2017 May 17 - June 29
2017 October 11 - December 21
2017 Proposal deadline: 08/01/17
2017 BTR deadline: 09/10/17
|"Gaining functional insight from SAXS: How in-line SEC and MALS/DLS can provide complementary structural information and quality assessment in polydisperse systems"
Alvin S. Acerbo, Michael J. Cook, Bill A. Miller, Scott E. Smith, Irina A. Kriksunov, Doletha M. E. Szebenyi, Richard E. Gillilan
MacCHESS, Cornell University
Abstract: Small Angle X-ray Scattering (SAXS) of biological macromolecules in solution is an increasingly popular tool for structural biologists and benefits greatly from the sensitivity and throughput that can be achieved at modern high brightness synchrotron sources. The critical need for highly monodisperse samples in SAXS analysis has stimulated a number of labs to develop in-line Size Exclusion Chromatography (SEC) at the beamline. Real-time SAXS on elution profiles not only improves monodispersity of samples and provides information on possible oligomeric states, but it also offers new modes of data analysis that can take advantage of the inherent concentration profiles underlying elution peaks and distributions of partially resolved species. Efforts to extend the synergy between SEC and SAXS to other biophysical methods are ongoing. The newly commissioned G1 BioSAXS facility at MacCHESS now offers the option of combining real-time SEC-SAXS with multi-angle static (MALS) and dynamic (DLS) light scattering along with refractive index (RI) detection. Here we present a brief overview of the performance and capabilities of the new BioSAXS station at MacCHESS with emphasis on detection limits and signal quality. In addition, we investigate how complementary light scattering techniques can be combined to offer new insights for complex inhomogeneous samples in terms of biological information and data quality assessment. We also discuss the limitations and possible future developments of these approaches as biologists seek to investigate more dynamic systems as well as shorter time scales.
|"Fabrication of Spoked Channel Arrays for confocal x-ray fluorescence microscopy"
David Agyeman-Budu1, Arthur Woll2 and Joel D Brock2,3
1Department of Materials Science and Engineering, Cornell University, Ithaca NY 14853
2Cornell High Energy Synchrotron Source, Ithaca NY 14853
3Department of Applied and Engineering Physics, Cornell University, Ithaca NY 14853
Abstract: Confocal x-ray fluorescence (XRF) microscopy as an imaging technique involves the use of two different optics: A focusing optic to excite fluorescent x-rays from a specific spot of interest in a heterogeneous sample and a collection optic to interrogate this point source of fluorescent x-rays. This setup allows the possibility to spatially sample an item of interest in 3 dimensions to generate a true spatially resolved chemical composition map.
What we have developed is a novel collection optic - the Spoked Channel Arrays (SCAs) which consists of a radial arrangement of lithographically fabricated collimating channels that are pointed in the direction of the single point source.
In contrast to polycapillaries which is the conventional collection optic for confocal XRF, SCAs exhibit a nearly energy-independent resolution and efficiency . With the initial design in Ref. 1, we were able to achieve a nearly energy-independent depth resolution below 2 microns for and energy range between 3-10 keV, degrading slightly to 3±0.5 microns at 1.7 keV. An improved design in Ref. 2 addressed the limitation of efficiency and the short working distance whereby the initial straight wall channel-cut arrays were defined by a set of staggered pillars instead. The optics have been tested at the APS beamline 20-ID-B for confocal XRF mapping and XAFS of an 11th century stained glass sample from the Paderborn Cathedral, a paint sample from an 18th century oil painting by Adriaen de Coorte and most recently, an archaeological bone sample excavated from a cemetery near English Harbor, Antigua.
In this poster, we also report further fabrication tweaks on how we are leveraging Aspect Ratio Dependent Etching (ARDE), which is usually an undesired characteristic to our favor, in an attempt to achieve a desirable channel depth profile. We also look at morphing which is also a technique used to retain the integrity of the channel profile as the channels are etched deeper. These were done with both silicon and germanium substrates which to expand the range of energies for which we can practically use this optic from 12keV in silicon up to 30keV with germanium.
|"Serial crystallography at synchrotron sources: Data Analysis"
Kartik Ayyer, Hugh Phillipp, Mark Tate, Veit Elser, Sol Gruner
Abstract: Serial crystallography at x-ray free electron lasers has allowed the structure determination of small crystals not solvable by conventional techniques. However, the limited beam-time at these sources means that there is a need for developing this capability at synchrotron sources. One big challenge is that for 1-2 um or smaller crystals, there aren't enough scattered photons to be able to index peaks from a single frame and determine its orientation. The EMC algorithm (Loh, Elser 2009), which was developed for single molecule imaging provides a way out of this quandary. To demonstrate its capability, we performed a proof-of-principle experiment with a highly attenuated source so that the data is of the same nature as above. We discuss the reconstruction procedure and the results with 3*10^-3 photons/pixel/frame. Along with the sparse nature of the data, another problem faced by the algorithm will be the relatively high fraction of background photons coming from sources other than the crystal. We also show the effect on reconstruction quality of a uniform random background.
|"Performance studies of the hard X-ray polarimeter X-Calibur"
Washington University in St.Louis
Abstract: X-ray polarimetry promises to give qualitatively new information about high-energy astrophysical sources, such as binary black hole systems. We designed a hard X-ray polarimeter, X-Calibur. Data with X-Calibur were taken at the CHESS X-ray beam facility in order to test the polarimeter and to study its performance using the polarized CHESS X-ray beam. The results of the measurements will be presented. A first flight of the polarimeter is scheduled from Ft. Sumner, NM, in fall 2014.
|"Establishing foundational structure-property relationships of nanocrystals and their assemblies"
Kaifu Biana, Zhongwu Wangb, Detlef Smilgiesb, and Tobias Hanratha
aSchool of Chemical and Biomolecular Engineering, bCornell High Energy Synchrotron Source, Cornell University, Ithaca, NY, 14853
Abstract: Assemblies of nanocrysals present many interesting scientific challenges at the confluence of hard and soft matter physics. The B1 station at CHESS presents unique experimental capabilities to probe novel materials under pressure. High-pressure experiments provide new insights into basic structure property relationships. This poster will summarize our three recent works at the B1 beamline: (1) pressure-dependent optical properties of PbS NCs, (2) size-dependent compressibility of PbS NCs, and (3) utilizing NC superlattice as a nanostructured pressure cell.
We investigated the pressure-dependent optical properties of PbS NCs. We found that the band gap Eg of PbS NCs decreases with pressure and the pressure coefficient dEg/dP further depends on the size of NCs. Combining structural information of both atomic lattice and inter-particle separation measured by in-situ high-pressure WAXS and SAXS theoretical calculation reproduced the experimentally obtained pressure-dependent variation of band gap. A second important discovery is the disappearance of the excitonic peak as the particles undergo the high-pressure rock-salt to orthorhombic phase transition. Taken together, our results provide new insights into the size- and pressure-dependent electronic structure of PbS NC quantum dots.
