Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session J22: Focus Session: Carbon Nanotubes: Optoelectronic Devices |
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Sponsoring Units: DMP Chair: Jiwoong Park, Cornell University Room: Portland Ballroom 252 |
Tuesday, March 16, 2010 11:15AM - 11:27AM |
J22.00001: Device fabrication with precisely placed carbon nanotubes of known chiral vector Christopher Allen, Mark Elkin, Can Zhang, Stephan Hofmann, Gavin Burnell, John Robertson, Bryan Hickey The electrical properties of single walled carbon nanotubes are strongly dependent on their precise atomic configuration and as such it is of great importance to be able to fabricate devices containing individual carbon nanotubes of known structure. We have developed a novel technique that allows for the determination of the chiral indices of an individual carbon nanotube followed by the precise placement of the tube onto pre-patterned electrodes. Carbon nanotubes are grown by chemical vapour deposition onto perforated TEM grids. Electron diffraction is performed on individual carbon nanotubes, the analysis of which reveals their structure. The desired carbon nanotube is then manipulated inside a combined STM-SEM system and placed with high precision onto pre-patterned electrodes. [Preview Abstract] |
Tuesday, March 16, 2010 11:27AM - 11:39AM |
J22.00002: Characterization of aligned single walled carbon nanotube high frequency devices Andrew Tunnell, Vince Ballarotto, Vinod Sangwan, Ellen Williams Parallel arrays of single-walled carbon nanotubes (CNTs) grown on quartz substrates have been incorporated into field effect transistors (FETs) that exhibit effective mobilities of 3000 cm$^{2}$/Vs and conductances as high as 800$\mu $S. To decrease the transistor switching time, parasitic capacitances have been reduced by minimizing gate source/drain overlap and the channel resistance has been decreased by increasing the density of CNTs and decreasing the channel length. Initial measurements on simple amplifiers using these optimized FETs show switching times less than 100 ns, a significant improvement from 100 $\mu $s with the previous device geometry. The high frequency performance of these devices will be presented. When patterned thin films of iron are used as the growth catalyst, aligned CNTs grow away from the catalyst area and dense random networks of CNTs grow in the regions where the iron was deposited. Devices using these dense random networks as source/drain electrodes will be compared with traditional metallic source/drain electrodes. [Preview Abstract] |
Tuesday, March 16, 2010 11:39AM - 11:51AM |
J22.00003: Narrow-band light emission from a single carbon nanotube p-n diode Megumi Kinoshita, Thomas Mueller, Mathias Steiner, Vasili Perebeinos, Ageeth Bol, Damon Farmer, Phaedon Avouris We present the first observation of electroluminescence from electrostatically-generated carbon nanotube (CNT) p-n junctions[1]. While CNT optoelectronics has made much progress in recent years, observations of emission from electrically excited CNT devices have been limited to the high-bias regime and with low efficiency. Furthermore, the resulting broad linewidths are broad, making it difficult to investigate electronic levels and carrier dynamics. We find that p-n junctions allow for better carrier control at lower power inputs, resulting in emission with near-zero threshold, low self-heating and efficiency two to three orders of magnitude greater compared to previous device configurations. This yields higher signal-to-noise ratio and narrower linewidths (down to $\sim $35 meV) that allows us to identify localized excitonic transitions that have previously been observed only in photoluminescent studies. [1] T. Mueller, M. Kinoshita, M. Steiner, V. Perebeinos, A. Bol, D. Farmer, and Ph. Avouris, Nature Nanotech., web publication, November 15 2009. [Preview Abstract] |
Tuesday, March 16, 2010 11:51AM - 12:27PM |
J22.00004: Semiconducting carbon nanotubes in optoelectronic and nanophotonic devices Invited Speaker: The exciting optical and electronic properties of semiconducting carbon nanotubes are inspiring more and more demonstrations of their applicability in nanometer scale optoelectronics and photonics. Integrated in a device, however, the physical properties of carbon nanotubes are subject to strong modifications. The presence of dielectric substrates, external electric fields and electrostatic doping significantly alters the optical properties of carbon nanotubes [1, 2]. Also, charge carriers involved in electrical transport along carbon nanotubes excite non-equilibrium phonon populations and couple to surface polar phonons of a dielectric substrate [3]. As a result, the response of carbon nanotubes to external perturbations will ultimately determine the overall performance of a carbon nanotube device. By combining electrical measurements and optical micro-spectroscopy, it is possible to observe experimentally the different effects on the single nanotube level and elucidate the role of the various physical interactions that occur simultaneously in an operating carbon nanotube transistor. \\[4pt] [1] M. Steiner et al., Applied Physics A 96, 271-282 (2009) \\[0pt] [2] M. Steiner et al., Nano Letters 9, 3477-3481 (2009) \\[0pt] [3] M. Steiner et al., Nature Nanotechnology 4, 320-324 (2009) [Preview Abstract] |
