Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session U7: Focus Session: Carbon Nanotubes: Devices |
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Sponsoring Units: DMP Chair: Junichiro Kono, Rice University Room: 303 |
Thursday, March 21, 2013 11:15AM - 11:51AM |
U7.00001: Gate Modulation of Contacts in Carbon Nanotube Devices Invited Speaker: Francois Leonard As the size of electronic devices is reduced, the electrical contacts play an increasingly important role. This is particularly true for contacts to nanomaterials, where new contact phenomena are often observed. In this talk, I will discuss recent numerical simulations to analyze experimental measurements of short-channel carbon nanotube transistors. The results indicate a strong gate modulation of the contact properties, an effect that is distinct from that observed in Schottky barrier nanotube transistors. This modulation of the contacts by the gate allows for the realization of superior subthreshold swings and improved scaling behavior, as observed experimentally. These results further elucidate the behavior of carbon nanotube/metal contacts, and should be useful in the design and optimization of high performance carbon nanotube electronics. [Preview Abstract] |
Thursday, March 21, 2013 11:51AM - 12:03PM |
U7.00002: Floating Electrode Transistor based on Single-walled Carbon Nanotube Networks for High Source--drain Voltage Operation Jeongsu Kim, Juhyung Lee, Hyungwoo Lee, Taekyeong Kim, Hye Jun Jin, Juyeon Shin, Youngki Shin, Sangho Park, Yoonho Khang, Seunghun Hong Thin film transistors (TFTs) based on single-walled carbon nanotubes (swCNTs) were reported to exhibit extraordinary characteristics in terms of their conductivity, transparency and flexibility. However, until now, most studies have focused on CNT-TFTs for an operation at a relatively low source--drain voltage below $\sim$ 10 V, while, for some applications such as LCD displays, one needs a rather high source--drain bias voltage. However, such a high voltage bias on source and drain electrodes may reduce the gating effect of conventional CNT-TFT devices by lowering the Schottky barrier and degrade its overall device performance. Herein, we developed floating electrode thin-film transistors (F-TFTs) based on semiconducting swCNT networks for a high source-drain voltage operation. In this device structure, the swCNT network channel was divided into a number of channels connected by floating metallic electrodes. At a high source-drain voltage, the F-TFTs showed a much higher on--off ratio than conventional swCNT-TFTs. This work should provide an important guideline in designing CNT-TFTs for high voltage applications. [Preview Abstract] |
Thursday, March 21, 2013 12:03PM - 12:15PM |
U7.00003: High Bias Characteristics of Individual, Suspended Carbon Nanotube p-n Junction Photodiodes Shun-Wen Chang, Kevin Bergemann, Rohan Dhall, Jeramy Zimmerman, Stephen Forrest, Stephen Cronin We have recently investigated p-n junction diodes formed by electrostatic doping of individual, suspended, single-walled carbon nanotubes (CNTs) using two gate electrodes positioned beneath a free standing nanotube that bridges source and drain electrodes. The electrostatic field imposed by the two gates polarizes the nanotube along its length, thereby allowing independent control of the ``doping'' in the nanotube without introducing impurities or defect states. These pn-devices exhibit rectifying diode behavior and finite photoresponse under illumination. Several interesting phenomena are observed at high bias that arise from Schottky contacts formed between the nanotube and its metal contact electrodes and electron tunneling between the n- and p-doped regions. A model is developed explaining this behavior showing evidence for plasmon-induced band gap shrinkage with electrostatic doping. [Preview Abstract] |
Thursday, March 21, 2013 12:15PM - 12:27PM |
U7.00004: ABSTRACT WITHDRAWN |
Thursday, March 21, 2013 12:27PM - 12:39PM |
U7.00005: Transport Study of Carbon Nanotube Networks with Different Ratios of Semiconducting and Metallic Nanotubes Xuan Wang, Erik H\'aroz, Qi Zhang, Junichiro Kono An important goal of current nanotechnology research is to obtain a quantitative understanding of how electrons drift and tunnel through junctions of nanostructures and how the overall electrical conductivity of networks of nanostructures is determined. Here, we present a comprehensive study of DC transport properties of macroscopic single-wall carbon nanotube (SWCNT) networks with different ratios of metallic and semiconducting nanotubes. The temperature-dependent resistivity shows that when the length of SWCNT is orders of magnitude smaller than the dimensions of the network, the resistance mainly comes from inter-tube junctions. However, the transport mechanism changes from fluctuation-induced tunneling in metallic-enriched networks to variable range hopping in semiconductor-enriched networks. The magneto resistance (MR) of these two networks also show distinct features. In a metallic enriched network, MR is negative up to 10 Tesla below 70 K which can be explained based on weak localization theory. One the other hand, in a semiconductor-enriched network, MR is mostly positive up to 10 Tesla below 10 K, which can be explained based on the shrinking of electron wave function due to the magnetic field. [Preview Abstract] |
