding the workings of battery materials. In this study, we show that inelastic scattering spectroscopy using high-energy x-ray photonsmore » (Compton scattering) can yield faithful momentum space images of the redox orbitals by considering lithium iron phosphate (LiFePO 4 or LFP) as an exemplar cathode battery material. Our analysis reveals a new link between voltage and the localization of transition metal 3d orbitals and provides insight into the puzzling mechanism of potential shift and how it is connected to the modification of the bond between the transition metal and oxygen atoms. Our study thus opens a novel spectroscopic pathway for improving the performance of battery materials.« less

Interplay Between Electron-Electron, Electron-Impurity and Electron-Boundary Scattering in a Two Dimensional Electron Gas (2DEG)

NASA Astrophysics Data System (ADS)

Abraham, Mathew C.; Ram, Rajeev J.; Gossard, A. C.

2003-03-01

A small group of experiments have been conducted over the past decade that explore the fact that even though electron-electron (e-e) scattering in a 2DEG is momentum conserving, its interplay with electron-impurity (e-i)and electron-boundary (e-b) scattering can change the resistance of bulk and mesoscopic devices respectively. The interplay between e-e and e-i scattering in a bulk sample has been shown to cause a fall in the resistivity as a function of electron temperature in the regime where the scattering length l_ee > l_ei and a rise when l_ee < l_ei. In contrast, the interplay between e-e and e-b scattering has been demonstrated to raise the resistivity of a mesoscopic sized wire as a function of electron temperature in the regime l_ee > lb and a fall when l_ee < l_b. We attempt to present a comprehensive picture of these two apparently competing effects by studying devices that are affected by both phenomena simultaneously.

Femtosecond time-resolved MeV electron diffraction

DOE PAGES

Zhu, Pengfei; Zhu, Y.; Hidaka, Y.; ...

2015-06-02

We report the experimental demonstration of femtosecond electron diffraction using high-brightness MeV electron beams. High-quality, single-shot electron diffraction patterns for both polycrystalline aluminum and single-crystal 1T-TaS 2 are obtained utilizing a 5 fC (~3 × 10 4 electrons) pulse of electrons at 2.8 MeV. The high quality of the electron diffraction patterns confirms that electron beam has a normalized emittance of ~50 nm rad. The transverse and longitudinal coherence length is ~11 and ~2.5 nm, respectively. The timing jitter between the pump laser and probe electron beam was found to be ~100 fs (rms). The temporal resolution is demonstrated bymore » observing the evolution of Bragg and superlattice peaks of 1T-TaS 2 following an 800 nm optical pump and was found to be 130 fs. Lastly, our results demonstrate the advantages of MeV electrons, including large elastic differential scattering cross-section and access to high-order reflections, and the feasibility of ultimately realizing below 10 fs time-resolved electron diffraction.« less

The Research Laboratory of Electronics Progress Report Number 136, 1 January-31 December 1993

DTIC Science & Technology

1994-06-01

beating of the pump and probe electric fields scatter cases, we have determined that the coherent pump light backwards into the probe direction with...and resolution, resultant beat frequency between the signal and the39th upper sideband of the comb was detected by a 1-GHz photodetector. We have...varies linearly with the modes and, as seen in the figure, no lock-in is applied rotation rate, hence is 90 degrees out-of- observed in the beat

Dynamical diffraction imaging (topography) with X-ray synchrotron radiation

NASA Technical Reports Server (NTRS)

Kuriyama, M.; Steiner, B. W.; Dobbyn, R. C.

1989-01-01

By contrast to electron microscopy, which yields information on the location of features in small regions of materials, X-ray diffraction imaging can portray minute deviations from perfect crystalline order over larger areas. Synchrotron radiation-based X-ray optics technology uses a highly parallel incident beam to eliminate ambiguities in the interpretation of image details; scattering phenomena previously unobserved are now readily detected. Synchrotron diffraction imaging renders high-resolution, real-time, in situ observations of materials under pertinent environmental conditions possible.

Static and Dynamic Electron Microscopy Investigations at the Atomic and Ultrafast Scales

NASA Astrophysics Data System (ADS)

Suri, Pranav Kumar

Advancements in the electron microscopy capabilities - aberration-corrected imaging, monochromatic spectroscopy, direct-electron detectors - have enabled routine visualization of atomic-scale processes with millisecond temporal resolutions in this decade. This, combined with progress in the transmission electron microscopy (TEM) specimen holder technology and nanofabrication techniques, allows comprehensive experiments on a wide range of materials in various phases via in situ methods. The development of ultrafast (sub-nanosecond) time-resolved TEM with ultrafast electron microscopy (UEM) has further pushed the envelope of in situ TEM to sub-nanosecond temporal resolution while maintaining sub-nanometer spatial resolution. A plethora of materials phenomena - including electron-phonon coupling, phonon transport, first-order phase transitions, bond rotation, plasmon dynamics, melting, and dopant atoms arrangement - are not yet clearly understood and could be benefitted with the current in situ TEM capabilities having atomic-level and ultrafast precision. Better understanding of these phenomena and intrinsic material dynamics (e.g. how phonons propagate in a material, what time-scales are involved in a first-order phase transition, how fast a material melts, where dopant atoms sit in a crystal) in new-generation and technologically important materials (e.g. two-dimensional layered materials, semiconductor and magnetic devices, rare-earth-element-free permanent magnets, unconventional superconductors) could bring a paradigm shift in their electronic, structural, magnetic, thermal and optical applications. Present research efforts, employing cutting-edge static and dynamic in situ electron microscopy resources at the University of Minnesota, are directed towards understanding the atomic-scale crystallographic structural transition and phonon transport in an iron-pnictide parent compound LaFeAsO, studying the mechanical stability of fast moving hard-drive heads in heat-assisted magnetic recording (HAMR) technology, exploring the possibility of ductile ceramics in magnesium oxide (MgO) nanomaterials, and revealing the atomic-structure of newly discovered rare-earth-element-free iron nitride (FeN) magnetic materials. Via atomic-resolution imaging and electron diffraction coupled with in situ TEM cooling on LaFeAsO, it was found that additional effects not related to the structural transition, namely dynamical scattering and electron channeling, can give signatures reminiscent of those typically associated with the symmetry change. UEM studies on LaFeAsO revealed direct, real-space imaging of the emergence and evolution of acoustic phonons and resolved dispersion behavior during propagation and scattering. Via UEM bright-field imaging, megahertz vibrational frequencies were observed upon laser-illumination in TEM specimens made out of HAMR devices which could be detrimental to their long-term thermal and structural reliability. Compression testing of 100-350 nm single-crystal MgO nanocubes shows size-dependent stresses and engineering strains of 4-13.8 GPa and 0.046-0.221 respectively at the first signs of yield accompanied by an absence of brittle fracture, which is a significant increase in plasticity of a brittle ceramic material. Atomic-scale characterization of FeN phases show that it is possible to detect interstitial locations of low atomic-number nitrogen atoms in iron crystal and hints at a development of novel routes (without involving rare-earth elements) for bulk permanent magnet synthesis.

Genuine binding energy of the hydrated electron

PubMed Central

Luckhaus, David; Yamamoto, Yo-ichi; Suzuki, Toshinori; Signorell, Ruth

2017-01-01

The unknown influence of inelastic and elastic scattering of slow electrons in water has made it difficult to clarify the role of the solvated electron in radiation chemistry and biology. We combine accurate scattering simulations with experimental photoemission spectroscopy of the hydrated electron in a liquid water microjet, with the aim of resolving ambiguities regarding the influence of electron scattering on binding energy spectra, photoelectron angular distributions, and probing depths. The scattering parameters used in the simulations are retrieved from independent photoemission experiments of water droplets. For the ground-state hydrated electron, we report genuine values devoid of scattering contributions for the vertical binding energy and the anisotropy parameter of 3.7 ± 0.1 eV and 0.6 ± 0.2, respectively. Our probing depths suggest that even vacuum ultraviolet probing is not particularly surface-selective. Our work demonstrates the importance of quantitative scattering simulations for a detailed analysis of key properties of the hydrated electron. PMID:28508051

The role of polarization coulomb field scattering in the electron mobility of AlGaN/AlN/GaN heterostructure field-effect transistors

NASA Astrophysics Data System (ADS)

Liu, Yan; Lin, Zhaojun; Zhao, Jingtao; Yang, Ming; Shi, Wenjing; Lv, Yuanjie; Feng, Zhihong

2016-04-01

The electron mobility for the prepared AlGaN/AlN/GaN heterostructure field-effect transistor (HFET) with the ratio of the gate length to the drain-to-source distance being less than 1/2 has been studied by comparing the measured electron mobility with the theoretical value. The measured electron mobility is derived from the measured capacitance-voltage (C-V) and current-voltage (I-V) characteristics, and the theoretical mobility is determined by using Matthiessen's law, involving six kinds of important scattering mechanisms. For the prepared device at room temperature, longitudinal optical phonon scattering (LO scattering) was found to have a remarkable effect on the value of the electron mobility, and polarization Coulomb field scattering (PCF scattering ) was found to be important to the changing trend of the electron mobility versus the two-dimensional electron gas (2DEG) density.

Preliminary frequency-domain analysis for the reconstructed spatial resolution of muon tomography

NASA Astrophysics Data System (ADS)

Yu, B.; Zhao, Z.; Wang, X.; Wang, Y.; Wu, D.; Zeng, Z.; Zeng, M.; Yi, H.; Luo, Z.; Yue, X.; Cheng, J.

2014-11-01

Muon tomography is an advanced technology to non-destructively detect high atomic number materials. It exploits the multiple Coulomb scattering information of muon to reconstruct the scattering density image of the traversed object. Because of the statistics of muon scattering, the measurement error of system and the data incompleteness, the reconstruction is always accompanied with a certain level of interference, which will influence the reconstructed spatial resolution. While statistical noises can be reduced by extending the measuring time, system parameters determine the ultimate spatial resolution that one system can reach. In this paper, an effective frequency-domain model is proposed to analyze the reconstructed spatial resolution of muon tomography. The proposed method modifies the resolution analysis in conventional computed tomography (CT) to fit the different imaging mechanism in muon scattering tomography. The measured scattering information is described in frequency domain, then a relationship between the measurements and the original image is proposed in Fourier domain, which is named as "Muon Central Slice Theorem". Furthermore, a preliminary analytical expression of the ultimate reconstructed spatial is derived, and the simulations are performed for validation. While the method is able to predict the ultimate spatial resolution of a given system, it can also be utilized for the optimization of system design and construction.

Room scatter effects in Total Skin Electron Irradiation: Monte Carlo simulation study.

PubMed

Nevelsky, Alexander; Borzov, Egor; Daniel, Shahar; Bar-Deroma, Raquel

2017-01-01

Total Skin Electron Irradiation (TSEI) is a complex technique which usually involves the use of large electron fields and the dual-field approach. In this situation, many electrons scattered from the treatment room floor are produced. However, no investigations of the effect of scattered electrons in TSEI treatments have been reported. The purpose of this work was to study the contribution of floor scattered electrons to skin dose during TSEI treatment using Monte Carlo (MC) simulations. All MC simulations were performed with the EGSnrc code. Influence of beam energy, dual-field angle, and floor material on the contribution of floor scatter was investigated. Spectrum of the scattered electrons was calculated. Measurements of dose profile were performed in order to verify MC calculations. Floor scatter dependency on the floor material was observed (at 20 cm from the floor, scatter contribution was about 21%, 18%, 15%, and 12% for iron, concrete, PVC, and water, respectively). Although total dose profiles exhibited slight variation as functions of beam energy and dual-field angle, no dependence of the floor scatter contribution on the beam energy or dual-field angle was found. The spectrum of the scattered electrons was almost uniform between a few hundred KeV to 4 MeV, and then decreased linearly to 6 MeV. For the TSEI technique, dose contribution due to the electrons scattered from the room floor may be clinically significant and should be taken into account during design and commissioning phases. MC calculations can be used for this task. © 2017 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.

HEPD on NEXTSat-1: A High Energy Particle Detector for Measurements of Precipitating Radiation Belt Electrons

NASA Astrophysics Data System (ADS)

Sohn, Jongdae; Lee, Jaejin; Min, Kyoungwook; Lee, Junchan; Lee, Seunguk; Lee, Daeyoung; Jo, Gyeongbok; Yi, Yu; Na, Gowoon; Kang, Kyung-In; Shin, Goo-Hwan

2018-05-01

Radiation belt particles of the inner magnetosphere precipitate into the atmosphere in the subauroral regions when they are pitch-angle scattered into the loss cone by wave-particle interactions. Such particle precipitations are known to be especially enhanced during space storms, though they can also occur during quiet times. The observed characteristics of precipitating electrons can be distinctively different, in their time series as well as in their spectra, depending on the waves involved. The present paper describes the High Energy Particle Detector (HEPD) on board the Next Generation Small Satellite-1 (NEXTSat-1), which will measure these radiation belt electrons from a low-Earth polar orbit satellite to study the mechanisms related to electron precipitation in the sub-auroral regions. The HEPD is based on silicon barrier detectors and consists of three telescopes that are mounted on the satellite to have angles of 0°. 45°, and 90°, respectively with the local geomagnetic field during observations. With a high time resolution of 32 Hz and a high spectral resolution of 11 channels over the energy range from 350 keV to 2 MeV, together with the pitch angle information provided by the three telescopes, HEPD is capable of identifying physical processes, such as microbursts and dust-side relativistic electron precipitation (DREP) events associated with electron precipitations. NextSat-1 is scheduled for launch in early 2018.

Environmental transmission electron microscopy for catalyst materials using a spherical aberration corrector.

PubMed

Takeda, Seiji; Kuwauchi, Yasufumi; Yoshida, Hideto

2015-04-01

Atomic resolution has been obtained using environmental transmission electron microscopy (ETEM) by installing a spherical aberration corrector (Cs-corrector) on the objective lens. Simultaneously, the technology for controlling the environment around a specimen in ETEM has advanced significantly in the past decade. Quantification methodology has recently been established for deriving relevant experimental data in catalyst materials from substantial and systematic ETEM observation at the atomic scale. With this background, this paper summarizes aspects of the evolutional microscopy technique: necessary conditions for atomic resolution in ETEM; reduction of the scattering of electrons by the medium surrounding a specimen; and an environmental cell for structural imaging of a crystalline specimen. The high spatial resolution of a Cs-corrected ETEM is demonstrated for different observation conditions. After statistical analysis combined with numerical image analysis of ETEM data is briefly described, the recent applications of the Cs-corrected ETEM to catalyst materials are reviewed. For gold nanoparticulate catalysts, the structural information on the reaction sites and adsorption sites are deduced. For Pt nanoparticulate catalysts, ETEM studies elucidate the correlation between the catalytic activity and the morphology of the nanoparticles. These studies also reveal oxidation and reduction on the topmost Pt surface layer at the atomic scale. Finally, current issues and the future perspectives of Cs-corrected ETEM are summarized, including the reproducibility of ETEM observation data, the control of environments, the critical evaluation of electron irradiation effects, the full implementation of transmission electron microscopy technology in ETEM, and the safety issues for an ETEM laboratory. Copyright © 2014 Elsevier B.V. All rights reserved.

First results from the Magnetospheric Multiscale mission

NASA Astrophysics Data System (ADS)

Lavraud, B.

2017-12-01

Since its launch in March 2015, NASA's Magnetospheric Multiscale mission (MMS) provides a wealth of unprecedented high resolution measurements of space plasma properties and dynamics in the near-Earth environment. MMS was designed in the first place to study the fundamental process of collision-less magnetic reconnection. The two first results reviewed here pertain to this topic and highlight how the extremely high resolution MMS data (electrons, in particular, with full three dimensional measurements at 30 ms in burst mode) have permitted to tackle electron dynamics in unprecedented details. The first result demonstrates how electrons become demagnetized and scattered near the magnetic reconnection X line as a result of increased magnetic field curvature, together with a decrease in its magnitude. The second result demonstrates that electrons form crescent-shaped, agyrotropic distribution functions very near the X line, suggestive of the existence of a perpendicular current aligned with the local electric field and consistent with the energy conversion expected in magnetic reconnection (such that J\\cdot E > 0). Aside from magnetic reconnection, we show how MMS contributes to topics such as wave properties and their interaction with particles. Thanks again to extremely high resolution measurements, the lossless and periodical energy exchange between wave electromagnetic fields and particles, as expected in the case of kinetic Alfvén waves, was confirmed. Although not discussed, MMS has the potential to solve many other outstanding issues in collision-less plasma physics, for example regarding shock or turbulence acceleration, with obvious broader impacts in astrophysics in general.

Assembly of Ring-Shaped Phosphorus within Carbon Nanotube Nanoreactors.

PubMed

Zhang, Jinying; Zhao, Dan; Xiao, Dingbin; Ma, Chuansheng; Du, Hongchu; Li, Xin; Zhang, Lihui; Huang, Jialiang; Huang, Hongyang; Jia, Chun-Lin; Tománek, David; Niu, Chunming

2017-02-06

A phosphorus allotrope that has not been observed so far, ring-shaped phosphorus consisting of alternate P 8 and P 2 structural units, has been assembled inside multi-walled carbon nanotube nanoreactors with inner diameters of 5-8 nm by a chemical vapor transport and reaction of red phosphorus at 500 °C. The ring-shaped nanostructures with surrounding graphene walls are stable under ambient conditions. The nanostructures were characterized by high-resolution transmission electron microscopy, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, Raman scattering, attenuated total reflectance Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Whistler Waves Driven by Anisotropic Strahl Velocity Distributions: Cluster Observations

NASA Technical Reports Server (NTRS)

Vinas, A.F.; Gurgiolo, C.; Nieves-Chinchilla, T.; Gary, S. P.; Goldstein, M. L.

2010-01-01

Observed properties of the strahl using high resolution 3D electron velocity distribution data obtained from the Cluster/PEACE experiment are used to investigate its linear stability. An automated method to isolate the strahl is used to allow its moments to be computed independent of the solar wind core+halo. Results show that the strahl can have a high temperature anisotropy (T(perpindicular)/T(parallell) approximately > 2). This anisotropy is shown to be an important free energy source for the excitation of high frequency whistler waves. The analysis suggests that the resultant whistler waves are strong enough to regulate the electron velocity distributions in the solar wind through pitch-angle scattering

Electron-impact excitation of the low-lying electronic states of HCN

NASA Technical Reports Server (NTRS)

Chutjian, A.; Tanaka, H.; Srivastava, S. K.; Wicke, B. G.

1977-01-01

The first study of the low-energy electron-impact excitation of low-lying electronic transitions in the HCN molecule is reported. Measurements were made at incident electron energies of 11.6 and 21.6 eV in the energy-loss range of 3-10 eV, and at scattering angles of 20-130 deg. Inelastic scattering spectra were placed on the absolute cross-section scale by determining first the ratio of inelastic-to-elastic scattering cross sections, and then separately measuring the absolute elastic scattering cross section. Several new electronic transitions are observed which are intrinsically overlapped in the molecule itself. Assignments of these electronic transitions are suggested. These assignments are based on present spectroscopic and cross-sections measurements, high-energy electron scattering spectra, optical absorption spectra, and ab initio molecular orbital calculations.

Doppler Broadening and its Contribution to Compton Energy-Absorption Cross Sections: An Analysis of the Compton Component in Terms of Mass-Energy Absorption Coefficient

NASA Astrophysics Data System (ADS)

Rao, D. V.; Takeda, T.; Itai, Y.; Akatsuka, T.; Cesareo, R.; Brunetti, A.; Gigante, G. E.

2002-09-01

Compton energy absorption cross sections are calculated using the formulas based on a relativistic impulse approximation to assess the contribution of Doppler broadening and to examine the Compton profile literature and explore what, if any, effect our knowledge of this line broadening has on the Compton component in terms of mass-energy absorption coefficient. Compton energy-absorption cross sections are evaluated for all elements, Z=1-100, and for photon energies 1 keV-100 MeV. Using these cross sections, the Compton component of the mass-energy absorption coefficient is derived in the energy region from 1 keV to 1 MeV for all the elements Z=1-100. The electron momentum prior to the scattering event should cause a Doppler broadening of the Compton line. The momentum resolution function is evaluated in terms of incident and scattered photon energy and scattering angle. The overall momentum resolution of each contribution is estimated for x-ray and γ-ray energies of experimental interest in the angular region 1°-180°. Also estimated is the Compton broadening using nonrelativistic formula in the angular region 1°-180°, for 17.44, 22.1, 58.83, and 60 keV photons for a few elements (H, C, N, O, P, S, K, and Ca) of biological importance.

Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses

PubMed Central

Canton, Sophie E.; Kjær, Kasper S.; Vankó, György; van Driel, Tim B.; Adachi, Shin-ichi; Bordage, Amélie; Bressler, Christian; Chabera, Pavel; Christensen, Morten; Dohn, Asmus O.; Galler, Andreas; Gawelda, Wojciech; Gosztola, David; Haldrup, Kristoffer; Harlang, Tobias; Liu, Yizhu; Møller, Klaus B.; Németh, Zoltán; Nozawa, Shunsuke; Pápai, Mátyás; Sato, Tokushi; Sato, Takahiro; Suarez-Alcantara, Karina; Togashi, Tadashi; Tono, Kensuke; Uhlig, Jens; Vithanage, Dimali A.; Wärnmark, Kenneth; Yabashi, Makina; Zhang, Jianxin; Sundström, Villy; Nielsen, Martin M.

2015-01-01

Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectroscopy with ultrafast X-ray emission spectroscopy and diffuse X-ray scattering at the SACLA facility to track the non-equilibrated electronic and structural dynamics within a bimetallic donor–acceptor complex that contains an optically dark centre. Exploiting the 100-fold increase in temporal resolution as compared with storage ring facilities, these measurements constitute the first X-ray-based visualization of a non-equilibrated intramolecular electron transfer process over large interatomic distances. Experimental and theoretical results establish that mediation through electronically excited molecular states is a key mechanistic feature. The present study demonstrates the extensive potential of femtosecond X-ray techniques as diagnostics of non-adiabatic electron transfer processes in synthetic and biological systems, and some directions for future studies, are outlined. PMID:25727920

Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses

DOE PAGES

Canton, Sophie E.; Kjær, Kasper S.; Vankó, György; ...

2015-03-02

Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectroscopy with ultrafast X-ray emission spectroscopy and diffuse X-ray scattering at the SACLA facility to track the non-equilibrated electronic and structural dynamics within a bimetallic donor–acceptor complex that contains an optically dark centre. Exploiting the 100-fold increase in temporal resolution as compared with storage ring facilities, these measurements constitute the first X-ray-based visualization of a non-equilibrated intramolecular electron transfer process over large interatomic distances.more » Thus experimental and theoretical results establish that mediation through electronically excited molecular states is a key mechanistic feature. The present study demonstrates the extensive potential of femtosecond X-ray techniques as diagnostics of non-adiabatic electron transfer processes in synthetic and biological systems, and some directions for future studies, are outlined.« less

Automatic energy calibration algorithm for an RBS setup

DOE Office of Scientific and Technical Information (OSTI.GOV)

Silva, Tiago F.; Moro, Marcos V.; Added, Nemitala

2013-05-06

This work describes a computer algorithm for automatic extraction of the energy calibration parameters from a Rutherford Back-Scattering Spectroscopy (RBS) spectrum. Parameters like the electronic gain, electronic offset and detection resolution (FWHM) of a RBS setup are usually determined using a standard sample. In our case, the standard sample comprises of a multi-elemental thin film made of a mixture of Ti-Al-Ta that is analyzed at the beginning of each run at defined beam energy. A computer program has been developed to extract automatically the calibration parameters from the spectrum of the standard sample. The code evaluates the first derivative ofmore » the energy spectrum, locates the trailing edges of the Al, Ti and Ta peaks and fits a first order polynomial for the energy-channel relation. The detection resolution is determined fitting the convolution of a pre-calculated theoretical spectrum. To test the code, data of two years have been analyzed and the results compared with the manual calculations done previously, obtaining good agreement.« less

Compact microwave imaging system to measure spatial distribution of plasma density

NASA Astrophysics Data System (ADS)

Ito, H.; Oba, R.; Yugami, N.; Nishida, Y.

