Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session K60: 2D Material Devices IIFocus Recordings Available
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Sponsoring Units: DMP Chair: Gregory Stephen, Laboratory for Physical Sciences Room: Hyatt Regency Hotel -DuSable C |
Tuesday, March 15, 2022 3:00PM - 3:36PM |
K60.00001: Skyrmions and Spin-Orbit-Torques in 2D Magnetic Heterostructures Invited Speaker: Kang-Lung Wang
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Tuesday, March 15, 2022 3:36PM - 4:12PM |
K60.00002: Protonic gate tuned magnetic properties in van der Waals materials and heterostructures Invited Speaker: Lan Wang Protonic gating is a newly developed innovative technique with the potential to open up pathways for new electronic, spintronic and valleytronic devices. Compared with gating techniques based on dielectric layers, ionic gating can provide several orders of magnitude larger charge tunability. Ionic gating is often implemented using a Li+ liquid electrolyte but this has three significant shortcomings; first, the liquid electrolyte can corrode the sample; second, the size of the Li+ ion limits the penetration depth and hence renders the method suitable only to ultra-thin samples; third, the liquid state is inconvenient for many experiments and applications and cannot be used at room temperature. Our protonic gating technique is based on a solid protonic electrolyte and eliminates these three shortcomings. In this report, I will present the recent experimental results of electron transport in 2D magnetic materials and heterostructures under protonic gate voltages. |
Tuesday, March 15, 2022 4:12PM - 4:24PM |
K60.00003: Transport in WSe2 proximitized to RuCl3 Jordan Pack, Bjarke S Jessen, Song Liu, Jiaqiang Yan, Kenji Watanabe, Takashi Taniguchi, David G Mandrus, James C Hone, Cory R Dean Semiconducting transition metal dichalcogenides have been predicted to host a variety of novel quantum transport properties. However, the lack of reliable, low resistance, ohmic contacts at low temperatures has hindered studies of many of these properties. It has recently been identified that there is a large charge transfer at the WSe2-RuCl3 interface which leaves WSe2 heavily hole-doped. This allows for a new class of devices incorporating both passive charge transfer interfaces and tunable electrostatic gates, which could enable more robust transport measurements in semiconducting TMDs. We will share measurements of transport through these heterostructures as well an assessment of the performance of electrical contacts incorporating RuCl3. |
Tuesday, March 15, 2022 4:24PM - 4:36PM |
K60.00004: Analysis of Charge transfer doping in RuCl3/semiconducting transition metal dichalcogenide heterostructures from first principles Dakotah M Kirk, Marcelo A Kuroda The use of a-RuCl3 has been proposed to achieve the emergence of novel phenomena at the interfaces of heterostructures formed with different two-dimensional materials. Here we rationalize the proximity induced changes in the electronic structure and charge transfer between RuCl3 and semiconducting transition metal dichalcogenides (TMDs) MoTe2 and WSe2. To this end we use first principles calculations with the density functional theory (DFT) accounting for the on-site Coulomb interaction and spin-orbit coupling. Analysis using the Bader charges shows that owing to its high work function a-RuCl3 becomes n-doped and its spin polarization decreases by approximately 0.2 /unit cell. In contrast, the TMD layers become p-doped (around 1013 cm-2) but proximity effects do not produce spin polarization. We find that spin-orbit coupling plays an important role due its effects both in the a-RuCl3 and the valence bands of MoTe2 and WSe2. Moreover, in-plane and out-of-plane strain considerably alters charge transfer. Results show that high work function metals may improve charge injection efficiency in these semiconducting TMD structures. |
Tuesday, March 15, 2022 4:36PM - 4:48PM |
