Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session A2: Focus Session: Beyond Graphene - Phosphorene I |
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Sponsoring Units: DMP Chair: Wenjuan Zhu, University of Illinois Room: 001B |
Monday, March 2, 2015 8:00AM - 8:12AM |
A2.00001: Electronic Bandgap and Edge Reconstruction in Phosphorene: An Experimental/Theoretical joint investigation Liangbo Liang, Jun Wang, Wenzhi Lin, Bobby G. Sumpter, Minghu Pan, Vincent Meunier Phosphorene, or monolayer black phosphorus, is a new 2D layered material with high hole mobility and direct semiconducting bandgap. However, the direct bandgap of phosphorene has not been directly measured, and the properties of its edges have not been considered in detail. In a joint experimental/theoretical work, we studied the electronic properties of phosphorene and its edges [Liang et al., Nano Letters, 2014, 14, 6400]. A detailed scanning tunneling microscopy/spectroscopy (STM/S) study with first-principles calculations reveals the presence of a semiconducting 2 eV gap, the direct bandgap for phosphorene. More importantly, we were able to identify a sharp mono-step in phosphorene that allowed us to perform the first-ever investigation of edges. STS measurements across the step edge indicate nontrivial multiple edge states located inside the 2 eV gap and below the Fermi level. To understand these edge states, we have modeled a series of 1D phosphorene nanoribbons including armchair- and zigzag-edged PNRs. Extensive density functional theory calculations show that edge reconstructions are responsible for energy positions of these edge states. The reconstructions self-passivate most edge dangling bonds by switching the coordination number of phosphorus from 3 to 4 or 5. [Preview Abstract] |
Monday, March 2, 2015 8:12AM - 8:24AM |
A2.00002: Band Gap, Excitons, Thermal Conductance, and Energy Applications of Few-Layer Black Phosphorus Li Yang I will present our recent works of the electronic structures, optical excitations, and thermal conductance of a class of newly emerging two-dimensional semiconductors, few-layer black phosphorus (phosphorene). Using first-principles calculations and models, we study several fundamental properties of few-layer black phosphorus. We predict the quasiparticle band gap, excitonic effects, and anisotropic optical spectra, which have been confirmed by recent experiments. Moreover, we predict that not only the electrical conductance but also the lattice thermal conductance is anisotropic, making this material a promising candidate for thermoelectric applications. [Preview Abstract] |
Monday, March 2, 2015 8:24AM - 8:36AM |
A2.00003: Tuning the exciton energy in single and multi-layer black phosphorus by strain and electric field Francois Peeters, Deniz Cakir, Andre Chaves, Hasan Sahin The effect of strain on the electronic and optical properties of single layer black phosphorus is investigated using first principles calculations. Biaxial strain is able to tune the optical band gap from 0.38 eV (at -8{\%} strain) to 2.07 eV (at 5.5{\%}). The exciton binding energy is found to be 0.40 eV for compressive biaxial strain of -8{\%} and becomes 0.83 eV for tensile strain of 4{\%}. The stack effect in the exciton energy is obtained by direct diagonalization of the effective mass Hamiltonian. The dependence on the number of phosphorus layers and the strength of the electric field is investigated. Band anisotropy becomes evident in the direction dependent field induced polarizability of the exciton. [Preview Abstract] |
Monday, March 2, 2015 8:36AM - 8:48AM |
A2.00004: Anisotropic polarization dependence of light scattering in black phosphorus Jae-Ung Lee, Jungcheol Kim, Jinhwan Lee, Changgu Lee, Hyeonsik Cheong We investigated anisotropic polarization dependence of light scattering in black phosphorus by optical microscopy and Raman spectroscopy. Due to a high carrier mobility ($\sim$ 300 V cm$^{2}$/s) and a high on/off ratio ($\sim$ 10$^{5})$, black phosphorus is attracting interest as a promising candidate for a field effect transistor. Black phosphorus has an anisotropic crystal structure, which leads to directional dependence of the mobility and infrared light absorption. We prepared samples on SiO$_{2}$/Si substrates by mechanical exfoliation. We chose a few-hundred-nanometer thick sample with well-defined edges. By using a polarized optical microscope, we found that the optical contrast depends on the crystal direction. By comparing results with TEM measurements, we can determine the crystallographic orientation of the sample. We also performed polarized Raman measurements with several excitation energies. The intensity of each mode is largely dependent on the incident polarization direction. Furthermore, these polarization dependences vary with the excitation energy. From the polarization dependence of the Raman intensity one can determine the crystallographic orientation of the sample. [Preview Abstract] |
