Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session K16: 2D Devices: Black PhosphorousFocus
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Sponsoring Units: DMP Chair: Marija Drndic, University of Pennsylvania Room: 315 |
Wednesday, March 16, 2016 8:00AM - 8:36AM |
K16.00001: Black phosphorus for future devices Invited Speaker: Vincent Meunier Black phosphorus (or “phosphorene” at the monolayer limit) has attracted significant attention as an emerging 2D material due to its unique properties compared with well-explored graphene and transition metal dichalcogenides such as MoS$_2$ and WSe$_2$. In bulk form, this monoelemental layered structure is a highly anisotropic semiconductor with a bandgap of 0.3 eV which presents marked distinctions in optical and electronic properties depending on crystalline directions. In addition, black phosphorus possesses a high carrier mobility, making it promising for applications in high frequency electronics. A large number of characterization studies have been performed to understand the intrinsic properties of BP. Here I wil present a number of investigations where first-principles modelling was combined with scanning tunneling microscopy (STM) [1], Raman spectroscopy [2], and transmission electron microscopy (TEM) [3] to assist in the design of phosphorene-based devices. \footnote{Collaborators on this research include: Liangbo Liang, Bobby G. Sumpter, Alex Puretzky, Minghu Pan, (Oak Ridge National Laboratory), Marija Drndic (University of Pennsylvania), Mildred Dresselhaus, Xi-Ling, Shengxi Huang (Massachusetts Institute of Technology)}. I will provide an overview of these studies and position them in the context of the very active research devoted to this material. In particular, I will show how low-frequency Raman spectra provide a unique handle on the physics of multilayered systems and how BP's structural anisotropy weaves its way to its unusual polarization dependent Raman signature. Finally, I will show recent progress where nanopores, nanobridges, and nanogaps have been sculpted directly from a few-layer BP sample using a TEM, and indicate the potential use of these results on the creation of phosphorene-based nanoelectronics. I wil conclude this talk with a critical look at the issues of phosphorene stability under ambient conditions. \\ References: [1] Nano Lett. 14, 6400-6406 (2014); [2] ACS Nano, 2015, 9 (6), pp 6333–6342 (2015); [3] unpublished [Preview Abstract] |
Wednesday, March 16, 2016 8:36AM - 8:48AM |
K16.00002: Strain Engineering of Phosphorene via Bending Deepti Verma, Traian Dumitrica Phosphorene (PE) - the newly discovered 2D derivative of Phosphorus - has an inherent band gap and a high current on/off ratio. Manipulating strain in PE films - strain engineering (SE) - will offer the opportunity to further tailor its electronic properties. Using objective boundary conditions (OBC) coupled with density functional tight binding model (DFTB), we calculate bending rigidity of PE and its 2D allotropes by modeling bent PE as large diameter nanotubes (PNTs). OBCs not only allow for drastic reductions in the number of atoms in simulations but also enable simulations of chiral PNTs, which is impossible with periodic boundary conditions. At the same time, the method describes how bending influences the electronic structure. We establish a robust platform for achieving SE for anisotropic 2D films. Using results from our calculations and orthotropic thin shell model we develop equivalent continuum structure (ECS) for PE and its allotropes upon bending. The developed ECS can be used for performing finite element simulations of PE films on substrates. [Preview Abstract] |
Wednesday, March 16, 2016 8:48AM - 9:00AM |
K16.00003: Quantum Hall Effect in Black Phosphorus/hBN Heterostructures Fangyuan Yang, Likai Li, Guo Jun Ye, Zuocheng Zhang, Zengwei Zhu, Wen Kai Lou, Liang Li, Kenji Watanabe, Takashi Taniguchi, Kai Chang, Yayu Wang, Xian Hui Chen, Yuanbo Zhang Black phosphorus field effect transistors have emerged as a new two-dimensional electron system (2DES) with high mobility. We achieved high mobilities by placing black phosphorus thin flakes on atomically flat hBN substrates. The mobility is further improved by placing a graphite back gate very close to the 2DES, which screens charged impurities. In this talk, we will present our observation of the integer quantum Hall effect in high mobility black phosphorus 2DEG. Temperature and angular dependent measurements reveal a wealth of information on the charge carriers in this new 2DES. [Preview Abstract] |
