Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session S40: Monolayer Devices |
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Sponsoring Units: DCMP Chair: Jingsong Xu, The Ohio State University Room: LACC 501C |
Thursday, March 8, 2018 11:15AM - 11:27AM |
S40.00001: Graphene Cantilever under Casimir Force Amel Derras-Chouk, Eugene Chudnovsky, Dmitry Garanin, Reem Jaafar Previously, one of the authors studied stability of the suspended graphene against sinking towards the underlying conductor due to Casimir force [1]. In this work we investigate stability and dynamics of a graphene nanocantilever. Analytical work is supplemented by numerical studies of the critical length of the cantilever above which it becomes unstable. The dependence of the instability threshold on temperature and flexural rigidity is obtained. It is argued that graphene cantilever may be an excellent tool for precision measurement of the Casimir force. |
Thursday, March 8, 2018 11:27AM - 11:39AM |
S40.00002: Electrically programmable quantum resistance standards with epitaxial graphene PN junctions Jiuning Hu, Mattias Kruskopf, Yanfei Yang, Chieh-W Liu, Chieh-I Liu, Jifa Tian, Biyi Wu, Albert Rigosi, George Jones, Alireza Panna, Marlin Kraft, Hsin Yen Lee, Kenji Watanabe, Takashi Taniguchi, Joseph Stroscio, Randolph Elmquist, David Newell Epitaxial graphene has been identified as an excellent platform for resistance standards based on the quantum Hall effect (QHE) because of the wide plateaus and large breakdown current. The bipolar nature of graphene also allows it to be electrically gated to form PN junctions for convenient scaling of QHE-based resistance standards. We have fabricated top gated epitaxial graphene PN junction samples using hexgonal boron nitride (hBN) as dielectric materials and have measured the samples with highly accurate resistance bridges. The four terminal longitudinal resistance across a single junction is well quantized at h/e2 with an error of about 0.1 ppm on one edge and is around milli-ohm on the opposite edge. We have determined the optimal conditions where the breakdown current is maximized. Measurement using cryogenic current comparator is ongoing and array of PN junctions is under fabrication. Our work opens the possibility to realize high accuracy electrical resistance standards that are programmable using external gating. |
Thursday, March 8, 2018 11:39AM - 11:51AM |
S40.00003: Giant Electron-Hole Transport Asymmetry in Ultra-Short Quantum Transistors Andrew Mcrae, Vahid Tayari, James Porter, Alexandre Champagne Making use of bipolar transport in single-wall carbon nanotube quantum transistors would permit a single device to operate as both a quantum dot and a ballistic conductor or as two quantum dots with different charging energies. Here we report ultra-clean 10 to 100 nm scale suspended nanotube transistors with a large electron-hole transport asymmetry. The devices consist of naked nanotube channels contacted with sections of tube under annealed gold. The annealed gold acts as an n-doping top gate, allowing coherent quantum transport, and can create nanometre-sharp barriers. These tunnel barriers define a single quantum dot whose charging energies to add an electron or a hole are vastly different (e−h charging energy asymmetry). We parameterize the e−h transport asymmetry by the ratio of the hole and electron charging energies ηe−h. This asymmetry is maximized for short channels and small band gap tubes. In a small band gap device, we demonstrate the fabrication of a dual functionality quantum device acting as a quantum dot for holes and a much longer quantum bus for electrons. In a 14 nm-long channel, ηe−h reaches up to 2.6 for a device with a band gap of 270 meV. The charging energies in this device exceed 100 meV. |
Thursday, March 8, 2018 11:51AM - 12:03PM |
