Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C15: 2D Materials (Semiconductors) -- Multilayers & Heterostructures IIFocus
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Sponsoring Units: DMP DCOMP Chair: James Hone, Columbia University Room: BCEC 154 |
Monday, March 4, 2019 2:30PM - 2:42PM |
C15.00001: Electronic and thermoelectric transport in two-dimensional layered-structure material Shi-Jun Liang, Junwen Zeng, Xin He, Lijun Zhang, David Singh, Feng Miao Electronic and thermoelectric transport properties have been the extensively studied topics in the two dimensional materials. Hicks and Dresselhaus predicted that the reduction in dimensionality of materials can enhance the thermopower power factor. However the observation of confinement-induced enhancement of thermoelectric power factor predicated by Hicks and Dresselhaus has been challenging. In this work, we firstly studied the electronic transport mechanism of InSe nanoflakes in the presence of the magnetic field and gate voltage. We observed the gate-tunable weak antilocalization phenomenon and a very long coherent length of up to 320 nm at 1.7 K. The scattering mechanisms were analysed in details. Furthermore, we investigated the thermoelectric properties in the InSe thin film and revealed that the Seebeck coefficient and power factor can be enhanced by the enhanced DOS arising from the size confinement effect when the thickness of InSe thin film is thinned down. Most importantly, we experimentally identified the condition for drastically enhancing the thermoelectric power factor in the 2D layered-structure materials. |
Monday, March 4, 2019 2:42PM - 2:54PM |
C15.00002: Moiré Valleytronics: Realizing Dense Arrays of Topological Helical Channels CHEN HU, Vincent Michaud-Rioux, Wang Yao, Hong Guo In hexagonal 2D crystals, the valley degree of freedom is characterized by non-trivial Berry curvatures. Velley-dependent topological helical channels are novel conducting states without back scattering, which can benefit to low power consumption in practical applications. We propose a general, robust and experimentally-feasible platform, the moiré valleytronics, to realize high-density arrays of 1D topological helical channels in real materials at room temperature. We demonstrate the idea using a long-period 1D moiré pattern of graphene on hBN by first-principles calculation. Through calculating the Berry curvature and topological charge of the electronic structure associated with various local graphene/hBN stackings in the moiré pattern, it is revealed that the helical channel arrays originate intrinsically from the periodic modulation of the local topological orders by the moiré pattern. |
Monday, March 4, 2019 2:54PM - 3:06PM |
C15.00003: WITHDRAWN ABSTRACT
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Monday, March 4, 2019 3:06PM - 3:18PM |
C15.00004: Optical properties of monolayer MoSe2/layered antiferromagnet heterostructures Masaru Onga, Yusuke Sugita, Toshiya Ideue, Yuji Nakagawa, Ryuji Suzuki, Yukitoshi Motome, Yoshihiro Iwasa Van der Waals heterostructure has attracted much interest because of its high extensibility by using various layered materials. Furthermore, the recent discovery of 2D magnets has provided us a new platform to investigate magnetic van der Waals heterointerfaces, leading to novel studies on spin-/valley-tronics [1]. |
Monday, March 4, 2019 3:18PM - 3:30PM |
C15.00005: Mobility and quantum mobility of a 2DEG in modern GaAs/AlGaAs heterostructures Michael Sammon, Tianran Chen, Michael Zudov, Boris Shklovskii In modern GaAs/AlGaAs heterostructures with record high mobilities, a two-dimensional electron gas (2DEG) in a quantum well is provided by two remote donor δ-layers placed on both sides of the well. Each δ-layer is located within a narrow GaAs layer, flanked by narrow AlAs layers which capture excess electrons from donors but leave each of them localized in a compact dipole atom with a donor. These excess electrons minimize their Coulomb energy and screen the random potential of charged impurities. We developed a theory of this screening and used it to calculate both the mobility and the quantum mobility of the 2DEG.[1,2] Our results show that the remote donor limited mobilities strongly increase with the filling fraction of excess electrons, and the calculated mobilities drastically exceed the measured values. This suggests that the mobiliites are limited either by background charged impurities, or the weakening of screening by additional disorder in the doping layer such as roughness at the GaAs/AlAs interface or spreading of the donors outside of the δ-layer. [1] M. Sammon, M. A. Zudov, B. I. Shklovskii, Phys. Rev. Materials 2, 064604 (2018). [2] M. Sammon, Tianran Chen, B. I. Shklovskii, Phys. Rev. Materials 2, 104001 (2018). |
Monday, March 4, 2019 3:30PM - 3:42PM |
