Cohesion strength and atomic structure of W-Cu graded interfaces

W-Cu graded interface is a solution to big differences of properties between W and Cu, while the number and composition of graded layers in the literature are quite different. The present first principles calculation reveals that W-rich graded interfaces possess higher strength and lower interface energy than Cu-rich counterparts. It shows that the differences of thermal expansion and Young's modulus between overlayer and substrate are decisive factors in the design of Cu-rich and W-rich graded interfaces, respectively. A graded structure of W₈Cu₁/W₇Cu₂/W₆Cu₃/Cu₆W₃/Cu₈W₁ is therefore suggested theoretically.