Raman characterisation and hardness properties of diamond-like carbon films grown by pulsed laser deposition technique

A detailed Raman analysis is carried out in order to explain the results of the systematic morphological and mechanical characterisation of unhydrogenated and hydrogenated amorphous carbon films prepared by the pulsed laser deposition at substrate temperatures ranging from 25 to 600°C. The carbon bonding modifications produced by the different deposition conditions are discussed via the quantitative analysis of the changes correspondingly induced into the shape of the Raman spectra. The indications coming from scanning electron microscopy, atomic force microscopy and hardness measurements are understood in terms of the different sp3- to sp2-bonding fraction attained and the role of both substrate temperature and growth ambient on the quality of the deposited films is clarified. The existence is demonstrated of a very narrow temperature window for the achievement of a high sp3-bond percentage in hydrogen-free films resulting in relevant hardness values and a correlation between mechanical strengths and shape of the Raman spectrum is tentatively established.