XSD Seminars are an open forum where speakers from the U.S. and abroad, as well as XSD, present their latest research. All are cordially invited to attend.
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Sensors and Systems for Digital Radiography
Speaker: Vivek V. Nagarkar, RMD Inc.
@ 1:30 PMView Description
At RMD we have developed modular digital imaging detectors for applications ranging from hypervelocity projectile tracking and ballistic impact analysis to medical X-ray CT and time-resolved diffraction studies. These systems benefit from recently discovered binary and ternary phase inorganic scintillators and novel ceramic scintillators that demonstrate unprecedented emission efficiencies (70,000 to 100,000 ph/MeV), high densities (5 to 9 g/cc), high effective atomic numbers (Z~50 to 70), and radiate in 450 to 650 nm range with fast decay. These recently discovered scintillators are being fabricated at RMD for use in digital radiography by novel processes like physical vapor deposition (PVD) or laser processing. Our advanced PVD techniques results in the formation of structured scintillators in microcolumnar and/or macrocolumnar format, while our laser processing techniques using solid state laser are capable of forming structured scintillators of arbitrary shapes.
Here we will present novel scintillators fabricated in microcolumnar or pixelated form that minimize the traditional tradeoff between spatial resolution and detector efficiency and are suitable for imaging low (8 keV) to high (450 kVp) energy X-rays and/or thermal neutrons. Performance characteristics of radiographic imaging detectors and systems will also be discussed.
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Optimum Performance of the Novel Accelerator for Iterative Phase Retrieval in the Fresnel Region Applied to X-ray Phase Contrast Imaging
Speaker: Nghia Vo, Diamond Light Source
@ 3:00 PMView Description
Iterative phase retrieval in the Fresnel region based on Gerchberg-Saxton algorithm suffers from slow convergence and stagnation. Recently, a novel accelerator, named random signed feedback (RSF), was proposed (http://dx.doi.org/10.1063/1.4769046) which shows a superior performance compared with other traditional techniques: hybrid input output (HIO) and conjugate gradient search (CGS). Its feasibility is confirmed by applying on X-ray phase contrast tomographic data, collected at beamline I12 Diamond Light Source, which shows promising results. In this talk, I will present how I investigated the RSF accelerator under various conditions to obtain its optimum performance.[ Hide ]
X-ray Diffraction from Perfect Crystals - the 100th Anniversary of the First Calculations by C.G. Darwin
Speaker: Denny Mills, Advanced Photon Source
@ 11:00 AMView Description
In 1914, C. G. Darwin published two papers* that established some of the basic features of x-ray diffraction in perfect crystals. One of those features was near-unity reflectivity over a narrow angular range at the Bragg condition, a phenomenon that is still known as the “Darwin width” of the reflection. The talk will briefly describe his calculational approach to scattering in perfect crystals, impact of those calculations, and other aspects of Darwin’s life and work.
*"The Theory of X-ray Reflexion", by C. G. Darwin, Philosophical Magazine, 27, (1914), p313-333 and “The Theory of X-ray Reflexion Part II”, by C. G. Darwin, Philosophical Magazine, 27, (1914), p675-690.
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Hybrid Pixel Array Detectors Enabling New Science
Speaker: Clemens Schulze-Briese, Dectris Ltd.
@ 2:00 PMView Description
PILATUS single photon counting Hybrid Pixel Device (HPD) detectors have transformed synchrotron research by enabling new data acquisition modes and even novel experiments. At the same time data quality has improved due to noise-free operation and direct conversion of the X-rays. Millisecond readout times and high-frame rates allow for hitherto unknown speed and efficiency of data acquisition.
At cryogenic temperatures, PILATUS allows to acquire data of optimal quality by collecting high multiplicity data at low dose rate, referred to as dose slicing. Monitoring data quality indicators as a function of frame number reveals the optimal data quality for a given crystal. This overcomes the problem of traditional data collection, where radiation damage may affect data accuracy before a complete data set is collected. In contrast, dose-sliced data collection always enables the exploration of the full diffraction potential of the crystal. The noise-free counting of PILATUS detectors allows the dose per frame to be reduced without loss of data accuracy due to read-out noise. Furthermore, high frame rates enable acquisition of optimally fine f-sliced, high multiplicity data in short time.
In room temperature data collection, the high frame rates featured by PILATUS3 detectors allow for outrunning of radiation damage. Recent experiments demonstrate a systematic increase in the dose tolerance of protein and virus crystals as a function of dose rate. PILATUS3 detectors allow even higher frame rates and further push the boundaries of this successful experimental strategy. Latest results obtained with PILATUS3 reveal a departure from a linear or exponential intensity decay in the diffracting power of protein crystals as a function of absorbed dose. A lag phase observed in these experiments raises the possibility of collecting substantially more data from crystals held at room temperature before a critical intensity decay is reached.
The new EIGER detector series presents a leap in HPD detector technology. Featuring 75 µm pixel size and frame rates up to 3000 Hz in combination with continuous read-out, EIGER detectors will open up new opportunities for advanced dose optimized data acquisition techniques.
