XDL2011 Workshop 6 Abstracts

Frontier Science with X-ray Correlation Spectroscopies using Continuous Sources
Wednesday, June 29th - Thursday, June 30th, 2011

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Organizers: Mark Sutton (McGill University), Simon Mochrie (Yale), & Arthur Woll (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.

X-ray Cross Correlation Analysis (XCCA) and Bond-order in Liquid and Glasses

Christian Gutt
Deutsches Elektronen-Synchrotron

The characterization of structural properties of disordered matter beyond the standard pair correlation function is a key point in advancing the understanding of the liquid and glassy state of matter. Bond-order and local symmetries are examples of higher-order correlation functions which can be traced in disordered materials by using cross correlation techniques. In this talk I will briefly mention the status quo of XCCA experiments at synchrotron and XFEL sources. I will discuss future applications of XCCA at ERL sources.

Nanoscal Dynamics, Atomic Diffusion

Bogdan Sepiol
University of Vienna

It is widely accepted that determining temperature-driven motion of single atoms in solids is more complex than figuring out the structure of a solid state of matter. Nevertheless, it seems evident that dynamical properties and especially atomic motion can play a crucial role in nanostructures operation. Gaining knowledge how individual atoms move and measuring their hopping rate is hence the aim of many experiments and theoretical studies. One shall also take into account that ab initio methods which are so booming in the structural studies are still uncertain in dynamical properties predictions. The only confident way in this situation is a comparison with a dedicated experiment.

Tracer methods have been applied to study diffusion in various crystalline¹ and amorphous systems², being, however, limited to their purely macroscopic nature. The highly desirable feat of probing the dynamics with spatial and temporal resolution turns out to be extremely challenging due to many serious limitations such as restricted number of suitable isotopes or low resolution in energy imposing very high temperatures of measurements. These exclude studying systems like metallic glasses which are unstable above a certain temperature.

Availability of coherent X-rays enabled in the last decade photon correlation spectroscopy studies of diffusion. The potential of XPCS for studying dynamics with atomic resolution has been demonstrated for the first time with the intermetallic alloy Cu₉₀Au₁₀ ³. This and few other systems could be still studied with the contemporary synchrotrons. Great success can be, however, guaranteed only by more powerful sources of coherent radiation like ERL/USRs. These new synchrotron sources will not only extend the number of systems accessible to diffusion studies to practically all compositions including even light-element alloys, but will also extend the upper limit of hopping rates. Moreover, having enough coherent intensity available, one could study some hidden information about the jump processes leaving a linear regime of scattering theory⁴. This work was supported by the Austrian FWF grant P22402.

This work was supported by the Austrian FWF grant P22402

References:

1. H. Mehrer; "Diffusion in Solids: Fundamentals, Methods, Materials, Diffusion-Controlled Processes" (Springer, Berlin /Heidelberg 2007)
2. F. Faupel et al., Rev. Mod. Phys. 73, 237 (2003)
3. M. Leitner et al., Nature Mat. 8, 717 (2009)
4. M. Leitner and G. Vogl, Journal of Physics: Condensed Matter, in press

Hierarchical Dynamics of Soft Matter and Opportunities at Japanese Future Light Sources

Yuya Shinohara
University of Tokyo

Soft matter shows hierarchical structure across multiple spatiotemporal scales; thus, its dynamics has been investigated by using several techniques such as XPCS, quasi-elastic neutron scattering, and NMR etc. At present, however, there is a spatiotemporal scale that is not available with the present techniques and light sources. In this talk, I will mention these topics and prospects using future light sources. Furthermore, I will briefly introduce ongoing projects of future light sources in Japan.

Prospects for X-ray Photon Correlation Spectroscopy from Liquid and Soft Matter Surfaces and Interfaces

Laurence Lurio
Northern Illinois University

XPCS measurements of liquid and soft matter surfaces and interfaces as performed at existing third generation synchrotron sources are severely flux limited. As a consequence, almost all successful measurements have been made on glassy systems possessing extremely slow dynamics. While fourth generation sources offer much higher instantaneous fluxes, along with the ability to measure picosecond dynamics, they are not optimized for measurements in the microsecond to millisecond regime. This range of time scales is needed for measuring dynamics of materials in water, of especial importance in biology. A range of experiments which could benefit from a bright, highly coherent source that allows XPCS with microsecond resolution at nanoscale wavelengths will be discussed. The technical feasibility of such experiments will also be appraised.

