The optical properties and dielectric constant of n-electrons in graphite are discussed. The behavior of the dielectric constant at higher frequency region is calculated and it is found the plasma excitation energy is at 6.83 eV.
Chakraborty, M., Das, B. K., Mishra, M. K., & Bandyopadhyay, M. (2011). Effect of Filament Position on Diffused Plasma Parameters. Chinese Journal of Physics, 49(6), 1199-1211. https://www.airitilibrary.com/Article/Detail?DocID=05779073-201112-201202230014-201202230014-75-87
Yu, T. M. (2002). Graphite furnace [master's thesis, The University of Hong Kong]. Airiti Library. https://www.airitilibrary.com/Article/Detail?DocID=U0029-1812201200004705