MILDRED S. DRESSELHAUS, Institute
Professor and Professor of Physics and Electrical Engineering
Research Interests
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.
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Biographical Sketch
Professor Mildred Dresselhaus is a native of the Bronx, New York
City, where she attended the New York City public schools through
junior high school, completing her high school education at Hunter
College High School in New York City. She began her higher education
at Hunter College in New York City and received a Fulbright Fellowship
to attend the Cavendish Laboratory, Cambridge University (1951-52).
Professor Dresselhaus received her master's degree at Radcliffe
College (1953) and her Ph.D. at the University of Chicago (1958).
Professor Dresselhaus began her MIT career at the Lincoln Laboratory.
During that time she switched from research on superconductivity
to magneto-optics, and carried out a series of experiments which
led to a fundamental understanding of the electronic structure of
semi-metals, especially graphite.
A leader in promoting opportunities for women in science and engineering,
Professor Dresselhaus received a Carnegie Foundation grant in 1973
to encourage women's study of traditionally male dominated fields,
such as physics. In 1973, she was appointed to The Abby Rockefeller
Mauze chair, an Institute-wide chair, endowed in support of the
scholarship of women in science and engineering.
Professor Dresselhaus has greatly enjoyed her career in science.
On her experience working with MIT students, she says, "I like
to be challenged. I welcome the hard questions and having to come
up with good explanations on the spot. That's an experience I really
enjoy." Thus far, she has graduated over 60 Ph.D. students.
This biographical text was adapted from Harvard Magazine's January-February
1980 feature article on Professor Mildred S. Dresselhaus.
Recent honors and awards include:
- Karl T. Compton Medal for Leadership in Physics, American Institute
of Physics, 2001
- Medal of Achievement in Carbon Science and Technology, American
Cabon Society, 2001
- Honorary Member of the Ioffe Institute, Russian Academy of Sciences,
St. Petersburg, Russia, 2000
- National Materials Advancement Award of the Federation of Materials
Societies, 2000
- Honorary Doctorate from the Catholic University of Leuven,
Belgium, February 2000
- Nicholson Medal, American Physical Society, March 2000
- Weizmann Institute's Millennial Lifetime Achievement Award,
June 2000
[top] Selected Publications
M. S. Dresselhaus and P. C. Eklund, Phonons in Carbon Nanotubes,
Advances in Physics 49, 705-814 (2000).
A. Jorio, G. Dresselhaus, M. S. Dresselhaus, M. Souza, M. S. S.
Dantas, M. A. Pimenta, A. M. Rao, R. Saito, C. Liu, and H. M. Cheng,
Polarized Raman Study of Single Wall Semiconducting Carbon Nanotubes,
Phys. Rev. Lett. 85, 2617-2620 (2000).
A. Jorio, R. Saito, J. H. Hafner, C. M. Lieber, M. Hunter, T. McClure,
G. Dresselhaus, and M. S. Dresselhaus, Structural (n,m) determination
of isolated single wall carbon nanotubes by resonant Raman scattering,
Phys. Rev. Lett. 86, 1118-1121 (2001).
A. Jorio, A. G. Souza Filho, G. Dresselhaus, M. S. Dresselhaus,
R. Saito, J. H. Hafner, C. M. Lieber, F. M. Matinaga, M. S. S. Dantas,
and M. A. Pimenta, Joint density of electronic states for one isolated
single wall carbon nanotube studied by resonant Raman scattering,
Phys. Rev. B 63, 245416 (2001).
A. G. Souza Filho, A. Jorio, J. H. Hafner, C. M. Lieber, R. Saito,
M. A. Pimenta, G. Dresselhaus, and M. S. Dresselhaus, Electronic
transition energy Eii for an isolated (n,m) single-wall carbon nanotube
obtained by anti-Stokes/Stokes resonant Raman intensity ratio, Phys.
Rev. B 63, 241404R (2001).
M. S. Dresselhaus, G. Dresselhaus, A. Jorio, A. G. Souza Filho,
and R. Saito, Raman Spectroscopy of Isolated Single Wall Carbon
Nanotubes, Carbon (2002). Submitted 10/13/01: LRR-66/01.
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