Performance of monolayer graphene nanomechanical resonators with electrical readout

Abstract

2The enormous stiffness and low density of graphene make it an ideal material for nanoelectromechanical (NEMS) applications. We demonstrate fabrication and electrical readout of monolayer graphene resonators, and test their response to changes in mass and temperature. The devices show resonances in the MHz range. The strong dependence of the resonant frequency on applied gate voltage can be fit to a membrane model, which yields the mass density and built-in strain. Upon removal and addition of mass, we observe changes in both the density and the strain, indicating that adsorbates impart tension to the graphene. Upon cooling, the frequency increases; the shift rate can be used to measure the unusual negative thermal expansion coefficient of graphene. The quality factor increases with decreasing temperature, reaching ~10 4 at 5 K. By establishing many of the basic attributes of monolayer graphene resonators, these studies lay the groundwork for applications, including high-sensitivity mass detectors.Since its discovery in 2004 1 , graphene has attracted attention because of its unusual two dimensional (2D) structure and potential for applications [2][3][4] . Due to its exceptional mechanical properties 5 and low mass density, graphene is an ideal material for use in nanoelectromechanical systems (NEMS), which are of great interest both for fundamental studies of mechanics at the nanoscale and for a variety of applications, including force 6 , position 7 and mass 8 sensing. Recent studies using optical and scanned probe detection have shown that micron-size graphene flakes can act as MHz-range NEMS resonators 9,10 . Electrical readout of these devices is important for integration and attractive for many applications. In addition, characterization of the basic attributes of these devices, including their response to applied voltage, added mass, and changes 3 in temperature, allows detailed modeling of their behavior, which is crucial for rational device design.Samples are fabricated by first locating monolayer graphene flakes on Si/SiO 2 substrates, then patterning metal electrodes and etching away the SiO 2 to yield suspended graphene. The ability to choose monolayers in advance provides control of device properties and facilitates electrical readout. The fabrication method also provides control over the lateral dimensions; devices can be either micron-wide sheets (Fig. 1a) or lithographically defined nanoribbons (Fig.1b). Because the etchant diffuses freely under the sheets, the SiO 2 is removed at the same rate everywhere under the graphene, so that the distance between the substrate and the suspended sheet is constant (~100 nm) across each device. For the same reason, the portion of each electrode that contacts the graphene is also suspended 11,12 , as depicted in Fig. 1c.Following previous work 13-15 , we implemented an all-electrical high-frequency mixing approach ( Fig. 1d) and 5). In addition to being of fundamental interest as a coupled nanoscale-microscale system, these resonances demonstrate that grap...

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“…Therefore it has found specific applications, e.g. in resonators [13][14][15], gas sensors [16], M/NEMS [17,18], pressure drums [19] or ballistic nanodevices [20,21] to name a few.…”

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