Engineering thermal conductivity at the nanoscale by He+ ion irradiation
The control of thermal conductivity of materials is key to advanced heat management for novel applications such as thermal insulation, thermoelectric energy harvesting, and efficient heat dissipation, although the methods have been restricted to the bulk-/microscale without flexibility in terms of tunable thermal conductivity value in one system. Here, we introduce helium (He+) ion irradiation to control thermal conductivities of silicon membrane which be able to have arbitrary values from single-crystalline to amorphous level. The continuous suppression of its thermal conductivity as the increase of He+ ion doses is nearly two orders of magnitude, well correlating with point defect generation and the gradual amorphization process of the lattice. Tuning the spot size, energy, and dose of the irradiation, we sculpture the Si membrane into arbitrary patterns that can be designed to control heat flow along the membrane, acting as a programmable nanoscale thermal metamaterial.
Speaker: Hwan Sung Choe
Department of Materials Science and Engineering, UC Berkeley
Omnidirectional Indoor Light Harvesting using Nanocone Metastructure Arrays
Speaker: Jipeng Qi
Department of Mechanical Engineering, UC Berkeley