Designed Synthesis and Structure-Property Relationships of Kinetically Stable [(PbSe)<inf>1+Î&amp;acute;</inf>]<inf>m</inf>(VSe<inf>2</inf>)<inf>1</inf> (m = 1, 2, 3, 4) Heterostructures

Understanding structure-function relationships is essential to guide the designed synthesis of novel materials with emergent properties. In this work, we targeted the metastable heterostructures [(PbSe)1+δ]m(VSe2)1, where m = 1-4, to test if the charge density wave (CDW) transition temperature increases as the layer thickness separating the VSe2 monolayers increases, as was observed when SnSe was the separating layer. The modulated elemental reactant approach was used to make the targeted products. This approach involves depositing elemental layers in which the number of atoms of each element per square angstrom in Pb|Se and V|Se bilayers equals the number calculated for a rock salt-structured PbSe bilayer and a CdI2-structured VSe2 slab, respectively. Layered elemental precursors with the correct composition and nanoarchitecture for each of the targeted compounds were prepared by repeatedly depositing a single V|Se bilayer followed by m Pb|Se bilayers. Precursors close to the targeted number of atoms per unit area were determined via X-ray fluorescence and the correct nanoarchitecture self-assembled to the targeted compounds during a low-temperature anneal. Resistivity measurements show that the number of PbSe layers per repeat unit (m) does not change the charge density transition onset temperature as previously reported for the analogous [(SnSe)1+δ]m(VSe2)1 compounds. The temperature dependence and absolute values of the resistivity of the m = 3 and 4 heterostructures scale as expected for composite behavior. The difference in the thickness dependence of the CDW transition between the PbSe- A nd SnSe-containing compounds highlights that the identity of the intervening rock salt layer plays a more important role in modifying the CDW onset temperature than the separation of the VSe2 layers.