HPD detectors with CdTe sensors extend the range of high quantum efficiency to 80 keV. This will allow to fully exploit the potential of new high energy and brightness undulator beamlines at unprecedented signal-to-noise ratios and data acquisition speeds.
An overview of the salient detector properties will be given and illustrated by experimental results in various applications. [ Hide ]
Physics and Chemistry of Vacancy Defects in Graphene Layers: Scanning Tunneling Microscopy and Density Functional Theory StudySpeaker: Maxim Ziatdinov , Tokyo Institute of Technology
431/C010 @ 11:00 AM
Synthesis of ITO Nanoparticles with Shape Control and their Assembly for Solution-Processed Transparent ElectrodesSpeaker: Jonghun Lee, Brown University
432/C010 @ 2:30 PM
Elucidating the Structure-Performance Relationship in Organic Photovoltaics (OPVs) by Grazing Incidence X-Ray Scattering
Speaker: Joseph Strzalka, X-ray Science Division/Time Resolved Research
@ 2:00 PMView Description
Since the introduction of the Bulk Heterojunction (BHJ) architecture in the mid- 90s, organic photovoltaic devices have made steady progress toward improved power conversion efficiency, and are now poised to move from niche products to large scale commercial applications. In the BHJ, the photoactive layer consists of electron donor and acceptor materials in a bicontinuous phase blended on the nanoscale. Grazing incidence x-ray scattering, capable of characterizing thin film nanomorphology of surfaces and interfaces, has emerged as a key technique for investigating OPV materials. The hierarchical variety of lengthscales present in OPV materials requires both grazing incidence small- and wide-angle x-ray scattering, the latter recently enabled by improvements to the GISAXS instrument at 8-ID-E. I will describe grazing-incidence studies at 8-ID-E that have contributed toward unraveling the complex relationship between OPV materials, processing and performance. [ Hide ]
Solving the Phase Diagram of the Model Quantum Magnet SrCu2(BO3)2
Speaker: Sara Haravifard, Argonne National Laboratory & The University of Chicago
@ 2:00 PMView Description
Low dimensional quantum magnets provide a framework for exotic phase behavior in new materials, with high temperature superconductivity being the most appreciated example. SrCu2(BO3)2 (SCBO), is a rare example of a quasi two-dimensional quantum magnet for which an exact theoretical solution exists. It serves as an experimental realization of the Shastry-Sutherland model for interacting S=1/2 dimers. The ratio of the intra and inter-dimer exchange interactions in this compound is close to a quantum critical point, where the ground state is predicted to transform from a gapped, non-magnetic singlet state to a gapless long-range ordered antiferromagnetic state as a function of the ratio of the strength of the magnetic interactions. We conducted high resolution neutron scattering measurements on SCBO in its singlet ground state which identified the most prominent features of the spin excitation spectrum, including the presence of one and two triplet excitations and weak dispersion characteristic of sub-leading terms in the spin Hamiltonian. Additionally, we investigated the pressure-driven quantum phase transition in SCBO using synchrotron X-ray diffraction and neutron scattering. In these studies we were able to investigate the evolution of both the magnetic and structural properties of SCBO up to pressures of 6 Gpa, following the development and evolution of long-range magnetic order. Moreover, the resemblance between the spin gap behavior in the Mott insulator SCBO and that associated with high temperature superconductors motivated us to explore the significance of doping on the phase diagram. [ Hide ]
Novel Industrial Ultrafast Lasers and their Applications in Free Electron Lasers and Synchrotrons
Speaker: Yoann A. Zaouter, Amplitude Systemes
@ 10:00 AMView Description
he aim of this presentation is to introduce the novel industrial ultrafast laser technologies that are developed at Amplitude Systemes.
