Intrinsic stress evolution in nanocrystalline diamond thin films with deposition temperature

et al. 2009

Phys. Rev. Lett.

Self Cite

First principles calculations were integrated with cohesive zone and growth chemistry models to demonstrate that adsorbed species can significantly alter stresses associated with grain boundary formation during polycrystalline film growth. Using diamond growth as an example, the results show that lower substrate temperatures increase the hydrogen content at the surface, which reduces tensile stress, widens the grain boundary separations, and permits additional atom insertions that can induce compressive stress. More generally, this work demonstrates that surface heteroatoms can lead to behavior which is not readily described by existing models of intrinsic stress evolution.

mentioning

confidence: 98%

“…Energy variation when two diamond ð100Þ-ð2 Â 1Þ surfaces approach each other at different H coverage. The atomic structure is for 25% H coverage, where light gray (green) atoms are H and dark gray atoms are C. [7]. The H content of these films was obtained from elastic recoil detection (ERD) measurements.…”

mentioning

confidence: 99%

Impact of Surface Chemistry on Grain Boundary Induced Intrinsic Stress Evolution during Polycrystalline Thin Film Growth

Sheldon

et al. 2009

Phys. Rev. Lett.

Self Cite

“…6 The poor adhesion of diamond coatings has been attributed to the high residual stress in the coatings and the weak interfaces between the coatings and substrates. In addition to reducing the residual stresses in diamond coatings, 7,8 many efforts, including preseeding, scratching, and adding an interlayer, have been made to enhance the interfacial adhesion of the diamond/metal systems. 9 Adding an appropriate interlayer between the diamond coating and substrate can effectively improve the interfacial adhesion.…”

Section: Introductionmentioning

confidence: 99%

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

Journal of Applied Physics

2010

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.

“…Significant progresses have been made in minimizing the coating residual stresses, including both reducing the deposition temperature to lower the thermal stress and engineering the structure of grain boundaries to release the intrinsic stress. 1,2 However, it remains a great challenge to strengthen and toughen the interface of CVD diamond coating/substrate. In this paper, we present a new and versatile interface adhesion mechanism controlling the nucleation, growth, and alignment of multiple microcracks in the interlayer by utilizing the anisotropic fracture characteristics of interlayer materials.…”

Section: Introductionmentioning

confidence: 99%

Enhance diamond coating adhesion by oriented interlayer microcracking

Journal of Applied Physics

Xiao

et al. 2009

In this paper, we report a microcrack toughening mechanism for enhancing the adhesion of diamond coating. The oriented microcracks were formed within the TiC interlayer to dissipate strain energy and accommodate deformation via the crack opening-closing mechanism, thus enhancing the coating/substrate interfacial toughness. The delamination of diamond coating was effectively prevented when the parallel microcracks were confined within the interlayer and arrested at interfaces of coating/interlayer/substrate. Density functional theory calculations revealed that the highly anisotropic fracture strength of the TiC phase energetically favors crack initiation and propagation along (100) planes only, which are 54.7° away from the interface. These microcracks are constrained inside the interlayer by the two strong interfaces in the substrate/interlayer/coating system. The new microcrack toughening mechanism with these combined features has a wide application to enhance the adhesion of thin-film coatings.