Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session T16: Focus Session: Graphene Electronic Devices I |
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Sponsoring Units: DMP Chair: Saiful Khondaker, University of Central Florida Room: 101AB |
Thursday, March 5, 2015 11:15AM - 11:27AM |
T16.00001: Electrolyte gating of graphene protected by boron nitride Kevin Tharratt, Patrick Gallagher, Menyoung Lee, Kenji Watanabe, Takashi Taniguchi, David Goldhaber-Gordon Electrolyte gating is a technique used to induce a high carrier density at a sample surface. We have recently shown that for strontium titanate surfaces protected by boron nitride, electrolyte gating can induce high carrier densities while maintaining high electron mobility and limiting electrochemical reactions at the sample. In this talk, we describe electrolyte-gating experiments on single-layer graphene sheets encapsulated by various thicknesses of boron nitride. We discuss the implications of our work for future electrolyte gating studies of materials protected by boron nitride. [Preview Abstract] |
Thursday, March 5, 2015 11:27AM - 11:39AM |
T16.00002: Perforated-Graphene Enabled Organic Vertical Field Effect Transistors Nicholas S. Cunningham, Maxime G. Lemaitre, Bo Liu, Mitchell A. McCarthy, Andrew G. Rinzler Following on the heels of the carbon nanotube enabled vertical field effect transistor (CN-VFET, B. Liu et al. Adv. Mater. 2008, 20, 3605--3609) graphene enabled vertical field effect transistors (G-VFETs, M. Lemaitre et al. ACS Nano 2012, 6, 9095-9102) provided an opportunity to distinguish between the mechanisms contributing to the excellent performance of these Schottky barrier controlled devices: barrier height lowering due to the gate field induced modulation of the Fermi level on the carbon side of the junction or tunneling through the barrier due to its gate field induced thinning. Devices fabricated with a continuous layer of graphene probed principally the barrier height lowering mechanism (responsible for 2 1/2 order of magnitude current modulation) while devices fabricated with graphene into which random, micron scale holes had been created probed tunneling as well (resulting in 6 orders of magnitude current modulation). The random hole density in the latter case was limited to 20{\%} of the graphene surface area. Here we describe the performance of devices in which ordered hole arrays permit the exploration of higher hole density G-VFETs. [Preview Abstract] |
Thursday, March 5, 2015 11:39AM - 11:51AM |
T16.00003: On-Chip Electrolytic Chemistry for the Tuning of Graphene Devices Scott Schmucker, Laura Ruppalt, James Culbertson, Jae Won Do, Joseph Lyding, Jeremy Robinson, Cory Cress The inherent interfacial nature of two-dimensional materials has motivated the tuning of these films by choice of substrate or chemical functionalization. Such parameters are generally selected during fabrication, and therefore remain static during device operation. However, the possibility of dynamic chemistry in a tunable solid-state system will enable the development of new devices which fully leverage the rich chemistry of graphenic materials. Here, we fabricate a novel device for localized, dynamic doping and functionalization of graphene that is compatible with CMOS processing. The device is enabled by a top-gated, solid electrochemical cell designed with calcium fluoride (CaF$_{\mathrm{2}})$ substituting the oxide of a traditional MOSFET. When the CaF$_{\mathrm{2}}$ is gated, F flows from cathode to anode, segregating Ca and F. In this work, one electrode is graphene. When saturated with fluorine, graphene undergoes covalent modification, becoming a wide-bandgap semiconductor. In contrast, when functionalized with calcium or dilute fluorine, graphene is electron or hole doped, respectively. With transport, Raman, and XPS, we demonstrate this lithographically localized and reversible modulation of graphene's electronic and chemical character. [Preview Abstract] |
(Author Not Attending)
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T16.00004: Ab initio quantum transport in N-doped graphene Jean-Christophe Charlier, Andr\'es R. Botello-M\'endez, Aur\'elien Lherbier Electronic structure and transport properties of N-doped graphene with a single sublattice preference~[1] are then investigated using both first-principles techniques and a real-space Kubo-Greenwood approach [2]. Such a breaking of the sublattice symmetry leads to the appearance of a true band gap in graphene electronic spectrum even for a random distribution of the N dopants. In addition, a natural spatial separation of both types of charge carriers at the band edge is observed, leading to a highly asymmetric electronic transport. For such N-doped graphene systems, the carrier at the conduction band edge present outstanding transport properties including long mean free paths, high mobilities and conductivities. Such a transport behavior can be explained by a non-diffusive regime (quasi-ballistic transport behavior at the conduction band edge), and originates from a low scattering rate [2]. The presence of a true band gap along with the persistence of carriers traveling in an unperturbed sublattice suggest the use of such N-doped graphene in G-FET applications, where a high Ion/Ioff ratio is expected.\\[4pt] [1] R. Lv, Q. Li, A.R. Botello-Mendez, et al. Nature - Scientific Reports 2, 586 (2012).\\[0pt] [2] Electronic and transport properties of unbalanced sublattice N-doping in graphene, A. Lherbier, A.R. Botello-M\'{e}ndez, and J.-C. Charlier, Nano Lett. 13, 1446-1450 (2013). [Preview Abstract] |
