Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session X13: 2D Materials (General) -- Mechanical Properties and Phases |
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Sponsoring Units: DMP Chair: Niyaz Beysengulov, Michigan State Univ Room: BCEC 153B |
Friday, March 8, 2019 8:00AM - 8:12AM |
X13.00001: Atomistic Origin of Phase Stability in Oxygen-Functionalized MXene Avanish Mishra, Pooja Srivastava, Abel Carreras, Isao Tanaka, Hiroshi Mizuseki, Kwang-Ryeol Lee, Abhishek Kumar Singh Oxygen-functionalized MXene, M2CO2 (M =group III−V metals), are two-dimensional (2D) materials with the immense possibility for device applications. Using first-principles calculations, we perform a study on the stability of M2CO2 MXenes. Depending on the position of O atoms, the M2CO2 can exist in two different phases. CB phase, where O at the top of carbon and metal atom. On the other side, O atom can occupy either the site on the top of the metal atom (BB′ phase). We found that for M = Sc and Y the CB phase is stable, whereas for M = Ti, Zr, Hf, V, Nb, and Ta the stable phase is BB′. The electron localization function and atom-projected density of states, provide a rational explanation for the relative stability. Instability of BB′- M2CO2 (M = Sc and Y) originates from the weakening of M−C interactions due to the motion of C atom in the−b plane. The insight into the stability of these competing structural phases of M2CO2 is an important step in the direction of identifying the stable phases of these 2D materials and their applications. |
Friday, March 8, 2019 8:12AM - 8:24AM |
X13.00002: DFT study of Ni-doped MoS2 as a solid lubricant for space applications Enrique Guerrero, Rijan Karkee, David Strubbe MoS2 is a layered material with interesting mechanical properties not unlike graphite. The weak Van der Waals forces between MoS2 sheets allow the material to be used as a solid lubricant with application in the low temperature and pressure environment in space, where liquid lubricants fail. Some preliminary studies suggest that doping with transition metals can improve tribology performance by reducing friction and wear. We use density functional theory (DFT) calculations to determine the structure and properties of bulk Ni-doped MoS2, considering formation energy of Ni in different sites as a function of growth conditions, and study the potential energy for sliding to connect to frictional forces measured in atomic-force microscopy (AFM). We calculate vibrations with density-functional perturbation theory (DFPT) for comparison to infrared and Raman spectra in experimental characterization. Our resulting DFT data will be used to parametrize classical force fields for larger-scale reactive molecular dynamics (MD) simulations that can directly address friction and wear. |
Friday, March 8, 2019 8:24AM - 8:36AM |
X13.00003: Effect of net charge on the relative stability of different 2D
boron allotropes Dan Liu, David Tomanek We study the effect of electron doping on the bonding character and |
Friday, March 8, 2019 8:36AM - 8:48AM |
X13.00004: VIBRATIONAL PROPERTIES OF PHOSPHORENE UNDER HIGH PRESSURE Manthila Rajapakse, Meysam Akhtar, Congyan Zhang, Md Rajib khan Musa, Ming Yu, Jacek Jasinski, Gamini Sumanasekera In this study, few layer phosphorene was subjected to high pressure using a Diamond Anvil Cell (DAC) and its vibrational properties were studied via in-situ Raman spectroscopy. Systematic shifting in the Raman frequency of A1g, B2g, and A2g modes were observed and theoretical calculations were performed to understand the relationship between the strain and the electronic/phononic band structure. The results from computational calculations carried out by employing the density functional theory (DFT) framework, as implemented in the Vienna Ab-initio Simulation Package (VASP) agree well with the experimental data. The results can enable rational engineering of strain towards additional functionalities and device applications of phosphorene and few-layer black phosphorous. |
Friday, March 8, 2019 8:48AM - 9:00AM |
X13.00005: Capillary Origami with Atomically Thin Sheets Michael Reynolds, Kathryn L McGill, Maritha Wang, Marc Miskin, Hui Gao, Fauzia Mujid, Kibum Kang, Jiwoong Park, Itai Cohen, Paul L McEuen The paper art of origami has inspired several works in which two-dimensional materials are cut and folded into desired geometries at the micron scale. At this scale, surface energies can easily dominate over bending energies, allowing sheets to be folded with droplets, a technique known as capillary origami. In this talk, we show capillary origami of monolayer molybdenum disulfide (MoS2) using droplets in water. By adding rigid panels to the MoS2, we demonstrate controllable folding of polyhedra. Finally, we show that these shapes can be self-folded by using partially miscible droplets in water. These results provide a new approach for creating pre-patterned three-dimensional devices using two-dimensional materials. |
Friday, March 8, 2019 9:00AM - 9:12AM |
X13.00006: Modeling the dynamics of a single graphene ripple with LAMMPs James Mangum, Paul Thibado In recent years, graphene has shown great promise for a variety of reasons, but most notably for its potential for energy harvesting. Graphene requires ripples to maintain stability. It has been speculated that kinetic energy of the spontaneous flipping of ripples may be converted into electrical energy using vibration energy harvesting technology. The dynamics of larger graphene sheets may be understood by running molecular dynamic simulations with nanoscale sheets that contain a single ripple. Creating single ripples in graphene requires introducing an optimal level of compressive strain, and freezing the molecules on the edge of the sheet. In this talk, we discuss single-ripple graphene dynamics, modeled on LAMMPs. This includes the effect that compressive strain has on flipping time, and equilibrium position. Additionally, videos of the output will be included to elucidate the mechanics of graphene ripple flipping. Our results will be compared to previous results. |