2004-10-01

We have developed an advanced microwave interferometric system operating in the K band (18-27 GHz) with the use of a fan-shaped microwave based on a heterodyne detection system for measuring the spatial distribution of the plasma density. In order to make a simple, low-cost, and compact microwave interferometer with better spatial resolution, a microwave scattering technique by a microstrip antenna array is employed. Experimental results show that the imaging system with the microstrip antenna array can have finer spatial resolution than one with the diode antenna array and reconstruct a good spatially resolved image of the finite size dielectric phantoms placed between the horn antenna and the micro strip antenna array. The precise two-dimensional electron density distribution of the cylindrical plasma produced by an electron cyclotron resonance has been observed. As a result, the present imaging system is more suitable for a two- or three-dimensional display of the objects or stationary plasmas and it is possible to realize a compact microwave imaging system.

Method of incident low-energy gamma-ray direction reconstruction in the GAMMA-400 gamma-ray space telescope

NASA Astrophysics Data System (ADS)

Kheymits, M. D.; Leonov, A. A.; Zverev, V. G.; Galper, A. M.; Arkhangelskaya, I. V.; Arkhangelskiy, A. I.; Suchkov, S. I.; Topchiev, N. P.; Yurkin, Yu T.; Bakaldin, A. V.; Dalkarov, O. D.

2016-02-01

The GAMMA-400 gamma-ray space-based telescope has as its main goals to measure cosmic γ-ray fluxes and the electron-positron cosmic-ray component produced, theoretically, in dark-matter-particles decay or annihilation processes, to search for discrete γ-ray sources and study them in detail, to examine the energy spectra of diffuse γ-rays — both galactic and extragalactic — and to study gamma-ray bursts (GRBs) and γ-rays from the active Sun. Scientific goals of GAMMA-400 telescope require fine angular resolution. The telescope is of a pair-production type. In the converter-tracker, the incident gamma-ray photon converts into electron-positron pair in the tungsten layer and then the tracks are detected by silicon- strip position-sensitive detectors. Multiple scattering processes become a significant obstacle in the incident-gamma direction reconstruction for energies below several gigaelectronvolts. The method of utilising this process to improve the resolution is proposed in the presented work.

Enhanced light element imaging in atomic resolution scanning transmission electron microscopy.

PubMed

Findlay, S D; Kohno, Y; Cardamone, L A; Ikuhara, Y; Shibata, N

2014-01-01

We show that an imaging mode based on taking the difference between signals recorded from the bright field (forward scattering region) in atomic resolution scanning transmission electron microscopy provides an enhancement of the detectability of light elements over existing techniques. In some instances this is an enhancement of the visibility of the light element columns relative to heavy element columns. In all cases explored it is an enhancement in the signal-to-noise ratio of the image at the light column site. The image formation mechanisms are explained and the technique is compared with earlier approaches. Experimental data, supported by simulation, are presented for imaging the oxygen columns in LaAlO₃. Case studies looking at imaging hydrogen columns in YH₂ and lithium columns in Al₃Li are also explored through simulation, particularly with respect to the dependence on defocus, probe-forming aperture angle and detector collection aperture angles. © 2013 Elsevier B.V. All rights reserved.

Thermal response of the F region ionosphere in artificial modification experiments by HF radio waves

NASA Technical Reports Server (NTRS)

Mantas, G. P.; Lahoz, C. H.; Carlson, H. C., Jr.

1981-01-01

The thermal response of the nighttime F region ionosphere to local heating by HF radio waves has been observed with the incoherent scatter radar at Arecibo, Puerto Rico. The observations consist of high-resolution space and time variation of the electron temperature as a high-power HF transmitter is switched on and off with a period 240 s. As soon as the HF transmitter is turned on, the electron temperature begins to rise rapidly in a narrow altitude region near 300 km, below the F2 layer peak. The electron temperature perturbation subsequently spreads over a broader altitude region. The observations are compared with the anticipated thermal response of the ionosphere based on numerical solutions of the coupled time-dependent heat conduction equations for the electron and composite ion gases and are found to be in good agreement over the entire altitude region covered by the observations.

Plasma characterization using ultraviolet Thomson scattering from ion-acoustic and electron plasma waves (invited).

PubMed

Follett, R K; Delettrez, J A; Edgell, D H; Henchen, R J; Katz, J; Myatt, J F; Froula, D H

2016-11-01

Collective Thomson scattering is a technique for measuring the plasma conditions in laser-plasma experiments. Simultaneous measurements of ion-acoustic and electron plasma-wave spectra were obtained using a 263.25-nm Thomson-scattering probe beam. A fully reflective collection system was used to record light scattered from electron plasma waves at electron densities greater than 10 21 cm -3 , which produced scattering peaks near 200 nm. An accurate analysis of the experimental Thomson-scattering spectra required accounting for plasma gradients, instrument sensitivity, optical effects, and background radiation. Practical techniques for including these effects when fitting Thomson-scattering spectra are presented and applied to the measured spectra to show the improvements in plasma characterization.

Positronium collisions with atoms and molecules

NASA Astrophysics Data System (ADS)

Fabrikant, I. I.; Gribakin, G. F.; Wilde, R. S.

2017-11-01

We review recent theoretical efforts to explain observed similarities between electron-atom and positronium(Ps)-atom scattering which also extends to molecular targets. In the range of the projectile velocities above the threshold for Ps ionization (break-up) this similarity can be explained in terms of quasi-free electron scattering and impulse approximation. However, for lower Ps velocities more sophisticated methods should be developed. Our calculations of Ps scattering by heavy noble-gas atoms agree well with experiments at Ps velocities above the Ps ionization threshold. However, in contrast to electron scattering cross sections, at lower velocities they exhibit maxima whereas the experimental cross sections tend to decrease toward lower velocities indicating the same similarity with electron scattering cross section observed above the threshold. Our preliminary results for Ps-N2 scattering confirm experimental observation of a resonance similar to the ∏ g resonance in electron-N2 scattering.

High-resolution imaging gamma-ray spectroscopy with externally segmented germanium detectors

NASA Technical Reports Server (NTRS)

Callas, J. L.; Mahoney, W. A.; Varnell, L. S.; Wheaton, W. A.

1993-01-01

Externally segmented germanium detectors promise a breakthrough in gamma-ray imaging capabilities while retaining the superb energy resolution of germanium spectrometers. An angular resolution of 0.2 deg becomes practical by combining position-sensitive germanium detectors having a segment thickness of a few millimeters with a one-dimensional coded aperture located about a meter from the detectors. Correspondingly higher angular resolutions are possible with larger separations between the detectors and the coded aperture. Two-dimensional images can be obtained by rotating the instrument. Although the basic concept is similar to optical or X-ray coded-aperture imaging techniques, several complicating effects arise because of the penetrating nature of gamma rays. The complications include partial transmission through the coded aperture elements, Compton scattering in the germanium detectors, and high background count rates. Extensive electron-photon Monte Carlo modeling of a realistic detector/coded-aperture/collimator system has been performed. Results show that these complicating effects can be characterized and accounted for with no significant loss in instrument sensitivity.

Development of a Germanium Small-Animal SPECT System

NASA Astrophysics Data System (ADS)

Johnson, Lindsay C.; Ovchinnikov, Oleg; Shokouhi, Sepideh; Peterson, Todd E.

2015-10-01

Advances in fabrication techniques, electronics, and mechanical cooling systems have given rise to germanium detectors suitable for biomedical imaging. We are developing a small-animal SPECT system that uses a double-sided Ge strip detector. The detector's excellent energy resolution may help to reduce scatter and simplify processing of multi-isotope imaging, while its ability to measure depth of interaction has the potential to mitigate parallax error in pinhole imaging. The detector's energy resolution is <; 1% FWHM at 140 keV and its spatial resolution is approximately 1.5 mm FWHM. The prototype system described has a single-pinhole collimator with a 1-mm diameter and a 70-degree opening angle with a focal length variable between 4.5 and 9 cm. Phantom images from the gantry-mounted system are presented, including the NEMA NU-2008 phantom and a hot-rod phantom. Additionally, the benefit of energy resolution is demonstrated by imaging a dual-isotope phantom with 99mTc and 123I without cross-talk correction.

Electron-exchange and quantum screening effects on the Thomson scattering process in quantum Fermi plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Gyeong Won; Jung, Young-Dae; Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, New York 12180-3590

2013-06-15

The influence of the electron-exchange and quantum screening on the Thomson scattering process is investigated in degenerate quantum Fermi plasmas. The Thomson scattering cross section in quantum plasmas is obtained by the plasma dielectric function and fluctuation-dissipation theorem as a function of the electron-exchange parameter, Fermi energy, plasmon energy, and wave number. It is shown that the electron-exchange effect enhances the Thomson scattering cross section in quantum plasmas. It is also shown that the differential Thomson scattering cross section has a minimum at the scattering angle Θ=π/2. It is also found that the Thomson scattering cross section increases with anmore » increase of the Fermi energy. In addition, the Thomson scattering cross section is found to be decreased with increasing plasmon energy.« less

Electron density inversed by plasma lines induced by suprathermal electron in the ionospheric modification experiment

NASA Astrophysics Data System (ADS)

Wang, Xiang; Zhou, Chen

2018-05-01

Incoherent scatter radar (ISR) is the most powerful ground-based measurement facility to study the ionosphere. The plasma lines are not routinely detected by the incoherent scatter radar due to the low intensity, which falls below the measured spectral noise level of the incoherent scatter radar. The plasma lines are occasionally enhanced by suprathermal electrons through the Landau damping process and detectable to the incoherent scatter radar. In this study, by using the European Incoherent Scatter Association (EISCAT) UHF incoherent scatter radar, the experiment observation presents that the enhanced plasma lines were observed. These plasma lines were considered as manifest of the suprathermal electrons generated by the high-frequency heating wave during the ionospheric modification. The electron density profile is also obtained from the enhanced plasma lines. This study can be a promising technique for obtaining the accurate electron density during ionospheric modification experiment.

Monte Carlo calculation of large and small-angle electron scattering in air

NASA Astrophysics Data System (ADS)

Cohen, B. I.; Higginson, D. P.; Eng, C. D.; Farmer, W. A.; Friedman, A.; Grote, D. P.; Larson, D. J.

2017-11-01

A Monte Carlo method for angle scattering of electrons in air that accommodates the small-angle multiple scattering and larger-angle single scattering limits is introduced. The algorithm is designed for use in a particle-in-cell simulation of electron transport and electromagnetic wave effects in air. The method is illustrated in example calculations.

Tailored Rh surface facilitates, enhancement of Raman scattering in trimetallic AuPt core/Rh shell composites: Experimental and theoretical evidences

NASA Astrophysics Data System (ADS)

Loganathan, B.; Chandraboss, V. L.; Senthilvelan, S.; Karthikeyan, B.

2016-01-01

We present a detailed analysis of surface-enhanced Raman scattering of 7-azaindole and L-cysteine adsorbed on a tailored Rh surface by using experimental and density functional theoretical (DFT) calculations. DFT with the B3LYP/Lanl2DZ basis set was used for the optimization of the ground state geometries and simulation of the surface-enhanced Raman spectrum of probe molecules adsorbed on Rh6 cluster. 7-azaindole and L-cysteine adsorption at the shell interface was ascertained from first-principles. In addition, characterization of synthesized trimetallic AuPt core/Rh shell colloidal nanocomposites has been analyzed by UV-visible spectroscopy, high-resolution transmission and scanning electron microscopy, selected area electron diffraction pattern analysis, energy-dispersive X-ray spectroscopy, atomic force, confocal Raman microscopy, FT-Raman and surface-enhanced Raman spectroscopic analysis. This analysis serves as the first step in gaining an accurate understanding of specific interactions at the interface of organic and biomolecules and to gain knowledge on the surface composition of trimetallic Au/Pt/Rh colloidal nanocomposites.

Diagnosis of Acceleration, Reconnection, Turbulence, and Heating

NASA Astrophysics Data System (ADS)

Dufor, Mikal T.; Jemiolo, Andrew J.; Keesee, Amy; Cassak, Paul; Tu, Weichao; Scime, Earl E.

2017-10-01

The DARTH (Diagnosis of Acceleration, Reconnection, Turbulence, and Heating) experiment is an intermediate-scale, experimental facility designed to study magnetic reconnection at and below the kinetic scale of ions and electrons. The experiment will have non-perturbative diagnostics with high temporal and three-dimensional spatial resolution, giving it the capability to investigate kinetic-scale physics. Of specific scientific interest are particle acceleration, plasma heating, turbulence and energy dissipation during reconnection. Here we will describe the magnetic field system and the two plasma guns used to create flux ropes that then merge through magnetic reconnection. We will also describe the key diagnostic systems: laser induced fluorescence (LIF) for ion vdf measurements, a 300 GHz microwave scattering system for sub-mm wavelength fluctuation measurements and a Thomson scattering laser for electron vdf measurements. The vacuum chamber is designed to provide unparalleled access for these particle diagnostics. The scientific goals of DARTH are to examine particle acceleration and heating during, the role of three-dimensional instabilities during reconnection, how reconnection ceases, and the role of impurities and asymmetries in reconnection. This work was supported by the by the O'Brien Energy Research Fund.

Fluctuating Charge-Order in Optimally Doped Bi- 2212 Revealed by Momentum-resolved Electron Energy Loss Spectroscopy

NASA Astrophysics Data System (ADS)

Husain, Ali; Vig, Sean; Kogar, Anshul; Mishra, Vivek; Rak, Melinda; Mitrano, Matteo; Johnson, Peter; Gu, Genda; Fradkin, Eduardo; Norman, Michael; Abbamonte, Peter

Static charge order is a ubiquitous feature of the underdoped cuprates. However, at optimal doping, charge-order has been thought to be completely suppressed, suggesting an interplay between the charge-ordering and superconducting order parameters. Using Momentum-resolved Electron Energy Loss Spectroscopy (M-EELS) we show the existence of diffuse fluctuating charge-order in the optimally doped cuprate Bi2Sr2CaCu2O8+δ (Bi-2212) at low-temperature. We present full momentum-space maps of both elastic and inelastic scattering at room temperature and below the superconducting transition with 4meV resolution. We show that the ``rods'' of diffuse scattering indicate nematic-like fluctuations, and the energy width defines a fluctuation timescale of 160 fs. We discuss the implications of fluctuating charge-order on the dynamics at optimal doping. This work was supported by the Gordon and Betty Moore Foundation's EPiQS Initiative through Grant GBMF-4542. An early prototype of the M-EELS instrument was supported by the DOE Center for Emergent Superconductivity under Award No. DE-AC02-98CH10886.

Formation of silver nanoparticle at phospholipid template using Langmuir-Blodgett technique and its Surface-enhanced Raman Spectroscopy application

NASA Astrophysics Data System (ADS)

Mahato, M.; Sarkar, R.; Pal, P.; Talapatra, G. B.

2015-10-01

The biosynthesis of metal nanoparticle and their suitable assembly has recently gained tremendous interest for its application in biomedical arena such as substrates for surface-enhanced Raman scattering and others. In this article, an easy, low-cost, fast, bio-friendly and toxic-reducing agent free protocol has been described for the preparation of silver nanoparticle film using biocompatible 1,2-dipalmitoyl-sn-glycero-3-phosphocholine phospholipid Langmuir monolayer template. Interactions, docking and attachment of silver ions to the above-mentioned phospholipid monolayer have been studied by surface pressure-area isotherm and compressibility analysis at the air-water interface. We have deposited the Langmuir-Blodgett monolayer/multilayer containing silver nanoparticle onto glass/SiO2/quartz substrates. The formation of phospholipid-silver nanoparticle complex in Langmuir-Blodgett film has been characterized by field emission-scanning electron microscopy and high-resolution tunneling electron microscopy images. We have applied this deposited film as a substrate for surface-enhanced Raman scattering application using rhodamine 123 to understand the existence of the surface plasmon activity of silver nanoparticle.

Depth resolved grazing incidence neutron scattering experiments from semi-infinite interfaces: a statistical analysis of the scattering contributions

NASA Astrophysics Data System (ADS)

Adlmann, Franz A.; Herbel, Jörg; Korolkovas, Airidas; Bliersbach, Andreas; Toperverg, Boris; Van Herck, Walter; Pálsson, Gunnar K.; Kitchen, Brian; Wolff, Max

2018-04-01

Grazing incidence neutron scattering experiments offer surface sensitivity by reflecting from an interface at momentum transfers close to total external reflection. Under these conditions the penetration depth is strongly non-linear and may change by many orders of magnitude. This fact imposes severe challenges for depth resolved experiments, since the brilliance of neutron beams is relatively low in comparison to e.g. synchrotron radiation. In this article we use probability density functions to calculate the contribution of scattering at different distances from an interface to the intensities registered on the detector. Our method has the particular advantage that the depth sensitivity is directly extracted from the scattering pattern itself. Hence for perfectly known samples exact resolution functions can be calculated and visa versa. We show that any tails in the resolution function, e.g. Gaussian shaped, hinders depth resolved experiments. More importantly we provide means for a descriptive statistical analysis of detector images with respect to the scattering contributions and show that even for perfect resolution near surface scattering is hardly accessible.

Spectrum bandwidth narrowing of Thomson scattering X-rays with energy chirped electron beams from laser wakefield acceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Tong; Chen, Min, E-mail: minchen@sjtu.edu.cn; Li, Fei-Yu

2014-01-06

We study incoherent Thomson scattering between an ultrashort laser pulse and an electron beam accelerated from a laser wakefield. The energy chirp effects of the accelerated electron beam on the final radiation spectrum bandwidth are investigated. It is found that the scattered X-ray radiation has the minimum spectrum width and highest intensity as electrons are accelerated up to around the dephasing point. Furthermore, it is proposed that the electron acceleration process inside the wakefield can be studied by use of 90° Thomson scattering. The dephasing position and beam energy chirp can be deduced from the intensity and bandwidth of themore » scattered radiation.« less

Plasma characterization using ultraviolet Thomson scattering from ion-acoustic and electron plasma waves (invited)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Follett, R. K., E-mail: rfollett@lle.rochester.edu; Delettrez, J. A.; Edgell, D. H.

2016-11-15

Collective Thomson scattering is a technique for measuring the plasma conditions in laser-plasma experiments. Simultaneous measurements of ion-acoustic and electron plasma-wave spectra were obtained using a 263.25-nm Thomson-scattering probe beam. A fully reflective collection system was used to record light scattered from electron plasma waves at electron densities greater than 10{sup 21} cm{sup −3}, which produced scattering peaks near 200 nm. An accurate analysis of the experimental Thomson-scattering spectra required accounting for plasma gradients, instrument sensitivity, optical effects, and background radiation. Practical techniques for including these effects when fitting Thomson-scattering spectra are presented and applied to the measured spectra tomore » show the improvements in plasma characterization.« less

Electronic excitation induced modifications in elongated iron nanoparticle encapsulated multiwalled carbon nanotubes under ion irradiation

NASA Astrophysics Data System (ADS)

Saikiran, V.; Bazylewski, P.; Sameera, I.; Bhatia, Ravi; Pathak, A. P.; Prasad, V.; Chang, G. S.

2018-05-01

Multi-wall carbon nanotubes (MWCNT) filled with Fe nanorods were shown to have contracted and deformed under heavy ion irradiation. In this study, 120 MeV Ag and 80 MeV Ni ion irradiation was performed to study the deformation and defects induced in iron filled MWCNT under heavy ion irradiation. The structural modifications induced due to electronic excitation by ion irradiation were investigated employing high-resolution transmission electron microscopy, micro-Raman scattering experiments, and synchrotron-based X-ray absorption and emission spectroscopy. We understand that the ion irradiation causes modifications in the Fe nanorods which result in compressions and expansions of the nanotubes, and in turn leads to the buckling of MWCNT. The G band of the Raman spectra shifts slightly towards higher wavenumber and the shoulder G‧ band enhances with the increase of ion irradiation fluence, where the buckling wavelength depends on the radius 'r' of the nanotubes as exp[(r)0.5]. The intensity ratio of the D to G Raman modes initially decreases at the lowest fluence, and then it increases with the increase in ion fluence. The electron diffraction pattern and the high resolution images clearly show the presence of ion induced defects on the walls of the tube and encapsulated iron nanorods.

Millimeter Wave and Terahertz Synthetic Aperture Radar for Locating Metallic Scatterers Embedded in Scattering Media

NASA Astrophysics Data System (ADS)

Richard, Jonathan T.; Everitt, Henry O.

2017-11-01

A rail-mounted synthetic aperture radar has been constructed to operate at W-band (75 - 110 GHz) and a THz band (325 - 500 GHz) in order to ascertain its ability to locate isolated small, visually obscured metallic scatterers embedded in highly scattering dielectric hosts that are either semi-transparent or opaque. A top view 2D algorithm was used to reconstruct scenes from the acquired data, locating metallic scatterers at W-band with high range and cross-range resolution of 4.3 and 2 mm, respectively, and with improved range resolution of 0.86 mm at the THz band. Millimeter-sized metallic scatterers were easily located when embedded in semi-transparent, highly scattering target hosts of Styrofoam and waxy packing foam but were more difficult to locate when embedded in relatively opaque, highly scattering Celotex panels. Although the THz band provided the expected greater spatial resolution, it required the target to be moved closer to the rail and had a more limited field of view that prevented some targets from being identified. Techniques for improving the signal to noise ratio are discussed. This work establishes a path for developing techniques to render a complete 3D reconstruction of a scene.

Relativistic electron scattering by magnetosonic waves: Effects of discrete wave emission and high wave amplitudes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Artemyev, A. V., E-mail: ante0226@gmail.com; Mourenas, D.; Krasnoselskikh, V. V.

2015-06-15

In this paper, we study relativistic electron scattering by fast magnetosonic waves. We compare results of test particle simulations and the quasi-linear theory for different spectra of waves to investigate how a fine structure of the wave emission can influence electron resonant scattering. We show that for a realistically wide distribution of wave normal angles θ (i.e., when the dispersion δθ≥0.5{sup °}), relativistic electron scattering is similar for a wide wave spectrum and for a spectrum consisting in well-separated ion cyclotron harmonics. Comparisons of test particle simulations with quasi-linear theory show that for δθ>0.5{sup °}, the quasi-linear approximation describes resonantmore » scattering correctly for a large enough plasma frequency. For a very narrow θ distribution (when δθ∼0.05{sup °}), however, the effect of a fine structure in the wave spectrum becomes important. In this case, quasi-linear theory clearly fails in describing accurately electron scattering by fast magnetosonic waves. We also study the effect of high wave amplitudes on relativistic electron scattering. For typical conditions in the earth's radiation belts, the quasi-linear approximation cannot accurately describe electron scattering for waves with averaged amplitudes >300 pT. We discuss various applications of the obtained results for modeling electron dynamics in the radiation belts and in the Earth's magnetotail.« less

A novel analytical model for scattering limited electron transport in nano-dimensional InAlAs/InGaAs heterostructure for cryogenic applications

NASA Astrophysics Data System (ADS)

Sharma, Neetika; Verma, Neha; Jogi, Jyotika

2017-11-01

This paper models the scattering limited electron transport in a nano-dimensional In0.52Al0.48As/In0.53Ga0.47As/InP heterostructure. An analytical model for temperature dependent sheet carrier concentration and carrier mobility in a two dimensional electron gas, confined in a triangular potential well has been developed. The model accounts for all the major scattering process including ionized impurity scattering and lattice scattering. Quantum mechanical variational technique is employed for studying the intrasubband scattering mechanism in the two dimensional electron gas. Results of various scattering limited structural parameters such as energy band-gap and functional parameters such as sheet carrier concentration, scattering rate and mobility are presented. The model corroborates the dominance of ionized impurity scattering mechanism at low temperatures and that of lattice scattering at high temperatures, both in turn limiting the carrier mobility. Net mobility obtained taking various scattering mechanisms into account has been found in agreement with earlier reported results, thus validating the model.

Monte Carlo calculation of large and small-angle electron scattering in air

DOE PAGES

Cohen, B. I.; Higginson, D. P.; Eng, C. D.; ...

2017-08-12

A Monte Carlo method for angle scattering of electrons in air that accommodates the small-angle multiple scattering and larger-angle single scattering limits is introduced. In this work, the algorithm is designed for use in a particle-in-cell simulation of electron transport and electromagnetic wave effects in air. The method is illustrated in example calculations.

Electromagnetic inverse scattering

NASA Technical Reports Server (NTRS)

Bojarski, N. N.

