XDL2011 Workshop 1 Abstracts

Diffraction Microscopy, Holography and Ptychography using Coherent Beams
Monday, June 6th - Tuesday, June 7th, 2011

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Organizers: Janos Kirz (Lawrence Berkeley National Lab), Qun Shen (National Synchrotron Light Source II), & Darren Dale (Cornell University)

Workshop Agenda (html)

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Energy Recovery Linac (ERL) and Ultimate Storage Ring (USR) Properties

Don Bilderback
Cornell University

ERLs and USRs are under consideration for next generation, high-duty cycle (>MHz rep rates), coherent x-rays sources. They both feature extremely high average spectral brightness, diffraction-limited performance and are the response to 3rd generation storage ring users/developers who would like "more x-ray flux, smaller x-ray beam size, more coherent x-ray flux on sample, higher energy resolution probes and/or short pulses for repetitive probing". In most cases, the x-ray beam should minimally impact the sample under study. We review the general features of ERLs and USRs in the context of the Cornell ERL and PEP-X as two well-developed examples from the x-ray community. Additionally, examples of utilization of the advanced properties of these machines will be given. The first example explores using the timing structure to repetitively probe the response of x-ray excited optical luminescence. The second uses the extremely high average brightness to conceptually develop ideas toward a confocal x-ray microscope that is designed to image single atoms based on either Thompson scattering or x-ray fluorescence.

X-ray Detectors: State-of-the-art & Future Possibilities

Sol Gruner
Cornell University

The state-of-the-art of quantitative imaging x-ray detectors is described. We then consider upcoming technologies that may be applied to imaging detectors to advance the state-of-the-art with respect to pixel size and functionality, spatial resolution, time resolution, analog dynamic range, and energy resolution. Specifically, we look into our crystal ball and ask what is likely feasible on a decade time scale, given adequate R&D, given current physical limits of materials and technology.

New Opportunities with Hard X-ray Diffraction Limited Sources

Qun Shen
National Synchrotron Light Source II

Recent advances in advanced synchrotron sources have opened up the possibilities of conducting research using coherent hard x-rays. In particular, energy recovery linac (ERL) sources, ultimate storage rings (USR), and free electron lasers (FEL) can deliver hard x-ray beams essentially at the diffraction limit, offering new opportunities to perform coherent diffraction and imaging experiments in ways that may be very different from the present state of the art. In this presentation, I will discuss the potential applications using coherent diffraction microscopy, ptychography, and nanocrystallography, all based on coherent x-rays. Recent technical developments in coherent beam definition and specimen handling will also be discussed.

Coherent Imaging Without a Laser: getting the most bang for your electrons

Garth Williams
Linac Coherent Light Source

Coherent imaging enjoys continued interest at third- and fourth-generation light sources as an alternate microscopy, whose reliance on a focusing optic is replaced by the increased capabilities of a detector and the numerical recovery of an image of the sample from far-field scattering data. Since its demonstration a dozen years ago, the method has been successfully applied to a wide range of samples, which are typically imaged with a few to tens of nanometers resolution. In the method's most tractable--and original--form, the experimental geometry demands a monochromatic and planar--and thus fully coherent--illumination that has extent larger than the transverse dimensions of the sample.

Recently, several groups have extended the range of applicability of the method, first by removing the requirement of an isolated sample and extended illumination and more recently by incorporating the explicit knowledge of the longitudinal and transverse coherence properties of the illumination. These modifications and their limitations will be discussed, as will the important advantages in the execution of the experiment that may be gained by removing the requirement of a fully coherent x-ray beam.

X-Ray Coherent Diffractive Imaging with an Extended Reference

James Fienup
University of Rochester

X-ray holography using a point-source reference has been a successful way of reconstructing images from x-ray diffraction data with a closed-form solution, but its achievable resolution suffers from difficulties in producing a sufficiently small and strong point in the vicinity of the object, owing to the difficulty in manufacturing high aspect ratio x-ray pinholes. Podorov, Pavlov and Paganin showed the ability to reconstruct an image in closed form when the object was imbedded in a rectangular aperture. Guizar-Sicairos and Fienup developed the theory and algorithms that greatly generalized the types of reference structures that can be placed near the object, allowing for manufacturable structures that result in finer resolution images, and demonstrated it experimentally in collaboration with researchers at SSRL and CEA-Saclay. This presentation will review the technique, discuss requirements, and open a discussion for future directions.

