"My research is directed toward advancing the understanding of the physics and applied physics of nanostructures by researching the fabrication and optical characterization of nanostructures and devices. In particular, I study photonic band gap devices, single molecule electronics, and semiconductor nanowires. Many of the nanostructures and devices are fabricated in my group using e-beam lithographic techniques."

(1) Single Molecule Electronics: Conductivity measurements of dimetal paddlewheel complexes: Collaborators: Senthil Rajagopal, Neil Smith, Jan M. Yarrison-Rice, Physics Department, Miami University Archana Jaiswal, Shouzhong Zou, Chemistry Department, Miami University Thomas Scott, Christina C. Urig, Hongcai Zhou, Chemistry Department, Miami University

Single molecule electronics is an exciting area with a rich variety of both basic and applied physics problems driven, in part, by the potential for molecular scale electronics. This work requires the combined capabilities of a synthetic chemist (Zou) and a probe spectroscopy chemist (Zhou) with e-beam fabrication and Raman spectroscopy (Yarrison-Rice) expertise. The research has been supported by an NSF-Nanotechnology Exploratory Research grant (NSF-0403669). A series of paddlewheel complexes that contain dimetal centers with different metal-metal bond orders are being synthesized. Their use as molecular wires, diodes, and transistors will be investigated. Senthil Rajagopal (MS Physics, Miami), Christina Urig (Chemistry, PhD, Miami), and Neil Smith (MS Physics, Miami) have been responsible for designing and fabricating nanoscale single electrode pairs as well as gated electrodes. Zhou and Yarrison-Rice's groups will close the gaps to the ~3 nm spacing and then probe the molecular electronic devices via I-V probe measurements and Raman spectroscopy.Single Cr:Au electrode pair with ~50 nm gap Single electrode pair closed via electrodeposition

(2) Photonic Band Gap Devices and Structures: Collaborators: Meron Tekeste, Katie Beddow, Jan M. Yarrison-Rice, Physics Department, Miami University Scott Masturzo, Joseph Boyd, ECECS, University of Cincinnati

The integration of electronics and optics through photonic band gap (PBG) structures is an area of promise for the field of telecommunications. These research projects combine modeling (using finite difference time domain calculations) with fabrication and characterization of several 2-D PBG structures using the unique capabilities of the e-beam lithography instrument at UC. Two major research projects and one research/teaching project are ongoing on photonic band gap (PBG) structures and devices. 1) Meron Tekeste (MS Physics, Miami) designed a highly efficient demultiplexer that can separate three different argon ion wavelengths into individual exit channels. 2) Scott Masturzo (ECECS PhD Student, UC)is studying the coupling of laser light into PBG waveguide structures using a grating etched into the 2D wafer. 3) Katie Beddow (BS Physics, Miami)just completed a study of traditional ridge waveguides and compared them to the efficiency of PBG waveguides as part of a project to develop a photonics experiment which involves photolithography and waveguide characterization for the Phy441/541 lab.

Wavelength demulitplexer simulation results. Left: 514.5 nm light is channeled out with 82% efficiency and Right: 496.5 nm light exits with 91% efficiency. [From: Tekeste and Yarrison-Rice, Opt. Exp. 14, 7931-7942 (2006).]

(3) CdS Nanowires and GaAs Nanowires: Collaborators: Senthil Rajagopal, and J.M. Yarrison-Rice, Physics Dept. Miami University Amensisa Abdi, Thang Hoang, Lyubov Titova, Howard. Jackson and Leigh Smith, Physics Department, University of Cincinnati Nanowires are intriguing, new semiconductor materials with nanometer diameters and micron length scales. We explore their basic optical characteristics and interactions, and see them as promising candidates for several unique electro-optic devices My research on nanowires has been based on 1) optical characterization using resonant Raman spectroscopy (Amensisa Abdi, Physics, PhD, University of Cincinnati) and photoluminescence and time-resolved luminescence spectroscopies, to probe the electronic landscape as well as their utility for nanoscale devices. A new direction we are just beginning to explore is 2) incorporating plasmonic resonators (Senthil Rajagopal, MS Physics, Miami), which are functionalized with carbohydrate ligands, with a nanowire photocurrent detector to create a new biosensor for specific detection of pathogens.

(4) Modeling Ridge Waveguides and Their Comparison to Photonic Bandgap Waveguides Katie Beddow, Meron Tekeste, Jan M. Yarrison-Rice, Physics Department, Miami University

Traditional ridge waveguides confine and direct light via total internal reflection due to differences in index of refraction of the waveguide core with respect to the surrounding material. Thus, when the waveguide bends or curves, light may be lost to its surroundings when the internal angle of the light is no longer larger than the critical angle. In comparison, PBG waveguides confine light due to the fact that air pores etched into the dielectric material have very high contrast in dielectric constant, and that the periodic nature of the air pores creates a material which is highly reflecting to particular wavelengths of light. So, if a PBG structure is designed with the correct dimensions, then light can be guided within the PBG lattice.

Traditional Ridge Waveguide: Electric field propagation amplitude as a function of distance in a) a linear waveguide(top left), b) in a bending waveguide (top right), and c) in a bending waveguide with too high a curvature (bottom left).

PBG Waveguides: Light propagating in a linear PBG waveguide (left) and through a tight bend PBG waveguide (right). Electric field propagation topography is shown from above the lattice