A swift technique to hydrophobize graphene and increase its mechanical stability and charge carrier density

Abstract

Despite the improvement of the quality of CVD grown single-layer graphene on copper substrates, transferring the two-dimensional layer without introducing any unintentional defects still poses a challenge. While many approaches focus on optimizing the transfer itself or on necessary post-transfer cleaning steps, we have focused on developing a pre-treatment of the monolayer graphene on copper to improve the quality and reproducibility of the transfer process. By pressing an ethylene-vinyl acetate copolymer foil onto the monolayer graphene on copper using a commercially available vacuum bag sealer graphene is stabilized by the attachment of functional carbon groups. As a result, we are able to transfer graphene without the need of any supporting layer in an all-H2O wet-chemical transfer step. Despite the general belief that the crumbling of graphene without a support layer in a H2O environment is caused due to differences in surface energy, we will show that this assumption is false and that this behavior is caused rather by the polar interactions between graphene and water. Suppressing these interactions protects graphene from ripping and results in extremely clean, highly crystalline graphene with a coverage close to 100%.

Apparent differences between single layer molybdenum disulphide fabricated via chemical vapour deposition and exfoliation

“…It is typical for MoS 2 to preferentially grow at imperfections such as step edges as demonstrated for 'bulk-graphene' highly oriented pyrolytic graphite (HOPG) substrates [47,55,56] and at artificially induced nm-sized defects [57]. The oriented growth of MoS 2 underlines the cleanliness of the graphene surface after our novel transfer technique [54]. The preferred orientation indicates, that the MoS 2 lattice points in the same crystallographic direction as the graphene lattice which is an important aspect for epitaxial growth.…”

“…51 The oriented growth of MoS 2 underlines the cleanliness of the graphene surface after our novel transfer technique. 48 It is worth noting, that the MoS 2 -graphene system based on directly grown MoS 2 (orange triangle) has very similar Raman modes in comparison to MoS 2 grown on HOPG (brown triangles). 41 The similarities of MoS 2 grown on HOPG and on graphene (flake size, nucleation at grain boundaries/step edges, orientation, Raman mode positions) confirm the claim that MoS 2 on HOPG is a good model system for MoS 2 on graphene.…”

“…6 (a)), which has been transferred from its growth substrate to SiO 2 by our recently reported polymer-free transfer technique. 48 Afterwards, MoS 2 is either transferred onto (Fig. 6 (b)) or grown by CVD on the resulting graphene-SiO 2 substrates (Fig.…”

“…The heterostructures have been prepared by two different routes, see figure 6. Both routes start with CVD graphene (figure 6 (a)), which has been transferred from its growth substrate to SiO 2 by our recently reported polymer-free transfer technique [54]. Afterwards, MoS 2 is either transferred onto (figure 6 (b)) or grown by CVD on the resulting graphene-SiO 2 substrates (figure 6 (c) and (d)).…”

“…The PMMA is removed by an acetone bath. For transferring graphene a polymer free wet transfer is used, which is reported in our previous work [54]. In case of growing MoS 2 onto the graphene-SiO 2 samples, the samples were pre-annealed in activated carbon for 20 min at 100 • C.…”