185. Threshold energy for the displacement of atoms in graphite

✍ Scribed by G.L Montet

• Publisher: Elsevier Science
• Year: 1965
• Tongue: English
• Weight: 133 KB
• Volume: 3
• Category: Article
• ISSN: 0008-6223
• DOI: 10.1016/0008-6223(65)90251-4

✦ Synopsis

The energy required to displace a carbon atom from its normal lattice site has been determined directly by detection of the lattice vacancies resulting from the displacement process. Annealed natural crystals of graphite containing less than 10-i' vacancies per carbon atom were irradiated at room temperature with electrons of selected energies in the range from 100 to 500 KeV. These crystals were then cleaved to a thickness of a few hundred ~~~o~, etched in a mixture of oxygen and chlorine to enlarge the lattice vacancies present in the surface planes, decorated by deposition of a thin layer of gold, and examined in an electron microscope. The vacancies then appear as rings of gold particles. Examination of crystals irradiated with electrons of energies less than 140 KeV showed that these irradiations produced no vacancies; whereas, examination of crystals irradiated with electrons of energies exceeding 150 KeV revealed a production of vacancies, the concentration increasing with the electron energy. From these observations it may be concluded that the displacement energy in graphite is approximately 30 eV. This value is in rough agreement with that found by Qgen, (') but is in disagreement with the value recently reported by Lucas and Mitchell(2) It may be that the orientation of the crystal with respect to the electron beam and its temperature during irradiation are important factors in the displacement process; perhaps the discrepancies can be explained by investigating the influence of these factors on the displacement energy. *Based on work performed under the auspices of the U.S. Atomic Energy Commission. 1. EGGEN D. T., Report MAA-SR-69 (1955). 2. LUCAS M. W. and MITCHELL E. W. J., Carbon 1, 345 (1964).