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Introduction

In the diamond crystal, each carbon atom is bound to its four nearest neighbours by sp3 bonds, forming a strong tetrahedral structure. But the thermodynamic stable structure for carbon at NPT is graphite, which contains planes of threefold coordinated carbon atoms, bound by strong sp2 bonds. The relative importance of this sp2and sp3 bonding to the electronic and physical properties represents a key issue in understanding the behavior of the diamond crystal under non-equilibrium conditions, such as those occurring during ion implantation, electron or neutron irradiation, or during chemical vapor deposition (CVD) diamond growth under bias.

To develop electronic devices in diamond, one is interested in doping this crystal by ion implantation or other methods (by diffusion or during the CVD process), and create shallow donor levels. But at specific conditions of temperature and pressure, ion impact in diamond creates compensating defects that may neutralize the dopant. It may also results in graphitization, due to the ability of carbon atoms to form the two types of bonds (sp2 and sp3). Furthermore, the creation of graphitic damage in an electrically insulating diamond matrix can give rise to the onset of an electrical conductivity. Thus, the procedure for obtaining conductivities due only to the dopant atoms is very complex. The understanding of the microscopic mechanisms underlying defect creation and amorphization in diamond induced by ion-impact is thus of great fundamental interest. Finding ways to avoid their formation is of enormous technological importance.

Calculations of structures, energies and stability of defects in diamond were carried out in the MSc thesis of David Saada, by means of Monte Carlo and molecular dynamics techniques. Damaged diamond samples were also obtained by energetic displacement of carbon atoms at a temperature of 0 K, revealing regions rich in sp2 bonds, the defects created in that manner being frozen in by the low temperature. Following this research, it is the purpose of the present study to investigate the behavior of the lattice damage under conditions of finite temperature, and to research for the appropriate annealing conditions to remove the lattice damage. By monitoring the temperature, implantation in diamond may be simulated, followed by annealing at different temperature. Such a study of interactions between defects, of defect cluster formation and of their mobility, would yield deep information on the energetic and structural aspects of damage formation and crystal relaxation during ion-implantion in diamond.


next up previous contents
Next: Diamond and graphite properties Up: No Title Previous: Contents
David Saada
2000-06-22