Melting transition in the van der Waals superlattice of self-intercalated 2H-TaS2

For layered materials, the introduction of an atomic species into the van der Waals gap – known as intercalation – provides an avenue for modification of the electronic, magnetic, and structural properties of the parent compound. Recently, a class of ultra-thin, self-intercalated transition metal dichalcogenide materials have been realized, and shown to exhibit structural and magnetic ordering. Here, we demonstrate the post-growth intercalation of Ta into 2H-TaS2 through annealing 60 nm thick sample films that are initially in the 1T phase to 600 K. A 2 x 2 superlattice associated with ordering of the intercalate is observed in these annealed samples, and the dynamics of this superlattice are probed with ultrafast electron diffraction revealing a Debye-Waller like response at room temperature. The superlattice exhibits a reversible equilibrium order-disorder melting transition around 483 K. Additionally, the in-plane resistivity vs. temperature reveals significant suppression of the 3 x 3 CDW transition at 75 K, but two new anomalies are present: one at 231 K and one at 271 K. This work expands on the growing study of self-intercalated TMD's and outlines a simple process for post growth intercalation.