Imaging With Coherent Beams: let's not do it in a vacuum

Chris Jacobsen
Northwestern University

Coherent beam imaging methods offer the potential for spatial resolution extension beyond what is provided by today's optics. However, is spatial resolution the main advantage of x-rays? Or should we be thinking along the lines of high energy physics, where the "specimen" (the interaction region) is surrounded by detectors to form as complete a picture as possible from the information the particle beam provides? In this sort of a view, one might wish to combine pixel array measurements of the forward-scattered beam for coherent imaging, measurements of crystallinity, and resolution extension; and energy-dispersive measurements for detecting fluorescent x-rays from trace elements. One might even consider collection of x-ray induced luminescence, and optical spectroscopy to monitor changes in the specimen. Finally, this information must be integrated and analyzed with more sophistication than simple examination of the data. In other words, coherent imaging should not be done in isolation.

Cryopreservation of Structural Integrity under High Pressure

Chae Un Kim
Cornell University

It has been recently shown that cryocooling under high pressure is useful for cryopreservation of macromolecular crystals for X-ray diffraction [1]. The method, high pressure cryocooling, involves cooling samples to cryogenic temperatures (~ 77 K) in high pressure Helium gas (up to 200 MPa). Several different kinds of macromolecular crystals have been successfully high-pressure cryocooled and excellent crystal diffraction has been obtained with little or no penetrating chemical cryoprotectants. A mechanism involving high-density amorphous (HDA) ice was proposed as to why the method works [2,3]. This method has great potential for cryopreservation of biological samples for X-ray diffraction microscopy (XDM). The presentation will detail the technical aspects of high pressure cryocooling for XDM. At the end, some challenging X-ray studies on the ice phases of water will be proposed to improve diffraction data quality in XDM, which may require an Energy Recovery Linac or Ultimate Storage Ring X-ray sources.

References:

1. Kim et al., Acta Cryst. D61 881-890 (2005)
2. Kim et al., J. Appl. Cryst., 41 1-7 (2008)
3. Kim et al., Proc. Natl. Acad. Sci., USA 106 4596-4600 (2009)

High-resolution Imaging of Biological Specimens

David Shapiro
National Synchrotron Light Source II

The Stony Brook University - Advanced Light Source (ALS) collaboration has produced the highest resolution x-ray images of yeast on record. 13 nm resolution has been demonstrated with dry cells but progress has been slow towards the ultimate goal of three dimensional imaging of frozen hydrated specimens, primarily because of the challenges involved with producing and maintaining a high quality cryogenic sample. This talk will provide a brief review of the ALS project followed by a discussion of novel soft x-ray beam-shaping techniques which will provide a more optimized illumination for biological specimens. A spatial filter with a gaussian transmission profile has been developed which can transmit a single coherent mode of radiation without edge diffraction. This filter produces a small, clean beam of soft x-rays without any parasitic diffraction. Furthermore, because of refraction, slight focusing of the x-ray beam occurs. Limitations on the filter's size make it best suited for storage rings with very low emittance and beamlines with a modest demagnification of the source. At the Coherent Soft X-ray beamline of the NSLS-II, it will deliver >1012 coherent photons/second in a 2-5 micron spot. This photon flux can be expected to provide 10 nm resolution data in ~20 ms. This illumination is therefore well suited for surveying densely packed biological specimens or for soft x-ray ptychography experiments.

Three-Dimensional Coherent Diffraction Imaging of Materials and Cells

Jianwei (John) Miao,
University of California, Los Angeles

Coherent diffraction imaging is a form of lensless microscopy, in which the diffraction pattern of a non-crystalline specimen or nanocrystal is measured and then directly phased to obtain an image. The well-known phase problem is solved by combining the oversampling method with iterative algorithms. In this talk, I will mainly present some of our recent results on 3D coherent diffraction imaging of materials and cells^1,2. I will also point out a new, but potentially important direction for 3D structural determination. Recently, 3 papers published in different fields, indicate the feasibility of 3D structural determination from a portion of reciprocal space data, including ankylography (3D structure from a single view)^3,4, super-resolution protein crystallography (obtaining highresolution structure from low-resolution data by Schroder et al.)⁵ and discrete tomography (3D structural determination from two projections by Van Aert et al.)⁶. I will make a brief connection among the 3 methods and then present some of our recent experimental results on ankylography by using an optical laser.

