Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session B36: Carbon Nanotubes: Devices and Applications |
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Sponsoring Units: DMP Chair: Masa Ishigami, University of Central Florida Room: 408 |
Monday, March 16, 2009 11:15AM - 11:27AM |
B36.00001: Density Functional Theory Design of All-metallic Single-wall Carbon Nanotubes Li Chen, Swastik Kar, Saroj Nayak, Pulickel Ajayan We have used density functional theory to investigate the structure and electronic properties of Pt nanocluster decoration of single-wall carbon nanotubes (SWNTs). Energy optimization shows that Pt prefers to form clusters rather than spread out and ``wet'' the SWNTs. Atom-by atom increase in the cluster size is associated with the appearance of a number of new bands in the electronic structure, especially near the Fermi level. These new bands serve to modify the density of states near the Fermi level. While metallic SWNTs remain metallic, semiconducting SWNTs lose their band-gap rapidly with the inclusion of more than 3 atoms per cluster, and continue to remain metallic for all tested cluster sizes (n=0-13 and 19). Room temperature (T=300K) calculations of conductance show that SWNTs of different chiralities (both metallic and semiconducting) remain metallic for beyond n=3, with conductance close to 4e$^{2}$/h. In some cases, the conductance is found to exceed this value. This gives an easy for designing ``all-metallic'' SWNT bundles. [Preview Abstract] |
Monday, March 16, 2009 11:27AM - 11:39AM |
B36.00002: Designing of Single Walled Carbon Nanotubes dispersions for industrial scale processing and roll-to-roll coating applications Budhadipta Dan, Matteo Pasquali Carbon nanotubes (CNTs) combine nanoscale size with high aspect ratio and unique properties, making them ideal candidate materials for high-impact applications. Yet, much as in polymer science and engg, such applications require appropriate fluid based dispersions which can undergo industrial processing that translate the properties of elemental molecules (SWNTs) into macroscopic materials. We report a detailed study on the flow behavior of aqueous SWNT dispersions involving surfactants, its dependence on SWNT {\&} surfactant concentration, and type of surfactant. We also design a SWNT dispersion for use in industrial roll-to-roll (rod based) thin film coating process. Purified, pristine SWNTs were dispersed in water at high concentrations using surfactants and analyzed using rheology and optical microscopy. A SWNT-SDBS-TritonX100 dispersion was found to have the appropriate viscoelastic and shear thinning behavior for rod coating. Rod coating, washing and sulfuric acid treatment resulted in highly uniform thin films of pure SWNT (sheet resistance of 100 and 300 $\Omega $/sq for respective transparency of 70{\%} and 90{\%}). The results presented here, both in terms of scientific understanding of how to control fluid and process, and in terms of a scalable technique, paves the way to the deployment of transparent conductive SWNT films in large scale commercial applications. [Preview Abstract] |
Monday, March 16, 2009 11:39AM - 11:51AM |
B36.00003: Stable Electron Field Emission afrom Opened-Tip Carbon Nanotube Bundles Archana Pandey, Abhishek Prasad, Jason Moscatello, Yoke Khin Yap Effective electron field emission from carbon nanotubes (CNTs) has been known for years but reliable commercial devices are still not available. Most reported works describe low emission threshold field ($E_{th})$ of CNTs and their device architectures. However, fundamental factors that determine stable emission from CNTs are still not clear. We previously reported that graphitic order of CNTs affects their emission stability [1]. Here, we found that both opened tip nanotubes and bundling, when introduced independently, can reduce $E_{th}$ of CNTs and enhance the emission stability. The combined of both factors, i.e., opened tip nanotube bundles are shown to emit electron continuously $>$ ten hours with notable stability. Theoretical simulation was conducted in supporting our explanation on these enhanced emission properties. SEM, TEM and Raman spectroscopy was conducted to characterize the as grown CNTs. Y. K. Yap acknowledges support from the Defense Advanced Research Projects Agency (DAAD17-03-C-0115, through Army Research Laboratory). [1]. Kayastha et al, Nanotechnology 18, 035206 (2007). [Preview Abstract] |
Monday, March 16, 2009 11:51AM - 12:03PM |
B36.00004: ABSTRACT WITHDRAWN |
Monday, March 16, 2009 12:03PM - 12:15PM |
