Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session S26: 2D Materials Beyond GrapheneFocus
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Sponsoring Units: DMP Chair: Chris Hinkle, University of Texas at Dallas Room: 325 |
Thursday, March 17, 2016 11:15AM - 11:51AM |
S26.00001: Two Dimensional Transition Metal Dichalcogenide and Their Heterostructures Through Chemical Vapor Deposition Synthesis Invited Speaker: Jing Kong In recent years tremendous efforts have been devoted to the research on two dimensional materials. Among them transition metal dichalcogenides (TMDs) have attracted significant attention owing to their unique structures, remarkable properties, and great potential for a wide range of applications in electronics,\underline {\textunderscore ENREF\textunderscore 1} optoeletronics, valleytronics, catalysis, etc. The synthesis of high quality large area mono- and few-layer TMD materials is highly desirable for their applications. In this talk I will present the chemical vapor deposition (CVD) approach we have developed to synthesis these TMD materials and their heterostructures. [Preview Abstract] |
Thursday, March 17, 2016 11:51AM - 12:27PM |
S26.00002: 2D Crystal heterostructures properties and growth by molecular beam epitaxy Invited Speaker: Grace Huili Xing Two-dimensional (2D) crystals such as transition metal dichalcogenides (TMDs) along with other families of layered materials including graphene, SnSe$_{2}$, GaSe, BN etc, has attracted intense attention from the scientific community. One monolayer of such materials represent the thinnest ``quantum wells''. These layered materials typically possess an in-plane hexagonal crystal structure, and can be stacked together by interlayer van der Waals interactions. Therefore, it is possible to create novel heterostructures by stacking materials with large lattice mismatches and different properties, for instance, superconductors (NbSe$_{2})$, metals, semi-metals (graphene), semiconductors (MoS$_{2})$ and insulators (BN). Numerous novel material properties and device concepts have been discovered, proposed and demonstrated lately. However, the low internal photoluminescence efficiency (IPE, \textless 1{\%}) and low carrier mobility observed in the 2D semiconductors suggest strongly that the materials under investigation today most likely suffer from a high concentration of defects. In this talk, I will share our progress and the challenges we face in terms of preparing, characterizing these 2D crystals as well as pursuing their applications. [Preview Abstract] |
Thursday, March 17, 2016 12:27PM - 12:39PM |
S26.00003: Quantum emission from hexagonal boron nitride monolayers Igor Aharonovich, ToanTrong Tran, Kerem Bray, Michael J. Ford, Milos Toth Artificial atomic systems in solids are widely considered the leading physical system for a variety of quantum technologies, including quantum communications, computing and metrology. To date, however, room-temperature quantum emitters have only been observed in wide-bandgap semiconductors such as diamond and silicon carbide, nanocrystal quantum dots, and most recently in carbon nanotubes. Here, we demonstrate room-temperature, polarized single-photon emission from a colour centre in two-dimensional hexagonal boron nitride. The emitters emit at the red and the near infrared spectral range and exhibit narrowband ultra bright emission (\textasciitilde full width at half maximum of below 10 nm with more than three million counts/s). Density functional theory calculations indicate that vacancy-related defects are a probable source of the emission. Our results demonstrate the unprecedented potential of van der Waals crystals for large-scale nanophotonics and quantum information processing. [Preview Abstract] |
Thursday, March 17, 2016 12:39PM - 12:51PM |
S26.00004: Synthesis and Oxidation Resistance of h-BN Thin Films David Stewart, Robert Meulenberg, Robert Lad Hexagonal boron nitride (h-BN) is an exciting 2D material for use in sensors and other electronic devices that operate in harsh, high temperature environments. Not only is h-BN a wide band gap material with excellent wear resistance and high temperature stability, but recent reports indicate that h-BN can prevent metallic substrates from oxidizing above 600$^\circ$C in low O$_2$ pressures. However, the PVD of highly crystalline h-BN films required for this oxidation protection has proven challenging. In this work, we have explored the growth of h-BN thin films by reactive RF magnetron sputtering from an elemental B target in an Ar/N$_2$ atmosphere. The film growth rate is extremely slow and the resulting films are atomically smooth and homogeneous. Using DC biasing during deposition and high temperature annealing treatments, the degree of film crystallinity can be controlled. The oxidation resistance of h-BN films deposited on inert sapphire and reactive metal substrates such as Zr and ZrB$_2$ has been examined by techniques such as XPS, XRD, and SEM after oxidation between 600 and 1200$^\circ$C under varying oxygen pressures. The success of h-BN as a passivation layer for metallic substrates in harsh environments is shown to depend greatly on its crystalline quality and defects. [Preview Abstract] |