Thursday, March 5, 2015 12:03PM - 12:39PM |
T16.00005: Hofstadter's Butterfly in the strongly interacting regime Invited Speaker: Cory Dean In 1976, Douglas Hofstadter predicted that in the presence of both a strong magnetic field, and a spatially varying periodic potential, Bloch electrons confined to a 2D quantum well exhibit a self-similar fractal energy spectrum known as the ``Hofstadter's Butterfly.'' In subsequent years, experimental discovery of the quantum Hall effect gave birth to an expansive field of research into 2D electronic systems in the presence of a magnetic field, however, direct confirmation of the fractal spectrum remained elusive. Recently we demonstrated that graphene, in which Bloch electrons can be described by Dirac fermions, provides a new opportunity to investigate this nearly 40 year old problem. In this talk I will discuss the experimental realization of Hofstader's butterfly by exploiting nano-scale interfacial effects between graphene and hexagonal boron nitride substrates, together with application of extremely high magnetic fields. Utilizing newly developed techniques to fabricate ultra-clean graphene devices, I will additionally demonstrate the capability to probe for the first time the effect of strong electron interactions within the fractal Hofstadter spectrum. [Preview Abstract] |
Thursday, March 5, 2015 12:39PM - 12:51PM |
T16.00006: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 12:51PM - 1:03PM |
T16.00007: Non-Equlibration of Edge States at the Graphene P-N Junction Interface Son Le, Nikolai Klimov, David Newell, Curt Richter, Jun Yan, Pratik Agnihotri, Everett Comfort, JiUng Lee The interaction of chiral quantized edge states at the graphene pn-junction (pnJ) interface at low temperature and high magnetic fields is topic of intense research recently [1]. It has been presumed that electron and hole edge states completely equilibrate with each other at the pnJ interface, creating an unique set of quantized longitudinal resistance values depending on the number of edge states that present in the device [2]. Experimentally, we have used a unique buried-split gate structure to electrostatically form a graphene pnJ with independent control of the number of edge state in the n- and p-regions of the device's channel. Measurement of both longitudinal and pseudo-Hall resistance shows quantized values that cannot be explained by using the complete equilibration model. We present a new ``non-equilibration'' model, in which only the lowest Landau level's (LLs) edge states equilibrate at the pnJ interface, while edge states arising from higher filling factor LLs propagate along the interface without equilibration. Our new model agrees with both the longitudinal and pseudo-Hall resistance results. \\[4pt] [1] J. R. Williams, L. DiCarlo, and C. M. Marcus, Science 317, 638 (2007).\\[0pt] [2] D. A. Abanin and L. S. Levitov Science 317, 641 (2007). [Preview Abstract] |
Thursday, March 5, 2015 1:03PM - 1:15PM |
T16.00008: Graphene/Lead (Pb)-based Cooper -pair splitter Ivan Borzenets, Yuya Shimazaki, Gareth Jones, Saverio Russo, Michihisa Yamamoto, Seigo Tarucha We have fabricated a Cooper-pair splitter device based on a superconductor- two normal leads, ``Y'' shaped junction with graphene as the base material. (Compared to nanowire-based devices, the two dimensional nature of graphene allows for the normal leads to be placed arbitrarily close together and in a non-parallel arrangement.) The superconducting lead is created by contacting graphene with lead (Pb), thus inducing a supercurrent via the proximity effect. The normal metal leads are patterned into quantum dots by etching nano-constrictions with self-aligned side gates. Quantum dots strongly suppress two electron processes, allowing only one electron to pass at a time. Thus, the Cooper-pair splitting efficiency is enhanced as the split electrons must necessarily tunnel through different quantum dots. Using a DC measurement we have demonstrated enhanced currents though both normal leads when both quantum dots are in resonance and the input lead is in the superconducting regime: demonstrating Cooper-pair splitting. (This is contrary to the classical regime of currents though a three resistor junction.) Shot noise measurements would demonstrate that the split electrons tunnel at the same time. Demonstrating that the split electrons have opposite spin would show that such a device could be used as a source of quantum entangled electrons. [Preview Abstract] |
Thursday, March 5, 2015 1:15PM - 1:27PM |
T16.00009: Electromechanically generating electricity with a gapped-graphene electric generator Donald Dressen, Jene Golovchenko We demonstrate the fabrication and operation of a gapped-graphene electric generator (G-GEG) device. The G-GEG generates electricity from the mechanical oscillation of droplets of electrolytes and ionic liquids. The spontaneous adsorption of ionic species on graphene charges opposing electric double-layer capacitors (EDLCs) on each half of the device. Modulating the area of contact between the droplet and graphene leads to adsorption/desorption of ions, effectively charging/discharging each EDLC and generating a current. The flow of current supports a potential difference across the G-GEG due to the device's internal impedance. Both the magnitude and polarity of the induced current and voltage show a strong dependence on the type of ionic species used, suggesting that certain ions interact more strongly with graphene than others. We find that a simple model circuit consisting of an AC current source in series with a resistor and a time-varying capacitor accurately predicts the device's dynamic behavior. Additionally, we discuss the effect of graphene's intrinsic quantum capacitance on the G-GEG's performance and speculate on the utility of the device in the context of energy harvesting. [Preview Abstract] |
