Controllable Synthesis of Bandgap-Tunable CuS_xSe_1-x Nanoplate Alloys

Composition engineering is an important approach for modulating the physical properties of alloyed semiconductors. In this work, ternary CuS_xSe_1-x nanoplates over the entire composition range of 0≤x≤1 have been controllably synthesized by means of a simple aqueous solution method at low temperature (90 °C). Reaction of Cu²⁺ cations with polysulfide/-selenide ((S_nSe_m)^2-) anions rather than independent S_n^2- and Se_m^2- anions is responsible for the low-temperature and rapid synthesis of CuS_xSe_1-x alloys, and leads to higher S/Se ratios in the alloys than that in reactants owing to different dissociation energies of the Se-Se and the S-S bonds. The lattice parameters 'a' and 'c' of the hexagonal CuS_xSe_1-x alloys decrease linearly, whereas the direct bandgaps increase quadratically along with the S content. Direct bandgaps of the alloys can be tuned over a wide range from 1.64 to 2.19 eV. Raman peaks of the S-Se stretching mode are observed, thus further confirming formation of the alloyed CuS_xSe_1-x phase. Great composers: Homogeneously alloyed CuS_xSe_1-x nanoplates have been controllably synthesized over the entire range of 0≤x≤1 by direct reaction of Cu²⁺ cations with polysulfide/-selenide ((S_nSe_m)^2-) anions. Tunable Raman and optical absorption properties of the CuS_xSe_1-x nanoplates were achieved by composition engineering.