The effect of temperature on the structural, electronic and optical properties of sp³-rich amorphous carbon

The effect of temperature on the structural, electronic and optical properties of dense tetrahedral amorphous carbon made of ∼80% sp³-bonded atoms is investigated using a combination of the classical Monte Carlo technique and density functional theory. A structural transformation accompanied by a slight decrease of the sp³ fraction is evidenced above a temperature of about 600 °C. A structural analysis in combination with energy-loss near-edge structure calculations shows that beyond this temperature, the sp²-bonded C sites arrange themselves so as to enhance the conjugation of the π electrons. The Tauc optical band gap deduced from the calculated dielectric function shows major changes beyond this temperature in accordance with experimental results. Energy-loss near-edge structure and band gap calculations additionally reveal a massive destabilization of the of sp³ bonding phase in favour of sp² bonding at a temperature of about 1300 °C which agrees very well with the reported value of 1100 °C.