A research Team at Rensselaer Polytechnic Institute has developed a new method for significantly increasing the heat transfer rate across two different materials.  Heat transfer is a critical aspect of many different technologies. As computer chips grow smaller and more complex, manufacturers are constantly in search of new and better means for removing excess heat from semiconductor devices to boost reliability and performance.

The moving of heat, particularly from a heat producing device such as a computer processor to the heat sink and fan is an important design issue – keeping the processor alive and other parts like the power supplies, transformers, mosfets and other parts would also scale up to other devices.  That would save a lot of equipment from an early demise, which could include a lot of hours and expense used to mange a recovery.

The list reaches into the future too.  New devices with advances in cooling computer chips and lighting-emitting diode (LED) devices, collecting solar power, harvesting waste heat, and other applications should get to market sooner. With photovoltaic devices, for example, better heat transfer leads to more efficient conversion of sunlight to electrical power. LED makers are also looking for ways to increase efficiency by reducing the percentage of input power lost as heat.  For improvements both in efficiency and costs heat management is an important matter.

Ganapati Ramanath, professor in the Department of Materials Science and Engineering at Rensselaer, who led the new study, said the ability to enhance and optimize interfacial thermal conductance should lead to new innovations in these and other applications.

Heat Transfer Nanoglue Graphic Representation. Click image for the largest view. Image Credit: Rensselaer Polytechnic Institute.

The interdisciplinary team at Rensselaer sandwiched a layer of ultrathin “nanoglue” between copper and silica, demonstrating a four-fold increase in thermal conductance at the interface between the two materials.  At less than a nanometer – or one billionth of a meter – thick, the nanoglue is a layer of molecules that form strong links with the copper (a metal) and the silica (a ceramic), which otherwise would not stick together well.

This kind of nanomolecular locking improves adhesion, and also helps to sync up the vibrations of atoms that make up the two materials which, in turn, facilitates more efficient transport of heat particles called phonons. Beyond copper and silica, the research team has demonstrated their approach works with other metal-ceramic interfaces.

Ramanath explains, “Interfaces between different materials are often heat-flow bottlenecks due to stifled phonon transport. Inserting a third material usually only makes things worse because of an additional interface created. However, our method of introducing an ultrathin nanolayer of organic molecules that strongly bond with both the materials at the interface gives rise to multi-fold increases in interfacial thermal conductance, contrary to poor heat conduction seen at inorganic-organic interfaces. This method to tune thermal conductance by controlling adhesion using an organic nanolayer works for multiple materials systems, and offers a new means for atomic- and molecular-level manipulation of multiple properties at different types of materials interfaces. Also, it’s cool to be able to do this rather unobtrusively by the simple method of self-assembly of a single layer of molecules.”

Results of the new study, titled “Bonding-Induced Thermal Conductance Enhancement At Inorganic Heterointerfaces Using Nanomolecular Monolayers,” were published online last week by Nature Materials, and will appear in an upcoming print edition of the journal.

Co-author Pawel Keblinski, professor in the Department of Materials Science and Engineering at Rensselaer discusses the experiments and theory to validate their findings with, “Our study establishes the correlation between interfacial bond strength and thermal conductance, which serves to underpin new theoretical descriptions and open up new ways to control interfacial heat transfer.”

Masashi Yamaguchi, associate professor in the Department of Physics, Applied Physics, and Astronomy at Rensselaer whips up some enthusiasm with, “It is truly remarkable that a single molecular layer can bring about such a large improvement in the thermal properties of interfaces by forming strong interfacial bonds. This would be useful for controlling heat transport for many applications in electronics, lighting, and energy generation.”

Out here in the real world the obvious question that comes up is just how manufacturing is going to machine the surfaces to get to the tolerances noted.  This is very demanding accuracy.

The improvement though is likely a starting place for further development and shows a new level of achievement.

The National Science Foundation (NSF), who is pretty happy with the results, backs the Rensselaer research.  Clark V. Cooper, senior advisor for science at the NSF Directorate for Mathematical and Physical Sciences, who formerly held the post of program director for Materials and Surface Engineering adds more depth to the work with, “The overarching goal of Professor Ramanath’s NSF-sponsored research is to elucidate, using first-principles-based models, the effects of molecular chemistry, chemical environment, interface topography, and thermo-mechanical cycling on the thermal conductance of metal-ceramic interfaces modified with molecular nanolayers. Consistent with NSF’s mission, the focus of his research is to advance fundamental science, but the potential societal benefits of the research are enormous.”

An NSF program director for the Division of Electrical, Communications, and Cyber Systems at the NSF Directorate for Engineering Anupama B. Kaul adds and amplifies the importance of the work with, “This is a fascinating example of the interplay between the physical, chemical, and mechanical properties working in unison at the nanoscale to determine the heat transport characteristics at dissimilar metal-ceramic interfaces. The fact that the organic nanomolecular layer is just a monolayer in thickness and yet has such an important influence on the thermal characteristics is truly remarkable. Dr. Ramanath’s results should be particularly valuable in nanoelectronics where heat management due to shrinking device dimensions continues to be an area of active research.”

The implications of the work are simply huge.  The amount of heat simply radiated off into space by humans is a stunning share of our energy budget.  A fast and efficient movement of heat to other uses is a goal worthy of enormous investment.  Well over half of the world’s energy is just lost as well as the money used to buy the energy and fuels. It’s a huge number.

We know a lot more of what its important to know.


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