Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B12: Transport, Optical, and Mechanical Properties of Carbon Nanotubes |
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Sponsoring Units: DCMP Chair: Ryuichi Tsuchikawa, University of Utah Room: BCEC 153A |
Monday, March 4, 2019 11:15AM - 11:27AM |
B12.00001: Reconfigurable Carbon Nanotube Network Devices Prathamesh Dhakras, Samuel LaGasse, Takashi Taniguchi, Kenji Watanabe, Sheng Wang, Lian-Mao Peng, Ji Ung Lee Semiconducting single-walled carbon nanotubes (SWNTs) are an attractive channel material for a wide range of applications, from flexible, low cost printed electronics to high performance field effect transistors. Though recent advances in developing high purity semiconducting SWNT solutions have yielded devices with excellent on/off ratios and improved ON currents, determining the true nature of conduction of a network with a mixture of metallic and semiconducting nanotubes remains a challenge. Here, we fabricated split-gate devices that can reconfigure as either a metal-oxide-semiconductor field effect transistor (MOSFET) or a p-n diode. The spacing between the split gates was varied from 10 μm down to 100 nm to allow a detailed comparison between properties of unipolar conduction (MOSFET) and that of ambipolar transport dominated by minority carriers (p-n Diode). In addition, we varied the metallic concentration of SWNTs in the network channel. We show that the conduction is determined not only by the metallic concentration, but also by the environment that acts as strong generation and recombination centers. |
Monday, March 4, 2019 11:27AM - 11:39AM |
B12.00002: Magneto-transport in Type-Enriched Single-Wall Carbon Nanotube Networks Xuan Wang, Weilu Gao, Xinwei Li, Qi Zhang, Sébastian Nanot, Erik H Haroz, Junichiro Kono, William Rice Single-wall carbon nanotubes (SWCNTs) exhibit a wide range of chirality-dependent physical phenomena. This dependency complicates in-depth understanding of ensemble behavior, since nanotube networks contain numerous chiralities. In particular, electronic-type mixing greatly hinders the development of a comprehensive picture of SWCNT ensemble electrical transport. Here, we systematically study temperature-dependent magnetoconductivity (MC) in semiconductor and metal SWCNTs. In the semiconductor-enriched network, we observe 2D variable-range hopping conduction from 5 to 290 K. Low-temperature MC reveals a large, negative MC from which we determine the wavefunction localization length and Fermi energy density of states. In contrast, the metal-enriched film shows positive MC that increases with decreasing temperature, a behavior we attribute to 2D weak localization. Using this model, we determine carrier phase coherence and describe the temperature-dependent conductivity. These extensive transport measurements on type-enriched SWCNTs provide insights, which pave the way for nanotube solid-state devices. |
Monday, March 4, 2019 11:39AM - 11:51AM |
B12.00003: Universal interaction-driven gap in metallic carbon nanotubes Mitchell J. Senger, Daniel McCulley, Lee Aspitarte, Neda Lotfizadeh, Vikram Deshpande, Ethan D. Minot Metallic carbon nanotubes (m-CNTs) exhibit a remarkably large energy gap for electronic excitations. The gap often exceeds 100 meV when the m-CNT is suspended in free space, but the gap disappears when the m-CNT lies on a metal surface. The theoretical description of this gap remains controversial and more experiments are needed. We have built ultra-clean suspended CNT devices from CNTs of known diameter and chiral angle. The CNT chirality is identified with spectrally resolved scanning photocurrent microscopy and the energy gap is determined by measuring thermally-activated electron transport. Our results show that the gap scales exactly as 1/D, with no dependence on chiral angle. We also demonstrate that the gap can be tuned by submerging the suspended m-CNT in dielectric liquids. Our results put new constraints on competing theoretical descriptions of a Mott insulator state versus an excitonic insulator state. |
Monday, March 4, 2019 11:51AM - 12:03PM |
B12.00004: Field-Enhanced Exciton Dissociation in Carbon Nanotube Photodiodes Daniel McCulley, Mitchell J. Senger, Andrea Bertoni, Ethan D. Minot Low-dimensional materials may be useful for building solar cells that harness carrier multiplication and circumvent the Shockley-Queisser limit. For example, quantum dot solar cells with an internal quantum efficiency (IQE) > 100% have been reported. In this work, we search for carrier multiplication effects in CNTs. We use individually-contacted, ultra-clean, suspended, semiconducting carbon nanotubes of known chiral index. Previous work on this system showed an IQE ~ 30% when the built-in electric field was ~ 4 V/um. Here we report an IQE ~ 80% when the electric field is increased to ~ 15 V/μm. At these high fields, photocurrent spectroscopy reveals extreme broadening of low-energy exciton peaks. We compare our results to theoretical predictions for field-induced exciton dissociation in CNTs, and develop a framework to describe the energy dissipation pathways. |
Monday, March 4, 2019 12:03PM - 12:15PM |
