Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session J7: Focus Session: Graphene Devices VI |
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Sponsoring Units: DMP Chair: Roman Gorbachev, University of Manchester Room: 303 |
Tuesday, March 19, 2013 2:30PM - 2:42PM |
J7.00001: Effects of optical and surface polar phonons on the optical conductivity of doped graphene Vasili Perebeinos, Benedikt Scharf, Jaroslav Fabian, Phaedon Avouris During the past decade, graphene has attracted immense interest, mainly due to its excellent transport and optical properties, which make it an attractive candidate for possible applications in nanoscale electronics and optoelectronics. Using the Kubo linear response formalism, we study the effects of intrinsic graphene optical and surface polar phonons (SPPs) on the optical conductivity of doped graphene. We find that inelastic electron-phonon scattering contributes significantly to the phonon-assisted absorption in the optical gap. At room temperature, this midgap absorption can be as large as about 20-25{\%} of the universal ac conductivity for graphene on polar substrates (such as Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ or HfO$_{\mathrm{2}})$ due to strong electron-SPP coupling. The midgap absorption, moreover, strongly depends on the substrates and doping levels used. We predict that with increasing temperature, the midgap absorption increases, while the Drude weight decreases. These predictions can serve as an experimental signature for the role of SPPs on transport and optical properties of graphene, which have important implications for the performance of graphene-based electronic devices and broadband modulators. [Preview Abstract] |
Tuesday, March 19, 2013 2:42PM - 2:54PM |
J7.00002: Electrically detected spin resonance in epitaxial graphene Ramesh Mani, John Hankinson, Claire Berger, Walter de Heer Graphene is an appealing material for electron-spin quantum computing (QC) and spintronics, due to the expected weak spin-orbit interaction, and the scarcity of nuclear spin in natural carbon. Due to QC and spintronics, the microwave control and electrical detection of spin have become topics of interest, now in graphene nanostructures, where the small number of spins limits the utility of traditional spin resonance. Here, we report results of an experimental study examining the microwave response of epitaxial graphene.[1] The results suggest the possibility of resistive detection of spin resonance, and they provide a measurement of the g-factor and the spin relaxation time in this novel system.\\ \\ \noindent [1] R. G. Mani, J. Hankinson, C. Berger, and W. de Heer, Nature Comm. 3, 996 (2012). [Preview Abstract] |
Tuesday, March 19, 2013 2:54PM - 3:06PM |
J7.00003: Growth, fabrication, and applications of graphene nanostructures Guangyu Zhang Recently, a broad category of research focused on graphene nanostructures, including graphene nanosheets and nanoribbons. These graphene nanostructures have unique properties related to their sizes, shapes, and edge configurations and might be used as building blocks for various miniaturized graphene-based devices. Large-are growth and scaled-up fabrication of high-quality graphene nanostructures are challenging. In this talk, I will introduce our recent progress on grow large area nanographene directly on substrates and scaled-up fabrication of graphene nanoribbons with controlled width and edge configurations (zigzag edges). Electronic and optical spectroscopy studies on the zigzag-edged graphene nanoribbons yield the experimentally observed metallic edge states and electron-phonon coupling effect. Nanographene-based piezoresistive strain sensors and resistive randomly accessed memories will also be introduced. [Preview Abstract] |
Tuesday, March 19, 2013 3:06PM - 3:42PM |
