Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session F35: Adatoms, Dopants, and Defects in 2D Materials |
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Sponsoring Units: DCMP Chair: Cory Cress, US Naval Research Laboratory Room: LACC 409B |
Tuesday, March 6, 2018 11:15AM - 11:27AM |
F35.00001: Scanning Tunneling Microscopy of dopants and defect structures in monolayer graphene Lavish Pabbi, Riju Banerjee, Bill Dusch, Anna Snelgrove, Tomotaroh Granzier-Nakajima, Tanushree Choudhury, Mauricio Terrones, Eric Hudson The ability of the Scanning Tunneling Microscope (STM) to study material surfaces with atomic resolution makes it a perfect tool for measuring local structural and electronic properties and their relationships. Here we report on an investigation of dopant and defect structures in monolayer graphene. Substitutional doping with boron and nitrogen adatoms, achieved by both gaseous and novel liquid precursor based growth methods, as well as He-ion plasma etching of epitaxially grown graphene on SiC, both produce a wide variety of defect structures with interesting topographic and spectroscopic features. Understanding the nature of these structures in graphene not only provides insight into the growth and structural dynamics of two-dimensional systems, and in particular into the nucleated growth of other 2D materials on defective graphene substrates, but also paves the way for tuning of electronic band-gap, conductivity, local spin and magnetic properties, enabling the development of chemical detectors and other advanced electronic devices. |
Tuesday, March 6, 2018 11:27AM - 11:39AM |
F35.00002: Transition metals dopant clusters in MoS 2 : a first principle study Kingsley Obodo, Cecil Ouma, Evans Benecha, Joshua Obodo, Moritz Braun Using first-principles calculation, we carried out a systematic study on the effect of transition metal (TM: Ti, V, Cr, Mn, Fe, Co, Ni) dopant lattice separation and clustering on MoS2 monolayer as potential spintronics, catalytic and optoelectronics material. The electronic and magnetic properties changed both as a function of the TM ion dopant and lattice separation. The calculated binding energies indicate that it is possible to introduce TM ions into the lattice of MoS2. The calculated clustering energies shows that TM ions exhibit dispersive distribution void of cluster formation in MoS2 lattice. Generally, there is a reduction in the electronic band of doped MoS2 compounds with a consistent red shift in the absorption spectra. The calculated redox potentials of H2O splitting lie properly astride the valence and conduction bands for Cr doped MoS2, indicating that this material is a potential photocatalyst. Increasing the atomic separation of the co-doped compounds strongly favors the anti-ferromagnetic configuration with increase in the overall magnetic moment. This theoretical investigation provides further insight into the application of TMDCs as ultra-thin spintronics materials. |
Tuesday, March 6, 2018 11:39AM - 11:51AM |
F35.00003: First-Principles Investigations of Graphene:hBN In-Plane Heterostructure and BN Co-Doped Graphene: Electronic Structure Trends Regiane Nascimento, David Prendergast, Helio Chacham, Ronaldo Batista Through DFT calculations, we have predicted the effects on energetic and electronic properties of hexagonal boron nitride (h-BN) doped graphene and graphene:h-BN strips in-plane heterostructures, with respect their edges shape and species occupancy. We have considered BN co-doped graphene supercells with BN concentrations varying from 2.08 up to 10.42%. For a given BN doping concentration, the band gap can vary over an order of magnitude depending on the placement of the B and N atoms. We propose an analytical tight-binding model that reproduces the dependence of the band gap on both the concentration and the morphology and provides an upper bound for the band gap at a given BN concentration. For graphene:h-BN in-plane heterostructure, our DFT calculations predict that the most stable interface in these heterostructures is the one of extended Klein type for graphene when the C-B bonds are present in the interface. Also, the graphene strip (GST) becomes metallic when it bonds to only one species (B or N). In this case, the strips may present a magnetic moment, which depends on the GST width, chirality, and species occupancy edge. The largest values of the magnetic moment are achieved for heterostructure with only C-N bonds in the zigzag and extended Klein interfaces. |
Tuesday, March 6, 2018 11:51AM - 12:03PM |
F35.00004: Abstract Withdrawn
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Tuesday, March 6, 2018 12:03PM - 12:15PM |
F35.00005: Ab Initio Calculations of Nitrogen Functionalization of Graphene Olivier Malenfant-Thuot, Germain Robert Bigras, Luc Stafford, Michel Cote Our collaboration between theorists and experimentalists aims to achieve nitrogen functionalization of graphene with the late-afterglow regime of a microwave plasma. We hope this technique will give us a better control on the functionalization due to the small density of interacting atoms in the late-afterglow and a drastic diminution of induced defects compared to standard plasma functionalization techniques. Using software packages ABINIT and BigDFT, we carried out first-principles calculations to study many different interactions possible between nitrogen atoms and graphene, both in-plane and on top of the sheet. Formation energies were obtained and compared to obtain insights into the configurations importance and stability. In order to understand the doping process at the atomic scale, we used the Nudged Elastic Band method to calculate energy barriers for different diffusion and absorption paths for adsorbed nitrogen atoms. |
