Graphene has exceptional optical, mechanical and electrical properties, making it an emerging material for novel optoelectronics, photonics and for flexible transparent electrode applications. However, the relatively high sheet resistance of graphene is a major constrain for many of these applications. Here we propose a new approach to achieve low sheet resistance in large-scale CVD monolayer graphene using non-volatile ferroelectric polymer gating. In this hybrid structure, large-scale graphene is heavily doped up to 3×10 13 cm -2 by non-volatile ferroelectric dipoles, yielding a low sheet resistance of 120 Ω/□ at ambient conditions. The graphene-ferroelectric transparent conductors (GFeTCs) exhibit more than 95 % transmittance from the visible to the near infrared range owing to the highly transparent nature of the ferroelectric polymer. Together with its excellent mechanical flexibility, chemical inertness and the simple fabrication process of ferroelectric polymers, the proposed GFeTCs represent a new route towards large-scale graphene based transparent electrodes and optoelectronics.KEYWORDS CVD graphene, ferroelectric polymer gating, sheet resistance, high transparency, mechanical flexibility, charged impurity scattering 2 Graphene keeps attracting much attention with enormous amount of experimental and theoretical activity, since its first micromechanical exfoliation in 2004. [1][2][3][4] As one atomic layer membrane, graphene is highly transparent (97.3 %) over a wide range of wavelengths from the visible to the near infrared (IR). 5Owing to its covalent carbon-carbon bonding, graphene is also one of the strongest materials with a remarkably high Young's modulus of ~ 1 TPa. 6 The combination of its high transparency, wideband tunability and excellent mechanical properties make graphene a very promising candidate for flexible electronics, optoelectronics and phonotics. 7-9The technical breakthrough of large-scale graphene synthesis has further accelerated the use of graphene films as transparent electrodes. 10,11To utilize graphene as transparent electrodes for applications such as solar cells 12 , organic light emitting diodes, 13 touch panels and displays 14, the key challenge is to reduce the sheet resistance to values comparable with indium tin oxide (ITO), which provides the best known combination of transparency (> 90 %) and sheet resistance (< 100 Ω/□). 8,15 Conventional methods to reduce the sheet resistance like electrostatic doping of graphene requires complex fabrication steps of dielectric deposition and gate electrode preparations, which are not practical for doping large-scale graphene and consume power to maintain the doping levels. 12,14 Chemical doping has been shown to effectively reduce the sheet resistance of graphene. [16][17][18][19] However, the doping mechanism of chemical dopants is not yet fully understood and the relationship between charge density and carrier mobility is still under debate. [20][21][22] Furthermore, the adsorption of moisture and other chemical molecul...

A flexible, transparent acoustic actuator and nanogenerator based on graphene/P(VDF-TrFE)/graphene multilayer film is demonstrated. P(VDF-TrFE) is used as an effective doping layer for graphene and contributes significantly to decreasing the sheet resistance of graphene to 188 ohm/sq. The potentiality of graphene/P(VDF-TrFE)/graphene multilayer film is realized in fabricating transparent, flexible acoustic devices and nanogenerators to represent its functionality. The acoustic actuator shows good performance and sensitivity over a broad range of frequency. The output voltage and the current density of the nanogenerator are estimated to be ∼3 V and ∼0.37 μAcm(-2), respectively, upon the application of pressure. These values are comparable to those reported earlier for ZnO- and PZT-based nanogenerators. Finally, the possibility of rollable devices based on graphene/P(VDF-TrFE)/graphene structure is also demonstrated under a dynamic mechanical loading condition.