B12.00005: Tip-enhanced Raman spectroscopy of CNTs in a picocavity Kai Nan, Sharad Ambardar, Dmitri Voronine Carbon nanotubes (CNTs) have optical and electronic properties which allow promising applications. Conventional atomic force microscopy (AFM) and tip-enhanced Raman scattering (TERS) provide topographic and chemically specific images that reveal nanoscale structure-functional relationships. By placing CNTs in a picocavity formed by a plasmonic scanning probe tip and a metallic surface we control the relative intensities of various CNT signals. We investigate the tip-sample distance dependence in the nanometer classical and sub-nanometer quantum plasmonic regimes. This quantum picophotonics approach provides a new platform for exploration of enhanced properties of low dimensional materials. |
Monday, March 4, 2019 12:15PM - 12:27PM |
B12.00006: Exciton Relaxation in Carbon Nanotubes via Electronic-to-Vibrational Energy Transfer Kirill Velizhanin Covalent functionalization of semiconducting single-wall carbon nanotubes (SWCNTs) can introduce new localized photoluminescent states that are strongly red-shifted from the emission commonly observed from the nanotube band-edge E11 exciton state. In addition to being the source of new photophysical behaviors, these states are drawing significant interest as the basis for emerging functionality. A particularly important feature of such exciton localization at defect sites is that, because the exciton is no longer free to diffusively sample photoluminescent quenching sites along the length of the SWCNT, its lifetime is significantly extended. |
Monday, March 4, 2019 12:27PM - 12:39PM |
B12.00007: Binding Energy and Lifetime of Excitons in Metallic Nanotubes Lei Shan, Megha Agarwal, Eugene Mishchenko Due to the large screening of Coulomb interaction between electrons in higher dimensions in metallic materials, a bound state of electron-hole pair cannot be formed. However, in lower dimensional materials such as carbon nanotubes due to less effective screening of electrons allows the formation of bound state of electron-hole pair whose radius, Rex » R. This is particularly unique to metallic nanotubes in a sense that the problem of describing excitons can now be considered 1D as compared to semiconducting nanotubes where exciton radius Rex ∼ R and excitons are neither 1D nor 2D. We are thus able to determine the binding energy of excitons in metallic nanotubes, is about 0.08 v/R. 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. |
Monday, March 4, 2019 12:39PM - 12:51PM |
B12.00008: Organic molecule adsorption effects on air-suspended carbon nanotubes Shunsuke Tanaka, Akihiro Ishii, Yuichiro K. Kato Environmental screening effects are large in carbon nanotubes due to their atomically thin nature, and therefore it is possible to control the optical properties with molecular adsorption [1,2]. Here, we investigate adsorption effects of copper phthalocyanine molecules on excitons and trions in air-suspended carbon nanotubes. By averaging the photoluminescence excitation spectra for tubes with the same chiralities, we observe that the exciton emission energy redshifts gradually with molecular deposition thickness. The trion emission is also observed at large deposition amounts, which could be due to charge transfer between the phthalocyanine molecules and carbon nanotubes. Analyzing the spectra for individual tubes, we find a good correlation between the exciton-trion energy separation and the exciton emission energy. |
Monday, March 4, 2019 12:51PM - 1:03PM |
B12.00009: Interlayer interactions and radial breathing mode in double- and triple-walled carbon nanotube bundles Jia Wern Hue, Thomas Ch Hirschmann, Stephen K. Doorn, Yoong Ahm Kim, Newton M Barbosa Neto, Paulo T Araujo A double-walled carbon nanotube (DWNT) can be considered a inner single-walled carbon nanotube (SWNT) protected by an outer SWNT. Likewise, a triple-walled carbon nanotube (TWNT) can considered an inner DWNT encapsulated by an outer SWNT. The signature in resonant Raman spectroscopy for carbon nanotubes is the radial breathing mode (RBM). For radial breathing modes (RBM), double- and triple-walled carbon nanotubes can be considered as coupled oscillators. The RBM frequency, ωRBM, is senstive to environmental factors and interlayer interactions. For interlayer interactions, it is necessary to take into account curvature effects, particularly for smaller tubes, whether the constituent tubes are commensurate, and whether the inner tubes are really isolated from the environment from the outer tubes. Another matter of interest is how do the magnitudes of the interlayer interactions compare. Resonant Raman spectra of a DWNT bundle and TWNT bundle were taken. From those spectra, chiral indices were assigned and tube diameters calculated. Then, a comparison to the SWNT ωRBM was made and the questions presented above answered. |
Monday, March 4, 2019 1:03PM - 1:15PM |
