Karl Ludwig
Faculty
(Professor)
Office: Metcalf Science Building, Room 450A
Phone: 617-353-9346
Lab: Metcalf Science Building, Room B46
Phone: 617-353-7291
Email: ludwig@physics.bu.edu
Website: http://physics.bu.edu/xrays
Availability (office hours): Spring 2008 Office Hours:
Monday 12-2 (held in SCI 121)
Thursday 1-2 (held in SCI 450A)
Other times by appointment.
Research Interests:
My research focus is investigating 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. Much of our research uses the high brightness of synchrotron x-ray sources – the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory on Long Island and the Advanced Photon Source (APS) at Argonne National Laboratory outside of Chicago. Where possible, we make contact with fundamental theory and simulation.
In the last few years, our detailed interest has been in two directions – understanding surface and thin film processes and investigating nanoscale dynamics in metallic alloys using coherent x-ray scattering. Our studies of surface and thin film processes 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.
Coherent x-ray scattering offers 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 seperation or stacking fault rearrangement) in the alloy.
Education:
Ph.D. in Applied Physics: Stanford University – 1986
M.S. in Applied Physics: Stanford University – 1982
B.A. magna cum laude in Physics: Cornell University – 1980
Research Descriptions:
Real-Time X-Ray Studies of Ion Bombardment/Plasma Processing
Ion bombardment of surfaces is at the core of sputtering and plasma processing technologies that are vital to several of the largest manufacturing industries in the world. However, recent experimental and theoretical studies of surface morphology evolution during ion sputter erosion suggest that there is a rich variety to surface morphology evolution during ion bombardment. Our group currently focuses on the low energy Ar+ ion bombardment of Si and GaSb surfaces. We study the evolution of Si and GaSb surface morphology using real-time x-ray scattering techniques and ex-situ AFM analysis. Synchrotron-based real-time x-ray studies offer at least five important advantages in gaining fundamental atomic-level insight into such processes: penetration of ambient gaseous/liquid environments, ability to vary depth of structural sensitivity, ability to probe structures from 0.1-100 nm in length scale, subsecond temporal resolution, and ease of interpretation. To take advantage of these powerful attributes, we have constructed a new facility in the back hutch of NSLS beamline X21, funded with NSF-MRI and NSF-IMR support, which is being spearheaded by collaborators at the University of Vermont (R. Headrick), Boston University (K. Ludwig and T. Moustakas).