Abstract: Disclosed are stack structures and their fabrication methods. The method comprises providing a growth chamber with a first two-dimensional material layer, forming a defect on a surface the first two-dimensional material layer, and forming a second two-dimensional material layer on the first two-dimensional material layer. The step of forming the second two-dimensional material layer includes supplying the growth chamber with a transition metal precursor and a chalcogen precursor, and reacting the first two-dimensional material layer and the transition metal precursor with each other.