Au Nanosheets-Assisted Structural Phase Transitions, In Situ Monitoring of the Enhanced Crystallinity, and Their Effect on the Optical and Dielectric Properties of CuSe/Au/CuSe Thin Films

Abstract

Herein, stacked layers of copper selenide thin films comprising Au nanosheets in its structure are fabricated and characterized. The CuSe/Au/CuSe (CAC) thin films are prepared by the thermal evaporation technique under a vacuum pressure of 10−5 mbar. It is shown that Au nanosheets improve the stoichiometric growth of the CuSe thin films and induce the structural phase transitions from cubic to hexagonal. In addition, the in situ monitoring of the structural modifications in the CAC in the temperature range of 293–473 K proves the permanent enhanced crystallinity of the films. Optically, while the Au nanosheets increase the light absorbability and redshifts the energy band gap of CuSe, the in situ heating blueshifts the energy band gap. Moreover, insertion of Au nanosheets between layers of CuSe and heating them at 473 K significantly increase the dielectric constant and the optical conductivity by more than five times. Moreover, the drift mobility of charged carriers, the scattering time at femtosecond level, and the plasmon frequency are remarkably enhanced. Values of plasmon frequency exceed 6.0 GHz nominating the CAC films as signal receivers suitable for 5G technology.