Preparing graphene and its derivatives on functional substrates may open enormous opportunities for exploring the intrinsic electronic properties and new functionalities of graphene. However, efforts in replacing SiO2 have been greatly hampered by a very low sample yield of the exfoliation and related transferring methods. Here, we report a new route in exploring new graphene physics and functionalities by transferring large-scale chemical vapor deposition single-layer and bilayer graphene to functional substrates. Using ferroelectric Pb(Zr0.3Ti0.7)O3 (PZT), we demonstrate ultra-low voltage operation of graphene field effect transistors within ±1 V with maximum doping exceeding 10 13 cm −2 and on-off ratios larger than 10 times. After polarizing PZT, switching of graphene field effect transistors are characterized by pronounced resistance hysteresis, suitable for ultra-fast non-volatile electronics.PACS numbers: 72.80.VpAs a one-atom-thick single crystal, graphene's electronic properties [1] are closely related to its supporting substrates. SiO 2 provides excellent optical contrast, the key in discovering graphene by micromechanical exfoliation, but with critical drawbacks, such as surface roughness, high concentration of surface impurity charges, surface optical phonons, hydrophilic surface properties, and low dielectric constant (κ SiO2 = 3.9). Such drawbacks not only limit the carrier mobility but also the dielectric gating strength by the maximum polarizability P max = ε 0 κ SiO2 E max ≈ 1.7 µC/cm 2 , where E max ≈ 0.5 V /nm is the breakdown field of SiO 2 . Substantial progresses in replacing SiO 2 have already been made, such as significant mobility enhancement of single-layer graphene on boron nitride [2], and non-volatile polymer (top) gating of single-layer graphene [3,4]. However, efforts in this direction are in general constrained by the difficulty of exfoliating and identifying in particular single and bilayer graphene on different substrates.The rapid progresses in Copper-based chemical vapor deposition methods (Cu-CVD) have now made waferscale graphene synthesis and graphene transfer feasible both for single-layer graphene (SLG) [2, 5] and bilayer graphene (BLG) [6], providing great advantages in substrate engineering of graphene for exploring new physics and functionalities [3,[7][8][9][10][11]. With respect to substrates, ferroelectric materials are unique both in non-volatile gating [3] and high polarizability up to 100 µC/cm 2 (6 × 10 14 cm −2 in charge density) [12], 60 times larger than SiO 2 . With such high gating strength, it is possible to heavily dope graphene beyond the linear band dispersion regime (∼ 1 eV) and reach the van Hove singularities [13]. Such high doping, which in contrast to electrolyte gating [14] is gate-tunable even at liquid helium temperature, may also be of great importance for verifying the recent theoretical prediction of strong electron-phonon interactions and high-temperature superconductivity in graphane and related materials [15]. For graphene electronics, this...

We report the fabrication of a flexible graphene-based nonvolatile memory device using Pb(Zr0.35,Ti0.65)O3 (PZT) as the ferroelectric material. The graphene and PZT ferroelectric layers were deposited using chemical vapor deposition and sol–gel methods, respectively. Such PZT films show a high remnant polarization (Pr) of 30 μC cm−2 and a coercive voltage (Vc) of 3.5 V under a voltage loop over ±11 V. The graphene–PZT ferroelectric nonvolatile memory on a plastic substrate displayed an on/off current ratio of 6.7, a memory window of 6 V and reliable operation. In addition, the device showed one order of magnitude lower operation voltage range than organic-based ferroelectric nonvolatile memory after removing the anti-ferroelectric behavior incorporating an electrolyte solution. The devices showed robust operation in bent states of bending radii up to 9 mm and in cycling tests of 200 times. The devices exhibited remarkable mechanical properties and were readily integrated with plastic substrates for the production of flexible circuits.

High-k dielectric oxides are supposedly ideal gate-materials for ultra-high doping in graphene and other 2D-crystals. Here, we report a temperature-dependent electronic transport study on chemical vapor deposited-graphene gated with SrTiO3 (STO) thin film substrate. At carrier densities away from charge neutrality point the temperature-dependent resistivity of our graphene samples on both STO and SiO2/Si substrates show metallic behavior with contributions from Coulomb scattering and flexural phonons attributable to the presence of characteristic quasi-periodic nano-ripple arrays. Significantly, for graphene samples on STO substrates we observe an anomalous ‘slope-break' in the temperature-dependent resistivity for T = 50 to 100 K accompanied by a decrease in mobility above 30 K. Furthermore, we observe an unusual decrease in the gate-induced doping-rate at low temperatures, despite an increase in dielectric constant of the substrate. We believe that a complex mechanism is at play as a consequence of the structural phase transition of the underlying substrate showing an anomalous transport behavior in graphene on STO. The anomalies are discussed in the context of Coulomb as well as phonon scattering.