Fast detection of water nanopockets underneath wet-transferred graphene

Abstract

We report an investigation of the graphene/substrate interface morphology in large-area polycrystalline graphene grown by chemical-vapour deposition and wet-transferred onto Si wafers. We combined spectroscopic ellipsometry, X-ray photoelectron spectroscopy and atomic-force microscopy in order to yield morphological and chemical information about the system. The data showed that wet-transferred samples may randomly exhibit nanosized relief patterns indicative of small water nanopockets trapped between graphene and the underlying substrate. These pockets affect the adhesion of graphene to the substrate, but can be efficiently removed upon a mild annealing in high vacuum. We show that ellipsometry is capable of successfully and reliably detecting, via multilayer dielectric modelling, both the presence of such a spurious intercalation layer and its removal. The fast, broadly applicable and non-invasive character of this technique can therefore promote its application for quickly and reliably assessing the degree of adhesion of graphene transferred onto target substrates, either for ex-post evaluation or in-line process monitoring

Efficient green emission from edge states in graphene perforated by nitrogen plasma treatment

“…Figures 2(a 2(c)). This is consistent with the complex morphology of the structure previously reported for CVD-grown graphene sheets wet-transferred onto a SiO 2 /Si substrate [45] and can be associated with the presence of nanopockets of intercalated water, residual PMMA and other residues from the used solvents (acetone and HCl, see section 2) trapped between the adjacent CVD graphene sheets. In addition, in the AFM image one can distinguish the dark-brown and black contrasts, which correspond to one-layer-deep holes existing in the upper BLG sheet.…”

“…The curved regions leading to local bonding distortions could result in some sp 3 orbital character, as well as in the π-orbital misalignment, which is expected to significantly increase the local reactivity in the process of graphene functionalization [42][43][44]. Then, microscopic corrugations in the two-dimensional structure of freely suspended graphene, as well as those appearing in the process of transfer of CVD-grown graphene sheets to a substrate [45], can give rise to enhanced etching effects occurring on exposure to plasma. Since the graphene rippling can be strongly suppressed by the interfacial van der Waals interactions in single-layer CVD graphene supported by substrate, in bi-or few-layer CVD graphene, where the adjacent graphene sheets are only weakly interacting due to the enlarged interlayer distance, the morphology aspects [34][35][36][37] may become important.…”

Local Optical Properties in CVD-Grown Monolayer WS2 Flakes

“…The resulting flakes have a triangular shape, the typical size of tens of microns across, and are randomly distributed on the substrate (Figure a). We first performed a laterally averaged spectroscopic ellipsometry, − acquiring Δ and Ψ spectra from an area of the sample containing ∼12 WS 2 flakes (experimental details are reported in the Methods section). The laterally averaged Δ and Ψ spectra are reported in Figure b,d, respectively.…”

Optical dielectric function of two-dimensional WS2 on epitaxial graphene

“…The optical properties of WS 2 were modelled by using four PSEMI and one Tauc-Lorentz terms. The PSEMI terms were chosen for their remakable flexibility [49], while the Tauc-Lorentz was meant to reproduce the onset of the electronic gap in WS 2 . Overall, the number of terms-5-was the minimum found necessary to reproduce all the experimental features.…”