Wednesday, March 16, 2016 9:00AM - 9:12AM |
K16.00004: Fabrication of suspended few-layer black phosphorus nanopores and nanoribbons via electron beam nanosculpting Paul Masih Das, Gopinath Danda, William Parkin, Andrew Cupo, Neerav Kharche, Xi Ling, Shengxi Huang, Mildred Dresselhaus, Vincent Meunier, Marija Drndic We present nanopores, nanoribbons, and nanogaps in suspended few-layer black phosphorus (BP) flakes that have been realized using in situ transmission electron microscope nanosculpting. Few-layer BP flakes were first produced through a liquid exfoliation procedure and suspended on holey SiN$_{x}$ membranes. We investigate the structural characteristics of few-layer BP and further show the time-dependent properties of various nanostructures under exposure to an electron beam. It is shown that high-resolution structural modification of nanopores and nanoribbons can be achieved with nanometer-scale precision on timescales of a few minutes. We also used density functional theory to provide a model for the observed anisotropy in edge formation by computing energy barriers for various edge geometries. [Preview Abstract] |
Wednesday, March 16, 2016 9:12AM - 9:24AM |
K16.00005: Highly Anisotropic intrinsic electronic transport properties of monolayer and bilayer phosphorene from first principles$^{1}$ Zhenghe Jin, Jeffrey Mullen, Ki Wook Kim We present an analysis of the electron(hole)-phonon scattering in monolayer and bilayer phosphorene using first principles. Density Functional Theory (DFT) and Density Functional Perturbation Theory (DFPT) are used to calculate the scattering matrix elements and full band Monte Carlo carrier transport simulation is employed to obtain the intrinsic electron/hole mobility. Room temperature mobility and saturation velocity in monolayer and bilayer phosphorene are extracted and significant layer number dependence in the mobility is revealed which results from the carrier-phonon interaction matrix elements. The transport properties are also varied with the crystal orientation with anisotropy mobility mostly attributed to the anisotropic band structure and effective masses. Our calculation reveals monolayer phosphorene has anisotropic hole transport property with the room temperature mobility in the armchair direction (458 cm$^{2}$/Vs) about five times larger than in the zigzag direction (90 cm$^{2}$/Vs). For bilayer phosphorene, the mobility on both directions increases to 1610 cm$^{2}$/Vs and 760 cm$^{2}$/Vs along armchair and zigzag direction respectively. The increased mobility in bilayer is consistent with the experiments which revealed low field mobility of over one thousand in multiple layer phosphorene structure, which provides optimal material for channel in field-effect transistor and a good opportunity for high-performance p-type device. $^{1\, }$This work was supported, in part, by SRC/NRI SWAN. [Preview Abstract] |
Wednesday, March 16, 2016 9:24AM - 9:36AM |
K16.00006: Realize Dirac cones in compressed black phosphorus Li Yang, Ruixiang Fei, Vy Tran Using the k$\cdot $p theory and first-principles simulations, we predict that applying a moderate uniaxial or hydrostatic pressure (\textgreater 0.6GPa) on bulk or multilayer black phosphorus (BP) can diminish its bandgap and produce one-dimensional and even two-dimensional (2D) Dirac cones. Similar to topological insulators, these 2D Dirac cones result from two competing mechanisms: the unique linear band dispersion tends to open a gap via a ``pseudo-spin-orbit'' coupling, while the band symmetries preserve the material's gapless spectrum. In particular, these Dirac cones in BP are bulk states that do not require time-reversal symmetry, thus they can keep the high carrier mobility even in the presence of surface or magnetic perturbations. Finally, our predictions have been confirmed by recent experiments. [Preview Abstract] |
