Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session P35: Novel 2D MaterialsFocus
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Sponsoring Units: DMP Chair: Giang Nguyen, Oak Ridge National Laboratory Room: LACC 409B |
Wednesday, March 7, 2018 2:30PM - 2:42PM |
P35.00001: Strains induce vector potentials in square buckled Rashba Lead Chalcogenides Paul Hanakata, Aleksandr Rodin, Harold Park, David Campbell, Antonio Castro Neto Recently, we have found a new class of two-dimensional (2D) ferroelectric Rashba semiconductors (FERSC) PbX (X=S, Se, Te) with tunable spin-orbitronic properties [1]. Our first-principles calculations, together with tight binding (TB) models, provide a framework to understand and design this new class of materials. One of the exciting features of many 2D materials is the tunability of their electronic and optical properties through strain engineering. Based on our previous TB results, we derive an effective low-energy Hamiltonian around the symmetry points that captures the effects of strains on the electronic properties of PbX. We find that strains induce vector potentials which shift the Dirac point and also induce anisotropy in the Rashba parameter. This effect is equivalent to application of an in-plane magnetic field. This finding will be important to understand the variations in local Rashba parameters in the real space due to effects caused by substrates and defects. |
Wednesday, March 7, 2018 2:42PM - 2:54PM |
P35.00002: Unraveling the properties of novel Ga2O3 nanolayers Hartwin Peelaers, Chris Van de Walle Ga2O3 is a wide-band-gap semiconductor with promising applications in transparent electronics and in power devices. It is not a layered material in bulk, but nevertheless nanolayers can be produced by exfoliation [1]. First-principles calculations based on hybrid functionals show that there is seemingly an absence of quantum confinement in the Ga2O3 nanolayers: the calculated nanolayer band gap, independent of thickness, is equal to the bulk band gap. |
Wednesday, March 7, 2018 2:54PM - 3:06PM |
P35.00003: Polytypic Phase Transitions in Metal and Semiconductor Intercalated Bi2Se3 Kristie Koski A clever route to achieve a 2D metal-semiconductor heterostructure or 2D semiconductor heterostructure is through intercalation of zero-valent atomic species. With intercalation of zero-valent elements, fundamentally new physical behaviors arise such as charge density waves or tunable phase transitions. In this talk, the pressure, temperature and concentration dependent phase diagrams of zero-valent metal and semiconductor intercalated bismuth selenide are investigated. Polytypic phase transitions associated with superlattice formation along with order-disorder phase transitions are demonstrated. Hexagonal and striped domain formation consistent with two-dimensional ordering of the intercalant and Pokrovksy-Talapov theory is identified as a function of concentration. These studies provide a complete picture of the structural behavior of zero-valent metal and semiconductor- intercalated Bi2Se3. |
Wednesday, March 7, 2018 3:06PM - 3:42PM |
P35.00004: Fundamental Insights and Perspectives into Novel 2D Anisotropic Materials Invited Speaker: Sefaattin Tongay Anisotropic 2D materials (pseudo-1D crystals) are a new class of materials in which atoms are |
Wednesday, March 7, 2018 3:42PM - 3:54PM |
P35.00005: Electronic and Vibrational Properties of New Polymorphs of NbS3: Phase-IV and Phase-V Bishwajit Debnath, Mathew Bloodgood, Ece Aytan, Tina Salguero, Alexander Balandin, Roger Lake Two new polymorphs of Niobium Trisulfide (NbS3), phase-IV and phase-V, have been grown and identified by single crystal x-ray diffraction. The polymorphs have monoclinic structure with space group P21/c and P21/m, respectively. We have calculated the electronic and vibrational properties of both polymorphs, using ab initio density function theory (DFT) at the PBE and HSE level of theory. Electronic band calculation suggests that phase-IV is a semiconductor with an indirect bandgap of ~0.2 eV (PBE), whereas phase-V is a metal. The phonon energy at the zone-center matches closely with the measured Raman spectra. Moreover, the full phonon dispersion reveals that phase-IV is dynamically stable (no negative phonon branches). On the contrary, phase-V exhibits several negative phonon pockets, specifically along the NbS3 nanowire growth direction. This is an indicator of a possible charge density wave (CDW) ground state in this polymorph. |
Wednesday, March 7, 2018 3:54PM - 4:06PM |
