Thermal boundary conductance of artificially and systematically designed grain boundaries of Silicon measured by laser heterodyne photothermal displacement method

The overall physical properties of polycrystalline materials vary depending on the microscopic individual grain boundary (GB) properties and their structures. Unlike previous studies that only examined the structure and properties of a specific GB, this study focuses on understanding the thermal boundary conductance (TBC) through artificial and systematic changes in the GB structures. This is achieved by combining an advanced technique to map local thermal expansion displacement using the laser heterodyne photothermal displacement method and a unique crystal growth method that induces spontaneous changes in the GB structures. As a result, we could quantify the TBC of the GB in silicon, considering the changes in three structural parameters of GB: azimuthal misorientation (α), asymmetry angle (β), and deviation angle (θ) from the growth direction. Our findings reveal that the TBC increases with increasing θ, whereas parameters α and β have negligible effects. The underlying physics of this relationship is discussed in terms of local carrier concentration and impurity segregation. These results demonstrate the crucial role of the GB structures in influencing the local TBC, shedding light on potential avenues for enhancing the macroscopic properties of polycrystalline materials by engineering GBs.