Friday, March 8, 2019 9:12AM - 9:24AM |
X13.00007: Organized Brownian Motion in Freestanding Graphene: A New Type of Thermal Motion Paul Thibado, Pradeep Kumar, Surendra Pal Singh, Miguel Ruiz Garcia, Antonio Lasanta, Luis Bonilla Conversion of omnipresent thermal motion into stored electrical charge has been achieved using vibration energy harvesting technology. Our studies demonstrate that the thermal movement of freestanding graphene produces an alternating electrical current when near a biased metal electrode. The magnitude of this induced electrical current is consistent with a constant-voltage, variable-capacitance power generator. The key mechanism behind this discovery is the spontaneous curvature inversion of ripples, during which thousands of atoms move coherently [PRL 117, 126801 (2016)]. The collective motion of the atoms is a many-body effect and represents a new type of thermal motion with long time correlations enabling energy extraction [PRL 71, 1477 (1993)]. Our results lay the groundwork for a new source of thermal power originating from organized Brownian motion. Circuit details and quantities of energy harvested from this new many-body thermal force will be highlighted in the presentation. |
Friday, March 8, 2019 9:24AM - 9:36AM |
X13.00008: Exploring out-of-plane Mechanics of Graphene Membrane by 3D Force Field Spectroscopy on various Nanotubes Makoto Ashino, Roland Martin Wiesendanger Bending rigidity and Gaussian modulus are key parameters to understand flexibilities of two-dimensional (2D) crystalline membrane embedded in three-dimensional (3D) space. These two parameters of graphene membranes are still unclear because of their difficulties to distinguish purely intrinsic characteristics from others due to thermal fluctuations, consequent local strains and so on. Here we present experimental determinations of those properties by analyzing noncontact interaction between the opposing two atoms of probe-tip apex and convexly-curved graphene folding into various nanotubes. We have quantitatively evaluated the relationship between out-of-plane displacement and elasticity of monolayer graphene by 3D force field spectroscopy at low temperature not only on folded nanotubes with well-defined curvatures but also on unfolded one (i.e. graphene nanoribbon) with unknown curvatures. The quantitative evaluations allow us to determine the smaller and locally different curvatures of unfolded monolayer. Our findings to separate the in-plane and out-of-plane contributions allow us to derive the substantially small bending modulus enough to expect the intrinsic characteristics of negligibly small (zero) modulus for the ultimate 2D membrane without any curvature. |
Friday, March 8, 2019 9:36AM - 9:48AM |
X13.00009: Probing the Domain Architecture in 2D α-Mo2C via Polarized Raman Tianshu Li, Weijun Luo, Hikari Kitadai, Xingzhi Wang, Xi Ling MXenes are a group of two-dimensional (2D) materials with excellent stability and intriguing properties. Here, we conduct a systematic study on the Raman spectra of α-Mo2C and use it to study the unique domain structure of 2D α-Mo2C crystals grown by chemical vapor deposition (CVD). Six experimentally observed Raman modes are assigned with the assistance of phonon dispersion calculated from density functional theory (DFT). Angle-resolved polarized Raman spectroscopy indicates the anisotropy of α-Mo2C in the b-c plane, which is further applied to study the domains of the CVD grown 2D α-Mo2C crystals with different morphologies. Most of the α-Mo2C flakes contain multiple domains and the c-axes of neighboring domains within the same flake tend to form a 60° or 120° angle, indicating the carbon chains in α-Mo2C align along three equivalent directions. This is attributed to weak Mo-C bonds in this interstitial carbide and the low formation energy of the carbon chains along certain directions. Our study demonstrates that polarized Raman spectroscopy is a powerful and effective way to characterize the domain structures in α-Mo2C, which will facilitate the further exploration of properties and applications of α-Mo2C, as well as other MXenes. |
Friday, March 8, 2019 9:48AM - 10:00AM |
X13.00010: On the mechanism for the 2D phase transition in freestanding group-IV monochalcogenide monolayers John Villanova, Salvador Barraza-Lopez Group-IV monochalcogenides monolayers MX (M=Ge,Sn ; X=S,Se) are low-dimensional semiconductors which exhibit significant piezoelectric and ferroelectric responses. Monochalcogenide monolayers undergo a structural phase transition from a rectangular unit cell to a square unit cell at a critical temperature. There exist two intriguing descriptions of this behavior: (1) a Landau-Ginzburg effective model and (2) a description of the order-disorder transition based on ab initio molecular dynamics. We explore the phase transition by examining the softening of the phonon modes of SnSe as a function of temperature, in order to shed light on the possible physical mechanism underpinning the transition. |
Friday, March 8, 2019 10:00AM - 10:12AM |