P35.00006: Exfoliation and characterization of the 1D van der Waals material tellurium Takayuki Hironaka, Xian Hu, Jeb Stacy, Ishiang Shih, Jin Hu, Gregory Salamo, Shui-Qing Yu, Hugh Churchill As 1D van der Waals or weakly bonded materials, crystalline trigonal tellurium (Te) and selenium (Se) have the potential to form single atom chains with helical structures. We report ultra-thin Te flakes and nanowires obtained by mechanical exfoliation [1]. Trigonal Te single crystals were exfoliated, without tape, on oxidized silicon substrates. Atomic force spectroscopy revealed that Te nanowires with heights of 1 - 2 nm and widths below 100 nm were fabricated. Anisotropic Te flakes with a thickness of 15 nm showed ridges running along the length of the flake surfaces, unlike 2D materials that typically have smooth surfaces. A1 and E Raman modes of a 30 nm thick flake were consistent with those of bulk Te, with a slight blueshift (4 cm-1). Polarized Raman spectroscopy was used to determine the crystal orientation of the flakes. Ongoing efforts to measure electronic transport of exfoliated Te will also be reported. |
Wednesday, March 7, 2018 4:06PM - 4:18PM |
P35.00007: Stable carbon monosulfide nanostructures: Chain arrays and monolayers Andres Ayuela, Tomás Alonso-Lanza, Jhon W. Gonzalez, Faustino Aguilera-Granja Herein we show using theoretical predictions that carbon monosulfide compounds exhibit a variety of layered nanostructures, such as chain arrays, monolayers, and thin films. We show that semiconductor chain arrays are the most stable because they are mainly dimensionality driven by sp2 hybridization of the carbon orbitals. In contrast to the thin films, the monolayers are stable at room temperature in a semiconductor phase, which is followed in energy by a metallic phase. Moreover, we study a semiconductor-to-metal phase transition in the carbon monosulfide monolayers by strain engineering to control the conductivity and carrier mobility. |
Wednesday, March 7, 2018 4:18PM - 4:30PM |
P35.00008: Computational study of a family of monolayer 2D semiconducting tellurides Huta Banjade, Jinbo Pan, Qimin Yan Discovery and design of 2D materials with suitable band gaps and high carrier mobility is of vital importance for photonics, optoelectronics, and high-speed electronics. In this work, based on first principles calculations using density functional theory (DFT) with PBE and HSE functionals, we introduce a family of monolayer isostructural semiconducting telluride M2N2Te8 with M = {Ti, Zr, Hf} from group IV and N= {Si, Ge} from group XIV of periodic table. These compounds have been identified to possess direct band gaps that are tunable from 1.0 eV to 1.3 eV which are well suited for photonics and optoelectronics applications. Additionally, anisotropic in-plane transport behavior is observed and small electron and hole (0.11 - 0.15 me) masses are identified along the dominant transport direction. High carrier mobility are observed in these compounds, which shows great promise for applications in high-speed electronic devices. Detailed analysis of electronic structures reveals the atomic origins of promising properties of this unique class of 2D telluride materials. |
Wednesday, March 7, 2018 4:30PM - 4:42PM |
P35.00009: Charged Impurity Limited Scattering and Mobility in p-type GaS, GaSe, InS and InSe Protik Das, Darshana Wickramaratne, Bishwajit Debnath, Gen Yin, Yafis Barlas, Roger Lake The valence bands of many monolayer and few-layer two-dimensional (2D) materials such as GaS, GaSe, InS, and InSe, have a “Mexican hat” dispersion in which the valence band edge is approximately a ring in the 2D Brillouin zone. This results in a singular density of states (DOS) at the band edge that diverges as 1/√E. The ionized impurity scattering rate depends on the DOS through both the integral over final states and the polarization function in the screened Coulomb potential. We calculated the static charge polarizability within the random phase approximation and evaluated the ionized impurity scattering rate and the mobility as a function of temperature and carrier concentration. The results are compared to those obtained from Thomas-Fermi screening and a parabolic dispersion. The underestimation of the ionized impurity scattering rate using Thomas Fermi screening is strongly temperature dependent ranging from 2 orders of magnitude at 5K to a factor of 4 at 300K. At 77K, for an ionized impurity density of 1011 cm-2, the hole mobility of GaS ranges from 20 cm2/Vs at a hole concentration of 1012 cm-2 to 200 cm2/Vs at 1013 cm-2. |
Wednesday, March 7, 2018 4:42PM - 4:54PM |
