No abstract

Tight-binding molecular dynamics simulations shed light into the fracture mechanisms and the ideal strength of tetrahedral amorphous carbon and of nanocomposite carbon containing diamond crystallites, two of the hardest materials. It is found that fracture in the nanocomposites, under tensile or shear load, occurs intergrain and so their ideal strength is similar to the pure amorphous phase. The onset of fracture takes place at weakly bonded sites in the amorphous matrix. On the other hand, the nanodiamond inclusions significantly enhance the elastic moduli, which approach those of diamond.

No abstract

No abstract

Monte Carlo simulations, supplemented by ab initio calculations, shed light into the energetics and thermodynamic stability of nanostructured amorphous carbon. The interaction of the embedded nanocrystals with the host amorphous matrix is shown to determine in a large degree the stability and the relative energy differences among carbon phases. Diamonds are stable structures in matrices with sp^3 fraction over 60%. Schwarzites are stable in low-coordinated networks. Other sp^2-bonded structures are metastable.Comment: 11 pages, 7 figure

No abstract

The initial stages of carbon alloying into the Si(001) surface are studied by scanning tunneling microscopy (STM) and density functional theory. Carbon increases the surface roughness compared to the clean surface and induces a c͑4 3 4͒ reconstruction. To explain experimental observations, we propose a novel surface reconstruction model that involves pairing of Si dimers mediated by the presence of a complex of a C dimer and four nearest neighbor subsurface C atoms. The model is backed by total energy and thermal stability simulations. Its calculated surface charge density agrees well with the filled state STM images. [S0031-9007(98)08302-1]

No abstract