Liquids relax and unify strain in graphene

Abstract

Solid substrates often induce non-uniform strain and doping in graphene monolayer, therefore altering the intrinsic properties of graphene, reducing its charge carrier mobilities and, consequently, the overall electrical performance. Here, we exploit confocal Raman spectroscopy to study graphene directly free-floating on the surface of water, and show that liquid supports relief the preexisting strain, have negligible doping effect and restore the uniformity of the properties throughout the graphene sheet. Such an effect originates from the structural adaptability and flexibility, lesser contamination and weaker intermolecular bonding of liquids compared to solid supports, independently of the chemical nature of the liquid. Moreover, we demonstrate that water provides a platform to study and distinguish chemical defects from substrate-induced defects, in the particular case of hydrogenated graphene. Liquid supports, thus, are advantageous over solid supports for a range of applications, particularly for monitoring changes in the graphene structure upon chemical modification.

Bifacial Multilayer Graphene Float Transfer

“…Furthermore, for few-layer graphene films with less structural rigidity, modification of the float transfer interface is essential. To reduce the surface tension responsible for graphene film dissociation, a water-immiscible organic solvent such as hexane [30] or cyclohexane [46,83] may be applied to allow interfacial caging of the graphene at an intermediate interface. By changing the separation interface from an air-water boundary with surface tension of 72 mN m −1 to a solvent-water boundary with surface tension <50 mN m −1 , [46,83,84] float transfer of few-layer graphene films may be realized.…”

“…To reduce the surface tension responsible for graphene film dissociation, a water-immiscible organic solvent such as hexane [30] or cyclohexane [46,83] may be applied to allow interfacial caging of the graphene at an intermediate interface. By changing the separation interface from an air-water boundary with surface tension of 72 mN m −1 to a solvent-water boundary with surface tension <50 mN m −1 , [46,83,84] float transfer of few-layer graphene films may be realized. We anticipate that future work to better understand the bifacial separation mechanism and to optimize its performance with these modifications will enable PMMA-free float transfer of thinner multilayer, or even monolayer, graphene films.…”

“…Similarly, we anticipate improved properties of the float transfer graphene film, as circumventing the polymer support may allow relaxation of the inherent mechanical strain from the native growth substrate. [45,46] Due to the multilayer nature of the films, strain information cannot confidently be extracted via Raman peak shift analysis; [47,48] however, a relative improvement in the inherent surface quality of float transferred graphene is anticipated in the electronic film properties.…”

Reversible hydrogenation restores defected graphene to graphene

“…Similar Raman spectra for DH-G and untreated G also corroborate the restored carbon lattices. In particular, the slight change in the width and intensity of the D peak in DH-G can be attributed to the strain in graphene introduced during the annealing process [46]. Strain fields in graphene induced by the underlying support are able to activate intrinsic defects like interstitials and vacancies along the grain boundaries, which normally does not contribute to the D peak in non-strained graphene [47].…”

Applications of Raman spectroscopy in two-dimensional materials

“…6(a) and 6(b)). 103 Similarly, Judek and coworkers studied the graphene-germanium interaction by Raman spectroscopy. The defects and strain increased for Hydrogen insert during the cooling process.…”