Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session A13: 2D Materials (General) -- TransportFocus
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Sponsoring Units: DMP DCOMP Chair: Daniel Ralph, Cornell University Room: BCEC 153B |
Monday, March 4, 2019 8:00AM - 8:12AM |
A13.00001: First-principles studies of the electronic structure and photophysics of monolayer WS2 with point defects Jun-Ho Lee, Sivan Refaely-Abramson, Diana Qiu, Bruno Schuler, Katherine Cochrane, Alexander Weber-Bargioni, Steven G. Louie, Jeffrey B Neaton Point defects in single-layer transition-metal dichalcogenides (TMDs) are common, and point defects in layered TMDs – including vacancies and chemical substitutions – have been reported to affect their electronic structure and photophysics. Here, we use first-principles density functional theory and the GW and GW-BSE calculations to explore the structure and the tunneling and optical properties of substitutional points defects in monolayer tungsten disulfide. Using a large supercell, we compute the atomic structure, quasiparticle band structure, defect states, and low-lying excitons for dilute defect concentrations. We compare our structure and quasiparticle excitation spectrum with state-of-the-art non-contact atomic force microscope and scanning tunneling spectroscopy measurements. |
Monday, March 4, 2019 8:12AM - 8:24AM |
A13.00002: Dopant induced electronic inhomogeneity of epitaxial bilayer graphene in SiC Shuai Zhang, Di Huang, Lehua Gu, Yuan Wang, Shiwei Wu Graphene has been a promising candidate for next-generation electronics due to its intriguing properties, particularly the high carrier mobility. Currently, wafer-scale single crystal graphene could be readily produced on silicon carbide (SiC) substrate by high-temperature annealing. But the mobility of epitaxial graphene is relatively lower than that by mechanical exfoliation. The underlying mechanism has not yet been resolved. Here we study the topography and electronic state of epitaxial graphene grown on 6H-SiC by scanning tunneling microscopy (STM) and spectroscopy (STS). We show that the nitrogen dopants inside SiC substrate result in the electronic inhomogeneity of epitaxial graphene, and give rise to electron-lack puddles. Our results provide the plausible microscopic mechanism for the low mobility in epitaxial graphene. |
Monday, March 4, 2019 8:24AM - 9:00AM |
A13.00003: The Intrinsic Carrier Mobility in Two-Dimensional Semiconductors Invited Speaker: Yuanyue Liu Two-dimensional (2D) semiconductors have attracted great interest for next-generation electronics and optoelectronics. However, they typically have a low mobility of electrons/holes, compared with Si/III-V semiconductors. Here I will discuss our recent theoretical understandings of the mobility-limiting factors in 2D semiconductors [1], and strategies of increasing the mobility. These results are based on the calculation of electron-phonon coupling matrix using density functional perturbation theory and the Wannier interpolation, as well as the Boltzmann transport theory. Moreover, I will also present a new approach for decoupling the entangled phonons to standard phonon modes [2], to analyze the electron-phonon coupling. |
Monday, March 4, 2019 9:00AM - 9:12AM |
A13.00004: Effect of current annealing to the transport properties of CVD graphene cooled with a biased gate voltage U. Kushan Wijewardena, Tharanga Nanayakkara, Rasanga Samaraweera, Binuka Gunawardana, C. Rasadi Munasinghe, Sajith Withanage, Annika Kriisa, Ramesh Mani Chemical vapor deposition of graphene is an excellent method for obtaining large area single-layer graphene. A topic of interest in this area is to characterize and reduce the impurity level in this material. In this experimental work, we investigate impurity effects on electron /hole transport in a graphene specimen by cooling down a graphene Hall bar device under different gate bias voltages. Further, we examine the impact of current annealing on the transport characteristics. Here we present results from the measurements carried out in a closed cycle refrigerator out over a broad temperature range (295K–15K), focusing on the charge neutrality point. |
Monday, March 4, 2019 9:12AM - 9:24AM |
A13.00005: Gateless and reversible carrier density tunability in epitaxial graphene devices functionalized with chromium tricarbonyl Albert Rigosi, Mattias Kruskopf, Heather M. Hill, Hanbyul Jin, Bi-Yi Wu, Philip E Johnson, Siyuan Zhang, Michael Berilla, Angela Hight Walker, Christina Hacker, David B Newell, Randolph E Elmquist Monolayer epitaxial graphene (EG) has been shown to have clearly superior properties for the development of quantized Hall resistance (QHR) standards. One major difficulty with QHR devices based on EG is that their electrical properties drift slowly over time if the device is stored in air due to adsorption of atmospheric molecular dopants. The crucial parameter for device stability is the charge carrier density, which determines the energy spacing of the Landau levels and thus the magnetic flux density required for precise QHR measurements. This work presents one solution to this problem of instability in air by functionalizing the surface of EG devices with chromium tricarbonyl - Cr(CO)3. Observations of carrier density stability in air over the course of one year are reported, as well as the ability to tune the carrier density by annealing the devices. For low temperature annealing, the presence of Cr(CO)3 stabilizes the electrical properties and allows for the reversible tuning of the carrier density in millimeter-scale graphene devices close to the Dirac point. Precision measurements in the quantum Hall regime show no detrimental effect on the carrier mobility. |
Monday, March 4, 2019 9:24AM - 9:36AM |
