Microstructure evolution of carbon films, grown by physical vapor deposition, when substrate temperature is increased

Abstract

We study how the increases of substrate temperature influence the structural properties of carbonfilms deposited by physical vapor deposition (PVD) techniques. We installed and adapted aheating system inside the deposition chamber, which can reach temperatures as high as 700◦C.Here we develop an experimental setup that allows us to obtain large films of the desiredmaterial on any substrate, with deposition times of the order of a minute. The characterizationis based mainly on the analysis of the Raman spectra, where the evolution of the G and D peakscorresponding to the material in its amorphous phase is observed. With the increase of substratetemperature, the 𝑠𝑝2 zones grow. A displacement to the right of the G peak and an increase inthe 𝐼𝐷∕𝐼𝐺 ratio is seen. At 700◦C a 2D zone at a frequency greater than 2000 cm−1 appears.Four Lorentzian-shaped bands are necessary to account for the peaks at this zone, whose centerscorrespond to different combinations of first-order ones. This shows that we are transitioningfrom an amorphous to a carbon phase with more ordered or graphitic zones and that we are nearthe crystallization point. This opens the path to produce structures similar to graphene using thismethod of deposition. The Tauc gap energy ratio decreases as temperature increases indicatingthat there is a graphitization of the sample. Transmission FTIR study is carried out at some ofthe intermediate temperatures, determining the type of bond at low frequencies. These bonds areconsistent with the ones of the hydrogenated amorphous carbon (a-C:H) structure.