Electromechanical Resonators from Graphene Sheets

Bunch, J. Scott; Zande, Arend M. van der; Verbridge, Scott S.; Frank, Ian W.; Tanenbaum, David M.; Parpia, J. M.; Craighead, Harold G.; McEuen, Paul L.

doi:10.1126/science.1136836

Cited by 2,678 publications

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References 22 publications

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“…In contrast to prior realizations of suspended graphene 17,18 which did not provide electrical contacts for transport measurements, the SG devices described here incorporate multiple electrodes that allow 4-lead transport measurements. The SG devices employed here were fabricated from conventional NSG devices using wet chemical etching (see supporting online material).…”

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Approaching ballistic transport in suspended graphene

et al. 2008

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The recent discovery of methods to isolate graphene 1-3 , a one-atom-thick layer of crystalline carbon, has raised the possibility of a new class of nano-electronics devices based on the extraordinary electrical transport and unusual physical properties 4,5 of this material. However, the experimental realization of devices displaying these properties was, until now, hampered by the influence of the ambient environment, primarily the substrate. Here we report on the fabrication of Suspended Graphene (SG) devices and on studies of their electrical transport properties. In these devices, environmental disturbances were minimized allowing unprecedented access to the intrinsic properties of graphene close to the Dirac Point (DP) where the energy dispersion of the carriers and their density-of-states vanish linearly giving rise to a range of exotic physical properties. We show that charge inhomogeneity is reduced by almost one order of magnitude compared to that in Non-Suspended Graphene (NSG) devices. Moreover, near the DP, the mobility exceeds 100,000 cm 2 /Vs, approaching theoretical predictions for evanescent transport in the ballistic model. The low energy excitation spectrum of graphene mimics relativistic particles -massless Dirac fermions (DF) -with an electron-hole symmetric conical energy dispersion and .vanishing density of states at the DP. Such unusual spectrum is expected to produce 1 novel electronic properties such as negative index of refraction 6 , specular Andreev reflections at graphene-superconductor junctions 7,8 , evanescent transport 9 , anomalous phonon softening 10 , etc. A basic assumption behind these intriguing predictions is that the graphene layer is minimally affected by interactions with the environment. However in reality the environment 11,12 and in particular the substrate 13 , can be quite invasive for such ultra-thin films. For example, the carrier mobility in graphene deposited on a substrate such as Si/SiO 2 deteriorates due to trapped charges in the oxide or to contaminants that get trapped at the graphene-substrate interface during fabrication. The substrate-induced charge inhomogeneity is particularly deleterious near the DP where screening is weak, 14,15 leading to reduced carrier mobility there. In addition, the atomic roughness of the substrate introduces short range scattering centers and may contribute to quench-condensation of ripples within the graphene layer 16 .In order to eliminate substrate induced perturbations, graphene films were suspended from Au/Ti contacts to bridge over a trench in a SiO 2 substrate. In contrast to prior realizations of suspended graphene 17,18 which did not provide electrical contacts for transport measurements, the SG devices described here incorporate multiple electrodes that allow 4-lead transport measurements. The SG devices employed here were fabricated from conventional NSG devices using wet chemical etching (see supporting online material). In a typical SG device, shown in Figure 1b, the graphene layer is suspended from the voltage l...

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Approaching ballistic transport in suspended graphene

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“…Using this measured leak rate, we estimate an upper bound for the average transmission probability of a He atom impinging on a graphene surface as dN dt 2d NV < 10 -11 (2) where dN/dt is the measured leak rate, d is the depth of the microchamber, and V is the velocity of He atoms (see Supporting Information). In all likelihood, the true permeability is orders of magnitude lower than the bound given above.…”

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Impermeable Atomic Membranes from Graphene Sheets