J7.00004: Toward Graphene-Based Microwave Photon Counter Invited Speaker: Kin Chung Fong Graphene is a material with remarkable electronic properties. However, the thermal properties of this two-dimensional Dirac Fermions, that determine the characteristics of photo detectors, plasmonic devices, and bolometers, are less explored. Here, we present our measurement of specific heat capacity, Wiedemann-Franz (WF), and electron-phonon (e-ph) thermal conductance from 0.3 to 100 K using the novel single layer graphene bolometer [1]. These measurements suggest that graphene-based devices can generate substantial advances in the areas of ultra-sensitive bolometry, calorimetry, microwave, and terahertz single photon detection for applications in areas such as observational astronomy, quantum information and measurement. The physics of the e-ph coupling and the possible violation of Wiedemann-Franz Law near the charge neutrality point in single layer graphene will be discussed.\\[4pt] This work is a collaboration with Emma Wollman, Harish Ravi, and K. C. Schwab of Caltech. This work has been supported by the FCRP Center on Functional Engineering Nano Architectonics (FENA) and U.S. NSF Contract No. (DMR-0804567).\\[4pt] [1] K.C. Fong and K.C. Schwab, Phys. Rev. X 2, 031006 (2012) [Preview Abstract] |
Tuesday, March 19, 2013 3:42PM - 3:54PM |
J7.00005: Photovoltaic response time in dual-gated bilayer graphene M.-H. Kim, J. Yan, R.J. Suess, T. Murphy, M.S. Fuhrer, H.D. Drew The intrinsic thermal response timescale of bilayer graphene is sub nanosecond, due to cooling of hot electrons mediated by acoustic phonon emission. We compare the response times of the photovoltaic and bolometric response as a function of temperature and dual-gate voltages in a gapped bilayer graphene device using a pulse coincidence technique at 1.5 $\mu$m. We find that the photovoltaic and bolometric response time are identical and vary from 100 ps to 10 ps for temperatures from 3 K to 100 K. This result shows that the near IR photovoltaic response of bilayer graphene is thermal over this temperature range. This work was supported by IARPA, the ONR MURI program, and the NSF (grants DMR-0804976 and DMR-1105224), and in part by the NSF MRSEC (grant DMR-0520471). [Preview Abstract] |
Tuesday, March 19, 2013 3:54PM - 4:06PM |
J7.00006: Graphene-Superconductor hybrid device as Bolometer Heli Vora, Naomi Mizuno, Piranavan Kumaravadivel, Bent Nielsen, Xu Du Low electronic heat capacity and small achievable volume has made graphene a promising candidate for a fast and sensitive bolometric detector. In our device scheme, in addition to low electron-phonon coupling we can further limit out-diffusion of hot electrons from graphene into the leads by placing tunnel-type superconducting contacts on graphene and preventing tunneling through the oxide barrier into the superconducting gap. We fabricate NbN contacts on graphene with a sandwich layer of titanium oxide tunnel barrier. Due to high dielectric constant of titanium oxide, our design allows device impedance matching with the antenna circuitry at THz frequencies, necessary to achieve practical device efficiency. We present our measurements of bolometric characteristics of thermal conductance, Noise equivalent Power (NEP) and responsivity for such a device. [Preview Abstract] |
Tuesday, March 19, 2013 4:06PM - 4:18PM |
J7.00007: Temporal characterization of hot-electron thermoelectric effect in monolayer graphene devices Ryan J. Suess, Xinghan Cai, Andrei Sushkov, Greg Jenkins, M.-H. Kim, Jun Yan, H. Dennis Drew, Thomas E. Murphy, Michael S. Fuhrer Graphene's unique electronic and optical properties have made it an attractive candidate material for photonics applications such as broadband optical detection. We report the temporal response of a monolayer graphene device with dissimilar metal electrodes in which optically induced hot-electrons are detected via a thermoelectric voltage induced between the electrodes. Measurements are carried out with a pulsed laser system (60 fs pulse width) at the telecom wavelength of 1.5 $\mu$m using an asynchronous optical sampling pulse coincidence technique. Graphene's weak electron-phonon coupling and our compact device geometry (comparable to the thermal diffusion length) result in a fast 10 - 20 ps non-linear thermal response that is nearly independent of temperature over the measured range of 15 - 150 K. Sensitivity of the devices response to optical power will also be discussed. These results are a follow-on to other talks reported by our group at this conference in which the fabrication, operating principal, and broad wavelength (THz to near IR) response of the graphene-based hot-electron bolometer are described. [Preview Abstract] |
