MS&E Seminar: Hongyu Chen

Hongyu Chen

Associate Professor and Associate Dean -College of Science

Nanyang Technological University, Singapore

Division of Chemistry and Biological Chemistry

In this talk, I will discuss the small modifications that lead to different growth of straight nanowires, spirals, single and dou-ble helices. Previously, we reported the synthesis of ultrathin (d = 5-7 nm) Au nanowires, which are directly grown from Au seeds anchored on a substrate in an aqueous solution at room temperature. These NWs are typically polycrystalline with random lattice orientation. The growth behavior is similar to the vapor-liquid-solid growth at high temperature, but the underlying mechanism is fundamentally different. The transition from the normal straight nanowires to the spiral nan-owires is not triggered by the presence of a particular reactant, but by the ratio of reactant concentration. We propose that disorganized ligand-Au cluster may partially block the Au-substrate interface, inducing imbalanced growth of the nan-owire and causing it to coil. Blocking a single corner of the active interface leads to spiral nanowires whereas inequivalent-ly blocking two corners leads to helical nanowires. Most recently, we found that a special ligand is able to form precipi-tates of metal-ligand complexes, out of which ultralong Au nano-helices were formed under ambient conditions. The floc-cules of ligand complex provide a robust environment for the sustained growth the nano-helices, leading to their record length and consistency. As the seeds are embedded in and asymmetrically blocked by the floccules, the extrusion of nan-owire follows a constant helicity but differs from other individuals in the same sample. The structural characteristics, handedness, and internal lattice structure of the helices are consistent with our hypothesis.

Biography:

Dr. Hongyu Chen obtained his B. Sc. from University of Science and Technology of China (USTC) in 1998. He then moved to Yale University and studied Mn complexes and water oxidation chemistry. After obtaining his Ph.D. degree in 2004, he worked as a post-doctoral fellow in Cornell University on the topic of protein-nanoparticle hybrids. In 2006, he joined the Division of Chemistry and Biological Chemistry in Nanyang Technological Universi-ty in Singapore, where he is currently an Associate Professor and Associate Dean (College of Science). His main research interest is in the development of new synthetic methodologies for nanostructures and the underlying mechanisms.

 

 

Date/Time:
Date(s) - Dec 11, 2015
10:30 am - 12:00 pm

Location:
2101 Engineering V
420 Westwood Plaza Los Angeles CA 90095