et al. 2008

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We demonstrate that a monolayer graphene membrane is impermeable to standard gases including helium. By applying a pressure difference across the membrane, we measure both the elastic constants and the mass of a single layer of graphene. This pressurized graphene membrane is the world's thinnest balloon and provides a unique separation barrier between 2 distinct regions that is only one atom thick.Membranes are fundamental components of a wide variety of physical, chemical, and biological systems, used in everything from cellular compartmentalization to mechanical pressure sensing. They divide space into two regions, each capable of possessing different physical or chemical properties. A simple example is the stretched surface of a balloon, where a pressure difference across the balloon is balanced by the surface tension in the membrane. Graphene, a single layer of graphite, is the ultimate limit: a chemically stable and electrically conducting membrane one atom in thickness. 1-3 An interesting question is whether such an atomic membrane can be impermeable to atoms, molecules and ions. In this letter, we address this question for gases. We show that these membranes are impermeable and can support pressure differences larger than one atmosphere. We use such pressure differences to tune the mechanical resonance frequency by ∼100 MHz. This allows us to measure the mass and elastic constants of graphene membranes. We demonstrate that atomic layers of graphene have stiffness similar to bulk graphite (E ∼ 1 TPa). These results show that single atomic sheets can be integrated with microfabricated structures to create a new class of atomic scale membrane-based devices.A schematic of the device geometry used heresa graphene-sealed microchambersis shown in Figure 1a. Graphene sheets are suspended over predefined wells in silicon oxide using mechanical exfoliation (see Supporting Information). Each graphene membrane is clamped on all sides by the van der Waals force between the graphene and SiO 2 , creating a ∼(µm) 3 volume of confined gas. The inset of Figure 1a shows an optical image of a single layer graphene sheet forming a sealed square drumhead with a width W ) 4.75 µm on each side. Raman spectroscopy was used to confirm that this graphene sheet was a single layer in thickness. [4][5][6] Chambers with graphene thickness from 1 to ∼75 layers were studied.After initial fabrication, the pressure inside the microchamber, p int , is atmospheric pressure (101 kPa). If the pressure external to the chamber, p ext , is changed, we found that p int will equilibrate to p ext on a time scale that ranges from minutes to days, depending on the gas species and the temperature. On shorter time scales than this equilibration time, a significant pressure difference ∆p ) p int -p ext can exist across the membrane, causing it to stretch like the surface of a balloon (Figure 1b). Examples are shown for ∆p > 0 in Figure 1c and ∆p < 0 in Figure 1d.To create a positive pressure difference, ∆p > 0, as shown in Figure 1c, we place a s...

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“…19,20 For the present samples, the tension is estimated to be a few nanonewtons, which is 2 orders of magnitude lower than that reported for mechanically exfoliated graphene. [21][22][23][24] The presence of such large tensions in the latter case has been attributed to macroscopic uncontrolled forces applied during the deposition process. By contrast, the solution-based approach used in this work leads to significantly lower tensions, allowing easy access to the intrinsic properties of these ultrathin membranes.…”

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Elastic Properties of Chemically Derived Single Graphene Sheets

2008

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The elastic modulus of freely suspended graphene monolayers, obtained via chemical reduction of graphene oxide, was determined through tip-induced deformation experiments. Despite their defect content, the single sheets exhibit an extraordinary stiffness (E ) 0.25 TPa) approaching that of pristine graphene, as well as a high flexibility which enables them to bend easily in their elastic regime. Built-in tensions are found to be significantly lower compared to mechanically exfoliated graphene. The high resilience of the sheets is demonstrated by their unaltered electrical conductivity after multiple deformations. The electrical conductivity of the sheets scales inversely with the elastic modulus, pointing toward a 2-fold role of the oxygen bridges, that is, to impart a bond reinforcement while at the same time impeding the charge transport.Recent experiments have revealed the thermodynamic stability of graphene under ambient conditions, 1-3 which strongly revived the interest in the electrical and mechanical properties of this fascinating carbon nanostructure. Two major methods have been established for the fabrication of graphene monolayers, namely, mechanical exfoliation of graphite 2 and vacuum graphitization of silicon carbide. 3,4 More recently, chemical reduction of graphene oxide (GO) has been reported as an alternative, solution-based route, for obtaining graphenelike sheets which offers the advantages of being cheap and up-scalable. [5][6][7][8] Even though GO is a good insulator, deoxygenation has been shown to substantially enhance its electrical conductivity, albeit the obtained values of ∼1 S/cm remain 2-3 orders of magnitude below that of pristine graphene. 6,7 Due to the limited efficiency of the reduction process, the obtained sheets still contain residual oxygenated functional groups of the starting material. Microscopic studies of the reduced GO also indicate the coexistence of graphitic regions with defect clusters 6,9 in agreement with proposed models. [9][10][11] In addition to its interesting electrical characteristics, this 2D material is expected to have also unique mechanical properties. Recent studies have witnessed its suitability for the fabrication of composites 12,13 and paperlike materials 14 with excellent mechanical properties. However, in order to promote its application in nanotechnology, the mechanical characterization of single sheets is of upmost relevance.Here we present a study of the mechanical and electrical properties of suspended, chemically reduced GO single sheets. Graphite oxide prepared via Hummers method 15 was dispersed in water, deposited onto a Si/SiO 2 substrate, and subsequently reduced by hydrogen plasma treatment. The obtained samples exhibited a high yield of monolayers with lateral dimensions of 0.1-5 µm. Preselected layers were then contacted by standard e-beam lithography with Ti/Au electrodes. In order to freely suspend the layers (Figure 1), the samples were wet etched by buffered hydrofluoric acid, followed by critical point drying to prevent ...

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Electromechanical Resonators from Graphene Sheets

Cited by 2,678 publications

References 22 publications

Approaching ballistic transport in suspended graphene

Approaching ballistic transport in suspended graphene

Impermeable Atomic Membranes from Graphene Sheets

Elastic Properties of Chemically Derived Single Graphene Sheets

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