Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session X12: Computational Materials Design - Novel 2D MaterialsFocus
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Sponsoring Units: DMP DCOMP Chair: Gus Hart, Brigham Young Univ - Provo Room: LACC 303B |
Friday, March 9, 2018 8:00AM - 8:12AM |
X12.00001: Data-driven discovery of functional 2D materials utilizing a computational database for electronic structures Jinbo Pan, Haowei Peng, Hua Wang, Jie Yu, Huta Banjade, Xiaofeng Qian, John Perdew, Qimin Yan Utilizing high-throughput first-principles computations based on density functional theory (DFT), we construct a comprehensive materials database including electronic structures of ~880 single-layer 2D compounds identified by data-mining the ICSD database. These 2D compounds are classified by their plane groups based on 2D symmetry operations. High-symmetry k-points in the first Brillouin zones are assigned for each plane group and full band structures of these 2D materials are evaluated using PBE and HSE06 hybrid functional. The electronic structure information provides a fertile ground for the future discovery of 2D compounds for solar energy conversion, electronics, and optoelectronics. As a benchmark of the power of this database for 2D materials discovery and design, we present the discovery of novel photocatalysts with optimal band energies and small exciton binding energies. |
Friday, March 9, 2018 8:12AM - 8:24AM |
X12.00002: Honeycomb Boron Allotropes with Dirac Cones: A True Analogue to Graphene Wencai Yi, Wei Liu, Jorge Botana, Zhen Liu, Jingyao Liu, Maosheng Miao Graphene has received much attention for its novel properties, especially Dirac points. Boron, the neighbor of carbon in the periodic table, has also been focused on its Dirac structures. Here, we propose a series of planar boron allotropes with honeycomb topology and demonstrate that their band structures exhibit Dirac cones at the K point, the same as graphene. In particular, the Dirac point of one honeycomb boron sheet locates precisely on the Fermi level, rendering it as a topologically equivalent material to graphene. Its Fermi velocity (vf) is 6.05 × 105 m/s, close to that of graphene. Although the freestanding honeycomb boron allotropes are higher in energy than α-sheet, our calculations show that a metal substrate can greatly stabilize these new allotropes. They are actually more stable than α-sheet on the Ag(111) surface. Furthermore, we find that the honeycomb boron form low-energy nanoribbons that may open gaps or exhibit strong ferromagnetism at the two edges in contrast to the antiferromagnetic coupling of the graphene nanoribbon edges. |
Friday, March 9, 2018 8:24AM - 8:36AM |
X12.00003: Nitrophosphorene: A 2D Semiconductor with Both Large Direct Gap and Superior Mobility Lei Zhao, Wencai Yi, Jorge Botana, Feng Long Gu, Maosheng Miao A new two-dimensional phosphorus nitride monolayer (P21/c-PN) with distinct structural and electronic properties is predicted based on first-principle calculations. The energy of this allotrope is slightly above the convex hull between black phosphorous and phosphorous nitride (P3N5) and is 46.4 meV/PN lower than the most stable phosphorus nitride allotropes in previous reports. Unlike pristine single-atom group V monolayers such as nitrogene, phosphorene, arsenene, and antimonene, P21/c-PN has an intrinsic direct band gap of 2.77 eV and remains as a direct gap semiconductor under compressive and tensile strains as large as 10%. Strikingly, P21/c-PN shows excellent electron mobility up to 290829.81 cm2 V-1s-1 along a direction, which is about 18 times of that in monolayer black phosphorus, and electric transport also show high anisotropy. This put P21/c-PN way above the general relation that carrier mobility is inversely proportional to bandgap, making it a very unique two-dimensional material for nanoelectronics devices. |
Friday, March 9, 2018 8:36AM - 8:48AM |
X12.00004: 2D Materials: A Wonderland of Nonlinear Optical Responses Hua Wang, Xiaofeng Qian Materials with strong nonlinear optical (NLO) responses are crucial for many technologically important applications. NLO responses are governed by intrinsic symmetry, transition dipole moments, local environment and dimensionality. I will present our recent first-principles theoretical discoveries and understandings of giant NLO responses in a number of 2D materials, and demonstrate that 2D materials provide perfect solid-state platform for exploring nonlinear nanooptics. Transition metal dichalcogenides and group IV monochalcogenides possess strong second order NLO responses, and the latter also hold giant ferroelectric-ferroelastic multiferroicity which is directly correlated with their NLO properties. We will present recent work on other 2D NLO properties and discuss the relationship between NLO responses and Berry connections. Our present findings open up new avenues for ultrathin nonlinear optoelectronics. References: 1) Giant Optical Second Harmonic Generation in Two-Dimensional Multiferroics. Nano Letters 17, 5027-5034 (2017). 2) Two-dimensional multiferroics in monolayer group IV monochalcogenides. 2D Materials 4, 015042 (2017). 3) Nonlinear Optical Responses in 2D Materials. to be submitted (2017). |
