Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session T7: Focus Session: Carbon Nanotubes: Transport and Electronic Properties |
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Sponsoring Units: DMP Chair: Phillip Collins, University of California, Riverside Room: 303 |
Thursday, March 21, 2013 8:00AM - 8:12AM |
T7.00001: Electrical Transport in Graphene-Carbon~nanotube Junctions Jhao-Wun Huang, Cheng Pan, Hang Zhang, Yongjin Lee, Fenglin Wang, Lei Jing, Marc Bockrath, Chun Ning Lau We fabricate suspended~graphene-carbon nanotube hybrid junctions by~transferring monolayer graphene sheets onto~single-walled carbon~nanotubes that are synthesized by chemical vapor deposition, and etching in hydrofluoric acid. The devices are measured as a function of magnetic field, gate voltage and electric field. We will present our latest transport data that will be~compared with theoretical models. [Preview Abstract] |
Thursday, March 21, 2013 8:12AM - 8:24AM |
T7.00002: Quasiparticle and exciton renormalization effects in carbon nanotubes near metallic surfaces Catalin Spataru We study theoretically the influence of a metallic surface on electron excitations (quasiparticles and excitons) in carbon nanotubes. Long-range polarization effects are included in the calculations using many-body \textit{ab initio} approaches such as the GW approximation [2] for the electron self-energy and the Bethe-Salpeter equation [3] for excitonic effects. In the case of semiconducting carbon nanotubes and when charge transfer effects between nanotube and metal are not important, we find that the image charge effect can lead to significant renormalization of the quasiparticle energies in nanotubes even for an apparent height (of the nanotube relative to the metallic surface) of the order of nm (in agreement with experiment [1]). The calculations reveal the important role played by the intrinsic dielectric screening properties of the nanotubes in establishing these renormalization effects. Also, we find that the optical gap of the nanotubes is barely affected by the metallic surface due to the weaker interaction between the exciton transition dipole in the nanotube and its induced image in the metallic surface.. [1] H. Lin et al, \textit{Nature Mater}. \textbf{9}, 235 (2010). [2] M.S. Hybertsen and S.G. Louie, \textit{Phys. Rev. B} \textbf{34}, 5390 (1986). [3] M. Rohlfing and S.G. Louie, \textit{Phys. Rev. B} \textbf{62}, 4927 (2000). [Preview Abstract] |
Thursday, March 21, 2013 8:24AM - 8:36AM |
T7.00003: Chirality dependence of exciton diffusion in air-suspended single-walled carbon nanotubes A. Ishii, A. Yokoyama, M. Yoshida, T. Shimada, Y. K. Kato In single-walled carbon nanotubes, exciton diffusion affects the photoluminescence quantum efficiency through substrate- and defect-induced nonradiative decay of excitons, and therefore quantitative characterization of exciton diffusion is important. In the case of air-suspended nanotubes, exciton diffusion lengths can be determined by analyzing the dependence of photoluminescence intensity on nanotube length.\footnote{S. Moritsubo \textit{et al.}, Phys. Rev. Lett. 104, 247402 (2010).} As this method requires $\sim$30 nanotubes for a particular chirality, we have constructed an automated micro-photoluminescence system to characterize air-suspended carbon nanotubes. A three-dimensional programmable stage is used to automatically locate and list the positions of bright nanotubes. Excitation wavelength, intensity, and polarization angle are automatically controlled to fully characterize these nanotubes. Using this system, measurements on hundreds of as-grown air-suspended carbon nanotubes are performed, and data from high quality individual tubes are selected to investigate the chirality dependence of exciton diffusion length. [Preview Abstract] |
Thursday, March 21, 2013 8:36AM - 9:12AM |
