  Structural engineering opens a door to manipulating the structures and thus
tuning the properties of two-dimensional materials. Here, we report a
reversible structural transition in honeycomb CuSe monolayer on Cu(111) through
scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES).
Direct selenization of Cu(111) gives rise to the formation of honeycomb CuSe
monolayers with 1D moir\'e structures (stripe-CuSe), due to the asymmetric
lattice distortions in CuSe induced by the lattice mismatch. Additional
deposition of Se combined with post annealing results in the formation of
honeycomb CuSe with quasi-ordered arrays of triangular holes (hole-CuSe),
namely, the structural transition from stripe-CuSe to hole-CuSe. Further,
annealing the hole-CuSe at higher temperature leads to the reverse structural
transition, namely from hole-CuSe to stripe-CuSe. AES measurement unravels the
Se content change in the reversible structural transition. Therefore, both the
Se coverage and annealing temperature play significant roles in the reversible
structural transition in CuSe on Cu(111). Our work provides insights in
understanding of the structural transitions in 2D materials.
