Density and localized states' impact on amorphous carbon electron transport mechanisms

Abstract

This work discusses the electron transport mechanisms that we obtained as a function of the density of amorphous carbon (a-C) ultra-thin films. We calculated the density of states (total and projected), degree of electronic states' localization, and transmission function using the density functional theory and nonequilibrium Green's functions method. We generated 25 sample a-C structures using ab-initio molecular dynamics within the isothermal-isobaric ensemble. We identified three transport regimes as a function of the density, varying from semimetallic in low-density samples (≤2.4 g/cm3) to thermally activated in high-density (≥2.9 g/cm3) tetrahedral a-C. The middle-range densities (2.4 g/cm3 ≤ρ≤ 2.9 g/cm3) are characterized by resonant tunneling and hopping transport. Our findings offer a different perspective from the tight-binding model proposed by Katkov and Bhattacharyya [J. Appl. Phys. 113, 183712 (2013)], and agree with experimental observations in low-dimensional carbon systems [see S. Bhattacharyya, Appl. Phys. Lett. 91, 21 (2007)]. Identifying transport regimes is crucial to the process of understanding and applying a-C thin film in electronic devices and electrode coating in biosensors.

First-principles study of structural and opto-electronic characteristics of ultra-thin amorphous carbon films

“…Davila et al calculated the density of states (DOS), degree of electronic states' localization, and transmission function for bulk a-C using the DFT. [9] Deringer et al used machine learning and DFT calculations to study the surface chemistry of tetrahedral a-C (ta-C) and estimate the surface energy of the amorphous form of this material. [10] Galli et al [11] and Mathioudakis et al [12] calculated the electronic properties of 54 carbon atoms and the mechanical properties of 216 atomic amorphous carbon networks by using first-principles calculations.…”