Exploring Voltage Mediated Delamination of Suspended 2D Materials as a Cause of Commonly Observed Breakdown

Abstract

2D barrier materials such as graphene, boron nitride and molybdenum disulfide hold great promise for important applications such as DNA sequencing, desalination, and biomolecular sensing. The 2D materials commonly span pores through an insulating membrane and electrical fields are applied to drive cross-barrier transport of charged solvated species. While the low voltage transmembrane transport is well understood and controllable, high voltage phenomena are uncontrolled and result in the apparent breakdown of the 2D material's critical insulating properties. Here we use suspended graphene over a 50 nm silicon nitride nanopore as a model system and show that delamination of the 2D-material occurs at higher voltages and can directly cause a number of the puzzling high voltage transport observations . We confirm the occurrence of delamination and observe via AFM measurement a micron scale delaminated patch in a system using CVD graphene. Furthermore, we show that the conductivity of the same system is strongly correlated to the area of delamination via coincident current measurements and optical imaging of the delaminated area. Finally, we demonstrate that delamination alone can cause a dramatic breakdown of barrier function through observation of a reversible increase in conductance of samples prepared with pristine defect-free graphene. These findings should have a great impact on the design and interpretation of 2D-barrier material for both experiments and applications.

Stress induced delamination of suspended MoS2 in aqueous environments

“…As observed previously in graphene, applying a high electric field can cause direct membrane delamination from the substrate 23 which can impact membrane conductance ( Fig. 1E ).…”

“…Such a loss in adhesion was found to occur after exceeding a threshold transmembrane voltage of 0.25–0.5 V depending on factors such as 2D film surface roughness, existing defects or surface folds. 23 The process was found to be reversible i.e. delaminated 2D material relaminates after the transmembrane potential difference is removed and the electrolyte intercalation between 2D film and substrate is no longer energetically favorable.…”

“…delaminated 2D material relaminates after the transmembrane potential difference is removed and the electrolyte intercalation between 2D film and substrate is no longer energetically favorable. 23 A possible mechanism used in the literature for similar effects would involve local Joule heating at the pore causing liquid superheating producing explosive nucleation of a vapor bubble. 32,33 In our case MoS 2 delamination via local bubbling on the MoS 2 /SiN interface is unlikely as we use an electrolyte solution that is undersaturated with gas and the starting ionic current through the pore is too small to induce significant Joule heating.…”

“…21 It has been established, that applying high voltage can be potentially damaging to the 2D material as it can cause membrane breakdown 11,22 and delamination through electrolyte intercalation. 23,24 Even though the strain-induced wrinkling and delamination was thoroughly studied, [25][26][27] it is not fully explored how applying hydrostatic pressure can influence the membrane performance and 2D film adhesion to the substrate in an aqueous environment. It was shown, that surface-related phenomena such as material damage, delamination or nanobubbles 28 can exhibit nonlinear current signals, 20,21,23 analogous to those reported as ionic coulomb blockade.…”

“…23,24 Even though the strain-induced wrinkling and delamination was thoroughly studied, [25][26][27] it is not fully explored how applying hydrostatic pressure can influence the membrane performance and 2D film adhesion to the substrate in an aqueous environment. It was shown, that surface-related phenomena such as material damage, delamination or nanobubbles 28 can exhibit nonlinear current signals, 20,21,23 analogous to those reported as ionic coulomb blockade. 29 Thus, even though MoS 2 was proven stable at working pressure of up to 3.5 bar, 20,30 further investigation of the application of both electrical fields and pressure is crucial to uncover adhesion-related artifacts, help understand the 2D-nanofluidic system and bring insights into designing an artifact-free 2D-material platforms.…”