Thursday, March 17, 2016 12:51PM - 1:03PM |
S26.00005: Surface Analysis of Hexagonal Boron Nitride Grown by Chemical Vapor Deposition Zachary Robinson, J.K. Hite, C.R. Eddy Jr., V.M. Bermudez, B.N. Feigelson Hexagonal boron nitride (hBN) is an important material for development of 2-dimensional heterostructures. Chemical vapor deposition of hBN on Cu-foil substrates is one possible route towards large-scale production of hBN films with low defect density. Therefore, studying the growth kinetics of hBN on different orientations of Cu is an important first step towards understanding and controlling the growth process. In this work, hBN was simultaneously grown on Cu(111), Cu(100), Cu(110), and Cu-foil in order to investigate how the different substrate orientations affect the hBN overlayer. The post-growth crystallographic orientations were measured with electron backscatter diffraction (EBSD), and film coverages we measured with XPS. In addition, a grazing-incidence infrared reflection absorption spectroscopy (IRRAS) technique was developed to quickly characterize each hBN film. It was found that the growth rate was inversely proportional to the surface free energy of the Cu surface, with Cu(111) having the most h-BN surface coverage. The Cu foil predominately crystallized with a (100) surface orientation, and had a film coverage very close to the Cu(100). [Preview Abstract] |
Thursday, March 17, 2016 1:03PM - 1:15PM |
S26.00006: Two-dimensional boron based nanomaterials: electronic, vibrational, Raman, and STM signatures Daniel V. P. Massote, Liangbo Liang, Neerav Kharche, Vincent Meunier Because boron has only three electrons on its outer shell, planar mono-elemental boron nanostructures are expected to be much more challenging to assemble than their carbon counterparts. Several studies proposed schemes in which boron is stabilized to form flat semiconducting sheets consisting of a hexagonal lattice of boron atoms with partial hexagon filling (PRL 99 115501, ACSNano 6 7443-7453) . Other structures were proposed based on results from an evolutionary algorithm (PRL 112 085502). These structures are metallic and one even features a distorted Dirac cone near the Fermi level. Experimental evidence for 2D boron is still lacking but the recently proposed molecular synthesis of a flat all-boron molecule is a promising route to achieve this goal (Nat.Comms. 5 3113). Our research aims at providing a first-principles based description of these materials' properties to help in their identification. DFT is used to calculate phonon dispersion and associated Raman scattering spectra. We report some marked discrepancy between our findings and results from the recent literature and address the deviation using two methods for phonon dispersion. We also simulated STM images at various bias potentials to reveal the electronic symmetry of each material. [Preview Abstract] |
Thursday, March 17, 2016 1:15PM - 1:27PM |
S26.00007: Observation of Dirac electrons in germanene on diboride thin films Antoine Fleurence, Rainer Friedlein, Hiroyuki Yamane, Howon Kim, Yuuto Awatani, Shinya Yoshimoto, Kozo Mukai, Takanori Koitaya, Yukio Hasegawa, Jun Yoshinobu, Nobuhiro Kosugi, Yukiko Yamada-Takamura Germanene is a single atom thick honeycomb lattice of Ge atoms. Just like silicene, free-standing germanene is predicted to feature $\pi $ bands forming graphene-like Dirac cones [1]. Epitaxial germanene was already claimed to form on number of substrates [2-4], but no evidence for the existence of a $\pi $ electronic system has been reported yet. In the present work, we demonstrate experimentally that Ge atoms segregated on the (0001) surface of zirconium diboride (ZrB$_{\mathrm{2}})$ thin films grown on Ge(111) form a germanene layer. ZrB$_{\mathrm{2}}$(0001) with germanene is (3$\surd $3X3$\surd $3)-reconstructed at low-temperature and ($\surd $3X$\surd $3)-reconstructed at room temperature. The (3$\surd $3X3$\surd $3) reconstruction originates from the matching of this unit cell with the (4X4) unit cell of a Ge honeycomb lattice. Evidence for its germanene nature stems from the observation of the Dirac cone-like dispersion at the K point of its Brillouin zone. [1] S. Cahangirov et al., Phys Rev. Lett. 102, 236804 (2009). [2] L. Li et al., Adv. Mater. 26, 4820 (2014). [3] M. E. D\'{a}vila et al., New J. Phys. 16, 095002 (2014). \newline [4] M. Derivaz et al., Nano Lett. 15, 2510 (2015). [Preview Abstract] |