K60.00005: Negative Magnetoresistance in Graphene Quantum Dot Devices DaVonne Henry, Luke St. Marie, Amjad Alqahtani, Yijing Liu, Rachael L Myers-Ward, D. Kurt Gaskill, Albert F Rigosi, Abdel El Fatimy, Petr Neugebauer, Amy Y Liu, Paola Barbara Graphene quantum dot devices have unique transport properties that differ from graphene devices without a quantum dot structure. The opening of a quantum confinement gap and Joule heating of the graphene's electrons lead to an activation energy mediated conductance through the device. Our measurements on these devices in a magnetic field oriented perpendicular to the graphene show a negative magnetoresistance as high as 40% at 1.3 K that decreases with increasing temperature to 5% at 150 K. The activation energies in zero-field and under parallel field are equivalent, indicating that the formation of Landau levels in the graphene is responsible for the magnetoresistance. This opens the possibility to control the level filling with a gate electrode, leading to a tunable magnetoresistance. |
Tuesday, March 15, 2022 4:48PM - 5:00PM |
K60.00006: First principles investigation of the effect of excess carriers and illumination on the band edge energies of semiconducting transition metal dichalcogenides Elizabeth Peterson, Aurelie Champagne, Jeffrey B Neaton Photovoltage, or the change in surface potential of a material under illumination, is a central quantity for characterizing complex semiconductors and for optoelectronic applications such as photocatalysis. In this work we use first principles calculations to understand photovoltage in the limit of well-defined semiconducting two-dimensional transition metal dichalcogenides, materials with strong light-matter interactions that have been reported to be photocatalytically active. We model the effect of excess free carriers using density functional theory (DFT), computing shifts in the absolute band edge energies as a function of carrier density. We use DFT calculations, as well as ab initio many-body perturbation theory calculations using the GW-Bethe-Salpeter equation approach, to study the effects of illumination on the band edges, to establish limits on possible photogenerated carrier concentrations, and to understand the maximum photovoltage that could be achieved in these systems. |
Tuesday, March 15, 2022 5:00PM - 5:12PM |
K60.00007: Layer dependent photo-response of Indium Selenide (InSe) field-effect transistors (FETs) Prasanna D Patil, Milinda P Wasala, Sujoy Ghosh, Lincoln Weber, Sidong Lei, Saikat Talapatra Recent interest in optoelectronic properties of 2D materials from group III-VI such as Indium Selenide (InSe) has increased due to their direct band gap in few-layered form. Understanding and optimizing the layer dependent properties of these materials is important for developing future optoelectronics devices. Here we report a detailed investigation of layer dependent (thickness 20 < t < 100 nm) photoconductive behavior of InSe based field-effect transistors (FETs). Our investigations indicate maximum responsivities of ~ 7.84 A/W and ~ 0.59 A/W were obtained for the devices with thickness 20 nm and 100 nm, respectively. We will discuss the correlation between layer thickness and figures of merit such as field effect mobility (μFE) and responsivity (R) etc. for the photo-FETs studied. |
Tuesday, March 15, 2022 5:12PM - 5:24PM |
K60.00008: Phonon limited mobility in h-BN encapsulated AB-stacked bilayer graphene Vasili Perebeinos, Davoud Adinehloo, Cheng Tan, James C Hone We report the electrical transport in h-BN encapsulated AB-stacked bilayer graphene theoretically and experimentally. Using the perturbation theory within the tight-binding model approach, we identify the dominant role of the shear phonon mode scattering on the carrier mobility in AB-stacked graphene bilayer at room temperature. The shear phonon mode is absent in free-standing monolayer graphene, which explains high mobilities in monolayer devices fabricated under similar conditions resulting in minimal Coulomb impurity scattering. At temperatures above 200K, the surface polar phonon scattering from boron-nitride (BN) substrate contributes significantly to the experimental mobilities of 15,000 -20,000 cm^2/Vs at room temperature and carrier concentration n~10^12 cm^2 reported here. A screened SPP potential for a dual gated bilayer and transferable tight-binding model allows us to predict mobility scaling with temperature and bandgap for both electrons and holes in agreement with the experiment. |
Tuesday, March 15, 2022 5:24PM - 5:36PM |