Tuesday, March 19, 2013 4:18PM - 4:30PM |
J7.00008: Sensitive bolometry using hot-electron thermoelectric effect in graphene devices Xinghan Cai, Ryan J. Suess, Andrei Sushkov, Greg Jenkins, M.-H. Kim, Jun Yan, H. Dennis Drew, Thomas E. Murphy, Michael S. Fuhrer Due to the weak electron-phonon coupling and strong electron-electron interaction in graphene, the hot-electron thermoelectric effect provides a highly sensitive detection mechanism for heat absorbed in the electronic system, either by radiation or Joule heating. We have fabricated graphene devices using mechanically exfoliated single layer graphene contacted by two dissimilar metal electrodes (chromium and gold) in order to generate an asymmetry in the device and a net thermoelectric response to heating. We measure the thermoelectric response to Joule heating by an AC 2$^{nd}$ harmonic method, and compare to the thermoelectric response due to optical excitation in the near infrared and at THz frequencies. We find a sensitivity exceeding 100 V/W at room temperature. We also demonstrate that the sensitivity can be significantly enhanced by patterning the graphene sheet into nanoribbon arrays. The transport measurements indicate that graphene is a promising candidate for sensitive broadband photo detectors at room temperature. Related work by our group showing that ultra-broadband detection of light can be realized in such devices will be presented in other talks at this meeting. [Preview Abstract] |
Tuesday, March 19, 2013 4:30PM - 4:42PM |
J7.00009: Large-scale 2D Electronics based on Single-layer MoS2 Han Wang, Lili Yu, Yi-Hsien Lee, Wenjing Fang, Allen Hsu, Patrick Herring, Matthew Chin, Madan Dubey, Lain-Jong Li, Jing Kong, Tomas Palacios 2D nanoelectronics based on MoS2 and other transition metal dichalcogenides (TMD) materials are attractive as high-mobility options in the emerging field of large-area low-cost electronics that is currently dominated by low-mobility amorphous silicon and organic semiconductors. Single-layer MoS2 can also complement graphene to build flexible digital and mixed-signal circuits, overcoming its lack of bandgap while still sharing many of graphene's excellent mechanical and thermal properties. This paper addresses several key challenges in the development of 2D nanoelectronics on MoS2 and TMD materials in general. First, large-area single-layer MoS2 material is grown by chemical vapor deposition (CVD) that makes the wafer-scale fabrication of MoS2 devices and circuits possible for the first time. Second, the top-gated transistors, fabricated for the first time on single-layer MoS2 grown by CVD, show multiple state-of-the-art characteristics, such as high mobility, ultra-high on/off current ratio, record current density and current saturation. Finally, key circuit building blocks for digital and analog electronics such as inverter, NAND gate, memory and ring oscillator are demonstrated for the first time. [Preview Abstract] |
Tuesday, March 19, 2013 4:42PM - 4:54PM |
J7.00010: Band-like transport in high mobility single-layer MoS$_{2}$ FETs Deep Jariwala, Vinod Sangwan, James Johns, Dattatray Late, Ken Everaerts, Julian McMorrow, Lincoln Lauhon, Vinayak Dravid, Tobin Marks, Mark Hersam The recent realization of monolayered MoS$_{2}$ as a direct band gap two-dimensional semiconductor in contrast to zero gap graphene, has attracted significant attention for digital electronic applications. In most measurements to date, single-layer MoS$_{2}$ field-effect transistors (FETs) have shown low field-effect mobility values that have been explained by Mott variable range hopping (VRH) transport. In contrast, here we report variable temperature measurements on high mobility (greater than 50 cm$^{2}$/V.s at room temperature) single-layer MoS$_{2}$ FETs that show band-like transport with monotonic increase in mobility with decreasing temperature suggesting phonon quenching at low temperatures as also observed for graphene. The magnitude of the drain current remains constant across the range of temperatures (5.7 - 298 K), while the threshold voltage displays a positive shift. In this presentation we emphasize on high quality single-layer MoS$_{2}$ FETs with band-like transport and the highest reported field-effect mobility values (120 cm$^{2}$/V.s at 5.7 K) in devices without encapsulation in a high-$\kappa $ dielectric. [Preview Abstract] |
