Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session P13: 2D Materials (General) -- Functionalization and Control of Electronic Properties |
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Sponsoring Units: DMP Chair: Kostyantyn Nasyedkin, Michigan State Univ Room: BCEC 153B |
Wednesday, March 6, 2019 2:30PM - 2:42PM |
P13.00001: Effect of MoS2 thickness on properties of adsorbed Au nanoparticles Duy Le, Talat S. Rahman Transition metal nanoparticles supported by MoS2 is a system of interest in catalytic applications. The question whether the thickness of MoS2 plays any critical role in determining the chemical activity of the supported nanoparticle is still debated. In this work, using density functional theory based calculations, we study the electronic density of states of Au nanoparticles of varying size supported by single layer, bilayer, and trilayer MoS2. We find that thickness of MoS2 support has only a minor effect on the d states (frontier orbitals) of Au nanoparticles. This effect is most notable on Au atoms located at the perimeter of the nanoparticles, which are in contact with the MoS2 basal plane. Using CO oxidation as a prototype, we comment on the implication of these findings on catalytic properties of MoS2-supported Au nanoparticles and compare with available experimental data. |
Wednesday, March 6, 2019 2:42PM - 2:54PM |
P13.00002: A complete picture for the band topology in twisted bilayer graphene Jianpeng Liu, Junwei Liu, Xi Dai We provide a complete picture for the band topology of twisted bilayer graphene. We propose that the electronic structure of twisted bilayer graphene can be understood as Dirac fermions under pseudo magnetic fields generated by the moir\'e pattern. The two low-energy flat bands from each valley originate from the two zeroth Landau levels of Dirac fermions under such opposite effective magnetic fields. They possess opposite sublattice polarizations and are decoupled from each other as a result of an emergent chiral symmetry in the low-energy subspace. They carry opposite Chern numbers $\pm1$ and give rise to the odd windings of the Wilson loops. |
Wednesday, March 6, 2019 2:54PM - 3:06PM |
P13.00003: Functionalization of hexagonal boron nitride – effect on chemical, morphological, electrical and thermal properties Evgeniya Lock, Karthik Sridhara, Zariana Mobley, Luke Nyakiti, Boris Feigelson, David Olson, John Gaskins, Patrick Hopkins Hexagonal boron nitride (h-BN) has gained significant importance in plasmonics and quantum electronics applications. In addition, there is a plethora of theoretical, yet relatively few experimental studies, showing modification of h-BN properties via functionalization, namely through induction of magnetism and band gap engineering. |
Wednesday, March 6, 2019 3:06PM - 3:18PM |
P13.00004: Density of States of Graphene Doped with Transition Metals SHOHAM Sen, Kaushik Dayal, Yang Wang We perform electronic structure calculations for Graphene using density |
Wednesday, March 6, 2019 3:18PM - 3:30PM |
P13.00005: Electronic transport in graphene decorated with adatoms or nanoparticles Jamie Elias, Joshua Cohen, Takashi Taniguchi, Kenji Watanabe, Fudong Wang, William Buhro, Arashdeep S Thind, Rohan Mishra, Erik Henriksen There is much interest in inducing a spin-orbit coupling into monolayer graphene in order to engineer the Kane-Mele Hamiltonian and thereby enable observation of the quantum spin Hall effect in graphene. Numerous adatoms have been studied toward this end. Here, we present measurements of monolayer graphene Hall bars with dilute coatings of either osmium adatoms or Bi2Te3 nanoparticles (NPs). With osmium adatoms, we find an unusual hole doping to occur, whereas most metals show electron doping. Nanoparticles of Bi2Te3 have recently been reported to yield possibly quantized transport [1]. We use high quality NPs, monodispersed with diameters of ~15 nm. Transport is studied after depositing the nanoparticles, and again after an argon anneal to remove the polyvinylidene fluoride coating on the NPs. In this case a small electron doping response is observed. Further measurements on higher density coatings of both osmium adatoms and Bi2Te3 nanoparticles will be discussed. |
Wednesday, March 6, 2019 3:30PM - 3:42PM |
P13.00006: Nearly Flat Unoccupied State in Intercalated Graphene: Observation and Interpretation Yi Lin, Ge Chen, Jerzy T. Sadowski, Yunzhe Li, Samuel Tenney, Jerry Dadap, Mark Hybertsen, Richard M Osgood By using two-photon-photoemission, we observe a near-zero-dispersion empty state in oxygen-intercalated graphene-Ir interface, approximately 2.6 eV above the Fermi energy and near the Brillouin zone center. DFT method and band-unfolding technique are used to calculate the spectral weights for the graphene-Ir supercells with and without the intercalants. The calculations reproduce the measurements. Our analysis reveals the nature of the observed nearly flat band to be the replicates states from near the Dirac cone that have little dispersion due to trigonal warping. This interpretation is further supported by the results from angle-resolved photoemission. Our work explicitly demonstrates the persisting perturbation on the graphene even for the intercalated quasi-freestanding graphene. Our work demonstrates a pathway for tailoring the graphene electronic structure and generating nearly flat bands by using intercalation. |