Thursday, March 5, 2015 1:27PM - 1:39PM |
T16.00010: Transport measurements of negative refractive behavior in ballistic graphene hetero junctions Gil-Ho Lee, Geon-Hyoung Park, Minsoo Kim, Jae Hyeong Lee, Hu-Jong Lee We investigated the electronic current refraction at p-n junctions (PNJs) in ballistic monolayer graphene. Given a peculiar band structure of the graphene, the transmission of electrons through a PNJ is predicted to be similar to the optical refraction at the boundary of metamaterials with negative refractive index. In consequence, electrons waves injected at a point in one side of a junction can be refocused into a single point in the other side of the junction, which demonstrates Veselago lensing for the electrons. By adopting high-yield dry-transfer technique, we fabricated fully ballistic graphene devices encapsulated by hexagonal boron nitrides with a local top gate. We will present the signatures of negative refractive transport behavior of electrons in PNJs and also discuss about the electronic current focusing in p-n-p heterojunctions in terms of Veselago lensing. [Preview Abstract] |
Thursday, March 5, 2015 1:39PM - 1:51PM |
T16.00011: A ballistic gate-tunable contact junction in graphene Quentin Wilmart, Michael Rosticher, Mohamed Boukhicha, Andreas Inhofer, Pascal Morfin, Gwendal Feve, Jean-Marc Berroir, Bernard Placais Field-effect control of carrier is very efficient in graphene and allows controlling the doping profile with a great accuracy and high spatial resolution. This is needed if one wants to implement Dirac fermion optics experiments or simply to improve the performance of graphene devices. In this work we realize graphene transistors equipped with a set of local back-gates that provide control of local electric fields in the $10^8 V/m$ range at the $10$ nanometer scale. In particular we demonstrate ballistic contact junctions using transistors with independent channel and contact back-gates. We shall discuss the possibilities offered by this technology for ballistic electronic and opto-electronic applications. [Preview Abstract] |
Thursday, March 5, 2015 1:51PM - 2:03PM |
T16.00012: Enhanced OFF state resistance in reconfigurable graphene p-n junction Pratik Agnihotri, Surajit Sutar, Everett Comfort, James Hone, Philip Kim, Ji Ung Lee Graphene, since its discovery, has proved to be a promising candidate to meet the challenges facing CMOS-based logic devices. PN junctions made of graphene have the unique property of angle dependent charge transport, which can be used for reconfigurable logic. Electrons in graphene behave like photons in optoelectronic devices with zero mass and linear energy dispersion relation. A graphene PN junction refracts electrons and can perform logic operations by focusing and defocusing the electron flow. In our work, we present the fabrication and characterization of graphene p-n junctions, formed using electrostatic doping techniques from buried split gates. Each gate can be individually biased to create all possible p-n configurations. Angle dependent charge transport studies are conducted on sandwich hexagonal boron nitride-graphene stack and on single domain CVD graphene on hexagonal boron nitride. Normal conduction modes which are perpendicular to the junction are blocked geometrically by rotating the channel with respect to the junction. Due to this effect conductance in graphene at charge neutrality point is lower than the minimum conductivity of graphene commonly reported in many articles as 4e$^{\mathrm{2}}$/h. [Preview Abstract] |
Thursday, March 5, 2015 2:03PM - 2:15PM |
T16.00013: Controllable P-N Junctions in Graphene-Ferroelectric Devices J. Henry Hinnefeld, Ruijuan Xu, Steven Rogers, Moonsub Shim, Lane Martin, Nadya Mason Graphene's linear dispersion relation and the attendant implications for bipolar electronics applications have motivated a range of experimental efforts aimed at producing p-n junctions in graphene. Recent experimental results indicate that the electrical polarization in ferroelectric substrates can modify the local doping in graphene, via a hysteretic gating effect. Here, we exploit this effect to create variably doped local regions in a graphene device having a single, universal back-gate. By patterning devices on a partially shielded ferroelectric substrate, we show through electrical transport measurements that p-,i- and n-doped regions can be induced in the system. We explore the competing effects of substrate polarization and interfacial charge-trap processes that contribute to this behavior, along with the time evolution of the effect and its dependence on the measurement conditions and device parameters. [Preview Abstract] |
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