Monday, March 2, 2015 8:48AM - 9:00AM |
A2.00005: Symmetry analysis of phosphorene: electronic structure with spin-orbit interaction Pengke Li, Ian Appelbaum We present a symmetry analysis of electronic band structure including spin-orbit interaction close to the insulating gap edge in monolayer black phosphorus (``phosphorene''). Expressions for energy dispersion relation and spin-dependent eigenstates for electrons and holes are found via simplification of a perturbative expansion in wave vector $k$ away from the zone center using elementary group theory. Importantly, we expose the underlying symmetries giving rise to substantial anisotropy in optical absorption, charge, and spin transport properties, and reveal the mechanism responsible for valence band distortion and possible lack of a true direct gap. We discovered that, spin flip processes are decoupled by symmetry from flexural phonons, allowing us to predict a spin lifetime comparable to bulk Si, vastly greater than graphene. [Preview Abstract] |
Monday, March 2, 2015 9:00AM - 9:12AM |
A2.00006: Tuning Electronic and magnetic properties of phosphorene by vacancies and adatoms Pooja Srivastava, K.P.S.S. Hembram, Hiroshi Mizuseki, Kwang-Ryeol Lee, Sang Soo Han, Seungchul Kim In the search of novel materials, phosphorene (2D layers of black phosphorus) has been synthesized recently. Intrinsic bandgap, hydrophilicity and anisotropic electron mobility make phosphorene different from graphene and also, its hole mobility is higher than that in MoS$_{2}$. All these properties make it a very promising material for electronics and optoelectronics applications. As with other as-synthesized materials, phosphorene exhibits defects such as vacancies, and these defects can affect the properties of the material significantly. The present work provides a detailed understanding of various vacancy defects (mono- and di-vacancies) and their effect on the electronic and magnetic properties of phosphorene. We have also studied the effects of omnipresent non-metallic C/N/O and transition metal (TM) Fe/Co/Ni on the electronic and magnetic properties of phosphorene. We show that, for various adatom adsorbed pristine/defected phosphorene structures the magnetic moment can be tuned via the control of Fermi level. The magnetism for non-metallic adatom adsorbed pristine/defective phosphorene systems can be switch ON/OFF. TM adatoms provide extra flexibility by tuning the magnitude as well. [Preview Abstract] |
Monday, March 2, 2015 9:12AM - 9:24AM |
A2.00007: Quantum Monte Carlo Studies of Bulk and Few- or Single-Layer Black Phosphorus Luke Shulenburger, Andrew Baczewski, Zhen Zhu, Jie Guan, David Tomanek The electronic and optical properties of phosphorus depend strongly on the structural properties of the material. Given the limited experimental information on the structure of phosphorene, it is natural to turn to electronic structure calculations to provide this information. Unfortunately, given phosphorus' propensity to form layered structures bound by van der Waals interactions, standard density functional theory methods provide results of uncertain accuracy. Recently, it has been demonstrated that Quantum Monte Carlo (QMC) methods achieve high accuracy when applied to solids in which van der Waals forces play a significant role. In this talk, we will present QMC results from our recent calculations on black phosphorus, focusing on the structural and energetic properties of monolayers, bilayers and bulk structures. [Preview Abstract] |
Monday, March 2, 2015 9:24AM - 9:36AM |