Tuesday, March 16, 2010 12:27PM - 12:39PM |
J22.00005: Electroluminescence from individual single-wall carbon nanotube transistors and suspended films Elyse Adam, Benoit Cardin St-Antoine, Pierre Levesque, David Menard, Richard Martel We performed electroluminescence experiments in the near infrared from individual single-walled carbon nanotube (SWNT) transistors and from suspended films of bulk SWNT. For SWNT transistors, we observed that the light emission intensity and the drain voltage (at constant current) follow a similar behavior during a gate voltage sweep. Also, the electroluminescence spectra for those devices present multi-peaks. The results are discussed using a simple electron-hole pair recombination mechanism and generation of heat. For thick (100-500 nm) and suspended films of SWNT, the light emission spectra present a shape that fits well with the Planck's law. This well-known spectral shape allows us to extract the temperature of the film as a function of the input power. [Preview Abstract] |
Tuesday, March 16, 2010 12:39PM - 12:51PM |
J22.00006: Wannier-functions disentanglement to determine Schottky barrier heights: application to CNT-metal systems Nicholas Singh-Miller, Nicola Marzari We study Schottky barrier heights in carbon nanotube CNT-metal junctions using pseudopotential plane-wave density functional calculations. We determine the barriers by two methods: first through a line-up of the local electrostatic potentials at the junction with respect to bulk reference systems, and second by directly extracting the band structure of the semiconducting nanotube from the entire manifold of the electronic states of the CNT-metal system. In the latter case a Wannier-functions approach is able to clearly disentangle the bands of interest from the rest of the manifold. Al(111) and Pd(111) surfaces are taken as examples of low and high work-function metals, contacted with a semiconducting (8,0) CNT. In all cases we find that a surface dipole forms that locally shifts the band structure of the CNT; control of this electrostatic dipole directly controls the SBH. [Preview Abstract] |
Tuesday, March 16, 2010 12:51PM - 1:03PM |
J22.00007: Contact Resistance in Metallic Carbon Nanotube Devices Michael Engel, Ralph Krupke Transport in metallic single-walled carbon nanotubes (m-SWNT) is of fundamental interest because of their 1D nature and strong electron-phonon coupling. To probe intrinsic transport properties contact resistance has to be minimized. Transparent contacts have already been achieved for rather large diameter tubes (d$>$2nm). For smaller diameter m-SWNT it is not clear whether this is possible or if there is a lower bound for the contact resistance. Here we investigate the two probe resistance of m-SWNT in the diameter range d=1.0-1.4nm. m-SWNT have been assembled onto predefined Palladium electrodes by low frequency dielectrophoresis. We observe that device resistance can be significantly reduced by current-induced annealing. Insight into the nature of the process is given by electron transport and correlated photocurrent and Raman spectroscopy measurements. [Preview Abstract] |
Tuesday, March 16, 2010 1:03PM - 1:15PM |
J22.00008: Type control of Single Walled Carbon Nanotube field effect transistors and Its application Un Jeong Kim, Shin Cheol Min, Hyung Bin Son, Seongmin Yee, Woojong Yu, Gyu Tae Kim, Young Hee Lee, Eunhong Lee, Wanjun Park, Jong Min Kim Permanently type controlled single walled carbon nanotube (SWNT) field effect transistors, from p-type, ambi-polar to n-type, have been fabricated by controlling deposition temperature of Al$_{2}$O$_{3}$ film as top-gate dielectric by atomic layer deposition (ALD). It is observed that threshold voltage (Vth) is almost linearly downshifted as a function of deposition temperature. Competition between electron transfer from the of Al$_{2}$O$_{3}$ layers to the SWNT surface and electron capture by oxygen molecules adsorbed on the tube wall seems to be the key point for the Vth change depending on the deposition temperature. To prove the high performance of type controlled SWNT network transistors, inverter, NAND, and NOR gate characteristics are successfully demonstrated. [Preview Abstract] |
