We have recently synthesized a colloidal solution of (what we think is) 2D heterostructure. We first prepared a colloidal solution of an exfoliated 2D material and synthesized a different quasi-2D material in that solution. We have shown that the second material is indeed synthesized. We have a strong hunch that the latter material is being synthesized on top of the exfoliated 2D material, but this is hard to verify. What is the best way of checking if the two materials are existing separately, forming heterostructure, or both?