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I have taught and done research at Haverford since 1992. I received a B.A. (physics) from Wesleyan in 1981, and a Ph.D. (physics) from Harvard in 1989. From 1989 to 1992, I was a postdoctoral researcher at the University of Texas at Austin. My wife, Marian McKenzie, is an elementary school librarian. We have a 9-year-old daughter, Grace, a 7-year-old son, Charlie, and a 4-year-old son Tommy.
In Spring 2005, I am teaching Solid State Physics and Electronic Instrumentation & Computers.
I write songs for use in physics courses, and run the world's premiere website devoted to collecting and organizing all songs about physics: PhysicsSongs.org
As the electronics industry continues the trend in miniaturization, it is fast approaching a serious technological barrier. Production linewidths for the highest-performance integrated circuits have already reached about 600 atoms, while the practical limit for conventional transistor operation appears to be a linewidth of about 200 atoms. Circuits that are self-assembled from functional molecular components may offer a way of circumventing this limit, lowering production costs, and increasing functionality by interfacing with biological and chemical systems.
Return to Research Interests Summary
There are two projects underway in this area:
| Recently, students from Prof. Julio DePaula's research group in the Haverford Chemistry Dept., working together with my students, discovered an amazing new self-assembling system. Simply adding hydrochloric acid to a solution of a carefully-chosen porphyrin (a chemical analog of chlorophyll) caused the formation of very straight, very long (by my standards), and very small diameter rods! (The rods are 3.8 nanometers in diameter, and up to 2000 nanometers long.) Similar rods, but made of chlorophyll, are observed in photosynthetic bacteria. So, the synthetic porphyrin nanorods may serve as a model system, helping us to understand the operation of the bacterial photosynthetic system. The porphyrin nanorods may also have important applications in nanotechnology, including possible use in an artificial photosynthetic system. |  |
Our experiments on the electrical conductivity of the rods show some very exciting behaviors. In the dark, the rods do not conduct. When light is applied, the conductivity jumps suddenly, then grows further (as shown in region i) over a period of several minutes. If the light is turned off, the system "remembers" this slow growth period for up to about 15 minutes! If the light is left on, but zero voltage is applied, the sample generates electrical current (as shown in region iii), with a trainable polarity. These effects are shown in the figure to the right. This work is done in collaboration with Prof. Alan Johnson and his research group at the University of Pennsylvania; all of the synthesis, Atomic Force Microscopy, and photoelectronic measurements are done at Haverford, while electron beam lithography to create the nanoscale contact pads we need for these measurements is done at Penn. This research is supported by grants from the Packard Foundation and the National Science Foundation ( |
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Carbon nanotubes show great promise for the construction of nanometer-scale electronic circuits. Perhaps most importantly, their ability to carry a large electrical current in a small diameter wire is more than 100 times better than conventional metals. We are trying to understand what allows such a huge current-carrying capacity, and what ultimately limits it. The limit in air is well-understood: the electrical current causes the nanotube to heat up, and eventually brings it to the temperature at which it burns. In principle, it should be possible to suppress this combustion by embedding the nanotube in a non-oxidizing medium. As a first step, researchers have measured the critical current in vacuum. Surprisingly, it was only 1.5 times higher than in air!
We believe this result was caused by residual oxygen in the vacuum system used for that study. Our vacuum system achieves much lower pressures, so low that during the course of a typical experiment (up to an hour), not even one oxygen molecule will contact the carbon nanotube. In addition to measuring the critical current under ultrahigh vacuum, we will also measure the electrical noise produced by the carbon nanotubes under high current. It appears that such measurements could give important information about the rather exotic interaction between electrons and crystal lattice vibrations in carbon nanotubes.
last updated 3-6-05
Department of Physics