Tuesday, March 6, 2018 12:15PM - 12:27PM |
F35.00006: Supercell DFT calculations of charged defects in monolayer h-BN Pradip Niraula, Angelo Bongiorno We use density functional theory (DFT) calculations to study the |
Tuesday, March 6, 2018 12:27PM - 12:39PM |
F35.00007: Gas adsorption, stabilities and electronic properties of graphene monolayers and bilayers doped with B and N Yoshitaka Fujimoto, Susumu Saito Graphene has received much interest as sensor device materials because of its high carrier mobility as well as high sensitivity to adsorbates. Substitutional doping with heteroatoms can modify the electronic properties and often enhance the chemical reactivity of graphene. Here, we report polluting or toxic gas molecule adsorption effects on the stabilities and the electronic properties of graphene monolayers and bilayers doped with boron and nitrogen atoms based on our first-principles density-functional calculations [1,2]. We find that, while abundant molecules in air (O2, N2 etc.) do not bind strongly, the single NO (NO2) as well as the double NO (NO2) molecules can bind on the B-doped monolayer graphene with chemical bonds. Furthermore, we also show that a pair of NO and NO2 molecules can bind chemically on the B-doped graphene. Owing to the formation of the chemical bonds, the charge transfers are shown to take place between the gas molecules and the graphene layers, and give rise to the change of the workfunction of the system. We also discuss the possibilities of designing sensors to detect only NOx molecules in air. [1] Y. Fujimoto and S. Saito, Chem. Phys. 478 (2016) 55. [2] Y. Fujimoto and S. Saito, submitted. |
Tuesday, March 6, 2018 12:39PM - 12:51PM |
F35.00008: Quantum and classical dynamics of intrinsic defects and equation of state of elemental boron Tadashi Ogitsu, Shuai Zhang, Burkhard Militzer, Heather Whitley Among of third group elements, boron exhibits relatively strong covalent character with trivalency leading to the strong tendency of forming icosahedra based building units: the property that leads to the complex allotropy. In case of beta-rhombohedral boron, it has been known that the basic skeleton deviates largely from the close shell electronic structure, and reconciled by large number of interstitials and vacancies, which forms quasi two-dimensional structure that can be mapped on to a frustrated Ising model. In this presentation, we will discuss the dynamical properties of these defect states at low and high temperatures. At low temperature, we show that tunneling splitting level of some interstitials are in a measurable energy scale owing partly to the close proximity of interstitial positions, while at high temperature, significant number of these defects become mobile where the skeletal atoms largely stay at the original crystallographic positions; the state that resembles to superionic solids. Finally, we will discuss about the inconsistency in the reported equation of states near the melting point. |
Tuesday, March 6, 2018 12:51PM - 1:03PM |
F35.00009: Electronic Properties of Defects in Few-Layer MoS2 Films Marcus Forst, Daniel Trainer, Marian Precner, Tomas Polakovic, Qiao Qiao, Yimei Zhu, Xiaoxing Xi, Goran Karapetrov, Maria Iavarone We report on structural and electronic properties of defects in chemical vapor-deposited monolayer and few-layer MoS2 films. Scanning tunneling microscopy, Kelvin probe force microscopy, and transmission electron microscopy were used to obtain quantitative measurements of the local density of states, work function and nature and mobility of defects. These defects include point defects such as S and Mo vacancies as well as extended defects such as film edges and grain boundaries. |
Tuesday, March 6, 2018 1:03PM - 1:15PM |
F35.00010: Electronic transport of osmium-decorated monolayer graphene Jamie Elias, Erik Henriksen With the goal of inducing a non-negligible spin-orbit coupling in graphene, we have measured monolayer graphene devices with dilute coatings of osmium adatoms. Evaporations are performed in situ, with a custom-built cryogenic probe including a thermal evaporator. Electronic transport is characterized before and after multiple evaporations. Notably, in contrast to other metal adatoms, osmium is found to hole-dope graphene. |
Tuesday, March 6, 2018 1:15PM - 1:27PM |
