New leak elements for helium based on single-layer graphene composite membranes

Graphene containing intrinsic pores with molecular dimensions is a highly promising material for standard leak elements because of its minimal and stable gas flow. However, the etching of polymethyl methacrylate (PMMA) during the typical graphene transfer process can cause the rupture of graphene on the porous substrate due to the surface tension as the etchant solution dries out. In this article, we simplified the typical graphene transfer process that enabled the transfer of a PMMA/graphene composite membrane onto a macroporous Cu gasket as the leak element and tested the leak rate, time stability, and response time of the composite membrane. The membrane permeation area depends on the pore size of the Cu substrate, which can be controlled by laser ablation or computer numerical control milling. To ensure the accuracy of time stability, the entire test lasted 60 days. The conductance results for two devices with a permeation size of 50 and 500 μm were about 10−17 and 10−14 m3 s−1, and the maximum variation of conductance in 60 days was 14% and 2.6%, respectively. Accordingly, the permeance of the composite membrane for helium can be calculated as 4.17 × 10−12–1.09 × 10−11 Pa m3 (cm2 s Pa)−1. Moreover, the composite membrane has been proven to have a rapid response of about 2 s to the upstream pressure.