Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session C57: Adsorption and Dopants in 2D MaterialsLive
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Sponsoring Units: DMP DCMP Chair: Shawna Hollen, Univ of New Hampshire |
Monday, March 15, 2021 3:00PM - 3:12PM Live |
C57.00001: Different MXenes but the same surface Rina Ibragimova, Patrick Rinke, Hannu-Pekka Komsa Two-dimensional (2D) transition metal carbides and nitrides MXenes offer rich chemistry with extraordinary properties. The surface of MXenes is terminated by -O, -OH, and -F groups during the synthesis. However, even as the number of explored MXenes keeps growing, there is limited understanding of how the surface composition depend on the type of transition metal, the choice of carbon vs. nitrogen, and the number of atomic layers. Using a multi-scale computational scheme, developed earlier [1], we simulate the distribution, and thermodynamically favorable composition of the functional groups on the surface of distinct MXenes. We consider the most popular MXene systems such as Ti2C, Ti3C2, Ti2N, Ti4N3, Nb2C, and Nb4C3. The surface accommodates mixtures of functional groups for all considered MXenes. The resulting distribution of functional groups is similar regardless of the type of metal, carbon or nitrogen species and number of atomic layers. However, these findings are important for an accurate prediction of the electronic properties and stability of the materials. As we demonstrate, the work function and the density of states sensitively depend on the composition of functional groups. |
Monday, March 15, 2021 3:12PM - 3:24PM Live |
C57.00002: Interaction Energies of Helium Atoms Adsorbed on Graphene Ethan Lauricella, Valeri Kotov, Adrian G Del Maestro, Juan M Vanegas We use density functional theory (DFT) calculations to characterize the interaction energy of helium atoms adsorbed on a graphene substrate. Two-dimensional graphene provides an exciting platform to study the formation of exotic helium phases such as superfluids or supersolids, since quantum phase transitions between such phases can be induced by modifying the lattice properties. For example, graphene’s lattice spacing, and by extension the van der Waals distance for a pair of adsorbed helium atoms, can be controlled through mechanical strain. We characterize the He-He interaction energies for atoms adsorbed on a periodic graphene sheet at nearest-neighbor lattice sites under various strain conditions. We show that strain can effectively tune the He-He interaction energy and describe our results within the context of an effective extended Bose-Hubbard (t-V-V’) model. |
Monday, March 15, 2021 3:24PM - 3:36PM Live |
C57.00003: Nanoporous 2D Materials Built from Organic Molecules and their Application in Gas Separation Isaiah Moses, Veronica Barone One of the important applications for which 2D materials are been sought for is as separation membranes since they offer the advantages of high energy efficiency, compactness and ease of operation compared to the conventional methods of separation such as cryogenic distillation and absorption/adsorption separation. Porous 2D materials are therefore been studied for applications as gas separation membranes for instance in the processing of natural gas to recover the valuable components and also to obtain the gas that meets the standard caloric values for consumption. In the present work, a number of organic molecules − benzene, borazine, pyridine, 1,3-diazine, 1,3,5-triazine, phosphinine and arsinine − have been used to build nanoporous atomically thin 2D materials [1]. Density functional theory and nudged elastic band theory have been employed to study the adsorption of the components of natural gas and their diffusion barriers through these holey materials. Our results show that these materials exhibit high selectivities for some gas species such as hydrogen and helium with respect to other constituents of the natural gas. |
Monday, March 15, 2021 3:36PM - 3:48PM Live |
C57.00004: Scanning tunneling microscopy and electronic transport of gold-decorated graphene devices Jake Riffle, Steven Arias, Shawna M Hollen Past studies on graphene show that scattering from disorder can give rise to weak Anderson localization, but a disorder-driven quantum metal-insulator transition has not been observed. Using a low temperature scanning tunneling microscope (STM) on graphene field effect transistors, we present simultaneous STM and electronic transport measurements of graphene devices decorated with gold adatoms. These data show quasiparticle scattering off of gold adatoms on graphene on SiO2/Si. We study the microscopic scattering mechanisms, including the effects of charge puddles versus point-like disorder, and correlate these mechanisms with macroscopic electronic transport. These experiments are the first steps toward understanding the phase space near disorder-tuned metal-insulator quantum phase transitions in 2D materials. |
Monday, March 15, 2021 3:48PM - 4:00PM Live |