Thursday, March 21, 2013 12:39PM - 12:51PM |
U7.00006: Electronic durability of flexible transparent coatings from type-specific single-wall carbon nanotubes John M. Harris, Matthew R. Semler, Jeffrey A. Fagan, Erik K. Hobbie The coupling between mechanical flexibility and electronic performance is evaluated for thin flexible coatings of metallic and semiconducting single-wall carbon nanotubes (SWCNTs) deposited on compliant polymer supports. The microstructure, transparency, and electronic properties of the films are independently characterized using a variety of techniques. Cyclic compression experiments suggest that thin films made from metallic SWCNTs show better durability as flexible transparent conductive coatings, which we attribute to a combination of superior mechanical performance and higher interfacial conductivity. We model the role of van der Waals forces in the strain response of the films. [Preview Abstract] |
Thursday, March 21, 2013 12:51PM - 1:03PM |
U7.00007: High-frequency performance of scaled carbon nanotube array field-effect transistors Ralph Krupke, Mathias Steiner, Michael Engel, Yu-Ming Lin, Yanging Wu, Keith Jenkins, Damon Farmer, Jefford Humes, Nathan Yoder, Jung-Woo Seo, Alexander Green, Mark Hersam, Phaedon Avouris We report the radio-frequency performance of carbon nanotube array transistors that have been realized through the aligned assembly of highly separated, semiconducting carbon nanotubes on a fully scalable device platform. At a gate length of 100 nm, we observe output current saturation and obtain as-measured, extrinsic current gain and power gain cut-off frequencies, respectively, of 7 GHz and 15GHz. While the extrinsic current gain is comparable to the state-of-the-art, the extrinsic power gain is improved. The de-embedded, intrinsic current gain and power gain cut-off frequencies of 153 GHz and 30 GHz are the highest values experimentally achieved to date. We analyze the consistency of DC and AC performance parameters and discuss the requirements for future applications of carbon nanotube array transistors in high-frequency electronics. [Preview Abstract] |
Thursday, March 21, 2013 1:03PM - 1:15PM |
U7.00008: Fabrication and Characterization of Self-Aligned T-gate High-Purity Semiconducting Carbon Nanotube RF Transistors Yuchi Che, Alexander Badmaev, Pyojae Kim, Alborz Jooyaie, Chongwu Zhou We applied the scalable self-aligned T-shaped gate design to semiconducting nanotube RF transistors. In this way, the channel length can be scaled down to 140 nm which enables quasi ballistic transport, and the gate dielectric is reduced to 2-3 nm aluminum oxide, leading to quasi quantum capacitance operation. As a result, our nanotube transistors exhibit excellent on-chip device performance and high linearity with channel length scaling down to 140 nm. With T-shaped gate structure, a cut-off frequency up to 22 GHz and power gain frequency of 10 GHz for separated nanotube transistor are achieved. The T-shaped gate design enables high-yield wafer-scale fabrication with controllable gate length scaling. Furthermore, we also characterized the linearity properties of nanotube transistors, with the 1-dB compression point measurement, in source/load pull setup, with positive power gain to our knowledge, for the first time. Above all, our work reveals that the semiconducting nanotube RF transistor is an interesting and promising direction in high frequency device and circuit exploration. [Preview Abstract] |
Thursday, March 21, 2013 1:15PM - 1:27PM |
U7.00009: Carbon Nanotube Thin Film Transistors Using Carbon Nanotube Electrodes Narae Kang, Biddut K. Sarker, Saiful I. Khondaker Carbon nanotubes (CNTs) have attracted a significant attention in recent years due to their exceptional electronics, optical and mechanical properties. In particular, CNT thin film transistors (TFTs) are considered as promising active components in the next-generation flexible, transparent, and invisible electronics. Due to lack of transparency and flexibility, metal electrodes are not suitable for CNT TFTs in their transparent and flexible electronic applications. In this talk, we will discuss the high-performance CNT TFTs where densely aligned array of metallic single walled carbon nanotubes (SWNTs) were used as source and drain electrodes while semiconducting enriched aligned SWNTs (s-SWNT) were used as a channel material. The both metallic SWNTs in the electrodes and s-SWNTs in the channel are aligned via dielectrophoresis using a high quality surfactant-free solution. We show that the performance of the s-SWNT devices with metallic SWNT electrodes is significantly improved than that of the devices with Pd electrodes. In order to find the information about injection barrier between s-SWNT and metallic SWNT interface, we carry out low temperature electron transport measurement of our devices. We will discuss the detailed analysis of the low temperature data. [Preview Abstract] |
Thursday, March 21, 2013 1:27PM - 1:39PM |
