Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session P12: 2D Materials: Probing and Tuning Electronic Structure |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Felix Lupke, Carnegie Mellon Room: BCEC 153A |
Wednesday, March 6, 2019 2:30PM - 2:42PM |
P12.00001: Scanning Probe Microscopy of Inhomogeneous States in 2D Materials Lavish Pabbi, Riju Banerjee, Tomotaroh Granzier-Nakajima, Anna Binion, 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. This ability is especially beneficial in the investigation of 2D materials, whereby their very nature there are frequently large variations in local structure, for example due to strain or changing substrate interactions, leading to concomitant variations in local electronic properties. As one example, I will here present results of recent STM measurements of single-layer graphene on copper, and on the graphene nano-ribbons that form when draped over copper step edges. In particular, I will focus on the interesting measurement challenge presented by the topological nature of the states that arise at the edges of these and other systems. |
Wednesday, March 6, 2019 2:42PM - 2:54PM |
P12.00002: Isotropic charge screening of the anisotropic black phosphorus revealed by potassium adatoms Zhen Tian, Jiamin Xue Recent angle-resolved photoemission spectroscopy and transport experiments have shown that at the macroscopic level the electronic structure of black phosphorus can be greatly modified by potassium adatoms. Understanding the effects of individual potassium adatoms at the microscopic level is of great importance. To this end, we use scanning tunneling microscopy to study black phosphorus with potassium adatoms. We find that the potassium atoms are almost fully ionized even at 4.5 K. The Fermi level of black phosphorus is shifted due to electron doping while the band gap shows no significant change. Due to the puckered anisotropic lattice structure, we find that potassium ions can easily migrate along the zigzag direction but not along the armchair direction. Using tip as a moving gate, we can control the ionization of potassium ions. With this technique, we probe the screening effect of charged impurities in black phosphorus at the atomic scale. Remarkably, we find that it shows in-plane isotropic screening behavior even though the underlying electronic dispersion and lattice structure has distinct anisotropy. We also construct two potassium-adatom clusters as a coupled system to study the interaction of them. These results reveal the rich anisotropic physics in black phosphorus. |
Wednesday, March 6, 2019 2:54PM - 3:06PM |
P12.00003: Substrate screening effects on the quasiparticle band gap and defect charge transition levels in MoS2. Mit Naik, Manish Jain Monolayer MoS2 has emerged as an interesting material for nanoelectronic and optoelectronic devices. The effect of substrate screening and defects on the electronic structure of MoS2 are important considerations in the design of such devices. We find a giant renormalization to the free-standing quasiparticle band gap in the presence of metallic substrates, in agreement with recent scanning tunneling spectroscopy and photoluminescence experiments. Our sulfur vacancy defect calculations using the DFT+GW formalism, reveal two CTLs in the pristine band gap of MoS2. The (0/-1) CTL is significantly renormalized with the choice of substrate, with respect to the pristine valence band maximum. The (+1/0) level, on the other hand, is pinned 100 meV above the pristine VBM for the different substrates. This opens up a pathway to effectively engineer defect charge transition levels in 2D materials through choice of substrate. |
Wednesday, March 6, 2019 3:06PM - 3:18PM |
P12.00004: Scanning Tunneling Microscopy Study of Epitaxial Growth of Wafer Scale, Single Atomic Sheet Honeycomb BeO Two-dimensional Insulator Madisen Holbrook, Hui Zhang, Fei Cheng, Hyoungdo Nam, Mengke Liu, Chi-Ruei Pan, Damien West, Shengbai Zhang, Mei-Yin Chou, Chih-Kang Shih We report the discovery of a novel 2D insulator comprised of a single atomic sheet honeycomb structure BeO, though its bulk counterpart has a wurtzite structure. Such a single sheet of BeO is grown epitaxially on Ag(111) thin films, also epitaxially grown on Si(111) wafers. Using scanning tunneling microscopy and spectroscopy (STM/S) we observe this novel BeO atomic sheet has a lattice constant