Our analysis of WAXS of PbS NCs under pressure also revealed that compressibility of PbS NCs, like many other properties, is size-dependent. We discovered a maximum stiffness at particle diameter of about 7 nm. We tentatively attribute this trend to a core-shell model. The size-dependent stiffness of NCs is caused by difference in the elasticity between atoms near the center of a NC and those at the surface.
Finally, we present our recent demonstration of the NC superlattice pressure cell. We showed, for the first time, opportunities introduced by the use of NC superlattice as an experimental platform to probe molecular bundles under uniaxial compression. We report a novel method to uniaxially compress molecules within specific confined spaces in a NC superlattice. We combined X-ray scattering experiments with density functional theory simulations to demonstrate our method to probe the elastic force of single molecule as a function of chain length. We see this methodology as an exciting new opportunity to investigate structure-function relationships of molecules under uniaxial compression.
|"3DXRD Martensite Variant Reconstruction Model"
Colorado School of Mines
Abstract: We present a polycrystal 3DXRD analysis technique that is being developed for phase transforming crystalline materials that includes the identification of the daughter phase variants born of each parent phase grain. The initial reconstruction technique draws upon a variant prediction model that uses grain orientation and elastic energy minimization based crystal mechanics of martensitic transformations to predict possible daughter variant orientations, and then interrogates 3DXRD data sets using a criteria of consistent volume and spatial location to correlate parent-daughter grain transformation. This technique will be demonstrated using synchotron-based X-ray diffraction (XRD) data collected on NiTi shape memory alloys at CHESS and APS.
|"Relationship between microstructure and mechanical behavior of polypropylene
Naigeng Chen, Meredith Silberstein, Margaret Koker
CHESS, Cornell University
Abstract: Non-woven fabrics have been widely used in the industry due to their good properties, including high surface area, high damage tolerance, high porosity and low cost. However, because of their mechanical behavior is still poorly understood, traditional non-woven fabric design process is almost empirically driven. This work aims at elucidate the effects of microstructure on the mechanical properties of nonwovens. A commercial polypropylene based geotextile, Dupont Typar SF, is used for this investigation.
The mechanical behaviors of this geotextile and its constituent fiber are characterized under uniaxial loading. The macroscopic behavior shows strain rate dependency, higher yield point and earlier breakage at a faster loading speed. Single fibers are extracted from the geotextile by tweezers. The yielding process starts at small strain level and continues to moderate deformation status. Multiple strain rate tests are conducted, and the mechanical behavior of non-woven constituent fiber exhibits minimal rate dependence.
The non-woven microstructure is studied by X-ray diffraction (XRD) and Micro Computed Tomography (µCT) methods. A customized setup is built at the Cornell High Energy Synchrotron Source (CHESS), which enables XRD and µCT during uniaxial deformation. The fiber orientation distribution can be calculated through in situ XRD data. For the µCT part, we pick 6 points on the monotonic loading curve of the nonwoven and perform µCT scans at each point. These points are chosen to span the elastic regime, small scale damage, yield, and large scale damage. Within this material, the fibers are thermally bonded to each other forming a uniformly distributed 2D network. As tensile stress is applied, the fibers in this network start to reorient. At the beginning of the deformation, the tension force straightens the axial directional fibers and breaks their bonds with attached transverse directional fibers. The specimen width decreases as the aligned fibers consolidate in-plane. At the later stage of the deformation, when significant macroscopic damage has occurred, only axial directional fibers connect the two ends of the sample. The thickness has increased significantly because many interlayer bonds and some of the fibers have broken. Portions of the non-woven separate apart from the original sample plane.
|"Possible Detection of UV induced band bending With X ray Emission Spectroscopy"
Graduate Student, School of Applied and Engineering Physics, Cornell University
Abstract: Band bending is a key step in many catalytic mechanisms, some of which are useful for energy applications. Conventional UV/visible/electronic spectroscopic methods cannot observe band bending in-situ. X ray Emission Spectroscopy (XES), using hard x rays, can provide element specific information about electronic levels and is suitable for in-situ probes. Here, we perform XES on SrTiO3 (STO) with oxygen vacancies, and demonstrate changes in XES intensity induced by applied UV. We tentatively attribute these changes to band bending induced by UV. This offers hope of in-situ observations of band bending, which may prove useful in elucidating catalytic mechanisms.
|"Shearing Using in-situ Grazing Incidence X-Ray Diffraction"
Gaurav Giri1, Detlef Smilgies2, Ruipeng Li2, Aram Amassian3 and Zhenan Bao1
1Department of Chemical Engineering, Stanford University
2Cornell High Energy Synchrotron Source (CHESS), Cornell University
3King Abdullah University of Science and Technology (KAUST), Saudi Arabia
Abstract: Organic electronics have been considered a leading candidate to make transparent and flexible electronics at a low cost. We have previously shown that the solution shearing method is a process that improves electrical performance for a range of OSCs, and the method is compatible with roll to roll industrial processing. This method can also tune the polymorph formation in OSCs, enabling high performance transistors without changing the OSC chemical structure. However, it is difficult to study the morphological and polymorph formations that enable high OTFT performance in situ. Not only does the thin film crystallize at a fast time scale, the evaporation front, where the crystal grows from the solution, is very small. The entire evaporation front can be less than 200 microns. Thus, the solution evolves into a crystallized thin film within seconds, and within an area less than 0.2 mm wide.
We use an X-ray 'microbeam' at the Cornell High Energy Synchrotron Source, with a beam width of < 20 microns, in conjunction with a high speed detector to resolve and follow crystallization from solution of the OSC during solution shearing. We have collected up to 100 frames per second X-ray images, and are able to create grazing incidence x-ray diffraction movies to easily see how crystallization occurs in the solution shearing system in real time. We also use an optical microscope trained at the evaporation front, which we can use to collect optical videos of the evaporation front at up to 10,000 frames per second. Being able to simultaneously study kinetic crystallization using both optical and X-ray movies helps us understand how different processing conditions result in various polymorphs. We study the model OSC 6,13-bis(triisopropyl)-silylethynyl pentacene (TIPS-pentacene) and show that confinement of the growing thin film plays a key role in forming metastable polymorphs, and that the film formation proceeds downwards from the air-solution interface. We generate metastable crystal polymorphs through other solution processing conditions as well.