T7.00004: Growth Mechanism of Well Aligned Semiconducting Single-walled Carbon Nanotubes Invited Speaker: Jie Liu Even though the devices made from individual nanotubes have shown outstanding performances such as high mobility, high current, high thermal conductivity, good chemical and mechanical stability, the high hope for the next generation of carbon nanotube based electronics is hampered by several major problems. Among them are the lack of reliable methods to control the alignment and position of nanotubes as well as and perhaps most problematically, the simultaneous growth of nanotubes with different chiralities, yielding random mixtures of metallic and semiconducting nanotubes. Even though the post-growth separation of metallic from semiconducting SWNTs have made good progress, the alignment and assembly of the separated nanotubes into devices are still challenging and not suitable for large scale fabrication. Consequently, a method that can directly produce well aligned arrays of pure semiconducting nanotubes is thought to be the ideal choice for large scale fabrication of nanotubes FETs. In this talk, we show that such a method is not a dream. Recently we have successfully synthesized high-density, horizontally aligned SWNTs on quartz wafers, and the thin-film transistors (TFTs) based on this SWNT array show high on-driving current density (up to $\sim$220 $\mu$A/$\mu$m). Additionally, through systematic studies, we proposed and confirmed the high growth selectivity originates from the etching effect and chemical reactivity difference of metallic and semiconducting nanotubes. Three important rules were summarized for achieving a high selectivity in growing semiconducting nanotubes by systematically investigating the relationship among water concentration, carbon feeding rate and the percentage of semiconducting nanotubes in the produced SWNT arrays. Furthermore, these three rules can also be applied to the growth of random SWNT networks on silicon wafers. This understanding will help us to develop better method to solve the most difficult problem which limited applications of carbon nanotubes in nanoelectronics – the coexistence of metallic and semiconducting nanotubes in samples produced by most, if not all, growth methods. Based on these results, the alignment and density will no longer be the bottlenecks for the surface growth of SWNTs anymore. [Preview Abstract] |
Thursday, March 21, 2013 9:12AM - 9:24AM |
T7.00005: Exciton diffusion in semiconducting single-wall carbon nanotubes studied by transient absorption microscopy Brian Ruzicka, Rui Wang, Jessica Lohrman, Shenqiang Ren, Hui Zhao We report a spatially resolved transient absorption study of exciton diffusion in a thin films of isolated semiconducting single-wall carbon nanotubes. Spatiotemporal dynamics of excitons injected by a tightly focused pump pulse are studied by measuring differential reflection and differential transmission of a time-delayed and spatially scanned probe pulse. We observe a bi-exponentially decaying signal with a fast time constant of 0.66 ps and a slower time constant of 2.8 ps. Both constants are independent of the pump fluence. The squared width of the exciton density profile increases linearly with time, as expected for a diffusion process. We measured a diffusion coefficient of 200 $\pm$ 10~cm$^2$/s at room temperature, which is independent of the pump fluence. We additionally investigated the diffusion coefficient at temperatures of 10 and 150 K and found diffusion coefficients of approximately 300 $\pm$ 10~cm$^2$/s at both. [Preview Abstract] |
Thursday, March 21, 2013 9:24AM - 9:36AM |
T7.00006: Intrinsic and Extrinsic Exciton Decay in HIPCO and COMOCAT Carbon Nanotubes Jeremy Allam, Tariq Sajjad, Zhongyang Wang, Sofia Siddique, Konstantin Litvinenko, Antony Moretti, Dirk Mersch, Izabella Jurewicz, Alan Dalton The luminescence efficiency of semiconducting carbon nanotubes is limited by non-radiative decay of the exciton population. A wide range of quasiexponential and power law decays with different exponents has been reported, and attributed to exciton trapping at defects and exciton-exciton annihilation. The role of diffusion has been controversial and reported diffusion coefficients for carbon nanotubes differ by several orders of magnitude. Here we investigate diffusion-assisted trapping and annihilation processes in HiPco and CoMoCat carbon nanotubes with different defect concentrations. At low excitation, the HiPco nanotubes show quasi-exponential trapping, however at high excitation the population follows a diffusion-limited power law. We attribute this to filling of saturable traps under strong excitation, as demonstrated in Monte Carlo simulations, and at the highest excitation levels the intrinsic behaviour is revealed with distinct regions where decay is limited either by the reaction rate or by Fickian diffusion. In the CoMoCat nanotubes, the same regimes are observed but the diffusion-limited exponent is reduced from -0.5 to -0.3 indicating sub-diffusive transport. We show that this is consistent with a moderate population of shallow traps. [Preview Abstract] |