Nanobiology: Membranes and Proteins in Motion

Maikel C. Rheinstädter
McMaster University

One of the major challenges of x-ray and neutron scattering is to contribute to biology and life-sciences. Modern facilities and scattering instrumentation are premier research tools to tackle this important challenge as they give access to molecular structure, dynamics and interactions in biological materials. There is a certain range of length and time scales where x-ray and neutron scattering have proven to work very successfully. One of the challenges is to push these limits to create an overlap with other techniques to maximize the accessible length and time scales. The interesting science is often linked to: small samples, weak scattering signals, high background, high energy resolution in combination with small angles to study slow dynamics of mesoscopic objects, Brillouin scattering at small angles and high energies with high energy resolution to study for instance hydration water dynamics, instruments with large detectors to study interactions between proteins for instance at energies of less than 1 meV with microeV resolution over a wide q-range.

I will present exciting recent results and potential applications to demonstrate capabilities of present and future scattering instrumentation.

XPCS on Surfaces: Challenges and Opportunities

Michael Pierce
Materials Science Division,
Argonne National Laboratory

X-ray Photon Correlation Spectroscopy(XPCS), the extension of dynamic light scattering from optical to x-ray regimes, has provided marvelous tool for examining nature on the nano-scale. XPCS stands to benefit a great deal in the future from continuous ERL sources, as well as advances in detector technology. XPCS has been successfully used in the past to study surface dynamics, and recently extended to structures such as surface reconstructions and atomic terraces. However, the extreme requirements of both high coherence and surface diffraction seriously constrain current study to high Z surfaces with relatively slow dynamics on the scale of 1 - 10^4 seconds. We will discuss some of the current experiments near and at this boundary. Some of the experiments have proven successful, while others are elusive with current light sources. Once this border is relaxed, study will shift to surfaces from a much wider range of materials that can exhibit faster timescale dynamics. In particular, areas of surface science that can exploit in-situ application XPCS to real environments, such as materials synthesis, catalysis, and phase transitions, will benefit from ERL sources.

Probing Magnetic Complexity with Coherent Soft X-ray Beams

Stephen Kevan
University of Oregon

Thermally-driven intermittency limits the utility of a nanoscale device to store, process, or transmit information, to sense the environment, to harvest and convert energy, and a host of other applications. Probing and understanding intermittency over a broad enough range of time and length scale will help us learn to control a diverse array of emergent material properties. High brightness x-ray facilities enable new classes of XPCS experiments that will bridge the dynamic and kinetic temporal regimes while maintaining nanoscale spatial sensitivity. I will show a few examples that illustrate how coherent soft x-ray beams can be used to probe thermal- and field-driven processes in complex magnetic systems and that also demonstrate what will be possible with significantly higher coherent flux at planned beam lines and facilities in the US.

Martensitic Transitions & Opportunities in Non-equilibrium Physics

Karl Ludwig
Boston University

TXPCS has been used primarily to examine the dynamics of fluctuations in equilibrium states. However the technique also offers the possibility of gaining unique insights into dynamics in non-equilibrium systems. Recently we have used XPCS to examine the heterogeneous dynamics during the isothermal transformation of the high-temperature fcc phase to the low-temperature hcp phase in cobalt. The process can conceptually be viewed as an initial period of rapid local transformation followed by a slower period during which stacking changes lead to strain relaxation. Coherent x-ray scattering measurements show that, during the latter part of the transformation, the kinetics is dominated by discontinuous sudden changes - avalanches. The spatial size of observed avalanches varies widely, from 100 nm to the upper detection limit of 10 μm, which was the size of the x-ray beam. An empirical avalanche amplitude is defined to quantify the avalanche behavior; it exhibits a power-law size distribution. The avalanche rate decreases with inverse time since onset of the transformation.

In considering future applications of XPCS to the investigation of non-equilibrium systems, a key concern is how experimental data can be analyzed and understood in the most general case, since linear response theory may no longer be a guide. One set of cases in which linear response theory may still be useful, however, is those non-equilibrium situations in which the system reaches a driven steady state. Possible examples of such situations include surface morphology evolution driven by ion bombardment or thin film growth. Coherent scattering would give information on surface dynamical that is not accessible from traditional incoherent experiments.