F35.00011: Transport Signatures of Spin-Orbit Coupling in Adatom-Decorated Graphene Min-Feng Tu, Roger Mong, Jason Alicea Graphene's Dirac band structure and open geometry underlie exciting prospects for engineering new physics via impurity-induced spin-orbit coupling. As a tantalizing example, previous theory works predicted a robust quantum-spin-Hall phase in graphene covered with dilute heavy adatoms such as In, Tl, and Os, though experiments to date have not detected the required enhancement of spin-orbit coupling. Motivated by these experiments, this talk will explore the consequences of adatom-generated spin-orbit couplings on magneto-transport in graphene. We attack the problem using diagrammatic techniques and Landauer-Buttiker transport simulation informed by microscopics, and study various coverages, chemical potentials, and disorder types. We find that the induced spin-orbit couplings can contribute to magneto-conductance differently from conventional intrinsic and Rasbha spin-orbit couplings. Our results provide a possible rationale for the absence of spin-orbit signatures in recent experiments, and also highlight a roadmap for their discovery in future work. |
Tuesday, March 6, 2018 1:27PM - 1:39PM |
F35.00012: Largely tunable anisotropic thermal conductivity of pristine and lithiated MoS2 Shunda Chen, Aditya Sood, Eric Pop, Kenneth Goodson, Davide Donadio Understanding heat transport in two-dimensional (2D) layered materials is of importance for potential applications in energy storage, nanoelectronics and optoelectronics. The vibrational properties of 2D layered materials could be tailored in several different ways either by chemical modifications or mechanically. Here we investigate heat transport in MoS2, upon lithium intercalation and cross-plane strain, by first principles calculations. We find that both the in-plane and cross-plane components of the thermal conductivity of MoS2 are extremely sensitive to both strain and electrochemical intercalation. Furthermore, since in-plane thermal conductivity and cross-plane thermal conductivity respond in different ways to intercalation and strain, the thermal conductivity anisotropy can be modulated over two orders of magnitude. The underlying mechanisms for such large tunability of the anisotropic thermal conductivity of MoS2 are explored by analyzing phonon dispersion relations, relaxation time and mean free paths. Since both intercalation and strain can be applied reversibly their stark effect on the thermal conductivity can be exploited to design novel phononic devices, as well as for thermal management in MoS2-based electronics and optoelectronic systems. |
Tuesday, March 6, 2018 1:39PM - 1:51PM |
F35.00013: Water Permeation Through Periodically Porous Graphene Jin Soo Lim, Gunn Kim, Efthimios Kaxiras Polyphenylene superhoneycomb network (PSN) is an experimentally realized periodically porous graphene with subnanometer-sized pores, which is a type of covalently linked hydrocarbon superhoneycomb network. Here, we report a computational study of permeation of a water molecule through monolayer PSN as well as N-substituted PSN, where a fraction of the H-terminated C atoms are substituted with N atoms. For the investigation, we performed first-principles calculations within van der Waals density functional theory. The lowest energy barrier was calculated to be 1.5 eV for permeation of vertically oriented water molecules through the pores of regular PSN. The pore expanded on the order of 0.1 Å to allow water permeation, with vertical displacements by ~0.8 Å owing to H-bonding with the water molecule. Upon N-substitution, the pore size increased slightly and the barrier was lowered to 0.5 eV, a more feasible value for permeation. Interestingly, we found horizontally oriented water molecules to pass through the pores more easily. Therefore, our results demonstrate that the introduction of N atoms can be a good strategy to enhance the applicability of PSN as a water purification membrane. |
Tuesday, March 6, 2018 1:51PM - 2:03PM |
F35.00014: Long-range exchange interaction between magnetic impurities in graphene Megha Agarwal, Eugene Mishchenko
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Tuesday, March 6, 2018 2:03PM - 2:15PM |
F35.00015: Engineering charge tunable one dimensional molecular array towards supercritical collapse states in graphene Hsin-Zon Tsai, Jiong Lu, Alpin Tatan, Sebastian Wickenburg, Arash Alahgholipour Omrani, Johannes Lischner, Kenji Watanabe, Takashi Taniguchi, Alex Zettl, Antonio Helio Castro Neto, Steven Louie, Vitor Pereira, Michael Crommie The ability to modify the electronic properties of monolayer graphene via molecular control creates new opportunities for fabricating nanoscale hybrid devices. Understanding the charge transfer properties and resulting electronic behavior of molecule/graphene interfaces is essential for tuning the electronic and magnetic characteristics of these hybrid devices. By controlling charged impurities through molecular self-assembly on a gated graphene device, we can switch the charge state of the molecule and engineer the wave function of relativistic electrons in graphene. Scanning tunneling spectroscopy is used to locally probe the electronic structure of graphene and the molecular nanostructures. Molecular self-assembly is controlled by the molecular coverage and edge-templated self-assembly in UHV condition. Relativistic electrons on graphene undergo a transition from subcritical to a supercritical regime as the packing density of the charged molecule array is increased. We found that one-dimensional supercritical states emerge in graphene when we tune the molecular array below the critical spacing. |
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