|"Instantaneous local moment in Fe-based superconductors"
H. Gretarsson1,2, A. Lupascu2, I. Jarrige3, Jungho Kim4, D. Casa4, K. D. Finkelstein5, and Young-June Kim1
1Max Planck Institute for Solid State Research, Stuttgart
2Department of Physics, University of Toronto
3CMP&MS Department, Brookhaven National Laboratory
4APS, Argonne National Laboratory
5Cornell High Energy Synchrotron Source, Cornell University
|"Diffraction Pattern Calculator (DPC) Toolkit: A user-friendly approach to crystal
structure identification from 2D grazing-incidence wide-angle X-ray scattering data"
Anna K. Hailey1, Detlef-M. Smilgies2, and Yueh-Lin Loo1
1Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ
2Cornell High Energy Synchrotron Source, Cornell University, Ithaca, NY
Abstract: DPC Toolkit helps users extract unit cell parameters from X-ray diffraction data collected on polycrystalline thin films. The input data requirements are minimal and easy-to-assemble from data collected with any position-sensitive detector, and the user is required to make as few initial assumptions about the crystal structure as possible. The program does not account for structure factors, which presuppose knowledge of the occupied lattice positions. Instead, the user may choose the space group to remove the reflections forbidden by the symmetry of the unit cell.
|"HIV-1 Tat membrane translocation probed by low-and wide-angle X-ray scattering, neutron scattering, CD spectroscopy and MD simulations"
Carnegie Mellon University
Abstract: In an effort to understand membrane translocation of a cell-penetrating peptide, interactions of HIV-1 Tat peptide (YGRKKRRQRRR) with DOPC, DOPC/DOPE, DOPC/DOPS, and nuclear membrane mimics were investigated using low- and wide-angle x-ray scattering (LAXS and WAXS), neutron scattering, and circular dichroism (CD) spectroscopy. The diffuse scattering analysis applied to LAXS collected at CHESS revealed that Tat-membrane interactions reduce the membrane thickness by ~1 Å. In DOPC and DOPC/DOPE membranes, the position of Tat was found to transition from the vicinity of the glycerol-carbonyl headgroup to the phosphate headgroup as Tat mole fraction was increased from 0.009 to 0.06. The area per lipid for DOPC and DOPC/DOPE membranes increased by ~2 Å2 at the highest Tat mole fraction. The membrane bending modulus was found to decrease by roughly a factor of 2 at the highest Tat mole fraction except for the nuclear mimic. The chain-orientational order parameter, Sxray, calculated from WAXS and corrected for mosaic spread, showed Tat slightly disordered chains. Neutron scattering collected at NIST from fully hydrated samples consisting of DOPC:DOPE (3:1) membranes and Tat at 0.06 mole fraction showed a prominent, broad peak corresponding to a Tat-membrane correlation of ~100 Å. The secondary structure of Tat calculated from CD spectra using DichroWEB was found to be the same in pure water as in lipid thin films and primarily consisted of ß-sheet and random coil with small helical content. Our findings are consistent with the results from MD simulations by Herce and Garcia, which suggested that Tat interacts with phosphate headgroups across the bilayer, facilitating the formation of pores. The ensemble of configurations obtained from a new MD simulation allows visualization of Tat/membrane interactions. Funded by GM44976, GM86801, DMR-0936384 (CHESS), and DOE(NIST).
|"Formation, Metastability, and Reversibility of Manganite Brownmillerite Epitaxial Films on SrTiO3"
Howie Joress1, Audrey E. White1,2, Matthew J. Ward1, Arthur R. Woll1, Joel D. Brock1,3
1Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York, USA
2Department of Materials Science and Engineering, Cornell University, Ithaca, New York, USA
3Applied and Engineering Physics, Cornell University, Ithaca, New York, USA
Abstract: Brownmillerite (BM) phases, which are related to Perovskite phases but contain ordered oxygen vacancies, are known to have better oxygen ion conductivity due to their ordered oxygen vacancies compared to their Perovskite counterparts and are therefore of interest as a potential cathode material for solid oxide fuel cells (SOFC). (La,Sr)MnO3-x (LSMO) is a common cathode material for SOFC. By using an oxygen poor, epitaxial Strontium Titanate (STO) capping layer an LSMO epitaxial film can be reduced from x≈0 to x=.5 and the transition from the Perovskite phase to a Brownmillerite (BM) phase can be induced.
Here we present our study of this transition by using real-time in-situ x-ray diffraction (XRD) during film growth by pulsed laser deposition to observe the formation and decay of the BM phase. In previous work, the manganite BM phase was metastable, deteriorating after STO deposition has stopped, and could only be stabilized by quenching from the growth conditions. We demonstrate that the BM phase can be repeatedly formed following decay by depositing additional STO. This suggests that the BM metastability is due to re-oxidation of the LSMO layer. Using this regrowth, we systematically study the effects of deposition pressure on the growth and stability of the BM phase. We find a strong correlation between the formation and stability of the BM phase and oxygen pressure during STO growth. By depositing the STO capping layer at our chamber's base vacuum level (10-7 Torr) we were able to stabilize the BM phase. We performed in-situ reflectivity measurements to characterize the growth morphology of the film which showed that the BM phase forms through columnar grain growth.
|"Instantiating Lamellar Annealed Ti-6Al-4V for Use in Simulating Deformation Induced Crystal Twinning"
Abstract: Many widely used structural alloys are polycrystalline materials. These materials contain regions - called grains - that differ in size, shape, crystallographic phase, and crystallographic orientations. The processing history that these alloys undergo (namely solidification and annealing) strongly influence the properties of the grains. These microstructural properties are what determine how the material behaves on the macroscopic level. Ti-6Al-4V is one of these materials. Containing two phases at room temperature - one having a cubic structure and the other hexagonal - Ti-6Al-4V has a microstructure which varies widely depending on its processing history. Being composed primarily of the hexagonal phase, this material presents an opportunity to study crystallographic twinning, as well. Twinning is a mode of deformation that has been observed in metals with a hexagonal crystal structure. Since a better understanding of these metals begins with an understanding of how the microstructure effects the macroscopic properties, it is necessary to have high fidelity representations of the microstructure and models which accurately simulate the deformation upon loading. This begins with the instantiation of the complex microstructure seen in one microstructural variant of Ti-6Al-4V - one with a fully lamellar microstructure. These virtual representations can then be used in a crystal plasticity model solved using the finite element method in order to simulate the material response upon loading. This model, however, only considers slip as a mode of deformation, and thus it is necessary to include twinning to better capture the actual response. These simulations may be compared to actual material responses observed using x-ray diffraction, which allows for a non-destructive method of measuring important material behavior through different stages of mechanical loading.
|"Microfabrication of Silicon X-ray Windows"
Abstract: The use of small angle x-ray scattering to study biological macromolecules requires minimization of scatter from x-ray windows around the sample. New x-ray windows were fabricated from silicon and silicon-on-insulator (SOI) wafers. These window have high transmission and low scatter, making them well suited for use in x-ray scattering experiments.
