Wednesday, June 24 • 1:30 PM – Biology/Physics Building (BPB), Rm. 130

Designing Shape Memory Materials for Damping, Actuation, and Energy Applications

Ying Chen

Assistant Professor of Materials Science and Engineering Rensselaer Polytechnic Institute, Troy, NY

Abstract: Shape memory alloys have the remarkable capability to switch between two “programmed” geometries upon the application and removal of stimuli such as stress, heat, or magnetic field. Their shape memory properties result from a diffusionless and crystallographically reversible martensitic phase transformation that occurs by shear. However, many polycrystalline shape memory alloys are limited by their inherent brittleness caused by severe stress concentration at grain boundaries during martensitic transformations. In this talk, I will present two strategies that we have developed to overcome this limitation. I will discuss our recent work on small scale oligocrystalline alloys with bamboo grain structures, and potential technological developments that can result from our understanding of the small-scale properties and size effects. When bulk polycrystalline structures are desirable, we design dual-phase alloys in which a ductile nontransforming second phase is precipitated along grain boundaries to cushion the grain boundaries and alleviate stress concentrations. Oligocrystalline and polycrystalline shape memory alloys with excellent shape memory properties and mechanical durability are promising for many damping, actuation, and energy applications.

Biographical Sketch: Dr. Ying Chen earned her B.S. in Materials Science and Engineering from Tsinghua University in Beijing, China in 2004 and Ph.D. in Materials Science and Engineering from MIT in 2008. She was a postdoctoral associate at the MIT Institute for Soldier Nanotechnologies from 2008 to 2010, before joining GE Global Research Center in Niskayuna, NY as a materials scientist. She worked on high temperature superalloys at GE GRC for a little over a year, and then joined the Rensselaer faculty at the end of 2011. Her research focuses on elucidating microstructure-mechanical property relationships in metallic materials using both experimental and mesoscale modeling approaches.

For additional information, please contact Prof. Michael T. Pettes at (860) 486-2855, pettes@engr.uconn.edu or Laurie Hockla at (860) 486-2189, hockla@engr.uconn.edu

Wednesday, June 10 • 1:30 PM – Biology/Physics Building (BPB), Rm. 130

Electronic Transport in Topological Insulator Nanostructures

Luis A. Jauregui

Postdoctoral Associate, Philip Kim Group Department of Physics, Harvard University, Cambridge, MA

Abstract: I will describe our recent transport experiments on topological insulator materials such as Bi2Te3 and BiSbTeSe2 nanoribbons (TINRs). We were able to successfully distinguish the bulk and surface carriers. The experiments have particularly revealed a list of unique transport signatures of the spin-helical, Dirac fermion topological surface states, and provide ways to access and utilize such surface states in novel topological quantum devices. Topological insulators (TI) are gapped band insulators in the bulk, but have nontrivial, “topologically protected”, spin-helical conducting states with gapless Dirac fermion dispersion on the surface. Such “topological surface states” are considered promising platforms to explore various novel physics ranging from quantum anomalous Hall effect, Majorana fermions to excitonic condensation. However, electronic transport of topological surface states in real TI materials is easily obscured by competing conduction channels that include the bulk as well as the “conventional” 2D electron gas (2DEG) formed by band bending at the surface. This is a major challenge in current experiments and device applications involving topological insulators. In this talk, I will describe our recent electron transport experiments on TI materials based on Bi2Te3 and BiSbTeSe2. We have explored ways to reduce the bulk conduction, and revealed a list of unique electronic transport signatures of the spin-helical, Dirac fermion topological surface states. In addition, we have also measured induced superconductivity in TINRs. These experiments may facilitate better access and control of TI surface states to explore the more exotic physics and applications in topological quantum devices.

Biographical Sketch: Dr. Luis Jauregui earned his B.S. in Electrical Engineering from National University of Engineering in Lima, Peru in 2007 and his Ph.D. in the area of micro and nanotechnology from the Department of Electrical and Computer Engineering at Purdue University in 2015. He was the recipient of the Intel Ph.D. fellowship for the years 2012 – 2013 and the Purdue Research Foundation Fellowships 2013 – 2015. Currently, he is a postdoctoral associate in the Department of Physics at Harvard University. His research focuses on experimental investigations of electron transport in low dimensional systems like nanowires, and two dimensional layered materials.

For additional information, please contact Prof. Michael T. Pettes at (860) 486-2855, pettes@engr.uconn.edu or Laurie Hockla at (860) 486-2189, hockla@engr.uconn.edu