In Raman spectroscopy, a laser interacts with the vibrating crystal lattice of materials, providing information about the chemical makeup of the materials.
"But we have not been able to incorporate in-situ stress or deformation into those chemical signatures," Tomar said. "Now we have combined nanomechanical measurements into Raman spectroscopy."
The researchers used the technique to study microscale silicon cantilevers, tiny diving-board shaped slivers about 7 microns thick, or roughly one-tenth the thickness of a human hair, and 225 microns long. The cantilevers were heated and stressed simultaneously. Surface stresses at the micro- and nanoscales were measured for the first time in conjunction with temperature change and a structure's deformation.
Findings show that heating a cantilever from 25 to 100 degrees Celsius while applying stress to the structure causes a dramatic increase in strain rate, or deformation.
The heating reduces bonding forces between atoms on the surface of the structures. The lower bonding force results in a "relaxed" state of the surface or near-surface atoms that progresses as the temperature increases, leading to cracks and device failure.
"The key is to be able to measure thermal and mechanical properties simultaneously because they are interrelated, and surface stress influences mechanical properties," Tomar said.
Findings are potentially important for the measurement of components in batteries to study stresses as they constantly expand and contract during charge-discharge cycles. Ordinary sensors are unable to withstand punishing conditions inside batteries.
However, because Raman spectroscopy uses a laser to conduct measurements, it does not have to be attached to the batteries, making possible a new type of sensor removed from the harsh conditions inside batteries.
"If you don't need onboard sensors you can go into extreme environments," he said. "You can learn how the stresses ar
|Contact: Emil Venere|