|"Molecular Order and Dynamics in Nanometeric Thin Layers of
Poly(styrene-block-isoprene-1.4) Diblock Copolymers"
Wycliffe K. Kipnusu1*, M.M. Elmahdy1,2, M. Tress1, M. Fuchs1, E.U. Mapesa1, J. Zhang3, Detlef-M. Smilgies4, C.M. Papadakis3 and F. Kremer1
1Institute of Experimental Physics I, Leipzig University, Linnéstrasse 5, 04103, Leipzig, Germany
2Department of Physics, Mansoura University, Mansoura 35516, Egypt
3Technische Universität München, Physik-Department, Physik weicher Materie, James-Franck-Straße 1, 85748 Garching, Germany
4CHESS, Wilson Laboratory, Cornell University, Ithaca, NY 14853, USA
*E-mail address: email@example.com
Abstract: Order and dynamics of poly(styrene-block-1,4-isoprene), P(S-b-I) diblock copolymers in nanometer thin layers with different isoprene volume fraction (fPI) and identical molecular weight of the styrene blocks are studied by a combination of Grazing-Incidence Small-Angle X-ray Scattering (GISAXS), Atomic Force Microscopy (AFM) and Broadband Dielectric Spectroscopy (BDS). GISAXS and AFM reveal randomly oriented lamellar structures in the films and a parallel orientation at the top surface, respectively. Using BDS, three well separated relaxation processes are detected, (i) and (ii) the dynamic glass transitions (segmental mode) in the styrene and isoprene blocks respectively and (iii) the normal mode relaxation representing fluctuations of the isoprene chain as a whole or parts of it. While the two former do not show any thickness dependence in their spectral positions, the latter becomes faster with decreasing sample thickness. This reflects the different length-scales of molecular fluctuations.
|"A New Double-Laue Monochromator for High-energy X-rays at CHESS"
CHESS, Cornell University
Abstract: A new double-Laue monochromator (DLM) for high-energy X-rays has been installed and commissioned. Main advantages of the Laue monochromators over the Bragg counterparts are smaller beam footprint on the monochromator crystals, and the ability to utilize the anticlastic bending in the meridional plane to eliminate the chromatic aberration of the diffracted beam by working on the Rowland circle.
The new DLM is an improved version of the prototype DLM that was built and commissioned earlier at CHESS. It consists of benders for sagittal focusing, tilt stages for diffraction angle adjustments, and several linear travel stages for aligning monochromator crystals. The design is first of its kind with both cryogenic cooling and remote fully adjustable degrees of freedom for bending and twisting of monochromator crystals. It is capable of delivering X-rays from 38 to 88 keV, with the beam size of 1 mm horizontally (focused) × 1.5 mm vertically (not focused). Measured ΔE/E is on the order of 10-3 and flux ranges from 1×1011 to 5×1012 ph/s, depending on energy.
Details of the design of the DLM and results from the commissioning experiments characterizing its performance will be presented.
|"Grain Mapping at CHESS: Commissioning experiments"
CHESS, Cornell University
Abstract: Grain mapping is a nondestructive method to acquire information about the shape, orientation, and location of grains within a bulk polycrystalline specimen. This technique is important to the structural materials community, especially in modeling applications, since it provides information about the detailed environment of neighboring grains. Grain mapping is performed experimentally by collecting diffraction patterns from both "near field" (specimen to detector distance on the order of 1 cm) and "far field" detectors (specimen to detector distance greater than 0.5 m). The far field data is reduced to index the orientation and approximate location of grains within the specimen. This information provides the context necessary to interpret the near field data to precisely solve for grain shape and location. This spring, we have commissioned this technique at CHESS for upcoming experiments at the new F2 high energy beamline. This commissioning experiment extends the capabilities for structural material studies during in-situ loading.
|"A Computational Challenge Problem in Materials Discovery"
Ronan Le Bras
Computer Science Dept, Cornell University
Abstract: Accelerating the pace of discovery of new materials would foster innovations and address pressing issues in sustainability. As the data collection reaches a highthroughput regime, the bottleneck of the discovery cycle becomes the data analysis itself. The goal is to encourage computer scientists to propose new computational methods for this data interpretation, by providing a problem description, data, visualization tools and evaluation metrics that transcend materials science research.
|"In-plane Anisotropy of OTFTs Cast by Doctor Blading Method"
CHESS, Cornell University
Abstract: The solution casting process of organic thin film transistors attracts increasing interest as the low cost and easy manufacture, depending on the discovery of the new materials, the development of new casting methods and the increasing knowledge of the casting process. Beyond the common casting methods like drop-casting and spin-coating, several new casting methods, such as doctor blading, inkjet printing, slot-die coating, etc. have been introduced to improve the device performance through the control of structure and morphology. Balding method, casting films through guiding solutions by a moving blade, is one of the promising methods to implement into roll-2-roll processing. The one dimensional movement of the blade could result the transistors with in-plane anisotropic performance.
Here, we demonstrate the in-plane anisotropy of the blade-cast OTFTs in mobility, structure and morphology. We present the evolution from anisotropic to isotropic films by controlling the blading speeds. Through in situ monitoring the casting process by µGIWAXS and high speed microscopy, we describe the transition of homogeneous to heterogeneous nucleation with the anisotropy evolution.
|"Crystallization Dynamics of the Methylammonium Lead Halide Perovskites"
Abstract: The organic-inorganic halide perovskites are an exciting class of perovskites that have shown incredible performance as a photovoltaic material over the last several years, with efficiencies over 15% from low temperature, solution processed devices. Our current work focuses on improving the crystal and film morphology through a better, fundamental understanding of the crystallization processes. Using synchrotron radiation allows us to track the crystal evolution in situ, qualify the distinct transitions, correlate those transitions to changes in processing conditions, and extract kinetic parameters for the formation of the desired structure. We then exploit the underlying processing-structure relationships to produce films with better coverage and stronger crystallographic orientation leading to increased device performance.
|"Atomic structure determination of Ta2O5 and mixed amorphous Ta2O5-GeO2 thin films
deposited on silicon nitride membranes"
Abstract: We systematically explore the local atomic structure of Ta2O5 and Ta2O5-GeO2 mixed amorphous thin film oxides deposited directly on silicon nitride membranes. To obtain a complete picture of the local atomic structure of this system, we combine pair distribution function methods, x-ray absorption spectroscopy, and computational simulations. Our study reveals the complex evolution in the local atomic structure as a function of composition.
|"Interplay of spin-orbit interactions, dimensionality, and octahedral rotations in semimetallic SrIrO3"
Abstract: We employ MBE and ARPES to reveal the electronic structure of SrIrO3 as an exotic narrowband semimetal. We discover remarkably narrow bands which originate from a consequence of strong spin-orbit interactions, dimensionality, and both in- and out-of-plane IrO6 octahedral rotations. The partial occupation of numerous bands with strongly mixed orbital characters signals the breakdown of the single-band Mott picture that characterizes its insulating two-dimensional counterpart, Sr2IrO4.