P35.00010: Mechanism Studies and Fabrication of Carbon Nanostructures Incorporated into Al Alloys by Electrocharging Assisted Process Xiaoxiao Ge, Chirstopher Klingshirn, Manfred Wuttig, Karen Gaskell, Peter Zavalij, Balu Balachandran, Daniel Cole, Liangbing Hu The incorporation of carbon (C) nanostructures into Al alloys, such as Al6061 and Al1350, has the potential to further improve the mechanical and electrical properties of these alloys. Previously, we reported on a novel electrocharging assisted process to incorporate up to 10 wt% C into the crystal structure of Al 6061 alloys to form “Al Covetic”. The C has been proved to transform into graphitic structures with high percent of sp2 bonding. The mechanism of Covetic conversion is controlled by a high current density which facilitates ionization of the C atoms and migration of the C ions similar to “electromigration in a plasma”. In this study, alternative C source, such as graphite powders or flakes, which are already crystalline, are used to obtain a network of C nanostructures that extends throughout the metal. Different fabrication conditions are tested, including different reaction time, the mode of current (pulsed vs constant), and different trajectories of the graphite cathode. The goal is to obtain the optimal condition to fabricate Covetic with uniform C distribution and better electrical and mechanical properties. Conductive AFM, nanomechnical and electrical resistivity measurements are performed on Covetic compared to the parent alloys. |
Wednesday, March 7, 2018 4:54PM - 5:06PM |
P35.00011: Insight investigation about the origin of activity of single atom N-doped graphene electro catalyst for hydrogen evolution reaction Md Delowar Hossain, Zhengtang Luo The world becomes getting warmer day by day due to extensive use of fossil fuels in primary energy mixture for energy production. As an alternative sustainable energy source, molecular hydrogen production through electrolytic reduction of water via hydrogen evolution reaction (HER) is a stronger candidate. Among all catalyst, platinum is the most efficient but the excessive cost and non-availability limits its industrial production of hydrogen. As an alternative of platinum now researchers are focused on single atom catalysis (SAC) with a fraction amount of transition metals supported by effective supporting materials. Here we report evaluation a series of transition metals based single atom catalysts supported by N-doped graphene by combining electrochemical measurement and density functional theory calculation. We find upper transitional metals coordinated with N show better activity towards HER than the post transitional metals. Also, we able to establish an activity trends with most active hybridized orbital of M-N4 and antibonding states resulting from H-interaction with adsorbent. So, we think that by theoretically predicted electronic properties and experimentally achieved electrochemical activity will open a new era to design highly efficient electro catalysts for HER. |
Wednesday, March 7, 2018 5:06PM - 5:18PM |
P35.00012: MBE Grown Super-saturated Aluminum Delta-doped Layers in Silicon Ke Tang, Hyun-soo Kim, Aruna Ramanayaka, Joseph Hagmann, Curt Richter, Michael Stewart, Joshua Pomeroy Recently, significant work has been demonstrated that 2D material systems are important in variety of fields including silicon quantum computing, nanowires, superconductivity, etc. However, most of the studies were focused on n-type dopant layers, a complimentary p-type system has yet to emerge. Here, we report on the detailed material synthesis of this “aluminum delta layer”. Our aluminum delta layers are grown on flash annealed Si (100) substrates by physical vapor deposition and followed by electron-beam evaporated Si epitaxial capping layer. Both in situ and ex situ annealing are studied for dopant activation. Mesa etched Hall bar devices are fabricated to characterize the material properties and the initial results show a p-type carrier contributing to the conduction with densities > 1014 hole/cm2, hole mobility > 102 cm2/Vs and approximately 1.1 holes per dopant atom. Scanning tunneling microscopy (STM) and reflection high-energy electron diffraction (RHEED) images taken during each step of the fabrication processes will also be presented. |
Wednesday, March 7, 2018 5:18PM - 5:30PM |
P35.00013: Hole carrier density and mobility of aluminum delta-doped layers in silicon Hyun-soo Kim, Aruna Ramanayaka, Ke Tang, Joseph Hagmann, Curt Richter, Michael Stewart, Joshua Pomeroy We have measured the hole carrier density and mobility of a two-dimensional hole gas in aluminum delta-doped layer in silicon with a narrow doping profile and high carrier density. The p-type delta layer has not been well studied unlike a n-type delta layer by phosphine gas dosing. I will present our Hall measurements at 4 K using mesa-etched Hall bar device fabricated in Al delta-doped layer in Si with the hole carrier concentration, np ≈ 1.6 x 1014 /cm2, and mobility, μh ≈ 15 cm2/Vs. These densities are close to where a theoretical study predicted superconducting Si heavily doped with Al near 1 K [1], opening up possibilities for semiconductor/superconductor hybrid systems. Comparison of STM analysis and Hall measurements show ≈ 1.1 ± 10 % holes per dopant atom. |
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