B12.00010: Energy barrier for carbon nanotube collapse Rodrigo Capaz, Rafael Rodrigues Del Grande, Alexandre Fonseca Small-diameter carbon nanotubes have circular cross section shapes, but the ground state of large diameter tubes correspond to a collapsed structure, stabilized by the van der Waals attraction of opposite sides of the nanotube wall. For those tubes, the circular cross section shape is metastable and it is interesting to investigate the energy barrier for jumping from one configuration to another. Previous theoretical works calculate the energy barrier by considering a transition pathway in which the nanotube collapses uniformly along its length, normally using periodic boundary conditions along the nanotube axis. This assumption is unphysical since it would give an infinite barrier for a nanotube of infinite length. In this work, we calculate the true energy barrier for carbon nanotube collapse by considering a transition pathway that consists of a local deformation that propagates itself along the carbon nanotube axis. This leads to finite and physically meaningful energy barriers in the limit of infinite nanotubes. For typical nanotube diameters, the energy barriers are so large than effectively prevent the collapse induced by temperature of an infinite nanotube. We also perform classical molecular dynamics that confirm these results. |
Monday, March 4, 2019 1:15PM - 1:27PM |
B12.00011: Snap-Through Buckling Bi-Stability in Suspended Carbon Nanotube Resonators Yuval Yaish, Tal Tabachnik, Sharon Rechnitz, Michael Shlafman, Shlomo Shlafman
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Monday, March 4, 2019 1:27PM - 1:39PM |
B12.00012: Solution Sorting of 10 µm Long Single-Walled Carbon Nanotubes Peng Wang, YuHuang Wang Single-walled carbon nanotubes (SWCNTs) that are ultralong (>10 µm) and electronically pure may enable stretchable thin film transistors, ballistic conductors, and ultra-strong fibers. However, nanotubes are cut to short pieces (typically less than 1 µm) by sonication during solution processing. In this presentation, I will discuss an invention from our lab called “superacid-surfactant exchange (S2E)” which allows for non-destructive dispersion and scalable sorting of ultralong SWCNTs in aqueous solutions. The length of the isolated SWCNTs readily reaches 10 µm, with a narrow distribution. We further show that these ultralong nanotubes can be further sorted by electronic type to attain an electron mobility exceeding 90 cm2 V-1 s-1 in fabricated thin film transistors. |
Monday, March 4, 2019 1:39PM - 1:51PM |
B12.00013: Synthesis and Characterization of Single Walled Carbon Nanotubes (SWNT) Through Direct Decomposition Ferrocene Thushani De Silva, Dinuka Har Gallaba, Robinson Karunanithy, Milinda Wasala, Xianfeng Zhang, Shifan Li, Iskinder Arsano, Pooplasingam Sivakumar, Mesfin Tsige, Xingmao Ma, aldo megone, Saikat Talapatra Carbon based nanostructures, specifically carbon nanotubes due to their unique surface adsorption properties can become the choice materials for several applications. Here we present our results on synthesis and characterization of single walled carbon nanotubes (SWNT) through direct decomposition of metallocene. Specifically, ferrocene was utilized in this study. The effect of growth conditions on physical properties of these SWNT materials were studied in detail through volumetric gas adsorption measurements, Raman spectroscopic characterization as well as UV-Vis spectroscopy measurements. The correlation of some of the physical properties as it related to the growth conditions will be discussed in light of these characterization results. |
Monday, March 4, 2019 1:51PM - 2:03PM |
B12.00014: Measuring the Electron Beam Induced Plasmon Response in Single-Walled Carbon Nanotube Devices Matthew Zotta, Sharadh Jois, Prathamesh Dhakras, Ji Ung Lee In this work, we examine the transport properties of individual single-walled carbon nanotubes, configured with split gates, as it is excited by a finely focused electron beam. We conduct the experiment in a scanning electron microscope (SEM) equipped with multiple nanoprobes. We measure the current from both ends of the nanotube as the electron beam is rastered to determine the mechanism of transport. Our analysis shows that the energetic beam launches plasmon excitations along the nanotube, which we measure as a sharp change in the current. The sign of the current on both ends of the nanotube is the same, which rules out other competing mechanisms, including electron-hole generation and thermal effects. We examine the transport properties as a function of beam energy and position, and nanotube doping. |
Monday, March 4, 2019 2:03PM - 2:15PM |
B12.00015: Intrinsically Ultrastrong Plasmon-Exciton Interactions in Crystallized Films of Carbon Nanotubes Abram Falk, Po-Hsun Ho, Damon Farmer, Phaedon Avouris We show that carbon nanotubes can be crystallized into chip-scale, two-dimensionally ordered films and that this new material enables intrinsically ultrastrong emitter-cavity interactions: rather than interacting with external cavities, nanotube excitons couple to the near-infrared plasmon resonances of the nanotubes themselves [1]. Our polycrystalline nanotube films have a hexagonal crystal structure, ~25 nm domains, and a 1.74 nm lattice constant. With this extremely high nanotube density and nearly ideal plasmon-exciton spatial overlap, plasmon-exciton coupling strengths reach 0.5 eV, which is 75% of the bare exciton energy and a near record for room-temperature ultrastrong coupling. Crystallized nanotube films provide a compelling foundation for high-ampacity conductors, low-power optical switches, and tunable optical antennas. |
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