Ludwig, Karl - Boston University - Department of Materials Science & Engineering

研究领域

Real-Time X-ray Studies of Materials Processes Our research investigates how materials evolve on atomic and nano- length scales as they change from one form to another. In particular, we use real-time x-ray techniques to examine structural evolution during phase transitions, thin film growth and surface processing. Many of the experiments use the high brightness of synchrotron x-ray sources – the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory on Long Island, the Advanced Photon Source (APS) at Argonne National Laboratory outside of Chicago, and the Linac Coherent Light Source (LCLS) at SLAC. We are actively involved in new beamlines planned for the NSLS-II project now under construction at Brookhaven and Ludwig is Spokesperson for the Integrated In-Situ and Resonant (ISR) beamline project there. Where possible, our research makes contact with fundamental theory and simulation. In the last few years, our detailed interest has been in three directions – understanding surface and thin film processes, investigating nanoscale dynamics in metallic alloys using coherent x-ray scattering and studying the relationship between atomic structure and function in solid oxide fuel cell cathodes. Many of our in-situ studies utilize a unique ultra-high vacuum growth and surface modification facility that we have helped develop on the insertion-device beamline X21 at the NSLS. We have been using it to examine surface morphology evolution during ion bombardment (which can cause the spontaneous growth of surface nanostructures) and issues related to the growth of wide-bandgap group III-V semiconductor films using plasma-assisted molecular beam epitaxy (in collaboration with Prof. Moustakas in Electrical Engineering). Coherent x-ray scattering provides the ability to probe nanoscale dynamics in metallic alloys and other materials systems. Partially coherent x-ray beams are created using small (10 micron) slits in conjunction with a high-brilliance 3rd generation synchrotron source, such as the APS. The disorder in the alloys produces speckle patterns in the scattered x-ray intensity. The evolution of the speckle pattern can then be related to the underlying dynamics of structural changes (e.g. ordering, phase separation or stacking fault rearrangement) in the alloy. The LCLS is the world’s first hard x-ray laser and offers unique new opportunies for coherent scattering on femtosecond time scales that we are now exploring. Solid oxide fuel cells offer the potential for highly efficient energy conversion, but improvements in cathode function are needed before their potential can be fully realized. In collaboration with Profs. Pal, Basu and Gopalan in Engineering and Prof. Smith in Physics, we are examining in-situ the near-surface atomic structure of cathode materials in order to better understand the relationship between function and structure.

