Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session P40: Properties of Nanowires, Nanorods, and Nanotubes |
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Sponsoring Units: DCMP Chair: Xuan Gao, Case Western Reserve University Room: LACC 501C |
Wednesday, March 7, 2018 2:30PM - 2:42PM |
P40.00001: Gallium Nitride Nanowires in Selected-Area Growth Arrays Measured via Optical Bragg Scattering for Mass Sensing John Houlton, M. Brubaker, K. Bertness, Charles Rogers We report the use of optical Bragg scattering to measure the mechanical resonance frequencies and quality factors (Q) of gallium nitride (GaN) nanowires (NWs) in selected-area growth arrays with applications as attogram-level mass sensors. The GaN NWs are grown by catalyst-free molecular beam epitaxy on silicon (111) wafers. Hexagonal arrays of approximately 100 GaN NWs with pitch spacings of 350-1100 nm have been prepared. Optical Bragg scattering from these arrays has been measured to be in good agreement with theoretical designs. The NWs contained in such arrays have diameters ranging from 100-300 nm and lengths from 3-10 μm. A HeNe laser operating at 633 nm and 5 mW of optical power is used to perform Bragg scattering homodyne detection to passively read out the thermally induced Brownian mechanical motion of the NWs. The first order cantilever-mode mechanical resonance frequencies of these NWs have been measured to be between 2-12 MHz. Our readout scheme allows the simultaneous detection of all lowest order mechanical resonances in a given array, enabling the simultaneous monitoring of roughly 100 mass sensors in a 10-100 μm2 area. Additionally, we investigate correlations among NW resonances. |
Wednesday, March 7, 2018 2:42PM - 2:54PM |
P40.00002: A Molecular Dynamics Study of the Brittle-to-Ductile Transition of Silicon Nanowires Using the MEAM Potential Wenting Xu, Woo kyun Kim Silicon nanowires (NWs) are novel nano-scale structures with a variety of potential applications such as electronic and optoelectronic devices including high-precision sensors and actuators. Recent experiments have found that Si NWs exhibit a strong size-dependent brittle-to-ductile transition (BDT) such that small-diameter Si NWs can sustain large plastic deformations at room temperature. In this study, the molecular dynamics (MD) methodology using the modified embedded atom method (MEAM) potential is employed to unveil the fundamental mechanisms governing the size-dependent BDT of Si NWs. The MD simulations mimic the uniaxial tensile test along the [110] direction on Si NWs with diameters of 2 to 7 nm at various temperatures and strain rates. The simulations test the validity of many different parameter sets of the MEAM potential for Si and the results show that only a certain type of MEAM parameter sets can reproduce the size-dependent BDT phenomenon. A subsequent systematic analysis reveals the key parameters and functional forms of MEAM that strongly affect this observation. This study also discusses the connection between the critical MEAM parameters and their physical meanings and ultimately postulates the main atomic-scale mechanisms of the BDT of Si NWs. |
Wednesday, March 7, 2018 2:54PM - 3:06PM |
P40.00003: Electric Polarization and End States in Boron Nitride Nanoribbons Fangzhou Zhao, Ting Cao, Yea-Lee Lee, Steven Louie Using first-principles calculations, we find that armchair BNNRs have an intrinsic electric polarization along the periodic direction for different ribbon widths. Like finite-length armchair graphene nanoribbons, finite-length armchair BNNRs also have end states at their zigzag ends. We are able to classify the end states by applying an electric field to offset the intrinsic polarization in BNNRs. We calculate the Zak phase of armchair BNNRs (whose unit cells do not have inversion or mirror symmetry) as a function of the width of the ribbon. We also study the relation between the Zak phase and the existence of end states. |
Wednesday, March 7, 2018 3:06PM - 3:18PM |