|"Quantitative analysis of crystal scale deformation heterogeneity during cyclic
plasticity using high-energy X-ray diffraction and finite-element simulation"
Mark Obstalecki, Su Leen Wong, Paul R. Dawson, Matthew P. Miller
Sibley School of Mechanical and Aerospace Engineering, Upson Hall, Cornell University, Ithaca, NY USA
Abstract: Modern high-energy X-ray diffraction (HEXD) experiments coupled with a crystal-based finite-element model employing forward projection of virtual X-rays through each element is applied to study cyclic plasticity. An Okegawa mold copper specimen was cyclically deformed in situ at the Advanced Photon Source. The strain amplitudes of the cyclic experiments reached well into the plastic regime and diffraction images were generated at several points in the loading history using a HEXD methodology. Four grains within the bulk of a polycrystalline sample were tracked and interrogated with X-rays. Diffraction peak data were reduced to center of mass (COM) and full width at half maximum (FWHM) values in the detector coordinates 2θ (radial) and η (azimuthal). The peaks evolved with cycles and changed significantly when the plastic strain amplitude was increased. Large changes in the peaks (especially the azimuthal FWHM values) were also observed during the course of one loading cycle; larger FWHM values were seen at the compressive end of the cycles. This trend was reversed when the sample was initially loaded in compression. Diffracted intensity distributions were also seen to change significantly from one grain to the next. Using a virtual diffractometer model, COM and FWHM values were computed from the modeling results by projecting virtual X-rays through the finite-element mesh and compared to the experimental data. The finite-element polycrystal model serves as the final step in the data reduction process, revealing significant spatial heterogeneity of orientation, stress and plastic strain rate istributions. Studying these distributions collectively will be necessary to fully understand the detailed elastic–plastic deformation behavior within each grain and to explore problems such as microcrack initiation hypotheses in polycrystalline materials.
|"Anomalous SAXS of DNA at Mn ion energies"
Suzette A. Pabit, Joshua M. Tokuda, Andrea M. Katz, Julie L. Sutton, George D. Calvey, Yujie Chen, Steve P. Meisburger, Ken D. Finkelstein and Lois Pollack
Abstract: DNA molecules are polyanionic polymers that are neutralized in solution by charge compensating cations. Characterization of the cations around DNA can be elusive because the majority of the ions form a diffuse "ion atmosphere" that is not amenable to investigation by traditional methods that rely on rigid structural features. We use Anamolous Small-Angle X-ray Scattering (ASAXS) to probe the interaction of DNA with its cationic cloud. In ASAXS, we tune x-ray energies to be near the absorption edge of the charge compensating ion under investigation. In the past, we have used ASAXS to study DNA interactions with the monovalent ion Rb+, divalent ion Sr2+ and trivalent ion Co(NH3)63+, all have x-ray absorption edges that are readily accessible for SAXS studies [1,2]. Very recently, due to the extended capabilities of the CHESS C-line station, we were able to successfully add the biologically relevant Mn2+ ion in our ASAXS repertoire. In this poster, we will discuss the necessary changes made at the C-line station to work near the absorption edge of Mn (6.55 keV). We will show preliminary ASAXS data and discuss its implications to the biophysical understanding of Mn ion-DNA interactions.
Acknowledgements: Special thanks to Chris Whiting, John Conrad and Tom Krawczyk for contributions on beam delivery and for the new optical table.
|"Connecting heterogeneous single slip to diffraction peak evolution in high energy
monochromatic X-ray experiments"
Abstract: Over the past decade, a new generation of characterization methods for polycrystalline metals using high-energy synchrotron x-ray diffraction and in-situ loading have been developed. Shifts of diffraction peaks from an individual crystal are consistent with straining and reorientation of the crystal lattice. Evolution of the spread of each reflection is associated with strain and orientation gradients. This work examines the pattern of diffracted intensity associated with orientation gradients due to plasticity-induced inhomogeneous slip. A simple model of a single crystal subjected to single slip is created using Nye's concept of lattice curvature and a mosaic of crystallites, which is then used to generate virtual crystals. Forward projected x-rays diffract from the crystal planes within the mosaic and create a specific pattern on the virtual detector. Some peaks expand, some contract, and others do not appreciably evolve. The model was validated using experimental data from a single crystal silicon sample oriented for single slip and compressed at 800°C at the A2 station at CHESS. The low defect concentration in a silicon single crystal makes it ideal for understanding slip mechanisms. At 800°C silicon deforms by restricted slip identical to an fcc metal. Excellent comparison with experimental data validated the simple model, which may be employed in the future to indicate slip system activity under single slip conditions.
|"High-Speed Imaging and Bunch Train Isolation with the KECK Pixel Array Detector"
Hugh T. Philipp1, Mark W. Tate1, Joel T. Weiss1, Prafull Purohit1, Darol Chamberlain2, and Sol M. Gruner1,2,3
1Department of Physics, Cornell University, Ithaca, NY 14853
2Cornell High Energy Synchrotron Source (CHESS), Cornell University, Ithaca, NY 14853
3Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853
Abstract: An x-ray imaging detector capable of isolating single bunch trains from a synchrotron source has been developed in the Gruner Group (Cornell University) and tested at CHESS. The KECK pixel array detector (KECK PAD) can image x-rays at frame rates up to 10 MHz and can be synchronized with the CESR timing signal to isolate diffraction from single bunch trains, providing time resolution for dynamic systems down to the duration of the bunch train. The detector works by using in-pixel, multi-frame analog storage to quickly collect successive images. The present system is 256 x 384 pixel, made by tiling 6 128 x 128 pixel detector modules. The poster will include results from the first measurements at CHESS showing bunch train isolation (Nov. 2013), and the first experimental application of the detector performed at CHESS in February, 2014.
|"Time-Resolved and Wide Dynamic Range Experiments with the Mixed-Mode Pixel Array
Katherine S. Shanks1, Hugh T. Philipp1, Mark W. Tate1, Joel T. Weiss1, Prafull Purohit1, Darol Chamberlain2, and Sol M. Gruner1,2,3
1Department of Physics, Cornell University, Ithaca, NY 14853
2Cornell High Energy Synchrotron Source (CHESS), Cornell University, Ithaca, NY 14853
3Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY 14853
Abstract: The Mixed-Mode Pixel Array Detector (MM-PAD) is a photon-integrating pixel array detector optimized for experiments requiring a high frame rate and/or wide dynamic range. A 500 µm thick, fully-depleted silicon sensor, giving approximately unity stopping power at 8 keV, is bonded pixel by pixel to a custom readout ASIC. A mixed analog and digital readout scheme is used to achieve a pixel well depth of 4x107 8 keV photons while maintaining single-photon sensitivity. Due to the photon-integrating pixel front-end, the MM-PAD can tolerate a sustained hit rate of 108 photons/pixel/s, exceeding the hit rate limit of presently-available photon-counting PADs. Additionally, the MM-PAD can frame continuously at over 1 kHz. A tiled unit with 256x384 pixels has been used in several experiments, including coherent diffractive imaging experiments at the APS and PETRA III, and time-resolved experiments at CHESS. Results from these experiments will be presented to demonstrate the detector capabilities.
