Multiphonon Tunneling Conduction of LocalizedπElectrons in Amorphous Carbon Films

The temperature dependence of the dc conductivity has been measured on sputtered amorphous carbon films. The conductivity is proportional to Tⁿ with n=15-17 over a wide temperature range, suggesting for the first time that the multiphonon tunneling transition with weak electron-lattice coupling of localized π electrons is a probable mechanism for charge transport. This may be attributed to the delocalized nature of the π defect in amorphous carbon.