P40.00004: Optoelectronic properties of tungsten disulfide nanotube p-n junctions Yijin Zhang, Masaru Onga, Feng Qin, Wu Shi, Alla Zak, Reshef Tenne, Jurgen Smet, Yoshihiro Iwasa Due to their favorable and rich electronic and optical properties, group-VI-B transition-metal dichalcogenides (TMDs) have attracted considerable interest. They have earned their position in the materials portfolio of the spintronics and valleytronics communities. The electrical performance of TMDs is enhanced by rolling up the two-dimensional (2D) sheets to form quasi-one-dimensional (1D) tubular structures. The fabrication of p-n junctions out of these tubular TMDs would boost their potential for optoelectronic devices as such junctions represent a fundamental building block. Here, we report the realization of a p-n junction out of a single, isolated WS2-nanotube (WS2-NT). Light-emitting diode operation and photovoltaic behavior were observed based on such p-n junctions. The emitted light as well as the photovoltaic effect exhibit strong linear polarization characteristics due to the quasi-1D nature. The external quantum efficiency for the photovoltaic effect reaches a value as high as 4.8 %, exceeding by far that of 2D TMDs and even approaching the internal quantum efficiency of the 2D TMDs. This efficiency improvement indicates that TMD nanotubes are superior candidates over 2D TMDs for optoelectronic applications. |
Wednesday, March 7, 2018 3:18PM - 3:30PM |
P40.00005: Imaging effects of interactions in semiconducting nanowires coupled to quantum dots. Jonathan Reiner, Abhay Nayak, Aviram Steinbook, Nurit Avraham, Jung-Hyun Kang, Stephan Plugge, Yuval Oreg, Hadas Shtrikman, Haim Beidenkopf Electrons confined to one dimension exhibit various counter-intuitive phenomena such as charge fractionalization, spin-charge separation, and Majorana end modes induced at nanowires rendered topologically superconducting. We perform spectroscopic mappings of the electronic states in semiconducting InAs nanowires through scanning tunneling microscopy. We identify an indirect charging mechanism where in-gap resonances act as a switch for the conductance of the one-dimensional states, resulting in negative differential conductance. The interaction between the resonances and the continuum is mediated by quantum dots that naturally form both in the gold droplets used to catalyze the nanowire growth as well as in aluminum droplets epitaxially grown on the nanowire side facets. The detection of this phenomena is enabled by maintaining the MBE grown nanowires under ultra-high vacuum. This allows us to visualize the electronic spectrum through local spectroscopy. This technology paves the way for the study of additional exotic phenomena in one dimensional nanowires such as induced topological superconductivity and Majorana end modes therein. |
Wednesday, March 7, 2018 3:30PM - 3:42PM |
P40.00006: Ultrafast Dynamics in Multiferroic BaTiO3-BiFeO3 (BTO-BFO) and PZT Nanorods Rathsara R. H. H. Mudiyanselage, Brenden Magill, John Burton, Giti Khodaparast, Han-Byul Kang, Min Gyu Kang, Deepam Maurya, Shashank Priya Multiferroic materials offer unique features, making them ideal candidates for many applications in photonics and spintronics. One such example is a four-state memory, where a reading and writing of a magnetic bit is done by a voltage pulse instead of a magnetic-field, allowing for faster, smaller, and more energy-efficient data-storage technologies. Multiferroic hetrostructures such BaTiO3-BiFeO3 (BT-BFO) and PZT nanorods are promising candidates for these applications as they exhibit enhanced magnetic and ferroelectric properties, improved magnetoelectric coupling, and enhanced switching response of their electrical polarization and magnetic orientations. In this study, we investigate ultrafast optical processes of BT-BFO and PZT nanorods with time resolved pump-probe spectroscopy. We observe tunability in ultrafast Time Resolved Differential Reflectivity (TRDR) dynamics, in a broad optical region (700 nm and 1000 nm). The observed tunability was enhanced by applying magnetic fields where the magneto-electric couplings can play a role. |
Wednesday, March 7, 2018 3:42PM - 3:54PM |
P40.00007: Diameter dependent superconductivity in individual WS2 nanotubes Feng Qin, Toshiya Ideue, Wu Shi, Xiao-Xiao Zhang, Masaro Yoshida, Alla Zak, Reshef Tenne, Tomoka Kikitsu, Daishi Inoue, Daisuke Hashizume, Yoshihiro Iwasa Transition metal dichalcogenides nanotube is a fascinating platform for the research of superconductivity due to its unique dimensionality and geometry. Especially, novel chiral superconducting transport originating from the nanotube chirality has been discovered recently [F. Qin et al., Nature Commun. 8, 14465 (2017)]. Here we report the diameter dependent superconductivity in individual WS2 nanotubes. The superconductivity is realized by electrochemical doping with ionic gate, in which the diameter of nanotube is estimated from the periodic oscillating magnetoresistance, known as Little Parks effect. The critical temperature of superconductivity displays a systematic behavior as a function of the diameter. The present results might offer the crucial information to understand the microscopic mechanism of superconductivity in individual nanotube. |
