211th ECS Meeting | Chicago, IL | May 7, 2007
Nanocars and Hybrid Silicon/Molecule Devices
Prof. Tour is currently the Chao Professor of Chemistry, Professor of Computer Science, and Professor of Mechanical Engineering and Materials Science at Rice. He is also Director of Rice University’s Carbon Nanotechnology Laboratory in the Smalley Institute for Nanoscale Science and Technology.
Dr. Tour began his lecture by pointing out that a key roadblock in molecular electronics was the difficulty in making good metal/molecule contacts. A way around this would be to eliminate this interface altogether and instead graft molecules directly on the Si surface in a “moleFET” configuration. Thus the current in this type of device would be driven through the Si base rather than through the molecules themselves. He then showed data on turn-on voltages in the transistor as a function of the molecular architecture. Three-terminal field effect transistors (FETs) using intrinsic Si nanowires were also discussed. Forming an F-terminated silicon oxide surface significantly decreased the resistivity and increased the mobility, enabling its use in memory devices.
The lecture then turned to the topic of molecular motors and nanocars. A key application here would be the transport of targeted chemicals along surfaces much like the body does naturally via “biochemical and biophysical machines.” Prof. Tour began this topic by contrasting the traditional “top-down” synthetic paradigm with a “bottom-up” molecular approach. Particularly striking was the analogy made in the top-down construction of a lectern which is fashioned from wood out of a tree. The lecture then focused on examples drawn from video demonstrations of a nanoCaterpillar, a nanoCooper, dipolar nanocar, nanotruck, nanoworm, nanobackhoe, and a nanotrain. Many of these fascinating nanoarchitectures exemplified synthetic motifs based on molecular self-assembly, metal complexation and hydrogen bonding.
Prof. Tour concluded his entertaining and fast-moving talk by noting that the hardest part of the nanocar project was not the synthesis but learning how to manipulate and move objects on a nanometer size scale. The needed tools such as scanning probe microscopies, in his opinion, are lagging behind the synthetic advances. For the nanotransporter concept to become practical, our ability to reproducibly observe and move nanometric objects will have to improve significantly along with continuing advances in our understanding of defects and molecule-surface interactions on surfaces such as Au (111) and Si (100).