References:

1. H. Jiang, D. Ramunno-Johnson, C. Song, B. Amirbekian, Y. Kohmura, Y. Nishino, Y. Takahashi, T. Ishikawa, and J. Miao; "Nanoscale Imaging of Mineral Crystals inside Biological Composite Materials Using X-ray Diffraction Microscopy," Phys. Rev. Lett. 100, 038103 (2008)
2. H. Jiang, C. Song, C.-C. Chen, R. Xu, R., K.S. Raines, B.P. Fahimian, C. Lu,. T.-H. Lee, A. Nakashima, J. Urano, T. Ishikawa, F. Tamanoi, and J. Miao; "Quantitative 3D Imaging of Whole, Unstained Cells by Using X-ray Diffraction Microscopy," Proc. Natl. Acad. Sci. USA 107, 11234-11239 (2010)
3. K.S. Raines, S. Salha, R.L. Sandberg, H. Jiang, J.A. Rodríguez, B.P. Fahimian, H.C. Kapteyn, J. Du and J. Miao, "Three-dimensional Structure Determination from a Single View," Nature 463, 214-217 (2010)
4. For those who are interested in ankylography, the basic ankylographic reconstruction codes have been posted on a public website (www.physics.ucla.edu/research/imaging/Ankylography), and can be freely downloaded and tested.
5. G.F. Schroder, M. Levitt, A.T. Brunger; "Super-resolution Biomolecular Crystallography with Low-resolution Data," Nature 464, 1218-1222 (2010)
6. S. Van Aert, K.J. Batenburg, M.D. Rossell, R. Erni, and G. Van Tendeloo; "Three Dimensional Atomic Imaging of Crystalline Nanoparticles," Nature 470, 374-377 (2011)

Ptychography in 2D and 3D

Pierre Thibault
Technische Universität München

I will first give a quick overview of the latest results in X-ray ptychography. My goal is to discuss the potential of the ERL in view of the current experimental bottlenecks in the application of hard X-ray ptychography. A clear classification of these bottlenecks is not as simple as it may seem, for apparent experimental problems can have unexpected algorithmic solutions, and conversely, seemingly innocuous setup limitations may lead to unrecoverable information loss. I will give examples of both cases. Thus the progress of data analysis techniques can strongly impact on the design of the future experiments, leading to my conclusion that efforts on the development of reconstruction frameworks must be made in parallel to the design of the source and the beamlines.

Spectromicroscopy, Resonant Scattering, Possible Extensions to Ptychographic Imaging

Harald Ade
North Carolina State University

Organic electronic devices have complex morphologies that are not fully understood and difficult to characterize. I will discuss the contributions to the advancement of these devices that sophisticated x-ray microscopy methods might be able to make as well as conditions that must be met in order to make such methods really useful as a tool to address engineering issues and processing optimization. These conditions include rapid data acquisition and analysis and artifact free, quantitative compositional and orientational mapping in 3D (revealing just structures, is not good enough). Quantitative imaging will most likely have to make use of carbon K-edge resonant effects. I will propose a set of test experiments that can more clearly show the utility of coherent diffraction imaging to polymeric systems in general and organic devices in particular.

Magnetic Domains and Dynamics

Oleg Shpyrko
University of California, San Diego

Coherent, tunable sources of x-ray radiation provide unique opportunities for studies of nanoscale domain structure and dynamics in self-organized electronic systems characterized by domain "texture", complex disorder and phase separation. Studies of these materials require coupling to charge, spin, orbital or lattice order parameters with spatial resolution of order of nanometers. Resonant x-ray scattering allows direct access to many of these order parameters, making x-rays arguably ideal probe for many of these electronic and magnetic nanoscale domains.

I will review our on-going efforts to study the nanoscale local structure and dynamics of electronic inhomogeneites and magnetic domains, and will discuss future directions that will become possibly at the next generation of synchrotron sources.

Resonant Coherent X-ray Imaging

Ian McNulty
Advanced Photon Source

Coherent x-ray imaging is poised to contribute immensely to our understanding of materials at the nanoscale. The selectivity of core electron resonances in the x-ray region provide unique and sensitive access to elemental makeup, chemical states, and ordering on length scales extending to atomic dimensions. When combined with polarized x-rays, resonant coherent imaging can be used to probe domain structure and its evolution in material systems ranging from magnetic films to the complex oxides. This talk discusses prospects for hard x-ray experiments using the next generation of coherent x-ray sources, supported by recent work including resonant coherent diffractive imaging of field-dependent ferromagnetic structure in GdFe multilayers and orbital ordering in LaMnO3.