In addition, the component of oxide layers (atoms above the deepest oxygen) on the surface is Cu79O89 (Cu71O89 for the 300 atoms case), indicating that the surface Cu is mainly Cu(II). After annealing, the component changes to Cu112O89 (Cu139O89 for the 300 atoms case) which is Cu(II) and Cu(I) and the thickness changes from 17 Å to 21 Å, which is comparable to the experimental findings (2∼3 nm) .