C15.00006: Atomic interaction through two-dimensional materials governed by competitive energy fluctuations Huashan Li, Wei Kong, Jeehwan Kim, Jeffrey C Grossman The rapid development of hybrid 2D materials has unveiled its potential to achieve complex functionality. The impact of 2D materials on intermolecular interactions of crystalline materials has not been fully understood. In this study, we computationally investigated a variety of heterojunctions with 2D materials sandwiched by 3D crystal layers.[1]The results suggest that transparency of 2D interlayer is governed by competition between the substrate potential energy fluctuation attenuated, and the binding energy fluctuation generated by 2D interlayer. Although the potential field from covalent-bonded materials is screened by a monolayer of graphene, that from ionic-bonded materials is strong enough to penetrate through a few layers of graphene. Such field penetration is substantially attenuated by 2D hBN, which itself has polarization in its atomic bonds. The insight has been verified by our experiments and further employed to control the transparency via modulating the nature and thickness of 2D interlayer, which eventually leads to the successful remote epitaxial growth of single-crystalline materials across the periodic table. |
Monday, March 4, 2019 3:42PM - 3:54PM |
C15.00007: Tunable band gap of graphyne-based homo- and hetero-structures: effects of stacking sequence, strain and external electric field Jiangni Yun, Yanni Zhang, Hong Guo Two-dimensional van der Waals (vdW) layered materials have attracted great attention for their possible applications in flexible electronics and optoelectronics. In this work, we report a comprehensive theoretical study of graphyne/graphyne (Gyne/Gyne), graphyne-like BN/graphyne-like BN (BNyne/BNyne) and graphyne/graphyne-like BN (Gyne/BNyne) bilayers by density functional theory. These bilayers exhibit distinct stacking dependent characteristics in the ground state electronic structure and have different responses to external strain and electric field. For Gyne/Gyne and Gyne/BNyne bilayers, a biaxial tensile strain increases the band gap while biaxial compressive strain or uniaxial strain, reduces it. For theBNyne/BNyne bilayer the trend is opposite. Under a vertical electric field, the band gap decreases in homo-bilayers Gyne/Gyne and BNyne/BNyne. For the hetero-bilayer Gyne/BNyne, band gap decreases under a positive electric fieldbut remain almost constant in negative electric field. These properties are understood by analyzing the calculated electronic density and potential. |
Monday, March 4, 2019 3:54PM - 4:06PM |
C15.00008: Microscopic theory of band gap opening and spin-orbit splitting in graphene/TMDC heterobilayers Alessandro David, Andor Kormanyos, Guido Burkard Bilayers of graphene and monolayer transition metal dichalcogenides (TMDCs) are fascinating van der Waals heterostructures with an interesting electronic band structure. Theoretical ab initio calculations have shown a gap opening and an induced spin-orbit splitting in the band structure of graphene from the TMDC layer [1, 2]. These results have been experimentally confirmed by recent magnetotransport experiments showing weak antilocalisation (WAL) [2, 3]. Using perturbation theory, we propose a microscopic model to explain the origin of the gap and of the spin-orbit splitting. We also consider the dependence of the spin-orbit splitting on the misalignment of graphene and TMDC layers. |
Monday, March 4, 2019 4:06PM - 4:18PM |
C15.00009: Graphene-Oxide-Semiconductor photodetector Ching-Ping Lee, Jen-Yu Wang, Dah-Chin Lin, Yung-Fu Chen, Cen-Shawn Wu, Jeng-Chung Chen The photodetection properties of a graphene-oxide-semiconductor (GOS) diode have been extensively investigated by measuring current-voltage characteristics under illumination with light-emitting diode (LED). We demonstrate that the newly developed GOS heterostructure, with graphene as a transparent gate electrode to form the inversion layer at the oxide-semiconductor interface, can function as a GOS field-effect transistor (GOSFET) operable at low temperature (T) down to 1.5 K. By studying the gate tunneling current in the GOSFET, we find that the dark current is below ~ 0.1 nA, which is almost two orders of magnitude smaller than that in graphene-Si (GS) Schottky detector diode. In addition, the GOS diode shows bilateral photoresponse under LED illumination as the polarity of bias voltage on graphene gate is altered. Consequently, it behaves as a p-i-n or n-i-p diode actively controlled by the applied bias. The responsibility R reaches ~ 100 mA/W at T = 100 K, approximately a factor of 100 higher than R of GS diode. Our work paves the way for the implementation of hybrid photodetecting devices fabricated by two-dimensional materials and conventional semiconductors with CMOS integrability. |
Monday, March 4, 2019 4:18PM - 4:30PM |
C15.00010: Coexistence of Different Charge Transfer Mechanisms in the Hot Carrier Dynamics of Hybrid Plasmonic Nanomaterials Jin Zhang Plasmon induced hot-electron dynamics at the interfaces of metallic nanostructures and semiconductors is of significant importance for photovoltaic and photocatalytic applications. Plasmon-driven charge separation processes were considered to be only dependent on the type of donor-acceptor interactions, i.e., conventional hot electron transfer mechanism for van der Waals interactions and plasmon-induced interfacial charge-transfer transition pathway for chemical bonds. Here we demonstrate the two mechanisms can coexist in a typical metal-semiconductor hybrid plasmonic nanomaterials, both happen on a faster time scale than carrier relaxation process. The origin of the two mechanisms is attributed to the spatial vertical and parallel modes of excited plasmon, where the vertical mode couples to semiconductors much strongly than the parallel one. Our findings provide a new insight into the photoinduced plasmonic carrier dynamics, which is relevant for many potential applications including solar energy conversion, efficient water splitting and photocatalysis. |