Tuesday, March 19, 2013 4:54PM - 5:06PM |
J7.00011: Wafer-scalable high-performance CVD graphene devices and analog circuits Li Tao, Jongho Lee, Huifeng Li, Richard Piner, Rodney Ruoff, Deji Akinwande Graphene field effect transistors (GFETs) will serve as an essential component for functional modules like amplifier and frequency doublers in analog circuits. The performance of these modules is directly related to the mobility of charge carriers in GFETs, which per this study has been greatly improved. Low-field electrostatic measurements show field mobility values up to 12k cm$^{\mathrm{2}}$/Vs at ambient conditions with our newly developed scalable CVD graphene. For both hole and electron transport, fabricated GFETs offer substantial amplification for small and large signals at quasi-static frequencies limited only by external capacitances at high-frequencies. GFETs biased at the peak transconductance point featured high small-signal gain with eventual output power compression similar to conventional transistor amplifiers. GFETs operating around the Dirac voltage afforded positive conversion gain for the first time, to our knowledge, in experimental graphene frequency doublers. This work suggests a realistic prospect for high performance linear and non-linear analog circuits based on the unique electron-hole symmetry and fast transport now accessible in wafer-scalable CVD graphene. *Support from NSF CAREER award (ECCS-1150034) and the W. M. Keck Foundation are appreicated. [Preview Abstract] |
Tuesday, March 19, 2013 5:06PM - 5:18PM |
J7.00012: Graphene Field-Effect Transistors with Gigahertz-Frequency Power Gain on Flexible Substrates Nicholas Petrone, Inanc Meric, Kenneth Shepard, James Hone The development of flexible electronics operating at radio-frequencies (RF) requires materials which combine excellent electronic performance and the ability to withstand high levels of strain. Graphene's unique electronic and mechanical properties make it a promising material for the fabrication of field-effect transistors (FETs) which require both high flexibility and high operating frequencies. Furthermore, large-area films of graphene which display excellent electronic properties, crucial for the commercial realization of graphene-based devices, can be synthesized facilely by chemical vapor deposition (CVD). We utilize CVD graphene to fabricate graphene FETs (GFETs) on flexible substrates. Our GFETs demonstrate unity-current-gain frequencies, $f_{T}$, and unity-power-gain frequencies, $f_{max}$, up to 10.7 and 3.7 GHz, respectively, with strain limits of 1.75{\%}. These devices represent the only reported technology to achieve gigahertz-frequency power gain at strain levels above 0.5{\%}. As such, they demonstrate the potential for CVD graphene to enable a broad range of flexible electronic technologies which require both high-flexibility and RF operation. [Preview Abstract] |
Tuesday, March 19, 2013 5:18PM - 5:30PM |
J7.00013: Optimization of Ferroelectric Polymer$\backslash $Graphene Films for Transparent and Flexible Electronics Orhan Kahya, Jing Wu, Guang-Xin Ni, Chee-Tat Toh, Sang-Hoon Bae, Jong-Hyun Ahn, Barbaros Oezyilmaz Nonvolatile, electrostatic doping of graphene-based devices with ferroelectric polymers such as Poly (vinylidene fluoride-trifluoroethylene) are promising for realizing ultra-fast, flexible memory devices, nanogenerators and actuators. More recently, the same approach has been shown to provide an alternative route in enabling graphene based transparent electrodes for touch screen applications. Here, we report a systematic study of optimizing the ferroelectric polymer-graphene heterostructure as a function of thickness, various copolymer blends and coating techniques. Optimized films show outstanding mechanical properties, low sheet resistance ($\sim$ 100$\Omega $/sq) and optical transparency levels as high as 96{\%}. [Preview Abstract] |
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