A2.00008: Atoms dictating shape: The discrete geometry of conformal two-dimensional materials Mehrshad Mehboudi, Kainen Utt, Humberto Terrones, Alejandro Pacheco, Edmund Harriss, Salvador Barraza-Lopez The electronic, optical, thermal, mechanical and chemical behavior of two-dimensional (2D) materials depends on their shape (geometry). 2D materials are \textit{nets }[1], with covalent bonds representing edges, and where atoms are vertices. Here we use a mathematical language to tell the shape of meshes and discuss the geometry of 2D materials of varied lattice structures, such as: hexagonal boron nitride, black phosphorus monolayers, low-buckled silicene, germanene, blue phosphorous, newly predicted III-V buckled 2D compounds such as AlP, conformal ``thicker'' layered materials such as 2D tin, ``single-layer'' transition metal dichalcogenides (MX$_{2}$'s), and a single-quintuple-layer of the topological insulator Bi$_{2}$Se$_{3}$. We characterize the geometry of each atom position without recourse to a continuum parametric model. The new framework generalizes the discrete geometry we introduced recently for graphene [2,3]. References: 1. Discrete Differential Geometry, edited by A. I. Bobenko, P. Schroder, J. M. Sullivan, and G. M. Ziegler, Oberwolfach Seminars Vol. 38 (Springer, Berlin, 2008), 1st ed. 2. Pacheco Sanjuan, A. A., Mehboudi, M., Harriss, E. O., Terrones, H., {\&} Barraza-Lopez, S. ACS Nano 8, 1136-1146 (2014). 3. Sanjuan, A. A. P., Wang, Z., Imani, H. P., Vanevi\'{c}, M., {\&} Barraza-Lopez, S. PRB 89, 121403(R) (2014). [Preview Abstract] |
Monday, March 2, 2015 9:36AM - 9:48AM |
A2.00009: Raman modes of exfoliated black phosphorus down to the monolayer Anne-Laurence Phaneuf-L'Heureux, Alexandre Favron, Etienne Gaufres, Richard Martel, Sebastien Francoeur Exfoliated black phosphorus layers, or 2D-phosphane, are a lamellar direct-gap semiconductor providing high mobilities and enabling a thickness-controlled band gap tunability ranging from 0.3 up to about 2 eV. Using Raman spectroscopy, we have studied vibrational modes of pristine and non-oxidized 2D-phosphane as a function of the number of layers involved ($n$), and also as a function of temperature, polarization, and excitation wavelength. The evolution of the width and of the frequency of A$^2_g$ as a function of $n$ presents a clear non-monotonic dependence. This can be explained by the presence of new nearly-degenerate Raman-allowed modes that are symmetry-forbidden in both bulk and monolayer samples. We also present Raman spectra of few-layer samples for excitation wavelengths in the viscinity of the expected band gap. [Preview Abstract] |
Monday, March 2, 2015 9:48AM - 10:00AM |
A2.00010: Raman signatures of degradation in mono-, bi- and trilayers of exfoliated black phosphorus Alexandre Favron, Etienne Gaufres, Frederic Fossard, Anne-Laurence Phaneuf-L'Heureux, Annick Loiseau, Richard Leonelli, Sebastien Francoeur, Richard Martel Thin layers of black phosphorus have recently raised interest for their two-dimensional (2D) semiconducting properties, such as tunable bandgap with layer thickness and high carrier mobilities. This lamellar crystal of P atoms can be exfoliated down to monolayer 2D-phosphane (also called phosphorene) using procedures similar to that for monolayer graphene. The devices are however challenging to fabricate due to fast degradation of the thin layers upon exposure to light in air. We investigated this degradation process using in-situ Raman and transmission electron spectroscopies and reported on a thickness dependent reactivity of the layers. Moreover, the degradation process was identified to be due to an ubiquitous photo-induced oxidation of the layers by adsorbed oxygen in water. Optimum experimental conditions to prepare n-layer 2D-phosphane in their pristine states were applied to determine the Raman signatures of degradation. Here, we report on the use of the ratio of intensity of the A1g over A2g modes as an assessment of the crystal quality. [Preview Abstract] |
Monday, March 2, 2015 10:00AM - 10:12AM |
A2.00011: Conical structures of black and blue two-dimensional phosphorus Kainen Utt, Mario Borunda, Salvador Barraza-Lopez Two-dimensional phosphorus [1,2], the most recent addition to the growing list of novel two-dimensional materials, has quickly become the focus of materials science. We create conical configurations of black phosphorus from planar structures with a disclination line [3], and the properties of these conical structures of phosphorus will be discussed here. [1] H. Liu et al. \textit{ACS Nano} \textbf{8}, 4033 (2014). [2] L. Li et al. \textit{Nature Nanotechnology} \textbf{9}, 372--377 (2014) [3] Y. Liu et al. \textit{Nano Letters} ASAP. DOI: 10.1021/nl5021393 (2014) [Preview Abstract] |
Monday, March 2, 2015 10:12AM - 10:24AM |
