|M.Sc Student||Sorkin Anastasia|
|Subject||Computational Study of Structures of Diamond and|
Amorphous Carbon under Extreme Heating and Cooling
|Department||Department of Physics||Supervisors||Dr. Joan Adler|
|Professor Emeritus Rafael Kalish|
Carbon is unique among the elements in its ability to
form strong chemical bonds with a variety of coordination numbers,
including two (e.g. linear chains or carbyne phase), three (e.g.
graphite) and four (e.g. diamond). Two specific amorphous forms of carbon
may be obtained: the diamondlike amorphous carbon, which will be
denoted by ta-C, and graphitelike amorphous carbon named a-C.
The former is mostly made of distorted fourfold sites, while the latter mainly consists of threefold sites. Doping by ion implantation in diamond may result in graphitization and give rise to the onset of electrical conductivity, due to the ability of carbon atoms to form the two types of bonds.
The purpose of this study is to understand the processes which occur in very hot layers of amorphous carbon surrounded by a cold crystal diamond layer or a cold diamond-like amorphous layer. We apply a tight-binding molecular dynamics method to investigate the characteristics of ta-C and a-C solids. The method incorporates electronic structure calculations in the molecular dynamics through an empirical tight-binding Hamiltonian.
The structure of the amorphous heated layers depends very strongly on temperature, size of hot layers and the structure of initial amorphous sample (in the cases, where the frozen layers are amorphous). As expected, threefold coordinated atoms appear in the structures at high temperature and the samples become conductive. Scaling is found in the curves of the dependence of the percent of fourfold coordinated atoms in the sample on heating temperature.