In this letter, we demonstrate a non-volatile memory device in a graphene FET structure using ferroelectric gating. The binary information, i.e. "1" and "0", is represented by the high and low resistance states of the graphene working channels and is switched by controlling the polarization of the ferroelectric thin film using gate voltage sweep. A non-volatile resistance change exceeding 200% is achieved in our graphene-ferroelectric hybrid devices. The experimental observations are explained by the electrostatic doping of graphene by electric dipoles at the ferroelectric/graphene interface. PACS numbers: Valid PACS appear hereThe discovery of graphene in 2004 [1, 2, 3] has triggered enormous experimental and theoretical efforts [4,5]. As a gapless semiconductor, charge carriers in graphene can be tuned continuously from electrons to holes crossing the charge neutral Dirac point using an external electric field. Unlike conventional semiconductors, the doping process does not influence the mobility of charge carriers in graphene, which can exceed 10 5 cm 2 V −1 s −1 at low temperature [6,7]. Such doping-independent mobility leads to the field-dependent conductance in graphene. Based on these two properties, many novel graphene-based device applications have been predicted or demonstrated [8,9,10,11,12,13,14,15,16], including the heavilyexplored graphene-based field-effect transistor (GFET) [17,18,19,20,21,22]. However, a paradigm shift in the microelectronics industry from Si to graphene also requires graphene-based memory applications. Despite graphene intrinsically having a high resistance state at the Dirac point and a low resistance state when heavily doped, reports on graphene for non-volatile information storage is rarely seen. This is due to the difficulty in maintaining the resistance states in graphene without an external electric field. One chemical modification approach to achieve non-volatile switching in graphene has been recently proposed by Echtermeyer et al [19]. Although this method can achieve very high on-off ratio, it alters the unique crystalline structure of graphene upon which many of the extraordinary electronic properties and hence most novel device concepts are based [4,5].In this letter, we show non-volatile switching in graphene by using ferroelectric gating without having to break the lattice symmetry. We demonstrate basic writing and reading processes of this novel grapheneferroelectric memory device structure combining the field-dependent conductance of graphene with the remnant electric field of ferroelectric thin films. A bistable * Electronic address: phyob@nus.edu.sg FIG. 1: (a) Sample geometry of a finished grapheneferroelectric memory device. (b) Optical image of a graphene sample showing the Hall-bar geometry of the bottom electrodes. (c) R vs VBG of the graphene sample before P(VDF-TrFE) coating, measured in two-terminal configuration. (d) AFM image of another graphene sample after P(VDF-TrFE) spin-coating. The contrast comes from the slightly different crystallization of P(...

Recent experiments on ferroelectric gating have introduced a novel functionality, i.e., nonvolatility, in graphene field-effect transistors. A comprehensive understanding in the nonlinear, hysteretic ferroelectric gating and an effective way to control it are still absent. In this Letter, we quantitatively characterize the hysteretic ferroelectric gating using the reference of an independent background doping (n(BG)) provided by normal dielectric gating. More importantly, we prove that n(BG) can be used to control the ferroelectric gating by unidirectionally shifting the hysteretic ferroelectric doping in graphene. Utilizing this electrostatic effect, we demonstrate symmetrical bit writing in graphene-ferroelectric field-effect transistors with resistance change over 500% and reproducible no-volatile switching over 10⁵ cycles.

High-quality large-sized hexagoal WSe2 crystals can be grown on dielectric substrates using atmospheric chemical vapor deposition in the presence of hydrogen gas. These hexagonal crystals (lateral width >160 um) have a carrier mobility of 100 cm(2) V(-1) s(-1) and a photoresponsivity of ≈1100 mA W(-1), which is comparable to that of exfoliated flakes.

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...

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In this work, a high-performance catalytic membrane, composed of ultrasmall gold nanoclusters (AuNCs) and high aspect-ratio carbon nanotubes (CNTs), was designed for the continuous-flow catalytic reactions. In this hybrid catalytic membrane, the Au core of the NCs serves as high-performance catalyst, and the ligand of the NCs plays two key roles: (1) as a well-defined surfactant assembly to effectively dissolve CNTs in aqueous solution and (2) as an efficient protecting ligand for Au core to avoid agglomeration. Due to the above-mentioned features, a homogeneous 3D self-support catalytic membrane can be readily fabricated by vacuum filtration of the hybrid AuNCs/CNTs. The catalytic activity of the as-designed catalytic membrane was evaluated using 4-nitrophenol hydrogenation as a model catalytic reaction. The data suggest that the continuous flow catalytic reactor could achieve complete conversion of the substrate (i.e., 4-nitrophenol) within a single flow through the membrane with a hydraulic residence time (τ) of 3.0 s. The catalytic membrane also showed enhanced catalytic kinetics as compared to the conventional batch reactor due to the convectively enhanced mass transfer. In addition, three important parameters, including the Au loading amount, substrate concentration, and flow rate, were identified as key factors that could affect the performance of the catalytic membrane.