Wednesday, March 16, 2016 9:36AM - 9:48AM |
K16.00007: Extraordinary Bending Effects in MoS2, Phosphorene, and Graphene Nanoribbons Liping YU, Adrienn Ruzsinszky, John Perdew The two-dimensional (2D) materials show great potential for flexible electronics and energy applications. They have remarkable mechanical, electronic, thermal and optical properties, which are often coupled to each other. In this talk, we shall present our first principles study on the bending effects in the electronic structure of MoS$_2$, phosphorene, and graphene nanoribbons. We predict that mechanical bending, as a unique attribute of thin 2D materials, can be used to control conductivity and Fermi-level shift. We find that bending can control the charge localization of top valence bands in both MoS$_2$ and phosphorene nanoribbons. The donor-like in-gap edge-states of armchair MoS$_2$ ribbon and their associated Fermi-level pinning can be removed by bending. A bending-controllable new in-gap state and accompanying direct-indirect gap transition are predicted in armchair phosphorene nanoribbon. We demonstrate that such emergent bending effects are realizable in experiment and can be attributed to the highly non-uniform and enormously large local in-plane strains induced by bending. The bending stiffness as wells as the effective thickness of 2D materials are also derived from first principles. [Preview Abstract] |
Wednesday, March 16, 2016 9:48AM - 10:00AM |
K16.00008: Synthesis of black phosphorus films and particles by ultra-fast laser ablation Gang Qiu, Qiong Nian, Yexin Deng, Biwei Deng, Shengyu Jin, Adam Charnas, Gary Cheng, Peide Ye Few-layer black phosphorus (BP) has become one of top interests among various 2D materials because of its outstanding electrical and optical properties. However, availability of large size BP thin films stands as a major roadblock against further research and its applications. Here we report a method of synthesis BP films and particles by employing ultra-fast laser ablation. We demonstrated that arbitrary BP film patterns can be defined by laser direct writing. BP particles were also achieved as byproduct through manipulating laser power and frequency. Physical mechanism of laser ablation process was investigated, which also provides an optimizing strategy of improving BP thin film quality. [Preview Abstract] |
Wednesday, March 16, 2016 10:00AM - 10:12AM |
K16.00009: Quasiparticle Band Gap and Band Gap Reduction of Multi-Layer Black Phosphorus in an External Electric Field Vy Tran, Li Yang Few-layer black phosphorus has emerged as a promising 2D semiconductor due to its highly tunable, direct band gap. In this talk, we examine the tunability of the band gap with respect to the number of layers and the under an external electric field. Using the results of DFT as well as many-body GW calculations, we explore the mechanism for the band gap reduction when increasing the number of layers in black phosphorus. We propose a simple model that describes this behavior, allowing us to calculate the band gap of multi-layer black phosphorus under an external electric field. The results are checked against \textit{ab-initio} calculations, which shows excellent agreement. This allows us to overcome the limitations of DFT and predict the band gap for much larger layer numbers and electric field strength. [Preview Abstract] |
Wednesday, March 16, 2016 10:12AM - 10:24AM |
K16.00010: An Accurate and Compact Tight-binding Model for Phosphorene Carlos Paez, Ana Pereira, Eduardo Mucciolo In recent years, a variety of tight-binding models have been proposed for phosphorene. Although capturing key features such as the main band gap and the effective masses near the gamma point, they are not sufficiently accurate for the determination of electronic transport properties, particularly when probing states near the vicinity of extreme points of the valence and conductance bands. We propose a new tight-binding model parameterization based on the hybridization of s and p orbitals. For that purpose, we use theslater-koster method to construct a four-band model. We optimized the tight-binding parameters to fit the main features of ab-initio electronic band structure calculations and to reproduce the correct orbital composition at high-symmetry and low-symmetry points. Using this new tight-binding model, we compute some electronic transport properties of phosphorene ribbons in the presence of disorder. [Preview Abstract] |