|"Operando X-Ray Scattering and Spectroscopic Analysis of Germanium Nanowire Anodes in Lithium-Ion Batteries"
Katharine E. Silberstein,† Michael A. Lowe,† Benjamin Richards,‡ Jie Gao,† Tobias Hanrath,§ and Héctor D. Abruña*,†
†Department of Chemistry and Chemical Biology, ‡Department of Materials Science and Engineering, and §School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, United States
Abstract: X-ray diffraction (XRD) and Fourier-transformed extended x-ray absorption fine structure (EXAFS) analysis of x-ray absorption spectroscopy (XAS) measurements have been employed to determine structural and bonding changes, as a function of lithium content/state of charge, of germanium nanowires used as the active anode material within lithium-ion batteries (LIBs). Our data, collected throughout the course of battery cycling (operando), indicate that lithium incorporation within the nanostructured germanium occurs heterogeneously, preferentially into amorphous regions over crystalline domains. Maintenance of molecular structural integrity within the germanium nanowire is dependent on depth of discharge. Discharging to a shallower cutoff voltage preserves partial crystallinity for several cycles.
|"Empirical-Numerical Consistency of Transformation-Plasticity Interactions in
Shape Memory Alloys"
Colorado School of Mines
Abstract: Micromechanical investigations of transformation and plasticity mechanisms in shape memory alloys have revealed that simultaneous activity of multiple inelastic mechanisms give rise to many remarkable asymmetric and anisotropic material behaviors. Results of in-situ diffraction experimentation that have motivated a new constitutive model for shape memory alloys will be presented, together with the model framework and demonstrations.
|"What's New at MacCHESS"
D. Szebenyi, A. Acerbo, R. Cerione, M. Cook, R. Gillilan, Q. Huang, C.-U. Kim, I. Kriksunov, T. Lukk, W. Miller, D. Schuller, S. Smith
MacCHESS, Cornell University
Abstract: MacCHESS conducts both core and collaborative research projects, and supports users doing "Macromolecular diffraction at CHESS". In 2013-2014, users employed CHESS facilities to collect crystallographic and small-angle solution scattering (BioSAXS) data on numerous molecules and complexes of biological interest. A sampling of users' important structural results, reported here, provides insight into how the key metabolic enzyme GAC works, how a bacterium hijacks a host cell's cytoskeleton to move, and how proteolysis inside a membrane protein is controlled.
Progress has been made in the major focus areas of MacCHESS:
BioSAXS – operations have moved from F2 to G1, resulting in improved beam intensity and collimation; DLS and MALS monitors are now available; in-line SEC-SAXS has been implemented; development of cryo-SAXS is continuing.
Pressure Cryocooling – a significant structure produced using data from pressure-cryocooled crystals of a collaborator was reported; the commercial version of the pressure-cryocooling apparatus, from Advanced Design Consulting, is on the market.
Microcrystallography – background reduction through the use of graphene-wrapped crystals is being explored; confocal microscopy and intrinsic protein fluorescence have been used to visualize mounted crystals; investigation of in-line use of collaborator Fraden's microfluidic chips continued.
Facility Upgrades – a prototype Eiger 1M detector was tested and shown to produce excellent data for both routine crystallography and diffuse scattering measurements. Initial tests of the UV-RIP method have been conducted, and development is in progress. Improvements to station automounters include a new puck-loading tool and compatibility with multiple types of puck.
|"The recent progress of CHESS capillary program"
Thomas Szebenyi and Rong Huang
CHESS, Cornell University
Abstract: CHESS has been making capillaries for many years and we are continuously improving capillary puller hardware and making improvements of capillary optical metrology.
For capillary metrology, we have implemented an air-bearing stage that can measure capillary profile without having capillary hung upright by thread. Measuring capillary profile with capillary laying down on this new stage can reduce signal noise caused by capillary vibration. With the new stage, we can also measure capillary inner diameter with glass index matching fluid (ALIO specifications - resolution = 5 nm, accuracy <= +/- 500 nm, repeatability <= +/- 40 nm).
For capillary puller, besides smaller changes such as upgrading tube rotation motors, we are also working on upgrading the main pulling stage with a higher quality granite supported stage by Aerotech (resolution = 100 nm, accuracy <= +/- 1000 nm, repeatability <= +/- 500 nm). The tension feedback system will also be upgraded with this new stage.
For capillary fabrication, our latest effort was to improve capillary straightness. There was some progress on this front but more progress is needed. In last year, we have successfully made some long capillaries with reasonable straightness. In addition to make straighter long capillaries for TXM applications, we will also try to make small focusing capillaries for CHESS microfocusing projects.
|"Using Contrast Variation with SAXS to Visualize DNA Dissociation from Nucleosome Core Particles"
Abstract: The organization of DNA in nucleosome core particles (NCP) is understood to play crucial regulatory roles in transcription, replication, recombination and repair. High resolution crystal structures deliver detailed snapshots of the NCP in its most stable conformations and reveal thousands of electrostatic interactions that mediate the stability of NCPs. However, many of the techniques that have been applied thus far are ill-suited for directly monitoring the intermediary and dissociated conformations of the NCP. To this end, we applied small angle X-ray scattering (SAXS) - a powerful technique for delivering low resolution structural details of biological molecules. Since SAXS studies of protein-nucleic acid complexes are complicated by the differences in scattering lengths between proteins and nucleic acids, we applied a contrast variation approach where we matched the solvent and protein contrasts to effectively probe the DNA component of the NCP alone. We systematically modulated the electrostatic interactions by adjusting the salt concentration of the solvent and visualized the conformational transition of the DNA from a bound to unbound state during NCP disassembly.
|"Nucleating Agents in Organic Semiconductors"
Neil D. Treat1, Jennifer Nukeda Malik1, Maged Abdelsamie3, Liyang Yu3, Ruipeng Li4, Detlef M. Smilgies4, Aram Amassian3, Craig J. Hawker2, Michael L. Chabinyc2, and Natalie Stingelin1
1Department of Materials and Centre for Plastic Electronics, Imperial College London, Exhibition Road, London SW7 2AZ
2Department of Materials and Materials Research Laboratory, University of California Santa Barbara, Santa Barbara, CA, 93106
3Physical Sciences and Engineering Division, Solar and Photovoltaic Engineering Research Center, King Abdullah University of Science and Technology (KAUST) Thuwal 23955-6900, Saudi Arabia
4Cornell High Energy Synchrotron Source, Wilson Laboratory, Cornell University, Ithaca, New York 14853, United States
Abstract: Manipulation of the solid-state structure and properties of a material by the addition of relatively small quantities of foreign species ("additives") has been widely exploited in materials ranging from metals to plastics. Additives including nucleating or clarifying agents have been utilized to regulate the solidification process (most prominently the rate of crystallite nucleation) of (semi-)crystalline polymer solids (e.g. isotactic polypropylene, i-PP). This control has been used to enhance the polymer’s mechanical and optical properties by controlling both their crystallite dimensions and 'shape'.[1,2] In this poster, we demonstrate that minute amounts (0.1 - 1 wt%) of commercially available nucleating agents can efficiently control the crystallization kinetics of a wide range of organic semiconductors (i.e. fullerenes, small molecules, and polymers) when processed from the melt, solution, or solid state without adversely affecting their electronic properties. Our findings demonstrate that the addition of nucleating agents is an elegant strategy to decouple processing conditions from the molecular ordering of a broad range of organic semiconductors.References
 Kristiansen, P. M.; Gress, A.; Smith, P.; Hanft, D.; Schmidt, H. W. Polymer 2006, 47, 249-253.
