Impurities and defects within crystals are effective scatterers of acoustic phonons, the quantized units of lattice vibration of the crystal. The symmetry of the crystal itself can result in elaborate, but predictable, patterns of phonon propagation through the crystal, and these can be visualized with phonon imaging techniques.
Using a wafer direct-bonding technique, in which two wafers can be ideally bonded together without introducing phonon scattering defects, Msall et al. show that the resultant phonon trajectories at the interface can be engineered by introducing a twist angle between the crystal orientations in the wafers. These trajectories first were simulated computationally and then determined experimentally. The agreement between the data demonstrate that such a technique may prove useful for phonon lensing or for applications requiring phonon management in which heat must be dissipated or directed in particular directions. -- ISO
Phys. Rev. Lett. 85, 598 (2000).