These lasers benefit from several technological breakthroughs such as direct diode pumping and novel laser architectures, and gain
media that allow the laser to operate simultaneously at high energies, average powers and therefore repetition rates. We will also
specifically show where they are used in FEL and synchrotron and how they advantageously can replace ageing laser technologies
and improve the reliability of photoinjectors, minimize the down times, improve signal to noise ratio of measurements, etc.[ Hide ]
Probing the Metal-Insulator Transition in Engineered NdNiO3
Speaker: Mary H. Upton, Inelastic X-ray & Nuclear Resonant Scattering (IXN)
@ 2:00 PMView Description
NdNiO3, along with other rare earth nickelates, has been the focus of intense research in the last decade due to its metal-insulator transition (MIT), occurring at ~210 K in NdNiO3. The transition temperature can be tuned (or suppressed) with strain giving rise to the possibility of engineered heterostructures. There are many competing models of the MIT, of which the true nature is not known. It has been suggested that the MIT results from the emergence of a low temperature charge ordered state involving the d electrons. Alternately, it may result from the opening of a charge transfer gap between the Ni d and O p electrons. We report on the effect of epitaxial strain and temperature on d-electrons in NdNiO3 as measured by bulk-sensitive resonant inelastic x-ray scattering.[ Hide ]
Engineering the Elasticity of Soft Colloidal Materials Through Surface Modification and Shape Anisotropy
Speaker: Lillian C. Hsiao, University of Michigan, Ann Arbor
@ 11:00 AMView Description
Designing complex fluids has always involved the arduous manipulation of system-specific parameters. Recently, we developed a general correlation to predict the flow behavior of a range of soft matter based on their microstructure. By applying the framework of structural rigidity at the macroscale (bridges, buildings, domes) to the microscale, we are able to explain the nonlinear elasticity of colloids flowing at high rates that are typical of industrial processing. In particular, we explore the idea that colloidal gels can be designed with better mechanical properties and stability without resorting to a greater quantity of materials, simply by incorporating particles with different shapes, sizes, and roughness. Biphasic particles with metallic facets have also been proposed to provide extraordinary structural strength due to their interaction anisotropy. We test these ideas by synthesizing monophasic and biphasic colloids of controlled roughness in various ellipsoidal shapes, dispersing the particles in refractive-index matched solvents, and inducing self-assembly and gelation with a measurable and tunable depletion attraction. To quantify their flow properties, rheological measurements are carried out in conjunction with microscopy experiments and direct force measurements using optical tweezers. Our understanding of gel physics and rheology shows that the trial-and-error engineering of viscoelasticity can be mitigated by applying the principle of structural rigidity to material design; for example, engineers can incorporate smaller ellipsoidal particles to increase yield stress without a significant increase in the production cost.[ Hide ]
Light-X-ray Scattering and Rheology of Soft Matter
Speaker: Yu-Ho Wen, Cornell University
@ 11:00 AMView Description
Soft matter is an important class of molecular materials, typically composed of polymers, colloids, and other mesoscopic constituents. They are indispensible in contemporary technological applications—for example, solid electrolytes in rechargeable lithium batteries and solution-cast thin film in polymer light-emitting diodes (PLEDs). Herein we report on the dynamics and structure of the two advanced materials—nanoparticle salts and conjugated polymers. The nanoparticle salts are created by cofunctionalization of metal oxide nanoparticles with tethered salts and neutral organic ligands, and are shown to exhibit equilibrium, Newtonian flow behaviors. We find that ionic cross-links between the salts can be created/weakened by variations of counterion size and dielectric medium. Scrutiny into the SAXS structure factors and plateau moduli further disclosed that nanoscale interparticle spacing imposed on tethered molecules produces topological constraints analogous to those in entangled polymers, uncovering the molecular origin of a similar plateau modulus shared with polymer-tethered nanoparticles and entangled polymer melts. Time-composition superposition of linear viscoelastic data further indicates stricking dynamical similarities between the two systems. In the second part, we propose a self-consistent formulation for analyzing the dynamic structure factor of aggregate species in conjugated polymer solutions, where a wide size distribution and unknown aggregate morphology, as well as pronounced interferences between translational and interior segmental motions of aggregate clusters have posed stringent challenges for conventional light-scattering analyses. Additionally, in situ rheological and turbidity measurements reveal that an externally imposed flow can result in instant and/or persistent changes in the bulk aggregation state of the precursor solutions.[ Hide ]
Hierarchical Semiconductor, Metal and Hybrid Nanostructures and the Study of their Light-Matter Interactions
Speaker: Anna Lee, University of Toronto
@ 2:00 PMView Description
The interdisciplinary work during my Ph.D. and post-doctoral studies (Dept. of Chemistry and Dept. of Electrical Engineering, University of Toronto) explore the optical properties of hierarchical structures composed of nanoscale building blocks ranging from metals to semiconductors and composites, organized through bottom-up design methods.
This talk is comprised of three main research projects for which the common thread is the rational design of nanoscale assembled structures and their interactions with light.
Recent advances in spectrally tunable solution-processed metal nanoparticles have provided unprecedented control over light at the nanoscale. The plasmonic properties of metal nanoparticles have been explored as optical signal enhancers for applications ranging from sensing to nanoelectronics. Specifically, (1) by following the dynamic generation of hot spots in self-assembled chains of gold nanorods (NRs), we have established a direct correlation between ensemble-averaged surface- enhanced Raman scattering (SERS) and extinction properties of these nanoscale chains in a solution state. Experimental results were supported by comprehensive finite-difference time-domain simulations. Building from this, (2) we studied an alternate geometry, namely side-by-side assembled NRs. There is a general misconception that aggregates of metal nanoparticles are more efficient SERS probes than individual nanoparticles, due to the enhancement of the electric field in the interparicle gaps. However, we have shown through theoretical and experimental analyses that this is not the case for side-by-side assembled gold NRs. (3) Progress in colloidal quantum dot photovoltaics offers the potential for low-cost, large-area solar power; however, these devices suffer from poor quantum efficiency in the more weakly-absorbed near infrared portion of the sun’s spectrum. Here, I will talk about a plasmonic-excitonic solar cell that combines two jointly-tuned solution processed infrared materials. We show through experiment and theory that a plasmonic- excitonic design using gold nanoshells with optimized single-particle scattering-to- absorption cross section ratios leads to a strong enhancement in near-field absorption and resultant photocurrent in the performance-limiting near infrared spectral region. The present work offers guidance towards the establishment of “design rules” for the development of colloidal nanoparticle assembled systems for plasmonic sensing applications.[ Hide ]