A2.00012: First-principles study of atomic adsorptions on phosphorene Jun-Ho Lee, Young-Woo Son Phosphorene with a moderate intrinsic band gap around 1eV and appropriate carrier mobility merits a next-generation electronic devices. One of the interesting characters of phosphorene is anisotropic electronic and optical properties due to its puckered atomic structures, providing an interesting realization of self-assembled low-dimensional nanostructure on it. In this study, we investigated electronic and magnetic properties of two-dimensional atomic layer formed on phosphorene by using density-functional theory calculations. We explored adsorption properties of various atoms on phosphorene and calculated energetics to predict two-dimensional atomic arrangements on top of phosphorene. In a strong spin-orbit system, we also found anisotropic spin splitting owing to its structural anisotropic. [Preview Abstract] |
Monday, March 2, 2015 10:24AM - 10:36AM |
A2.00013: Electronic band structure of surface-doped black phosphorus Jimin Kim, Sae Hee Ryu, Yeongsup Sohn, Keun Su Kim There are rapidly growing interests in the study of few-layer black phosphorus owing to its promising device characteristics that may impact our future electronics technology. The low-energy band structure of black phosphorus has been widely predicted to be controllable by external perturbations, such as strain and doping. In this work, we attempt to control the electronic band structure of black phosphorous by in-situ surface deposition of alkali-metal atoms. We found that surface doping induces steep band bending towards the bulk, leading to the emergence of new 2D electronic states that are confined within only few phosphorene layers of black phosphorus. Using angle-resolved photoemission spectroscopy, we directly measured the electronic band structure and its evolution as a function of dopant density. [Preview Abstract] |
Monday, March 2, 2015 10:36AM - 10:48AM |
A2.00014: Van der waals heterostructure of phosphorene and graphene: Tuning the Shottky barrier and doping by electrostatic gating Jose Eduardo Padilha de Sousa, Adalberto Fazzio, Antonio Jose Roque da Silva Van der Waals heterostructures of 2D materials is one of the most promising approaches in terms of the new nanodevices. One of these 2D materials that have attracted a lot of attention from a broad community is the phosphorene, an elemental material composed only of phosphorus. If one wishes to build devices, two important points must always be addressed: how to make contacts - and the value of the resulting Schottky Barrier Height (SBH) - and how to control the charge doping level. In the present work we study the structural and electronic properties of single and bilayer phosphorene with graphene. We show that both the properties of graphene and phosphorene are preserved upon its contact. We also show that via the application of a perpendicular electric field it is possible to tune the position of the band structure of phosphorene with respect to that of graphene. This leads to a great control of the Schottky barrier height and doping of phosphorene, which are important features in the design of new devices based on this kind of structure. [Preview Abstract] |
Monday, March 2, 2015 10:48AM - 11:00AM |
A2.00015: Low-frequency interlayer breathing mode in few-layer black phosphorus Xi Ling, Shengxi Huang, Liangbo Liang, Vincent Meunier, Mildred Dresselhaus Black phosphorus (BP), as a layered material, has attracted intense interest recently. Many interesting electronic and optoelectronic properties are being explored based on its unique anisotropic structure. In this work, we studied the Raman spectra in few-layer BP, including the intralayer and interlayer vibrational modes. Besides the three typical Raman modes A$_{g}^{1}$ ($\sim$ 359 cm$^{-1})$, B$_{2g}$ ($\sim$ 437 cm$^{-1})$, and A$_{g}^{2}$ ($\sim$ 466 cm$^{-1})$, low-frequency modes were observed in few-layer BP, as predicted by the first-principles density functional theory (DFT) calculation. The interlayer breathing mode at around 87 cm$^{-1}$ was assigned as A$_{g}^{0}$, since the DFT calculation result showed it has the symmetry of A$_{g}^{0}$. In addition, the polarization dependence of the Raman modes in BP is studied systematically. Both the DFT calculation and the experimental results show that the polarization dependence profiles are sensitive to the crystal orientation of BP. In addition, the temperature dependence of the modes is studied in the range of -150 $^{\circ}$C to room temperature. It is found that the A$_{g}^{0}$ mode has almost no dependence on the temperature change, and the out-of-plane mode (A$_{g}^{1})$ has weaker dependence than the in-plane modes (B$_{2g}$ and A$_{g}^{2})$. [Preview Abstract] |
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