Wednesday, March 16, 2016 10:24AM - 10:36AM |
K16.00011: Weak Localization in few layer Black Phosphorus Nathaniel Gillgren, Yanmeng Shi, Timothy Espiritu, Kenji Watanabe, Takahashi Taniguchi, Chun Ning (Jeanie) Lau Few-layer black phosphorus has recently attracted interest from the scientific community due to its high mobility, tunable band gap, and large anisotropy. Recent experiments have demonstrated that black phosphorus provides a promising candidate to explore the physics of 2D semiconductors. In this study we explore the magnetotransport of few-layer black phosphorus-boron nitride hetereostructure devices at low magnetic fields. Weak localization is observed at low temperatures. We extract the dephasing length and measure its dependence on temperature, carrier density and electric field. [Preview Abstract] |
Wednesday, March 16, 2016 10:36AM - 10:48AM |
K16.00012: Chemically Controlling Black Phosphorus Exfoliation to Achieve Variable-Sized Phosphorene Amy Ng, Thomas Sutto, Yexin Deng, Rhonda Stroud, Todd Brintlinger, Peide Ye, Nabil Bassim Phosphorene is the 2-dimensional form of phosphorus and a close relative of graphene. It has a nonzero fundamental band gap that gives rise to semiconductor properties, which makes it highly desirable for numerous applications in optoelectronics and as a replacement channel for conventional semiconductor devices. However, difficulties in isolating large area single-, few-, or multi-layer sheets are an impediment to realizing the aforementioned applications. We are investigating multiple chemical routes for optimal production of phosphorene sheets. Utilizing various solvent systems, ranging from a simple ethanol to dimethylformamide to more viscous ionic liquids, we have obtained flakes of differing thicknesses and sizes. We characterized the structure and composition of the resulting phosphorene sheets with aberration-corrected scanning transmission electron microscopy in addition to optical/macroscopic studies. Flake size, quality, and quantity obtained as a function of the solvent system, where factors such as viscosity, surface tension, chemical behavior, and degree of agitation, will be presented. [Preview Abstract] |
Wednesday, March 16, 2016 10:48AM - 11:00AM |
K16.00013: Negative differential resistance observed from vertical p$^{\mathrm{+}}$-n$^{\mathrm{+}}$ junction device with two-dimensional black phosphorous Daeyeong Lee, Young Dae Jang, Jaehwan Kweon, Jungjin Ryu, Euyheon Hwang, Won Jong Yoo A vertical p$^{\mathrm{+}}$-n$^{\mathrm{+}}$ homojunction was fabricated by using black phosphorus (BP) as a van der Waals two-dimensional (2D) material. The top and bottom layers of the materials were doped by chemical dopants of gold chloride (AuCl$_{\mathrm{3}})$ for p-type doping and benzyl viologen (BV) for n-type doping. The negative differential resistance (NDR) effect was clearly observed from the output curves of the fabricated BP vertical devices. The thickness range of the 2D material showing NDR and the peak to valley current ratio of NDR are found to be strongly dependent on doping condition, gate voltage, and BP's degradation level. Furthermore, the carrier transport of the p$^{\mathrm{+}}$-n$^{\mathrm{+}}$ junction was simulated by using density functional theory (DFT) and non-equilibrium Green's function (NEGF). Both the experimental and simulation results confirmed that the NDR is attributed to the band-to-band tunneling (BTBT) across the 2D BP p$^{\mathrm{+}}$-n$^{\mathrm{+}}$ junction, and further quantitative details on the carrier transport in the vertical p$^{\mathrm{+}}$-n$^{\mathrm{+}}$ junction devices were explored, according to the analyses of the measured transfer curves and the DFT simulation results. [Preview Abstract] |
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