Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session R37: Devices from 2D Materials IV - OptoelectronicsFocus
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Sponsoring Units: DMP Chair: Zhipei Sun, Aalto University Room: LACC 411 |
Thursday, March 8, 2018 8:00AM - 8:12AM |
R37.00001: Abstract Withdrawn
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Thursday, March 8, 2018 8:12AM - 8:24AM |
R37.00002: Photoresponse in metallic layered transition metal dichalcogenides Talip Kasirga, Naveed Mehmood, Hamid Rasouli, Onur Cakiroglu Photocurrent generation is a key process in optoelectronics. In recent years, photoresponse from semiconducting layered transition-metal dichalcogenides have been studied extensively with the hope of finding applications in flexible optoelectronics as well utilising the new degrees of freedom. Photocurrent generation in metallic transition metal dichalcogenides, however, is unexpected as the possible mechanisms for the photoresponse are typically not prevalent for several reasons. In this report, using scanning photocurrent microscopy, we show a significant photoresponse from thin layered metallic transition metal dichalcogenides. In particular we studied thin metallic niobium disulfide flakes (3R) and explain the possible underlying mechanisms. |
Thursday, March 8, 2018 8:24AM - 8:36AM |
R37.00003: Engineering the Persistent Optical Gating Effect of 2D Materials on SrTiO3 Joost van Bree, Erzsebet Vincent, Andrew Yeats, Meng Ye, Giulia Galli, David Awschalom Reducing the dimensionality of bulk materials to atomically thin films allows for exploration of novel phases. The carrier density often plays a crucial role in accessing these phases. Using a persistent all-optical gating effect, local control over the carrier density in graphene, MoS2, phosphorene, and a thin layer of (Bi,Sb)2Te3 on SrTiO3 substrates has been recently demonstrated [1,2,3]. The effect is postulated to originate from a reversible optically modulated space-charge region in the SrTiO3, though exact details of the mechanism, such as the role of various defects and its relation to other optically induced persistent phenomena, have remained unclear. Using Kelvin probe microscopy, conductivity measurements, and optical transmission spectroscopy of graphene on SrTiO3, combined with density-functional calculations, we address outstanding questions on the role of defects, and provide ways to engineer and enhance the effect. |
Thursday, March 8, 2018 8:36AM - 8:48AM |
R37.00004: Graphene Circular p-n Junction: from Optical Guiding to Quantum Dot Physics Jinhai Mao, Yuhang Jiang, Dean Moldovan, Massoud Ramezani Masir, Guohong Li, Kenji Watanabe, Takashi Taniguchi, François Peeters, Eva Andrei The miniaturization limits on traditional semiconductor-electronics have led to proposals of an alternative platform based on the photon-like propagation of the Dirac-electrons in graphene. However, the chiral nature of these carriers and the associated Klein tunneling makes it difficult to control their motion electrostatically with standard gate voltages. We have devised a local dual-gate technique that produces a circular graphene p-n junction whose size can be continuously tuned from the nanometer-scale, where quantum effects are dominant, to the micrometer scale where optical-guiding takes over1. By varying the parameters of the junction we investigate the mechanism of gate controlled trapping, detrapping and guiding of electrons. Furthermore, applying an external magnetic field enables us to study the crossover from Landau quantization to quantum dot physics and electron lensing. |
Thursday, March 8, 2018 8:48AM - 9:00AM |
