Researchers demonstrate that a single-layer graphene membrane is impermeable to standard gases, including helium. By applying pressure differences across the membrane, they measure the elastic constants and mass of a single-layer graphene. This ultra-thin membrane acts as a unique separation barrier between two regions, only one atom thick. Graphene, a single layer of graphite, is chemically stable and electrically conductive, making it an ideal candidate for atomic-scale membranes. The study shows that graphene membranes are impermeable to atoms, molecules, and ions, supporting pressure differences larger than one atmosphere. Using these pressure differences, they tune the mechanical resonance frequency by ~100 MHz, allowing them to measure the mass and elastic constants of graphene membranes. The results show that single atomic sheets can be integrated with microfabricated structures to create new atomic-scale membrane-based devices. The study describes a graphene-sealed microchamber, where graphene sheets are suspended over predefined wells in silicon oxide using mechanical exfoliation. Each graphene membrane is clamped on all sides by the van der Waals force between the graphene and SiO₂, creating a ~ (μm)³ volume of confined gas. The membrane is impermeable to gases, and the leak rate is not dependent on the membrane thickness, suggesting it is through the glass walls or the graphene-SiO₂ interface. The study estimates the leak rate of helium to be ~1-5×10⁶ atoms/sec, which is close to the measured values. The impermeability of the graphene membrane allows for controlled strain application, enabling the measurement of elastic properties and mass of the graphene. The elastic constants of graphene are determined to be Et/(1-ν) = 390 ± 20 N/m, consistent with experimental and theoretical values for bulk graphite and graphene. The surface tension in the pressurized membrane is obtained from the Young-Laplace equation, and the shape of the bulged membrane provides information about the surface tension. The study also shows that the pressure-induced strain can be used to control the resonance frequency of the suspended graphene, allowing for the determination of the mass per area of the membranes. The mass of the monolayer graphene is found to be 9.6 ± 0.6 × 10⁻⁷ kg/m², which is 30% higher than the theoretical value for a single layer of graphene. The study also demonstrates that the tension in the membrane is dominated by self-tensioning, which smooths corrugations in the graphene. The results show that graphene membranes are essentially impermeable to all standard gases, including helium. These membranes have potential applications in various fields, including pressure sensing, chemical reactions, phase transitions, and photon detection. They can also be used for ultrafiltration and as a unique separation barrier between two distinct phases of matter. The study provides a direct measurement of the mass of graphene, which is important for nanomeResearchers demonstrate that a single-layer graphene membrane is impermeable to standard gases, including helium. By applying pressure differences across the membrane, they measure the elastic constants and mass of a single-layer graphene. This ultra-thin membrane acts as a unique separation barrier between two regions, only one atom thick. Graphene, a single layer of graphite, is chemically stable and electrically conductive, making it an ideal candidate for atomic-scale membranes. The study shows that graphene membranes are impermeable to atoms, molecules, and ions, supporting pressure differences larger than one atmosphere. Using these pressure differences, they tune the mechanical resonance frequency by ~100 MHz, allowing them to measure the mass and elastic constants of graphene membranes. The results show that single atomic sheets can be integrated with microfabricated structures to create new atomic-scale membrane-based devices. The study describes a graphene-sealed microchamber, where graphene sheets are suspended over predefined wells in silicon oxide using mechanical exfoliation. Each graphene membrane is clamped on all sides by the van der Waals force between the graphene and SiO₂, creating a ~ (μm)³ volume of confined gas. The membrane is impermeable to gases, and the leak rate is not dependent on the membrane thickness, suggesting it is through the glass walls or the graphene-SiO₂ interface. The study estimates the leak rate of helium to be ~1-5×10⁶ atoms/sec, which is close to the measured values. The impermeability of the graphene membrane allows for controlled strain application, enabling the measurement of elastic properties and mass of the graphene. The elastic constants of graphene are determined to be Et/(1-ν) = 390 ± 20 N/m, consistent with experimental and theoretical values for bulk graphite and graphene. The surface tension in the pressurized membrane is obtained from the Young-Laplace equation, and the shape of the bulged membrane provides information about the surface tension. The study also shows that the pressure-induced strain can be used to control the resonance frequency of the suspended graphene, allowing for the determination of the mass per area of the membranes. The mass of the monolayer graphene is found to be 9.6 ± 0.6 × 10⁻⁷ kg/m², which is 30% higher than the theoretical value for a single layer of graphene. The study also demonstrates that the tension in the membrane is dominated by self-tensioning, which smooths corrugations in the graphene. The results show that graphene membranes are essentially impermeable to all standard gases, including helium. These membranes have potential applications in various fields, including pressure sensing, chemical reactions, phase transitions, and photon detection. They can also be used for ultrafiltration and as a unique separation barrier between two distinct phases of matter. The study provides a direct measurement of the mass of graphene, which is important for nanome