近期论文

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“X-ray Photon Correlation Spectroscopy in Systems without Long-Range Order: Existence of an Intermediate-Field Regime”, K. Ludwig, J. Synchrotron Rad. 19, 66 (2012). “Hard X-ray Fluorescence Measurements of Heteroepitaxial Solid Oxide Fuel Cell Cathode Materials”, J.N. Davis, L.J.Miara, L. Saraf, T.C. Kaspar, S. Gopalan, U.B. Pal, J.C. Woicik, S.N. Basu and K.F. Ludwig, ECS Transactions, in press. “Tuning the Pore Size of Ink-Bottle Mesopores by Atomic Layer Deposition”, J. Dendooven, B. Goris, K. Devloo-Casier, Kilian, E. Levrau, Elisabeth, E. Biermans, Ellen, M. Baklanov, K. Ludwig, P. Van Der Voort, S. Bals and C. Detavernier, submitted to Chemistry of Materials. “Time-Resolved Measurements of Nanoscale Surface Pattern Formation Kinetics in Two Dimensions on Ion Irradiated Si”, E. Anzenberg, C.S. Madi, M.J. Aziz and K.F. Ludwig, Jr., Physical Review B, in press. “In Situ Synchrotron Based X-ray Fluorescence and Scattering Measurements During Atomic Layer Deposition: Initial Growth of HfO2 on Si and Ge Substrates”, K. Devloo-Casier, J. Dendooven, K.F. Ludwig, G. Lekens, J. D’Haen and C. Detavernier, Appl. Phys. Lett. 98, 231905 (2011). “Direct Measurement of Microstructural Avalanches During the Martensitic Transition of Cobalt Using Coherent X-ray Scattering”, Christopher Sanborn, Karl F. Ludwig, Michael C. Rogers and Mark Sutton, Phys. Rev. Lett. 107, 015702 (2011). “Tailoring Nanoporous Materials by Atomic Layer Deposition”, C. Detavernier, J. Dendooven, S. Pulinthanathu Sree, K.F. Ludwig and J. Martens, Chem. Soc. Rev. 40, 5242 (2011) . “In Situ X-Ray Fluorescence Measurements During Atomic Layer Deposition: Nucleation and Growth of TiO2 on Planar Substrates and in Nanoporous Films”, J. Dendooven, S. Pulinthanathu Sree, K. De Keyser, D. Deduytsche, J. Martens, K. Ludwig and C. Detavernier, J. Phys. Chem. C 115, 6605 (2011). “Mass Redistribution Causes the Structural Richness of Ion-Irradiated Surfaces”, C. Madi, E. Anzenberg, K.F. Ludwig, Jr. and M.J. Aziz, Phys. Rev. Lett. 106, 066101 (2011). “Growth Kinetics of AlN and GaN Films Grown by Molecular Beam Epitaxy on R-Plane Sapphire Substrates”, R. Chandrasekaran, T.D. Moustakas, A. Ozcan, K. Ludwig, L. Zhou and D. Smith, J. Appl. Phys. 108, 0143501 (2010). “In Situ X-ray Studies of Native and Mo-Seeded Surface Nanostructuring during Ion Bombardment of Si(100)”, G. Ozaydin-Ince and K.F. Ludwig, Jr., J. Phys.: Condens. Matter. 21, 224008 (2009). “Mechanisms of Pattern Formation and Smoothing Induced by Ion-Beam Erosion”, Hua Zhou, Lan Zhou, Gozde Ozaydin, Karl F. Ludwig, Jr., and Randall Headrick, Phys. Rev. B 78, 165404 (2008). “Effects of Mo Seeding on the Formation of Si Nanodots During Low-Energy Ion Bombardment”, Gozde Ozaydin, Karl F. Ludwig, Jr., Hua Zhou and Randall L. Headrick, Journal of Vacuum Science and Technology B 26, 551 (2008). “Real-Time Studies of Gallium Adsorption and Desorption Kinetics by Grazing Incidence Small-Angle X-ray Scattering and X-ray Fluorescence”, Yiyi Wang, Ahmet Ozcan, Karl Ludwig and Anirban Bhattacharyya, J. Appl. Phys. 103, 103538 (2008). “Transition Behavior of Surface Morphology Evolution of Si(100) During Low-Energy Normal-Incidence Ar+ Ion Bombardment”, Gozde Ozaydin, Karl F. Ludwig, Jr., Hua Zhou, Lan Zhou and Randall L. Headrick, J. Appl. Phys. 103, 033512 (2008). “GaN Quantum Dot Superlattices Grown by Molecular Beam Epitaxy at High Temperature”, Tao Xu, Lin Zhou, Yiyi Wang, Ahmet Ozcan, K.F. Ludwig, David Smith and T.D. Moustakas, J. Appl. Phys. 102, 073517 (2007). “Real-Time X-Ray Studies of Gallium Nitride Nanodot Formation by Droplet Heteroepitaxy”, Yiyi Wang, Ahmet S. Özcan, Christopher Sanborn, Karl F. Ludwig, Anirban Bhattacharyya, Ramya Chandrasekaran, Theodore D. Moustakas, Lin Zhou and David J. Smith, J. Appl. Phys. 102, 073522 (2007). “Real-Time X-ray Studies of the Growth of Mo-Seeded Si nanodots by Low-Energy Ion Bombardment”, Gozde Ozaydin, Ahmet S. Özcan and Yiyi Wang, Karl F. Ludwig, Hua Zhou and Randall L. Headrick, Nucl. Inst. Meth. Phys. Res. B 264, 47 (2007). “Experimental Methods: High-Resolution Scattering Methods and Time-Resolved Diffraction”, B. Sepiol and K. Ludwig in Alloy Physics A Comprehensive Reference, W. Pfeiler, Ed. (Wiley, 2007). “Growth of on-polar (11-20) and semi-polar (11-26) AlN and GaN films on R-Plane sapphire”, R. Chandrasekaran, A.S. Ozcan, D. Deniz, K.F. Ludwig and T.D. Moustakas, Phys. Stat. Sol. (c) 4, 1689 (2007). “Wavelength Tunability of Ion-bombardment Induced Ripples on Sapphire investigated with small-angle x-ray scattering and atomic force microscopy”, Hua Zhou, Yiping Wang, Lan Zhou, Randall L. Headrick, Ahmet S. Ozcan, Yiyi Wang, Gozde Ozaydin, and Karl F. Ludwig Jr., and D. Peter Siddons, Phys. Rev. B 75, 155416 (2007).