 Wunderlich, B., Macromolecular Physics: Crystal nucleation, growth, annealing. Academic Press: 1976.
|"CONNECTING THE PARTICLES IN THE BOX - CREATING HEXAMER NANOCRYSTAL CLUSTERS WITHIN AN AB6 BINARY NANOCRYSTAL SUPERLATTICE"
Abstract: Binary nanocrystal superlattices present unique opportunities to create novel interconnected nanostructures by partial fusion of specific components of the superlattice. Here, we demonstrate the binary AB6 superlattice of PbSe and Fe2O3 nanocrystals as a model system to transform the body-centered hexamer of PbSe nanocrystals into a single fused particle. We present detailed structural analysis of the superlattices by combining high-resolution X-ray scattering and electron microscopy. Molecular dynamics simulations show optimum separation of nanocrystals in agreement with the experiment and provide insights into the molecular configuration of surface ligands. We describe the concept of nanocrystal superlattices as a versatile 'nanoreactor' to create and study novel materials based on precisely defined size, composition and structure of nanocrystals into a mesostructured cluster. We demonstrate 'controlled fusion' of nanocrystals in the clusters in reactions initiated by thermal treatment and laser spike annealing.
|"Use of mosaic spread to correct lipid chain order parameter Sxray"
Dr. Stephanie Tristram-Nagle
Research Professor, Biological Physics Group, Physics, Carnegie Mellon University
Abstract: The Nagle/Tristram-Nagle Lab collects low angle and wide angle X-ray scattering
(LAXS and WAXS) data at the Cornell High Energy Synchrotron Source (CHESS) in order to study the
structure and properties of the underlying lipid bilayer in cell membranes. My job (Leah Langer) this
semester was to help analyze the recently collected WAXS data. The samples are 2,000 bilayers stacked
on a silicon wafer. The bilayers are fully hydrated and then X-rayed. Our samples contained a peptide
from the HIV virus, MA+, the myristoylated form of the 31-amino acid terminus of the larger MA protein, which
interacts with membranes during viral budding. The WAXS data are used to calculate Sxray, which is a measure
of lipid chain order. The Sxray values first obtained are not exactly correct because the samples had a
measurable mosaic spread. I used LAXS images at a fixed angle and a known lab procedure using Matlab
and Origin to determine the mosaic spread. Once determined, I then used an existing procedure with Matlab and
Mathematica to correct Sxray for the mosaic spread on some of the samples.
|"Characterizing Copper Oxygen Intermediates with X-ray spectroscopy: a Comparison of Valence to Core XES and HERFD-XAS"
Abstract: Characterization of active catalytic cycle intermediates remains an important challenge in inorganic chemistry. Probing of reaction mixtures requires the development and fine tuning of novel spectroscopies capable of characterizing impure species. We will report on the use of high energy resolution fluorescence detected X-ray absorption spectroscopy (HERFD-XAS) and valence to core X-ray emission spectroscopy (V2C-XES) in conjunction with DFT to study a recently reported Cu/O2 catalytic cycle.
|"Proposed Spectroscopy Beamline Upgrade at CHESS"
Matthew J. Ward and Karl W. Smolenski
Abstract: A spectroscopy beamilne upgrade for CHESS will allow for the study of fast (i.e., 10's of ms) chemical transformations in-situ using quick x-ray absorption spectroscopy (QXAS), both in the near edge region (XANES) and the extended region (EXAFS). The use of a special tapered undulator source in conjunction with both a standard double crystal monochromator (DCM) and a special QXAS monochromator will allow for two different modes of operation: tapered undulator with a QXAS monochromator and standard undulator with a DCM. In QXAS mode the chemistry beamline will have simmilar performance in terms of flux and time resolution to the SuperXAS beamline at the SLS, which is the world's best QXAS beamline; there are currently no comparable QXAS beamlines in operation at any other US lightsource. In DCM mode the standard undulator will provide a high- flux source for x-ray absorption spectroscopy (XAS), which, in conjunction with a set of Kirpatrick-Baez (KB) mirrors will allow for micro XANES and EXAFS measurements. These two powerful modes of operation, QXAS and high flux – microfocused XAS, in combination with air-sensitive and hazardous gas handling capabilities will allow for the study of exciting new chemistry as well as current critical research in chemical and energy science. In particular the spectroscopy beamline upgrade at CHESS will provide state of the art capabilities for research on chemical transformations, catalysis, new energy materials (i.e. photocatalysts, solid oxide fuel cells, battery materials), and hydrogen storage materials.
|"X-ray observations of chemical transformations in nanocrystals"
Matthew J. Ward, Margaret K.A. Koker, Don-Hyung Ha, Andrew H. Caldwell, Robert Hovden, David A. Muller, and Richard D. Robinson
Abstract: Dual interface formation in copper sulfide nanocrystals (NCs) undergoing cation exchange to zinc sulfide has been observed, creating epitaxial copper sulfide heterostructures within spherical zinc sulfide NCs. From copper K-edge X-ray absorption near edge structures (XANES) and wide angle x-ray scattering (WAXS) measurements we observe a solid-solid phase transformation of the initial copper sulfide phase in heterostructured NCs. As the cation exchange reaction progresses, and Cu ions are replaced by Zn ions at the interfaces, the Cu ions are accommodated in intrinsic Cu vacancy sites present in the initial roxbyite (Cu1.81S) phase of copper sulfide, inducing a phase transition to djurleite (Cu1.94S) / low chalcocite (Cu2S), which are more thermodynamically stable phases than roxbyite. Further reaction leads to a thinner copper sulfide layer, and the epitaxial strain at the interfaces between copper sulfide and ZnS increases. This strain energy reaches a maximum when the thickness of the copper sulfide disk is 5 nm and induces another phase transformation back to roxbyite. This second phase transition occurs to minimize strain energy, as the roxbyite structure shares a similar sulfur sublattice with wurtzite ZnS.