K60.00009: Vacancy-dependent electrical transport in vertical transition metal dichalcogenide memristors: first principles study Lu Wang, Dakotah M Kirk, Marcelo A Kuroda Nonvolatile resistive switching devices have garnered considerable attention owing to their demonstrations in the ongoing development of next-generation flexible memory and neuromorphic computing systems. Recently, such memristive devices based on two-dimensional materials have been experimented on the benefit of size scaling1-3. However, the underlying mechanisms in these promising experiments are yet to be elucidated. Here, we study changes in the electronic band structures and transport properties of hybrid heterostructures formed with monolayer MoSe2 and Au electrodes using the first-principles calculations. Specifically, we analyze changes introduced in pristine systems due to the presence of different types of defects including vacancies (e.g. VSe, VMo, and V2Se) and substitutions (e.g. AuSe and AuMo) using density functional theory in combination with quantum ballistic transport calculations. The presence of vacancies significantly reduces van der Waals gap between the electrode and the monolayer MoSe2. Additionally, through the analysis of their band structures, we find that chalcogen vacancies result in the formation of midgap states near the Fermi level of the electrode. These changes in the geometric and electronic structures also translate into an increase of electrical conductivity with respect to the pristine heterostructures, offering a plausible explanation to the mechanism governing transition metal dichalcogenide (TMD)-based memristors at the atomic scale. Furthermore, we compare the results of hybrid heterostructures formed with other noble metals and TMDs. Outcomes of this work may shed light on the design of versatile memristors scaled based on these few-atom-thick crystalline layers. |
Tuesday, March 15, 2022 5:36PM - 5:48PM |
K60.00010: Theoretical Study of Anisotropic Pseudospin Tunneling in Two-Dimensional Black Phosphorus Junctions Young Woo Choi, Hyoung Joon Choi We investigate the role of pseudospin structure of few-layer black phosphorus (BP) in interband tunneling properties in lateral BP junctions [1]. We find that interband tunneling is critically dependent on junction directions because of the anisotropic pseudospin structure of BP. When the armchair direction of BP is normal to the interface, pseudospins of incident and transmitted carriers are nearly aligned so that interband tunneling is highly effective, analogous to the Klein tunneling in graphene. However, when the zigzag direction is normal to the interface, interband tunneling is suppressed by misaligned pseudospins. We also study junctions of band-gap inverted BP where the electronic structure is characterized by two Dirac cones. In this case, intervalley tunneling is prohibited either by momentum conservation or by pseudospin mismatch while intravalley tunneling is Klein-like irrespective of the junction direction. These results provide a foundation for developing high-performance devices from BP and other pseudospin materials. |
Tuesday, March 15, 2022 5:48PM - 6:00PM |
K60.00011: Numerical simulation studies with heterostructure of transition metal dichalcogenides HeeBong Yang, Christian Spudat, Daozhi Shen, Adam W Tsen, Na Young Kim Transition metal dichalcogenides (TMDs) are intriguing two-dimensional materials that have been intensively studied for almost two decades due to the attractive physical properties: controllable energy band gap which covers the visible and near-infrared wavelength range, strong light-matter interaction, strong spin-orbit coupling, direct bandgap with monolayer, and valleytronic properties. Although a monolayer has a drawback of low light absorption due to the thin physical structure, heterostructures of TMDs showing improved sensitivity of light are exploited in photonic devices. Large numbers of TMD heterostructure photodetectors have been demonstrated from zero-bandgap to wide-bandgap values over 3.1 eV. These studies are qualitatively explained by band alignment engineering but have not been intensively studied with thorough numerical simulations. In this presentation, we performed a variety of TMD material combination studies under finite element numerical simulation with COMSOL Multiphysics which elaborate how the transport properties behave in dark and photocurrent. Furthermore, we examined interesting results from the combination of a TMD heterostructure and a graphene structure. |
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