Thursday, March 21, 2013 9:36AM - 9:48AM |
T7.00007: Quantum dot in semiconducting single walled carbon nanotube on thin hexagonal boron nitride Zhengyi Zhang, Arend van der Sande, Mitsuhide Takekoshi, Xiao Guo, Philip Kim, James Hone Carbon nanotube(CNT) is one of the best available systems to study the one dimensional physics. However, so far most of the studies are based on the devices made of CNT on SiO$_{\mathrm{2}}$/Si substrate, which introduces a large amount of trapped charges causing the spatial variation of the Fermi energy of CNT. It separates CNT into multiple islands preventing its formation of single, well defined quantum dot. Recently it is found that suspended metallic nanotube shows 100meV band gap, 20 times compared with the one on SiO$_{\mathrm{2}}$/Si substrate, which also suggests the trapped charges can obscure many intrinsic properties of CNTs. In this study, we perform the transport measurements of ultra-clean semiconducting CNT transferred on to 5nm thick of hexagonal boron nitride(h-BN) with 10nm thick graphite as back gate. At room temperature, it shows nearly hysteresis free low bias transport. And a clear coulomb blockade feature is observed at 2K in vacuum, which was only obtained in clean suspended nanotubes before. These all suggest that h-BN is an ultraclean and uniform substrate for study of the intrinsic nature of CNT. [Preview Abstract] |
Thursday, March 21, 2013 9:48AM - 10:00AM |
T7.00008: Poole-Frenkel emission by carbon nanotube defect sites Deng Pan, Elliot J. Fuller, Brad L. Corso, Osman Gul, Philip G. Collins Single walled carbon nanotubes (SWCNTs) have a conductance that is particularly sensitive to the presence of defects and disorder. Here, we combine three-terminal transport measurements with Kelvin Probe Force Microscopy (KPFM) to investigate the electronic transmission of individual SWCNT defects. A unique strength of the work is the ability to fully characterize each SWCNT before and after the chemical addition of a particular defect. In transport, the additional resistance caused by a defect is studied as a function of bias, backgate and temperature. KPFM, on the other hand, directly images the spatial, bias-dependent voltage drop in the vicinity of the defect. The two types of measurement agree remarkably well and are consistent with a Poole-Frenkel emission model, in which a shallow trap state has a gate-dependent depth and width. The effective width of a defect trap is determined to be remarkably large and gate dependent, ranging from 400 to 1400 nm. The value might seem unphysical, if not for the fact that KPFM spatially resolves this potential drop and its gradient. Evidently, the SWCNT's very small carrier density and screening lengths lead to anomalously wide effective barriers, helping to explain the extreme sensitivity of SWCNTs to point defects. [Preview Abstract] |
Thursday, March 21, 2013 10:00AM - 10:12AM |
T7.00009: Impact of charged impurity scattering in carbon nanotubes Ryuichi Tsuchikawa, Jonathan Edmiston, Daniel Heligman, Masahiro Ishigami, Xiao Guo, Zhengyi Zhang, James Hone We have measured the transport property of carbon nanotubes as a function of density of charged impurities. Length-dependent resistance measurements were used to eliminate the contribution from the contact resistance in our data. By knowing the exact density of charged impurities on nanotubes, we measure the scattering cross section of individual adsorbed charge impurity. Measurements on different nanotubes are used to reveal the effect of pseudospin conservation on electronic transport in metallic and semiconducting carbon nanotubes upon addition of long-range impurities experimentally. These findings will be outlined in this talk. [Preview Abstract] |
Thursday, March 21, 2013 10:12AM - 10:24AM |