of 2.65 Å and a band gap of 6 eV. We also found the BeO has a weak van der Waals (vdW) interaction with the Ag(111) substrate, which agrees well with predictions of our density functional theory calculations. Moiré pattern analysis shows the BeO honeycomb structure maintains long range phase coherence in atomic registry even across Ag steps. This novel material provides a scalable platform for 2D electronics, as an attractive 2D insulator due to its potentially much higher thermal conductivity than that of hBN. More significantly, the ability to create a single crystalline atomic sheet with no bulk counterpart of similar structure opens a new avenue toward tailoring novel 2D electronic materials. |
Wednesday, March 6, 2019 3:18PM - 3:30PM |
P12.00005: The Band Structure and Contact Issues of Quasi One Dimensional TiS3 Simeon Gilbert, Hemian Yi, Takashi Komesu, Alexey Lipatov, Guanhua Hao, Andrew J Yost, Alexander Sinitskii, Jose Avila, Chaoyu Chen, Maria Asensio, Peter A Dowben Titanium trisulfide (TiS3) is a transition metal trichalcogenide whose atoms form chains of trigonal prisms creating a quasi-one-dimensional structure. This 1D structure results in an anisotropic band structure and edge perfection that can reduce the edge scattering effects experienced in sub 10 nm field-effect transistors. Furthermore, a recent theoretical study indicates that monolayer TiS3 is a direct-gap semiconductor with a bandgap of ~1 eV and an electron mobility near 10,000 cm2V-1s-1 making TiS3 an ideal candidate for high mobility transistors. Our recent work directly measured the in-plane anisotropy of few layer TiS3 flakes using nanospot angle resolved photoemission spectroscopy. The effective hole mass at the top of the valence band was found to be -0.95 ± 0.09 me along the chain direction and -0.37 ± 0.1 me perpendicular to the chain direction. The measured mobility for TiS3 transistors has remained well below the predicted value, but it is common for contact issues to lower the measured mobility. The interactions between TiS3 and Au or Pt contacts have been investigated using x-ray photoemission spectroscopy which shows that strong bonding with sulfur is the key to prevent Schottky barrier formation. |
Wednesday, March 6, 2019 3:30PM - 3:42PM |
P12.00006: Bulk compressibility measurements of WSe2 heterostructures Qianhui Shi, En-Min Shih, Daniel A Rhodes, Bumho Kim, Takashi Taniguchi, Kenji Watanabe, James Hone, Cory R Dean 2D semiconductors have attracted a great deal of attention due to their unique properties including strong spin-orbit coupling, large effective mass and high tunability. However, quantum transport studies have been complicated by the difficulties in making Ohmic contacts. Non-ideal contacts also limit studies in more complex structures such as twisted bilayers and double-layers which may host interesting correlated phases. Here we report on magneto-capacitance measurements on WSe2 heterostructures which probe the bulk electronic compressibility. This approach has a much lower requirement on the contact quality and allows improved resolution of both zero-field and finite field features, and over a wider range of density than previously accessible. |
Wednesday, March 6, 2019 3:42PM - 3:54PM |
P12.00007: Flavor Symmetry and Ferroelectric Nematics in Transition Metal Dichalcogenides Patrick Cheung, Zhi-qiang Bao, Fan Zhang Recent magneto-transport experiments have provided compelling evidence for the presence of an energetically isolated threefold Q-valley degeneracy in few-layer transition metal dichalcogenides. We study the flavor SU(3) symmetry breaking when each Landau level triplet is one-third filled or empty and predict that a pure flavor nematic phase and a flavorless charge-density-wave phase will occur respectively below and above a critical magnetic field. Surprisingly, electrons carry flavor-dependent electric dipole moments even at zero magnetic field, rendering the nematics ferroelectric, allowing electric-field manipulation of the flavors, and leading to the concept of flavortronics. |
Wednesday, March 6, 2019 3:54PM - 4:06PM |