Wednesday, March 6, 2019 3:42PM - 3:54PM |
P13.00007: Scanning tunneling microscopy and spectroscopy of wet chemically synthesized porous graphene nanoribbons Kaitlyn Parsons, Adrian Radocea, Mohammad Pour, Tao Sun, Alexander Sinitskii, N. R. Aluru, Joseph W Lyding The bottom-up wet chemical synthesis of graphene nanoribbons (GNRs) opens interesting opportunities for tailoring the GNR structure with atomic precision [1]. Atomically precise porous GNRs are a new chemically synthesized variation for which the fabrication procedure yielding multiple pores in a single ribbon and the electronic details of the ribbon have not been reported. In this work, porous GNRs are dry contact transferred in ultrahigh vacuum to clean silicon and III-V semiconducting substrates and examined using UHV scanning tunneling microscopy (STM) and spectroscopy (STS). STM imaging confirms the expected porous structure and indicates a unique electronic feature at the graphene nanopores, and STS measurements indicate a 2.0 eV bandgap. These results are compared to first-principles DFT simulations in which an increased local density of states at the pores is predicted. A GW correction predicts a 3.24 eV bandgap. Illumination of pore effects enables tunability of GNR electronic properties. |
Wednesday, March 6, 2019 3:54PM - 4:06PM |
P13.00008: Nitrogen Plasma-treated Continuous Monolayer MoS2 Film for Improving Hydrogen Evolution Reaction Anh Duc Nguyen, Tri Nguyen, Tam Chinh Le, Farman Ullah, Zeeshan Tahir, Sung-An Lee, Song-Do Kim, Yong Soo Kim Large density of active sites and near zero Gibbs free energy renders two-dimensional (2D) MoS2 is ideal platforms to investigate low-cost hydrogen evolution reaction (HER) compared to the noble metal in terms of cost. Recently reported metal-organic chemical vapor deposition (MOCVD) is a good synthetic method for continuous and conformal monolayer transition metal dichacogenide. [1,2] However, the intrinsic defects and the grain boundaries in MOCVD-grown TMDC are still limited to provide enough active sites for high efficient HER. In this work, we employed nitrogen plasma to enhance the active sites on the continuous MoS2 surface for further improving the ratio of the edge to basal sites. Initially, the optical properties were investigated by using in-situ PL and Raman spectroscopy. Furthermore, the surface morphology was examined by using FE-SEM and in-situ AFM. The HER results shows that the sample treated for 20 minutes at 0.02 mA and 20 kV showed the best performance. The sample showed reduced onset overpotential of -0.25 mV compared to the as-grown MoS2 (-0.48 mV). [1] K. Kang, et al., Nature 520, 656 (2015). [2] E. Kim, et al., Nanoscale 10, 18920 (2018). |
Wednesday, March 6, 2019 4:06PM - 4:18PM |
P13.00009: Photo-oxidation: Finding the Ambient Air Oxidation Mechanism of WS2 Jimmy Kotsakidis, Quianhui Zhang, Amadeo Lopez Vazquez de Parga, Shaun Johnstone, Changxi Zheng, Marc Currie, Kristian Helmerson, David Kurt Gaskill, Michael Fuhrer Monolayer WS2 exhibits exceptional optical and electronic properties, however, it also oxidizes in ambient conditions leading to the degradation of its optical and electrical performance over time. |
Wednesday, March 6, 2019 4:18PM - 4:30PM |
P13.00010: Wide-area versus focused low-energy electron-beam irradiation of multilayer graphene on SiO2/Si substrate. John Femi-Oyetoro, Kevin Yao, Kevin Roccapriore, Phillip Ecton, Runtian Tang, Jason Jones, Ashley Mhlanga, Guido Verbeck, Jose Perez We carried out an investigation into the mechanism for the etching of exfoliated graphene multilayer on 300nm thick SiO2/Si substrates. A recent mechanism was proposed in which the etching was due to dissociated oxygen from the SiO2 substrate. Oxygen is released from underneath the substrate and etches the graphene layer from below. In order to test the mechanism, we carried out electron beam irradiation on focused areas, using an SEM/e-beam lithography system at energies from 1.5 to 30 keV. We found no evidence for graphene etching. We also carried out wide area electron irradiation using a plasma electron source for graphene exfoliated on a variety of conducting and dielectric substrates. We conclude that low-energy electron etching of graphene is due to sputtering by residual gas ions in the environment. |
Wednesday, March 6, 2019 4:30PM - 4:42PM |
P13.00011: Planar alignment of graphene sheets by a rotating magnetic field for full exploitation of graphene as a two dimension material Feng Lin, Guang Yang, Chao Niu, Yanan Wang, Zhuan Zhu, Haokun Luo, Chong Dai, Yandi Hu, Jonathan Hu, Xufeng Zhou, Zhaoping Liu, Zhiming Wang, Jiming Bao Planar alignment of disc-like nanomaterials is required to transfer their superior anisotropic properties from microscopic individual structures to macroscopic collective assemblies. However, such alignment by electrical or magnetic feld is challenging due to their additional degrees of orientational freedom compared to that of rod-like nanostructures. Here, the realization of planar alignment of suspended graphene sheets using a rotating magnetic feld produced by a pair of small NdFeB magnets and subsequent demonstration of high optical anisotropy and potential novel device applications is reported. Compared to partially aligned sheets with a static magnetic feld, planar aligned graphene suspensions exhibit a near-perfect order parameter, much higher birefringence and anisotropic absorption/transmission. By immobilizing and patterning aligned graphene in a UV-curable polymer resin, we further demonstrated an all-graphene permanent display, which exhibits wide-angle, high dark-bright contrast in either transmission or reflection mode without any polarizing optics. The ability to control and pattern graphene orientation in all three dimensions opens up new exploration and broad device applications of graphene. |