U7.00010: Dipole induced conductance modulation in chromophore-functionalized single-walled carbon nanotubes Yuanchun Zhao, Changshui Huang, Myungwoong Kim, Padma Gopalan, Mark Eriksson Single-walled carbon nanotubes (SWNTs) are highly sensitive to local electrostatic environments, making SWNT field-effect transistors (FETs) of interest for a number of sensor applications and optoelectronic devices. Here we demonstrate a direct correlation between the conduction of SWNTs and their surrounding dipolar environments. We use azobenzene-based dipolar chromophores, Disperse Red 1 (DR1) and its derivatives to functionalize the sidewalls of SWNTs. The chromophores are coupled with a pyrenebutyric group for realizing noncovalent attachment and to attempt to direct their dipole moments. The functionalizing chromophores produce a dipole field that shifts the threshold voltage (Vth) of the nanotube FET. Under light illumination, these molecules isomerize from the ground trans state to the excited cis state, leading to a decrease of their dipole moments. This dipole moment change acts as an additional gate, causing a shift in Vth. Our results provide a new insight into the photogating mechanisms of the nanotube-chromophore hybrid devices, and they reveal the possibility to modulate optoelectronic properties of nanotube-hybrid devices by designing chromophores with required photosensitive features. [Preview Abstract] |
Thursday, March 21, 2013 1:39PM - 1:51PM |
U7.00011: Working cycles of devices based on bistable carbon nanotubes Oleg Shklyaev, Eric Mockensturm, Vincent Crespi Shape-changing nanotubes are an example of variable-shape sp2 carbon-based systems where the competition between strain and surface energies can be moderated by an externally controllable stimuli such as applied voltage, temperature, or pressure of gas encapsulated inside the tube. Using any of these stimuli one can transition a bistable carbon nanotube between the collapsed and inflated states and thus perform mechanical work. During the working cycle of such a device, energy from an electric or heat source is transferred to mechanical energy. Combinations of these stimuli allow the system to convert energy between different sources using the bistable shape-changing tube as a mediator. For example, coupling a bistable carbon nanotube to the heat and charge reservoirs can enable energy transfer between heat and electric forms. The developed theory can be extended to other nano-systems which change configurations in response to external stimuli. [Preview Abstract] |
Thursday, March 21, 2013 1:51PM - 2:03PM |
U7.00012: Targeted Placement of Gold Nanoparticles on SWCNT Transistors Using Electrodeposition Yian Liu, Paola Barbara, Makarand Paranjape We present a simple in-situ electrochemical method to target the deposition of gold and other metallic nanoparticles along a single-walled carbon nanotube (SWCNT) field effect transistor (CNTFET). The transistors, fabricated on SiO$_{\mathrm{2}}$/Si substrates, are passivated by a thin layer of poly(methyl-methacrylate), or PMMA. Areas of the PMMA along the carbon nanotube are exposed using electron-beam lithography to target the locations where Au nanoparticles need to be placed. An appropriate potential difference is applied between an in-situ sacrificial gold electrode and the SWCNT, all immersed under a droplet of electrolyte solution. By adjusting the applied voltage and time of deposition, the size of the Au nanoparticle can be controlled from 10 nm to over 100 nm. This method provides better control and is much easier to carry out compared to other site-specific deposition techniques. Such decorated Au nanoparticle/CNTFET heterostructures will allow for a better understanding of single-electron transport behavior, as well as finding application in site-specific biomolecule anchoring for the development of highly sensitive and selective biosensors. [Preview Abstract] |
Thursday, March 21, 2013 2:03PM - 2:15PM |
U7.00013: Band Gap Modification in Metallic Nanotubes Due to Nanotube-Substrate Interaction Moh Amer, Adam Bushmaker, Steve Cronin Previous work shows that a small band gap exists in metallic nanotubes. Here we give a detailed comparison between ultra-clean suspended and on-substrate carbon nanotubes (CNTs) in order to quantify the effect of the substrate on the effective band gap of quasi-metallic nanotubes [1]. Individual CNTs are grown across two sets of electrodes, resulting in one segment of the nanotube that is suspended across a trench and the other segment supported on the substrate. A significant change in the conductance of the suspended segment is observed ($\Delta G/G=$0.84) with applied gate voltage. This change is attributed to the existence of the small band gap. The on-substrate segment, however, only shows a change in the measured conductance of $\Delta G/G=$0.11.We used a Landauer model to extract the band gap of these devices. From these fits, the band gaps in the suspended region range from 75 to 100 meV, but are only 5-14.3 meV when the nanotube is in contact with the substrate. The decreased band gap is attributed to localized doping caused by trapped charges in the substrate that result in inhomogeneous broadening of the Fermi energy, which in turn limits our ability to modulate the conductance.\\[4pt] [1] Moh. R. Amer, A.B., and Stephen B. Cronin, The Influence of Substrate in Determining the Band Gap of Metallic Carbon Nanotubes. Nano Letters, 2012. 12: p. DOI:10.1021/nl302321k. [Preview Abstract] |
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