The first part of the talk will focus on electrical and electro-thermal transport in transparent conductors based on nanostructured networks. Nanostructured conductors being considered as potential replacements for transparent conducting oxides include large-area graphene (grown by chemical vapor deposition) and random networks of metallic nanowires. The performance of these materials is limited by high-resistance grain boundaries and wire-wire junction resistances, respectively. Hybrid networks consisting of a network of metallic nanowires coupled with a single layer of graphene have been proposed and demonstrated experimentally, including sheet resistances below 20 ohms per square at 90% transparency. The basic model of conduction consists of co-percolation between the two conductive layers (nanowire network and graphene), with each layer bridging the conductive gaps in the other layer. In this presentation, we describe current-voltage characteristics and transient thermoreflectance (TR) imaging of nanowires and hybrid networks. Transient TR imaging provides information on the time-dependence of self-heating and cooling, with various magnifications providing resolutions ranging from individual hot-spots (e.g. nanowire junctions) to macroscopic regions. A thermal conductance model considering both vertical (substrate) and lateral (heat spreading through network) elements can be used to understand thermal transport in the device. Since self-heating occurs at resistive links in conductive pathways, the ability to resolve local heating versus diffusion effects allows a more detailed understanding of the distribution of conductive paths and resistance bottlenecks in the distributed conductors. Extensions to other materials systems will also be discussed. The second part of the talk will focus on array-based electrochemical biosensors. On-chip arrays of biosensors could allow mapping of biomolecule gradients and cellular flux in a physiological environment and would be well suited for portable applications. This presentation will describe the fabrication of an individually addressable glucose biosensor array on a silicon substrate. The response of an individually operating electrode versus the response of the same electrode operated in an array was analyzed in order to quantify inter-electrode and position-dependent effects. The biosensor array has been employed to measure an artificial concentration gradients and transients of glucose and hydrogen peroxide.
David B. Janes received the B.A. degree in Physics from Augustana College in 1980 and the B.S.E.E., M.S.E.E. and Ph.D. degrees from the University of Illinois at Urbana-Champaign in 1980, 1981 and 1989, respectively. From 1981 to 1985, he worked as a research scientist at the Research Division of Raytheon Company, working on microwave devices and integrated circuits. Since 1989, he has been at Purdue University, where he is a Professor of Electrical and Computer Engineering. His current research projects include nanowire and other low-dimensional transistors for low-noise and thin-film electronics, 2-D/1-D hybrid systems for transparent conductors and IR/photovoltaic applications, and chemical/biological sensors. He has published over 100 referred journal papers and is a co-inventor on 3 patents. He has served in leadership roles in conferences and professional societies, including co-chairing the IEEE Nanotechnology Conference and serving as an officer in the Electronic Materials Committee and the Electronic, Magnetics and Photonics Division of the American Vacuum Society. He has also served as Co-Chair of the Engineering Diversity Action Committee, which promote awareness of diversity issues within college, including diversity presentations to first-year engineering students. Since 2012, Janes has served as a Global Affairs Fellow and Faculty Coordinator of Institutional Partnerships, in Purdue’s Office of Corporate and Global Partnerships, focusing on global engagement strategies and institutional partnerships. In this role, he has facilitated partnerships with a number of universities, coordinated development of a university-wide engagement strategy for India, developed case studies in global engagement, and co-developed the Latin American Technical, Research and Administrative Leaders (LATeRAL) program and the Networks of Excellence program. Janes has also held leadership positions in major centers. From 2001-2003, he was Research Program Coordinator for the Birck Nanotechnology Center in Purdue’s Discovery Park. From 2003-2007, he was Technical Director of the Institute for Nanoelectronics and Computing, a NASA-supported research and education center. In this role, Janes was responsible for technical direction of center research, and served as primary contact with partners at minority institutions, external reviewer for research programs at NASA-affiliated labs, director/recruiter for graduate fellowship program and co-director of undergraduate research program.