A13.00006: Electronic properties of armchair transition metal dichalcogenides nanoribbons deposited with atomic chains. Chi-Hsuan Lee, Chih-Kai Yang Electronic properties of armchair transition metal dichalcogenides (TMD) nanoribbons bonded with atomic chains are studied using density-functional calculations. The pure armchair TMD nanoribbon with 15 dimer lines possesses non-magnetic band structures with a moderate energy gap. Their edge states near the Fermi level exhibit different kinds of behavior in accordance to the different elements. Energy bands of the deposited atomic chains hybridize with the edge states of the ribbon and induce various magnetic properties, with different locations of deposition taken into account. The results are useful for fabricating novel nanoelectronic devices. |
Monday, March 4, 2019 9:36AM - 9:48AM |
A13.00007: ABSTRACT WITHDRAWN
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Monday, March 4, 2019 9:48AM - 10:00AM |
A13.00008: Tuning Charge Transport in Voltage-Reduced Graphene Oxide through Defect Control and Quantum Confinement Kevin Silverstein, Christian E Halbig, Austin C Faucett, Jeremy Mehta, Anju Sharma, Siegfried Eigler, Jeffrey M. Mativetsky Graphene oxide (GO) is a versatile two-dimensional nanomaterial that is being explored for its tunable electrical, optical, and chemical properties. This tunability is afforded by reduction which removes oxygen-containing functional groups, restores the sp2 carbon lattice, and converts the electrically insulating material to one that is conducting. Here, we use voltage reduction, a simple and environmentally benign procedure, to manipulate the electrical properties of GO from insulating to conducting, and potentially semiconducting. A low-defect form of GO, oxo-G, was synthesized and voltage-reduced to produce a highly conductive graphene derivative. Variable temperature electrical resistance measurements reveal a transition from hopping transport to a temperature-stable resistance over a broad temperature range, making this material promising for use in sensors and other applications that require temperature-stable performance. Nanopatterning was also employed, by using a conductive atomic force microscope probe to initiate voltage reduction. Preliminary data suggests possible transport gap opening due to quantum confinement. |
Monday, March 4, 2019 10:00AM - 10:12AM |
A13.00009: The role of defects in the performance of graphene hot-electron devices. A El Fatimy, Peize Han, Luke St. Marie, Nicholas Quirk, Matthew T Dejarld, Rachael Myers-Ward, Kevin Daniels, Shojan Pavunny, David Kurt Gaskill, Yigit Aytac, Thomas E Murphy, Paola Barbara Defect-mediated electron-phonon collisions (supercollisions) play an important role in the cooling dynamics of hot electrons in graphene, but their impact on the performance of optoelectonic devices is still largely unexplored. Here we study supercollisions in hot-electron bolometers based on quantum dots of epitaxial graphene grown on SiC. We find that the fabrication process substantially affects the defect density and that a higher defect density greatly enhances the device performance, yielding faster response time and lower thermal conductance in a wide range of power and temperature. |
Monday, March 4, 2019 10:12AM - 10:24AM |
A13.00010: WITHDRAWN ABSTRACT
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Monday, March 4, 2019 10:24AM - 10:36AM |
A13.00011: Charge transfer in few-layer InSe/gas Interface Hansika Sirikumara, Milinda Wasala, Ananth Panchamukhi, Prasanna Dnyaneshwar Patil, Aron C Walber, Sidong Lei, Robert Vajtai, Pulickel M Ajayan, Saikat Talapatra, Thushari Jayasekera Few-layer InSe shows a strong potential for gas sensing applications primarily due to high sensitivity of electron lone pairs on Se to external gas molecules. Based on the results from first principles Density Functional Theory calculations, we carefully analyzed electronic band structures of few-layer InSe/Gas configurations. Our calculations show that charge transfer across few-layer InSe/gas system depends on the orientation and the type of the gas molecules. Therefore, it was seen that for certain gas molecules such as ethanol, the InSe layers are p-doped, while for other molecules such as methanol the InSe layers are n-doped. These results were verified through gas sensing experiments using few layer InSe FET devices. Further we show, while majority charge transfer happens through InSe/Gas interface, the polarity of external molecule can tune interlayer spacing through an induced dipole moment between the layers. The change in interlayer spacing is not monotonic, which results in pinning of impurity band with respect to valence band maximum. Fundamental understanding of charge transfer in few-layer InSe/gas interfaces at the atomic level is expected to pave the path for designing gas sensing devices based on few-layer InSe |
Monday, March 4, 2019 10:36AM - 10:48AM |
A13.00012: Redox-Governed Charge Doping in WS2 and Graphene Sunmin Ryu, Kwanghee Park, Ha neul Kang Low dimensional materials often undergo spontaneous hole doping in the ambient conditions, the detailed mechanism of which has yet to be revealed. In this work, we propose a mechanism based on a redox couple of O2/H2O and verified it for two model systems: photoluminescence (PL) modulation in single-layer WS2 and thermally-activated phonon hardening in graphene with both supported on silica substrates. The PL modulation was directly correlated with the concentration of oxygen both in gaseous and aqueous states. Wide-field PL imaging, however, showed distinctively different spatial propagations of the modulation for the two states, revealing the microscopic picture of the charge doping in WS2. The mechanistic details and thermodynamic driving force for the charge doping will also be discussed in conjunction with the activated hole doping in graphene probed by Raman spectroscopy. |
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