Wednesday, March 7, 2018 3:54PM - 4:06PM |
P40.00008: Conductivity Measurements in Hexagonal-Core Silicon Nanowire Transistors Marc Collette, Oussama Moutanabbir, Alexandre Champagne The ability to control both the channel conductivity and the contact resistance of a silicon nanowire (SiNW) field-effect transistor by modulating the crystal phase during growth could open the door to new applications and performance tunability. Here, we present transport data in polytypic hexagonal-core cubic-shell single SiNW transistors and extract both their contact and channel resistance, comparing them to equivalent single-crystal (cubic) counterpart. A tunable volume of ordered stacking faults (hexagonality) during their VLS growth were introduced in the SiNW. We show that in these hexagonal-core nanowires there is a decrease in channel conductivity, mainly due to a reduction of charge carriers available in the silicon channel (from 1019 cm-3 in single-crystal to 1017 cm-3 at high hexagonal volume). We also demonstrate an increase in Schottky barrier height between the metal contacts and the hexagonal-core SiNW as a function of the hexagonal volume fraction (from 0.54 eV to 0.67 eV). |
Wednesday, March 7, 2018 4:06PM - 4:18PM |
P40.00009: A Scalable and Patternable Method for the Fabrication of Vertically Aligned BN and BN/C Nanofiber Array Hu Long, Thang Pham, Zhen Guo, Hiroya Ishida, Aiming Yan, Wu Shi, Sally Turner, Stephen Gilbert, Alex Zettl There is an increasing amount of research interest in one dimensional boron nitride (BN) nanomaterials due to their outstanding mechanical, electrical and thermal properties. However, vertically aligned BN nanotubes and nanofibers are difficult to synthesize and are rarely reported. Here, large scale vertically aligned BN and BN/C nanofiber arrays were successfully fabricated through a cost-effective top-down synthesis approach. The process mainly consists of four critical steps including standard lithography, oxygen plasma etching, carbonization and BN coating or conversion. Vertically aligned BN nanofibers with a diameter around 20-50 nm and high aspect ratio are uniformly produced over large area. The simplicity and scalability of this process makes the process highly controllable and reproducible. The as-synthesized vertically aligned BN and BNC nanofibers have outstanding thermal, field emission properties, are possible candidates for next-generation thermal interface and field emission materials. |
Wednesday, March 7, 2018 4:18PM - 4:30PM |
P40.00010: Growth and Charaterization of templated InAs Nanowires Kristopher Cerveny, Martin Friedl, Pirmin Weigele, Taras Patlatiuk, Gozde Tutuncuoglu, Heidi Potts, Anna Fontcuberta i Morral, Dominik Zumbuhl We have investigated InAs nanowires (NWs) grown epitaxially on horizontal templates with the goal of defect-free NWs for spintronics and quantum computation. We outline a proof-of-concept for this novel wire architecture including a gating scheme and a recipe for ohmic contacts based on sulfur passivation and angle evaporation. We present 2- and 4-wire measurements in magnetic fields at room temperature and down to 1.5 K. We obtain ~10 kOhm contact resistances and a linear scaling of wire resistance over lengths exceeding 10 um for bulk Si doping. Weak localization measurements with theory fits in the dirty-metal regime allow extraction of coherence and spin-orbit lengths as well as mean free path. Templated growth allows for scalable, top-down and on-demand placing and networking of NWs into 2D architectures as well as stacking of wires into parallel double or multiwire layouts, thus potentially providing a platform for Majorana fermions and parafermions1 for topological qubits. |
Wednesday, March 7, 2018 4:30PM - 4:42PM |
P40.00011: Torsional Resonators Based on Inorganic Nanotubes Roi Levi, Yiftach Divon, Dan Yudilevich, Dmitri Golberg, David Teich, Gotthard Seifert, Reshef Tenne, Assaf Ya’akobovitz, Ernesto Joselevich The use of various inorganic nanostructures such as nanotubes (INT) and 2D sheets in nano-electro-mechanical systems (NEMS) is the subject of intensive research in recent years. WS2 nanotubes exhibit superior mechanical properties, interesting stick-slip mechanical phenomena1, significant field-effect mobility, high current carrying capacity2 and thus are a natural candidate for electro-mechanical devices. |
Wednesday, March 7, 2018 4:42PM - 4:54PM |
