A new study demonstrates that 167 MeV Xe ion irradiation can nano-pattern single-crystal yttrium aluminium garnet (YAG) with long amorphous cylindrical tracks, creating a crystalline–amorphous composite with strongly directional heat transport. Using high-resolution microscopy, molecular dynamics simulations, and multiple thermoreflectance techniques, the researchers showed that heat flows preferentially along the ion-beam direction while radial transport is increasingly suppressed as ion fluence rises. The work establishes swift heavy ion patterning as a precise route for engineering thermal anisotropy in robust functional materials.

Key findings

• Swift heavy ion irradiation produced microscale-long amorphous nano-tracks embedded in a crystalline YAG matrix, with the amorphous fraction tunable from isolated tracks to partial overlap by changing ion fluence.
• Thermal conductivity decreased in both directions with increasing irradiation, but the reduction was much stronger in the radial direction: at the highest fluence, cross-plane conductivity fell by about 6 times, while in-plane conductivity fell by about 15 times.
• The irradiated layer reached an in-plane thermal conductivity of 0.9 W/m·K, reflecting very strong suppression of lateral heat flow.
• Heat was conducted mainly along the ion-beam direction because elongated surviving crystalline domains acted as preferential axial pathways, while radial transport was damped by phonon scattering at multiple amorphous–crystalline boundaries.
• High-resolution STEM and simulations confirmed that the ion tracks consisted of an amorphous core with a defect-rich shell, and the Klemens model successfully estimated track dimensions consistent with microscopy and molecular dynamics results.
• The thermal anisotropy increased with ion-track density, showing that the degree of directionality can be systematically tuned by ion fluence.

Why it matters
Managing heat directionally is a major challenge in advanced electronics, memory devices, smart materials, and radiation-hardened systems. This study shows that swift heavy ion nano-patterning can convert a robust crystalline insulator into a material with controllable orientation-dependent thermal transport, opening a practical path toward next-generation thermal management platforms where heat must be guided in one direction and blocked in another.