Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session S30: 2D Materials Modeling of Synthesis and DefectsFocus

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Sponsoring Units: DMP Chair: Elton Santos, Queen's University Belfast UK Room: 293 
Thursday, March 16, 2017 11:15AM  11:27AM 
S30.00001: Influence of Misorientation on Graphene Moir\'{e} Patterns Marie Smirman, Doaa Taha, Arunima Singh, ZhiFeng Huang, Ken Elder In this work the influence of filmsubstrate misorientation on the straininduced ordering of graphene films on various metallic surfaces is examined using a mesoscopic continuum model and firstprinciples atomistic calculations. The periodicity and free energy of the Moir\'{e} patterns that emerge are studied as a function of filmsubstrate adhesion strength for misfit strains far from and close to an incommensuratecommensurate phase transition. Interestingly the lowest energy states are found to be at small but finite misorientation even though these states have a higher domain wall density than the zeromisorientation states. Firstprinciples density functional theory calculations are used to connect the results with experimental findings in graphene epitaxy. This combination of mesoscopic and atomistic approaches can be applied to the study of a wide range of strained 2D material systems including the IIINitride monolayer systems. [Preview Abstract] 
Thursday, March 16, 2017 11:27AM  11:39AM 
S30.00002: Mechanical Behavior of Nanocomposite Structures from Interlayer Bonding in Twisted Bilayer Graphene Mengxi Chen, Andre Muniz, Dimitrios Maroudas We report a systematic computational analysis of the mechanical behavior of graphenediamond nanocomposites formed through interlayer covalent bonding of twisted bilayer graphene with commensurate bilayers. The interlayer bonding is induced by patterned hydrogenation that leads to formation of superlattices of 2D nanodiamond domains embedded between the two graphene layers with the periodicity of the underlying Moir\'{e} pattern. The analysis is based on moleculardynamics (MD) simulations of uniaxial tensile straining tests according to a reliable interatomic bondorder potential. The mechanical response of the nanocomposites is explored as a function of their structural parameters, which include the bilayer's twist angle, the stacking type of the nanodomains where the interlayer bonds are formed, the interlayer bond density, and the concentration of \textit{sp}$^{\mathrm{3}}$bonded C atoms. We determine the mechanical properties of these 2D materials and identify a range of structural parameters over which their fracture is ductile, mediated by void formation and growth, in contrast to the typical brittle fracture of graphene. We analyze the ductile fracture mechanisms and systematically probe the brittletoductile transition. [Preview Abstract] 
Thursday, March 16, 2017 11:39AM  11:51AM 
S30.00003: Molecular Simulation of MoS$_{\mathbf{2}}$\textbf{ Exfoliation} Guoqing Zhou, Rajiv Kalia, Aiichiro Nakano, Priya Vashishta Liquid exfoliation is widely used to synthesize a variety of twodimensional materials such as graphene and atomically thin layers of boron nitride and transition metal dichalcogenides. We perform molecular dynamics (MD) simulations to study the mechanism of exfoliation in MoS$_{2}$. The wettability of water and water/2propanol (IPA) on MoS$_{2}$ is investigated and the results are compared with experimental data on interfacial energies to fit the force fields of the MD simulation. With the optimized force fields, we perform shock simulations of nanobubble collapse and study the generation of high speed nanojets from nanobubble collapse in the water/IPA mixture. Results will be reported on the exfoliation of MoS$_{2}$ into atomically thin layers by the impact of nanojets. [Preview Abstract] 
Thursday, March 16, 2017 11:51AM  12:03PM 
S30.00004: Enhancing the Hydrogen Activation Reaction of Nonprecious Metal Substrates via Confined Catalysis Underneath 2D Materials Yinong Zhou, Wei Chen, Ping Cui, Jiang Zeng, Zhuonan Lin, Feng Liu, Efthimios Kaxiras, Zhenyu Zhang In the hydrogen evolution reaction (HER), the reactivity as a function of the H adsorption energy on different metal substrates follows a wellknown volcano curve, peaked at Pt. The goal of turning nonprecious metals into efficient catalysts is a fundamental challenge. Here, we present DFT calculation results toward achieving this goal by exploiting the synergistic power of marginal and confined catalysis. We first show that the volcano curve stays qualitatively intact when van der Waals attraction is included. We then show that the H adsorption energy is lowered when H is confined between graphene and the metal surfaces, with Ni exhibiting the largest change. In particular, the graphenemodified volcano curve peaks around Ni, and the corresponding HER rate is comparable to that of bare Pt. These findings demonstrate that graphenecovered Ni is an appealing effective, stable, and economical catalytic platform for HER. The above studies are being also extended to MoS$_{\mathrm{2}}$covered metal substrates, which may peak at a different metal in the volcano curve. [Preview Abstract] 
