Ion-Implantation Studies of Graphite
- PDF / 446,294 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 62 Downloads / 286 Views
ION-IMPLANTATION STUDIES OF GRAPHITE
B.S.
ELMAN,t M. HOM,-
E.W.
MABY'
AND M.S.
DRESSELHAUS't
Center for Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA ABSTRACT Ion implantation of highly oriented pyrolytic graphite (HOPG) is studied using various characterization techniques, including Raman spectroscopy and Secondary Ion Mass Spectroscopy (SIMS). Particular attention is given to the annealing of the implantation-induced lattice damage using both hot substrate implantation (200 < Ti < 10000C) and postimplantation annealing. The Raman spectra provide detailed information on the implantation-induced structural disorder by analysis of the disorder-induced and Raman-allowed features in the first- and second-order spectra. SIMS measurements show that the implanted profile is essentially the same for hot substrate and room temperature implantation for the case of HOPG. It is shown that implantation at elevated temperatures prevents amorphization more effectively than implantation at room temperature and subsequent annealing at the same elevated temperature. The annealing results show that fundamentally different defects are created during room temperature and hot substrate implantation. INTRODUCTION In previous publications [1-4] we have shown that under various experimental
conditions, ion implantation of several different atomic species into highly oriented pyrolytic graphite (HOPG) results in bombardment-induced disorder. It was demonstrated that very high temperatures (-3000*C) were required for complete annealing of lattice damage. The annealing temperatures are shown to be dependent on ion fluence $, especially when t exceeds a mass-dependent critical value. This annealing behavior is similar to that observed for the case of implantation into diamond [51, the cubic crystalline form of carbon. Since ion implantation is the only effective mechanism for introducing impurities into diamond, concurrent bombardment damage imposes a major limitation on efforts to achieve implanted layers with sufficient impurity concentrations to exhibit useful semiconducting properties. Implantation damage in diamond is 1 5 difficult to anneal 15,6] and at large fluences (typically greater then 5x10 2 cm- ), irreversible phase changes to graphite occur 17]; this is manifested as an instability of the diamond crystal at high temperature (> 15000C) and normal pressure (8]. The electrical and other physical properties of the implanted layer are dominated by bombardment disorder, and the specific role of the added impurity is difficult to interpret. The undesired consequences of ion implantation damage in different materials can be alleviated if the implantation is performed at high temperature and at moderate ion beam current [8]. Under these conditions, the bombardment disorder is annealed in situ and does not exceed a Particular steady-state level. Hot stage implantati.f-i-nnealS out each individtDepartment of Physics. °Department of Electrical Engineering and Computer Science. Ma
Data Loading...