P40.00012: Study of optical anisotropy in a quasi-1D crystal, BaTiS3 Shanyuan Niu, Graham Joe, Huan Zhao, Matthew Mecklenburg, Han Wang, Mikhail Kats, Jayakanth Ravichandran Optical anisotropy is a key element to control the polarization of light in polarizing optics, light modulators, imaging and communication systems. While artificial form birefringent architectures can possess larger optical anisotropy than natural anisotropic crystals, their deployment is limited by the demanding fabrication. We demonstrate the realization of giant optical anisotropy via engineering the polarizability tensor in a natural material, BaTiS3, which has a highly anisotropic quasi-1D structure and features easily accessible in-plane anisotropy. We report the observation of a large, broadband infrared birefringence and linear dichroism. As-grown crystals demonstrate strong dichroism with two distinct optical absorption edges for linear polarization along two crystallographic directions. The birefringence magnitude of BaTiS3 is compared with various widely used natural anisotropic crystals. |
Wednesday, March 7, 2018 4:54PM - 5:06PM |
P40.00013: Binding energy and lifetime of excitons in metallic nanotubes Lei Shan, Megha Agarwal, Eugene Mishchenko The difficulty of describing excitons in semiconducting SWNTs analytically lies with the fact that excitons can neither be considered strictly 1D nor 2D objects. However, the situation changes in the case of metallic nanotubes where, by virtue of screening from gapless metallic subbands, the radius of the exciton becomes much larger than the radius of the nanotube Rex » R. We develop the theory of excitons in metallic nanotubes, determine their binding energy and show that it represents about 0.1 of the band gap, in agreement with the existing experimental data. Additionally, because of the presence of the gapless subbands, there are processes where bound excitons are scattered into unbound electron-hole pairs belonging to the gapless subbands. Such processes lead to a finite exciton lifetime and the broadening of its spectral function. We calculate the corresponding decay rate of the excitons. |
Wednesday, March 7, 2018 5:06PM - 5:18PM |
P40.00014: Direct Mapping of Reduced Resistivity and Electrical Noise Sources in Metallic Carbon Nanotube-Metal Hybrid Thin Films Narae Shin, Jeongsu Kim, Shashank Shekhar, Seunghun Hong We report a method for the nanoscale mapping of localized resistivity and noise source activities in metallic carbon nanotube (CNT)-metal hybrid thin films. In this work, a gold thin film was deposited on metallic CNT networks, and a current-noise map on the hybrid thin films was measured and analyzed, enabling the study of noise source activities in the films. The regions with CNTs embedded under the gold thin film showed the significantly reduced resistivity and noise source densities compared with pristine gold films, showing that not only conductivity but also noise characteristics of metallic electrodes can be improved by embedding CNTs in the hybrid film. Interestingly, we found distinctive correlations between the resistivity and noise source density on both CNT and gold film regions, implying that CNT-gold hybrid thin films have a conduction and noise characteristics like diffusive conductors. This method provides valuable insights about the charge transports in metallic CNT-metal hybrid films and can be utilized for various basic researches and practical applications using carbon nanotube-based devices. |
Wednesday, March 7, 2018 5:18PM - 5:30PM |
P40.00015: Plasmonic Band Structures in Doped Graphene Tubes Yingying Zhu, Yu Zhou, Kun Zhang, Hongwei Wu, Ruwen Peng, Renhao Fan, Mu Wang In this work, we present theoretically the transport of plasmonic waves in doped graphene tube, which is made by rolling planar graphene sheet into a cylinder and periodic doping is applied on it. It is shown that periodic modulation of the Fermi level along the tube can open gaps in the dispersion relations of graphene plasmons and eventually create plasmonic band structures. The propagation of graphene plasmons is forbidden within the bandgaps; while within the band, the plasmonic waves present axially-extended field distributions and propagate along the tubes, yet well confined around the curved graphene surface. Furthermore, the bandgaps, propagation constants and propagation lengths of the modes in plasmonic band structures are significantly tuned by varying the Fermi level of graphene, which provides active controls over the plasmonic waves. Our proposed structures here may provide an approach to dynamically control the plasmonic waves in graphene-based subwavelength waveguides. |
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