1972-01-01

A three-dimensional electromagnetic inverse scattering identity, based on the physical optics approximation, is developed for the monostatic scattered far field cross section of perfect conductors. Uniqueness of this inverse identity is proven. This identity requires complete scattering information for all frequencies and aspect angles. A nonsingular integral equation is developed for the arbitrary case of incomplete frequence and/or aspect angle scattering information. A general closed-form solution to this integral equation is developed, which yields the shape of the scatterer from such incomplete information. A specific practical radar solution is presented. The resolution of this solution is developed, yielding short-pulse target resolution radar system parameter equations. The special cases of two- and one-dimensional inverse scattering and the special case of a priori knowledge of scatterer symmetry are treated in some detail. The merits of this solution over the conventional radar imaging technique are discussed.

Comparative electron temperature measurements of Thomson scattering and electron cyclotron emission diagnostics in TCABR plasmas.

PubMed

Alonso, M P; Figueiredo, A C A; Borges, F O; Elizondo, J I; Galvão, R M O; Severo, J H F; Usuriaga, O C; Berni, L A; Machida, M

2010-10-01

We present the first simultaneous measurements of the Thomson scattering and electron cyclotron emission radiometer diagnostics performed at TCABR tokamak with Alfvén wave heating. The Thomson scattering diagnostic is an upgraded version of the one previously installed at the ISTTOK tokamak, while the electron cyclotron emission radiometer employs a heterodyne sweeping radiometer. For purely Ohmic discharges, the electron temperature measurements from both diagnostics are in good agreement. Additional Alfvén wave heating does not affect the capability of the Thomson scattering diagnostic to measure the instantaneous electron temperature, whereas measurements from the electron cyclotron emission radiometer become underestimates of the actual temperature values.

The Radiation Belt Electron Scattering by Magnetosonic Wave: Dependence on Key Parameters

NASA Astrophysics Data System (ADS)

Lei, Mingda; Xie, Lun; Li, Jinxing; Pu, Zuyin; Fu, Suiyan; Ni, Binbin; Hua, Man; Chen, Lunjin; Li, Wen

2017-12-01

Magnetosonic (MS) waves have been found capable of creating radiation belt electron butterfly distributions in the inner magnetosphere. To investigate the physical nature of the interactions between radiation belt electrons and MS waves, and to explore a preferential condition for MS waves to scatter electrons efficiently, we performed a comprehensive parametric study of MS wave-electron interactions using test particle simulations. The diffusion coefficients simulated by varying the MS wave frequency show that the scattering effect of MS waves is frequency insensitive at low harmonics (f < 20 fcp), which has great implications on modeling the electron scattering caused by MS waves with harmonic structures. The electron scattering caused by MS waves is very sensitive to wave normal angles, and MS waves with off 90° wave normal angles scatter electrons more efficiently. By simulating the diffusion coefficients and the electron phase space density evolution at different L shells under different plasma environment circumstances, we find that MS waves can readily produce electron butterfly distributions in the inner part of the plasmasphere where the ratio of electron plasma-to-gyrofrequency (fpe/fce) is large, while they may essentially form a two-peak distribution outside the plasmapause and in the inner radiation belt where fpe/fce is small.

Tomographic reconstruction of ionospheric electron density during the storm of 5-6 August 2011 using multi-source data

PubMed Central

Tang, Jun; Yao, Yibin; Zhang, Liang; Kong, Jian

2015-01-01

The insufficiency of data is the essential reason for ill-posed problem existed in computerized ionospheric tomography (CIT) technique. Therefore, the method of integrating multi-source data is proposed. Currently, the multiple satellite navigation systems and various ionospheric observing instruments provide abundant data which can be employed to reconstruct ionospheric electron density (IED). In order to improve the vertical resolution of IED, we do research on IED reconstruction by integration of ground-based GPS data, occultation data from the LEO satellite, satellite altimetry data from Jason-1 and Jason-2 and ionosonde data. We used the CIT results to compare with incoherent scatter radar (ISR) observations, and found that the multi-source data fusion was effective and reliable to reconstruct electron density, showing its superiority than CIT with GPS data alone. PMID:26266764

Tomographic reconstruction of ionospheric electron density during the storm of 5-6 August 2011 using multi-source data.

PubMed

Tang, Jun; Yao, Yibin; Zhang, Liang; Kong, Jian

2015-08-12

The insufficiency of data is the essential reason for ill-posed problem existed in computerized ionospheric tomography (CIT) technique. Therefore, the method of integrating multi-source data is proposed. Currently, the multiple satellite navigation systems and various ionospheric observing instruments provide abundant data which can be employed to reconstruct ionospheric electron density (IED). In order to improve the vertical resolution of IED, we do research on IED reconstruction by integration of ground-based GPS data, occultation data from the LEO satellite, satellite altimetry data from Jason-1 and Jason-2 and ionosonde data. We used the CIT results to compare with incoherent scatter radar (ISR) observations, and found that the multi-source data fusion was effective and reliable to reconstruct electron density, showing its superiority than CIT with GPS data alone.

A Shear Strain Route Dependency of Martensite Formation in 316L Stainless Steel.

PubMed

Kang, Suk Hoon; Kim, Tae Kyu; Jang, Jinsung; Oh, Kyu Hwan

2015-06-01

In this study, the effect of simple shearing on microstructure evolution and mechanical properties of 316L austenitic stainless steel were investigated. Two different shear strain routes were obtained by twisting cylindrical specimens in the forward and backward directions. The strain-induced martensite phase was effectively obtained by alteration of the routes. Formation of the martensite phase clearly resulted in significant hardening of the steel. Grain-size reduction and strain-induced martensitic transformation within the deformed structures of the strained specimens were characterized by scanning electron microscopy - electron back-scattered diffraction, X-ray diffraction, and the TEM-ASTAR (transmission electron microscopy - analytical scanning transmission atomic resolution, automatic crystal orientation/phase mapping for TEM) system. Significant numbers of twin networks were formed by alteration of the shear strain routes, and the martensite phases were nucleated at the twin interfaces.

Relative merits and limiting factors for x-ray and electron microscopy of thick, hydrated organic materials

DOE PAGES

Du, Ming; Jacobsen, Chris

2017-10-07

Electron and x-ray microscopes allow one to image the entire, unlabeled structure of hydrated materials at a resolution well beyond what visible light microscopes can achieve. However, both approaches involve ionizing radiation, so that radiation damage must be considered as one of the limits to imaging. Drawing upon earlier work, we describe here a unified approach to estimating the image contrast (and thus the required exposure and corresponding radiation dose) in both x-ray and electron microscopy. This approach accounts for factors such as plural and inelastic scattering, and (in electron microscopy) the use of energy filters to obtain so-called "zeromore » loss" images. As expected, it shows that electron microscopy offers lower dose for specimens thinner than about 1 mu m (such as for studies of macromolecules, viruses, bacteria and archaebacteria, and thin sectioned material), while x-ray microscopy offers superior characteristics for imaging thicker specimen such as whole eukaryotic cells, thick-sectioned tissues, and organs. The required radiation dose scales strongly as a function of the desired spatial resolution, allowing one to understand the limits of live and frozen hydrated specimen imaging. Lastly, we consider the factors limiting x-ray microscopy of thicker materials, suggesting that specimens as thick as a whole mouse brain can be imaged with x-ray microscopes without significant image degradation should appropriate image reconstruction methods be identified.« less

Relative merits and limiting factors for x-ray and electron microscopy of thick, hydrated organic materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, Ming; Jacobsen, Chris

Electron and x-ray microscopes allow one to image the entire, unlabeled structure of hydrated materials at a resolution well beyond what visible light microscopes can achieve. However, both approaches involve ionizing radiation, so that radiation damage must be considered as one of the limits to imaging. Drawing upon earlier work, we describe here a unified approach to estimating the image contrast (and thus the required exposure and corresponding radiation dose) in both x-ray and electron microscopy. This approach accounts for factors such as plural and inelastic scattering, and (in electron microscopy) the use of energy filters to obtain so-called "zeromore » loss" images. As expected, it shows that electron microscopy offers lower dose for specimens thinner than about 1 mu m (such as for studies of macromolecules, viruses, bacteria and archaebacteria, and thin sectioned material), while x-ray microscopy offers superior characteristics for imaging thicker specimen such as whole eukaryotic cells, thick-sectioned tissues, and organs. The required radiation dose scales strongly as a function of the desired spatial resolution, allowing one to understand the limits of live and frozen hydrated specimen imaging. Lastly, we consider the factors limiting x-ray microscopy of thicker materials, suggesting that specimens as thick as a whole mouse brain can be imaged with x-ray microscopes without significant image degradation should appropriate image reconstruction methods be identified.« less

Ab initio molecular dynamics calculations on scattering of hyperthermal H atoms from Cu(111) and Au(111)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kroes, Geert-Jan, E-mail: g.j.kroes@chem.leidenuniv.nl; Pavanello, Michele; Blanco-Rey, María

2014-08-07

Energy loss from the translational motion of an atom or molecule impinging on a metal surface to the surface may determine whether the incident particle can trap on the surface, and whether it has enough energy left to react with another molecule present at the surface. Although this is relevant to heterogeneous catalysis, the relative extent to which energy loss of hot atoms takes place to phonons or electron-hole pair (ehp) excitation, and its dependence on the system's parameters, remain largely unknown. We address these questions for two systems that present an extreme case of the mass ratio of themore » incident atom to the surface atom, i.e., H + Cu(111) and H + Au(111), by presenting adiabatic ab initio molecular dynamics (AIMD) predictions of the energy loss and angular distributions for an incidence energy of 5 eV. The results are compared to the results of AIMDEFp calculations modeling energy loss to ehp excitation using an electronic friction (“EF”) model applied to the AIMD trajectories, so that the energy loss to the electrons is calculated “post” (“p”) the computation of the AIMD trajectory. The AIMD calculations predict average energy losses of 0.38 eV for Cu(111) and 0.13-0.14 eV for Au(111) for H-atoms that scatter from these surfaces without penetrating the surface. These energies closely correspond with energy losses predicted with Baule models, which is suggestive of structure scattering. The predicted adiabatic integral energy loss spectra (integrated over all final scattering angles) all display a lowest energy peak at an energy corresponding to approximately 80% of the average adiabatic energy loss for non-penetrative scattering. In the adiabatic limit, this suggests a way of determining the approximate average energy loss of non-penetratively scattered H-atoms from the integral energy loss spectrum of all scattered H-atoms. The AIMDEFp calculations predict that in each case the lowest energy loss peak should show additional energy loss in the range 0.2-0.3 eV due to ehp excitation, which should be possible to observe. The average non-adiabatic energy losses for non-penetrative scattering exceed the adiabatic losses to phonons by 0.9-1.0 eV. This suggests that for scattering of hyperthermal H-atoms from coinage metals the dominant energy dissipation channel should be to ehp excitation. These predictions can be tested by experiments that combine techniques for generating H-atom beams that are well resolved in translational energy and for detecting the scattered atoms with high energy-resolution.« less

Beam deceleration for block-face scanning electron microscopy of embedded biological tissue.

PubMed

Ohta, Keisuke; Sadayama, Shoji; Togo, Akinobu; Higashi, Ryuhei; Tanoue, Ryuichiro; Nakamura, Kei-ichiro

2012-04-01

The beam deceleration (BD) method for scanning electron microscopes (SEM) also referred to as "retarding" was applied to back-scattered electron (BSE) imaging of the flat block face of a resin embedded biological specimen under low accelerating voltage and low beam current conditions. BSE imaging was performed with 0-4 kV of BD on en bloc stained rat hepatocyte. BD drastically enhanced the compositional contrast of the specimen and also improved the resolution at low landing energy levels (1.5-3 keV) and a low beam current (10 pA). These effects also functioned in long working distance observation, however, stage tilting caused uncorrectable astigmatism in BD observation. Stage tilting is mechanically required for a FIB/SEM, so we designed a novel specimen holder to minimize the unfavorable tilting effect. The FIB/SEM 3D reconstruction using the new holder showed a reasonable contrast and resolution high enough to analyze individual cell organelles and also the mitochondrial cristae structures (~5 nm) of the hepatocyte. These results indicate the advantages of BD for block face imaging of biological materials such as cells and tissues under low-voltage and low beam current conditions. Copyright © 2011 Elsevier Ltd. All rights reserved.

Structural studies of RNA-protein complexes: A hybrid approach involving hydrodynamics, scattering, and computational methods.

PubMed

Patel, Trushar R; Chojnowski, Grzegorz; Astha; Koul, Amit; McKenna, Sean A; Bujnicki, Janusz M

2017-04-15

The diverse functional cellular roles played by ribonucleic acids (RNA) have emphasized the need to develop rapid and accurate methodologies to elucidate the relationship between the structure and function of RNA. Structural biology tools such as X-ray crystallography and Nuclear Magnetic Resonance are highly useful methods to obtain atomic-level resolution models of macromolecules. However, both methods have sample, time, and technical limitations that prevent their application to a number of macromolecules of interest. An emerging alternative to high-resolution structural techniques is to employ a hybrid approach that combines low-resolution shape information about macromolecules and their complexes from experimental hydrodynamic (e.g. analytical ultracentrifugation) and solution scattering measurements (e.g., solution X-ray or neutron scattering), with computational modeling to obtain atomic-level models. While promising, scattering methods rely on aggregation-free, monodispersed preparations and therefore the careful development of a quality control pipeline is fundamental to an unbiased and reliable structural determination. This review article describes hydrodynamic techniques that are highly valuable for homogeneity studies, scattering techniques useful to study the low-resolution shape, and strategies for computational modeling to obtain high-resolution 3D structural models of RNAs, proteins, and RNA-protein complexes. Copyright © 2016 The Author(s). Published by Elsevier Inc. All rights reserved.

Method for Measuring the Volume-Scattering Function of Water

NASA Technical Reports Server (NTRS)

Agrawal, Yogesh C.

2009-01-01

The volume scattering function (VSF) of seawater affects visibility, remote sensing properties, in-water light propagation, lidar performance, and the like. Currently, it s possible to measure only small forward angles of VSF, or to use cumbersome, large, and non-autonomous systems. This innovation is a method of measuring the full range of VSF using a portable instrument. A single rapid-sensing photosensor is used to scan a green laser beam, which delivers the desired measurement. By using a single sensor, inter-calibration is avoided. A compact design is achieved by using drift-free detector electronics, fiber optics, and a new type of photomultiplier. This provides a high angular resolution of 1 or better, as well as the ability to focus in on a VSF region of particular interest. Currently, the total scattering of light is measured as a difference from the other two parts of the light budget equation. This innovation will allow the direct calculation of the total scattering of light by taking an integral of the VSF over all angles. This directly provides one of the three components of the light budget equation, allowing greater versatility in its calculation.

Experimental evaluation of environmental scanning electron microscopes at high chamber pressure.

PubMed

Fitzek, H; Schroettner, H; Wagner, J; Hofer, F; Rattenberger, J

2015-11-01

In environmental scanning electron microscopy (ESEM) high pressure applications have become increasingly important. Wet or biological samples can be investigated without time-consuming sample preparation and potential artefacts from this preparation can be neglected. Unfortunately, the signal-to-noise ratio strongly decreases with increasing chamber pressure. To evaluate the high pressure performance of ESEM and to compare different electron microscopes, information about spatial resolution and detector type is not enough. On the one hand, the scattering of the primary electron beam increases, which vanishes the contrast in images; and on the other hand, the secondary electrons (SE) signal amplification decreases. The stagnation gas thickness (effective distance the beam has to travel through the imaging gas) as well as the SE detection system depend on the microscope and for a complete and serious evaluation of an ESEM or low vacuum SEM it is necessary to specify these two parameters. A method is presented to determine the fraction of scattered and unscattered electrons and to calculate the stagnation gas thickness (θ). To evaluate the high pressure performance of the SE detection system, a method is presented that allows for an analysis of a single image and the calculation of the signal-to-noise ratio of this image. All investigations are performed on an FEI ESEM Quanta 600 (field emission gun) and an FEI ESEM Quanta 200 (thermionic gun). These methods and measurements should represent opportunities for evaluating the high pressure performance of an ESEM. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

Two-potential approach for electron-molecular collisions at intermediate and high energies - Application to e-N2 scatterings

NASA Technical Reports Server (NTRS)

Choi, B. H.; Poe, R. T.; Sun, J. C.; Shan, Y.

1979-01-01

A general theoretical approach is proposed for the calculation of elastic, vibrational, and rotational transitions for electron-molecule scattering at intermediate and high-electron-impact energies. In this formulation, contributions to the scattering process come from the incoherent sum of two dominant potentials: a short-range shielded nuclear Coulomb potential from individual atomic centers, and a permanent/induced long-range potential. Application to e-N2 scattering from 50-500 eV incident electron energies has yielded good agreement with absolutely calibrated experiments. Comparisons with other theoretical approaches are made. The physical picture as well as the general features of electron-molecule scattering process are discussed within the framework of the two-potential approach.

Correlation spectrometer for filtering of (quasi) elastic neutron scattering with variable resolution

NASA Astrophysics Data System (ADS)

Magazù, Salvatore; Mezei, Ferenc; Migliardo, Federica

2018-05-01

In a variety of applications of inelastic neutron scattering spectroscopy the goal is to single out the elastic scattering contribution from the total scattered spectrum as a function of momentum transfer and sample environment parameters. The elastic part of the spectrum is defined in such a case by the energy resolution of the spectrometer. Variable elastic energy resolution offers a way to distinguish between elastic and quasi-elastic intensities. Correlation spectroscopy lends itself as an efficient, high intensity approach for accomplishing this both at continuous and pulsed neutron sources. On the one hand, in beam modulation methods the Liouville theorem coupling between intensity and resolution is relaxed and time-of-flight velocity analysis of the neutron velocity distribution can be performed with 50 % duty factor exposure for all available resolutions. On the other hand, the (quasi)elastic part of the spectrum generally contains the major part of the integrated intensity at a given detector, and thus correlation spectroscopy can be applied with most favorable signal to statistical noise ratio. The novel spectrometer CORELLI at SNS is an example for this type of application of the correlation technique at a pulsed source. On a continuous neutron source a statistical chopper can be used for quasi-random time dependent beam modulation and the total time-of-flight of the neutron from the statistical chopper to detection is determined by the analysis of the correlation between the temporal fluctuation of the neutron detection rate and the statistical chopper beam modulation pattern. The correlation analysis can either be used for the determination of the incoming neutron velocity or for the scattered neutron velocity, depending of the position of the statistical chopper along the neutron trajectory. These two options are considered together with an evaluation of spectrometer performance compared to conventional spectroscopy, in particular for variable resolution elastic neutron scattering (RENS) studies of relaxation processes and the evolution of mean square displacements. A particular focus of our analysis is the unique feature of correlation spectroscopy of delivering high and resolution independent beam intensity, thus the same statistical chopper scan contains both high intensity and high resolution information at the same time, and can be evaluated both ways. This flexibility for variable resolution data handling represents an additional asset for correlation spectroscopy in variable resolution work. Changing the beam width for the same statistical chopper allows us to additionally trade resolution for intensity in two different experimental runs, similarly for conventional single slit chopper spectroscopy. The combination of these two approaches is a capability of particular value in neutron spectroscopy studies requiring variable energy resolution, such as the systematic study of quasi-elastic scattering and mean square displacement. Furthermore the statistical chopper approach is particularly advantageous for studying samples with low scattering intensity in the presence of a high, sample independent background.

Precision calculation of the lowest 1S resonance in e-H scattering. [electron-hydrogen scattering

NASA Technical Reports Server (NTRS)

Ho, Y. K.; Bhatia, A. K.; Temkin, A.

1977-01-01

The position and width of the lowest resonance in electron-hydrogen scattering have been calculated using a Hylleraas correlation function with up to 95 terms in the optical potential formalism. The results should be useful as calibration points for experimental electron scattering purposes. A formula relating the conventional (Breit-Wigner) width with the Feschbach formalism is derived.

Investigation of superelastic electron scattering by laser-excited Ba - Experimental procedures and results

NASA Technical Reports Server (NTRS)

Register, D. F.; Trajmar, S.; Fineman, M. A.; Poe, R. T.; Csanak, G.; Jensen, S. W.

1983-01-01

Differential (in angle) electron scattering experiments on laser-excited Ba-138 1P were carried out at 30- and 100-eV impact energies. The laser light was linearly polarized and located in the scattering plane. The superelastic scattering signal was measured as a function of polarization direction of the laser light with respect to the scattering plane. It was found at low electron scattering angles that the superelastic scattering signal was asymmetric to reflection of the polarization vector with respect to the scattering plane. This is in contradiction with theoretical predictions. An attempt was made to pinpoint the reason for this observation, and a detailed investigation of the influence of experimental conditions on the superelastic scattering was undertaken. No explanation for the asymmetry has as yet been found.

Precision determination of electron scattering angle by differential nuclear recoil energy method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liyanage, N.; Saenboonruang, K.

2015-12-01

The accurate determination of the scattered electron angle is crucial to electron scattering experiments, both with open-geometry large-acceptance spectrometers and ones with dipole-type magnetic spectrometers for electron detection. In particular, for small central-angle experiments using dipole-type magnetic spectrometers, in which surveys are used to measure the spectrometer angle with respect to the primary electron beam, the importance of the scattering angle determination is emphasized. However, given the complexities of large experiments and spectrometers, the accuracy of such surveys is limited and insufficient to meet demands of some experiments. In this article, we present a new technique for determination of themore » electron scattering angle based on an accurate measurement of the primary beam energy and the principle of differential nuclear recoil. This technique was used to determine the scattering angle for several experiments carried out at the Experimental Hall A, Jefferson Lab. Results have shown that the new technique greatly improved the accuracy of the angle determination compared to surveys.« less

Precision Determination of Electron Scattering Angle by Differential Nuclear Recoil Energy Method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liyanage, Nilanga; Saenboonruang, Kiadtisak

2015-09-01

The accurate determination of the scattered electron angle is crucial to electron scattering experiments, both with open-geometry large-acceptance spectrometers and ones with dipole-type magnetic spectrometers for electron detection. In particular, for small central-angle experiments using dipole-type magnetic spectrometers, in which surveys are used to measure the spectrometer angle with respect to the primary electron beam, the importance of the scattering angle determination is emphasized. However, given the complexities of large experiments and spectrometers, the accuracy of such surveys is limited and insufficient to meet demands of some experiments. In this article, we present a new technique for determination of themore » electron scattering angle based on an accurate measurement of the primary beam energy and the principle of differential nuclear recoil. This technique was used to determine the scattering angle for several experiments carried out at the Experimental Hall A, Jefferson Lab. Results have shown that the new technique greatly improved the accuracy of the angle determination compared to surveys.« less

Comptonization of thermal photons by relativistic electron beams

NASA Technical Reports Server (NTRS)

Daugherty, Joseph K.; Harding, Alice K.

1989-01-01

This paper presents a numerical calculation of gamma-ray emission produced by Compton scattering of relativistic electron beams on background thermal radiation, which includes spatial dependence of electron energy losses and cyclotron resonance scattering in a strong magnetic field. In the first version, the scattering is described by the fully relativistic Klein-Nishina cross section, but the magnetic field is neglected. In the second version, the scattering is described by the magnetic resonant cross section in the Thomson limit. It is found that when the magnetic field is not included, electron energy losses are important only at higher neutron star surface temperatures (T about 3,000,000 K). In the presence of a strong magnetic field, (10 to the 12th G), resonant scattering greatly increases electron energy losses, making scattering very efficient even at lower surface temperatures. Resulting photon and electron spectra for both cases ae discussed in relation to models for pulsar X-ray and gamma-ray emission.

Complete solution of electronic excitation and ionization in electron-hydrogen molecule scattering

DOE PAGES

Zammit, Mark C.; Savage, Jeremy S.; Fursa, Dmitry V.; ...

2016-06-08

The convergent close-coupling method has been used to solve the electron-hydrogen molecule scattering problem in the fixed-nuclei approximation. Excellent agreement with experiment is found for the grand total, elastic, electronic-excitation, and total ionization cross sections from the very low to the very high energies. This shows that for the electronic degrees of freedom the method provides a complete treatment of electron scattering on molecules as it does for atoms.

A long baseline RICH with a 27-kiloton water target and radiator for detection of neutrino oscillations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ypsilantis, T.; Seguinot, J.; Zichichi, A.