Friday, March 9, 2018 8:48AM - 9:00AM |
X12.00005: A new class of crystal structure for two-dimensional materials Kisung Chae, Young-Woo Son Two-dimensional (2D) layered materials have recently been studied extensively owing to their unusual physical properties. Not only they offer superior mechanical, transport, energy harvesting properties, they also host intriguing electronic structures of Dirac Fermions. Together with various exfoliation techniques available, diverse families of 2D materials and their heterojunctions will enrich the structure-property relations. Here, we demonstrate a new class of 2D materials, which are composed of six group IV (C, Si, Ge, Sn) and two group VI (O, S, Se, Te) elements. The microscopic crystal structure of the new 2D materials with a space group of Cmme (No. 67) are remarkably distinctive from the previously known 2D materials such as transition metal dichalcogenides, metal halides, and layered III-VI and V-VI compounds. Furthermore, we find that their electronic structures vary significantly depending on the group IV elements consisting of the crystal. Some of the crystals are direct bandgap semiconductors with sizes up to 1.2 eV, while others are quantum spin Hall insulators with their spin-orbit bandgap sizes ranging from a few tens to hundreds of meV. We believe that the new 2D materials presented in this work can extend the library of 2D materials. |
Friday, March 9, 2018 9:00AM - 9:12AM |
X12.00006: Goniopolarity of Thermal Transport Behavior in Layered 2D Materials Yaxian Wang, Bin He, Maxx Arguilla, Nicholas Cultrara, Joshua Goldberger, Joseph Heremans, Wolfgang Windl NaSn2As2 has recently been synthesized and was found to be an exfoliatable van der Waals Zintl phase, opening new opportunities for electronic and spintronic design on the few-atom-thick scale. Although the band structure may suggest NaSn2As2 to be in the range of metal to semi-metal, it shows strong anisotropy especially in its “polarity”, characterized by its dominant carrier type, which strongly affects its electronic and thermal properties. We used DFT calculations to investigate band structure and Fermi surface, which agree well with ARPES measurements. In addition, we employed BoltzTraP code to calculate the transport behavior in in/cross-plane directions, which predicts strongly anisotropic carrier transport and directionally dependent polarity – “goniopolarity” – in this layered material. It is confirmed by experimental thermopower measurements which find opposite sign for two directions. It indicates thermal transport is based on both electrons and holes, making this layered material an intrinsic 2-carrier system. We show from simulations on a model band structure that this can happen for a single-band system with appropriately shaped Fermi surface with the right fraction of concave vs. convex areas, which allows exploration and design of other new goniopolar materials. |
Friday, March 9, 2018 9:12AM - 9:24AM |
X12.00007: Designing New Two-Dimensional Janus Nanomaterials by Anionic Exchange Woosun Jang, Aloysius Soon Two-dimensional nanomaterials have played a key role in the recent advances in nanoscience for a decade, especially in the area of energy technology. Of late, a new class of 2D material has been suggested and experimentally realized – namely, the Janus monolayer. Different from preceding 2D materials, such as graphene and transition metal dichalcogenides, Janus monolayers lack the inversion symmetry in both in-plane and out-of-plane directions, and this leads to new anisotropic physiochemical properties which can be potentially useful for key energy applications. In this work, we design and investigate various novel two-dimensional Janus materials, via the anionic exchange method. In particular, by starting from the well-known MoS2 and WS2 monolayers, we substitute the top and bottom sulfur layers using a combination of group V and VII anions. Density-functional theory calculations are then performed to examine their anisotropic material properties. |
Friday, March 9, 2018 9:24AM - 9:36AM |
X12.00008: Effects of structural degeneracies on properties of two-dimensional materials Salvador Barraza-Lopez Over the past two years, my group has been involved on the prediction and subsequent verification of two-dimensional structural phase transitions in two-dimensional materials beyond graphene that arise due to structural degeneracies on unit cells with reduced symmetries. The realization of these structural transitions is important in the context of a theory for two-dimensional materials that is overwhelmingly developed for structures at zero temperature, and in this presentation I will provide a short account of these developments, and opportunities for further work. |
