Development of a Scanning Transmission X-ray Microscope Dedicated to Synthetic and Natural Polymer Research |
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Dept. of Physics, North Carolina State University, Raleigh, NC 27695 E. Rightor, G. Mitchell, Dow Chemical, A. Hitchcock, McMaster, C. Zimba, NIST, A. Warwick, ALS M. Rafailovich, and J. Sokolov, SUNY@Stony Brook, G. Cody, Geophysical Laboratory |
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In many applications, the physio-mechanical properties of polymer systems
can be tailored by altering the chemical and morphological structure. In
most cases, the polymer system of interest is not a homogeneous or single-component
system, but is a blend, composite, or copolymer. Sophisticated analytical
methods are required for their characterization. Amongst them is the novel
technique of Near Edge X-ray Absorption Fine Structure (NEXAFS) microscopy.
It has an advantage of about three orders of magnitude over the equivalent
electron microscopy technique in being able to spectroscopically analyze
and image small sample areas of radiation sensitive materials such as polymers.
In addition, x-ray linear dichroism microscopy can determine orientation
of chemical moieties at high spatial resolution. These inherent advantages
of x-ray microscopy have opened up new avenues for the characterization
of polymers. Limited access at existing Scanning Transmission X-ray Microscopes
(STXMs) makes it, however, difficult to have systematic polymer science
programs. Our studies of polymer blends, dynamics in constrained films,
interface reactions and diffusions, organic geochemistry, as well as other
polymer problems are severely limited and are primarily feasibility studies.
We propose to build a STXM dedicated to polymer applications (The Polymer
STXM) at the Advanced Light Source (ALS) to carry out our science programs.
This facility would be the sole endstation at an optimized bending magnet
beamline and would increase instrument time for polymer applications by
an additional 4500 hrs/year of operation. We will provide at least 25%
of instrument time to qualified independent investigators through a peer
reviewed competition administrated by the ALS. The ALS has agreed to spend
considerable resources ($450k) to provide the synchrotron beamline/monochromator.
This proposal will seek funds for the microscope itself. We will not clone
any existing STXM, but combine the best subsystems of each in a unique
way in order to improve overall performance. We will, for example, scan
for the first time the zone plate rather than the sample, which will greatly
improve flexibility regarding samples (heating, colling, strain). We will
also add more efficient detectors, interferometric position encoding, an
indexing sample stage, and on-line Principle Component Analysis as new
features.
Existing STXMs at the ALS and the National Synchrotron Light Source (NSLS) are operated on undulator sources. These sources have superior brightness and should result in superior data acquisition rates. However, for polymer applications, an optimized STXM coupled to a bending magnet at the ALS will have data acquisition rates (@ ?E=150 meV, 40 nm spatial resolution) that are at least as high as typical rates during the last few years at the NSLS and ALS. All slits and the optics can be overfilled substantially at a bending magnet and the alignment remains untouched. Together with the single purpose STXM that we propose, this will greatly improve the reliability, stability, signal-to-noise characteristics and productivity per user-hour. Our “revolutionary” approach of coupling to a bending magnet will significantly lower the necessary investment from about $4,000,000 for the undulator and its beamline to about $450,000 for a front end and the beamline at a bending magnet. Since there are still plenty of unused bending magnet sources, the potential for developing or constructing many STXM improves dramatically. Our instrument could also be coupled to bending magnets at an upgraded NSLS or SSRL. The equipment development and construction program is for three years and the initial scientific goals are strongly linked to currently funded and planned research of the PI’s and their collaborators. For first results: see "Polymer STXM First Results" |