P12.00008: ARPES microscopy of hBN flakes Roland Koch, Jyoti Katoch, Simon K Moser, Daniel Schwarz, Roland Kawakami, Aaron Bostwick, Eli Rotenberg, Chris Jozwiak, Soren Ulstrup Hexagonal boron nitride (hBN) is an essential component in van der Waals heterostructures. It provides high-quality and weakly interacting interfaces that preserve the electronic properties of adjacent materials. We will present the full valence-band (VB) electronic structure of micrometer-sized exfoliated flakes of hBN using angle-resolved photoemission spectroscopy with micrometer and nanometer spatial resolution. We identify the π - and σ -band dispersions, the hBN stacking order, and determine a total VB bandwidth of 19.4 eV. We compare these results with electronic structure data for epitaxial hBN on graphene on silicon carbide grown in situ using a borazine precursor. The epitaxial growth and electronic properties are investigated using photoemission electron microscopy. Our measurements show that the fundamental electronic properties of hBN are highly dependent on the fabrication strategy. |
Wednesday, March 6, 2019 4:06PM - 4:18PM |
P12.00009: Large-Area Epitaxial Growth of Curvature-Stabilized ABC Trilayer Graphene with Tunable Band Gap Zhaoli Gao, Sheng Wang, Joel M Berry, Qicheng Zhang, Julian Gebhardt, William Parkin, Jose Avila, Hemian Yi, Chaoyu Chen, Sebastian Hurtado Parra, Marija Drndić, Andrew Rappe, David Srolovitz, J. M. Kikkawa, Zhengtang Luo, Maria C. Asensio, Feng Wang, Alan T Johnson The physical properties of epitaxially-grown layered van der Waals (vdW) materials can be engineered to an extraordinary degree by manipulating the number of atomic layers, their compositions, and their relative stacking configurations and twist angles. vdW trilayer graphene (TLG) can stack in either a semi-metallic ABA configuration or a semi-conducting ABC configuration with a gate-tunable band gap but to this point has only been produced via exfoliation, which greatly limits its scientific and technological development. Here we present a scalable approach to epitaxial TLG growth via chemical vapor deposition that reliably enhances the fraction and size of ABC stacked TLG domains compared to other methods. The key insight is that nanoscale substrate curvature can locally stabilize ABC domains, typically leading to alternating regions of ABC and ABA on topographically corrugated growth substrates. Unambiguous electronic signatures of ABC-TLG were revealed by nano angle-resolved photoemission spectroscopy and infrared scanning near-field microscopy. The ABC fraction remains high after transfer onto a device substrate, as confirmed by transport measurements showing a sizable and tunable ABC-TLG band gap. |
Wednesday, March 6, 2019 4:18PM - 4:30PM |
P12.00010: Spin and valley degree of freedom in a bulk massless-Dirac electron system, α-(BEDT-TTF)2I3 under magnetic fields Kazuya Miyagawa, Matsuno Manabu, Michihiro Hirata, Tamura Masafumi, Kazushi Kanoda Since the discovery of massless-Dirac Fermions (MDF) in graphene, MDF states have found in a |
Wednesday, March 6, 2019 4:30PM - 4:42PM |
P12.00011: Strain-dependent ab-initio tight binding Hamiltonians for T-type transition metal dichalcogenides Daniel Larson, Shiang Fang, Wei Chen, Jennifer Coulter, Steven Torrisi, Stephen Carr, Efthimios Kaxiras Many transition metal dichalcogenides (TMDs) adopt a T-structure in which the metal atom is octahedrally coordinated by the chalcogens. In particular, MX2 with M=(Nb, Ta, Ti) and X=(S, Se) all exhibit fascinating electronic properties including various charge density wave phases. Using Density Functional Theory followed by a Wannier transformation we extract the strain-dependent tight binding parameters for single-layer TMDs. The resulting tight binding Hamiltonian respects the crystal symmetry and gives a very accurate yet simple description of the electronic band structure which is easily augmented to include spin-orbit effects and interlayer couplings. The knowledge of the strain dependence of the electronic properties is critical in order to correct for the effects of relaxation in realistic simulations of twisted nanostructures. |
Wednesday, March 6, 2019 4:42PM - 4:54PM |
P12.00012: Interplay between p- and d- orbitals yields multiple Dirac states in two-dimensional ZrB2 and CrB4 Alejandro Lopez Bezanilla Theoretical evidence of the existence of 12 Dirac cones in the low-spectrum diagram of transition metal-rich monolayered hexagonal networks is provided. Both Zr and Cr are efficient in creating six additional cones with respect to graphene when combined with boron honeycomb lattices. The four d-electrons of Cr, and similarly the two d-electrons of Zr, are yielded to the B sublattices creating an isoelectronic structure to graphene where the interplay between p- and d-orbitals leads to the appearance of Dirac states on both one- and two-dimensional geometries. Ab initio calculations show that, although spin–orbit interaction splits the cone-shaped valence and conduction bands, monolayered ZrB2 and CrB4 are semimetals with compensated electron–hole pockets. |