Thursday, March 16, 2017 12:03PM  12:15PM 
S30.00005: Coupling between shear and tensile strains in layered twodimensional crystals Sungjong Woo, YoungWoo Son We report a theoretical study revealing unavoidable coupling between shear and tensile strains in several layered twodimensional crystals. It is shown that the coupling can explain a recent Raman experiment exhibiting an anomalous splitting in the low frequency interlayer shear modes of bilayer MoS$_2$ under uniaxial strain. We have found that the splitting comes from the straininduced interlayer sliding. Our calculation shows that the direction of the induced sliding is related to the straininduced polarization, piezoelectricity, that is calculated using electronic Berry phase, thus connecting piezoelectricity of a layered material with its elastic effect. We will present the results of our calculations for sheartensile strain coupling of graphene, $h$BN, and MoS$_2$ respectively and demonstrate that the Raman measurement can determine the offdiagonal elements of compliance tensor of the layered materials. [Preview Abstract] 
Thursday, March 16, 2017 12:15PM  12:27PM 
S30.00006: Longwavelength vibrational modes in quasi2D and tubular quasi1D structures. Dan Liu, David Tomanek, Arthur G. Every We propose a continuum elasticity theory approach to predict longwavelength vibrational modes of quasitwodimensional and quasionedimensional tubular structures, such as empty and liquidfilled tubules, which are very hard to reproduce using the forceconstantmatrix based atomistic approach based on {\em ab initio} calculation. We characterize the elastic behavior of these structures by a $(3{\times}3)$ elastic matrix characterizing a 2D membrane or a tubular wall, as well as the flexural rigidity of the membrane or the wall structure. We derive simple quantitative expressions for frequencies of longwavelength acoustic modes, which we determine using 2D elastic constants calculated by {\em ab initio} density functional theory. Our results accurately reproduce observed and calculated longwavelength phonon spectra of 2D graphene, 2D phosphorene, 1D microtubules of tubulin and 1D carbon nanotubes. [Preview Abstract] 
Thursday, March 16, 2017 12:27PM  12:39PM 
S30.00007: Polariton at the boundary of 2D and 1Dmaterials: Existence of a distinct class of nonperturbative solutions of coupled Dyson equations Slava V Rotkin, Alexey G. Petrov The Hamiltonian of two stronglycoupled fields in spaces of different dimensions is revisited. Starting with the formalism of coupled Dyson equations, a distinct family of nonperturbative solutions is derived. Such a (quasilocalized) solution appears at the dimensional boundary (aka interface). In case the fields are harmonic, an analytical solution is found for hybrid modes. This general approach can be applied to a wide range of quantummechanical problems. An explicit example of a hybrid plasmonic mode for coupled 2d(graphene) and 1d(nanowire) system is given. [Preview Abstract] 
Thursday, March 16, 2017 12:39PM  12:51PM 
S30.00008: Grain boundary properties and collective dynamics of inversion domains in binary twodimensional materials Doaa Taha, Simiso Mkhonta, Ken Elder, ZhiFeng Huang Grain boundary structures and dynamics of binary twodimensional materials are investigated through the development of a phase field crystal model. The model is parameterized for the study of hexagonal boron nitride monolayers, to identify the angle dependence of grain boundary energy and defect structures for both symmetric and asymmetric tilt boundaries. Our results not only reproduce all types of dislocation cores observed in previous experiments and firstprinciples calculations, but also predict some new defect structures for various grain boundary misorientations, particularly the 60degree inversion domains. In addition, we identify a new mechanism of grain coarsening dynamics, as originated from the impinging of 60degree misoriented grains and the subsequent formation of triangle or truncatedtriangle shaped domains that are separated from the surrounding matrix via inversion domain boundaries. The domain evolution and shrinking processes are governed by the collective atomic displacement of the connected squareoctagon (4\textbar 8) pairs along the boundary lines and the heartshaped defects at the junctions. This defectmediated collective dynamics of inversion domains is important for understanding the complex mechanisms of grain growth in binary 2D materials. [Preview Abstract] 
Thursday, March 16, 2017 12:51PM  1:03PM 
S30.00009: Structural phase transitions in twodimensional atomic materials Salvador BarrazaLopez Over a year ago, we introduced the concept of structural phase transitions in monochalcogenide monolayers such as GeS, GeSe, SnS and SnSe; we determined that monochalcogenides with small mean atomic number may be able to undergo phase transitions prior to melting [1] and that these materials remain semiconducting on a structural transition that changes the coordination number from three to five. Then, we were the first to demonstrate sudden changes in optical properties, and a quenching of the electric dipole in these twodimensional ferroelectrics at the transition temperature [2]. In this talk, the three conditions that generalize these transitions to other twodimensional materials will be presented [3]. References: 1. M. Mehboudi et al. Nano Lett. 16, 1704 (2016). 2. M. Mehboudi et al. arXiv:1603.03748. 3. G. G. Naumis, S. BarrazaLopez, M. OlivaLeyva, and H. Terrones. Rep. Prog. Phys. (forthcoming). [Preview Abstract] 
