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

Structure, Mechanical, and Optoelectronic Properties of Amorphous and
Nanostructured Carbon
G. Kopidakis 1,* , C. Mathioudakis 1 , I. N. Remediakis 1,2 , M. G. Fyta 2 , and P. C. Kelires 2,3
1 Department of Materials Science and Technology, University of Crete, P. O. Box 2208, 710 03 Heraklion, Crete,
Greece
2 Physics Department, University of Crete, P. O. Box 2208, 710 03 Heraklion, Crete, Greece
3 Department of Mechanical Engineering and Materials Science and Technology, Cyprus University of Technology,
P.O. Box 50329, 3036 Limassol, Cyprus
* E-mail: kopidaki@materials.uoc.gr
Recent advances in materials deposition and characterization techniques have exploited the unique bonding nature of
carbon atoms and lead to the discovery of a variety of carbon allotropes. Besides some well known nanostructured
forms, such as fullerenes and nanotubes, diamond-amorphous carbon heterostructures have emerged with promising
mechanical and optoelectronic properties. Nanocomposite carbon, in which diamond nanocrystals are embedded in
amorphous carbon (a-C) matrix, as well as ultrananocrystalline diamond films are carbon nanostructures with
fundamental and technological interest. They intermingle properties of nanocrystals with those of the amorphous phase
and open up possibilities for tailoring carbon-based materials properties for specific applications through nanostructure
modification or doping.
In order to investigate theoretically these mixed phases we use empirical potential Monte Carlo and Tight-Binding
Molecular Dynamics (TBMD) simulations. TBMD is a semi-empirical method that allows for accurate calculations in
relatively large systems and for long simulation times. Our previous studies of pure a-C networks with TBMD over the
whole range of possible densities, have resolved long-standing issues related to the structural, mechanical, electronic,
and optical properties of these materials, directly connecting our theoretical results with experiment [1-3].
Fig.1 Atomic structure of interfaces of high density a-C with low index faces of diamond (100) (left), (110) (centre),
(111) (right). Grey atoms are 4-fold, white are 3-fold coordinated.
In the present work, TBMD simulations allow us to obtain the detailed atomic-scale picture of a-C/diamond
interfaces and predict their structural and electronic properties, which are crucial to understand nanocomposite carbon
[4]. We find that such interfaces are stable, with a-C covalently bonded to the diamond surfaces. The atomic and
electronic structure of the a-C region is consistent with previous results on pure a-C and does not depend critically on
the diamond face exposed. However, diamond surface properties influence the relative stability of interfaces with high
density a-C. In this case, the interfacial region is small and very dense a-C grows on diamond (Fig. 1). At lower
densities, carbon atoms nucleate on diamond surfaces and create a more extended intermediate region between
diamond and lower density a-C. The shape of faceted diamond nanocrystals embedded in a-C is predicted using the
Wulff construction with appropriately defined interface energies. These predictions are verified by empirical potential
simulations of nanodiamond inclusions in a-C matrix (Fig. 2).
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