1997-01-01

A 27 kt water volume is investigated as a target for a long baseline neutrino beam from CERN to Gran Sasso. Charged secondaries from the neutrino interactions produce Cherenkov photons in water which are imaged as rings by a spherical mirror. The photon detector elements are 14 400 photomultipliers (PM`s) of 127 mm diameter or 3600 HPD`s of 250 mm diameter with single photon sensitivity. A coincidence signal of about 300 pixel elements in time with the SPS beam starts readout in bins of 1 ns over a period of 128 ns. Momentum, direction, and velocity of hadrons and muconsmore » are determined from the width, center, and radius of the rings, respectively. Momentum is measured if multiple scattering dominates the ring width, as is the case for most of the particles of interest. Momentum, direction, and velocity of hadrons and muons are determined from the width, center, and radius of the rings, respectively. Momentum is measured if multiple scattering dominates the ring width, as is the case for most of the particles of interest. Momentum resolutions of 1-10%, mass resolutions of 5-50 MeV, and direction resolutions of < 1 mrad are achievable. Thresholds in water for muons, pions, kaons, and protons are 0.12, 0.16, 0.55, and 1.05 GeV/c, respectively. Electrons and gammas can be measured with energy resolution {sigma}{sub E}/E{approx}8.5%/{radical}E(GeV) and with direction resolution {approx} 1 mrad. The detector can be sited either inside a Gran Sasso tunnel or above ground because it is directional and the SPS beam is pulsed; thus the rejection of cosmic ray background is excellent.« less

SoftWAXS: a computational tool for modeling wide-angle X-ray solution scattering from biomolecules.

PubMed

Bardhan, Jaydeep; Park, Sanghyun; Makowski, Lee

2009-10-01

This paper describes a computational approach to estimating wide-angle X-ray solution scattering (WAXS) from proteins, which has been implemented in a computer program called SoftWAXS. The accuracy and efficiency of SoftWAXS are analyzed for analytically solvable model problems as well as for proteins. Key features of the approach include a numerical procedure for performing the required spherical averaging and explicit representation of the solute-solvent boundary and the surface of the hydration layer. These features allow the Fourier transform of the excluded volume and hydration layer to be computed directly and with high accuracy. This approach will allow future investigation of different treatments of the electron density in the hydration shell. Numerical results illustrate the differences between this approach to modeling the excluded volume and a widely used model that treats the excluded-volume function as a sum of Gaussians representing the individual atomic excluded volumes. Comparison of the results obtained here with those from explicit-solvent molecular dynamics clarifies shortcomings inherent to the representation of solvent as a time-averaged electron-density profile. In addition, an assessment is made of how the calculated scattering patterns depend on input parameters such as the solute-atom radii, the width of the hydration shell and the hydration-layer contrast. These results suggest that obtaining predictive calculations of high-resolution WAXS patterns may require sophisticated treatments of solvent.

WE-G-204-06: Grid-Line Artifact Minimization for High Resolution Detectors Using Iterative Residual Scatter Correction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rana, R; Bednarek, D; Rudin, S

2015-06-15

Purpose: Anti-scatter grid-line artifacts are more prominent for high-resolution x-ray detectors since the fraction of a pixel blocked by the grid septa is large. Direct logarithmic subtraction of the artifact pattern is limited by residual scattered radiation and we investigate an iterative method for scatter correction. Methods: A stationary Smit-Rοntgen anti-scatter grid was used with a high resolution Dexela 1207 CMOS X-ray detector (75 µm pixel size) to image an artery block (Nuclear Associates, Model 76-705) placed within a uniform head equivalent phantom as the scattering source. The image of the phantom was divided by a flat-field image obtained withoutmore » scatter but with the grid to eliminate grid-line artifacts. Constant scatter values were subtracted from the phantom image before dividing by the averaged flat-field-with-grid image. The standard deviation of pixel values for a fixed region of the resultant images with different subtracted scatter values provided a measure of the remaining grid-line artifacts. Results: A plot of the standard deviation of image pixel values versus the subtracted scatter value shows that the image structure noise reaches a minimum before going up again as the scatter value is increased. This minimum corresponds to a minimization of the grid-line artifacts as demonstrated in line profile plots obtained through each of the images perpendicular to the grid lines. Artifact-free images of the artery block were obtained with the optimal scatter value obtained by this iterative approach. Conclusion: Residual scatter subtraction can provide improved grid-line artifact elimination when using the flat-field with grid “subtraction” technique. The standard deviation of image pixel values can be used to determine the optimal scatter value to subtract to obtain a minimization of grid line artifacts with high resolution x-ray imaging detectors. This study was supported by NIH Grant R01EB002873 and an equipment grant from Toshiba Medical Systems Corp.« less

Measurement of eye aberrations in a speckle field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Larichev, A V; Ivanov, P V; Iroshnikov, N G

2001-12-31

The influence of speckles on the performance of a Shark-Hartmann wavefront sensor is investigated in the eye aberration studies. The dependence of the phase distortion measurement error on the characteristic speckle size is determined experimentally. Scanning of the reference source was used to suppress the speckle structure of the laser beam scattered by the retina. The technique developed by us made it possible to study the time dependence of the human eye aberrations with a resolution of 30 ms. (laser applications and other topics in quantum electronics)

On possibility of time reversal symmetry violation in neutrino elastic scattering on polarized electron target

NASA Astrophysics Data System (ADS)

Sobków, W.; Błaut, A.

2018-03-01

In this paper we indicate a possibility of utilizing the elastic scattering of Dirac low-energy (˜ 1 MeV) electron neutrinos (ν _es) on a polarized electron target (PET) in testing the time reversal symmetry violation (TRSV). We consider a scenario in which the incoming ν _e beam is a superposition of left chiral (LC) and right chiral (RC) states. LC ν _e interact mainly by the standard V-A and small admixture of non-standard scalar S_L, pseudoscalar P_L, tensor T_L interactions, while RC ones are only detected by the exotic V + A and S_R, P_R, T_R interactions. As a result of the superposition of the two chiralities the transverse components of ν e spin polarization (T-even and T-odd) may appear. We compute the differential cross section as a function of the recoil electron azimuthal angle and scattered electron energy, and show how the interference terms between standard V-A and exotic S_R, P_R, T_R couplings depend on the various angular correlations among the transversal ν _e spin polarization, the polarization of the electron target, the incoming neutrino momentum and the outgoing electron momentum in the limit of relativistic ν _e. We illustrate how the maximal value of recoil electrons azimuthal asymmetry and the asymmetry axis location of outgoing electrons depend on the azimuthal angle of the transversal component of the ν _e spin polarization, both for the time reversal symmetry conservation (TRSC) and TRSV. Next, we display that the electron energy spectrum and polar angle distribution of the recoil electrons are also sensitive to the interference terms between V-A and S_R, P_R, T_R couplings, proportional to the T-even and T-odd angular correlations among the transversal ν _e polarization, the electron polarization of the target, and the incoming ν _e momentum, respectively. We also discuss the possibility of testing the TRSV by observing the azimuthal asymmetry of outgoing electrons, using the PET without the impact of the transversal ν polarization related to the production process. In this scenario the predicted effects depend only on the interferences between S_R and T_R couplings. Our model-independent analysis is carried out for the flavor ν _e. To make such tests feasible, the intense (polarized) artificial ν _e source, PET and the appropriate detector measuring the directionality of the outgoing electrons and/or the recoil electrons energy with a high resolution have to be identified.

Hard X-ray Emission from Galaxy Clusters Observed with INTEGRAL and Prospects for Simbol-X

NASA Astrophysics Data System (ADS)

Eckert, D.; Paltani, S.; Courvoisier, T. J.-L.

2009-05-01

Some galaxy clusters are known to contain a large population of relativistic electrons, which produce radio emission through synchrotron radiation. Therefore, it is expected that inverse-Compton scattering of the relativistic electrons with the CMB produce non-thermal emission which should be observable in the hard X-ray domain. Here we focus on the recent results by INTEGRAL, which shed a new light on the non-thermal emission thanks to its angular resolution and sensitivity in the hard X-ray range. We also present the exciting prospects in this field for Simbol-X, which will allow us to detect the non-thermal emission in a number of clusters and map the magnetic field throughout the intra-cluster medium.

Low-Temperature Scanning Capacitance Probe for Imaging Electron Motion

NASA Astrophysics Data System (ADS)

Bhandari, S.; Westervelt, R. M.

2014-12-01

Novel techniques to probe electronic properties at the nanoscale can shed light on the physics of nanoscale devices. In particular, studying the scattering of electrons from edges and apertures at the nanoscale and imaging the electron profile in a quantum dot, have been of interest [1]. In this paper, we present the design and implementation of a cooled scanning capacitance probe that operates at liquid He temperatures to image electron waves in nanodevices. The conducting tip of a scanned probe microscope is held above the nanoscale structure, and an applied sample-to-tip voltage creates an image charge that is measured by a cooled charge amplifier [2] adjacent to the tip. The circuit is based on a low-capacitance, high- electron-mobility transistor (Fujitsu FHX35X). The input is a capacitance bridge formed by a low capacitance pinched-off HEMT transistor and tip-sample capacitance. We have achieved low noise level (0.13 e/VHz) and high spatial resolution (100 nm) for this technique, which promises to be a useful tool to study electronic behavior in nanoscale devices.

Prospects for higher spatial resolution quantitative X-ray analysis using transition element L-lines

NASA Astrophysics Data System (ADS)

Statham, P.; Holland, J.

2014-03-01

Lowering electron beam kV reduces electron scattering and improves spatial resolution of X-ray analysis. However, a previous round robin analysis of steels at 5 - 6 kV using Lα-lines for the first row transition elements gave poor accuracies. Our experiments on SS63 steel using Lα-lines show similar biases in Cr and Ni that cannot be corrected with changes to self-absorption coefficients or carbon coating. The inaccuracy may be caused by different probabilities for emission and anomalous self-absorption for the La-line between specimen and pure element standard. Analysis using Ll(L3-M1)-lines gives more accurate results for SS63 plausibly because the M1-shell is not so vulnerable to the atomic environment as the unfilled M4,5-shell. However, Ll-intensities are very weak and WDS analysis may be impractical for some applications. EDS with large area SDD offers orders of magnitude faster analysis and achieves similar results to WDS analysis with Lα-lines but poorer energy resolution precludes the use of Ll-lines in most situations. EDS analysis of K-lines at low overvoltage is an alternative strategy for improving spatial resolution that could give higher accuracy. The trade-off between low kV versus low overvoltage is explored in terms of sensitivity for element detection for different elements.

3-D Spatial Resolution of 350 μm Pitch Pixelated CdZnTe Detectors for Imaging Applications.

PubMed

Yin, Yongzhi; Chen, Ximeng; Wu, Heyu; Komarov, Sergey; Garson, Alfred; Li, Qiang; Guo, Qingzhen; Krawczynski, Henric; Meng, Ling-Jian; Tai, Yuan-Chuan

2013-02-01

We are currently investigating the feasibility of using highly pixelated Cadmium Zinc Telluride (CdZnTe) detectors for sub-500 μ m resolution PET imaging applications. A 20 mm × 20 mm × 5 mm CdZnTe substrate was fabricated with 350 μ m pitch pixels (250 μ m anode pixels with 100 μ m gap) and coplanar cathode. Charge sharing among the pixels of a 350 μ m pitch detector was studied using collimated 122 keV and 511 keV gamma ray sources. For a 350 μ m pitch CdZnTe detector, scatter plots of the charge signal of two neighboring pixels clearly show more charge sharing when the collimated beam hits the gap between adjacent pixels. Using collimated Co-57 and Ge-68 sources, we measured the count profiles and estimated the intrinsic spatial resolution of 350 μ m pitch detector biased at -1000 V. Depth of interaction was analyzed based on two methods, i.e., cathode/anode ratio and electron drift time, in both 122 keV and 511 keV measurements. For single-pixel photopeak events, a linear correlation between cathode/anode ratio and electron drift time was shown, which would be useful for estimating the DOI information and preserving image resolution in CdZnTe PET imaging applications.

3-D Spatial Resolution of 350 μm Pitch Pixelated CdZnTe Detectors for Imaging Applications

PubMed Central

Yin, Yongzhi; Chen, Ximeng; Wu, Heyu; Komarov, Sergey; Garson, Alfred; Li, Qiang; Guo, Qingzhen; Krawczynski, Henric; Meng, Ling-Jian; Tai, Yuan-Chuan

2016-01-01

We are currently investigating the feasibility of using highly pixelated Cadmium Zinc Telluride (CdZnTe) detectors for sub-500 μm resolution PET imaging applications. A 20 mm × 20 mm × 5 mm CdZnTe substrate was fabricated with 350 μm pitch pixels (250 μm anode pixels with 100 μm gap) and coplanar cathode. Charge sharing among the pixels of a 350 μm pitch detector was studied using collimated 122 keV and 511 keV gamma ray sources. For a 350 μm pitch CdZnTe detector, scatter plots of the charge signal of two neighboring pixels clearly show more charge sharing when the collimated beam hits the gap between adjacent pixels. Using collimated Co-57 and Ge-68 sources, we measured the count profiles and estimated the intrinsic spatial resolution of 350 μm pitch detector biased at −1000 V. Depth of interaction was analyzed based on two methods, i.e., cathode/anode ratio and electron drift time, in both 122 keV and 511 keV measurements. For single-pixel photopeak events, a linear correlation between cathode/anode ratio and electron drift time was shown, which would be useful for estimating the DOI information and preserving image resolution in CdZnTe PET imaging applications. PMID:28250476

Single-photon semiconductor photodiodes for distributed optical fiber sensors: state of the art and perspectives

NASA Astrophysics Data System (ADS)

Ripamonti, Giancarlo; Lacaita, Andrea L.

1993-03-01

The extreme sensitivity and time resolution of Geiger-mode avalanche photodiodes (GM- APDs) have already been exploited for optical time domain reflectometry (OTDR). Better than 1 cm spatial resolution in Rayleigh scattering detection was demonstrated. Distributed and quasi-distributed optical fiber sensors can take advantage of the capabilities of GM-APDs. Extensive studies have recently disclosed the main characteristics and limitations of silicon devices, both commercially available and developmental. In this paper we report an analysis of the performance of these detectors. The main characteristics of GM-APDs of interest for distributed optical fiber sensors are briefly reviewed. Command electronics (active quenching) is then introduced. The detector timing performance sets the maximum spatial resolution in experiments employing OTDR techniques. We highlight that the achievable time resolution depends on the physics of the avalanche spreading over the device area. On the basis of these results, trade-off between the important parameters (quantum efficiency, time resolution, background noise, and afterpulsing effects) is considered. Finally, we show first results on Germanium devices, capable of single photon sensitivity at 1.3 and 1.5 micrometers with sub- nanosecond time resolution.

Theory of Raman scattering in coupled electron-phonon systems

NASA Astrophysics Data System (ADS)

Itai, K.

1992-01-01

The Raman spectrum is calculated for a coupled conduction-electron-phonon system in the zero-momentum-transfer limit. The Raman scattering is due to electron-hole excitations and phonons as well. The phonons of those branches that contribute to the electron self-energy and the correction of the electron-phonon vertex are assumed to have flat energy dispersion (the Einstein phonons). The effect of electron-impurity scattering is also incorporated. Both the electron-phonon interaction and the electron-impurity interaction cause the fluctuation of the electron distribution between different parts of the Fermi surface, which results in overdamped zero-sound modes of various symmetries. The scattering cross section is obtained by solving the Bethe-Salpeter equation. The spectrum shows a lower threshold at the smallest Einstein phonon energy when only the electron-phonon interaction is taken into consideration. When impurities are also taken into consideration, the threshold disappears.

Using the Flipchem Photochemistry Model When Fitting Incoherent Scatter Radar Data

NASA Astrophysics Data System (ADS)

Reimer, A. S.; Varney, R. H.

2017-12-01

The North face Resolute Bay Incoherent Scatter Radar (RISR-N) routinely images the dynamics of the polar ionosphere, providing measurements of the plasma density, electron temperature, ion temperature, and line of sight velocity with seconds to minutes time resolution. RISR-N does not directly measure ionospheric parameters, but backscattered signals, recording them as voltage samples. Using signal processing techniques, radar autocorrelation functions (ACF) are estimated from the voltage samples. A model of the signal ACF is then fitted to the ACF using non-linear least-squares techniques to obtain the best-fit ionospheric parameters. The signal model, and therefore the fitted parameters, depend on the ionospheric ion composition that is used [e.g. Zettergren et. al. (2010), Zou et. al. (2017)].The software used to process RISR-N ACF data includes the "flipchem" model, which is an ion photochemistry model developed by Richards [2011] that was adapted from the Field LineInterhemispheric Plasma (FLIP) model. Flipchem requires neutral densities, neutral temperatures, electron density, ion temperature, electron temperature, solar zenith angle, and F10.7 as inputs to compute ion densities, which are input to the signal model. A description of how the flipchem model is used in RISR-N fitting software will be presented. Additionally, a statistical comparison of the fitted electron density, ion temperature, electron temperature, and velocity obtained using a flipchem ionosphere, a pure O+ ionosphere, and a Chapman O+ ionosphere will be presented. The comparison covers nearly two years of RISR-N data (April 2015 - December 2016). Richards, P. G. (2011), Reexamination of ionospheric photochemistry, J. Geophys. Res., 116, A08307, doi:10.1029/2011JA016613.Zettergren, M., Semeter, J., Burnett, B., Oliver, W., Heinselman, C., Blelly, P.-L., and Diaz, M.: Dynamic variability in F-region ionospheric composition at auroral arc boundaries, Ann. Geophys., 28, 651-664, https://doi.org/10.5194/angeo-28-651-2010, 2010.Zou, S., D. Ozturk, R. Varney, and A. Reimer (2017), Effects of sudden commencement on the ionosphere: PFISR observations and global MHD simulation, Geophys. Res. Lett., 44, 3047-3058, doi:10.1002/2017GL072678.

Electron Microscopy and Analytical X-ray Characterization of Compositional and Nanoscale Structural Changes in Fossil Bone

NASA Astrophysics Data System (ADS)

Boatman, Elizabeth Marie

The nanoscale structure of compact bone contains several features that are direct indicators of bulk tissue mechanical properties. Fossil bone tissues represent unique opportunities to understand the compact bone structure/property relationships from a deep time perspective, offering a possible array of new insights into bone diseases, biomimicry of composite materials, and basic knowledge of bioapatite composition and nanoscale bone structure. To date, most work with fossil bone has employed microscale techniques and has counter-indicated the survival of bioapatite and other nanoscale structural features. The obvious disconnect between the use of microscale techniques and the discernment of nanoscale structure has prompted this work. The goal of this study was to characterize the nanoscale constituents of fossil compact bone by applying a suite of diffraction, microscopy, and spectrometry techniques, representing the highest levels of spatial and energy resolution available today, and capable of complementary structural and compositional characterization from the micro- to the nanoscale. Fossil dinosaur and crocodile long bone specimens, as well as modern ratite and crocodile femurs, were acquired from the UC Museum of Paleontology. Preserved physiological features of significance were documented with scanning electron microscopy back-scattered imaging. Electron microprobe wavelength-dispersive X-ray spectroscopy (WDS) revealed fossil bone compositions enriched in fluorine with a complementary loss of oxygen. X-ray diffraction analyses demonstrated that all specimens were composed of apatite. Transmission electron microscopy (TEM) imaging revealed preserved nanocrystallinity in the fossil bones and electron diffraction studies further identified these nanocrystallites as apatite. Tomographic analyses of nanoscale elements imaged by TEM and small angle X-ray scattering were performed, with the results of each analysis further indicating that nanoscale structure is highly conserved in these four fossil specimens. Finally, the results of this study indicate that bioapatite can be preserved in even the most ancient vertebrate specimens, further supporting the idea that fossilization is a preservational process. This work also underlines the importance of using appropriately selected characterization and analytical techniques for the study of fossil bone, especially from the perspective of spatial resolution and the scale of the bone structural features in question.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jana, R. N.; Meikap, A. K.

The results of a comprehensive study of weak electron localization (WEL) and electron-electron interaction (EEI) effects in disordered V{sub 75}X{sub 25} (X = Pd, Al) alloys has been reported. The resistivity in absence of magnetic field shows a minimum at temperature T = T{sub m} and follows T{sup 1/2} law within the temperature range 5 K ≤ T ≤ T{sub m}, which suggests predominant EEI effect. Magnetoresistivity is positive due to strong spin-orbit interaction. The dephasing scattering time is dominated by the electron-phonon scattering. The electron-phonon scattering rate shows quadratic temperature dependence behavior, which is explained by the theory ofmore » incomplete dragging at the random scattering potential by phonons. The zero temperature scattering time strongly depends on the disorder and its magnitude decreases with increasing disorder.« less

Measurement of Tensor Analyzing Powers for Elastic Electron Scattering from a Polarized 2H Target Internal to a Storage Ring

DOE Office of Scientific and Technical Information (OSTI.GOV)

M. Ferro-Luzzi; M. Bouwhuis; E. Passchier

1996-09-23

We report an absolute measurement of the tensor analyzing powers T20 and T22 in elastic electron-deuteron scattering at a momentum transfer of 1.6 fm{sup -1}. The novel approach of this measurement is the use of a tensor polarized 2H target internal to an electron storage ring, with in situ measurement of the polarization of the target gas. Scattered electrons and recoil deuterons were detected in coincidence with two large acceptance nonmagnetic detectors. The techniques demonstrated have broad applicability to further measurements of spin-dependent electron scattering.

Time-Resolved IR-Absorption Spectroscopy of Hot-Electron Dynamics in Satellite and Upper Conduction Bands in GaP

NASA Technical Reports Server (NTRS)

Cavicchia, M. A.; Alfano, R. R.

1995-01-01

The relaxation dynamics of hot electrons in the X6 and X7 satellite and upper conduction bands in GaP was directly measured by femtosecond UV-pump-IR-probe absorption spectroscopy. From a fit to the induced IR-absorption spectra the dominant scattering mechanism giving rise to the absorption at early delay times was determined to be intervalley scattering of electrons out of the X7 upper conduction-band valley. For long delay times the dominant scattering mechanism is electron-hole scattering. Electron transport dynamics of the upper conduction band of GaP has been time resolved.

When holography meets coherent diffraction imaging.

PubMed

Latychevskaia, Tatiana; Longchamp, Jean-Nicolas; Fink, Hans-Werner

2012-12-17

The phase problem is inherent to crystallographic, astronomical and optical imaging where only the intensity of the scattered signal is detected and the phase information is lost and must somehow be recovered to reconstruct the object's structure. Modern imaging techniques at the molecular scale rely on utilizing novel coherent light sources like X-ray free electron lasers for the ultimate goal of visualizing such objects as individual biomolecules rather than crystals. Here, unlike in the case of crystals where structures can be solved by model building and phase refinement, the phase distribution of the wave scattered by an individual molecule must directly be recovered. There are two well-known solutions to the phase problem: holography and coherent diffraction imaging (CDI). Both techniques have their pros and cons. In holography, the reconstruction of the scattered complex-valued object wave is directly provided by a well-defined reference wave that must cover the entire detector area which often is an experimental challenge. CDI provides the highest possible, only wavelength limited, resolution, but the phase recovery is an iterative process which requires some pre-defined information about the object and whose outcome is not always uniquely-defined. Moreover, the diffraction patterns must be recorded under oversampling conditions, a pre-requisite to be able to solve the phase problem. Here, we report how holography and CDI can be merged into one superior technique: holographic coherent diffraction imaging (HCDI). An inline hologram can be recorded by employing a modified CDI experimental scheme. We demonstrate that the amplitude of the Fourier transform of an inline hologram is related to the complex-valued visibility, thus providing information on both, the amplitude and the phase of the scattered wave in the plane of the diffraction pattern. With the phase information available, the condition of oversampling the diffraction patterns can be relaxed, and the phase problem can be solved in a fast and unambiguous manner. We demonstrate the reconstruction of various diffraction patterns of objects recorded with visible light as well as with low-energy electrons. Although we have demonstrated our HCDI method using laser light and low-energy electrons, it can also be applied to any other coherent radiation such as X-rays or high-energy electrons.

Electron scattering by highly polar molecules. III - CsCl

NASA Technical Reports Server (NTRS)

Vuskovic, L.; Srivastava, S. K.

