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Novel suspended graphene devices for extreme sensing

The extreme resolution of CO2 gas molecules sensing, i.e., detection of single molecule, is reported. The suspended bilayer graphene beam is exploited in order to isolate the sensing part of the device from the substrate noise. Using the electrostatic force, the central part of the suspended beam is pulled-down to bottom metal electrode, which leads to two slanted graphene beams in suspension with built-in tensile strain. This novel design of suspended graphene beam architecture avoids any further mechanical deflection of pulled-down beams on to the substrate when the electric field is applied from the substrate. The step-like changes in the graphene beam resistance with a quantized value of ~62 Ω are measured when exposed to low concentration CO2 molecules. These discrete responses are clear evidence to individual CO2 molecule adsorption onto the slanted graphene beam. In order to enhance the molecular adsorption rate, the electrical field is introduced around the suspended graphene region by applying the back-gate voltage. The first-principles calculations and molecular dynamics simulations elucidate the role of van der Waals interaction between molecules and graphene during detection and the back gate effects on accelerating the molecules adsorption.