Synthesis and Thermal Properties of Solid-State Structural Isomers: Ordered Intergrowths of SnSe and MoSe_2

摘要

A family of structural isomers [(SnSe)_(1.05)]_m(MoSe_2)_n were prepared using the modulated elemental reactant method by varying the layer sequence and layer thicknesses in the precursor. By varying the sequence of Sn-Se and Mo-Se layer pairs deposited and annealing the precursors to self-assemble the targeted compound, all six possible isomers [(SnSe)_(1.05)]_4(MoSe_2)_4, [(SnSe)_(1.05)]_3(MoSe_2)_3[(SnSe)_(1.05)]_1(MoSe_2)_1, [(SnSe)_(1.05)]_3(MoSe_2)_2[(SnSe)_(1.05)]_1(MoSe_2)_2, [(SnSe)_(1.05)]_2(MoSe_2)_3[(SnSe)_(1.05)]_2(MoSe_2)_1, [(SnSe)_(1.05)]_2(MoSe_2)_1[(SnSe)_(1.05)]_1(MoSe_2)_2[(SnSe)_(1.05)]_1(MoSe_2)_1, and [(SnSe)_(1.05)]_2(MoSe_2)_2[(SnSe)_(1.05)]_1(MoSe_2)_1[(SnSe)_(1.05)]_1(MoSe_2)_1 were prepared. The structures were characterized by X-ray diffraction and electron microscopy which showed that all of the compounds have very similar c-axis lattice parameters and in-plane constituent lattice parameters yet distinct isomeric structures. These studies confirm that the structure, order, and thickness of the constituent layers match that of the precursors. The cross-plane thermal conductivity is found to be very low (～0.08 Wm~(-1) K~(-1)) and independent of the number of SnSe-MoSe_2 interfaces within uncertainty. The poor thermal transport in these layered isomers is attributed to a large cross-plane thermal resistance created by SnSe-MoSe_2 and MoSe_2-MoSe_2 turbostratically disordered van der Waals interfaces, the density of which has less variation among the different compounds than the SnSe-MoSe_2 interface density alone.