Small-rotation-angle moiré structures of 2H TaSe₂ monolayers on Au(111)

Direct synthesis of two-dimensional (2D) materials with moiré patterns can provide 2D moiré structures with a clean interface and be useful for future electronics applications. However, the synthesis of moiré structures with small rotation angles is challenging since such structures possess the tendency to untwist during high temperature synthesis. Here, we study the moiré structures formed by epitaxially grown 2H TaSe₂ monolayers on Au(111). By resolving atomic configurations using scanning tunneling microscopy (STM), we reveal the as-grown TaSe₂ monolayers demonstrate small rotation angles between 0° to 3° with respect to the underlying Au lattices. We demonstrate that the deposition sequence of Se and Ta during growth can make an important difference: first depositing Se on Au predominantly gives small rotation angles, while first depositing Ta on Au predominantly results in perfectly aligned lattices. Further, we unveil that defects, including hole and line defects, are closely related to the changing orientations of moiré superlattices. Our work provides important insights for the synthesis of small-twist-angle moiré structures and will facilitate future studies of TaSe₂ and moiré physics and devices in general.