T7.00010: Photon Statistics of Single Carbon Nanotubes at Room Temperature Xuedan Ma, Juan Duque, Jared Crochet, Benjamin Mangum, Stephen Doorn, Han Htoon Different from zero-dimensional systems such as atoms, molecules, and quantum dots, semiconducting single-walled carbon nanotubes (SWNTs) are ideal one-dimensional systems that allow free diffusion of excitons along their length. Studies have also shown that multiple excitons exist within the diffusion length can annihilate via Auger process. Interplay of Auger process and exciton diffusion therefore could have interesting effects on photon emission statistics of SWNTs.~ Current existing studies [1] on photon emission statistics were conducted at low temperature where excitons were localized to quantum-dot-like states. To this end we conduct room temperature 2$^{\mathrm{nd}}$ order photon correlation spectroscopy studies on high quality SWNTs capable of emitting continuous photoluminescence along their length which could extend up to several micrometers.~We observed the degree of photon-bunching lower than 0.5 at the lowest pumping powers. We will also present a correlation between the diffusion length and the degree of photon-bunching. Our study could have implications toward utilizing SWNTs as room temperature single photon sources.\\[4pt] [1] A. Hoegele, C. Galland, M. Winger, A. Imamoglu, Phys. Rev. Lett. 2008, 100, 217401. [Preview Abstract] |
Thursday, March 21, 2013 10:24AM - 10:36AM |
T7.00011: Optical Behaviors of Single-Wall Carbon Nanotubes in Complex Environments Juan G. Duque, Jared Crochet, Brahim lounis, Laurent Cognet, Stephen Doorn The optical properties of single-walled carbon nanotubes (SWNTs) offer great promises. However, the realization of their potential is limited by degree of interactions with their immediate surroundings. Here, we present an innovative approach to control and manipulate the intrinsic optical properties of SWNTs to develop optical sensors as a direct or indirect means to measure physical changes and convert such a response to a signal. We probe the mechanism of photoluminescence brightening via surfactant restructuring using time-resolved PL measurements and show an original way to visualize complex fluid behaviors controlling the intrinsic optical properties of SWNTs. [Preview Abstract] |
Thursday, March 21, 2013 10:36AM - 10:48AM |
T7.00012: Optical coupling of air-suspended carbon nanotubes to silicon microdisk resonators S. Imamura, R. Watahiki, R. Miura, T. Shimada, Y.K. Kato Optical coupling of individual air-suspended single-walled carbon nanotubes to whispering-gallery modes in silicon microdisk resonators is studied. We fabricate silicon microdisks with diameters of ${\sim}$3 $\mu$m on SiO$_2$ supporting posts from silicon-on-insulator substrates, and synthesize carbon nanotubes from patterned catalysts by alcohol chemical vapor deposition to suspend them onto the microdisks. Interactions between carbon nanotubes and evanescent fields of microdisk modes are investigated by microspectroscopy at room temperature. We observe microdisk modes with quality factors of ${\sim}$3000 at wavelengths longer than those of silicon emission, even at positions that are a few micrometers from the suspended carbon nanotubes. In addition, as microdisk modes also exist at excitation laser wavelengths, the photoluminescence intensity can be resonantly enhanced by tuning the laser wavelength to those modes. [Preview Abstract] |
Thursday, March 21, 2013 10:48AM - 11:00AM |
T7.00013: Effects of longitudinal electric fields on carbon nanotube photoluminescence Y. Kumamoto, M. Yoshida, A. Yokoyama, S. Yasukochi, Y. K. Kato We investigate modulation of single-walled carbon nanotube photoluminescence with electric fields along the tube axis by using field-effect transistor structures. The nanotubes are synthesized with chemical vapor deposition, and measurements are performed on as-grown tubes suspended over trenches formed between source and drain electrodes. As gate-voltage induced carrier doping causes peak shifts and quenching of photoluminescence,\footnote{S. Yasukochi \textit{et al.}, Phys. Rev. B 84, 121409(R) (2011).} care must be taken to identify the effects of longitudinal electric fields. In order to suppress the doping effects at the center of the nanotubes, we apply symmetric bias voltages between source and drain while keeping the gate at zero voltage. In addition, we use Si substrates with 1-$\mu$m thick oxide layer to reduce the gate effects at the ends of the nanotubes. After identification of individual nanotubes by photoluminescence imaging and excitation spectroscopy, we collect luminescence spectra as a function of bias voltage. As the bias is increased, we observe moderate reduction of emission intensity whose voltage dependence cannot be accounted for by gate-induced quenching. Furthermore, broadening of nanotube emission peak with increasing bias voltage is also observed. [Preview Abstract] |
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