Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session Y2: Electrostatic Levitation and High Energy X-rays |
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Sponsoring Units: DCMP Chair: Kenneth F. Kelton, Washington University Room: Baltimore Convention Center Ballroom III |
Friday, March 17, 2006 8:00AM - 8:36AM |
Y2.00001: Floating the Ball: Advances in the technology of electrostatic levitation Invited Speaker: Electrostatic Levitation (ESL) is an emerging technology. The MSFC ESL is a NASA facility that supports investigations of refractory solids and melts. The facility can be used to process a wide variety of materials including metals, alloys, ceramics, glasses and semiconductors. Containerless processing via ESL provides a high-purity environment for the study of high temperature materials and access to metastable states. Scientific topics investigated in the facility include nucleation, undercooling, metastable state formation and metallic glass formation. Additionally, the MSFC ESL provides data for the determination of phase diagrams, time-temperature-transition diagrams, viscosity, surface tension, density, heat capacity and creep resistance. In order to support a diverse research community, the MSFC ESL facility has developed a number of technical capabilities, including a portable system for in situ studies of structural transformations during processing at the high-energy X-ray beamline at the Advanced Photon Source of Argonne National Laboratory. The capabilities of the MSFC ESL facilities will be discussed and selected results of materials processing and characterization studies will be presented. [Preview Abstract] |
Friday, March 17, 2006 8:36AM - 9:12AM |
Y2.00002: New insights into the thermophysical properties of materials using electrostatic levitation Invited Speaker: Electrostatic Levitation (ESL) allows non-contact measurement of the thermophysical properties of materials in both the solid and liquid states, from over 3500°C to deep in the undercooled liquid, for a wide range of materials including metals, ceramics, and semiconductors. The combination of ESL with synchrotron x-ray structural measurements allows unprecedented insight into the relation between structure and properties in reactive and undercooled materials. Of the many different thermophysical and thermomechanical properties that have been measured using levitation techniques, four will be discussed. The density of the sample is calculated from the shape of the free surface in video images and the known mass. The surface tension and viscosity are determined from the natural frequency and damping, respectively, of free surface oscillations. Creep is measured by observing the changes in free surface shape due to centrifugal acceleration in a rapidly rotating drop. Combined with the x-ray structure measurements, these mechanical measurements can reveal the development of texture and strain-induced phase transformations. Any of these measurements may be performed on the same sample, in the same environment, at the same time as the x-ray structural measurements, allowing direct observation of the effect of changes in the structure of the sample on the thermophysical properties. [Preview Abstract] |
Friday, March 17, 2006 9:12AM - 9:48AM |
Y2.00003: A Deeper View of Materials: Coupling electrostatic levitation and high energy x-ray diffraction Invited Speaker: The ability to measure changes in the atomic scale structure, associated with novel thermophysical properties, will lead to tremendous advances in our understanding of the underlying physics of materials. This talk will focus on the integration of electrostatic levitation (ESL) techniques and high energy x-ray diffraction. The use of high energy x-rays (E $>$ 100 keV) offers several distinct advantages over conventional x-ray methods. First and foremost, high energy x-rays are required for full penetration of the levitated samples, which are typically 2-3 millimeters in diameter. This ensures that the bulk, rather than near-surface, structures are sampled in the measurement. A second important benefit of high energy x-rays lies in the fact that diffraction patterns can be collected over a relatively wide momentum transfer range for a small range of angles. The relatively small range of scattering angles required for most measurements allows the use of area detectors for fast data acquisition while the sample is either held at a constant temperature or during continuous heating/cooling cycles. The latter method is particularly suitable for continuous studies of phase transformations as the sample is heated from room temperature to the liquidus temperature and above, or cooled from high temperatures. This is, perhaps, best illustrated by recent work on the atomic scale structure of deeply undercooled liquid metals and semiconductors, such as silicon, where time resolved (100ms/frame) data have shown that, in contrast to previous structural measurements and several theoretical treatments, there is no evidence for a liquid-liquid phase transition in the undercooled regime. [Preview Abstract] |
Friday, March 17, 2006 9:48AM - 10:24AM |
Y2.00004: X-ray photoelectron spectroscopy in the hard x-ray regime Invited Speaker: Photoelectron spectroscopy is by now a very widely used tool for the study of atoms, molecules, solids, surfaces, and nanoscale structures. Until very recently, the exciting radiation has been limited to the energy range below about 2 keV. However, within the past few years, a few experimental projects have been initiated in which photon energies in the 5-15 keV range are employed. By matching the characteristics of undulator beamlines at third-generation synchrotron radiation sources to the optical properties of the electron spectrometer, it has proven possible to overcome the reduced photoelectric cross sections at such high energies and to study both core and valence electronic levels with resolutions down to ca. 50 meV [1]. Such hard x-ray photoelectron spectroscopy (HXPS or HAXPES) has the advantage of being more bulk sensitive, with electron inelastic attenuation lengths in the 50-150 Angstrom range. In this talk, I will discuss the advantages and disadvantages of this new direction, including highlights from recent work, as well as suggested future avenues for HXPS studies. [1] Nuclear Instruments and Methods A \underline {547}, 24 (2005), special issue dedicated to hard x-ray photoelectron spectroscopy, edited by J. Zegenhagen and C. Kunz. [Preview Abstract] |
Friday, March 17, 2006 10:24AM - 11:00AM |
Y2.00005: Hard x-ray photoelectron spectroscopy and x-ray standing waves Invited Speaker: Using the brilliant undulator radiation available from the third generation synchrotron sources, hard x-ray photoelectron spectroscopy (HAXPES) has become an emerging field in the recent years. With the excitation energy used in HAXPES one can benefits from the large mean free path of fast electrons ($\sim $ 5 nm for electrons of 6 keV kinetic energy) in probing the bulk electronic properties of materials. For high-resolution studies, photon energy bandwidth narrower than 100 meV is also readily achievable in the hard x-ray range with crystal monochromators. In addition, working with hard x-ray offers the possibility for combining photoelectron spectroscopy with x-ray standing wave (XSW) method. With the high spatial resolution from XSWs, this unique combination can provide site-specific, chemical and electronic information for studying surfaces, buried interfaces, thin films and bulk crystals. In this talk, I will briefly mention some HAXPES experiments detecting electrons up to 14.5 keV [1,2]. I will then sketch the principle of combining XSWs with HAXPES and present results from some recent applications using this combination: (1) chemical state-specific surface structure determination with core-level photoemission, (2) site-specific valence x-ray photoelectron spectroscopy and (3) XSW imaging with core-level photoemission. [1] S. Thiess, C. Kunz, B.C.C. Cowie, T.-L. Lee, M. Renier, and J. Zegenhagen. Solid State Communications 132, 589 (2004) [2] C. Kunz, S. Thiess, B.C.C. Cowie, T.-L. Lee, and J. Zegenhagen, Nuclear Instruments and Methods A 547, 73 (2005). [Preview Abstract] |
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