Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session S16: Focus Session: Graphene Devices: Function, Fabrication, and Characterization: van der Waals Heterostructures |
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Sponsoring Units: DMP Chair: Akm Newaz, San Francisco State University Room: 101AB |
Thursday, March 5, 2015 8:00AM - 8:12AM |
S16.00001: Bilayer Graphene-Hexagonal Boron Nitride Heterostructure Negative Differential Resistance Interlayer Tunnel FETs Sangwoo Kang, Babak Fallahazad, Kayoung Lee, Hema Movva, Kyounghwan Kim, Chris Corbet, Takashi Taniguchi, Kenji Watanabe, Luigi Colombo, Leonard Register, Emanuel Tutuc, Sanjay Banerjee We present the operation of a vertical tunneling field effect transistor using a stacked double bilayer graphene (BLG) and hexagonal boron nitride (hBN) heterostructure. The device is fabricated with the so-called Van der Waals transfer method with the edges of the top and bottom BLG flakes being rotationally aligned to roughly 60$^{\circ}$. The device shows multiple negative differential resistance (NDR) peaks which can be adjusted through the gate bias. Temperature dependent measurements show that the peak width of the differential conductance broadens and the height lowered when the temperature is increased, which is indicative of resonant tunneling. Through electrostatic calculations, it is shown that the multiple peaks occur when the two conduction bands at the K-point of the top and bottom bilayer graphene become aligned at certain bias conditions. It is also shown that by adjusting the rotational alignment of the bands of the top and bottom BLG through an in-plane magnetic field, the conductance peaks can be broadened. In addition, utilizing the NDR characteristic of the device, one-transistor latch or SRAM operation is demonstrated. [Preview Abstract] |
Thursday, March 5, 2015 8:12AM - 8:24AM |
S16.00002: Resonant Tunneling in Double Bilayer Graphene Heterostructures Babak Fallahazad, Kayoung Lee, Sangwoo Kang, Jiamin Xue, Stefano Larentis, Christopher Corbet, Kyounghwan Kim, Hema Movva, Takashi Taniguchi, Kenji Watanabe, Leonard Register, Sanjay Banerjee, Emanuel Tutuc We present the realization and characterization of independently contacted and rotationally aligned double bilayer graphene heterostructures, that show gate-tunable tunneling resonances and negative differential resistance in their interlayer current-voltage characteristics. Our devices are fabricated by successively stacking mechanically exfoliated bilayer graphene and hexagonal boron nitride dielectric using a layer-by-layer transfer technique. The bilayers are rotationally aligned during the device fabrication by selecting flakes with straight edges, and using them as a reference for alignment. We determine the heterostructure energy band alignment at the tunneling resonance using the individual layer carrier densities, and including the chemical potential dependence on the carrier density. Our analysis show that the tunneling resonances occur when the charge neutrality points of the two bilayer graphene are energetically aligned, which suggests the resonances stem from the momentum conserving tunneling. [Preview Abstract] |
Thursday, March 5, 2015 8:24AM - 9:00AM |
S16.00003: Graphene superlattices in van der Waals heterostructures Invited Speaker: Vladimir Falko The technological development of graphene has generated new high-quality systems offer access to the earlier inaccessible extremes of quantum physics. When graphene is placed on an atomically flat substrate with hexagonal lattice with a close lattice constant, such as boron nitride (hBN), and their crystalline axes are aligned, a long-wavelength perfectly periodic moir\'{e} pattern forms for electrons in graphene. Various regimes of possible moir\'{e} minibands at zero magnetic field [Phys. Rev. B 87, 245408 (2013); Phys. Rev. B~88, 205418; Phys. Rev. B 88, 155415 (2013); New J. Phys, 15, 123009 (2013)] and strong magnetic field [Nature 497, 594 (2013), Nature Physics 10, 525 (2014); Phys Rev B 89, 075401 (2014)] will be discussed. Experimentally available magnetic fields are enough to provide flux $\varphi $ through the moir\'{e} superlattice cell comparable to the magnetic flux quantum $\varphi_{0}$ and reach the regime of fractal Hofstadter spectra. As a result, a single device can offer a multiplicity of two-dimensional electron systems, realised at rational flux values $\varphi = \varphi_{0}$, $\varphi_{0}$/2, 2$\varphi_{0}$/3, etc., each with its own intricate topological properties, including quantum Hall effect physics related to the effective Landau levels emerging from these magnetic minibands at the nearby range of magnetic fields. [Preview Abstract] |
Thursday, March 5, 2015 9:00AM - 9:12AM |
S16.00004: A boron nitride - graphene - C$_{60}$ heterostructure Claudia Ojeda-Aristizabal, Elton J.G. Santos, Seita Onishi, Haider Rasool, Jairo Velasco Jr., Salman Kahn, Aiming Yan, Alex Zettl We have fabricated a new van-der-Waals heterostructure composed by BN/graphene/C$_{60}$. We performed transport measurements on the preliminary BN/graphene device finding a sharp Dirac point at the neutrality point. After the deposition of a C$_{60}$ thin film by thermal evaporation, we have observed a significant n-doping of the heterostructure. This suggests an unusual electron transfer from C$_{60}$ into the BN/graphene structure. This BN/graphene/C$_{60}$ heterostructure can be of interest in photovoltaic applications. It can be used to build devices like p-n junctions, where C$_{60}$ can be easily deposited in defined regions of a graphene junction by the use of a shadow mask. Our results are contrasted with theoretical calculations. [Preview Abstract] |