C57.00005: Disordered hyperuniform networks and their application in atomic-scale low-dimensional materials Duyu Chen, Yu Zheng, Lei Liu, Ge Zhang, Mohan Chen, Yang Jiao, Houlong Zhuang Disordered hyperuniformity is a recently discovered novel state of many-body systems that possesses vanishing normalized infinite-wavelength density fluctuations and a hidden long-range order similar to a perfect crystal, and yet is statistically isotropic with no Bragg peaks like a liquid or glass. In this work we present a series of research centered around a new concept called "disordered hyperuniform quantum materials", i.e., disordered hyperuniform atomic-scale low-dimensional materials where quantum effects are significant. In particular, we discover a hyperuniformity-preserving topological transformation in two-dimensional networks that involves continuous introduction of Stone-Wales (SW) defects. Our findings have important implications for amorphous 2D materials such as graphene and silica. Importantly, we find that when adding disorder in a hyperuniform manner, silica systems exhibit a transition from insulating to metallic behavior, which is in contrast to the conventional wisdom that disorder generally diminishes electronic transport. |
Monday, March 15, 2021 4:00PM - 4:12PM Live |
C57.00006: Spectroscopic Characterization and Molecular Dynamics Simulation of Pristine and Functionalized Graphene nanoplatelets (GnPs) Olasunbo Farinre, Sugata Chowdhury, Prabhakar Misra The present study focuses on investigating Graphene nanoplatelets (GnPs) for toxic gas sensing applications due to their large surface area and low cost of fabrication. We have used Raman, SEM, FTIR and XRD techniques for structural and spectroscopic characterization of pristine and functionalized GnPs (with carboxyl). The major vibrational modes of graphene: D, G and 2D peaks appear in the Raman spectra of pristine and functionalized GnPs. A red-shift in the frequency of the 2D peak observed in the Raman spectra of GnPs functionalized with 35 wt.% carboxyl group is indicative of an electron donor when carboxyl is attached to the layer edges. XRD spectra show that an increase in the FWHM of the GnPs reflect a smaller crystallite size ranging from 3.5-16 nm. In addition, we performed MD simulation on trilayer graphene to compare with our experimental data based on the 3-6 layers of graphene present in the individual platelet sheets. Our calculated D, G and 2D peaks from the MD simulation were found to be: 1331 cm-1, 1581 cm-1 and 2662 cm-1, respectively, which agree well with our Raman results. These results are promising and show that GnPs are suitable candidates for applications in highly sensitive and selective toxic gas sensors. |
Monday, March 15, 2021 4:12PM - 4:24PM Live |
C57.00007: Phase stability and Raman/IR signatures of Ni-doped MoS2 from DFT studies Enrique Guerrero, Rijan Karkee, David A Strubbe Doping MoS2 with Ni is known to enhance lubrication and catalysis. While much of the experiment and theory regarding doped MoS2 has focused mostly on monolayers or finite particles, theoretical studies of bulk Ni-doped MoS2 are lacking and the mechanisms by which Ni alters bulk properties are largely unsettled. We use density functional theory calculations to determine the structure, mechanical properties, electronic properties, and formation energies of bulk Ni-doped MoS2 while varying the doping concentration. We find four meta-stable structures of Ni-doped MoS2: Mo or S substitution, and tetrahedral (t-site) or octahedral (o-site) intercalation. To aid in experimental identification, we calculate the infrared and Raman spectra and identify the features unique to each dopant site. We compute formation energies of these structures with respect to chemical potentials to guide experimental synthesis and we find the t-site structure to be particularly stable. Intercalation forms strong interlayer covalent bonds and does not increase the c-parameter. Doping creates new states present in the electronic density of states in MoS2 and shifts the Fermi level. These results are being used to parametrize force fields for study of Mo2 friction. arXiv: 2010.02198 |
Monday, March 15, 2021 4:24PM - 4:36PM Live |
C57.00008: Structural studies of Ni-doped MoS2 monolayers and polytypes using density functional theory Rijan Karkee, Enrique Guerrero, David A Strubbe The crystal structure of MoS2 gives rise to interesting properties for applications such as solid lubricants, optoelectronics, and catalysis. Transition-metal doping has been shown to enhance performance in solid lubrication and catalysis. We study the structure and properties of Ni-doped MoS2 in the 1H and 1T monolayer and 2H and 3R bulk polytypes, using density functional theory. The doping formation energy for intercalation/adsorption shows that the most favorable sites are tetrahedral intercalation in bulk phases, Mo-atop in 1H and hollow site in 1T. We find the possibility of phase change from 2H to 3R with Mo or S substitution; also, Mo substitution induces metallic behavior in 3R and 2H, and both Mo and S substitution induce in-gap states in 1H, which could have interesting optoelectronic applications. Doping the 1T phase resulted in reconstructions leading to a metal-semiconductor transition. We find that Ni doping strengthens the layer binding which can explain the mechanism of low wear. This work gives insight into the previously unclear structure of Ni-doped MoS2, the relation of energy and structures of doped monolayers and bulk systems, the electronic properties under doping, and the effect of doping on interlayer interactions. (arxiv: 2008.04301) |