1981-01-01

Utilizing a crossed electron-beam-molecular-beam scattering geometry, relative values of differential electron scattering cross sections for cesium chloride at 5 and 20 eV electron impact energies and at scattering angles between 10 and 120 deg have been measured. These relative cross sections have been normalized to the cross section at 15 deg scattering angle calculated by the hybrid S-matrix technique. In the angular range between 0 and 10 deg and between 120 and 180 deg extrapolations have been made to obtain integral and momentum transfer cross sections. An energy-loss spectrum is also presented which gives various spectral features lying between the 4 and 10 eV regions in CsCl.

New beam line for time-of-flight medium energy ion scattering with large area position sensitive detector

NASA Astrophysics Data System (ADS)

Linnarsson, M. K.; Hallén, A.; Åström, J.; Primetzhofer, D.; Legendre, S.; Possnert, G.

2012-09-01

A new beam line for medium energy ion mass scattering (MEIS) has been designed and set up at the Ångström laboratory, Uppsala University, Sweden. This MEIS system is based on a time-of-flight (ToF) concept and the electronics for beam chopping relies on a 4 MHz function generator. Repetition rates can be varied between 1 MHz and 63 kHz and pulse widths below 1 ns are typically obtained by including beam bunching. A 6-axis goniometer is used at the target station. Scattering angle and energy of backscattered ions are extracted from a time-resolved and position-sensitive detector. Examples of the performance are given for three kinds of probing ions, 1H+, 4He+, and 11B+. Depth resolution is in the nanometer range and 1 and 2 nm thick Pt layers can easily be resolved. Mass resolution between nearby isotopes can be obtained as illustrated by Ga isotopes in GaAs. Taking advantage of the large size detector, a direct imaging (blocking pattern) of crystal channels are shown for hexagonal, 4H-SiC. The ToF-MEIS system described in this paper is intended for use in semiconductor and thin film areas. For example, depth profiling in the sub nanometer range for device development of contacts and dielectric interfaces. In addition to applied projects, fundamental studies of stopping cross sections in this medium energy range will also be conducted.

Development of a Compton camera for prompt-gamma medical imaging

NASA Astrophysics Data System (ADS)

Aldawood, S.; Thirolf, P. G.; Miani, A.; Böhmer, M.; Dedes, G.; Gernhäuser, R.; Lang, C.; Liprandi, S.; Maier, L.; Marinšek, T.; Mayerhofer, M.; Schaart, D. R.; Lozano, I. Valencia; Parodi, K.

2017-11-01

A Compton camera-based detector system for photon detection from nuclear reactions induced by proton (or heavier ion) beams is under development at LMU Munich, targeting the online range verification of the particle beam in hadron therapy via prompt-gamma imaging. The detector is designed to be capable to reconstruct the photon source origin not only from the Compton scattering kinematics of the primary photon, but also to allow for tracking of the secondary Compton-scattered electrons, thus enabling a γ-source reconstruction also from incompletely absorbed photon events. The Compton camera consists of a monolithic LaBr3:Ce scintillation crystal, read out by a multi-anode PMT acting as absorber, preceded by a stacked array of 6 double-sided silicon strip detectors as scatterers. The detector components have been characterized both under offline and online conditions. The LaBr3:Ce crystal exhibits an excellent time and energy resolution. Using intense collimated 137Cs and 60Co sources, the monolithic scintillator was scanned on a fine 2D grid to generate a reference library of light amplitude distributions that allows for reconstructing the photon interaction position using a k-Nearest Neighbour (k-NN) algorithm. Systematic studies were performed to investigate the performance of the reconstruction algorithm, revealing an improvement of the spatial resolution with increasing photon energy to an optimum value of 3.7(1)mm at 1.33 MeV, achieved with the Categorical Average Pattern (CAP) modification of the k-NN algorithm.

High Spectral Resolution Lidar: System Calibration

NASA Astrophysics Data System (ADS)

Vivek Vivekanandan, J.; Morley, Bruce; Spuler, Scott; Eloranta, Edwin

2015-04-01

One of the unique features of the high spectral resolution lidar (HSRL) is simultaneous measurements of backscatter and extinction of atmosphere. It separates molecular scattering from aerosol and cloud particle backscatter based on their Doppler spectrum width. Scattering from aerosol and cloud particle are referred as Mie scattering. Molecular or Rayleigh scattering is used as a reference for estimating aerosol extinction and backscatter cross-section. Absolute accuracy of the backscattered signals and their separation into Rayleigh and Mie scattering depends on spectral purity of the transmitted signals, accurate measurement of transmit power, and precise performance of filters. Internal calibration is used to characterize optical subsystems Descriptions of high spectral resolution lidar system and its measurement technique can be found in Eloronta (2005) and Hair et al.(2001). Four photon counting detectors are used to measure the backscatter from the combined Rayleigh and molecular scattering (high and low gain), molecular scattering and cross-polarized signal. All of the detectors are sensitive to crosstalk or leakage through the optical filters used to separate the received signals and special data files are used to remove these effects as much as possible. Received signals are normalized with respect to the combined channel response to Mie and Rayleigh scattering. The laser transmit frequency is continually monitored and tuned to the 1109 Iodine absorption line. Aerosol backscatter cross-section is measured by referencing the aerosol return signal to the molecular return signal. Extinction measurements are calculated based on the differences between the expected (theoretical) and actual change in the molecular return. In this paper an overview of calibration of the HSRL is presented. References: Eloranta, E. W., High Spectral Resolution Lidar in Lidar: Range-Resolved Optical Remote Sensing of the Atmosphere, Klaus Weitkamp editor, Springer Series in Optical Sciences, Springer-Verlag, New York, 2005. Hair, JW; Caldwell, LM; Krueger, D. A.Krueger, and C.Y. She 2001: High-spectral-resolution lidar with iodine-vapor filters: measurement of atmospheric-state and aerosol profiles. Appl. Optics, 40, 5280-5294.

Comparison between beamforming and super resolution imaging algorithms for non-destructive evaluation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fan, Chengguang; Drinkwater, Bruce W.

In this paper the performance of total focusing method is compared with the widely used time-reversal MUSIC super resolution technique. The algorithms are tested with simulated and experimental ultrasonic array data, each containing different noise levels. The simulated time domain signals allow the effects of array geometry, frequency, scatterer location, scatterer size, scatterer separation and random noise to be carefully controlled. The performance of the imaging algorithms is evaluated in terms of resolution and sensitivity to random noise. It is shown that for the low noise situation, time-reversal MUSIC provides enhanced lateral resolution when compared to the total focusing method.more » However, for higher noise levels, the total focusing method shows robustness, whilst the performance of time-reversal MUSIC is significantly degraded.« less

Electron mobility of two-dimensional electron gas in InGaN heterostructures: Effects of alloy disorder and random dipole scatterings

NASA Astrophysics Data System (ADS)

Hoshino, Tomoki; Mori, Nobuya

2018-04-01

InGaN has a smaller electron effective mass and is expected to be used as a channel material for high-electron-mobility transistors. However, it is an alloy semiconductor with a random distribution of atoms, which introduces additional scattering mechanisms: alloy disorder and random dipole scatterings. In this work, we calculate the electron mobility in InGaN- and GaN-channel high-electron-mobility transistors (HEMTs) while taking into account acoustic deformation potential, polar optical phonon, alloy disorder, and random dipole scatterings. For InGaN-channel HEMTs, we find that not only alloy disorder but also random dipole scattering has a strong impact on the electron mobility and it significantly decreases as the In mole fraction of the channel increases. Our calculation also shows that the channel thickness w dependence of the mobility is rather weak when w > 1 nm for In0.1Ga0.9N-channel HEMTs.

Comparison of caprock pore networks which potentially will be impacted by carbon sequestration projects.

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCray, John; Navarre-Sitchler, Alexis; Mouzakis, Katherine

Injection of CO2 into underground rock formations can reduce atmospheric CO2 emissions. Caprocks present above potential storage formations are the main structural trap inhibiting CO2 from leaking into overlying aquifers or back to the Earth's surface. Dissolution and precipitation of caprock minerals resulting from reaction with CO2 may alter the pore network where many pores are of the micrometer to nanometer scale, thus altering the structural trapping potential of the caprock. However, the distribution, geometry and volume of pores at these scales are poorly characterized. In order to evaluate the overall risk of leakage of CO2 from storage formations, amore » first critical step is understanding the distribution and shape of pores in a variety of different caprocks. As the caprock is often comprised of mudstones, we analyzed samples from several mudstone formations with small angle neutron scattering (SANS) and high-resolution transmission electron microscopy (TEM) imaging to compare the pore networks. Mudstones were chosen from current or potential sites for carbon sequestration projects including the Marine Tuscaloosa Group, the Lower Tuscaloosa Group, the upper and lower shale members of the Kirtland Formation, and the Pennsylvanian Gothic shale. Expandable clay contents ranged from 10% to approximately 40% in the Gothic shale and Kirtland Formation, respectively. During SANS, neutrons effectively scatter from interfaces between materials with differing scattering length density (i.e., minerals and pores). The intensity of scattered neutrons, I(Q), where Q is the scattering vector, gives information about the volume and arrangement of pores in the sample. The slope of the scattering data when plotted as log I(Q) vs. log Q provides information about the fractality or geometry of the pore network. On such plots slopes from -2 to -3 represent mass fractals while slopes from -3 to -4 represent surface fractals. Scattering data showed surface fractal dimensions for the Kirtland formation and one sample from the Tuscaloosa formation close to 3, indicating very rough surfaces. In contrast, scattering data for the Gothic shale formation exhibited mass fractal behavior. In one sample of the Tuscaloosa formation the data are described by a surface fractal at low Q (larger pores) and a mass fractal at high Q (smaller pores), indicating two pore populations contributing to the scattering behavior. These small angle neutron scattering results, combined with high-resolution TEM imaging, provided a means for both qualitative and quantitative analysis of the differences in pore networks between these various mudstones.« less

Dual-axis confocal microscope for high-resolution in vivo imaging

PubMed Central

Wang, Thomas D.; Mandella, Michael J.; Contag, Christopher H.; Kino, Gordon S.

2007-01-01

We describe a novel confocal microscope that uses separate low-numerical-aperture objectives with the illumination and collection axes crossed at angle θ from the midline. This architecture collects images in scattering media with high transverse and axial resolution, long working distance, large field of view, and reduced noise from scattered light. We measured transverse and axial (FWHM) resolution of 1.3 and 2.1 μm, respectively, in free space, and confirm subcellular resolution in excised esophageal mucosa. The optics may be scaled to millimeter dimensions and fiber coupled for collection of high-resolution images in vivo. PMID:12659264

Experimental electron energy-loss spectra and cross sections for the 4/2/S - 4/2/P transition in Zn II

NASA Technical Reports Server (NTRS)

Chutjian, A.; Newell, W. R.

1982-01-01

Electron energy-loss spectra and differential cross sections are reported for inelastic scattering from Zn II. Measurements were carried out in a crossed electron beam-ion beam apparatus, at incident electron energies of 30, 40, 50, 60, 75, 85, and 100 eV, and at a scattering angle of 14 deg. The present results are the first reported measurements of inelastic electron scattering from an ion.

UHF Radar observations at HAARP with HF pump frequencies near electron gyro-harmonics and associated ionospheric effects

NASA Astrophysics Data System (ADS)

Watkins, Brenton; Fallen, Christopher; Secan, James

Results for HF modification experiments at the HAARP facility in Alaska are presented for experiments with the HF pump frequency near third and fourth electron gyro-harmonics. A UHF diagnostic radar with range resolution of 600 m was used to determine time-dependent altitudes of scattering from plasma turbulence during heating experiments. Experiments were conducted with multiple HF frequencies stepped by 20 kHz above and below the gyro-harmonic values. During times of HF heating the HAARP facility has sufficient power to enhance large-scale ionospheric densities in the lower ionosphere (about 150-200 km altitude) and also in the topside ionosphere (above about 350 km). In the lower ionosphere, time-dependent decreases of the altitude of radar scatter result from electron density enhancements. The effects are substantially different even for relatively small frequency steps of 20 kHz. In all cases the time-varying altitude decrease of radar scatter stops about 5-10 km below the gyro-harmonic altitude that is frequency dependent; we infer that electron density enhancements stop at this altitude where the radar signals stop decreasing with altitude. Experiments with corresponding total electron content (TEC) data show that for HF interaction altitudes above about 170 km there is substantial topside electron density increases due to upward electron thermal conduction. For lower altitudes of HF interaction the majority of the thermal energy is transferred to the neutral gas and no significant topside density increases are observed. By selecting an appropriate HF frequency a little greater than the gyro-harmonic value we have demonstrated that the ionospheric response to HF heating is a self-oscillating mode where the HF interaction altitude moves up and down with a period of several minutes. If the interaction region is above about 170 km this also produces a continuously enhanced topside electron density and upward plasma flux. Experiments using an FM scan with the HF frequency increasing near the gyro-harmonic value were conducted. The FM scan rate was sufficiently slow that the electron density was approximately in an equilibrium state. For these experiments the altitude of the HF interaction follows a near straight line downward parallel to the altitude-dependent gyro-harmonic level.

Listening to light scattering in turbid media: quantitative optical scattering imaging using photoacoustic measurements with one-wavelength illumination

NASA Astrophysics Data System (ADS)

Yuan, Zhen; Li, Xiaoqi; Xi, Lei

2014-06-01

Biomedical photoacoustic tomography (PAT), as a potential imaging modality, can visualize tissue structure and function with high spatial resolution and excellent optical contrast. It is widely recognized that the ability of quantitatively imaging optical absorption and scattering coefficients from photoacoustic measurements is essential before PAT can become a powerful imaging modality. Existing quantitative PAT (qPAT), while successful, has been focused on recovering absorption coefficient only by assuming scattering coefficient a constant. An effective method for photoacoustically recovering optical scattering coefficient is presently not available. Here we propose and experimentally validate such a method for quantitative scattering coefficient imaging using photoacoustic data from one-wavelength illumination. The reconstruction method developed combines conventional PAT with the photon diffusion equation in a novel way to realize the recovery of scattering coefficient. We demonstrate the method using various objects having scattering contrast only or both absorption and scattering contrasts embedded in turbid media. The listening-to-light-scattering method described will be able to provide high resolution scattering imaging for various biomedical applications ranging from breast to brain imaging.

Surface roughness scattering of electrons in bulk mosfets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zuverink, Amanda Renee

2015-11-01

Surface-roughness scattering of electrons at the Si-SiO 2 interface is a very important consideration when analyzing Si metal-oxide-semiconductor field-effect transistors (MOSFETs). Scattering reduces the mobility of the electrons and degrades the device performance. 250-nm and 50-nm bulk MOSFETs were simulated with varying device parameters and mesh sizes in order to compare the effects of surface-roughness scattering in multiple devices. The simulation framework includes the ensemble Monte Carlo method used to solve the Boltzmann transport equation coupled with a successive over-relaxation method used to solve the two-dimensional Poisson's equation. Four methods for simulating the surface-roughness scattering of electrons were implemented onmore » both devices and compared: the constant specularity parameter, the momentum-dependent specularity parameter, and the real-space-roughness method with both uniform and varying electric fields. The specularity parameter is the probability of an electron scattering speculariy from a rough surface. It can be chosen as a constant, characterizing partially diffuse scattering of all electrons from the surface the same way, or it can be momentum dependent, where the size of rms roughness and the normal component of the electron wave number determine the probability of electron-momentum randomization. The real-space rough surface method uses the rms roughness height and correlation length of an actual MOSFET to simulate a rough interface. Due to their charge, electrons scatter from the electric field and not directly from the surface. If the electric field is kept uniform, the electrons do not perceive the roughness and scatter as if from a at surface. However, if the field is allowed to vary, the electrons scatter from the varying electric field as they would in a MOSFET. These methods were implemented for both the 50-nm and 250-nm MOSFETs, and using the rms roughness heights and correlation lengths for real devices. The current-voltage and mobility-electric field curves were plotted for each method on the two devices and compared. The conclusion is that the specularity-parameter methods are valuable as simple models for relatively smooth interfaces. However, they have limitations, as they cannot accurately describe the drastic reduction in the current and the electron mobility that occur in MOSFETs with very rough Si-SiO 2 interfaces.« less

Trans-dimensional joint inversion of seabed scattering and reflection data.

PubMed

Steininger, Gavin; Dettmer, Jan; Dosso, Stan E; Holland, Charles W

2013-03-01

This paper examines joint inversion of acoustic scattering and reflection data to resolve seabed interface roughness parameters (spectral strength, exponent, and cutoff) and geoacoustic profiles. Trans-dimensional (trans-D) Bayesian sampling is applied with both the number of sediment layers and the order (zeroth or first) of auto-regressive parameters in the error model treated as unknowns. A prior distribution that allows fluid sediment layers over an elastic basement in a trans-D inversion is derived and implemented. Three cases are considered: Scattering-only inversion, joint scattering and reflection inversion, and joint inversion with the trans-D auto-regressive error model. Including reflection data improves the resolution of scattering and geoacoustic parameters. The trans-D auto-regressive model further improves scattering resolution and correctly differentiates between strongly and weakly correlated residual errors.

C-Phycocyanin Hydration Water Dynamics in the Presence of Trehalose: An Incoherent Elastic Neutron Scattering Study at Different Energy Resolutions

PubMed Central

Gabel, Frank; Bellissent-Funel, Marie-Claire

2007-01-01

We present a study of C-phycocyanin hydration water dynamics in the presence of trehalose by incoherent elastic neutron scattering. By combining data from two backscattering spectrometers with a 10-fold difference in energy resolution we extract a scattering law S(Q,ω) from the Q-dependence of the elastic intensities without sampling the quasielastic range. The hydration water is described by two dynamically different populations—one diffusing inside a sphere and the other diffusing quasifreely—with a population ratio that depends on temperature. The scattering law derived describes the experimental data from both instruments excellently over a large temperature range (235–320 K). The effective diffusion coefficient extracted is reduced by a factor of 10–15 with respect to bulk water at corresponding temperatures. Our approach demonstrates the benefits and the efficiency of using different energy resolutions in incoherent elastic neutron scattering over a large angular range for the study of biological macromolecules and hydration water. PMID:17350998

Three-Dimensional Orientation of Anisotropic Plasmonic Aggregates at Intracellular Nuclear Indentation Sites by Integrated Light Sheet Super-Resolution Microscopy.

PubMed

Chakkarapani, Suresh Kumar; Sun, Yucheng; Lee, Seungah; Fang, Ning; Kang, Seong Ho

2018-05-22

Three-dimensional (3D) orientations of individual anisotropic plasmonic nanoparticles in aggregates were observed in real time by integrated light sheet super-resolution microscopy ( iLSRM). Asymmetric light scattering of a gold nanorod (AuNR) was used to trigger signals based on the polarizer angle. Controlled photoswitching was achieved by turning the polarizer and obtaining a series of images at different polarization directions. 3D subdiffraction-limited super-resolution images were obtained by superlocalization of scattering signals as a function of the anisotropic optical properties of AuNRs. Varying the polarizer angle allowed resolution of the orientation of individual AuNRs. 3D images of individual nanoparticles were resolved in aggregated regions, resulting in as low as 64 nm axial resolution and 28 nm spatial resolution. The proposed imaging setup and localization approach demonstrates a convenient method for imaging under a noisy environment where the majority of scattering noise comes from cellular components. This integrated 3D iLSRM and localization technique was shown to be reliable and useful in the field of 3D nonfluorescence super-resolution imaging.

High energy Coulomb-scattered electrons for relativistic particle beams and diagnostics

DOE PAGES

Thieberger, P.; Altinbas, Z.; Carlson, C.; ...

2016-03-29

A new system used for monitoring energetic Coulomb-scattered electrons as the main diagnostic for accurately aligning the electron and ion beams in the new Relativistic Heavy Ion Collider (RHIC) electron lenses is described in detail. The theory of electron scattering from relativistic ions is developed and applied to the design and implementation of the system used to achieve and maintain the alignment. Commissioning with gold and 3He beams is then described as well as the successful utilization of the new system during the 2015 RHIC polarized proton run. Systematic errors of the new method are then estimated. Lastly, some possiblemore » future applications of Coulomb-scattered electrons for beam diagnostics are briefly discussed.« less

Absolute vibrational cross sections for 1-19 eV electron scattering from condensed tetrahydrofuran (THF).

PubMed

Lemelin, V; Bass, A D; Cloutier, P; Sanche, L

2016-02-21

Absolute cross sections (CSs) for vibrational excitation by 1-19 eV electrons impacting on condensed tetrahydrofuran (THF) were measured with a high-resolution electron energy loss spectrometer. Experiments were performed under ultra-high vacuum (3 × 10(-11) Torr) at a temperature of about 20 K. The magnitudes of the vibrational CSs lie within the 10(-17) cm(2) range. Features observed near 4.5, 9.5, and 12.5 eV in the incident energy dependence of the CSs were compared to the results of theoretical calculations and other experiments on gas and solid-phase THF. These three resonances are attributed to the formation of shape or core-excited shape resonances. Another maximum observed around 2.5 eV is not found in the calculations but has been observed in gas-phase studies; it is attributed to the formation of a shape resonance.

Electron transport in erbium arsenide:indium gallium(aluminum)arsenide metal/semiconductor nanocomposites for thermoelectric power generation

NASA Astrophysics Data System (ADS)

Bahk, Je-Hyeong

Electron transport in thin film ErAs:InGa(Al)As metal/semiconductor nanocomposite materials grown by molecular beam epitaxy is investigated experimentally and theoretically for efficient thermoelectric power generation. Thermoelectric properties such as the Seebeck coefficient, the electrical conductivity, and the thermal conductivity are measured for the various compositions of the material up to 840 K. A special sample preparation method is proposed to protect the thin films from damage and/or decomposition, and prevent the parasitic substrate conduction effect during the high temperature measurements. The sample preparation method includes surface passivation, high temperature metallization with a diffusion barrier, and the covalent oxide bonding technique for substrate removal. The experimental results for the nanocomposite materials are analyzed using the Boltzmann transport equation under the relaxation time approximation. The scattering characteristics of free electrons in the InGa(Al)As is defined by four major scattering mechanisms such as the polar optical phonon scattering, the ionized impurity scattering, the alloy scattering, and the acoustic phonon deformation potential scattering. Combining these scattering mechanisms, the electron transport model successfully fits the temperature-dependent thermoelectric properties of Si-doped InGaAlAs materials, and predicts the figure of merits at various doping levels in various Al compositions. The nanoparticle-electron interaction is modeled as a momentum scattering for free electrons caused by the electrostatic potential perturbation around nanoparticles and the band offset at the interface. The ErAs nanoparticles are assumed to be semi-metals that can donate electrons to the matrix, and positively charged after the charge transfer to build up the screened coulomb potential outside them. The nanoparticle scattering rate is calculated for this potential profile using the partial wave method, and used to analyze the enhancement of the Seebeck coefficient. Finally, the experimental results for the various compositions of the ErAs:InGa(Al)As nanocomposites are fit using the electron transport model and the nanoparticle scattering. It is shown that nanoparticle scattering can enhance the power factor via energy-dependent electron scattering in ErAs:InGaAs system. The figure of merit for the 0.6% ErAs:(InGaAs)0.8(InAlAs) 0.2 lattice matched to InP is measured to be 1.3 at 800 K, and the theory predicts that it can reach 1.9 at 1000 K.

LETTER TO THE EDITOR: Differential electron scattering from the (010) excited vibrational mode of N2O

NASA Astrophysics Data System (ADS)

Akther, P.; Johnstone, W. M.; El-Zein, A. A. A.; Campbell, L.; Teubner, P. J. O.; Brunger, M. J.; Newell, W. R.

2002-11-01

In this letter we report differential superelastic, elastic and inelastic electron scattering measurements from nitrous oxide (N2O) in its (010)* excited vibrational quantum. The incident electron energy was 2.5 eV and the scattered electron angular range was 10°- 40°. Unlike our previous results (1999 J. Phys. B: At. Mol. Opt. Phys. 32 5779) with the isoelectronic molecule carbon dioxide (CO2), where the elastic differential cross sections (DCSs) for scattering from the (010)* mode were 2.3 times larger than those for elastic scattering from the ground (000) state, in N2O the corresponding (010)* elastic cross sections are usually only a fraction of those for the ground state. To the best of our knowledge, the present data are the first DCSs which have been reported in the literature for electron scattering from an excited vibrational level of the N2O molecule.

