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 much hindered by its intrinsic properties. Metastable silicon phases, such as Si-III, IV and XII prepared using extreme pressure method, provide a unique "genetic bank" with diverse structures and exotic characteristics, however, exploration on their inherent physical properties remains immature. Herein, we demonstrate the phase engineering strategy to modulate the thermal conductivity and mechanical properties of metastable silicon. The thermal conductivity obtained via Raman optothermal approach presents the broad tunability across various Si-I, III, XII and IV phases. The hardness and Young's modulus of Si-IV are remarkably greater than those of Si-III/XII mixture, confirmed by nanoindentation technique. Moreover, it was found that the pressure-induced structural defects can substantially degrade the thermal and mechanical properties of silicon. This systematic investigation can offer feasible route to design novel semiconductors and further advance their desirable applications in advanced nanodevices and mechanical transducers.