Thursday, March 16, 2017 1:03PM  1:39PM 
S30.00010: Predictive modeling of 2D materials, from synthesis to properties Invited Speaker: Boris Yakobson Comprehensive tools of materials modeling are derived from the principles of physics and chemistry, empowered by high performance computing. Together, this allows one to make verifiable predictions of novel physical structures with specific, often useful or even extraordinary, properties. Examples from our work will be presented, first being growth and unusual morphology of binary compositions of metal dichalcogenides MX2 [1], where a combination of DFT and phasefield simulations proves useful. Second, prediction of pure monoelemental boron 2D B and its particular structures, which culminated in recent experimental confirmations, while also promises new 2Dsuperconductor [2]. We will also discuss its physical properties like superconductivity [2] or plasmonics [2]. Third, we will discuss new physics emerging in heterojunctions, in either stacked or coplanar configurations [3]. [1] V. Artyukhov et al. Phys. Rev. Lett. 114, 115502 (2015) \textbar \textbar V. A.  Z.Hu et al. Nano Lett. 16, 3696 (2016). [2] Z. Zhang et al. Nature Chem. 8, 525 (2016) \textbar \textbar Z. Zhang et al. Angewandte Chemie Int. Ed. 54, 13022 (2015) \textbar \textbar E. Penev  A. Kutana et al. Nano Lett. 16, 2522 (2016) \textbar \textbar Z. Zhang, Nano Lett. 6, 6622 (2016) \textbar \textbar A. Brotchie, Nature Reviews, doi:10.1038/natrevmats.2016.83 (2016) \textbar \textbar S. Shirodkar, Y. Huang et al. (unpublished). [3] J. Yuan, Z. Zhang et al. ACS Nano, 9, 555 (2015) \textbar \textbar H. Yu, A. Kutana et al. Nano Lett. 16, 5032 (2016). [Preview Abstract] 
Thursday, March 16, 2017 1:39PM  1:51PM 
S30.00011: Spontaneous Mechanical Buckling in TwoDimensional Materials: A Power Source for Ambient Vibration Energy Harvesters Paul Thibado, Pradeep Kumar, Surendra Singh InternetofThings (IoT) is projected to become a multitrilliondollar market, but most applications cannot afford replacing batteries on such a large scale, driving the need for battery alternatives. We recently discovered that freestanding graphene membranes are in perpetual motion when held at room temperature [Phys. Rev. Lett. 117, 126801 (2016)]. Surprisingly, the random updown motion of the membrane does not follow classical Brownian motion, but instead is superdiffusive at short times and subdiffusive at long times. Furthermore, the velocity probability distribution function is nonGaussian and follows the heavytailed CauchyLorentz distribution, consistent with L\'{e}vy flights. Molecular dynamics simulations reveal that mechanical buckling is spontaneously occurring, and that this is the mechanism responsible for the anomalous movement. Bucking in this system occurs when the local material suddenly flips from concave to convex. The higher kinetic energy associated with this motion is derived from the surrounding thermal waste heat, and it may be converted into an electrical current and used as the active component of small power generators known as ambient vibration energy harvesters. \linebreak * thibado@uark.edu [Preview Abstract] 
Thursday, March 16, 2017 1:51PM  2:03PM 
S30.00012: Ferroelectricity and Phase Transitions in twodimensional materials Ruixiang Fei, Wei Kang, Li Yang Ferroelectricity usually fades away as materials are thinned down below a critical value. We reveal that the unique ionicpotential anharmonicity can induce spontaneous inplane electrical polarization and ferroelectricity in monolayer groupIV monochalcogenides MX (M$=$ Ge, Sn; X$=$ S, Se). An effective Hamiltonian has been successfully extracted from the parametrized energy space, making it possible to study the ferroelectric phase transitions in a singleatom layer. The ferroelectricity in these materials is found to be robust and the corresponding Curie temperatures are higher than room temperature, making them promising for realizing ultrathin ferroelectric devices of broad interest. We further provide the phase diagram and predict other potentially twodimensional ferroelectric materials. [Preview Abstract] 
Thursday, March 16, 2017 2:03PM  2:15PM 
S30.00013: Photostriction in two dimensional ferroelectrics Raad Haleoot, Charles Paillard, Bin Xu, Bothina Hamad, Laurent Bellaiche, Salvador BarrazaLopez Within densityfunctional theory, we study lightinduced structural deformations in two dimensional ferroelectrics due to their noncentrosymmetric nature. This effect, known as photostriction, was recently studied in bulk ferroelectrics [1]. [1] C. Paillard et al. \textit{Physical Review Letters}. 116(24):247401, 2016. [Preview Abstract] 
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