Thomson scattering from a three-component plasma.

PubMed

Johnson, W R; Nilsen, J

2014-02-01

A model for a three-component plasma consisting of two distinct ionic species and electrons is developed and applied to study x-ray Thomson scattering. Ions of a specific type are assumed to be identical and are treated in the average-atom approximation. Given the plasma temperature and density, the model predicts mass densities, effective ionic charges, and cell volumes for each ionic type, together with the plasma chemical potential and free-electron density. Additionally, the average-atom treatment of individual ions provides a quantum-mechanical description of bound and continuum electrons. The model is used to obtain parameters needed to determine the dynamic structure factors for x-ray Thomson scattering from a three-component plasma. The contribution from inelastic scattering by free electrons is evaluated in the random-phase approximation. The contribution from inelastic scattering by bound electrons is evaluated using the bound-state and scattering wave functions obtained from the average-atom calculations. Finally, the partial static structure factors for elastic scattering by ions are evaluated using a two-component version of the Ornstein-Zernike equations with hypernetted chain closure, in which electron-ion interactions are accounted for using screened ion-ion interaction potentials. The model is used to predict the x-ray Thomson scattering spectrum from a CH plasma and the resulting spectrum is compared with experimental results obtained by Feltcher et al. [Phys. Plasmas 20, 056316 (2013)].

The interaction of low-energy electrons with fructose molecules

NASA Astrophysics Data System (ADS)

Chernyshova, I. V.; Kontrosh, E. E.; Markush, P. P.; Shpenik, O. B.

2017-11-01

Using a hypocycloidal electronic spectrometer, the interactions of low energy electrons (0-8.50 eV) with fructose molecules, namely, electron scattering and dissociative attachment, are studied. The results of these studies showed that the fragmentation of fructose molecules occurs effectively even at an electron energy close to zero. In the total electron-scattering cross section by molecules, resonance features (at energies 3.10 and 5.00 eV) were first observed near the formation thresholds of light ion fragments OH- and H-. The correlation of the features observed in the cross sections of electron scattering and dissociative attachment is analyzed.

The DarkLight Experiment at the JLab FEL

NASA Astrophysics Data System (ADS)

Fisher, Peter

2013-10-01

DarkLight will study the production of gauge bosons associated with Dark Forces theories in the scattering of 100 MeV electrons on proton a target. DarkLight is a spectrometer to measure all the final state particles in e- + p -->e- + p +e- +e+ . QED allows this process and the invariant mass distribution of the e+e- pair is a continuum from nearly zero to nearly the electron beam energy. Dark Forces theories, which allow the dark matter mass scale to be over 1 TeV, predict a gauge boson A' in the mass range of 10-1,000 MeV and decays to an electron-positron pair with an invariant mass of mA'. We aim to search for this process using the 100 MeV, 10 mA electron beam at the JLab Free Electron Laser impinging on a hydrogen target with a 1019 cm-2 density. The resulting luminosity of 6 ×1035/cm2-s gives the experiment enough sensitivity to probe A' couplings of 10-9 α . DarkLight is unique in its design to detect all four particles in the final state. The leptons will be measured in a large high-rate TPC and a silicon sensor will measure the protons. A 0.5 T solenoidal magnetic field provides the momentum resolution and focuses the copious Møller scattering background down the beam line, away from the detectors. A first beam test has shown the FEL beam is compatible with the target design and that the hall backgrounds are manageable. The experiment has been approved by Jefferson Lab for first running in 2017.

Microstructural features of carious human enamel imaged with back-scattered electrons.

PubMed

Pearce, E I; Nelson, D G

1989-02-01

We have used back-scattered electrons (BE) in the scanning electron microscope to produce mineral density images of enamel. Flat surfaces of artificially-carious enamel, softened in an intra-oral experiment, and naturally-carious (white spot) enamel were polished to a high gloss with diamond lapping compound, rendering them almost featureless by secondary electron scanning electron microscopy. They were then examined at 10 to 30 kV in a Philips 505 instrument fitted with a 4-quadrant BE detector. Study of surfaces prepared approximately parallel to the natural surface showed that mineral was lost from both prism core and the interprismatic region, leaving a thin mineral-rich rim at the prism periphery. The same lesions viewed longitudinally on a surface prepared perpendicular to the natural surface showed mineral-rich bands at the prism margins in the outer enamel. Near the advancing front of the lesion, the prism junctions were widened and the prism cores sometimes hypermineralized. Natural lesions sectioned in the prism long axis showed features previously seen with other techniques, e.g., cross-striations and striae of Retzius, but in much greater detail. Mineral enrichment at the prism periphery in the lesion body and a widening of the prism junction at the advancing fronts of lesions in permanent teeth were most obvious. Calculations showed that with an accelerating voltage of 30 kV, the images reflected mineral density up to 4 microns beneath the surface. BE microscopy produces a high-resolution image of mineral loss or gain in carious enamel, with relatively easy sample preparation.

Low-energy electron scattering from atomic hydrogen. II. Elastic and inelastic scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

James, K.E. Jr.; Childers, J.G.; Khakoo, M.A.

2004-02-01

We present measurements of differential cross sections for elastic electron scattering from atomic hydrogen at 20 eV and 40 eV incident electron energies and ratios of differential cross sections for electron-impact excitation of atomic hydrogen to the n=2, 3, and 4 levels at incident electron energies of 14.6 eV, 15.6 eV, 17.6 eV, 20 eV, 25 eV, and 40 eV with scattering angles ranging from 10 deg. to 130 deg. We compare our results to available experimental measurements and recent convergent close-coupling calculations. Our results resolve significant discrepancies that existed between theory and past experiments.

A Concept for a High-Energy Gamma-ray Polarimeter

NASA Technical Reports Server (NTRS)

Bloser, P. F.; Hunter, S. D.; Depaola, G. O.; Longo, F.

2003-01-01

We present a concept for an imaging gamma-ray polarimeter operating from approx. 50 MeV to approx. 1 GeV. Such an instrument would be valuable for the study of high-energy pulsars, active galactic nuclei, supernova remnants, and gamma-ray bursts. The concept makes use of pixelized gas micro-well detectors, under development at Goddard Space Flight Center, to record the electron-positron tracks from pair-production events in a large gas volume. Pixelized micro-well detectors have the potential to form large-volume 3-D track imagers with approx. 100 micron (rms) position resolution at moderate cost. The combination of high spatial resolution and a continuous low-density gas medium permits many thousands of measurements per radiation length, allowing the particle tracks to be imaged accurately before multiple scattering masks their original directions. The polarization of the incoming radiation may then be determined from the azimuthal distribution of the electron-positron pairs. We have performed Geant4 simulations of these processes to estimate the polarization sensitivity as a function of instrument parameters and event selection criteria.

Rippling ultrafast dynamics of suspended 2D monolayers, graphene

PubMed Central

Hu, Jianbo; Vanacore, Giovanni M.; Cepellotti, Andrea; Marzari, Nicola; Zewail, Ahmed H.

2016-01-01

Here, using ultrafast electron crystallography (UEC), we report the observation of rippling dynamics in suspended monolayer graphene, the prototypical and most-studied 2D material. The high scattering cross-section for electron/matter interaction, the atomic-scale spatial resolution, and the ultrafast temporal resolution of UEC represent the key elements that make this technique a unique tool for the dynamic investigation of 2D materials, and nanostructures in general. We find that, at early time after the ultrafast optical excitation, graphene undergoes a lattice expansion on a time scale of 5 ps, which is due to the excitation of short-wavelength in-plane acoustic phonon modes that stretch the graphene plane. On a longer time scale, a slower thermal contraction with a time constant of 50 ps is observed and associated with the excitation of out-of-plane phonon modes, which drive the lattice toward thermal equilibrium with the well-known negative thermal expansion coefficient of graphene. From our results and first-principles lattice dynamics and out-of-equilibrium relaxation calculations, we quantitatively elucidate the deformation dynamics of the graphene unit cell. PMID:27791028

Rippling ultrafast dynamics of suspended 2D monolayers, graphene.

PubMed

Hu, Jianbo; Vanacore, Giovanni M; Cepellotti, Andrea; Marzari, Nicola; Zewail, Ahmed H

2016-10-25

Here, using ultrafast electron crystallography (UEC), we report the observation of rippling dynamics in suspended monolayer graphene, the prototypical and most-studied 2D material. The high scattering cross-section for electron/matter interaction, the atomic-scale spatial resolution, and the ultrafast temporal resolution of UEC represent the key elements that make this technique a unique tool for the dynamic investigation of 2D materials, and nanostructures in general. We find that, at early time after the ultrafast optical excitation, graphene undergoes a lattice expansion on a time scale of 5 ps, which is due to the excitation of short-wavelength in-plane acoustic phonon modes that stretch the graphene plane. On a longer time scale, a slower thermal contraction with a time constant of 50 ps is observed and associated with the excitation of out-of-plane phonon modes, which drive the lattice toward thermal equilibrium with the well-known negative thermal expansion coefficient of graphene. From our results and first-principles lattice dynamics and out-of-equilibrium relaxation calculations, we quantitatively elucidate the deformation dynamics of the graphene unit cell.

Crystallization and preliminary X-ray analysis of the inducible lysine decarboxylase from Escherichia coli

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alexopoulos, Eftichia; Department of Medical Biophysics, University of Toronto, Division of Cancer Genomics and Proteomics, Ontario Cancer Institute, Toronto Medical Discovery Tower, 101 College Street, Toronto, Ontario M5G 1L7; Kanjee, Usheer

2008-08-01

The structure of the decameric inducible lysine decarboxylase from E. coli was determined by SIRAS using a hexatantalum dodecabromide (Ta{sub 6}Br{sub 12}{sup 2+}) derivative. Model building and refinement are under way. The decameric inducible lysine decarboxylase (LdcI) from Escherichia coli has been crystallized in space groups C2 and C222{sub 1}; the Ta{sub 6}Br{sub 12}{sup 2+} cluster was used to derivatize the C2 crystals. The method of single isomorphous replacement with anomalous scattering (SIRAS) as implemented in SHELXD was used to solve the Ta{sub 6}Br{sub 12}{sup 2+}-derivatized structure to 5 Å resolution. Many of the Ta{sub 6}Br{sub 12}{sup 2+}-binding sites hadmore » twofold and fivefold noncrystallographic symmetry. Taking advantage of this feature, phase modification was performed in DM. The electron-density map of LdcI displays many features in agreement with the low-resolution negative-stain electron-density map [Snider et al. (2006 ▶), J. Biol. Chem.281, 1532–1546].« less

An analytic formula for the relativistic incoherent Thomson backscattering spectrum for a drifting bi-Maxwellian plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Naito, O.

2015-08-15

An analytic formula has been derived for the relativistic incoherent Thomson backscattering spectrum for a drifting anisotropic plasma when the scattering vector is parallel to the drifting direction. The shape of the scattering spectrum is insensitive to the electron temperature perpendicular to the scattering vector, but its amplitude may be modulated. As a result, while the measured temperature correctly represents the electron distribution parallel to the scattering vector, the electron density may be underestimated when the perpendicular temperature is higher than the parallel temperature. Since the scattering spectrum in shorter wavelengths is greatly enhanced by the existence of drift, themore » diagnostics might be used to measure local electron current density in fusion plasmas.« less

PF-AR NW14, a new time-resolved diffraction/scattering beamline

NASA Astrophysics Data System (ADS)

Nozawa, Shunsuke; Adachi, Shin-ichi; Tazaki, Ryoko; Takahashi, Jun-ichi; Itatani, Jiro; Daimon, Masahiro; Mori, Takeharu; Sawa, Hiroshi; Kawata, Hiroshi; Koshihara, Shin-ya

2005-01-01

NW14 is a new insertion device beamline at the Photon Factory Advanced Ring (PF-AR), which is a unique ring with full-time single-bunched operation, aiming for timeresolved x-ray diffraction/scattering and XAFS experiments. The primary scientific goal of this beamline is to observe the ultrafast dynamics of condensed matter systems such as organic and inorganic crystals, biological systems and liquids triggered by optical pulses. With the large photon fluxes derived from the undulator, it should become possible to take a snapshoot an atomic-scale image of the electron density distribution. By combining a series of images it is possible to produce a movie of the photo-induced dynamics with 50-ps resolution. The construction of the beamline is being funded by the ERATO Koshihara Non-equilibrium Dynamics Project of the Japan Science and Technology Agency (JST), and the beamline will be operational from autumn 2005.

Femtosecond X-ray coherent diffraction of aligned amyloid fibrils on low background graphene.

PubMed

Seuring, Carolin; Ayyer, Kartik; Filippaki, Eleftheria; Barthelmess, Miriam; Longchamp, Jean-Nicolas; Ringler, Philippe; Pardini, Tommaso; Wojtas, David H; Coleman, Matthew A; Dörner, Katerina; Fuglerud, Silje; Hammarin, Greger; Habenstein, Birgit; Langkilde, Annette E; Loquet, Antoine; Meents, Alke; Riek, Roland; Stahlberg, Henning; Boutet, Sébastien; Hunter, Mark S; Koglin, Jason; Liang, Mengning; Ginn, Helen M; Millane, Rick P; Frank, Matthias; Barty, Anton; Chapman, Henry N

2018-05-09

Here we present a new approach to diffraction imaging of amyloid fibrils, combining a free-standing graphene support and single nanofocused X-ray pulses of femtosecond duration from an X-ray free-electron laser. Due to the very low background scattering from the graphene support and mutual alignment of filaments, diffraction from tobacco mosaic virus (TMV) filaments and amyloid protofibrils is obtained to 2.7 Å and 2.4 Å resolution in single diffraction patterns, respectively. Some TMV diffraction patterns exhibit asymmetry that indicates the presence of a limited number of axial rotations in the XFEL focus. Signal-to-noise levels from individual diffraction patterns are enhanced using computational alignment and merging, giving patterns that are superior to those obtainable from synchrotron radiation sources. We anticipate that our approach will be a starting point for further investigations into unsolved structures of filaments and other weakly scattering objects.

Molecular structures and intramolecular dynamics of pentahalides

NASA Astrophysics Data System (ADS)

Ischenko, A. A.

2017-03-01

This paper reviews advances of modern gas electron diffraction (GED) method combined with high-resolution spectroscopy and quantum chemical calculations in studies of the impact of intramolecular dynamics in free molecules of pentahalides. Some recently developed approaches to the electron diffraction data interpretation, based on direct incorporation of the adiabatic potential energy surface parameters to the diffraction intensity are described. In this way, complementary data of different experimental and computational methods can be directly combined for solving problems of the molecular structure and its dynamics. The possibility to evaluate some important parameters of the adiabatic potential energy surface - barriers to pseudorotation and saddle point of intermediate configuration from diffraction intensities in solving the inverse GED problem is demonstrated on several examples. With increasing accuracy of the electron diffraction intensities and the development of the theoretical background of electron scattering and data interpretation, it has become possible to investigate complex nuclear dynamics in fluxional systems by the GED method. Results of other research groups are also included in the discussion.

A streaming multi-GPU implementation of image simulation algorithms for scanning transmission electron microscopy

DOE PAGES

Pryor, Alan; Ophus, Colin; Miao, Jianwei

2017-10-25

Simulation of atomic-resolution image formation in scanning transmission electron microscopy can require significant computation times using traditional methods. A recently developed method, termed plane-wave reciprocal-space interpolated scattering matrix (PRISM), demonstrates potential for significant acceleration of such simulations with negligible loss of accuracy. In this paper, we present a software package called Prismatic for parallelized simulation of image formation in scanning transmission electron microscopy (STEM) using both the PRISM and multislice methods. By distributing the workload between multiple CUDA-enabled GPUs and multicore processors, accelerations as high as 1000 × for PRISM and 15 × for multislice are achieved relative to traditionalmore » multislice implementations using a single 4-GPU machine. We demonstrate a potentially important application of Prismatic, using it to compute images for atomic electron tomography at sufficient speeds to include in the reconstruction pipeline. Prismatic is freely available both as an open-source CUDA/C++ package with a graphical user interface and as a Python package, PyPrismatic.« less

Upgrades at the Duke Free Electron Laser Laboratory

NASA Astrophysics Data System (ADS)

Howell, Calvin R.

2004-11-01

Major upgrades to the storage-ring based photon sources at the Duke Free Electron Laser Laboratory (DFELL) are underway. The photon sources at the DFELL are well suited for research in the areas of medicine, biophysics, accelerator physics, nuclear physics and material science. These upgrades, which will be completed by the summer 2006, will significantly enhance the capabilities of the ultraviolet (UV) free-electron laser (FEL) and the high intensity gamma-ray source (HIGS). The HIGS is a relatively new research facility at the DFELL that is operated jointly by the DFELL and the Triangle Universities Nuclear Laboratory. The gamma-ray beam is produced by Compton back scattering of the UV photons inside the FEL optical cavity off the circulating electrons in the storage ring. The gamma-ray beam is 100% polarized and its energy resolution is selected by collimation. The capabilities of the upgraded facility will be described, the status of the upgrades will be summarized, and the proposed first-generation research program at HIGS will be presented.

Applications and limitations of electron correlation microscopy to study relaxation dynamics in supercooled liquids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Pei; He, Li; Besser, Matthew F.

Here, electron correlation microscopy (ECM) is a way to measure structural relaxation times, τ, of liquids with nanometer-scale spatial resolution using coherent electron scattering equivalent of photon correlation spectroscopy. We have applied ECM with a 3.5 nm diameter probe to Pt 57.5Cu 14.7Ni 5.3P 22.5 amorphous nanorods and Pd 40Ni 40P 20 bulk metallic glass (BMG) heated inside the STEM into the supercooled liquid region. These data demonstrate that the ECM technique is limited by the characteristics of the time series, which must be at least 40τ to obtain a well-converged correlation function g 2(t), and the time per frame,more » which must be less than 0.1τ to obtain sufficient sampling. A high-speed direct electron camera enables fast acquisition and affords reliable g 2(t) data even with low signal per frame.« less

Applications and limitations of electron correlation microscopy to study relaxation dynamics in supercooled liquids

DOE PAGES

Zhang, Pei; He, Li; Besser, Matthew F.; ...

2016-09-08

Here, electron correlation microscopy (ECM) is a way to measure structural relaxation times, τ, of liquids with nanometer-scale spatial resolution using coherent electron scattering equivalent of photon correlation spectroscopy. We have applied ECM with a 3.5 nm diameter probe to Pt 57.5Cu 14.7Ni 5.3P 22.5 amorphous nanorods and Pd 40Ni 40P 20 bulk metallic glass (BMG) heated inside the STEM into the supercooled liquid region. These data demonstrate that the ECM technique is limited by the characteristics of the time series, which must be at least 40τ to obtain a well-converged correlation function g 2(t), and the time per frame,more » which must be less than 0.1τ to obtain sufficient sampling. A high-speed direct electron camera enables fast acquisition and affords reliable g 2(t) data even with low signal per frame.« less

High-resolution in situ observations of electron precipitation-causing EMIC waves

DOE PAGES

Rodger, Craig J.; Hendry, Aaron T.; Clilverd, Mark A.; ...

2015-11-21

Electromagnetic ion cyclotron (EMIC) waves are thought to be important drivers of energetic electron losses from the outer radiation belt through precipitation into the atmosphere. While the theoretical possibility of pitch angle scattering-driven losses from these waves has been recognized for more than four decades, there have been limited experimental precipitation observations to support this concept. We have combined satellite-based observations of the characteristics of EMIC waves, with satellite and ground-based observations of the EMIC-induced electron precipitation. In a detailed case study, supplemented by an additional four examples, we are able to constrain for the first time the location, size,more » and energy range of EMIC-induced electron precipitation inferred from coincident precipitation data and relate them to the EMIC wave frequency, wave power, and ion band of the wave as measured in situ by the Van Allen Probes. As a result, these observations will better constrain modeling into the importance of EMIC wave-particle interactions.« less

A streaming multi-GPU implementation of image simulation algorithms for scanning transmission electron microscopy.

PubMed

Pryor, Alan; Ophus, Colin; Miao, Jianwei

2017-01-01

Simulation of atomic-resolution image formation in scanning transmission electron microscopy can require significant computation times using traditional methods. A recently developed method, termed plane-wave reciprocal-space interpolated scattering matrix (PRISM), demonstrates potential for significant acceleration of such simulations with negligible loss of accuracy. Here, we present a software package called Prismatic for parallelized simulation of image formation in scanning transmission electron microscopy (STEM) using both the PRISM and multislice methods. By distributing the workload between multiple CUDA-enabled GPUs and multicore processors, accelerations as high as 1000 × for PRISM and 15 × for multislice are achieved relative to traditional multislice implementations using a single 4-GPU machine. We demonstrate a potentially important application of Prismatic , using it to compute images for atomic electron tomography at sufficient speeds to include in the reconstruction pipeline. Prismatic is freely available both as an open-source CUDA/C++ package with a graphical user interface and as a Python package, PyPrismatic .

A streaming multi-GPU implementation of image simulation algorithms for scanning transmission electron microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pryor, Alan; Ophus, Colin; Miao, Jianwei

Simulation of atomic-resolution image formation in scanning transmission electron microscopy can require significant computation times using traditional methods. A recently developed method, termed plane-wave reciprocal-space interpolated scattering matrix (PRISM), demonstrates potential for significant acceleration of such simulations with negligible loss of accuracy. In this paper, we present a software package called Prismatic for parallelized simulation of image formation in scanning transmission electron microscopy (STEM) using both the PRISM and multislice methods. By distributing the workload between multiple CUDA-enabled GPUs and multicore processors, accelerations as high as 1000 × for PRISM and 15 × for multislice are achieved relative to traditionalmore » multislice implementations using a single 4-GPU machine. We demonstrate a potentially important application of Prismatic, using it to compute images for atomic electron tomography at sufficient speeds to include in the reconstruction pipeline. Prismatic is freely available both as an open-source CUDA/C++ package with a graphical user interface and as a Python package, PyPrismatic.« less

Comprehensive investigation of the electronic excitation of W(CO)6 by photoabsorption and theoretical analysis in the energy region from 3.9 to 10.8 eV.

PubMed

Mendes, Mónica; Regeta, Khrystyna; Ferreira da Silva, Filipe; Jones, Nykola C; Hoffmann, Søren Vrønning; García, Gustavo; Daniel, Chantal; Limão-Vieira, Paulo

2017-01-01

High-resolution vacuum ultraviolet photoabsorption measurements in the wavelength range of 115-320 nm (10.8-3.9 eV) have been performed together with comprehensive relativistic time-dependent density functional calculations (TDDFT) on the low-lying excited sates of tungsten hexacarbonyl, W(CO) 6 . The higher resolution obtained reveals previously unresolved spectral features of W(CO) 6 . The spectrum shows two higher-energy bands (in the energy ranges of 7.22-8.12 eV and 8.15-9.05 eV), one of them with clear vibrational structure, and a few lower-energy shoulders in addition to a couple of lower-energy metal-to-ligand charge-transfer (MLCT) bands reported in the literature before. Absolute photoabsorption cross sections are reported and, where possible, compared to previously published results. On the basis of this combined experimental/theoretical study the absorption spectrum of the complex has been totally re-assigned between 3.9 and 10.8 eV under the light of spin-orbit coupling (SOC) effects. The present comprehensive knowledge of the nature of the electronically excited states may be of relevance to estimate neutral dissociation cross sections of W(CO) 6 , a precursor molecule in focused electron beam induced deposition (FEBID) processes, from electron scattering measurements.

