Chwen-Yang Shew, Assistant Professor of Chemistry at The Graduate Center and the College of Staten Island, and Godfrey Gumbs, the Chianta-Stoll Professor of Physics at The Graduate Center and Hunter College are currently pursuing research that is aimed at understanding the microscopic properties of complex polymers, semiconductor nanostructures, and carbon nanotubes from a theoretical point of view. They have employed both computer simulations and theoretical methods in their investigations of these systems. The ongoing projects currently being carried out by their groups include: (1) electro-active as well as inhomogeneous polymers in external electric fields; (2) single-electron transport in nanocircuits, their entanglement and the potential applications to single-photon sources and spintronics for quantum computing; (3) the many-body effects of dielectric screening on the collective excitations of nanostructures; and (4) microscopic theory for electron energy loss spectroscopy of cylindrical nanotubes.
Electro-active polymers in external electric fields: Electro-active polymers display strong response to electric fields and undergo substantial deformation under electric fields. In this project, Dr. Shew has developed several models to elucidate the effects of electric fields on the behavior of electro-active polymeric materials and his theoretical modeling offers detailed information of their molecular levels. Commonly used plastics are made of inhomogeneous polymers with sufficient toughness to maintain the shape of products and to resist wear. Recently, Dr. Shew developed a model which allows one to quantify experimental results related to the presence of cavities. In addition to plastics, the model is also applicable to other complex inhomogeneous systems, such as gels.
Single-electron transport: Single electron transport using surface acoustic waves
(SAWs) in piezoelectric heterostructures has been realized experimentally. Dr. Gumbs recently explained the quantization of the acoustoelectric current with the use of a microscopic model. He has suggested their potential device applications to acoustic spintronics for quantum optics and computing with the use of SAW nanocircuits. He is calculating the quantum entanglement of an interacting pair of electrons in a SAW nanocircuit and the gate errors associated with leakage of these electrons from their prepared state.
Many-body effects on the Collective excitations of Nanostructures: The optical and transport properties of nanostructures are governed by their collective excitations such as plasmons. Dr. Gumbs is carrying out detailed calculations of these modes of excitations in heterostructures consisting of layers of positive (p-type) and negative (n-type) carriers and the role they play in determining the electrical conductivity.
Electron energy loss spectroscopy (EELS) for multi-walled and single-walled nanotubes: EELS is a valuable experimental tool for determining the collective excitations of condensed matter. Dr. Gumbs' group at Hunter is developing a detailed theory for predicting and analyzing the collective plasmon excitations of cylindrical nanotubes. Carbon nanotubes -- rolled-up sheets of graphite only angstroms in diameter -- have potential applications as electronic devices like diodes and transistors, in flat panel displays, because of the enhanced electric fields they can emit; they also have possible applications in the recording industry when magnetic materials such as cobalt are inserted into their cores.
The projects of Dr. Shew have been supported by a PSC-CUNY award and New York Fine Chemicals. Dr. Gumbs' work is being supported by grants from the National Science Foundation, the Centers for Research Excellence in Science and Technology (CREST), the National Institute of Health, and a PSC-CUNY award. Dr. Gumbs and Dr. Shew were jointly awarded a CUNY Incentive Collaborative Research grant to conduct research on single photon sources generated by single electrons recombining with holes in a SAW nanocircuit.