X13.00011: Delocalization of Impact Energy in Multilayer Graphene Subjected to Supersonic Impact in Vacuum Wanting Xie, Jae-Hwang Lee We employed vacuum micro-ballistic characterization for the first time to explore the ballistic perforation dynamics of multilayer graphene (MLG). The vacuum level is approximately 1/3,000 of the atmospheric pressure to avoid undesired effects from air, including aerodynamic friction of a projectile or a membrane specimen. 3.7 um diameter silica spheres were accelerated to 300 – 900 m/s as projectiles and a suspended graphene membrane was subjected to projectile’s impact. With an ultrafast microscopic imaging system (40 million frames per second), accurate velocities of the projectile before and after penetration were obtained. We studied the residual speed as a function of impact speed. The specific penetration energy of MLG was quantified with respect to projectile’s impact speeds and specimen’s thicknesses. As a result, MLG demonstrated twice better performance in vacuum compared to that in air, opposite to conventional predictions. The penetration features near the impact region were examined by scanning electron microscopy to uncover the correlations with the energy dissipation. |
Friday, March 8, 2019 10:12AM - 10:24AM |
X13.00012: The governing role of interlayer chemical bonding in polar properties of the van-der-Waals ferroelectric CuInP2S6 John Brehm, Marius Chyasnavichus, Sabine Neumayer, Nina Balke, Michael Susner, Michael A McGuire, Panchapakesan Ganesh, Petro Maksymovych, Sokrates T Pantelides
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Friday, March 8, 2019 10:24AM - 10:36AM |
X13.00013: Mechanical and Electrical Studies of Two-dimensional Covalent Organic Frameworks Ruofan Li, Michio Matsumoto, Amanda Corcos, Halleh Balch, Raghunath Dasari, Austin Evans, Gregory Stiehl, Seth R. Marder, Feng Wang, William Dichtel, Daniel Ralph Two-dimensional (2D) covalent organic frameworks (COFs) are a promising new class of 2D materials with the potential for highly-tunable chemical, mechanical, electrical, and optical properties. As porous polymers, 2D COFs are predicted to have a combination of low mass density and high mechanical strength. Here we discuss mechanical and electrical measurements on COF thin films. For the mechanical measurements, we have developed a protocol for synthesizing COF films as thin as 1.5 nm at a liquid-liquid interface, lifting and drying them on a PDMS stamp, and then performing a dry transfer onto a prepatterned substrate to make suspended COF films. The transferred films exhibit excellent uniformity, smoothness, and cleanliness. We report results for the 2D Young’s modulus and mechanical strength using nanoindentation measurements performed using an atomic force microscope. We will also discuss initial electrical measurements on COF films designed to have small energy gaps. |
Friday, March 8, 2019 10:36AM - 10:48AM |
X13.00014: Buckling of thermalized sheets Ali Morshedifard, Miguel Ruiz Garcia, Mohammad Javad Abdolhosseini Qomi, Andrej Kosmrlj Two dimensional atomically thin membranes (ATMs), such as graphene and transition metal dichalcogenides, display exceptional properties that have been exploited in advanced electronic applications. In this talk, we utilize tools from statistical physics and molecular dynamics simulations to investigate how thermal fluctuation affect buckling of ATMs. Of special interest are ATMs that are larger than the characteristic thermal length scale lth, which is a function of temperature and material constants. Both simulations and theory predict that for small sheets of size L<<lth the critical buckling load coincides with the classical continuum theory σ ~ L^(-2). However, for large sheets of size L>>lth thermal fluctuations effectively stiffen the bending rigidity, which increases the critical buckling load that scales as σ ~ L^(-2+η). Here η~0.8 is the universal exponent that is related to the increased bending rigidity. We demonstrate that the critical buckling load scales the same way for both periodic and clamped boundary conditions. These results shed light on fundamental mechanisms that underlie buckling of ATMs and make possible accurate predictions that can be used for design purposes in applications. |
Friday, March 8, 2019 10:48AM - 11:00AM |
X13.00015: Friction Anisotropy of MoS2 Investigated via Atomic Force Microscopy Ogulcan Acikgoz, Mehmet Baykara Two-dimensional (2D) materials are of particular interest as solid lubricants for nano- and micro-scale devices as traditional fluid-based lubrication schemes fail at such small length scales due to problems including but not limited to surface tension. Among various 2D materials investigated as solid lubricants, MoS2 is of special importance for space applications since its lubricative properties do not degrade but rather improve under vacuum conditions. A particular aspect that has so far not been addressed in detail within this context is the direction dependence, i.e. anisotropy, of the frictional properties of MoS2, which could be an important design parameter for various applications. Here, we perform atomic force microscopy (AFM) measurements on CVD-grown and mechanically-exfoliated MoS2 to investigate the potential occurrence of friction anisotropy. Results indicate that (i) both CVD-grown and mechanically-exfoliated MoS2 exhibit strong friction anisotropy and remarkably, (ii) the periodicity associated with the anisotropy is not exclusively determined by the atomic structure of MoS2, but is a function of the AFM probe employed in the experiments. |
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