Comprehensive investigation of the electronic excitation of W(CO)6 by photoabsorption and theoretical analysis in the energy region from 3.9 to 10.8 eV

PubMed Central

Mendes, Mónica; Regeta, Khrystyna; Ferreira da Silva, Filipe; Jones, Nykola C; Hoffmann, Søren Vrønning; García, Gustavo

2017-01-01

High-resolution vacuum ultraviolet photoabsorption measurements in the wavelength range of 115–320 nm (10.8–3.9 eV) have been performed together with comprehensive relativistic time-dependent density functional calculations (TDDFT) on the low-lying excited sates of tungsten hexacarbonyl, W(CO)6. The higher resolution obtained reveals previously unresolved spectral features of W(CO)6. The spectrum shows two higher-energy bands (in the energy ranges of 7.22–8.12 eV and 8.15–9.05 eV), one of them with clear vibrational structure, and a few lower-energy shoulders in addition to a couple of lower-energy metal-to-ligand charge-transfer (MLCT) bands reported in the literature before. Absolute photoabsorption cross sections are reported and, where possible, compared to previously published results. On the basis of this combined experimental/theoretical study the absorption spectrum of the complex has been totally re-assigned between 3.9 and 10.8 eV under the light of spin–orbit coupling (SOC) effects. The present comprehensive knowledge of the nature of the electronically excited states may be of relevance to estimate neutral dissociation cross sections of W(CO)6, a precursor molecule in focused electron beam induced deposition (FEBID) processes, from electron scattering measurements. PMID:29114447

High-resolution Compton scattering study of the electron momentum density in Al

NASA Astrophysics Data System (ADS)

Ohata, T.; Itou, M.; Matsumoto, I.; Sakurai, Y.; Kawata, H.; Shiotani, N.; Kaprzyk, S.; Mijnarends, P. E.; Bansil, A.

2000-12-01

We report high-resolution Compton profiles (CP's) of Al along the three principal symmetry directions at a photon energy of 59.38 keV, together with corresponding highly accurate theoretical profiles obtained within the local-density approximation (LDA) based band-theory framework. A good accord between theory and experiment is found with respect to the overall shapes of the CP's and their first and second derivatives, as well as the anisotropies in the CP's defined as differences between pairs of various CP's. There are, however, discrepancies in that, in comparison to the LDA predictions, the measured profiles are lower at low momenta, show a Fermi cutoff that is broader, and display a tail that is higher at momenta above the Fermi momentum. A number of simple model calculations are carried out in order to gain insight into the nature of the underlying 3D momentum density in Al and the role of the Fermi surface in inducing fine structure in the CP's. The present results when compared with those on Li show clearly that the size of discrepancies between theoretical and experimental CP's is markedly smaller in Al than in Li. This indicates that, with increasing electron density, the conventional picture of the electron gas becomes more representative of the momentum density and that shortcomings of the LDA framework in describing the electron correlation effects become less important.

A United Effort for Crystal Growth, Neutron Scattering, and X-ray Scattering Studies of Novel Correlated Electron Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Young S.

2015-02-12

The research accomplishments during the award involved experimental studies of correlated electron systems and quantum magnetism. The techniques of crystal growth, neutron scattering, x-ray scattering, and thermodynamic & transport measurements were employed, and graduate students and postdoctoral research associates were trained in these techniques.

Spin-dependence of the electron scattering cross section by a magnetic layer system and the magneto-resistance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, J.T.; Tang, F.; Brown, W.D.

1998-12-20

The authors present a theoretical model for calculating the spin-dependent cross section of the scattering of electrons by a magnetic layer system. The model demonstrates that the cross sections of the scattering are different for spin up and spin down electrons. The model assumes that the electrical resistivity in a conductor is proportional to the scattering cross section of the electron in it. It is believed to support the two channel mechanism in interpreting magneto-resistance (MR). Based on the model without considering the scattering due to the interfacial roughness and the spin flipping scattering, the authors have established a relationshipmore » between MR and the square of the magnetic moment in the bulk sample without considering the scattering due to the interfacial roughness and the spin flipping scattering. It can also qualitatively explain the MR difference between the current in plane (CIP) and current perpendicular to the plane (CPP) configurations. The predictions by the model agree well with the experimental findings.« less

Electron scattering in large water clusters from photoelectron imaging with high harmonic radiation.

PubMed

Gartmann, Thomas E; Hartweg, Sebastian; Ban, Loren; Chasovskikh, Egor; Yoder, Bruce L; Signorell, Ruth

2018-06-06

Low-energy electron scattering in water clusters (H2O)n with average cluster sizes of n < 700 is investigated by angle-resolved photoelectron spectroscopy using high harmonic radiation at photon energies of 14.0, 20.3, and 26.5 eV for ionization from the three outermost valence orbitals. The measurements probe the evolution of the photoelectron anisotropy parameter β as a function of cluster size. A remarkably steep decrease of β with increasing cluster size is observed, which for the largest clusters reaches liquid bulk values. Detailed electron scattering calculations reveal that neither gas nor condensed phase scattering can explain the cluster data. Qualitative agreement between experiment and simulations is obtained with scattering calculations that treat cluster scattering as an intermediate case between gas and condensed phase scattering.

Measurement of the dynamic charge response of materials using low-energy, momentum-resolved electron energy-loss spectroscopy (M-EELS)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Husain, Ali A.; Mitrano, Matteo; Rak, Melinda S.

One of the most fundamental properties of an interacting electron system is its frequency- and wave-vector-dependent density response function, χ(q,ω). The imaginary part, χ"(q,ω), defines the fundamental bosonic charge excitations of the system, exhibiting peaks wherever collective modes are present. χ quantifies the electronic compressibility of a material, its response to external fields, its ability to screen charge, and its tendency to form charge density waves. Unfortunately, there has never been a fully momentum-resolved means to measure χ(q,ω) at the meV energy scale relevant to modern electronic materials. Here, we demonstrate a way to measure χ with quantitative momentum resolutionmore » by applying alignment techniques from x-ray and neutron scattering to surface high-resolution electron energy-loss spectroscopy (HR-EELS). This approach, which we refer to here as M-EELS" allows direct measurement of χ"(q,ω) with meV resolution while controlling the momentum with an accuracy better than a percent of a typical Brillouin zone. We apply this technique to finite-{\\bf q} excitations in the optimally-doped high temperature superconductor, Bi 2Sr 2CaCu 2O 8+x (Bi2212), which exhibits several phonons potentially relevant to dispersion anomalies observed in ARPES and STM experiments. In conclusion, our study defines a path to studying the long-sought collective charge modes in quantum materials at the meV scale and with full momentum control.« less

Measurement of the dynamic charge response of materials using low-energy, momentum-resolved electron energy-loss spectroscopy (M-EELS)

DOE PAGES

Husain, Ali A.; Mitrano, Matteo; Rak, Melinda S.; ...

2017-10-06

One of the most fundamental properties of an interacting electron system is its frequency- and wave-vector-dependent density response function, χ(q,ω). The imaginary part, χ"(q,ω), defines the fundamental bosonic charge excitations of the system, exhibiting peaks wherever collective modes are present. χ quantifies the electronic compressibility of a material, its response to external fields, its ability to screen charge, and its tendency to form charge density waves. Unfortunately, there has never been a fully momentum-resolved means to measure χ(q,ω) at the meV energy scale relevant to modern electronic materials. Here, we demonstrate a way to measure χ with quantitative momentum resolutionmore » by applying alignment techniques from x-ray and neutron scattering to surface high-resolution electron energy-loss spectroscopy (HR-EELS). This approach, which we refer to here as M-EELS" allows direct measurement of χ"(q,ω) with meV resolution while controlling the momentum with an accuracy better than a percent of a typical Brillouin zone. We apply this technique to finite-{\\bf q} excitations in the optimally-doped high temperature superconductor, Bi 2Sr 2CaCu 2O 8+x (Bi2212), which exhibits several phonons potentially relevant to dispersion anomalies observed in ARPES and STM experiments. In conclusion, our study defines a path to studying the long-sought collective charge modes in quantum materials at the meV scale and with full momentum control.« less

Relative merits and limiting factors for x-ray and electron microscopy of thick, hydrated organic materials.

PubMed

Du, Ming; Jacobsen, Chris

2018-01-01

Electron and x-ray microscopes allow one to image the entire, unlabeled structure of hydrated materials at a resolution well beyond what visible light microscopes can achieve. However, both approaches involve ionizing radiation, so that radiation damage must be considered as one of the limits to imaging. Drawing upon earlier work, we describe here a unified approach to estimating the image contrast (and thus the required exposure and corresponding radiation dose) in both x-ray and electron microscopy. This approach accounts for factors such as plural and inelastic scattering, and (in electron microscopy) the use of energy filters to obtain so-called "zero loss" images. As expected, it shows that electron microscopy offers lower dose for specimens thinner than about 1 µm (such as for studies of macromolecules, viruses, bacteria and archaebacteria, and thin sectioned material), while x-ray microscopy offers superior characteristics for imaging thicker specimen such as whole eukaryotic cells, thick-sectioned tissues, and organs. The required radiation dose scales strongly as a function of the desired spatial resolution, allowing one to understand the limits of live and frozen hydrated specimen imaging. Finally, we consider the factors limiting x-ray microscopy of thicker materials, suggesting that specimens as thick as a whole mouse brain can be imaged with x-ray microscopes without significant image degradation should appropriate image reconstruction methods be identified. Copyright © 2017 Elsevier B.V. All rights reserved.

Phonon spectroscopy with sub-meV resolution by femtosecond x-ray diffuse scattering

DOE PAGES

Zhu, Diling; Robert, Aymeric; Henighan, Tom; ...

2015-08-10

We present a reconstruction of the transverse acoustic phonon dispersion of germanium from femtosecond time-resolved x-ray diffuse scattering measurements at the Linac Coherent Light Source. We demonstrate an energy resolution of 0.3 meV with a momentum resolution of 0.01 nm -1 using 10-keV x rays with a bandwidth of ~ 1 eV. This high resolution was achieved simultaneously for a large section of reciprocal space including regions closely following three of the principal symmetry directions. The phonon dispersion was reconstructed with less than 3 h of measurement time, during which neither the x-ray energy, the sample orientation, nor the detectormore » position were scanned. In conclusion, these results demonstrate how time-domain measurements can complement conventional frequency domain inelastic-scattering techniques.« less

Excitation of phonons in medium-energy electron diffraction

NASA Astrophysics Data System (ADS)

Alvarez, M. A. Vicente; Ascolani, H.; Zampieri, G.

1996-03-01

The ``elastic'' backscattering of electrons from crystalline surfaces presents two regimes: a low-energy regime, in which the characteristic low-energy electron diffraction (LEED) pattern is observed, and a medium-energy regime, in which the diffraction pattern is similar to those observed in x-ray photoemission diffraction (XPD) and Auger electron diffraction (AED) experiments. We present a model for the electron scattering which, including the vibrational degrees of freedom of the crystal, contains both regimes and explains the passage from one regime to the other. Our model is based on a separation of the electron and atomic motions (adiabatic approximation) and on a cluster-type formulation of the multiple scattering of the electron. The inelastic scattering events (excitation and/or absorption of phonons) are treated as coherent processes and no break of the phase relation between the incident and the exit paths of the electron is assumed. The LEED and the medium-energy electron diffraction regimes appear naturally in this model as the limit cases of completely elastic scattering and of inelastic scattering with excitation and/or absorption of multiple phonons. Intensity patterns calculated with this model are in very good agreement with recent experiments of electron scattering on Cu(001) at low and medium energies. We show that there is a correspondence between the type of intensity pattern and the mean number of phonons excited and/or absorbed during the scattering: a LEED-like pattern is observed when this mean number is less than 2, LEED-like and XPD/AED-like features coexist when this number is 3-4, and a XPD/AED-like pattern is observed when this number is greater than 5-6.

Disorder dependence electron phonon scattering rate of V82Pd18 - xFex alloys at low temperature

NASA Astrophysics Data System (ADS)

Jana, R. N.; Meikap, A. K.

2018-04-01

We have systematically investigated the disorder dependence electron phonon scattering rate in three dimensional disordered V82Pd18 - xFex alloys. A minimum in temperature dependence resistivity curve has been observed at low temperature T =Tm. In the temperature range 5 K ≤ T ≤Tm the resistivity correction follows ρo 5 / 2T 1 / 2 law. The dephasing scattering time has been calculated from analysis of magnetoresistivity by weak localization theory. The electron dephasing time is dominated by electron-phonon scattering and follows anomalous temperature (T) and disorder (ρ0) dependence behaviour like τe-ph-1 ∝T2 /ρ0, where ρ0 is the impurity resistivity. The magnitude of the saturated dephasing scattering time (τ0) at zero temperature decreases with increasing disorder of the samples. Such anomalous behaviour of dephasing scattering rate is still unresolved.

Electron and positron interaction with pyrimidine: A theoretical investigation

NASA Astrophysics Data System (ADS)

Sinha, Nidhi; Antony, Bobby

2018-03-01

Pyrimidine (C4H4N2) is considered as the building block of nucleobases, viz., cytosine, thymine and uracil. They provide a blueprint for probing the scattering of radiation by DNA and RNA bases. In this article, we report the elastic and total scattering cross-sections for electron and positron scattering from the pyrimidine molecule, employing a spherical complex optical potential (SCOP) formalism for an extensive energy range of 10 eV to 5 keV. In the case of positron scattering, the original SCOP formalism is modified to adequately solve the positron-target dynamics. Moreover, a reasonable agreement is observed between the present results and other available datasets, for both electron and positron scattering. The cross-sections for electron and positron impact scattering by pyrimidine are necessary input data for codes that seek to simulate radiation damage, and hence are useful to model biomolecular systems.

Electron scattering from gas phase cis-diamminedichloroplatinum(II): Quantum analysis of resonance dynamics

NASA Astrophysics Data System (ADS)

Carey, Ralph; Lucchese, Robert R.; Gianturco, F. A.

2013-05-01

We present scattering calculations of electron collisions with the platinum-containing compound cis-diamminedichloroplatinum (CDDP), commonly known as cisplatin, between 0.5 eV and 6 eV, and the corresponding isolated Pt atom from 0.1 eV to 10 eV. We find evidence of resonances in e--CDDP scattering, using an ab initio description of the target. We computed scattering matrix elements from equations incorporating exchange and polarization effects through the use of the static-exchange plus density functional correlation potential. Additionally, we made use of a purely local adiabatic model potential that allows Siegert eigenstates to be calculated, thereby allowing inspection of the possible resonant scattering wave functions. The total cross section for electron scattering from (5d10) 1S Pt displays a large magnitude, monotonic decay from the initial collision energies, with no apparent resonance scattering features in any scattering symmetry. By contrast, the e--CDDP scattering cross section shows a small feature near 3.8 eV, which results from a narrow, well localized resonance of b2 symmetry. These findings are then related to the possible electron-mediated mechanism of the action of CDDP on DNA replication as suggested by recent experiments.

Graphene Dendrimer-stabilized silver nanoparticles for detection of methimazole using Surface-enhanced Raman scattering with computational assignment

NASA Astrophysics Data System (ADS)

Saleh, Tawfik A.; Al-Shalalfeh, Mutasem M.; Al-Saadi, Abdulaziz A.

2016-08-01

Graphene functionalized with polyamidoamine dendrimer, decorated with silver nanoparticles (G-D-Ag), was synthesized and evaluated as a substrate with surface-enhanced Raman scattering (SERS) for methimazole (MTZ) detection. Sodium borohydride was used as a reducing agent to cultivate silver nanoparticles on the dendrimer. The obtained G-D-Ag was characterized by using UV-vis spectroscopy, scanning electron microscope (SEM), high-resolution transmission electron microscope (TEM), Fourier-transformed infrared (FT-IR) and Raman spectroscopy. The SEM image indicated the successful formation of the G-D-Ag. The behavior of MTZ on the G-D-Ag as a reliable and robust substrate was investigated by SERS, which indicated mostly a chemical interaction between G-D-Ag and MTZ. The bands of the MTZ normal spectra at 1538, 1463, 1342, 1278, 1156, 1092, 1016, 600, 525 and 410 cm-1 were enhanced due to the SERS effect. Correlations between the logarithmical scale of MTZ concentrations and SERS signal intensities were established, and a low detection limit of 1.43 × 10-12 M was successfully obtained. The density functional theory (DFT) approach was utilized to provide reliable assignment of the key Raman bands.

Raman and fluorescence contributions to the resonant inelastic soft x-ray scattering on LaAlO3/SrTiO3 heterostructures

NASA Astrophysics Data System (ADS)

Pfaff, F.; Fujiwara, H.; Berner, G.; Yamasaki, A.; Niwa, H.; Kiuchi, H.; Gloskovskii, A.; Drube, W.; Gabel, J.; Kirilmaz, O.; Sekiyama, A.; Miyawaki, J.; Harada, Y.; Suga, S.; Sing, M.; Claessen, R.

2018-01-01

We present a detailed study of the Ti 3 d carriers at the interface of LaAlO3/SrTiO3 heterostructures by high-resolution resonant inelastic soft x-ray scattering (RIXS), with special focus on the roles of overlayer thickness and oxygen vacancies. Our measurements show the existence of interfacial Ti 3 d electrons already below the critical thickness for conductivity. The (total) interface charge carrier density increases up to a LaAlO3 overlayer thickness of 6 unit cells before it levels out. Furthermore, we observe strong Ti 3 d charge carrier doping by oxygen vacancies. The RIXS data combined with photoelectron spectroscopy and transport measurements indicate the simultaneous presence of localized and itinerant charge carriers. At variance with previous interpretations, we show that in our excitation energy dependent RIXS measurements the amounts of localized and itinerant Ti 3 d electrons in the ground state do not scale with the intensities of the Raman and fluorescence peaks, respectively. Rather, we attribute the observation of either Raman components or fluorescence signal to the specific nature of the intermediate state reached in the RIXS excitation process.

Graphene Dendrimer-stabilized silver nanoparticles for detection of methimazole using Surface-enhanced Raman scattering with computational assignment

PubMed Central

Saleh, Tawfik A.; Al-Shalalfeh, Mutasem M.; Al-Saadi, Abdulaziz A.

2016-01-01

Graphene functionalized with polyamidoamine dendrimer, decorated with silver nanoparticles (G-D-Ag), was synthesized and evaluated as a substrate with surface-enhanced Raman scattering (SERS) for methimazole (MTZ) detection. Sodium borohydride was used as a reducing agent to cultivate silver nanoparticles on the dendrimer. The obtained G-D-Ag was characterized by using UV-vis spectroscopy, scanning electron microscope (SEM), high-resolution transmission electron microscope (TEM), Fourier-transformed infrared (FT-IR) and Raman spectroscopy. The SEM image indicated the successful formation of the G-D-Ag. The behavior of MTZ on the G-D-Ag as a reliable and robust substrate was investigated by SERS, which indicated mostly a chemical interaction between G-D-Ag and MTZ. The bands of the MTZ normal spectra at 1538, 1463, 1342, 1278, 1156, 1092, 1016, 600, 525 and 410 cm−1 were enhanced due to the SERS effect. Correlations between the logarithmical scale of MTZ concentrations and SERS signal intensities were established, and a low detection limit of 1.43 × 10−12 M was successfully obtained. The density functional theory (DFT) approach was utilized to provide reliable assignment of the key Raman bands. PMID:27572919

Electron- and positron-molecule scattering: development of the molecular convergent close-coupling method

NASA Astrophysics Data System (ADS)

Zammit, Mark C.; Fursa, Dmitry V.; Savage, Jeremy S.; Bray, Igor

2017-06-01

Starting from first principles, this tutorial describes the development of the adiabatic-nuclei convergent close-coupling (CCC) method and its application to electron and (single-centre) positron scattering from diatomic molecules. We give full details of the single-centre expansion CCC method, namely the formulation of the molecular target structure; solving the momentum-space coupled-channel Lippmann-Schwinger equation; deriving adiabatic-nuclei cross sections and calculating V-matrix elements. Selected results are presented for electron and positron scattering from molecular hydrogen H2 and electron scattering from the vibrationally excited molecular hydrogen ion {{{H}}}2+ and its isotopologues (D2 +, {{{T}}}2+, HD+, HT+ and TD+). Convergence in both the close-coupling (target state) and projectile partial-wave expansions of fixed-nuclei electron- and positron-molecule scattering calculations is demonstrated over a broad energy-range and discussed in detail. In general, the CCC results are in good agreement with experiments.

First principles calculation of lattice thermal conductivity of metals considering phonon-phonon and phonon-electron scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Yan; Lu, Zexi; Ruan, Xiulin, E-mail: ruan@purdue.edu

2016-06-14

The effect of phonon-electron (p-e) scattering on lattice thermal conductivity is investigated for Cu, Ag, Au, Al, Pt, and Ni. We evaluate both phonon-phonon (p-p) and p-e scattering rates from first principles and calculate the lattice thermal conductivity (κ{sub L}). It is found that p-e scattering plays an important role in determining the κ{sub L} of Pt and Ni at room temperature, while it has negligible effect on the κ{sub L} of Cu, Ag, Au, and Al. Specifically, the room temperature κ{sub L}s of Cu, Ag, Au, and Al predicted from density-functional theory calculations with the local density approximation aremore » 16.9, 5.2, 2.6, and 5.8 W/m K, respectively, when only p-p scattering is considered, while it is almost unchanged when p-e scattering is also taken into account. However, the κ{sub L} of Pt and Ni is reduced from 7.1 and 33.2 W/m K to 5.8 and 23.2 W/m K by p-e scattering. Even though Al has quite high electron-phonon coupling constant, a quantity that characterizes the rate of heat transfer from hot electrons to cold phonons in the two-temperature model, p-e scattering is not effective in reducing κ{sub L} owing to the relatively low p-e scattering rates in Al. The difference in the strength of p-e scattering in different metals can be qualitatively understood by checking the amount of electron density of states that is overlapped with the Fermi window. Moreover, κ{sub L} is found to be comparable to the electronic thermal conductivity in Ni.« less

Guide-star-based computational adaptive optics for broadband interferometric tomography

PubMed Central

Adie, Steven G.; Shemonski, Nathan D.; Graf, Benedikt W.; Ahmad, Adeel; Scott Carney, P.; Boppart, Stephen A.

2012-01-01

We present a method for the numerical correction of optical aberrations based on indirect sensing of the scattered wavefront from point-like scatterers (“guide stars”) within a three-dimensional broadband interferometric tomogram. This method enables the correction of high-order monochromatic and chromatic aberrations utilizing guide stars that are revealed after numerical compensation of defocus and low-order aberrations of the optical system. Guide-star-based aberration correction in a silicone phantom with sparse sub-resolution-sized scatterers demonstrates improvement of resolution and signal-to-noise ratio over a large isotome. Results in highly scattering muscle tissue showed improved resolution of fine structure over an extended volume. Guide-star-based computational adaptive optics expands upon the use of image metrics for numerically optimizing the aberration correction in broadband interferometric tomography, and is analogous to phase-conjugation and time-reversal methods for focusing in turbid media. PMID:23284179

Micrometer-resolution imaging using MÖNCH: towards G2-less grating interferometry

PubMed Central

Cartier, Sebastian; Kagias, Matias; Bergamaschi, Anna; Wang, Zhentian; Dinapoli, Roberto; Mozzanica, Aldo; Ramilli, Marco; Schmitt, Bernd; Brückner, Martin; Fröjdh, Erik; Greiffenberg, Dominic; Mayilyan, Davit; Mezza, Davide; Redford, Sophie; Ruder, Christian; Schädler, Lukas; Shi, Xintian; Thattil, Dhanya; Tinti, Gemma; Zhang, Jiaguo; Stampanoni, Marco

2016-01-01

MÖNCH is a 25 µm-pitch charge-integrating detector aimed at exploring the limits of current hybrid silicon detector technology. The small pixel size makes it ideal for high-resolution imaging. With an electronic noise of about 110 eV r.m.s., it opens new perspectives for many synchrotron applications where currently the detector is the limiting factor, e.g. inelastic X-ray scattering, Laue diffraction and soft X-ray or high-resolution color imaging. Due to the small pixel pitch, the charge cloud generated by absorbed X-rays is shared between neighboring pixels for most of the photons. Therefore, at low photon fluxes, interpolation algorithms can be applied to determine the absorption position of each photon with a resolution of the order of 1 µm. In this work, the characterization results of one of the MÖNCH prototypes are presented under low-flux conditions. A custom interpolation algorithm is described and applied to the data to obtain high-resolution images. Images obtained in grating interferometry experiments without the use of the absorption grating G2 are shown and discussed. Perspectives for the future developments of the MÖNCH detector are also presented. PMID:27787252

Resonant inelastic X-ray scattering spectrometer with 25meV resolution at the Cu K -edge

DOE PAGES

Ketenoglu, Didem; Harder, Manuel; Klementiev, Konstantin; ...