Thursday, March 5, 2015 9:12AM - 9:24AM |
S16.00005: Tunneling measurements in graphene-hexagonal boron nitride-based heterostructures U. Chandni, K. Watanabe, T. Taniguchi, J.P. Eisenstein Van der Waals heterostructures is an emerging field involving the study of layered materials consisting of various crystalline atomic planes exfoliated from bulk crystals and then stacked, often by hand, in custom-made patterns. Vertical tunneling structures made out of such quasi-2D crystals are potentially very interesting and may provide a new playground to observe electron-electron interaction effects in graphene and related materials. In the present work, we report the fabrication and study of several such tunnel junctions, including metal-hexagonal boron nitride (hBN)-metal, metal-hBN-graphite and metal-hBN-graphene devices. Tunneling measurements done at low temperatures and high magnetic fields reveal interesting and distinct features in each of these designs. [Preview Abstract] |
Thursday, March 5, 2015 9:24AM - 9:36AM |
S16.00006: Ultra-sensitive Hall sensors based on graphene boron nitride heterostructures Jan Dauber, Abhay A. Sagade, Martin Oellers, Kenji Watanabe, Takashi Taniguchi, Daniel Neumaier, Christoph Stampfer Recent developments of encapsulating graphene in hexagonal boron nitride lead to well protected graphene with very high material quality. This opens interesting possibilities for applications, such as graphene-based Hall sensors. Magnetic field sensors using Hall effect are widely used in different fields of applications, e.g. automotive and consumer electronics. Their performance benefits greatly from high room temperature mobility and low charge carrier density, which makes graphene boron nitride heterostructures a promising material for these devices. Here, we present the fabrication and characterization of Hall sensor elements based on graphene boron nitride heterostructures. We show a detailed characterization including Hall effect measurements under ambient and vacuum conditions. We achieve current- and voltage-related sensitivity up to 5700 V/AT and 3V/VT, respectively, outpacing state-of-the-art silicon and III/V Hall sensor devices. Finally, we determine a magnetic resolution limited by low frequency electric noise less than 0.5 mG/?Hz. [Preview Abstract] |
Thursday, March 5, 2015 9:36AM - 9:48AM |
S16.00007: Colossal Coulomb Drag in Double Bilayer Graphene Heterostructures Kayoung Lee, Jaimin Xue, Takashi Taniguchi, Kenji Watanabe, Emanuel Tutuc Double-layer electron systems, where charge carriers are apart into two parallel layers, have been of interest thanks to their various interlayer interaction phenomena. One of the peculiar interaction features is Coulomb drag, in which current flowing in one layer (drive layer) induces voltage drop in the opposite layer (drag layer) via interlayer momentum transfer. Recent progress in the fabrication of heterostructures consisting of atomic layer materials such as graphene and hexagonal boron nitride (hBN) has led to high mobility double layer systems. Here we probe Coulomb drag in double bilayer graphene heterostructures separated by 2 $-$ 5 nm thick hBN dielectrics. At temperatures ($T)$ lower than 30 K, we observe an anomalous Coulomb drag in the vicinity of the drag layer charge neutrality points, which increases as $T$ is reduced. At $T \quad =$ 1.4 K, the lowest temperature studied here, the drag resistivity becomes comparable to the layer resistivity at a finite drag layer density $n_{\mathrm{drag}} \quad \approx $ 1 $-$ 4 \textbullet 10$^{\mathrm{11}}$ cm$^{\mathrm{-2}}$. The ratio of the drag to layer resistivity increases as the hBN thickness reduces, and also as the drag layer mobility increases. At $T$ \textgreater 50K, we observe diffusive drag, which increases with $T$. [Preview Abstract] |
Thursday, March 5, 2015 9:48AM - 10:00AM |
S16.00008: Encapsulated Superconducting Graphene Nanodevices for Transport and Spectroscopic Studies Joel I-Jan Wang, Patrick Back, Yu-An Chen, Kenji Watanabe, Takashi Taniguchi, Pablo Jarillo-Herrero Through proximity effect, graphene provides an ideal platform to study mesoscopic superconductivity and other quantum phenomena when it is in contact with superconductors. The advancement in the fabrication techniques of 2-D Van der Waals heterostructures has brought the superconducting graphene nanodevice into ballistic regime and made it suitable for a variety of studies. We show superconducting graphene nanodevices encapsulated in hexagonal boron nitride (hBN) thin films. The pristine graphene can be proximitized by superconducting leads, manipulated by local gating and probed by tunneling leads in order to explore various kinds of physics. [Preview Abstract] |
Thursday, March 5, 2015 10:00AM - 10:12AM |