Monday, March 15, 2021 4:36PM - 4:48PM Live |
C57.00009: The local quantum cluster typical medium approach for disordered systems. Aric Moilanen, Ka-Ming Tam, Wasim Mondal, Yang Wang, Markus Eisenbach, Liviu Chioncel, Vladimir Dobrosavljevic, Hanna Terletska Due to the non-self-averaging nature of strong disorder Anderson localized states, the effective medium theories based on the linear (algebraic) averaging over disorder, often fail to capture the localized states. Recently, it has been shown that the typical medium treatment that utilizes the geometric averaging over disorder can successfully detect the disorder localized states. Constructing a proper numerical ansatz that can capture the localized states is often a challenge, especially for more complex systems with the disorder. We have recently revised our quantum cluster typical medium approach (TM-DCA) and constructed a simplified local quantum cluster ansatz for the typical density of states. We performed a careful systematic analysis of the new local quantum cluster ansatz for both the box and binary disorder distributions in the three-dimensional Anderson model. Our results show that, close to the Anderson transition, the local effects are dominant. We found that the new approach allows us to properly capture the critical value of disorder for the phase transition in a less expensive computational way, however, the convergence of the mobility edges is slow with respect to the cluster size. |
Monday, March 15, 2021 4:48PM - 5:00PM Live |
C57.00010: Revealing the strong coupling of atomic motion to interlayer excitons through photocurrent imaging at room temperature. Trevor Arp, Fatemeh Barati, Shanshan Su, Roger Lake, Justin Song, Mark Rudner, Vivek M Aji, Nathaniel Monroe Gabor In atomically thin van der Waals crystals photoexcited excitons are expected to be delocalized over many atomic sites, weakening the electron-phonon coupling strength. Surprisingly, we show that a heterostructure composed of stacked layers exhibits interlayer excitons that are strongly coupled to atomic vibrational motion. To overcome the small oscillator strength of interlayer excitons, we use photocurrent measurements for their high sensitivity and relatively large quantum efficiency. Using Multi-Parameter Dynamic Photoresponse Microscopy on heterostructures made of monolayer MoSe2 and bilayer WSe2 encapsulated with hBN, we isolate the signal from the interlayer exciton under precise charge neutrality conditions. We vary the voltage across the material interface while maintaining charge neutrality, thus tuning the potential energy landscape of the interlayer exciton. This results in photoconductance oscillations with a period of 30 meV, the energy of the dominant phonon mode. Interestingly, even as the interlayer exciton exhibits signatures of localization and strong coupling to atomic motion, the large interlayer photocurrent measured in the heterojunction means that the electrons and holes that make up the interlayer exciton are delocalized and move freely in the MoSe2/WSe2. |
Monday, March 15, 2021 5:00PM - 5:12PM Live |
C57.00011: Exciton and trion photoluminescence evolution in 2D MoS2 treated with controlled thermal annealing Dario Mastrippolito, Stefano Palleschi, Gianluca D'Olimpio, Antonio Politano, Michele Nardone, Paola Benassi, Luca Ottaviano MoS2, isolated into the monolayer phase, is the subject of intense research works due to its rich physics and unique excitonic properties. In this study, we investigate the response of A-type excitons (one neutral exciton and one trion) of mechanically exfoliated MoS2 monolayers, via post exfoliation thermal annealing, in the 200–300 °C annealing temperature range, by means of room temperature photoluminescence (PL). Thermal annealing, in this temperature range, introduces point defects (sulfur vacancies). This induces a variation of doping, via oxygen adsorption on vacancies once exposed to air, and allows tuning the intensity of the PL yield. The PL yield increase is quantified for each post-annealing temperature, reaching a gain of 4 times to 300 °C annealed sample. The PL signal of the 200 °C annealed sample is dominated by the trion, while the PL signal of the 300 °C annealed one is dominated by the neutral exciton, and the PL spectral weight of excitons is perfectly tunable in this temperature range. We also demonstrate that the thermal annealing, in the 200–300 °C annealing temperature range, causes a slight variation of doping with values comparable to those of the as-exfoliated MoS2. |
