Adhesion at diamond/metal interfaces: A density functional theory study

Abstract

Experimental studies on relationships between the electron work function, adhesion, and friction for 3d transition metals J. Appl. Phys. 95, 7961 (2004) To understand the basic material properties required in selecting a metallic interlayer for enhanced adhesion of diamond coatings on the substrates, the interfaces between diamond and metals with different carbide formation enthalpies ͑Cu, Ti, and Al͒ are studied using density functional theory. It is found that the work of separation decreases, while the interface energy increases, with the carbide formation enthalpy ⌬H f ͑TiϽ AlϽ Cu͒. By comparing the work of separation at the interface with the work of decohesion of the metal, we found that the fracture is more likely to initiate in the metal phase near the interface; therefore a metal phase with a larger surface energy, ␥ s ͑TiϾ CuϾ Al͒, is needed to achieve a higher overall interface strength. In addition, when the surface energy is larger than the interface energy, a wetted diamond/metal interface is formed during diamond nucleation, providing the strongest adhesion compared to other growth modes. These results indicate that a strong carbide-forming ability and a large surface energy of the interlayer promote nucleation and enhance the adhesion and interface strength of the coating/substrate system.

Qualitative link between work of adhesion and thermal conductance of metal/diamond interfaces

“…Two observations arise: i) when interfacial hydrogen is present a negligible amount of electrons are shared between the metal and the carbon atoms, which explains the weak interfacial bonding as ob- Table II, ii) more electrons are shared through the Ni/C than through the Cu/C interface, corroborating the lower work of adhesion found for the latter case (Table II). For the Ni/C case, we find a high W adh value of 5 Jm −2 , which is close to that of the Ti/C interface found by Guo et al 31 , 5.77 Jm −2 . The fact that configuration A has higher W adh in this case disagrees with the results by Pickett et al 59 , who found that configuration B has a higher W adh value.…”

“…In this work, we explore the link between the work of adhesion (W adh ) between Cu or Ni thin films and a diamond substrate calculated using DFT and the TBC of these interfaces as measured by TDTR. We also extend this analysis to the Al and Ti/diamond systems since the values of W adh in these cases already exist in the literature 30,31 . Even though the interfacial stiffness is the quantity expected to influence directly the passage of phonons through a metal/diamond interface, the work of adhesion is the quantity preferred in this study as it is easier to measure.…”

“…Moreover, none of these techniques make sure that the delamination occurs at the interface and not in the few layers surrounding it 29 . An altogether different approach that does not suffer from these issues is to employ theoretical methods such as calculations within the framework of Density-Functional-Theory (DFT) to address the problem of adhesion 30,31 .…”

Thermal boundary conductance of transition metals on diamond

“…Another explanation would be that the species passivating the diamond surface differ from one sample to the other, for example, due to slight misorientations of the crystal. Indeed, the presence of hydrogen at a metal/diamond interface has already been observed to reduce substantially the TBC Lyeo and Cahill, 2006), its binding force (Guo et al, 2010;Qi and Hector, 2003) as well as its electrical properties (Kageshima and Kasu, 2009) and the polishing process is expected to leave a mainly hydrogenated surface; but the hydrogen surface density changes with orientation (Kawarada, 1996). However, the presence of oxygen seems to be bene cial and is known to change signi cantly other interfacial properties, for example, work function (Gamo et al, 2007a(Gamo et al, , 2007b and electronic properties (Mori et al, 1991;Zheng et al, 2001).…”

Adhesion strength and nucleation thermodynamics of four metals (Al, Cu, Ti, Zr) on AlN substrates

“…Surface energies and interface energies are thermodynamically well defined, and are often important parameters for many thermodynamic models [12][13][14], but are difficult to measure experimentally. Computations and simulations have become an alternative and effective tool for obtaining these parameters.…”