S16.00009: Tunnelling in graphene - boron nitride - graphene heterostructures: momentum and chirality conservation Artem Mishchenko, Jhih-Sian Tu, Yang Cao, John Wallbank, Mark Greenaway, Mengjian Zhu, Colin Woods, Vladimir Fal'ko, Laurence Eaves, Andre Geim, Konstantin Novoselov A new series of tunnel transistors will be presented: devices in which the two graphene layers are crystallographically aligned to a high degree of precision during the fabrication procedure. This critical step leads to resonant tunnelling and negative differential conductance in these heterostructures due to energy, momentum and chirality conservation, when two graphenes are rotationally aligned. I will also provide an intuitive geometric explanation of the physics of these twist-controlled transistors and show how the resonance peak and negative differential conductance in the device characteristics induce a tuneable radiofrequency oscillatory current that has potential for future high-frequency technology (potentially in THz regime). [Preview Abstract] |
Thursday, March 5, 2015 10:12AM - 10:24AM |
S16.00010: Electronic Transport in Graphene on hBN with impurities: DFT-NEGF Study Tomoaki Kaneko, Takahisa Ohno Graphene on hBN substrate shows much higher mobility compared with graphene on SiO$_2$ substrate. However, such good performance can be seen only for high quality hBN substrate. To understand such property, we performed the transport calculation of graphene adsorbed on hBN with impurities based on the density functional theories (DFT) and nonequilibrium Green's function method (NEGF). In this study, we consider the graphene adsorbed on monolayer hBN and we introduced carbon and oxygen impurities in hBN by replacing the B or N atoms. We employed PHASE code for the structure optimization and ASCOT code for transport calculation. We found that doping from hBN and impurity levels reduce the conductance. For the scattering by impurity levels, the stacking structure of graphene and hBN plays importance role. [Preview Abstract] |
Thursday, March 5, 2015 10:24AM - 10:36AM |
S16.00011: Electric field effects in graphene-complex-oxide heterostructures Giriraj Jnawali, Mengchen Huang, Jen-Feng Hsu, Feng Bi, Lu Chen, Rongpu Zhou, Hyungwoo Lee, Sangwoo Ryu, Chang-Beom Eom, Patrick Irvin, Brian D'Urso, Jeremy Levy Graphene has excellent electrical, chemical, and mechanical properties, which makes it a promising material for developing nanoscale electronic devices, while complex-oxide heterostructure provide sharply confined multifunctional interfaces that can be tailored at nanoscale dimensions. The combination--graphene-complex oxide heterostructures--merge the multifunctional properties of oxide interfaces such as high dielectric constant, metal-insulator-transition, magnetism, and superconductivity, with the unique electronic properties of graphene. Here we demonstrate some simple three-terminal field-effect devices that combine the electronic properties of these two systems. Nanoscale devices are fabricated from graphene/LaAlO$_3$/SrTiO$_3$ heterostructures using c-AFM lithography. We demonstrate field effects in both the graphene and LaAlO$_3$/SrTiO$_3$ interface. These novel heterostructures open new avenues for creating devices that combine the most interesting and unique properties of the coupled two-dimensional electron system. [Preview Abstract] |
Thursday, March 5, 2015 10:36AM - 10:48AM |
S16.00012: Inelastic vertical tunneling in graphene-based heterostructures Sergio de la Barrera, Randall Feenstra Lateral momentum conservation of tunneling states in graphene / hexagonal boron nitride / graphene heterostructures causes intriguing resonant behavior and negative differential resistance. We explain this phenomenon in terms of a simple model which includes electrostatic gating, rotational alignment between graphene layers, elastic scattering, and inelastic tunneling effects for both monolayer and bilayer graphene. We highlight recent experimental efforts to observe these effects in fabricated devices\footnote{Mishchenko et al., Nat. Nano. \textbf{9}, 808 (2014).} and compare with theory to validate our theoretical model. In order to improve future fabrication, we discuss disorder mechanisms, the differences between monolayer and bilayer graphene configurations, and the critical parameters which govern the characteristics of these devices. [Preview Abstract] |
Thursday, March 5, 2015 10:48AM - 11:00AM |
S16.00013: Sensitive room-temperature graphene-BN atomic stack terahertz detector Jiayue Tong, Martin Muthee, Shao-Yu Chen, Sigfrid K Yngvesson, Jun Yan Due to its high mobility, weak electron-phonon interaction and tunable broadband optical response, graphene is a promising material for high-speed optoelectronics such as terahertz (THz) detectors. In this presentation, I will discuss our studies of THz detection with graphene-BN heterostructure devices. Using a double-patch antenna that operates at around 1.9THz and an on-chip silicon lens, we demonstrate that asymmetrically-contacted graphene-BN heterostructure samples can efficiently detect THz laser radiation. Strong polarization dependence of our device indicates significant sensitivity improvement by antenna coupling and silicon lens coupling. We also find that responsivity can be tuned by changing the charge carrier density. Our work expands the methodology for making graphene-based THz detectors. [Preview Abstract] |
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