Vin Crespi
Vin Crespi, Associate Professor of Physics, is part of a growing number of materials researchers across campus that spend virtually all of their research effort simulating new and existing materials at the atomic scale using sophisticated computer code. His current research includes three different emphases: nanotubes, metastable semiconductor alloys and 3-dimensionally confined magnetic systems. In many cases, he aims to stay one step ahead of the experimentalists, predicting new materials before they have been synthesized.
His recent work on nanotubes involves trying to predict tribological behavior of carbon nanotubes consisting of two concentric walls. Single walled carbon nanotubes (SWNT) are single planes of six-member sp2 bonded carbon atoms wrapped into a tube. Experimentally and theoretically nanotubes display an intriguing variety of unique electrical, physical and chemical properties. Crespi was fascinated by the possibility of inserting one SWNT with hexagonal rings oriented at one angle to the nanotube axis into a second, larger SWNT with rings oriented at a different angle. The repeat distance of the lattice at these two angles would be different, leading to an infinite number of permutations in energy between the two nanotubes as the outer tube moves along the length of the inner tube. His conclusion: nanotubes with this structure would slide with nearly zero friction, since all positions have identical energy.
Lately, he has turned his attention to hypothesizing new nanotube materials. His models have predicted it may be possible to produce a thinner, stiffer nanotube consisting of entirely sp3 bonded carbon atoms by tying up one of the four available carbon electrons with an atom such as fluorine.[Phys. Rev. Lett. 87, 125502 (2001)] Work is currently under way elsewhere to synthesize this new material.
Since the carbon nanotube field is becoming a little crowded, Crespi has moved on to an entirely new class of nanotube materials based on B2O and BeB2. These materials are similar to graphite in that they are planar materials that could, under the right conditions, be persuaded to roll themselves into nanotubes.
Crespi is Associate Director of Penn State's interdisciplinary center on Collective Phenomena in Restricted Geometries, an NSF Materials Research Science and Engineering Center (MRSEC). In his MRSEC-related research, he has proposed using a regular array of silica spheres to serve as a template into which to infiltrate ferromagnetic materials. The dimensions of the resulting "Swiss cheese" ferromagnet will set up a dilemma for the magnetic domains. On the one hand magnetic fields do not like surfaces - which they would encounter at every silica sphere. On the other hand, they do not like to bend - which they would be forced to do in order to avoid surfaces. Crespi's simulations predict that there will be a complex series of clockwise and counterclockwise magnetic "hurricanes". The application of external magnetic fields will dramatically change the distribution of these tiny hurricanes.
Crespi came to Penn State in 1997 after postdoctoral appointments at Lawrence Berkeley National Lab and University of California at Berkeley. He received his Ph.D. in physics from Berkeley in 1994 under the direction of Marvin Cohen. He is the recipient of many prestigious awards including an NSF CAREER and the David and Lucille Packard Foundation Fellowship. He maintains an excellent website with many examples of his research at http://www.phys.psu.edu/~crespi/.
