Synthesis and Thermal Properties of Solid-State Structural Isomers: Ordered lntergrowths of SnSe and MoSe2

A family of structural isomers [(SnSe)(1.05)](m)(MoSe2)(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)(MoSe2)(4), [(SnSe)(1).(05)](3)(MoSe2)(3)[(SnSe)(1.05)](1)(MoSe2)(1), [(SnSe)(1.05)](3)(MoSe2)(2)[(SnSe)(1.05)](1)(MoSe2)(2), [(SnSe)(1.05)](2)(MoSe2)(3)[(SnSe)(1.05)](2)(MoSe2)(1), [(SnSe)(1.05)](2)(MoSe2)(1)[(SnSe)(1.05)](1)(MoSe2)(2)[(SnSe)(1.05)](1)(MoSe2)(1), and [(SnSe)(1.05)](2)(MoSe2)(2)[(SnSe)(1.05)](1)(MoSe2)(1)[(SnSe)(1.05)](1)(MoSe2)(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 (similar to 0.08 Wm(-1) K-1) and independent of the number of SnSe-MoSe2 interfaces within uncertainty. The poor thermal transport in these layered isomers is attributed to a large cross-plane thermal resistance created by SnSe-MoSe2 and MoSe2-MoSe2 turbostratically disordered van der Waals interfaces, the density of which has less variation among the different compounds than the SnSe-MoSe2 interface density alone.