Monday, March 15, 2021 5:12PM - 5:24PM Live |
C57.00012: Studying magnetic and defect properties of two-dimensional NiI2 layers Luqing Wang, Qunfei Zhou, Dmitry Lebedev, Mark C Hersam, Pierre Darancet, Maria Chan Magnetism is one of the most attractive properties which endows materials with not only rich physical phenomena but also potential device applications. The interplay between quantum confinement effects due to reduced dimensionality in two-dimensional (2D) materials and magnetism may further introduce interesting properties which distinguish 2D materials from their bulk counterparts. Recent years, several atomically thin magnetic materials such as CrI3, VSe2 and MnO2 have been synthesized, and experimental synthetic methods advance the exploration of this field. In this work, we perform density functional theory (DFT) calculations to investigate the magnetic properties and defect effects of two-dimensional NiI2 layers. Stacking orders and magnetic orders of NiI2 from single-layer up to multilayers are determined, to reveal the layer-dependent effects on the magnetic properties. Also, the structures and properties of point defects and complex defects in single-layer NiI2 are exhaustively investigated, to explore the defect effects on the magnetic properties. Furthermore, defects in multilayer NiI2 will be examined to study the mixed effects of defects and quantum confinement. |
Monday, March 15, 2021 5:24PM - 5:36PM Live |
C57.00013: Methane Adsorption on MoS2 Surfaces Dinuka Gallaba, Brice A Russell, Aaron Walber, Thushari Jayasekera, Aldo Dante Migone, Saikat Talapatra In order to develop layered van der Waals materials for niche application leading to chemical sensing, gas storage, catalysis etc. it is essential to have a clear understanding of the adsorption behavior of various gases on the surfaces of these materials. Among a variety of layered materials available, the potential uses of Molybdenum di Sulfide (MoS2) in the abovementioned areas of applications are hypothesized. However, a thorough understanding of adsorption behavior of gases on MoS2 surfaces are required in order to assess their viability for such applications. Here, we will present our combined investigation of volumetric adsorption measurement as well as Density Functional Theory (DFT) calculation results of adsorption of Methane on MoS2 surfaces. By studying the low coverage adsorption isotherms on bulk MoS2 as well as micron size MoS2 flakes, isosteric heats of adsorption of methane on MoS2 material was obtained. These findings will be analyzed in the light of the DFT calculations in order to present a clear understanding of the adsorption behavior of methane on MoS2. |
Monday, March 15, 2021 5:36PM - 5:48PM Not Participating |
C57.00014: Electronic, vibronic, and magnetic properties of a carbon radical anion in 2D WS2 Katherine Cochrane, Jun-Ho Lee, Christoph Kastl, Jonah Haber, Tianyi Zhang, Azimkhan Kozhakhmetov, Joshua Robinson, Mauricio Terrones, Jascha Repp, Jeffrey Neaton, Alexander Weber-Bargioni, Bruno Schuler Two-dimensional transition metal dichalcogenides (2D-TMDs) are a promising class of materials with many novel applications due to a variety of electronic and optoelectronic properties combined with a synthetic flexibility and tunability. In particular, point defects within these materials have been identified as potential qubits for quantum information applications. In order to realize this goal, these defects must be characterized and controlled. |
Monday, March 15, 2021 5:48PM - 6:00PM On Demand |
C57.00015: A first-principles study of graphene sheets with metal dimer defects Mahesh Bhatt, Gunn Kim Graphene is a promising candidate as a two-dimensional support material for catalysis. However, more research is still needed on the catalytic properties of this material from a theoretical perspective. Factors such as defects and doping can significantly influence the structural, chemical, electrical, and magnetic properties of graphene. The physical properties of a single atom or a dimer of Fe, Co, and Ni covalently bonded to the four pyridinic nitrogen atoms substituted in graphene is an exciting topic. In this study, we used VASP to explore the electronic structure of the defective graphene systems. For various dopant models with a single metal atom and the dimer, we calculated the densities of states to study the electronic structure and magnetism of these systems. Our computational results showed that a single Fe atom and a Fe-Fe dimer are promising for doping. In the heterogeneous dimer structures, we found that the spin magnetic moments of the metal atoms may disappear or decrease, depending on which two atoms are paired. In future, we will study the molecular adsorption properties on these systems. |
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