Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session W53: 2D Photonics and OptoelectronicsFocus
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Sponsoring Units: DMP Chair: Stephen Wu, University of Rochester Room: Mile High Ballroom 1F |
Friday, March 6, 2020 8:00AM - 8:12AM |
W53.00001: Two-dimensional ReS2 for nonlinear photonics Benjamin Smith, Kristina Rusimova, Andriy Gorbach, Juejun Hu, Skylar Deckoff-Jones, Daniel Wolverson The layered transition metal dichalcogenides (TMDs) have been the focus of increasing research in photonics, in part due to their large nonlinear optical (NLO) susceptibilities. Amongst the TMD family, the semiconducting rhenium dichalcogenides (ReX2, where X = S or Se) are unusual due to their highly-anisotropic in-plane crystal structure. A Peierls distortion of the crystal lattice results in the formation of chains of Re atoms along one of the crystallographic directions. This structure leads to anisotropic optical, electrical and mechanical properties. Here, we demonstrate that this anisotropic crystal structure is highly useful for incorporating such 2D flakes within waveguides. It is shown that ReS2 flakes preferentially cleave along the a axis, producing flakes with long and narrow dimensions. This allows for waveguide integration with a long interaction length between the propagating light and the NLO material. ReS2 flakes were exfoliated and characterised using Raman and atomic force microscopy (AFM). Waveguide devices incorporating these flakes were fabricated. |
Friday, March 6, 2020 8:12AM - 8:24AM |
W53.00002: THz Photoconductive Antennas Using Thin Black Phosphorus M. Hasan Doha, Ahmad F. Rawwagah, Josh P. Thompson, Arash Fereidouni, Kenji Watanabe, Takashi Taniguchi, Miaoqing Huang, Magda O. El-Shenawee, Hugh Churchill We report the fabrication and characterization of THz photoconductive antennas using thin (~50 nm) black phosphorus (BP) as the photoconductor and hexagonal boron nitride (hBN) as a capping layer to prevent oxidation of BP and enhance absorption. Dipole antennas were fabricated on oxidized high-resistivity silicon substrates, and BP and hBN flakes were picked up and transferred onto the antennas inside a nitrogen glovebox. BP flakes were aligned with the armchair axis along the anode-cathode gap of the antenna, with crystal orientation measured using reflection anisotropy. The transfer matrix technique was used to optimize the thickness of BP and hBN for maximum absorption. Photocurrent imaging under illumination with ~100 fs pulses at 1550 nm showed a bias-dependent maximum photocurrent near the anode side of the antenna gap with a responsivity at 50 kHz of about 0.2 mA/W at a source-drain bias of -100 mV. We will also report ongoing measurements to compare THz output power of these antennas with reference devices in which silicon is used as the photoconductor. |
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W53.00003: Defect and interface engineering for high-performance 2D photodetectors zhenhua ni, Ting Zheng The performance of photodetectors based on two-dimensional (2D) materials is strongly influenced by defects and the interface [1]. The de-trap time of carriers from a deep trap could be prolonged by several orders of magnitude as compared to shallow trap, resulting in additional decay time of the device. We demonstrate that the trap states in 2D ReS2 could be efficiently modulated by defect engineering through molecule decoration, and the both the response time and responsivity of the device is greatly improved [2]. We further elaborate that plasmon-induced hot electron transfer (HET) from tungsten suboxide nanocrystals to graphene is a sufficient fast process (<150 fs) to prevent carrier cooling and trapping processes. A fast near infrared (NIR) detector empowered by HET is demonstrated, and the response time is three-orders of magnitude faster than that based on common band-edge electron transfer [3]. Our results indicate that defect and interface engineering is a new strategy for implementation of efficient and high-speed photoelectric devices. |
Friday, March 6, 2020 8:24AM - 9:00AM |
W53.00004: Lithographic bandgap engineering of graphene on the 10 nm scale: the role of edges Invited Speaker: Peter Bøggild In the light of graphene’s rich electronic properties and potentially high performance in applications, one of the most obnoxious roadblocks have been to pattern graphene on a small scale. Early theoretical work predicted that the bandstructure of graphene could be engineered by nanopatterning, such as nanoribbons and antidot lattices. Unfortunately, edge disorder and contamination associated with typical lithographic processes have strong detrimental effects on the transport properties. This has held back efforts to utilize quantum confinement in practical graphene devices as well as downscaling graphene components to a scale comparable to mainstream silicon electronics. The key is to control the chemistry and roughness of the edges, which has a striking impact on charge distribution and scattering in graphene, as illustrated by breakdown of the Quantum Hall Effect and ferroelectric behavior in graphene devices. By careful patterning through the hexagonal boron nitride encapsulation layer, we fabricated graphene devices with 35 nm pitch hole arrays and nm-scale edge roughness, yet exceptionally high carrier mobility. The distinct magnetotransport features are in quantitative agreement with zero-parameter tight-binding calculations and analytical models, including a ca. 150 meV bandgap. In addition we find that the subtle moiré-superlattice signatures associated with a small finite twist angle between the graphene and hexagonal boron nitride survives the aggressive lithographic patterning, suggesting that nanoscale circuits and components that exploit the novel properties of twisted 2D layers are feasible. |
