Dresselhaus has laid the foundation for our understanding of the influence of reduced dimensionality on the fundamental thermal and electrical properties of materials. Her early work on graphite intercalation compounds and carbon fibers presaged the discoveries of C60, the fullerenes, nanotubes, and graphene. She investigated the effects of phonon confinement and electron-phonon interactions in nanostructures, and provided the key insights that underlie today's research into nanostructured thermoelectrics. She showed that in nanostructures it is possible to decouple thermal and electrical transport, with significant implications for energy use. Thanks to Dresselhaus's work, we have an improved understanding of how energy flows and dissipates on the nanoscale.
Mildred DresselhausThe story of carbon is interwoven with the story of nanoscience. The 1996 Chemistry Nobel Prize for the discovery of fullerenes, the 2008 Kavli Nanoscience Prize for the discovery of nanotubes, and the 2010 Physics Nobel Prize for graphene all recognize the remarkable phenomena that occur in highly controlled carbon-based nanostructures. As early as the 1960's, Dresselhaus led one of the very first groups that explored the carbon materials that form the basis for 2D graphene and 1D carbon nanotubes. These early experiments helped to map out the electronic band structure of these materials, critical to further understanding the unique properties they might possess. Dresselhaus studied intercalated two-dimensional graphene sheets and provided important insights into the properties of not only 2D graphene, but also of the rich interactions between graphene and the surrounding materials. Her early work on carbon fibers, beginning in the 1980's, provided Dresselhaus with the understanding and perspective to postulate the existence and unusual attributes of one-dimensional 'single wall carbon nanotubes (SWNTs)', years in advance of their actual discovery. A key prediction included the possibility that SWNTs could behave like either metals or semiconductors, depending on their chirality. Dresselhaus and coworkers pointed out that nanotubes can be viewed as arising from the folding of a single sheet of carbon, like a piece of paper that is wrapped at different spiral angles. They showed that this very simple rearrangement of their structure completely controlled their properties. This prediction was subsequently shown to be true. Through her studies of the fundamental physics of carbon-based solids, Dresselhaus laid the foundation for knowledge that has been integral to today's nanoscience of carbon.
Dresselhaus studied the transport and optical properties of nanostructured matter with an exquisite selection of experimental techniques providing unprecedented microscopic understanding. Regarding carbon nanostructures, she pioneered Raman spectroscopy as a sensitive tool for the characterization of materials one atomic layer in wall thickness, namely carbon nanotubes and graphene. Diameter selective resonance enhancement led to the observation of Raman spectra from one single nanotube. The high sensitivity of Raman spectroscopy to diameter and chirality made the technique the prime method for the characterization of carbon nanotubes. The success story has been seamlessly adapted to the characterization of graphene and is in use in hundreds of laboratories worldwide as a fundamental diagnostic tool for carbon-based nanostructures.
Materials are held together by electrons shared between atoms. When the energy of an electron in a solid is altered, the local bonding of the solid is perturbed, resulting in a change in the position of the atoms that make up the solid. In nanoscale materials, the spatial extent of electrons and phonons can be modulated, leading to dramatically different behaviors compared with extended solids. Dresselhaus has investigated this very fundamental electron–phonon interaction in nanostructures using the powerful techniques of Raman and Resonance Raman spectroscopy.
This science also laid a foundation for practical work today aimed at controlling how energy flows. Thermoelectric materials have the ability to convert heat energy to an electrical signal or, alternatively, to utilize electrical energy to actively cool a material. Nature provides materials in which the electrical and thermal conductivity are strongly linked, resulting in a seeming limit to the achievable efficiency of a thermoelectric. Dresselhaus demonstrated that in a one-dimensional structure, it is possible to separately adjust electrical and thermal conductivity, and that this should allow the creation of new generations of thermoelectric refrigerators and new ways of scavenging waste heat for useful purposes.