Tunable thermal conductivity and mechanical properties of metastable silicon by phase engineering

The extensive applications of cubic silicon in flexible transistors and infrared detectors are greatly hindered by its intrinsic properties. Metastable silicon phases, such as Si-III, IV, and XII, prepared using extreme pressure methods, provide a unique “genetic bank” with diverse structures and exotic characteristics. However, exploration of their inherent physical properties remains underdeveloped. Herein, we demonstrate the phase engineering strategy to modulate the thermal conductivity and mechanical properties of metastable silicon. The thermal conductivity, obtained via the Raman optothermal approach, exhibits broad tunability across various Si-I, III, XII, and IV phases. The hardness and Young’s modulus of Si-IV are significantly greater than those of the Si-III/XII mixture, as confirmed by the nanoindentation technique. Moreover, it was found that pressure-induced structural defects can substantially degrade the thermal and mechanical properties of silicon. This systematic investigation offers a feasible route for designing novel semiconductors and further advancing their desirable applications in advanced nanodevices and mechanical transducers.