Direct physical exfoliation of few-layer graphene from graphite grown on a nickel foil using polydimethylsiloxane with tunable elasticity and adhesion

Abstract

We firstly introduce a facile method for the site-specific direct physical exfoliation of few-layer graphene sheets from cheap and easily enlargeable graphite grown on a Ni foil using an optimized polydimethylsiloxane (PDMS) stamp. By decreasing the PDMS cross-linking time, the PDMS elasticity is reduced to ∼52 kPa, similar to that of a typical gel. As a result of this process, the PDMS becomes more flexible yet remains in a handleable state as a stamp. Furthermore, the PDMS adhesion to a graphite/Ni surface, as measured by the peel strength, increases to ∼5.1 N m⁻¹, which is approximately 17 times greater than that of typical PDMS. These optimized properties allow the PDMS stamp to have improved contact with the graphite/Ni surface, including the graphite wrinkles. This process is verified, and changes in surface morphology are observed using a 3D laser scanning microscope. Under conformal contact, the optimized PDMS stamp demonstrates the site-specific direct physical exfoliation of few-layer graphene sheets including mono- and bi-layer graphene sheets from the graphite/Ni substrate without the use of special equipment, conditions or chemicals. The number of layers of the exfoliated graphene and its high quality are revealed by the measured Raman spectroscopy. The exfoliation method using tunable elasticity and adhesion of the PDMS stamp can be used not only for cost-effective mass production of defect-less few-layer graphene from the graphite substrate for micro/nano device arrays but also for nano-contact printing of various structures, devices and cells.

Hydration layers trapped between graphene and a hydrophilic substrate

“…The adhesion energy between graphene and various substrates is found to range over three orders of magnitude [51], from 0.007 − J m 2 for graphene on PDMS [52] to 0.72 − J m 2 for graphene on copper [53]. Hence, the value found for graphene/CaF 2 (111) is on the high side and it should be easy to, for instance, transfer graphene from a PDMS stamp to a CaF 2 (111) substrate [54][55][56].…”

Extended PDMS stiffness range for flexible systems

“…Much work has been done into the investigation of the mechanical properties of PDMS and their potential tunability [26,28,21,29,30,16,31,32,17,33,4,[34][35][36][37]. The largest observed tensile stiffness, using 10:1 PDMS, to date is less than 4 MPa [30] after 7 days post-baking at 100 • C and less than 3 MPa for post-baking at 200 • C during 18 min [37].…”

Recent Developments in Graphene and Graphene Oxide: Properties, Synthesis, and Modifications: A Review

“…Mechanical exfoliation has been facilitated using a method called "polymer stamp" for making large area graphene layers. [126,132] This helps by controlling the process parameters and by using highly ordered pyrolytic graphite (HOPG) as the substrate.…”