“How electrons flow through molecular wires has been studied, but less attention has been given to how the heat flows,” said Dana Dlott, a physical chemist at the University of Illinois. “One of the problems has been the lack of a measurement technique that could operate over short distances, short time intervals and large temperature bursts.”
As reported in the Aug. 10 issue of the journal Science, Dlott, engineering professor David Cahill and colleagues at Illinois have now developed an ultrafast thermal measurement technique capable of exploring heat transport in extended molecules fastened at one end to a metal surface.
“The ability to selectively probe the atomic groups that terminate the chains allows us to investigate the transport of heat through the chain molecules themselves,” Dlott said.
To study heat flow through long-chain hydrocarbon molecules anchored to a gold substrate, the researchers used an ultrafast laser spectrometer technique with picosecond time resolution (a picosecond is 1 million-millionth part of a second).
First, the flash from a femtosecond laser (a femtosecond is 1,000th of a picosecond) heated the substrate to about 800 degrees Celsius in one picosecond. This heat flowed quickly into the base of the hydrocarbon molecules and through the chains.
When heat reached the methyl groups at the ends of the chains, which were originally lined up in order, they began to shake and twist. An extremely sensitive form of coherent vibrational spectroscopy was used to probe this disordering.
The researchers’ study showed how the familiar concepts of heat transport do not apply at the level of individual molecules.
One cool finding, for example, is that heating the molecule to 800 degrees Celsius doesn’t destroy it. “Because the molecule stays hot for only a billionth of a second, it doesn’t have time to evaporate, burn up or chemically react,” said Cahill, a Willett Professor of Materials Science and Engineering.
Another surprising finding is that heat moves ballistically – that is, at a constant velocity – through the molecule. Each time two more carbon atoms were added to the chains, the heat took a little longer, about one-quarter of a picosecond, to reach the end.
“Heat usually travels at different velocities as it diffuses through its surroundings,” said Cahill, who also is a researcher at the Frederick Seitz Materials Science Laboratory and at the Coordinated Science Laboratory, both on the Illinois campus.
“We found the leading edge of the heat burst traveled ballistically along the hydrocarbon chains at a velocity of 1 kilometer per second.”
The researchers also determined the overall rate of heat flow in the molecule. They calculated a thermal conductance of 50 picowatts per degree Celsius.
“This is a new way of measuring temperature within a molecule,” Dlott said. “It’s the first step toward making a more precise thermometer with very high spatial resolution and with very high time resolution.”
With Dlott and Cahill, co-authors of the paper are postdoctoral research associates Zhaohui Wang, Alexei Lagutchev and Nak-Hyun Seong, and graduate students Jeffrey A. Carter and Yee Kan Koh.
The work was funded by the U.S. Department of Energy, the National Science Foundation and the Air Force Office of Scientific Research.
James E. Kloeppel | University of Illinois
Smallest transistor worldwide switches current with a single atom in solid electrolyte
17.08.2018 | Karlsruher Institut für Technologie (KIT)
Protecting the power grid: Advanced plasma switch for more efficient transmission
17.08.2018 | DOE/Princeton Plasma Physics Laboratory
New design tool automatically creates nanostructure 3D-print templates for user-given colors
Scientists present work at prestigious SIGGRAPH conference
Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and...
Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...
Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.
When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...
Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.
Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....
Proteins must be folded correctly to fulfill their molecular functions in cells. Molecular assistants called chaperones help proteins exploit their inbuilt folding potential and reach the correct three-dimensional structure. Researchers at the Max Planck Institute of Biochemistry (MPIB) have demonstrated that actin, the most abundant protein in higher developed cells, does not have the inbuilt potential to fold and instead requires special assistance to fold into its active state. The chaperone TRiC uses a previously undescribed mechanism to perform actin folding. The study was recently published in the journal Cell.
Actin is the most abundant protein in highly developed cells and has diverse functions in processes like cell stabilization, cell division and muscle...
17.08.2018 | Event News
08.08.2018 | Event News
27.07.2018 | Event News
17.08.2018 | Physics and Astronomy
17.08.2018 | Information Technology
17.08.2018 | Life Sciences