Electricity generated by temperature differences

Electricity generated by temperature differences doesn’t appear to be affected measurably by grain boundaries placed in its way in nanoscale gold wires.

By Mike Williams September 11, 2020

Using a novel optical detection system, researchers at Rice University found that electricity generated by temperature differences doesn’t appear to be affected measurably by grain boundaries placed in its way in nanoscale gold wires, while strain and other defects in the material can change this “thermoelectric” response.

The phenomenon could allow for the detection of crystalline defects in conducting materials that are difficult to spot and characterize with even the most advanced microscopic methods.

The result was a surprise to researchers led by Rice physicist Doug Natelson and doctoral alumna Charlotte Evans, now a staff scientist at Sandia National Laboratories, who pursued the explanation after seeing measurements they couldn’t explain a few years ago.

“A lot of times, people think about the thermoelectric effect when they’re building solar panels or generating power from this or that,” Evans said. “We argue instead that the thermoelectric effect is a really interesting diagnostic tool.”

Grain boundaries are the planes in materials where misaligned crystals meet, forcing atoms along the edge to adjust as they bind to their neighbors. Measurements in bi-crystal gold nanowires produced by the group of Stanford University electrical engineer and co-author Jonathan Fan showed no detectable effect on thermoelectric voltages at the grain boundary. The electrons in the metal simply ignored the single grain boundary.

Rice’s optical detection system reveals small structural defects in a gold nanowire that may appear to be a perfect crystal under a scanning electron microscope. The discovery has implications for making better thin-film electronic devices. Courtesy: Charlotte Evans, Natelson Research Group/Rice University[/caption]

“If you look at the plain EBSD data, it looks as though you have a pristine crystal,” she said. “And it’s not until you post-process the data and look at how each pixel varies from the next that you would see small distortions along the length of the wire. It’s complicated to detect. That’s why it’s so remarkable that we could detect these little variations with a laser.”

“So if you want to do something clever and exploit the thermoelectric response, you need to understand the devices you’re making with standard, top-down fabrication methods,” Natelson said. “The stress and strain and what seemed like minor structural imperfections can have an easily detectable influence.”

– Edited by Chris Vavra, associate editor, Control Engineering, CFE Media and Technology, cvavra@cfemedia.com.


Author Bio: Mike Williams is a senior media relations specialist in Rice University's Office of Public Affairs.