Atomic structures and electronic properties of Ni or N modified Cu/diamond interface
The interfacial stability of copper/diamond directly affects its mechanical properties and thermal conductivity. The atomic structures and electronic properties of Cu/diamond and Cu/X/diamond interfaces have been identified to investigate the effect of interfacial additive X (X = Ni or N) on the low-index interfacial adhesion of copper/diamond composites. For unmodified composites, the interfacial stability decreases in the order of Cu(0 0 1)/diamond(0 0 1) > Cu(1 1 1)/diamond(1 1 1) > Cu(0 1 1)/diamond(0 1 1). The metallic interfacial additive Ni is found to enhance the Cu(0 1 1)/diamond(0 1 1) interfacial stability and exchange the interfacial stability sequence of (0 1 1) and (1 1 1) composites. The nonmetallic element N will promote the stability of Cu(1 1 1)/diamond(1 1 1) but not alter the stability order of the composites at different interfaces. To explain the origin of interfacial stability, a series of analyses on atomic structures and electronic properties have been carried out, including the identification of the type of formed interfacial boundaries, the measurement of interfacial bond lengths, and the calculations of density of states, bond populations, and atomic charge. The stability of the interface is found to be related to the type of formed interfacial boundary and bond, the interfacial bond populations, and the interfacial bond numbers. The layer-projected density of states reveals that all of the considered interfaces exhibit metal characteristics. The interfacial Ni additive is found to be an electron donor contributing the electrons to its bonded Cu and C atoms while the interfacial N atom is an electron acceptor where it mainly accepts the electrons from its bonded Cu and C.