S40.00004: Strain-Engineered Ultrhigh Mobility Phosphorene for Radio Frequency Transistor from First Principles Ruhao Fang, Xiangyuan Cui, Rongkun Zheng Two-dimensional phosphorene has been considered as a potential candidate for field-effect transistors due to its high hole mobility. Here we present a systematic ab-initio investigation of anisotropic electrical structure of few layer phosphorene under strains in both zigzag and armchair directions. Among these cases, the monolayer under 7.5~10% strain along zigzag direction shows an exceptional ~106 cm2V-1s-1 carrier mobility, which is significantly higher than non-strain case. Along with the Silvaco simulation for designed field0effect transistor(FET) devices, our results suggest that phosphorene based FETs have potential application in radio frequency devices. |
Thursday, March 8, 2018 12:03PM - 12:15PM |
S40.00005: Graphene Quantum Strain Transistors Andrew Mcrae, Guoqing Wei, Alexandre Champagne We present an applied theoretical model for ballistic transport in uniaxially strained graphene. This model combines theoretical transport models with realistic experimental limitations originating from suspended device design, materials, and instrumentation. We find clear theoretical evidence for the possibility of high on/off ratio transistors in uniaxially strained ballistic graphene. We refer to these devices as graphene quantum strain transistors. We include realistic values for device dimensions (L = 100 nm, W = 1000 nm), contact doping (0.05 - 0.25 eV), and experimentally available strain (2.5 - 5.0 %) in a break-junction geometry. In this model, we consider first order strain effects which deform the Dirac cones, and shift the energy and momentum positions of the Dirac points. At sufficient strains, there is total internal reflection of the charge carriers at low gate voltages. As a result, we calculate on/off ratios > 104 in our graphene quantum strain transistors, tunable by both strain and gate voltage. We show how experimental strain-tunable transport can be used to calibrate the applied strain, and determine crystal chirality and contact doping of the devices. Finally, we present initial experimental data which supports the predictions of our model. |
Thursday, March 8, 2018 12:15PM - 12:27PM |
S40.00006: Investigation of Thickness-dependent Avalanche Breakdown Phenomena in MoS2 Field-Effect Transistors Jinsu Pak, Yeonsik Jang, Kyungjune Cho, Tae-Young Kim, Jae-Keun Kim, Barbara Yuri Choi, Jiwon Shin, Seungjun Chung, Takhee Lee Recently, two-dimensional (2D) molybdenum disulfide (MoS2) has been widely investigated to realize field-effect transistor (FET) applications.[1] Although their electrical characteristics have been extensively studied, there is no report on the electrical properties of MoS2 FETs under a high electric field due to their limited efficiency of energy dissipation from atomically-thin thickness. |
Thursday, March 8, 2018 12:27PM - 12:39PM |
S40.00007: Transport and resistance noise spectroscopy of Bi2S3 nanobeam transistors Ahmed Ali, Colin Kilcoyne, Ali Alsaqqa, Ajara A Rahman, Luisa Whittaker-Brooks, Sambandamurthy Ganapathy Semiconducting chalcogenides have attracted interest due to the interesting properties they display, especially in low dimensional structures. Bi2S3 nanostructures exhibit valuable physical properties such as high bulk mobility, small bandgap, and low thermal conductivity and serve as good candidates for electrical and thermoelectric applications. Bi2S3, like many other sulfide compounds, is prone to sulfur vacancies which generate midgap states in the band structure thereby altering the electrical and optical properties. The electrical transport and resistance noise behavior of Bi2S3 nanobeam field effect transistors are investigated over a wide range of frequency, temperature, and gate voltage. As the gate voltage is swept from the OFF state to the ON state of the transistor, the noise magnitude shows orders of magnitude raise indicating that the Fermi level passes through a high density of unoccupied states. The results will be discussed to understand the presence of midgap states and trapping/de-trapping of charge carriers in these states as the charge carrier density is modulated. |
Thursday, March 8, 2018 12:39PM - 12:51PM |