R37.00005: Internal Photoemission Spectroscopy of 2-D Semiconductor Transition Metal Dichalcogenides Qin Zhang, Siyuan Zhang, brent sperling, David Gundlach, Nhan Nguyen Semiconductor transition metal dichalcogenides MX2 (M=Mo, W; X= S, Se) have received tremendous attention for electronic and optoelectronic applications, with their direct bandgaps in the near-infrared to visible region in their 2-D monolayer limit. In particular, MX2 Van der Waals heterostructures only with a staggered band alignment have been proposed as a structure that can separate photoexcited electrons and holes in different layers by charge transfer. It is thus important to know what the form of the band alignment of these hetorostructures is in order to realize appropriate device designs. Here we present the internal photoemission spectroscopy (IPE) approach to determine the band offsets of exfoliated large-area MoS2, MoSe2, WS2, and WSe2 monolayer. Experimentally, the quality and uniformity of the MX2 monolayers are confirmed by Raman mapping and photoluminescence spectroscopy. The band offsets are measured in relative to the Al2O3 conduction band minimum from which we can determine whether the corresponding heterostructures fabricated from these MX2 monolayers have a staggered band alignment configuration. |
Thursday, March 8, 2018 9:00AM - 9:12AM |
R37.00006: Field-Effect Induced Linear Dichroism in Black Phosphorus from the Visible to Mid-Infrared William Whitney, Michelle Sherrott, Deep Jariwala, Cora Went, Joeson Wong, George Rossman, Harry Atwater The incorporation of electrically tunable materials into photonic structures such as waveguides and metasurfaces enables dynamic control of light propagation, a critical functionality for emerging optical technologies. Atomically-thin, 2D crystals are ideal materials for this application, as their optical properties are modulated effectively by electrostatic gating. Few-layer black phosphorus is uniquely promising, as its absorption edge is tunable with thickness from the visible to the mid-infrared, and its optoelectronic properties exhibit strong anisotropy within the Van der Waals plane. |
Thursday, March 8, 2018 9:12AM - 9:48AM |
R37.00007: Nano-optoelectronics with 2d material heterostructures: fundamentals and applications Invited Speaker: Frank Koppens I will review both fundamentals and applications associated to the interactions of light with graphene and heterostructures of 2d materials. |
Thursday, March 8, 2018 9:48AM - 10:00AM |
R37.00008: Large Photo-Thermal Effect in Sub-40 nm h-BN Nanostructures Patterned Via High-Resolution Ion Beam Josue Lopez, Antonio Ambrosio, Siyuan Dai, Chuong Huynh, David Bell, Xiao Lin, Nicholas Rivera, Shengxi Huang, Qiong Ma, Soeren Eyhusen, Ido Kaminer, Kenji Watanabe, Takashi Taniguchi, Jing Kong, Dimitri Basov, Pablo Jarillo-Herrero, Marin Soljacic
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Thursday, March 8, 2018 10:00AM - 10:12AM |
R37.00009: Charge-Transfer in Organic-TMDC Heterojunctions Probed by SERS Teodor Stanev, Sam Amsterdam, Alexander Lou, Mark Hersam, Tobin Marks, Nathaniel Stern Heterojunctions fabricated with 2D materials can give rise to unique effects at the interface of the composite layers. Organic molecules have the attraction of synthetically tunable electronic and optical properties and facile processing, which can lead to controllable opto-electronic coupling to 2D substrates such as 2D transition metal dichalcogenides (TMDCs). Phthalocyanines (Pc) are a class of organic dye molecules consisting of a planar macrocycle bonded to a metal core atom. These molecules can be configured with different metal cores to induce distinct phenomena such as metal-insulator transitions and ferromagnetism, potentially providing a mechanism to influence 2D heterostructures. We report surface-enhanced Raman scattering in TMDC/Pc heterojunctions, how it depends on the metal core, the underlying TMDC, layer number, and the excitation laser energy. Observed trends include a strong dependence on the metal core and laser energy, showing up to 40x enhancement in signal intensity. This Raman enhancement in organic/TMDC systems demonstrates the importance of band and energy level alignment on charge transfer across van der Waals interfaces. |
Thursday, March 8, 2018 10:12AM - 10:24AM |