2015-06-27

An unparalleled resolution is reported with an inelastic X-ray scattering instrument at the CuK-edge. Based on a segmented concave analyzer, featuring single-crystal quartz (SiO 2) pixels, the spectrometer delivers a resolution near 25meV (FWHM) at 8981eV. Besides the quartz analyzer, the performance of the spectrometer relies on a four-bounce Si(553) high-resolution monochromator and focusing Kirkpatrick–Baez optics. The measured resolution agrees with the ray-tracing simulation of an ideal spectrometer. The performance of the spectrometer is demonstrated by reproducing the phonon dispersion curve of a beryllium single-crystal.

Pump-probe experiments at the TEMPO beamline using the low-α operation mode of Synchrotron SOLEIL.

PubMed

Silly, Mathieu G; Ferté, Tom; Tordeux, Marie Agnes; Pierucci, Debora; Beaulieu, Nathan; Chauvet, Christian; Pressacco, Federico; Sirotti, Fausto; Popescu, Horia; Lopez-Flores, Victor; Tortarolo, Marina; Sacchi, Maurizio; Jaouen, Nicolas; Hollander, Philippe; Ricaud, Jean Paul; Bergeard, Nicolas; Boeglin, Christine; Tudu, Bharati; Delaunay, Renaud; Luning, Jan; Malinowski, Gregory; Hehn, Michel; Baumier, Cédric; Fortuna, Franck; Krizmancic, Damjan; Stebel, Luigi; Sergo, Rudi; Cautero, Giuseppe

2017-07-01

The SOLEIL synchrotron radiation source is regularly operated in special filling modes dedicated to pump-probe experiments. Among others, the low-α mode operation is characterized by shorter pulse duration and represents the natural bridge between 50 ps synchrotron pulses and femtosecond experiments. Here, the capabilities in low-α mode of the experimental set-ups developed at the TEMPO beamline to perform pump-probe experiments with soft X-rays based on photoelectron or photon detection are presented. A 282 kHz repetition-rate femtosecond laser is synchronized with the synchrotron radiation time structure to induce fast electronic and/or magnetic excitations. Detection is performed using a two-dimensional space resolution plus time resolution detector based on microchannel plates equipped with a delay line. Results of time-resolved photoelectron spectroscopy, circular dichroism and magnetic scattering experiments are reported, and their respective advantages and limitations in the framework of high-time-resolution pump-probe experiments compared and discussed.

In Situ observation of dark current emission in a high gradient rf photocathode gun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, Jiahang; Shi, Jiaru; Antipov, Sergey P.

Undesirable electron field emission (also known as dark current) in high gradient rf photocathode guns deteriorates the quality of the photoemission current and limits the operational gradient. To improve the understanding of dark current emission, a high-resolution (~100 μm) dark current imaging experiment has been performed in an L-band photocathode gun operating at ~100 MV/m of surface gradient. Scattered strong emission areas with high current have been observed on the cathode. The field enhancement factor β of selected regions on the cathode has been measured. Finally, the postexaminations with scanning electron microscopy and white light interferometry reveal the origins ofmore » ~75% strong emission areas overlap with the spots where rf breakdown has occurred.« less

In Situ observation of dark current emission in a high gradient rf photocathode gun

DOE PAGES

Shao, Jiahang; Shi, Jiaru; Antipov, Sergey P.; ...

2016-08-15

Undesirable electron field emission (also known as dark current) in high gradient rf photocathode guns deteriorates the quality of the photoemission current and limits the operational gradient. To improve the understanding of dark current emission, a high-resolution (~100 μm) dark current imaging experiment has been performed in an L-band photocathode gun operating at ~100 MV/m of surface gradient. Scattered strong emission areas with high current have been observed on the cathode. The field enhancement factor β of selected regions on the cathode has been measured. Finally, the postexaminations with scanning electron microscopy and white light interferometry reveal the origins ofmore » ~75% strong emission areas overlap with the spots where rf breakdown has occurred.« less

Infrared vibrational nanocrystallography and nanoimaging

PubMed Central

Muller, Eric A.; Pollard, Benjamin; Bechtel, Hans A.; van Blerkom, Peter; Raschke, Markus B.

2016-01-01

Molecular solids and polymers can form low-symmetry crystal structures that exhibit anisotropic electron and ion mobility in engineered devices or biological systems. The distribution of molecular orientation and disorder then controls the macroscopic material response, yet it is difficult to image with conventional techniques on the nanoscale. We demonstrated a new form of optical nanocrystallography that combines scattering-type scanning near-field optical microscopy with both optical antenna and tip-selective infrared vibrational spectroscopy. From the symmetry-selective probing of molecular bond orientation with nanometer spatial resolution, we determined crystalline phases and orientation in aggregates and films of the organic electronic material perylenetetracarboxylic dianhydride. Mapping disorder within and between individual nanoscale domains, the correlative hybrid imaging of nanoscale heterogeneity provides insight into defect formation and propagation during growth in functional molecular solids. PMID:27730212

Natural Environment Characterization Using Hybrid Tomographic Aproaches

NASA Astrophysics Data System (ADS)

Huang, Yue; Ferro-Famil, Laurent; Reigber, Andreas

2011-03-01

SAR tomography (SARTOM) is the extension of conventional two-dimensional SAR imaging principle to three dimensions [1]. A real 3D imaging of a scene is achieved by the formation of an additional synthetic aperture in elevation and the coherent combination of images acquired from several parallel flight tracks. This imaging technique allows a direct localization of multiple scattering contributions in a same resolution cell, leading to a refined analysis of volume structures, like forests or dense urban areas. In order to improve the vertical resolution with respect to classical Fourier-based methods, High-Resolution (HR) approaches are used in this paper to perform SAR tomography. Both nonparametric spectral estimators, like Beamforming and Capon and parametric ones, like MUSIC, Maximum Likelihood, are applied to real data sets and compared in terms of scatterer location accuracy and resolution. It is known that nonparametric approaches are in general more robust to focusing artefacts, whereas parametric approaches are characterized by a better vertical resolution. It has been shown [2], [3] that the performance of these spectral analysis approaches is conditioned by the nature of the scattering response of the observed objects. In the scenario of hybrid environments where objects with a deterministic response are embedded in a speckle affected environment, the parameter estimation for this type of scatterers becomes a problem of mixed-spectrum estimation. The impenetrable medium like the ground or object, possesses an isolated localized phase center in the vertical direction, leading to a discrete (line) spectrum. This type of scatterers can be considered as 'h-localized', named 'Isolated Scatterers' (IS). Whereas natural environments consist of a large number of elementary scatterers successively distributed in the vertical direction. This type of scatterers can be described as 'h-distributed' scatterers and characterized by a continuous spectrum. Therefore, the usual spectral estimators may reach some limitations due to their lack of adaptation to both the statistical features of the backscattered information and the type of spectrum of the considered media. In order to overcome this problem, a tomographic focusing approach based on hybrid spectral estimators is introduced and extended to the polarimetric case. It contains two parallel procedures: one is to detect and localize isolated scatterers and the other one is to characterize the natural environment by estimating the heights of the ground and the tree top. These two decoupled procedures permit to more precisely characterize the scenario of hybrid environments.

Unambiguous determination of H-atom positions: comparing results from neutron and high-resolution X-ray crystallography.

PubMed

Gardberg, Anna S; Del Castillo, Alexis Rae; Weiss, Kevin L; Meilleur, Flora; Blakeley, Matthew P; Myles, Dean A A

2010-05-01

The locations of H atoms in biological structures can be difficult to determine using X-ray diffraction methods. Neutron diffraction offers a relatively greater scattering magnitude from H and D atoms. Here, 1.65 A resolution neutron diffraction studies of fully perdeuterated and selectively CH(3)-protonated perdeuterated crystals of Pyrococcus furiosus rubredoxin (D-rubredoxin and HD-rubredoxin, respectively) at room temperature (RT) are described, as well as 1.1 A resolution X-ray diffraction studies of the same protein at both RT and 100 K. The two techniques are quantitatively compared in terms of their power to directly provide atomic positions for D atoms and analyze the role played by atomic thermal motion by computing the sigma level at the D-atom coordinate in simulated-annealing composite D-OMIT maps. It is shown that 1.65 A resolution RT neutron data for perdeuterated rubredoxin are approximately 8 times more likely overall to provide high-confidence positions for D atoms than 1.1 A resolution X-ray data at 100 K or RT. At or above the 1.0sigma level, the joint X-ray/neutron (XN) structures define 342/378 (90%) and 291/365 (80%) of the D-atom positions for D-rubredoxin and HD-rubredoxin, respectively. The X-ray-only 1.1 A resolution 100 K structures determine only 19/388 (5%) and 8/388 (2%) of the D-atom positions above the 1.0sigma level for D-rubredoxin and HD-rubredoxin, respectively. Furthermore, the improved model obtained from joint XN refinement yielded improved electron-density maps, permitting the location of more D atoms than electron-density maps from models refined against X-ray data only.

Scatterings and Quantum Effects in (Al ,In )N /GaN Heterostructures for High-Power and High-Frequency Electronics

NASA Astrophysics Data System (ADS)

Wang, Leizhi; Yin, Ming; Khan, Asif; Muhtadi, Sakib; Asif, Fatima; Choi, Eun Sang; Datta, Timir

2018-02-01

Charge transport in the wide-band-gap (Al ,In )N /GaN heterostructures with high carrier density approximately 2 ×1013 cm-2 is investigated over a large range of temperature (270 mK ≤T ≤280 K ) and magnetic field (0 ≤B ≤18 T ). We observe the first evidence of weak localization in the two-dimensional electron gas in this system. From the Shubnikov-de Haas (SdH) oscillations a relatively light effective mass of 0.23 me is determined. Furthermore, the linear dependence with temperature (T <20 K ) of the inelastic scattering rate (τi-1∝T ) is attributed to the phase breaking by electron-electron scattering. Also in the same temperature range the less-than unit ratio of quantum lifetime to Hall transport time (τq/τt<1 ) is taken to signify the dominance of small-angle scattering. Above 20 K, with increasing temperature scattering changes from acoustic phonon to optical phonon scattering, resulting in a rapid decrease in carrier mobility and increase in sheet resistance. Suppression of such scatterings will lead to higher mobility and a way forward to high-power and high-frequency electronics.

Anomalous Electron Spectrum and Its Relation to Peak Structure of Electron Scattering Rate in Cuprate Superconductors

NASA Astrophysics Data System (ADS)

Gao, Deheng; Mou, Yingping; Feng, Shiping

2018-02-01

The recent discovery of a direct link between the sharp peak in the electron quasiparticle scattering rate of cuprate superconductors and the well-known peak-dip-hump structure in the electron quasiparticle excitation spectrum is calling for an explanation. Within the framework of the kinetic-energy-driven superconducting mechanism, the complicated line-shape in the electron quasiparticle excitation spectrum of cuprate superconductors is investigated. It is shown that the interaction between electrons by the exchange of spin excitations generates a notable peak structure in the electron quasiparticle scattering rate around the antinodal and nodal regions. However, this peak structure disappears at the hot spots, which leads to that the striking peak-dip-hump structure is developed around the antinodal and nodal regions, and vanishes at the hot spots. The theory also confirms that the sharp peak observed in the electron quasiparticle scattering rate is directly responsible for the remarkable peak-dip-hump structure in the electron quasiparticle excitation spectrum of cuprate superconductors.

Influence of local-field corrections on Thomson scattering in collision-dominated two-component plasmas.

PubMed

Fortmann, Carsten; Wierling, August; Röpke, Gerd

2010-02-01

The dynamic structure factor, which determines the Thomson scattering spectrum, is calculated via an extended Mermin approach. It incorporates the dynamical collision frequency as well as the local-field correction factor. This allows to study systematically the impact of electron-ion collisions as well as electron-electron correlations due to degeneracy and short-range interaction on the characteristics of the Thomson scattering signal. As such, the plasmon dispersion and damping width is calculated for a two-component plasma, where the electron subsystem is completely degenerate. Strong deviations of the plasmon resonance position due to the electron-electron correlations are observed at increasing Brueckner parameters r(s). These results are of paramount importance for the interpretation of collective Thomson scattering spectra, as the determination of the free electron density from the plasmon resonance position requires a precise theory of the plasmon dispersion. Implications due to different approximations for the electron-electron correlation, i.e., different forms of the one-component local-field correction, are discussed.

A study of core Thomson scattering measurements in ITER using a multi-laser approach

NASA Astrophysics Data System (ADS)

Kurskiev, G. S.; Sdvizhenskii, P. A.; Bassan, M.; Andrew, P.; Bazhenov, A. N.; Bukreev, I. M.; Chernakov, P. V.; Kochergin, M. M.; Kukushkin, A. B.; Kukushkin, A. S.; Mukhin, E. E.; Razdobarin, A. G.; Samsonov, D. S.; Semenov, V. V.; Tolstyakov, S. Yu.; Kajita, S.; Masyukevich, S. V.

2015-05-01

The electron component is the main channel for anomalous power loss and the main indicator of transient processes in the tokamak plasma. The electron temperature and density profiles mainly determine the operational mode of the machine. This imposes demanding requirements on the precision and on the spatial and temporal resolution of the Thomson scattering (TS) measurements. Measurements of such high electron temperature with good accuracy in a large fusion device such as ITER using TS encounter a number of physical problems. The 40 keV TS spectrum has a significant blue shift. Due to the transmission functions of the fibres and to their darkening that can occur under a strong neutron irradiation, the operational wavelength range is bounded on the blue side. For example, high temperature measurements become impossible with the 1064 nm probing wavelength since the TS signal within the boundaries of the operational window weakly depends on Te. The second problem is connected with the TS calibration. The TS system for a large fusion machine like ITER will have a set of optical components inaccessible for maintenance, and their spectral characteristics may change with time. Since the present concept of the TS system for ITER relies on the classical approach to measuring the shape of the scattered spectra using wide spectral channels, the diagnostic will be very sensitive to the changes in the optical transmission. The third complication is connected with the deviation of the electron velocity distribution function from a Maxwellian that can happen under a strong ECRH/ECCD, and it may additionally hamper the measurements. This paper analyses the advantages of a ‘multi-laser approach’ implementation for the current design of the core TS system. Such an approach assumes simultaneous plasma probing with different wavelengths that allows the measurement accuracy to be improved significantly and to perform the spectral calibration of the TS system. Comparative analysis of the conservative and advanced approaches is given.

Nucleon Form Factors above 6 GeV

DOE R&D Accomplishments Database

Taylor, R. E.

1967-09-01

This report describes the results from a preliminary analysis of an elastic electron-proton scattering experiment... . We have measured cross sections for e-p scattering in the range of q{sup 2} from 0.7 to 25.0 (GeV/c){sup 2}, providing a large region of overlap with previous measurements. In this experiment we measure the cross section by observing electrons scattered from a beam passing through a liquid hydrogen target. The scattered particles are momentum analyzed by a magnetic spectrometer and identified as electrons in a total absorption shower counter. Data have been obtained with primary electron energies from 4.0 to 17.9 GeV and at scattering angles from 12.5 to 35.0 degrees. In general, only one measurement of a cross section has been made at each momentum transfer.

Measurement of Tensor Analyzing Powers for Elastic Electron Scattering from a Polarized {sup 2}H Target Internal to a Storage Ring

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferro-Luzzi, M.; Bouwhuis, M.; Passchier, E.

1996-09-01

We report an absolute measurement of the tensor analyzing powers {ital T}{sub 20} and {ital T}{sub 22} in elastic electron-deuteron scattering at a momentum transfer of 1.6 fm{sup {minus}1}. The novel approach of this measurement is the use of a tensor polarized {sup 2}H target internal to an electron storage ring, with {ital in} {ital situ} measurement of the polarization of the target gas. Scattered electrons and recoil deuterons were detected in coincidence with two large acceptance nonmagnetic detectors. The techniques demonstrated have broad applicability to further measurements of spin-dependent electron scattering. {copyright} {ital 1996 The American Physical Society.}

First results from the Thomson scattering diagnostic on Proto-MPEX

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biewer, Theodore M; Meitner, Steven J; Rapp, Juergen

2016-01-01

A Thomson scattering diagnostic has been successfully implemented on the prototype Material Plasma Exposure eXperiment (Proto-MPEX) at Oak Ridge National Laboratory. The diagnostic collects the light scattered by plasma electrons and spectroscopically resolves the Doppler shift imparted to the light by the velocity of the electrons. The spread in velocities is proportional to the electron temperature, while the total number of photons is proportional to the electron density. Thomson scattering is a technique used on many devices to measure the electron temperature (Te) and electron density (ne) of the plasma. A challenging aspect of the technique is to discriminate themore » small number of Thomson scattered photons against the large peak of background photons from the high-power laser used to probe the plasma. A variety of methods are used to mitigate the background photons in Proto-MPEX, including Brewster angled windows, viewing dumps, and light baffles. With these methods, first results were measured from Argon plasmas in Proto-MPEX, indicating Te ~ 2 eV and ne ~ 1x1019 m-3. The configuration of the Proto-MPEX Thomson scattering diagnostic will be described and plans for improvement will be given.« less

Enhanced dye-sensitized solar cells performance using anatase TiO2 mesocrystals with the Wulff construction of nearly 100% exposed {101} facets as effective light scattering layer.

PubMed

Zhou, Yu; Wang, Xinyu; Wang, Hai; Song, Yeping; Fang, Liang; Ye, Naiqing; Wang, Linjiang

2014-03-28

Anatase TiO2 mesocrystals with a Wulff construction of nearly 100% exposed {101} facets were successfully synthesized by a facile, green solvothermal method. Their morphology, and crystal structure are characterized by powder X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). Accordingly, a possible growth mechanism of anatase TiO2 mesocrystals is elucidated in this work. The as-prepared single anatase TiO2 mesocrystal's mean center diameter is about 500 nm, and the length is about 1 μm. They exhibit high light adsorbance, high reflectance and low transmittance in the visible region due to the unique nearly 100% exposed {101} facets. When utilized as the scattering layer in dye-sensitized solar cells (DSSCs), such mesocrystals effectively enhanced light harvesting and led to an increase of the photocurrent of the DSSCs. As a result, by using an anatase TiO2 mesocrystal film as a scattering overlayer of a compact commercial P25 TiO2 nanoparticle film, the double layered DSSCs show a power conversion efficiency of 7.23%, indicating a great improvement compared to the DSSCs based on a P25 film (5.39%) and anatase TiO2 mesocrystal films, respectively. The synergetic effect of P25 and the mesocrystals as well as the latters unique feature of a Wulff construction of nearly 100% exposed (101) facets are probably responsible for the enhanced photoelectrical performance. In particular, we explore the possibility of the low surface area and exposed {101} facets as an efficient light scattering layer of DSSCs. Our work suggests that anatase TiO2 mesocrystals with the Wulff construction is a promising candidate as a superior scattering material for high-performance DSSCs.

Electronic Holography with a Broad Spectrum Laser for Time Gated Imaging Through Highly Scattering Media.

NASA Astrophysics Data System (ADS)

Shih, Marian Pei-Ling

The problem of optical imaging through a highly scattering volume diffuser, in particular, biological tissue, has received renewed interest in recent years because of a search for alternative imaging diagnostics in the optical wavelengths for the early detection of human breast cancer. This dissertation discusses the optical imaging of objects obscured by diffusers that contribute an otherwise overwhelming degree of multiple scatter. Many optical imaging techniques are based on the first-arriving light principle. These methods usually combine a transilluminating optical short pulse with a time windowing gate in order to form a flat shadowgraph image of absorbing objects either embedded within or hidden behind a scattering medium. The gate selectively records an image of the first-arriving light, while simultaneously rejecting the later-arriving scattered light. One set of the many implementations of the first -arriving light principle relies on the gating property of holography. This thesis presents several holographic optical gating experiments that demonstrate the role that the temporal coherence function of the illumination source plays in the imaging of all objects with short coherence length holography, with special emphasis on the application to image through diffusers and its resolution capabilities. Previous researchers have already successfully combined electronic holography, holography in which the recording medium is a two dimensional detector array instead of photographic film, with light-in-flight holography into a short coherence length holography method that images through various types of multiply scattering random media, including chicken breast tissue and wax. This thesis reports further experimental exploration of the short coherence holography method for imaging through severely scattering diffusers. There is a study on the effectiveness of spatial filtering of the first-arriving light, as well as a report of the imaging, by means of the short coherence holographic method, of an absorber through a living human hand. This thesis also includes both theoretical analyses and experimental results of a spectral dispersion holography system which, instead of optically synthesizing the broad spectrum illumination source that is used for the short coherence holography method, digitally synthesizes a broad spectrum hologram from a collection of single frequency component holograms. This system has the time gating properties of short coherence length holography, as well as experimentally demonstrated applications for imaging through multiply scattering media.

Means and method for calibrating a photon detector utilizing electron-photon coincidence

NASA Technical Reports Server (NTRS)

Srivastava, S. K. (Inventor)

1984-01-01

An arrangement for calibrating a photon detector particularly applicable for the ultraviolet and vacuum ultraviolet regions is based on electron photon coincidence utilizing crossed electron beam atom beam collisions. Atoms are excited by electrons which lose a known amount of energy and scatter with a known remaining energy, while the excited atoms emit photons of known radiation. Electrons of the known remaining energy are separated from other electrons and are counted. Photons emitted in a direction related to the particular direction of scattered electrons are detected to serve as a standard. Each of the electrons is used to initiate the measurements of a time interval which terminates with the arrival of a photon exciting the photon detector. Only the number of time intervals related to the coincidence correlation and of electrons scattered in the particular direction with the known remaining energy and photons of a particular radiation level emitted due to the collisions of such scattered electrons are counted. The detector calibration is related to the number of counted electrons and photons.

Measurement of the reaction 2H(e,e') at 180 degrees close to the deuteron breakup threshold.

PubMed

Ryezayeva, N; Arenhövel, H; Burda, O; Byelikov, A; Chernykh, M; Enders, J; Griesshammer, H W; Kalmykov, Y; von Neumann-Cosel, P; Ozel, B; Poltoratska, I; Pysmenetska, I; Rangacharyulu, C; Rathi, S; Richter, A; Schrieder, G; Shevchenko, A; Yevetska, O

2008-05-02

Inclusive inelastic electron scattering off the deuteron under 180 degrees has been studied at the S-DALINAC close to the breakup threshold at momentum transfers q=0.27 fm;{-1} and 0.74 fm;{-1} with good energy resolution sufficient to map in detail the spin flip M1 response, which governs the starting reaction pn-->dgamma of big-bang nucleosynthesis over most of the relevant temperature region. Results from potential model calculations and (for q=0.27 fm;{-1}) from pionless nuclear effective field theory are in excellent agreement with the data.

Resonant inelastic x-ray scattering on iso-C₂H₂Cl₂ around the chlorine K-edge: structural and dynamical aspects.

PubMed

Kawerk, Elie; Carniato, Stéphane; Journel, Loïc; Marchenko, Tatiana; Piancastelli, Maria Novella; Žitnik, Matjaž; Bučar, Klemen; Bohnic, Rok; Kavčič, Matjaž; Céolin, Denis; Khoury, Antonio; Simon, Marc

2014-10-14

We report a theoretical and experimental study of the high resolution resonant K(α) X-ray emission lines around the chlorine K-edge in gas phase 1,1-dichloroethylene. With the help of ab initio electronic structure calculations and cross section evaluation, we interpret the lowest lying peak in the X-ray absorption and emission spectra. The behavior of the K(α) emission lines with respect to frequency detuning highlights the existence of femtosecond nuclear dynamics on the dissociative Potential Energy Surface of the first K-shell core-excited state.

Resonant inelastic x-ray scattering on iso-C2H2Cl2 around the chlorine K-edge: Structural and dynamical aspects

NASA Astrophysics Data System (ADS)

Kawerk, Elie; Carniato, Stéphane; Journel, Loïc; Marchenko, Tatiana; Piancastelli, Maria Novella; Žitnik, Matjaž; Bučar, Klemen; Bohnic, Rok; Kavčič, Matjaž; Céolin, Denis; Khoury, Antonio; Simon, Marc

2014-10-01

We report a theoretical and experimental study of the high resolution resonant Kα X-ray emission lines around the chlorine K-edge in gas phase 1,1-dichloroethylene. With the help of ab initio electronic structure calculations and cross section evaluation, we interpret the lowest lying peak in the X-ray absorption and emission spectra. The behavior of the Kα emission lines with respect to frequency detuning highlights the existence of femtosecond nuclear dynamics on the dissociative Potential Energy Surface of the first K-shell core-excited state.