S40.00008: Nonlinear response of a ballistic graphene transistor with an ac-driven gate: high harmonic generation, THz detection, and non-adiabatic pumping Tomas Lofwander, Oleksii Shevtsov, Yevgeniy Korniyenko We present results for time-dependent electron transport in a ballistic graphene field-effect transistor with an ac-driven gate [1-4]. Nonlinear response to the ac drive is derived utilizing Floquet theory for scattering states in combination with Landauer-Buettiker theory for transport, current and noise. Inelastic scattering induced by the ac drive can excite quasibound states in the channel that leads to resonance promotion of higher-order sidebands. We propose that the device operated in the weak-drive regime can be used to detect THz radiation, while in the strong-drive regime, it can be used as a frequency multiplier. For a set-up with an asymmetric doping profile between source and drain, we explore resonant single-parameter pumping. |
Thursday, March 8, 2018 12:51PM - 1:03PM |
S40.00009: Field-effect transistors with parallel arrays of atomically precise graphene nanoribbons Juan Llinas, Gabriela Borin Barin, Kyunghoon Lee, Shuang Wu, Akimitsu Narita, Klaus Müllen, Roman Fasel, Jeffrey Bokor Bottom-up synthesized graphene nanoribbons (GNRs) have promising properties for high-performance field-effect transistors (FETs). We have demonstrated FETs with individual, randomly oriented 9-atom wide GNRs that exhibit high on-current and on-off ratio. However, it is challenging to improve the device yield and to control the number of GNRs in the channel due to the random orientation of the GNRs. In order to demonstrate a practical FET for digital logic applications, the current of the FET must scale with electrode width and the device yield must be improved to 100%. Here, we demonstrate FETs with parallel arrays of GNRs grown on Au(788) crystals and transferred via a bubble transfer technique. We observe greatly improved device yield and compare the electrical characteristics of these devices to other devices incorporating dense, parallel arrays of 1-dimensional semiconductors. |
Thursday, March 8, 2018 1:03PM - 1:15PM |
S40.00010: Photogating in few-layered ReS2 Phototransistors Carlos Garcia, Nihar Pradhan, Luis Balicas, Stephen McGill Two-dimensional layered transition metal dichalcogenides (TMDs) have shown much promise due to their remarkable electro-optical properties and potential uses as photodetectors. We measured the photoconductivity on few-layered (≤ 10 layers) ReS2 field-effect transistors (FET) in both two-terminal and four-terminal configurations using a 532 nm excitation source. The photocurrent was measured as a function of incident optical power, drain-source voltage, and back-gate voltage. We obtained a maximum responsivity (R) of 45 A/W corresponding to an external quantum efficiency (EQE) of ~10,500% in the four-terminal configuration. We also observed photogating, in which varying the incident optical power shifts the FET threshold voltage. We will present our results and discuss their implications for the presence of trap states and the effect on the overall channel carrier density. |
Thursday, March 8, 2018 1:15PM - 1:27PM |
S40.00011: Nonlinear optical effects in intrinsic and doped 2D semiconductors Fabio Hipolito, Alireza Taghizadeh, Thomas Pedersen We present a general method to compute the nonlinear optical response, using the length gauge that avoids unphysical divergences otherwise present in the evaluation of the nonlinear current density response. |
Thursday, March 8, 2018 1:27PM - 1:39PM |
S40.00012: Carrier Trapping by Oxygen Impurities in Molybdenum Diselenide Ke Chen, Anupam Roy, Amritesh Rai, Sanjay Banerjee, Yaguo Wang Trapping of photo-excited carriers by oxygen impurities is studied with ultrafast pump-probe spectroscopy. In exfoliated multilayer MoSe2, oxygen impurities are intentionally created with Ar+ plasma irradiation and air exposure. After plasma treatment, the signal of transient absorption shows a signature of defect capturing carriers. In CVD grown monolayer MoSe2, oxygen impurities are induced during the growth process and confirmed with X-ray photoelectron spectroscopy. For both samples, the observed defect state filling shows a clear saturation at high exciton densities, from which the trapping defect densities are estimated from the transient absorption signal. In CVD grown monolayer MoSe2, the defect density is around 0.5x1012/cm2. In plasma treated exfoliated sample, the trapping defect density increases with plasma irradiation time. First principle calculations with density functional theory reveal that oxygen atoms occupying Mo vacancies create mid-gap defect states, which are responsible for the carrier trapping, while oxygen atoms occupying chalcogen vacancies can remove the mid-gap state. |
