MIT Institute Professor Mildred Dresselhaus has been named winner of the 2008 Oliver E. Buckley Condensed Matter Prize from the American Physical Society.
Dresselhaus, who will receive $10,000 for the prize, was cited "for pioneering contributions to the understanding of electronic properties of materials, especially novel forms of carbon."
The prize was endowed in 1952 by AT&T Bell Laboratories (now Bell Laboratories, Lucent Technologies) to recognize and encourage outstanding theoretical or experimental contributions to condensed matter physics. It is named in memory of Oliver E. Buckley, an influential president of Bell Labs.
MILDRED S. DRESSELHAUS, Institute Professor and Professor of Physics and Electrical Engineering
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Recent research activities in the Dresselhaus group that have attracted wide attention are in the areas of carbon nanotubes, bismuth nanowires and low dimensional thermoelectricty.
Regarding carbon nanotubes, which were previously predicted to be either semiconducting or metallic depending on their geometries, we have been developing the method of Raman spectroscopy as a sensitive tool for the characterization of single wall carbon nanotubes, one atomic layer in wall thickness. This work started in earnest with the initial observation (with Rao et al. at the University of Kentucky in 1997) of the Raman spectra from bundles of single wall carbon nanotubes and showing a strong enhancement of the spectra through a diameter selective resonance Raman effect. Next we showed characteristic differences between the Raman profile of the G-band depending on whether the nanotubes were metallic or semiconducting. This work eventually led to the observation of Raman spectra from one single nanotube, with intensities under good resonance conditions comparable to that from the silicon substrate, even though the ratio of carbon to silicon atoms in the light beam was approximately only one carbon atom to one hundred million silicon atoms. All Raman features normally observed in single wall nanotube (SWNT) bundles are also observed in spectra at the single nanotube level, including the radial breathing mode, the G-band, the D-band and the G'-band. However, at the single nanotube level, the characteristics of each feature can be studied in detail, including its dependence on diameter, chirality, laser excitation energy and closeness to resonance with electronic transitions. Of particular importance is the uniqueness of the electronic transition energies for each nanotube, which are described in terms of two integers (n, m) which uniquely specify the geometrical structure of the nanotube, including its diameter and chirality. The high sensitivity of the Raman spectra to diameter and chirality, particularly for the characteristics of the radial breathing mode, which are also uniquely related to the same (n, m) indices, thereby providing a structural determination of (n, m) at the single nanotube level. The (n, m) assignments made to individual carbon nanotubes are corroborated by measuring the characteristics of other features in the Raman spectra that are sensitive to nanotube diameter and chirality. Raman spectroscopy potentially provides a convenient way to characterize nanotubes for their (n, m) indices, in a manner that is compatible with the measurement of other nanotube properties, such as transport, mechanical and electronic properties at the single nanotube level, and the dependence of these properties on nanotube diameter and chirality.
We have devised a way to prepare arrays of aligned bismuth nanowires down to 7 nm diameter (embedded in an anodic alumina template), 50-100 microns in length, with a wire density of ~ 1011/cm2, with their wire axes along a common crystalline orientation, and preserving the crystal structure of bulk bismuth. We previously predicted a semimetal-semiconductor transition in bismuth nanowires as a function of nanowire diameter due to quantum confinement effects, and we have now succeeded in observing this effect through transport measurements. We are now studying the transport and optical properties of the nanowire arrays with particular relevance to enhancing their thermoelectric properties. For scientific studies we are developing techniques to make measurements of the resistance of single quantum wires as a function of nanowire diameter using a 4-probe method. The doping of bismuth with antimony, which is isoelectronic to bismuth, is of special interest for achieving an enhancement in thermoelectric performance, especially for p-type legs in thermoelectric devices. For this reason we are now studying the structure, electronic and transport properties of bismuth-antimony nanowires as a function of nanowire diameter and antimony concentration