11 research outputs found
Probing the sp^2 dependence of elastic moduli in ultrahard diamond films
The structural and elastic properties of diamond nanocomposites and
ultrananocrystalline diamond films (UNCD) are investigated using both empirical
potentials and tight binding schemes. We find that both materials are extremely
hard, but their superb diamondlike properties are limited by their sp^2
component. In diamond composites, the sp^2 atoms are found in the matrix and
far from the interface with the inclusion, and they are responsible for the
softening of the material. In UNCD, the sp^2 atoms are located in the grain
boundaries. They offer relaxation mechanisms which relieve the strain but, on
the other hand, impose deformations that lead to softening. The higher the sp^2
component the less rigid these materials are.Comment: 10 pages, 3 figures. to appear in Diamond and Relarted Material
Structure, stability and stress properties of amorphous and nanostructured carbon films
Structural and mechanical properties of amorphous and nanocomposite carbon
are investigated using tight-binding molecular dynamics and Monte Carlo
simulations. In the case of amorphous carbon, we show that the variation of
sp^3 fraction as a function of density is linear over the whole range of
possible densities, and that the bulk moduli follow closely the power-law
variation suggested by Thorpe. We also review earlier work pertained to the
intrinsic stress state of tetrahedral amorphous carbon. In the case of
nanocomposites, we show that the diamond inclusions are stable only in dense
amorphous tetrahedral matrices. Their hardness is considerably higher than that
of pure amorphous carbon films. Fully relaxed diamond nanocomposites possess
zero average intrinsic stress.Comment: 10 pages, 6 figure
Iron Oxide Nanoparticles Employed as Seeds for the Induction of Microcrystalline Diamond Synthesis
Iron nanoparticles were employed to induce the synthesis of diamond on molybdenum, silicon, and quartz substrates. Diamond films were grown using conventional conditions for diamond synthesis by hot filament chemical vapor deposition, except that dispersed iron oxide nanoparticles replaced the seeding. X-ray diffraction, visible, and ultraviolet Raman Spectroscopy, energy-filtered transmission electron microscopy , electron energy-loss spectroscopy, and X-ray photoelectron spectroscopy (XPS) were employed to study the carbon bonding nature of the films and to analyze the carbon clustering around the seed nanoparticles leading to diamond synthesis. The results indicate that iron oxide nanoparticles lose the O atoms, becoming thus active C traps that induce the formation of a dense region of trigonally and tetrahedrally bonded carbon around them with the ensuing precipitation of diamond-type bonds that develop into microcrystalline diamond films under chemical vapor deposition conditions. This approach to diamond induction can be combined with dip pen nanolithography for the selective deposition of diamond and diamond patterning while avoiding surface damage associated to diamond-seeding methods
Mimicking DNA stretching with the Static Mode method: Shear stress versus transverse pulling stress
International audienceDNA sequencing using nanopores is closer than ever to become a reality, but further research and development still need to be done, especially to unravel the atomic-scale mechanisms of induced DNA stretching. At this level, molecular modeling and simulation are essential to investigate DNA conformational flexibility and its response to the forces involved. In this work, through a “Static Mode” approach, we present a directed exploration of the deformations of a 27-mer subjected to externally imposed forces, as it could be in a nanopore. We show how the DNA sugar-phosphate backbone undergoes the majority of the induced deformation, before the base pairing is affected, and to what extent unzipping initiation depends on the force direction