Tuesday, March 16, 2010 1:15PM - 1:27PM |
J22.00009: Photo-induced thermoelectric response in suspended single-walled carbon nanotube films Benoit St-Antoine, David Menard, Richard Martel A study was carried out on the position dependent photovoltage of suspended single-walled carbon nanotube films in vacuum. The photoresponse of such films was found to be driven by a thermal mechanism, rather than by direct photoexcitation of carriers. [1] A model was developed which establishes a relation between the photoresponse profile and the local Seebeck coefficient of the film, thus opening up new perspectives for material characterization. The technique was demonstrated by monitoring the doping changes in the nanotube films obtained by successive current conditioning steps. Since the Seebeck coefficient of carbon nanotubes spans a considerable range depending on their doping state, the photovoltage amplitude can be tuned and large responses have been measured (up to 0.75mV for 1.2mW). \\[4pt] [1] B. St-Antoine et al. Nano Lett. 9, 3503 (2009) [Preview Abstract] |
Tuesday, March 16, 2010 1:27PM - 1:39PM |
J22.00010: Very Stable Electron Field Emitters based on Vertically-aligned Carbon Nanotubes Embedded in Poly-methyl Metha Acrylate (PMMA) Matrix Archana Pandey, Abhishek Prasad, Yoke Khin Yap Tremendous efforts were evidenced on the study of electron field emission from carbon nanotubes (CNTs) for more than a decade. However, commercial field emission products based on CNTs is still not available. Apparently, emission stability is one of the major issues and the understanding on this is still lacking. We have focused our efforts in understanding the basic factors that contribute towards stable field emission from CNTs. We previously reported that self-assembled conical bundles of opened-tip CNTs are stable field emitter [1]. Here, we describe a lithography free process to increase the long term emission stability of vertically-aligned multiwalled carbon nanotubes (VA-MWCNTs). We found that the emission threshold ($E_{th})$ of VA-MWCNTs was reduced by more than two-fold when VA-MWCNTs were embedded in PMMA. These emitters were tested for continuous emission at a current density $>$1.2mA/cm2 for 40 hours with $>$96{\%} stability and emission density. Multiple theoretical models and simulation were conducted to explain these observations. Details of these analyses will be presented in the meeting.[1] Pandey et al, Carbon 48, 287 (2010) + cover image in the 48/3 issue (2010). Y. K. Yap acknowledges supports from DARPA (DAAD17-03-C-0115). [Preview Abstract] |
Tuesday, March 16, 2010 1:39PM - 2:15PM |
J22.00011: Extremely Efficient Multiple Electron-hole Pair Generation in Carbon Nanotube Photodiodes Invited Speaker: The efficient generation of multiple electron-hole (e-h) pairs from a single photon could improve the efficiency of photovoltaic solar cells beyond standard thermodynamic limits [1] and has been the focus of much recent work in semiconductor nanomaterials [2,3]. In single walled carbon nanotubes (SWNTs), the small Fermi velocity and low dielectric constant suggests that electron-electron interactions are very strong and that high-energy carriers should efficiently generate e-h pairs. Here, I will discuss observations of highly efficient generation of e-h pairs due to impact excitation in SWNT p-n junction photodiodes [4]. To investigate optoelectronic transport properties of individual SWNT photodiodes, we focus a laser beam over the device while monitoring the electronic characteristics. Optical excitation into the second electronic subband $E_{22}$\textit{ $\sim $ 2 E}$_{GAP}$ leads to striking photocurrent steps in the device $I-V_{SD}$ characteristics that occur at voltage intervals of the band gap energy $E_{GAP} / e$. Spatially and spectrally resolved photocurrent combined with temperature-dependent studies suggest that these steps result from efficient generation of multiple e-h pairs from a single hot $E_{22}$ carrier. We conclude that in the SWNT photodiode, a single photon with energy greater than$ 2E_{GAP}$ is converted into multiple e-h pairs, leading to enhanced photocurrent and increased photo-conversion efficiency. [1] W. Shockley, and H. J. Queisser, \textit{Journal of Applied Physics} \textbf{32}, 510 (1961). [2] R. D. Schaller, and V. I. Klimov, \textit{Physical Review Letters} \textbf{92} (18), 186601 (2004). [3] R. J. Ellingson, et al, \textit{Nano Letters}, \textbf{5} (5), 865-871 (2005). [4] Nathaniel M. Gabor, Zhaohui Zhong, Ken Bosnick, Jiwoong Park, and Paul McEuen, \textit{Science}, \textbf{325}, 1367 (2009). [Preview Abstract] |
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