Friday, March 9, 2018 9:36AM - 9:48AM |
X12.00009: A materials informatics approach to the study of van der Waals materials Trevor David Rhone, Shaan Desai, Philip Kim, Amir Yacoby, Efthimios Kaxiras The explosion in the recent number of proposed van der Waals (vdW) materials, alongside the emergence of materials databases, has increased the promise of uncovering novel physics and developing new applications for 2D atomic crystals. Though this large number of newly identified vdW materials comes with the potential for discovery, immense challenges also emerge. That is, traditional experimental and theoretical methods for the study of a large database of materials are slow and expensive. A novel approach to materials investigation is desirable. With the advent of materials informatics (the combination of statistical tools, computational methods and materials science) one is able to efficiently screen a large database of materials and make predictions of desirable properties. We will discuss how materials informatics can be used for a high-throughput study of 2D atomic crystals. In particular, we show how machine learning can be used to efficiently predict the heat of formation (i.e. stability) of known 2D atomic crystals, as well as candidates for entirely new layered materials. |
Friday, March 9, 2018 9:48AM - 10:00AM |
X12.00010: Electronic properties of a new family of Group 14-15 2D layered materials from first principles Muhammad Sufyan Ramzan, Agnieszka Kuc, Thomas Heine The prompt and successful research on graphene and transition metal dichalcogenides (TMDCs) such as MoS2, MoSe2, WS2 etc., encourages materials research community to discover new systems with finite band gaps and interesting electronic properties for various applications. The knowledge of broad spectrum of these layered materials will enable scientists to further engineer their properties on demand, opening the enormous prospects for their application in electronics, photonics and other applications. In the present work motivated by work of Jing et al1, using density functional theory approach, we investigated structures, stability and electronic properties of Group 14-15 compounds. We found that these materials show strong interlayer quantum confinement effect, resulting is semiconductor-metal transition when increasing the number of layers from 1 layer up to multilayers and bulk systems. Cleavage energies show possibility of mechanical exfoliation of these materials. These electronic properties offer possibility of single-materials nanodevices. |
Friday, March 9, 2018 10:00AM - 10:12AM |
X12.00011: Integration of high-throughput, provenance and dissemination: the case of novel 2D materials Giovanni Pizzi, Nicolas Mounet, Nicola Marzari Computational discovery of novel materials often requires high-throughput searches relying on complex workflows. However, these can be difficult to detail and reproduce. Frameworks like AiiDA [1] allow automated calculations and storage preserving full provenance, with no additional effort required. I will argue why this is essential using as case study the search for novel 2D materials [2] where, starting from ~110,000 unique experimentally-known 3D compounds we identify with high-throughput van-der-Waals DFT calculations 1825 potentially-exfoliable compounds. This portfolio can be further refined and used to compute vibrational, electronic, magnetic, and topological properties. For instance, we are able to identify 56 promising ferro- and antiferromagnetic systems. By uploading all data (automatically stored by AiiDA) to our platform materialscloud.org, results can be disseminated seamlessly, with DOIs assigned to the datasets and interactive browsing of the provenance to understand, reproduce and reuse the results. |
Friday, March 9, 2018 10:12AM - 10:24AM |
X12.00012: New two-dimensional anisotropic monolayers of phosphide binary compounds with wide fundamental bandgaps Congyan Zhang, Ming Yu The newly discovered 2D GaP and InP layers have unique anisotropic structural, electronic, and mechanical properties. Their crystalline structures show orthorhombic lattices symmetry and high buckling of 2.14 Å-2.46 Å. The speeds of sound in their phono dispersions along the Γ-Y direction are higher than those along the Γ-X direction, reflecting anisotropy in their elastic constants which were further confirmed from their strong directional dependence of Young’s moduli. They have wide fundamental bandgaps (2.89 eV for GaP and 2.59 eV for InP, respectively), which were found to be tunable under the strain either along armchair or zigzag directions. A direct-indirect bandgap transition was found under certain strains along zigzag or biaxial orientations, reflecting their promising applications for the strain-induced bandgap engineering in nanoelectronics and photovoltaics. |
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