|"In-Situ GISAXS of Nanoparticles at a Fluid Interface"
Abstract: Our group recently demonstrated nanoparticle (NP) assemblies that combine high spatial coherence and strong interparticle electronic coupling. Convective assembly of a colloidal NP suspension at the surface of ethylene glycol results in the formation of a two-dimensional (2D) superlattice. Subsequent thermal or chemical methods were then applied to control NP surface chemistry in order to promote epitaxial connections between NPs and symmetry transformation in the superlattice.
|"Unit cell shift in thaumatin crystals within graphene at ambient conditions"
MacCHESS, Cornell University
Abstract: The crystal structure of sweet tasting protein, Thaumatin I from the African berry Thaumatococcus daniellii, was solved nearly 10 years ago. Historically, the protein forms 3 different crystal structures of space groups C2 with a=118, b=45, c=38 Å, P2(1)2(1)2(1) with a=44, b=64 and c=73 Å, and a tetragonal form P4(1)2(1)2 with a=b=59 and c=152 Å. Last year, Wierman et. al. showed a new method to reduce background scatter by the use of atomically thin graphene sheets as a crystal mounting platform for protein crystals. More recently in trials over three months, we discovered a new re-packing of the thaumatin unit cell, which we present here. In one case, we observe the sudden shift in the size and mosaicity of the unit cell while imaging at room temperature. What remains to be determined, is the nature of this repacking, and whether storage time for protein crystals within graphene can extend for months at room temperature.
|"First, rapid XRF mapping results with the Maia detector at CHESS"
CHESS, Cornell University
Abstract: The Maia detector is a cutting edge, 384-pixel, energy-dispersive detector with maximum count rates of up to 10 million counts/second. CHESS recently purchased this detector, and performed a commissioning run at the G3 hutch in March 2014. Several days of beamtime resulted in a series of beautiful, never-before-seen views of the elemental distribution in a number of biological objects. Results and plans for the Maia user program will be presented.
|"Structural Rearrangement of Gold Nanocrystals Superlattice Mediated by Halide Ions
or Silicon Nanocrystals Framework"
The University of Texas at Austin
Abstract: As analogs to solid materials, nanocrystal superlattices, also called "artificial solids", have been shown to subject to structural polymorphism and rearrangements. The solid-solid phase transitions of solid material could be mediated by adding impurities or alloying, and similar phenomenon are expected for nanocrystal superlattices. Here, we show structural rearrangements of gold nanocrystal superlattices are mediated by adding halide ion impurities or alloying with silicon nanocrystals.
|"Complex macrophase separated nanostructure induced by microphase separation in lamellar diblock copolymer thin films"
J. Zhang1, D. Posselt2, Detlef-M. Smilgies3, J. Perlich4, Konstantinos Kyriakos1, Sebastian Jaksch1, and C.M. Papadakis1
1Technische Universität München, Physik-Department, Fachgebiet Physik weicher Materie , James-Franck-Str.1, 85747 Garching (Germany)
2IMFUFA - Department of Mathematics and Physics, University of Roskilde, P.O. Box 260, 4000 Roskilde, Denmark
3Cornell High Energy Synchrotron Source (CHESS), Wilson Laboratory, Cornell University, Ithaca, New York 14853, U.S.A.
4Deutsches Elektronen-Synchrotron (DESY) , Notkestrasse 85, 22603 Hamburg, Germany
Abstract: Although self-assembly of block copolymers offer a rich variety of periodic nanoscale patterns,1 there are still major challenges to overcome in order to realize real applications.2 One of the key challenges is to control a self-assembling system to create a specific structure. It is known that macrophase separation can be induced by microphase separation in binary blends of diblock copolymers.3 The question arises whether, in thin film geometry, the macrophase separation effect can be exploited to create a specific structure with regularly arranged domains, e.g., by achieving microphase separation first and then controlling the macrophase separation process afterwards by solvent vapor annealing (SVA).
In the present work, we use a binary blend of compositionally symmetric poly(styrene-b-butadiene) (P(S-b-B)) diblock copolymers differing in molar mass. Thin films were prepared by spin coating the polymer solution onto silicon wafers. The fast solvent removal rate results in a microphase separated structure in block copolymer blends. The dependence of the morphology on Φβ was studied using AFM and GISAXS before and after SVA.
|"Nano-fabrication of capillary beamstops"
Mengtian Zhao1, David Agyeman-Budu2, Nicolaie Moldovan3, Arthur Woll1, Tom Szebenyi1, Rong Huang1
1Cornell High Energy Synchrotron Source
2Dept of Materials Science and Engr. Cornell University
3Advanced Diamond Technologies, Inc.
Abstract: X-ray beam stops are needed at synchrotron beamlines for the use of X-ray focusing optics, such as singe-bounce capillaries and Fresnel zone plates. At CHESS, when capillaries are used to focus X-rays, gold beamstops as small as 30 um in diameter with thickness above 50 um are needed. We have used photolithography and electroplating technique at Cornell Nanofabrication Facility to develop these beamstops. Our current studies focused on making these beam stops starting from SOI wafers with device layer thicknesses of 5 or 10 um. Our goal is to make the gold beamstops on top of Si membranes, formed by the device layer after opening a window in the Si handling layer to let X-rays pass. The beam stop structures themselves are fabricated by electroforming gold in cylindrical openings in thick photoresist (>50 μm) used as molds. The challenges are in the photolithography step to fabricate high aspect ratio resist molds with straight vertical walls, the cleaning of resist residues on the bottom of the holes, and in electroplating high density gold in the high aspect ratio holes.
Many fabrication procedures have been involved, starting from CAD design of masks, deposition of thin layers of low-stress nitride (LS-SiN), to evaporation of seed layers, coating of Ominicoat and photoresist layers, baking, exposure, development, descum, electroplating, KOH etching and photoresist removal.
For the lithographic formation of the molds, several photoresists were tested and the scope was narrowed down to two negative tone photoresists: KMPR 1050 and SU-8 3035. The latter was finally chosen because it gave more consistent results whereas the KMPR 1050 often created messy patterns. Many experiments were performed to optimize the electroplating parameters. In the first batch of beamstops fabricated, large effective current was used. This created hollow caves inside the beamstops and rough surfaces. As an improvement, the effective current was kept at an extremely low value in the second batch of beamstops, yielding topographically-satisfactory beamstops. Profilometry was performed to measure the electroplating progress throughout the process. To remove the handling Si layer around the beamstops, KOH etching was performed after electroplating but before photoresist removal. We also found out that the etching duration has to be carefully calculated and monitored, and the etching has to be terminated as soon as the desired thickness of etching was reached. Too much over etching could even damage the SiO2 layer and beam stops.
In short, we have successfully made some beamstops mostly with diameters larger than 100 um. SEM and preliminary tests with X-ray transmission imaging showed that the shapes of all beamstops are cylindrical with straight side walls. However, most of the beamstops of diameters < 100 μm did not survive well the fabrication procedure and further improvement is needed in fabrication process.