LSXS 2007 - Abstracts

LSXS 2007 — Abstracts

November 7
Liquid Surface Scattering Facilities at APS Ivan Kuzmenko, APS XOR/CMC-9ID, Argonne National Laboratory Worldwide, four light sources operate liquid surface scattering beamlines: APS (3), NSLS (2), ESRF (2), and DESY (1). The characteristics of LSS beamlines at APS (6-ID, 9-ID, 15-ID) and the science areas at each were briefly summarized.
Scientific Opportunities in the Field of Liquid Surface Scattering Mark Schlossman, University of Illinois at Chicago Liquid interfaces play an important role in many chemical and biological systems, in addition to being interesting model systems to study the statistical physics of interfaces and membranes. This talk offers a tour through many research areas that can--or acould--be addressed with liquid surface and interface scattering. Topics discussed include the relationship of interfacial tension to molecular ordering, ways of looking at interfacial fluctuations, the many uses of Langumuir monolayers to probe in-plane order (and some open questions), issues with correctly measuring inhomogeneous interfaces (e.g., in the presence of surfactants), moving beyond monolayers (to wetting transitions, coupled capillary waves, termination of bulk phases), studies of interfacial electrical properties, and interfacial ordering of biomembrane proteins at interfaces.
Liquid Surface Scattering Geometry and Reciprocal Space Mati Meron, CARS, The University of Chicago In choosing geometries for liquid surface scattering, it is important to understand some of the issues arising from the fact that, although the radiative momentum exchange q is a 3D vector, the components are not independent. In general, the incident (α) and scattered (β) angles relate to q_z, while φ (the angle between the y axis and the projection of the scattered radiation in the xy plane) is related to q_xy. In particular, in reflectivity measurements, when φ is kept fixed, the q_xy parameter must be considered carefully because varying α and β, especially at larger angles, generally varies both q_z and q_xy. Related problems occur if φ is zero; with care, these can be accommodated with data transformation.
X-ray Off-Specular Diffuse Scattering and Grazing Incidence X-ray Off-Specular Scattering Oleg Shpyrko, University of California, San Diego One specific way in which liquids are different from solids is that liquid surfaces are not static. Even in the absence of externally induced vibrations, liquid surfaces exhibit thermally excited capillary wave fluctuations. This lecture will review ways in which these nanoscopic surface fluctuation modes can be characterized with x-ray off-specular diffuse scattering. Analysis of capillary wave contributions is typically crucial to understanding the surface structure of liquids, since x-ray reflectivity effectively is a measure of a convolution of intrinsic surface density profile with capillary wave roughness. In addition to the theory of off-specular diffuse scattering and capillary wave contributions, the lecture will discuss practical details such as resolution effects and subtraction of bulk scattering contributions, as well as review highlights of recent experimental measurements.
Introduction to Experiment 1: Surface Scattering of a Monolayer of Gold Nanospheres on the Surface of Water Binhua Lin, CARS, The University of Chicago We will measure the ordering and morphology of gold nanospheres (7 nm in diameter) floating on the surface of water using x-ray reflectivity and grazing incident x-ray diffraction. We obtain information on the morphology of the film of the spheres normal to the surface using x-ray reflectivity, and the packing pattern of the spheres along the surface using grazing incident x-ray diffraction.
Introduction to Experiment 2: Comparative Study of Phospholipids at Air-Liquid Interface Ivan Kuzmenko, APS XOR/CMC-9ID, Argonne National Laboratory
November 8
Grazing Incidence X-ray Diffraction Ka Yee Lee, The University of Chicago
X-ray Reflectivity Pulak Dutta, Department of Physics, Northwestern University In the previous day's lectures, attendees will already have seen some results obtained using X-ray reflectivity. This lecture will go into more detail about the technique, the necessary data analysis, and the special requirements of liquid surfaces and interfaces. We will discuss what can be done with this technique using a variety of examples. Finally, we will speculate about what might be done in future.
Data Collection Strategies and Detectors Oleg Shpyrko, University of California, San Diego This lecture will focus on practical aspects of typical experimental measurements performed at liquid surface x-ray scattering facilities. Among the major challenges is detection of scattering signal with intensity variations by as much as 10 orders of magnitude over a single measurement, sensitivity of the liquid surfaces to vibration or radiation damage, as well as finite curvature and beam footprint effects. The lecture will review efficient strategies involved in collection of x-ray reflectivity, grazing incidence and off-specular diffuse scattering data as well as experimental artifacts, controls, and background subtraction. Additionally, I will briefly review pros and cons of various x-ray detector solutions, from scintillators, solid state detectors, pin diodes, and ion chambers to position-sensitive detectors such as linear wire detectors and area detectors such as charge coupled devices (CCD), image plates, and multiwire detectors.
Data Analysis and Interpretation Steve Danauskas, The University of Chicago X-ray reflectivity measurements of films at the air/water interface provide a means to greatly enhance our understanding of structure and molecular interactions. However, because of the loss of phase information, it is not possible to obtain the electron density profile of a film directly from the collected data. I will discuss procedures of modeling x-ray reflectivity data using both "box model" non-linear least squares refinement and model-independent methodologies. Model independent fitting provides a robust technique for fitting reflectivity data that removes experimenter bias from the process. Additionally, model-independent methods can also generate electron density profiles that are inaccessible from the model-dependent electron density profile calculations and more closely model the physical system.

