Polymer-free fabrication of ultra-large suspended graphene membranes

We report a scalable, polymer-free transfer method for fabricating ultra-large suspended few-layer graphene membranes. Building on a previously established approach for supported films, we demonstrate for the first time that this method enables freestanding membranes spanning 150 µm holes with high yield and mechanical integrity. The resulting triple-layer graphene membranes are free of polymer residues and show uniform doping and strain, as confirmed by spatially resolved Raman spectroscopy. Terahertz time-domain spectroscopy reveals high carrier mobilities despite finite p-type doping, consistent with a suspended, contamination-free architecture. Membrane topography was characterized by three-dimensional optical profilometry, showing predominantly planar or sloped profiles with sub-micrometer deviations—suitable for sub-nanosecond timing applications. As a proof of concept, we integrated the membranes into a time-of-flight (ToF) mass spectrometry setup, where they serve as efficient ion–electron converters with electron yields consistent with theoretical expectations. Beyond ToF applications, our method provides a general platform for creating ultrathin, freestanding two-dimensional membranes, including graphene-supported MoS2 films, with potential relevance for nanoelectromechanical systems, sensing, ultrafast ion-beam experiments, and membrane-based optoelectronics.