xxiii πανελληνιο ÏƒÏ Î½ÎµÎ´ÏÎ¹Î¿ Ï†Ï ÏƒÎ¹ÎºÎ·Ï‚ στερεας καταστασης & επιστημης ...

Fig.2 Top: cubic diamond nanocrystal embedded in a-C matrix before relaxation (left) and after relaxation (right).
Bottom: spherical diamond nanocrystal in a-C before relaxation (left) and after relaxation (right). On the left, white
atoms belong to the amorphous matrix and dark grey atoms to the diamond crystal. On the right, white and light grey
atoms are 4-fold and 3-fold coordinated a-C atoms, respectively, while dark grey are crystalline atoms.
We find a universal dependence of compressibility on the mass density that is valid for all carbon-based materials
studied here [5]. Compressibility decreases with increasing fraction of the diamond phase. On the other hand, the
optoelectronic properties of these materials are dominated by the amorphous phase: the calculated electronic density of
states, dielectric function and other related properties are found to be very similar to the respective quantities of pure a-
C. Our results suggest that the optoelectronic and mechanical properties of nanostructured amorphous carbon can be
tuned independently, as they rely on different phases of this composite material.
In the case of ultrananocrystalline diamond, our theoretical predictions about the dependence of mechanical
properties on the grain size may be applicable to nanocrystalline materials in general.
REFERENCES
1. C. Mathioudakis, G. Kopidakis, P.C. Kelires, C.Z. Wang, and K.M. Ho, “Physical Trends in Amorphous Carbon: A
Tight-Binding Molecular Dynamics Study”, Phys. Rev. B, 70, 125202 (2004).
2. C. Mathioudakis, G. Kopidakis, P.C. Kelires, M. Gioti, P. Patsalas, and S. Logothetidis, “Electronic and Optical
Properties of a-C from Tight-Binding Molecular Dynamics Simulations”, Thin Solid Films, 482, 151 (2005).
3. C. Mathioudakis, G. Kopidakis, P. Patsalas, and P.C. Kelires, “Disorder and Optical Properties of Amorphous
Carbon”, submitted.
4. G. Kopidakis, I.N. Remediakis, M.G. Fyta, and P.C. Kelires, “Atomic and Electronic Structure of Crystalline-
Amorphous Carbon Interfaces”, submitted.
5. I.N. Remediakis, M.G. Fyta, C. Mathioudakis, G. Kopidakis, and P.C. Kelires, “Structure, Elastic Properties and
Strength of Amorphous and Nanocomposite Carbon”, submitted.
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