November 7

Liquid Surface Scattering Facilities at APS
Ivan Kuzmenko, APS XOR/CMC-9ID, Argonne National Laboratory

Worldwide, four light sources operate liquid surface scattering beamlines: APS (3), NSLS (2), ESRF (2), and DESY (1). The characteristics of LSS beamlines at APS (6-ID, 9-ID, 15-ID) and the science areas at each were briefly summarized.

Scientific Opportunities in the Field of Liquid Surface Scattering
Mark Schlossman, University of Illinois at Chicago

Liquid interfaces play an important role in many chemical and biological systems, in addition to being interesting model systems to study the statistical physics of interfaces and membranes. This talk offers a tour through many research areas that can--or acould--be addressed with liquid surface and interface scattering. Topics discussed include the relationship of interfacial tension to molecular ordering, ways of looking at interfacial fluctuations, the many uses of Langumuir monolayers to probe in-plane order (and some open questions), issues with correctly measuring inhomogeneous interfaces (e.g., in the presence of surfactants), moving beyond monolayers (to wetting transitions, coupled capillary waves, termination of bulk phases), studies of interfacial electrical properties, and interfacial ordering of biomembrane proteins at interfaces.

Liquid Surface Scattering Geometry and Reciprocal Space
Mati Meron, CARS, The University of Chicago

In choosing geometries for liquid surface scattering, it is important to understand some of the issues arising from the fact that, although the radiative momentum exchange q is a 3D vector, the components are not independent. In general, the incident (α) and scattered (β) angles relate to q_z, while φ (the angle between the y axis and the projection of the scattered radiation in the xy plane) is related to q_xy. In particular, in reflectivity measurements, when φ is kept fixed, the q_xy parameter must be considered carefully because varying α and β, especially at larger angles, generally varies both q_z and q_xy. Related problems occur if φ is zero; with care, these can be accommodated with data transformation.

X-ray Off-Specular Diffuse Scattering and Grazing Incidence X-ray Off-Specular Scattering
Oleg Shpyrko, University of California, San Diego

One specific way in which liquids are different from solids is that liquid surfaces are not static. Even in the absence of externally induced vibrations, liquid surfaces exhibit thermally excited capillary wave fluctuations. This lecture will review ways in which these nanoscopic surface fluctuation modes can be characterized with x-ray off-specular diffuse scattering. Analysis of capillary wave contributions is typically crucial to understanding the surface structure of liquids, since x-ray reflectivity effectively is a measure of a convolution of intrinsic surface density profile with capillary wave roughness.

In addition to the theory of off-specular diffuse scattering and capillary wave contributions, the lecture will discuss practical details such as resolution effects and subtraction of bulk scattering contributions, as well as review highlights of recent experimental measurements.

Introduction to Experiment 1: Surface Scattering of a Monolayer of Gold Nanospheres on the Surface of Water
Binhua Lin, CARS, The University of Chicago

We will measure the ordering and morphology of gold nanospheres (7 nm in diameter) floating on the surface of water using x-ray reflectivity and grazing incident x-ray diffraction. We obtain information on the morphology of the film of the spheres normal to the surface using x-ray reflectivity, and the packing pattern of the spheres along the surface using grazing incident x-ray diffraction.

Introduction to Experiment 2: Comparative Study of Phospholipids at Air-Liquid Interface
Ivan Kuzmenko, APS XOR/CMC-9ID, Argonne National Laboratory

November 8

Grazing Incidence X-ray Diffraction
Ka Yee Lee, The University of Chicago

X-ray Reflectivity
Pulak Dutta, Department of Physics, Northwestern University

In the previous day's lectures, attendees will already have seen some results obtained using X-ray reflectivity. This lecture will go into more detail about the technique, the necessary data analysis, and the special requirements of liquid surfaces and interfaces. We will discuss what can be done with this technique using a variety of examples. Finally, we will speculate about what might be done in future.

Data Collection Strategies and Detectors
Oleg Shpyrko, University of California, San Diego

This lecture will focus on practical aspects of typical experimental measurements performed at liquid surface x-ray scattering facilities. Among the major challenges is detection of scattering signal with intensity variations by as much as 10 orders of magnitude over a single measurement, sensitivity of the liquid surfaces to vibration or radiation damage, as well as finite curvature and beam footprint effects. The lecture will review efficient strategies involved in collection of x-ray reflectivity, grazing incidence and off-specular diffuse scattering data as well as experimental artifacts, controls, and background subtraction. Additionally, I will briefly review pros and cons of various x-ray detector solutions, from scintillators, solid state detectors, pin diodes, and ion chambers to position-sensitive detectors such as linear wire detectors and area detectors such as charge coupled devices (CCD), image plates, and multiwire detectors.

Data Analysis and Interpretation
Steve Danauskas, The University of Chicago

X-ray reflectivity measurements of films at the air/water interface provide a means to greatly enhance our understanding of structure and molecular interactions. However, because of the loss of phase information, it is not possible to obtain the electron density profile of a film directly from the collected data. I will discuss procedures of modeling x-ray reflectivity data using both "box model" non-linear least squares refinement and model-independent methodologies. Model independent fitting provides a robust technique for fitting reflectivity data that removes experimenter bias from the process. Additionally, model-independent methods can also generate electron density profiles that are inaccessible from the model-dependent electron density profile calculations and more closely model the physical system.

2007 School on Liquid Surface X-ray Scattering: Theory and Experimental Methods

November 7-9, 2007
Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, USA