Thursday, March 8, 2018 1:39PM - 1:51PM |
S40.00013: Near-field Surface Waves in Few-Layer MoS2 Yohannes Abate, Viktoriia Babicheva, Sampath Gamage, stephen Cronin, Vlad Yakovlev Abstract. Recently emerged layered transition metal dichalcogenides have attracted great interest due to their intriguing fundamental physical properties and potential applications in optoelectronics. Using nano-imaging and theoretical modeling, we study propagating surface waves in the visible spectral range that are excited at sharp edges of layered transition metal dichalcogenides (TMDC) such as molybdenum disulfide and tungsten diselenide. By measuring how the fringes change when the sample is rotated with respect to the incident beam, we obtain evidence that exfoliated MoS2 on a silicon substrate supports two types of Zenneck surface waves that are predicted to exist in materials with large real and imaginary parts of the permittivity. We have compared MoS2 interference fringes with those formed on layered insulator such as hexagonal boron nitride where only leaky modes are possible due to its small permittivity. Interpretation of experimental data is supported by theoretical models. |
Thursday, March 8, 2018 1:51PM - 2:03PM |
S40.00014: Observation of Anisotropic Effects in Electron Transport in layered TiS2 Single Crystals. Dhavala Suri, Ram Shanker Patel In this work we present our investigations on transition metal dichalcogenide - TiS2 single crystals and show a detailed investigation of resistivity measurements performed in the current in-plane (CIP) and current perpendicular-to-plane (CPP) configurations. We observe a strong structural anisotropy (~103) through resistivity measurements in the two configurations. The CIP resistivity varies as T3 at low temperatures (9 - 30 K), following Bloch - Wilson scattering. From 31 - 300 K, the temperature varies as T1.6 and is attributed to strong coupling between electron and acoustic phonons. The CPP configuration shows similar behavior up to 200 K. However, the CPP resistivity diverges as T5 above 200 K up to room temperature which is highly interesting. We are able to induce exactly the same behavior in the CIP configuration through ion beam irradiation. We suggest that the T5 dependence in the CPP mode of pristine sample and CIP mode of irradiated sample is due to flexural phonons. This result is intriguing and opens up opportunities for further theoretical and experimental investigations on TiS2. |
Thursday, March 8, 2018 2:03PM - 2:15PM |
S40.00015: Single atomic layer protective barrier for Cu photocathodes Fangze Liu, Hisato Yamaguchi, Vitaly Pavlenko, Mark Hoffbauer, Kevin Jensen, Claudia Villarrubia, Aditya Mohite, Nathan Moody We describe an initial study to evaluate the efficacy of single-layer graphene and hexagonal boron nitride (hBN) films on photoemission properties of Cu cathodes. Many cathode material systems can benefit from a protective, passivating surface layer, so long as this layer does not significantly hinder the emission of the electron beam or increase beam emittance. Graphene and hBN are known to be excellent barriers for protecting transition metal surface, as well as reducing the work function of these metals. We utilize Cu, a well-known photoemitter and growth substrate for graphene and hBN, as a platform for understanding the key features as a passivating layer for photocathodes. Photoelectric work function and quantum efficiency were measured by UV-Vis photoemission yield spectra. The protected Cu photocathodes exhibit lower work function and higher quantum efficiency. These cathodes are also resilient to degradation when subjected to atmospheric conditions. Moreover, the validation of graphene/hBN-photocathode compatibility opens a new route to the lifetime-extension for photocathodes, especially for those more fragile III–V or alkali-antimonide semiconductor families. |
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