The layers of exfoliation graphene obtained by scotch taping of highly oriented pyrolythic graphite could be controlled precisely using an atomic layer etching (ALET) technology. Using the ALET, that is, by adsorbing oxygen radicals chemically on the graphene surface during the adsorption step and by removing the chemisorbed species only by Ar particle beam irradiation during the desorption step, exactly one monolayer of graphene could be removed during each etch cycle. The removal of each graphene layer by each ALET etch cycle could be observed through the optical microscope. In addition, the decrease of graphene layers could be also observed through the peak position change/broadening of G ' Raman peak. However, after the ALET, physical damage on the graphene surface could be also observed by the increase of D peak and decrease of G ' peak using the Raman spectra. The damaged graphene could be partially recovered by annealing at 1000°C for 30 minutes in 130 mTorr H 2 /He environment.
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Kim et al. (2011) studied this question.