טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentAnastasia Sorkin
SubjectComputational Study of Structures of Diamond and
Amorphous Carbon under Extreme Heating and Cooling
DepartmentDepartment of Physics
Supervisors Dr. Adler Joan
Professor Emeritus Kalish Rafael


Abstract

 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.