Directly Measuring How Surface Defects Affect Phonon Propagation

For the first time, researchers have directly measured how much “lifetime shortening” acoustic phonons (the primary carriers of heat) experience from surface defects. This process is a key bottleneck for thermal management in modern microelectronics, but it has been “extremely challenging to measure” until now [1].

Using a highly sensitive Helium Spin Echo (HeSE) spectrometer, the team studied a nickel (Ni(111)) surface. They precisely controlled the number of surface defects using argon sputtering to create them and annealing to remove them.

They found:

• Phonon lifetimes decreased (and linewidths broadened) linearly as the surface defect density increased.
• This defect-induced scattering adds a temperature-independent component to the phonon’s decay, meaning the defects contribute a fixed amount of scattering regardless of the temperature.

This work provides the first quantitative estimate for this fundamental scattering rate , which is critical for engineering the thermal properties of future electronics, especially 2D materials.

[1] PHYSICAL REVIEW LETTERS 132, 056202 (2024).