Wednesday, March 6, 2019 4:54PM - 5:06PM |
P12.00013: The effect of the adsorption of the toxic hydrazine on the electronic structure of the WS2 monolayer: the first principle calculations Md Rajib khan Musa, Congyan Zhang, Adel Alruqi, Gamini Sumanasekera, Ming Yu Two-dimensional layered WS2 possesses novel electronic properties and has various promised applications. Its sensitivity to various molecules [1] makes it possible as sensor. Our recent experiment results show that its resistance changes dramatically with the response to the toxic hydrazine vapor. Our first-principle calculations also found the effect of the adsorption of the hydrazine on the electronic structure of WS2 monolayer. In particular, the impurity state associated with the toxic hydrazine just pin at the middle of the band gap, resulting to an n-type like behavior. A detail discussion will be presented. References: [1] Changjie Zhou, Weihuang Yang, and Huili Zhu, J. Chem. Phys. 142, 214704 (2015). |
Wednesday, March 6, 2019 5:06PM - 5:18PM |
P12.00014: Symmetry controlled adsorption of di-iodobenzene on MoS2 Zahra Hooshmand Gharehbagh, Prescott E Evans, Duy Le, Peter A Dowben, Talat S. Rahman In a joint experimental and theoretical study, we have uncovered evidence of the importance of symmetry in the adsorption of the isomers of di-iodobenzene on MoS2(0001). The intensity ratio of iodine to molybdenum measured, as a function of exposure for different isomers of the di-iodobenzene, show that while for ortho (1,2-) and para (1,4-) di-iodobenzene the rate of adsorption at 100 K is very low, that for meta (1,3-)di-iodobenzene is considerably more facile. We have applied van der Waals corrected density functional theory based calculations to understand the subtleties in the electronic structure and geometry of adsorption of these three di-iodobenzene isomers on MoS2(0001). All three are found to weakly chemisorb onto MoS2(0001) with the same binding strength as well as adopt similar configurations. The calculated electron affinity of the three molecules also do not show a specific trend that would verify experimental data. However analysis of the frontier orbitals indicate that those of 1,3-di-iodobenzene is strongly affected by interactions with MoS2, while that of the other two isomers remain unchanged. Our results show that symmetry is the identifying factor in the adsorption characteristics of di-iodobenzene on MoS2. |
Wednesday, March 6, 2019 5:18PM - 5:30PM |
P12.00015: Portable Surface-Enhanced Raman Spectroscopy of Pyridine and Diazines on MoS2 Robert Hart, Sharad Ambardar, Prasana Sahoo, Dmitri Voronine Raman spectroscopy is a widely used analytical technique for biosensing applications. It has been commonly applied to bulk samples. However, the applications to small amounts of chemical substances is challenging due to weak signals. Surface-enhanced Raman scattering (SERS) can be used to improve sensitivity by the electromagnetic enhancement mechanism using plasmonic nanoparticles or by the chemical mechanism using atomically-thin semiconducting 2D materials. Also, portable Raman spectroscopy instrumentation is needed for medical and industrial point-of-care applications. We investigate the effects of the addition of few-layer molybdenum disulfide (MoS2) nanocrystals on the enhancement of Raman signals of pyridine and its diazine derivatives. The introduction of MoS2 leads to the shifts of the Raman peak positions and changes in the relative peak intensities and overall signal strength of respective ν1 mode for each of the diazines and pyridine, as well as affecting a range of other modes for each compound, observed using a handheld Raman spectrometer, an effect most apparent in the pyrimidine ν1 mode. This information can be valuable to a number of potential fields including studies in biophotonics, which could have numerous industrial, medical and public safety applications. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700