R37.00010: Efficient Carrier-to-exciton Conversion in Field Emission Tunnel Diodes based on MIS-type van der Waals Heterostack Junyong Wang, Goki Eda Van der Waals (vdW) heterostructures comprising of two-dimensional (2D) crystals offer promising prospects for realizing ultrathin electronic and photonic devices with precisely tailored functionalities. Efficient excitonic electroluminescence (EL) is a fundamental requirement for the realization of practical excitonic devices. We report on efficient carrier-to-exciton conversion and planer electroluminescence from tunnel diodes based on a metal-insulator-semiconductor van der Waals heterostack consisting of few-layer graphene (FLG), hexagonal boron nitride (hBN), and monolayer tungsten disulfide (WS2). These devices exhibit excitonic electroluminescence with extremely low threshold current density of a few pA μm-2. Our observations indicate that the efficiency of our devices is not limited by carrier-to-exciton conversion efficiency but by the inherent exciton-to-photon yield of the material. The device characteristics indicate that the light emission is triggered by injection of hot minority carriers (holes) to n-doped WS2 by Fowler-Nordheim tunneling and that hBN serves as an efficient hole-transport and electron-blocking layer. |
Thursday, March 8, 2018 10:24AM - 10:36AM |
R37.00011: Circular Photogalvanic Effects in WTe2 and MoTe2 Se Joon Lim, Claudia Felser, Aharon Kapitulnik We investigate the generation and temperature dependent evolution of spin photocurrents in WTe2 with the circular photogalvanic effect. A large transverse spin photocurrent is observed when the light scattering plane coincides with one of the high-symmetry planes of the crystal, consistent with symmetry arguments. Upon lowering the temperature, its magnitude starts to decrease below 150 K, which coincides with the temperature below which hole pockets start to form in the Fermi surface. Around 50 K, the spin photocurrent switches its polarity and flows in the opposite direction. A similar behavior is observed in MoTe2. |
Thursday, March 8, 2018 10:36AM - 10:48AM |
R37.00012: Optical Second-harmonic Spectroscopy of In2Se3 Yujin Cho, Di Wu, Ramon Carriles, Bernardo Mendoza, Keji Lai, Michael Downer Van der Waals 2D materials have good mechanical and electrical properties and maintain them in layers less than 10 nm. In2Se3, in particular, has potential applications as photo-electric devices such as solar cells or phase-change memories. One quintuple layer (~ 1 nm) of In2Se3 consists of five atomic layers alternating between In and Se, and belongs to R3m symmetry group. Rotational anisotropic second-harmonic generation (RASHG) microscopy confirmed the three-fold crystal structure at room temperature.[1] We found three different stacking order samples; all layers oriented along the same direction, one layer rotated by 180 degrees with respect to the layers below, and one rotated by 90 degrees. The fundamental wavelength was tuned from visible light range to near IR, and nonlinear second-harmonic spectroscopic response of a few layers (1-3 layers) with different stacking order was measured to see the effect of interlayer coupling and the number of layers on nonlinear optical properties. We will present SHG experimental results showing four resonance peaks in this range, and relate them to the underlying nonlinear susceptibility tensor components. |
Thursday, March 8, 2018 10:48AM - 11:00AM |
R37.00013: Fundamental and optical band gaps of layered In2Se3 Wei Li, Fernando P. Sabino, Anderson Janotti Indium selenide is a promising material for photodetectors due to the highly efficient absorption, fast response, and high sensitivity extending into ultraviolet, visible, and near-infrared spectral regions. Despite these promising properties, the reports on the electronic structure and the values for the direct vs. indirect band gaps of In2Se3 remain quite controversial, with results varying in a wide range, from 0.7 to 1.4 eV. Using hybrid density functional calculations, we investigated the electronic and optical properties of layered phases of In2Se3: α phase (space group R3m), β phase (space group R-3m), and δ phase (space group P-3m1). We report fundamental and optical band gaps for the three phases, the real and imaginary dielectric functions, and absorption coefficients. The results are then discussed in the light of available experimental data. |
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