Monday, March 4, 2019 4:30PM - 4:42PM |
C15.00011: Layer dependence of excitonic absorption peaks in few layer hexagonal BN Fulvio Paleari, Thomas Galvani, Hakim Amara, François Ducastelle, Alejandro Molina-Sanchez, Ludger Wirtz The dependence of optical spectra on the number of layers in 2D materials is crucial for their characterization. While Raman spectra can be intuitively interpreted by the splitting of phonon modes in few-layer systems, much less is known about the splitting of excitonic peaks in absorption spectra. |
Monday, March 4, 2019 4:42PM - 4:54PM |
C15.00012: Rapid bimolecular and defect-assisted carrier recombination in hexagonal Boron Nitride Ioannis Chatzakis, Roderick Davidson II, Adam Dunkelberger, Andrea Grafton, Joshua D Caldwell, Song Liu, Jaime A. Freitas, Jr., James Clifford Culbertson, James H. Edgar, Daniel Ratchford, Chase Ellis, Alex Giles, Joseph G Tischler, Jeffrey Owrutsky Hexagonal boron nitride (hBN) is an indirect wide band gap semiconductor that holds great promise for optoelectronic devices in the ultraviolet regime. Here we report the dynamics of photoexcited charge carriers at room temperature in exfoliated monoisotopic 10B enriched hBN. Two recombination mechanisms were identified, and their associated time scales measured, using ultrafast two-photon pump, infrared probe transient transmission spectroscopy. Initially, when the free carrier density is high, bimolecular decay dominates recombination with a rate constant of (1.33 ± 0.09) × 10-7 cm-3/s. At later times, the recombination of the free carriers is characterized by an exponential decay with a time constant on the order of a nanosecond, determined by the density of the impurities/defects in the lattice. |
Monday, March 4, 2019 4:54PM - 5:06PM |
C15.00013: Understanding the electrical behaviors in van der Waals heterostructure field-effect transistor based on band alignment Seonyeong Kim, Taekwang Kim, Somyeong Shin, Hyewon Du, Minho Song, Hansung Kim, Dain Kang, Chang-Won Lee, Sunae Seo Van der Waals heterostructures based on 2D layered materials have been extensively studied because their unique electronic properties, which can be controlled by optimally selecting the band alignments. Although the rectifying behavior is usually observed in output characteristics of these heterostructures, the underlying transport mechanism have not been fully understood. Here, we investigate transport properties of multilayer MoTe2/SnS2 heterostructure field-effect transistor (hetero-FET) fabricated by exfoliating each material and manually stacking them and observe gate-tunable diode-like current rectification. With the qualitative band analysis, we noticed that the interfacial barrier by band bending plays a crucial role to realize the transport properties of hetero-FETs, especially rectification behavior. Our experimental study offers the inspiration for understanding the transport behavior and reference to novel hetero-FETs. |
Monday, March 4, 2019 5:06PM - 5:18PM |
C15.00014: Demonstrating Band Design in Two-Dimensional Covalent Organic Frameworks Halleh Balch, Austin Evans, Raghunath Dasari, Simil Thomas, Kaitlin Slicker, Hong Li, Ruofan Li, Dan Ralph, Jean-Luc E Bredas, Seth R. Marder, William Dichtel, Feng Wang Two dimensional covalent organic frameworks (COFs) are periodic lattices whose rational design can yield novel optoelectronic properties and new heterostructure devices. Analogous to graphene and the inorganic family of 2D materials, 2D COFs are covalently bonded in-plane with out-of-plane bonding through Van der Waals interactions. To date, 2D COF properties are limited by large molecular bandgaps, low intermolecular coupling, and poor control of the material morphology. Here, we report the rational design and characterization of a new, highly conjugated, semiconducting 2D framework. We characterize the structure by X-ray scattering, TEM, and AFM, and demonstrate facile manipulation onto arbitrary experimental platforms. We further employ broadband optical and vibrational spectroscopies to observe electronic behavior emergent in this highly conjugated system. |
Monday, March 4, 2019 5:18PM - 5:30PM |
C15.00015: Topological phase diagram of BiTeX/graphene hybrid systems László Oroszlany, Zoltán Tajkov, János Koltai, Gergo Kukucska Tuning spin-orbit interaction in graphene samples promises several revolutionary applications. One of the most striking effects is the appearance of a quantum spin Hall phase as proposed by Kane and Mele. Since the intrinsic spin-orbit coupling is weak in graphene one needs to turn to alternative methods in order to reach the topological phase. Combining graphene with other novel layered materials is a possible way for engineering the band structure of charge carriers. |
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