Fullerene-like Carbon Nitride: A Resilient Coating Material
- PDF / 972,010 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 67 Downloads / 194 Views
Fullerene-like Carbon Nitride: A Resilient Coating Material
Lars Hultman, Jörg Neidhardt, Niklas Hellgren, Hans Sjöström, and Jan-Eric Sundgren Abstract Carbon nitride is an emerging material for wear-resistant coatings. The fullerene-like CNx compounds generally exhibit extreme elasticity in combination with a low work of indentation hardness.Yet CNx shows a low-to-moderate resistance to penetration, depending on deposition conditions. Since the deformation energy is predominantly stored elastically, the material possesses an extremely resilient character. This new class of materials consists of sp 2-coordinated basal planes that are buckled from the incorporation of pentagons and cross-linked at sp 3-hybridized C sites, both of which are caused by structural incorporation of nitrogen. Carbon nitride thus deforms elastically due to bending of the structural units. The orientation, radius of curvature of the basal planes, and the degree of cross-linking between them defines the structure and properties of the material. Due to the unique deformation behavior, the hardness requires special care to assess, but can be very high for films with a large degree of cross-linking. This article is a review of the research on CNx films deposited by reactive magnetron sputtering, with examples from our recent work. The findings are significant for the design of fracture-tough materials. Keywords: carbon nitride, fullerene-related materials, superhard coating materials, thin films.
194
Fullerene-like Materials Fullerene-like or fullerene-related solid materials are emerging on a broad front. They consist of inherently bent and/or intersecting basal planes, such as would be obtained by inserting odd-member rings in a hexagon mesh. Materials systems include CNx and C,15–17 BNC,18,19 BN,20 MoS2,21 TlO,22 NbS2,23 and WS2.24 Out of these, only the C, C-N, and B-N-C systems have been shown to exhibit the crosslinking of basal planes that enables the material to be mechanically strong in three dimensions. Fullerene-like CNx compounds exhibit a large variation in the degree of basal-plane curvature and cross-linking. Thus, they constitute solid materials with a large spread in physical properties such as elastic modulus and electrical conductivity, while having extraordinary strength in common. Figure 1 shows an example of a pronounced fullerene-like CNx film material. The plan-view (normal to the substrate) high-resolution transmission electron microscopy image shows a CN0.12 film deposited at 450C by reactive magnetron sputtering.7 Lattice fringes of curved planes with a separation of 3.5 Å are resolved. The lower-right inset in Figure 1 shows a schematic illustration5 of the buckling of an sp 2-coordinated basal plane caused by the incorporation of pentagons.
Structure-Zone Diagrams
A New Compound Material It is unusual for a material to find largescale application only a few years after its discovery. But this has been the case for carbon nitride materials, which are already widely used as protective coatings on hard disks an
Data Loading...