Wednesday, March 6, 2019 4:42PM - 4:54PM |
P13.00012: Chemical enhancement of Raman scattering on graphene oxide in the quantum plasmonic regime Sharad Ambardar, Dmitri Voronine Optoelectronic and mechanical properties of graphene oxide have been widely investigated. We observed two chemical enhancement mechanisms, one from the gold plasmonic tip via the tip-enhanced Raman spectroscopy (TERS) and the other from graphene oxide via the surface-enhanced Raman spectroscopy (SERS). We observed strong chemical enhancement from the gold plasmonic tip in the quantum plasmonic regime when the tip-sample distance is less than 1 nm. We improve the efficiency of the chemical enhancement by varying the tip-sample distance which allows us to clearly observe the effect of graphene oxide using nanoscale TERS imaging. Strong chemical enhancement can be used to improve the quality of sensors and nanophotonic devices on non-metallic substrates. |
Wednesday, March 6, 2019 4:54PM - 5:06PM |
P13.00013: Large-scale reactive molecular dynamics simulations of structural transitions in transition metal dichalcogenides Cole Miles, Chunruo Duan, Despina Louca, Gia-Wei Chern We present extensive molecular dynamics (MD) simulations of structural phase transitions in transition metal dichalcogenides (TMD). These quasi-two-dimensional materials are described by the general formula MX2 with M a transition metal atom (Mo, W, etc) and X a chalcogen atom (S, Se, Te). The crystal structure of a TMD consists of Van der Waals bonded layers, resembling that of graphene. TMDs are hosts of exotic quantum states with potential technological applications. Our work is motivated by recent experiments on MoTe2, showing diffuse scattering in the vicinity of the 1T'-Td structural transition which is indicative of stacking disorders resulting from layer misalignments along the c-axis. We performed large-scale MD simulations based on reactive force field potentials to investigate the kinetics of this intriguing first-order transition. In particular, our results show that the transition can be viewed as a sequence of 2D structural transitions as the system goes through a series of local free-energy minima. |
Wednesday, March 6, 2019 5:06PM - 5:18PM |
P13.00014: Angle-resolved photoemission spectroscopy on wet-transferred highly oriented MoS2 monolayers on HOPG substrates Woojoo Lee, Li-Shuan Lu, Wei-Chen Chueh, Wen-Hao Chang, Chih-Kang Shih The ability to create a large area of monolayer 2D electronic materials with the same orientation on different substrates will play a very critical role for scalable flatland electronics. It has been shown that highly-oriented monolayer (ML) MoS2 can be grown on a carefully prepared sapphire substrate with nearly full coverage and transferred to different substrates [1]. However, it is still unclear whether such a transfer process will introduce unwanted defects that will affect the electronic structure. Here, we report successful preparation of high quality ML MoS2 transferred to HOPG substrates by using a wet transfer method. With a proper treatment, we reveal detailed electronic band structure using high resolution angle-resolved photoemission spectroscopy. Due to the fact that these MoS2 monolayers are highly oriented and interaction with a substrate is very weak [2], we are able to resolve the electronic band structure clearly including K point band splitting. |
(Author Not Attending)
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P13.00015: Multifunctional nanoporous graphene Aran Garcia-Lekue, Cesar Moreno, Manuel Vilas-Varela, Bernhard Kretz, Marius V. Costache, Marcos Paradinas, Mirko Panighel, Gustavo Ceballos, Sergio O. Valenzuela, Diego Peña, Aitor Mugarza Nanoporous graphene shows a great potential as an active component of field effect transistors and as an atom-thick selective molecular nanosieve. Recently, we have reported the bottom-up formation and electronic characterization of atomically precise nanoporous graphene comprising an ordered array of pores separated by ribbons, which can be tuned down to the one nanometer range [1]. Our combined Density Functional Theory (DFT) and Scanning Tunneling Spectroscopy (STS) study reveals a highly anisotropic electronic structure, where orthogonal one-dimensional electronic bands with an energy gap of ~1 eV coexist with a novel family of confined pore states. These properties can be tuned by changing, e.g. the size and morphology of the pore, making this 2D mesh a highly versatile semiconductor for simultaneous sieving and electrical sensing of molecular species. [1] C. Moreno et al., Science 360, 199 (2018) |
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