Thursday, March 17, 2016 1:27PM - 1:39PM |
S26.00008: Silicene Evolution from Silicon Herringbones on Ru(0001) Yanfang Zhang, Li Huang, Wenyan Xu, Yande Que, En Li, Jinbo Pan, Shixuan Du, Yunqi Liu, Yuyang Zhang, Sokrates T. Pantelides, Hongjun Gao Silicon-based 2D materials can potentionally be integrated into Si-based electronics. Buckled silicene, an analog of graphene, was recently fabricated on a Ag (111) substrate and used to make a field effect transistor. Here, we report that, when Ru (0001) is used as a substrate, low Si coverage produces a herringbone structure, a new silicon phase. With increasing Si coverage, the elbow sites of the herringbone develop into nucleation sites of silicene. At even higher coverage, narrow Si ribbons with honeycomb structure develop between herringbones. Finally, with even higher Si coverage, a ($\surd $3 x$\surd $3) silicene monolayer forms in registry on ($\surd $7 x$\surd $7) Ru(0001). Scanning tunneling microscopy (STM) was used to image the structures. The growth process was confirmed by density functional theory (DFT) calculations. This work may contribute to precise control of growth of silicene and other silicon structures. [Preview Abstract] |
Thursday, March 17, 2016 1:39PM - 1:51PM |
S26.00009: Phosphorenes with Non-Honeycomb Structures: A Much Extended Family Menghao Wu, Huahua Fu, Ling Zhou, Kailun Yao, Xiao Cheng Zeng We predict a new class of monolayer phosphorous allotropes, namely, $\varepsilon $-P, $\zeta $-P, $\eta $-P and $\theta $-P. Distinctly different from the monolayer $\alpha $-P (black) and previously predicted $\beta $-P (Phys. Rev. Lett. \textbf{112}, 176802 (2014)), $\gamma $-P and $\delta $-P (Phys. Rev. Lett. \textbf{113}, 046804 (2014)) with buckled honeycomb lattice, the new allotropes are composed of P$_{\mathrm{4}}$ square or P$_{\mathrm{5}}$ pentagon units that favor tricoordination for P atoms. The new four phases, together with 5 hybrid phases, are confirmed stable by first-principles calculations. In particularly, the $\theta $-P is shown to be equally stable as the $\alpha $-P (black) and more stable than all previously reported phosphorene allotropes. Prediction of nonvolatile ferroelastic switching and structural transformation among different phases under strains points out their potential applications via strain engineering. [Preview Abstract] |
Thursday, March 17, 2016 1:51PM - 2:03PM |
S26.00010: Synthesis and characterizations of heterojunction of monolayer semiconductors. Yi-Hsien Lee, Xin-Quan Zhang, Yu-Wen Tseng, Kuan-Hua Huang, Chun-An Chen, Bo-Han Chen Monolayers of van der Waals materials, including graphene, and MoS$_{\mathrm{2}}$, offered a burgeoning field in fundamental physics, and optoelectronics.[1-5] Recently, atomically thin heterostructures of monolayer TMDc with various geometrical and energy band alignments are expected to be the key materials for next generation flexible optoelectronics. The individual TMDc monolayers can be adjoined vertically or laterally to construct diverse heterostructures which are difficult to reach with the laborious pick up-and-transfer method of the exfoliated flakes. The ability to produce copious amounts of high quality layered heterostructures on diverse surfaces is highly desirable but it has remained a challenging issue. Here, we have achieved a direct synthesis of various heterostructures of monolayer TMDc.[6] The synthesis was performed using CVD with aromatic molecules as seeding promoters. We will discuss possible growth behaviors, and we examine the symmetry and the interface of these heterostructures using optical analysis and scanning TEM. Reference: [1] Xiaoze Liu et al, Nature Photonics, 9, p.30 (2015) [2] Yi-Hsien Lee, et al, Adv. Mater., 24, p.2320 (2012) [3] Yi-Hsien Lee, et al., Nano Lett., 13, 1852 (2013) [4] Xi-Ling et al, Nano Lett., 14, p.464 (2014) [5] Lili Yu et al, Nano Lett, 14, p.3055 (2014) [6] Xin-Quan Zhang et al, Nano Lett, 15, p.410 (2015) [Preview Abstract] |
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