Lyman L. Handy Colloquium

"Opportunities and Challenges in Nanostructured Materials"Professor Jagdish (Jay) Narayan
Department of Materials Science and Engineering
North Carolina State University
Raleigh, NC ABSTRACT
This talk addresses some of the fundamental issues and critical advantages in reducing the grain size/ feature size to the nanoscale regime. We find that as the grain size or feature size is reduced, there is a critical size below which the defect content can be frozen or reduced virtually to zero. This critical size for most defects in materials falls in the nanoscale regime. Thus, nanostructured materials offer a unique opportunity to realize the property of a perfect material. However, with this opportunity comes a great challenge in terms of engineering a large fraction of atoms near the surfaces/interfaces. Another challenge is to self-assemble nanounits with desired structure and orientation with respect to the matrix. This often requires thin film epitaxy across the misfit scale with lattice misfit ranging from about 1% to 50%. Using a new paradigm of domain matching epitaxy (DME), we are able to deal with thin film epitaxy across the misfit scale within the continuum ground state energy description of the strained system. The DME framework is based upon matching of integral multiples of lattice planes, where there is one dislocation in each domain corresponding to missing (compressive strain) or extra (tensile strain) half plane. According to the DME paradigm, 2.0% and 25% misfits correspond to 49/50 and 3/4 planar matching, respectively. The misfit in between the integral multiples of planes is accommodated by the principle of domain variation. The limiting factors in DME are associated with matching of interface interatomic potentials, lattice relaxation, overlapping of dislocation cores and bending of lattice planes. For large misfit systems, strain free energy often dominates over chemical free energy. We focus on integration of systems based on III-nitrides, II-oxides, and perovskites.Thursday, September 14, 2006
12:45 p.m.
OHE 122
Refreshments will be served after the seminar in the HED Lobby
The Scientific Community is cordially invited.

Location: Olin Hall of Engineering (OHE) - 122

Audiences: Everyone Is Invited

Contact: Petra Pearce