Activation energy in metal-containing DLC films with various metals of various concentrations

The activation energy of (Co, Mo, W)-containing diamond-like carbon (DLC) films with different metal concentrations was investigated. The films were deposited onto silicon substrates by radio frequency discharged methane plasma and a co-sputtering of the metal target. The structure of the films was analyzed by Raman spectroscopy and using a transmission electron microscope. The results indicated that crystalline metal clusters are dispersed in amorphous carbon insulating matrix, and hence the metal-containing DLC films investigated can be classified as granular films. The temperature dependence of the resistance was also measured. From the temperature dependence, the activation energy was calculated numerically using σ = σ₀exp(- E / kT). The calculated activation energy rapidly decreases as the metal concentration increases. This is because of the increase in the average size of the metal clusters. A detailed discussion is presented in terms of the radius of the metal clusters inside the films.