Trade.Information

Details

Nanoelectromechanical systems (NEMS) devices have the potential to revolutionize the world of sensors: motion, chemical, temperature, etc. But taking electromechanical devices from the micro scale down to the nano requires finding a means to dissipate the heat output of this tiny gadgetry. In a paper that recently appeared in the journal Nano Letters, Professor Markus Buehler and postdoctoral associate Zhiping Xu of MIT's Department of Civil and Environmental Engineering say the solution is to build these devices using a thermal material that naturally dissipates heat from the device's center through a hierarchical branched network of carbon nanotubes. The template for this thermal material's design is a living cell, specifically, the hierarchical protein networks that allow a cell's nucleus to communicate with the cell's outermost regions. "The structure now used when designing materials with carbon nanotubes resembles spaghetti," said Buehler, who studies protein-based materials at the nano and atomistic scales with the goal of using biomimetic-engineering principles to design human-made materials. "We show that a precise arrangement of carbon nanotubes similar to those found in the cytoskeleton of cells will create a thermal material that effectively dissipates heat, which could prevent a NEMS device from failing or melting." NEMS devices are characterized by extremely small, high-density heat sources that can't be cooled by traditional means. Even the microelectromechanical systems (MEMS) devices used in automobiles and electronics are hard to cool, because conventional thermal management strategies such as fans, fluids, pastes and wiring often don't work at these small scales; heat buildup in MEMS frequently leads to catastrophic device failure, which limits the reliability of larger systems. But the number of heat-conducting fibers or carbon nanotubes (CNTs) that can be connected to the heat source at the center of a NEMS device is limited by the physical size of the heat source itself. Buehler and Xu demonstrate that a simple geometric structure - a branched-tree hierarchy of at least two branches sprouting off each branch - is far more effective at heat dissipation than the non-hierarchical "spaghetti" of most existing CNT-based material. They show that a single fiber (or branch) connected to the heat source, with 99 additional branched links between it and the heat sink, will provide the same dissipation effect as if 50 long fibers were connected directly to the heat source. If five carbon nanotubes are arranged in direct connection to the heat source, each of which uses this branched-tree hierarchical structure, the heat dissipation will be the equivalent of 250 direct connections from the heat source to an external heat sink. "Our paper provides a breakthrough in the understanding of how nanostructural elements can be utilized effectively to bridge scales from the nano to macro through formation of hierarchical structures," said Xu. "The results could change the way nanodevices are designed and fabricated by enabling technological innovations for highly integrated systems." This research is funded by DARPA (the U.S. Defense Advanced Research Projects Agency) and the MIT Energy Initiative. ABOUT Markus J. Buehler : Esther and Harold E. Edgerton Assistant Professor Research Interests Materials science and mechanics of natural and biological protein materials - how protein materials define our body and how they fail catastrophically (fracture, deformation), large-scale atomistic modeling, protein based materials and biopolymers, interaction of chemistry and mechanics, bridging chemical scales to continuum theories of materials, modeling of bio-nano-materials phenomena, multiple-scale simulation, development of multi-scale simulation tools. Teaching Interests * Mechanics of materials, materials science, multi-scale modeling and simulation, biomechanics, molecular mechanics. Awards and Honors * U.S. Navy Young Investigator Award 2008 * DARPA Young Faculty Award 2008 * AFOSR Young Investigator Award 2008 * Plenary speaker, National Academy of Engineering, Indo-American Frontiers of Engineering Symposium (IAFOE, 2008) * Gustav-Magenwirth Award 2007 (to student T. Ackbarow) * Invited plenary speaker, NSF-UCWSI, Workshop and Summer Institute (Beijing, China, 2007) * Invitee, National Academy of Engineering – Frontiers of Engineering (2007) * Esther and Harold E. Edgerton Career Development Professorship (2007) * National Science Foundation CAREER Award (2007) * Plenary speaker at the 3rd International Conference on Advanced Materials and Nanotechnology (Wellington, New Zealand, 2007) * Keynote speaker at the 2nd International Conference on Mechanics of Biomaterials and Tissues (Hawaii, 2007) * Visiting Professor at A*STAR IHPC in Singapore (August, 2006) Selected Publications 1. M.J. Buehler, S. Keten, T. Ackbarow, "Theoretical and computational hierarchical nanomechanics of protein materials: Deformation and fracture", Progress in Materials Science (in press) 2. S. Keten and M.J. Buehler, "Asymptotic strength limit of hydrogen bond assemblies in proteins at vanishing pulling rates", Physical Review Letters, Vol. 100, paper number 198301 3. S. Keten and M.J. Buehler, “Geometric Confinement Governs the Rupture Strength of H-bond Assemblies at a Critical Length Scale”, Nano Letters, Vol. 8(2), 2008 4. T. Ackbarow, X. Chen, S. Keten, M.J. Buehler, “Hierarchies, multiple energy barriers and robustness govern the fracture mechanics of alpha-helical and beta-sheet protein domains”, P. Natl. Acad. Sci. USA, 2007 (cover article) 5. M.J. Buehler. H. Tang, A. C.T. van Duin, W.A. Goddard III, “Threshold Crack Speed Controls Dynamical Fracture of Silicon Single Crystals”, Physical Review Letters, Vol. 99, p. 165502, 2007 6. M.J. Buehler and T. Ackbarow, “Fracture mechanics of protein materials”, Materials Today, Vol. 10(9), pp. 46-58, 2007 (cover article) 7. M.J. Buehler and S.Y. Wong, "Entropic elasticity controls nanomechanics of single tropocollagen molecules", Biophys. J., Vol. 93(1), pp. 37-43, 2007 8. M.J. Buehler, "Defining nascent bone by the molecular nanomechanics of mineralized collagen fibrils", Nanotechnology, Vol. 18, 295102, 2007 Contact info : MIT Room 1-235A B77 Massachusetts Avenue Cambridge, MA, 02139 Telephone: 617.452.2750 e-mail: mbuehler@mit.edu