By Josh Perry, Editor
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A team of engineers from Stanford University (Palo Alto, Calif.) have developed a nanoscale thermal transistor that conducts heat away from electronic components to limit the impact of excessive heat, according to a report from the school.

A nanoscale thermal transistor could switch heat transfer on an off to protect electronics. (Wikimedia Commons)

“Researchers have been trying to develop heat switches for years,” the report explained. “Previous thermal transistors proved too big, too slow and not sensitive enough for practical use. The challenge has been finding a nanoscale technology that could toggle on and off repeatedly, have a large hot-to-cool switching contrast and no moving parts.”

The thermal transistor was composed of a 10-nanometer thick layer of molybdenum disulfide. The material was soaked in a liquid with lithium ions. Applying an electrical charge caused the lithium atoms to infuse into the molybdenum disulfide crystals. When the lithium concentration increased, they pushed apart the crystal’s atoms and made it harder for heat transfer to occur.

“Besides enabling dynamic heat control, the team’s results provide new insights into what causes lithium ion batteries to fail,” the article added. “As the porous materials in a battery are infused with lithium, they impede the flow of heat and can cause temperatures to shoot up. Thinking about this process is crucial to designing safer batteries.”

Even the researchers insist that the development of working nanoscale thermal transistors in electronics applications is a long way away and the potential applications for this technology are largely unknown. The article said, “The researchers say this technology is comparable to where the first electronic transistors were some 70 years ago, when even the inventors couldn’t fully envision what they had made possible.”

The research was recently published in Nature Communications. The abstract read:

“The ability to actively regulate heat flow at the nanoscale could be a game changer for applications in thermal management and energy harvesting. Such a breakthrough could also enable the control of heat flow using thermal circuits, in a manner analogous to electronic circuits.

“Here we demonstrate switchable thermal transistors with an order of magnitude thermal on/off ratio, based on reversible electrochemical lithium intercalation in MoS₂ thin films. We use spatially-resolved time-domain thermoreflectance to map the lithium ion distribution during device operation, and atomic force microscopy to show that the lithiated state correlates with increased thickness and surface roughness.

“First principles calculations reveal that the thermal conductance modulation is due to phonon scattering by lithium rattler modes, c-axis strain, and stacking disorder.

“This study lays the foundation for electrochemically-driven nanoscale thermal regulators, and establishes thermal metrology as a useful probe of spatio-temporal intercalant dynamics in nanomaterials.”