Friday, March 6, 2020 9:00AM - 9:12AM |
W53.00005: Graphene Double-Layer Heterostructure Photodetectors with Broadband, High and Fast Responsivity at Room Temperature Ho Vinh, Yifei Wang, Zachary Henschel, Michael P. Cooney, Vinh Q Nguyen The hybrid semiconductor/graphene photodetectors have been intensively investigating due to their applications ranging from imaging, sensing to communications in the infrared region. Integration of colloidal semiconductor quantum dots with graphene can increase the responsivity of such photodetectors. However, the response time is in millisecond to second scale, caused by optical traps at interfaces between semiconductor quantum dots and graphene. Another limitation is that the operation bandwidth still has not expanded beyond near-infrared region due to the bandgap of semiconductor quantum dots. Here, we report photodetectors based on two graphene single-layers separated by a 5-nm Ti2O3 thin-film engineered by the e-beam evaporation method. The Ti2O3 barrier is utilized as a tunneling charge transport channel between two graphene layers to reduce the charge recombination, and also as a mean for light absorber. Our devices show a high responsivity together with a fast response time in the nano-second scale, and a broadband spectral response at room temperature. |
Friday, March 6, 2020 9:12AM - 9:24AM |
W53.00006: Mismatch-free tunnel spin contacts by photo-induced molecular functionalization of single layer graphene Noel Natera Cordero, Jesus Toscano-Figueroa, Victor Guarochico, Denis Bandurin, Christopher Robert Anderson, Irina Grigorieva, Ivan Jesus Vera Marun A major issue preventing efficient spin injection in graphene is the mismatch between the contact and the spin impedance of the channel. This is of particular relevance for ultra-thin (0.6 nm) alumina tunnel barriers. We overcame this problem by growing the alumina barriers on graphene functionalized with phenyl radicals. The functionalization is achieved by using a laser beam to catalyse a photochemical reaction in benzoyl peroxide. The sub-micron spatial resolution enabled by the focused laser beam allows a direct comparison of different functionalization levels within a single graphene flake. Raman spectroscopy and Atomic Force Microscopy showed a dependence of the roughness of the tunnel barrier on the level of functionalization with the roughness of the barrier on functionalized graphene, reduced to half of that on pristine graphene. This functionalization mitigates the impedance mismatch problem, leading to an order of magnitude increase in the spin valve response. |
Friday, March 6, 2020 9:24AM - 9:36AM |
W53.00007: High-performance WSe2 lateral pn-homojunction achieved with oxygen plasma-treatment for broadband photodetector applications Sekhar Babu Mitta, FIDA ALI, Yang Zheng, Won Jong Yoo 2D transition metal dichalcogenides have shown significant potential for developing future nanoscale optoelectronic devices, among them, bulk tungsten diselenide (WSe2) with an indirect bandgap (1.2 eV) is a promising material for optoelectronic applications due to its tunable energy bands, fast charge transfer, and strong optical absorption. Here, we demonstrate the fabrication of WSe2 lateral pn-homojunction via oxygen (O2) plasma-doping for high-performance broadband photodetector applications. The WSe2 pn-homojunction photodetectors display higher photoresponsivities of 250 mA/W and 2000 mA/W, EQE of 97 % and 420 %, and detectivity of 7.7 × 109 Jones and 7.2 × 1010 Jones for visible (520 nm) and near IR (852 nm) laser illuminations, respectively at Vg = 0V and Vd = 1V. The O2 plasma-doping enables an effective charge generation and separations at the junctions upon the laser illuminations and resulting in superior optoelectronic properties which aid us in the development of lateral pn-homojunction as promising broadband photodetectors. |
Friday, March 6, 2020 9:36AM - 9:48AM |
W53.00008: Stamping of Naked and Suspended 2D Materials to Engineer Light Absorption Israel Rebollo, Fernanda Cristina Rodrigues Machado, Gareth J Melin, Alexandre Champagne We present a nitrocellulose-based method to manipulate naked and suspended 2DM one by one. We make optical measurements on several heterostructures to demonstrate the ability to tune graphene light absorption by a factor of 20. We show spatially-deterministic micron-scale positioning of graphene, boron nitride, and MoS2 naked crystals. Raman spectroscopy confirms the low defect density introduced upon transfer. We detail micro-Raman measurements on a suspended graphene heterostructure of about 12 µm2 to test the validity of an exclusive absorption model based on first-principles calculations [1]. We build several other graphene heterostructures with 2 distinct geometries to engineer the exclusive graphene light absorption. Future applications include optical transducers where a small gate voltage moves a suspended 2DM to vastly enhance or suppress its exclusive light absorption. |
Friday, March 6, 2020 9:48AM - 10:00AM |
W53.00009: Novel Plasmonic Waveguides from Coulomb Engineered Two-Dimensional Materials Zhihao Jiang, Stephan Wolfgang Haas, Malte Roesner Plasmonic excitations in two-dimensional (2D) materials are strongly affected by the screening environment, which allows us to control them by the dielectric properties of the substrate. Here we present how these plasmonic excitations can be spatially confined within a homogeneous 2D material with the help of structured heterogeneous dielectric substrates. By using this environmentally-imprinted plasmonic confinement to spatially guide the propagating surface plasmons within the 2D material we can construct fundamentally new plasmonic waveguides. |
Friday, March 6, 2020 10:00AM - 10:12AM |
W53.00010: Enhanced resonant Raman spectrum of multilayer WS2 with thin film plasmonic cavity Chun Yuan Wang, Meng Hsien Lin, Hung Ying Chen, Jiamin Quan, Junho Choi, Xiaoqin (Elaine) Li, Shangjr Gwo, Chih-Kang Shih Interactions of tightly bound electron-hole pairs (excitons) and the lattice vibration modes (photon) in two-dimension (2D) transition metal dichalcogenide (TMD) crystal is a subject of considerable current interest. Here, we report investigations of exciton resonance Raman spectroscopy assisted by plasmonic thin film cavity from single monolayer to tens of monolayers in WS2. Without the plasmonic cavity and under A exciton resonant excitation condition, the Raman response indeed shows strong enhancement relative to the no-resonance condition, as reported by others previously [1]. With plasmonic cavity, the Raman signal is enhanced further as anticipated [2]. However, we find the enhancement factor show dramatic dependence on the TMD layer thickness with an optimal thickness in the range of few nanometer. More specifically, we find that at this range of thickness, the Raman enhancement is more than 2 orders of magnitude higher than that for the monolayer case. Possible mechanisms will be discussed. |
Friday, March 6, 2020 10:12AM - 10:24AM |
W53.00011: Optical temperature determination during laser annealing of graphite oxide Shashank ram Nandyala, Joseph R Murphy, Michael A Seas, Vivek Jain, Subash Kattel, Jon M Pikal, Patrick A Johnson, John Ackerman, WIlliam Rice Highly conductive, graphene-like, reduced graphite oxide (rGO) can be synthesized from graphite oxide (GO) via photochemical methods, solution chemistry, and high-temperature treatments. In order to develop intricate circuitry and conductive patterns out of rGO, controlled laser-based annealing of GO has been extensively developed. Here, we show that this laser-based technique creates a localized, optically induced thermal reaction in GO. We determine the local temperature at the irradiation spot by comparing the Stokes and anti-Stokes scattering intensities giving us a simultaneous measure of temperature during annealing. Using this technique, we compare the optically induced GO-to-rGO transition with standard induction furnace annealing. The optically created rGO patterns, which we show can be produced in air, argon, and vacuum environments, are characterized using electrical conductivity and Raman scattering. Our ability to generate conductive circuits using optical annealing of GO creates new opportunities for economical carbon-based electronics. |
Friday, March 6, 2020 10:24AM - 10:36AM |
W53.00012: Optical probe of the low doping regime in graphene: Comparison of Raman spectroscopy and transport measurements Zhuofa Chen, Mounika Vutukuru, Anna K Swan Identifying charge density fluctuations and impurities in graphene is vital for high-quality graphene-based devices. Here, we developed an optical probe to evaluate the doping level and charge fluctuation in the range from 1010 cm-2 to 1012 cm-2 by using the Raman 2D peak. We compare charge density estimated from Raman measurements with electrical transport measurement, the benchmark method for evaluating charge density fluctuations and other scattering mechanism. At low doping level(< 1012 cm-2), the 2D Raman peak becomes asymmetric and can be fitted by two peaks, and the 2D peak-split(in cm-1) correlates with charge density with high precision (2×1010 cm-2 per 2D peak-split wavenumber). Our work provides a simple and non-invasive optical method to quantify the doping levels of graphene from 1010 cm-2 to 1012 cm-2, two orders of magnitude higher precision than previously reported optical methods [1]. The 2D peak-split method provides a platform for evaluating the quality of graphene before building high-quality graphene devices. |
Friday, March 6, 2020 10:36AM - 10:48AM |
W53.00013: Probing strong light-matter interaction in the optically thin limit Eric Yue Ma, Tony F Heinz Sharp and isolated resonances in condensed-matter systems yield pronounced signatures in dielectric function, which, in turn, are manifest in the reflectance and transmittance spectra. A canonical example is the Reststrahlen band, extended spectral bands with near-unity reflectance, known to occur in ionic crystals near their optical phonon frequencies in the mid-infrared. Although Reststrahlen bands in bulk materials have been extensively studied, their behavior in the optically thin limit has not been examined systematically. With the advent of 2D van der Waals materials, it has become possible to probe materials with precise thicknesses across several orders of magnitudes, with essentially no change to the dielectric function down to the few- or monolayer limit. Here we present a systematic study of Reststrahlen-like reflection bands when the material transitions from optically thick to optically thin. We describe, experimentally and theoretically, the evolution of the reflectance spectra and their relation to radiative and nonradiative rates. |
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