B36.00005: Fabricating Substrates to Combine Electron Microscopy and Diffraction with Electrical Characterization of Single and Double-Walled Carbon Nanotubes Scott Paulson, Lok-kin Tsuii, Joseph Hardcastle Carbon nanotubes based electronics make model systems for pursuing electronic devices at the nanometer scale. They are chemically robust, and have well defined easily predictable electronic structure. However, device integration requires not just an understanding of the nanotube properties, but also the properties of interfaces between neighboring elements. Ideally the structure-property relationship of the interface between two nanotubes would consist of complete electrical characterization coupled with atomic scale structural information. The former is achieved by lithographic patterning of a nanotube into a circuit, the latter through high resolution TEM imaging and diffraction. Unfortunately, typical TEM preparation of nanotubes is not compatible with lithographic processing and vice-versa. In this talk we will present a fabrication process that integrates carbon nanotubes into devices on a TEM compatible substrate. Sample devices will be shown, and preliminary data will be presented. [Preview Abstract] |
Monday, March 16, 2009 12:15PM - 12:27PM |
B36.00006: Transfer Printed Parallel Carbon Nanotube Devices Andrew Tunnell, Vinod Sangwan, Vincent Ballarotto, Daniel Hines, Michael Fuhrer, Ellen Williams Carbon nanotube (CNT) device properties can be improved by increasing the density and alignment of tubes and avoiding the problems associated with random networks. We are optimizing this approach by preparing devices composed of parallel arrays of CNTs fabricated on quartz and plastic substrates. CNT growth catalysts, ferric nitrate, ferritin and iron, are a point of control of the density and degree of alignment of the grown tubes. Though ferric nitrate produced a denser network, ferritin allows a high degree of alignment, and iron will also be tested. Plastic devices with a 5 $\mu $m channel length and a 22.5 mm width were prepared with approximately 1 channel crossing tube per 4$\mu $m of width. The density is improved by repeatedly printing more CNT's to the same area. The metallic tubes were removed by selective electrical breakdown, marginally increasing the on/off current ratio while decreasing the On current from 800$\mu $A to 450$\mu $A (at Vgs=-20V, Vds=-10V). Results from optimized devices prepared with patterned iron as the growth catalyst will also be presented. [Preview Abstract] |
Monday, March 16, 2009 12:27PM - 12:39PM |
B36.00007: ABSTRACT WITHDRAWN |
Monday, March 16, 2009 12:39PM - 12:51PM |
B36.00008: Textured Network Devices: Overcoming Fundamental Limitations of Nanotube/Nanowire Network-based devices Minbaek Lee, Seunghun Hong, Meg Noah, Young-Kyun Kwon, June Park, Maeng-Je Seong Thin film devices based on single-walled carbon nanotube (swCNT) networks were extensively studied for various practical applications such as transistors, sensors, etc. However, those devices have been suffering various limitations such as poor on-off ratio due to metallic swCNTs in the networks, decreased mobility and conductance for devices with reduced linewidth due to the percolation problem, etc. Herein, we present a simple but efficient strategy to significantly improve the performance of swCNT network device by controlling the network structures. In this strategy, surface molecular patterns were utilized to prepare swCNT network-based devices with desired connectivity. We will discuss systematic study about the effect of swCNT network connectivity, as well as enhancements of on-off ratio, mobility and conductance of textured network-based transistors. [Preview Abstract] |
Monday, March 16, 2009 12:51PM - 1:03PM |
B36.00009: CMOS-analogous wafer-scale nanotube-on-insulator approach for submicron devices and integrated circuits using aligned nanotubes Koungmin Ryu, Alexander Badmaev, Chuan Wang, Chongwu Zhou Massive aligned carbon nanotubes hold great potential but also face significant integration / assembly challenge for future beyond-silicon nanoelectronics. We report our recent advance on full wafer-scale processing of massively aligned carbon nanotube arrays for high performance submicron channel transistors and integrated nanotube circuits, including the following essential components. 1) The massively highly aligned nanotubes were successfully grown on 4 inch quartz and sapphire wafers via meticulous temperature control, and then transferred onto Si/SiO$_{2}$ wafers using our facile transfer printing method. 2) Wafer-scale device fabrication was performed on 4 inch Si/SiO$_{2}$ wafer to yield submicron channel transistors and circuits with high on-current density $\sim $ 20 $\mu $A/$\mu $m and good on/off ratio. 3) Chemical doping methods were successfully demonstrated to get CMOS inverters with a gain $\sim $5. 4) Defect-tolerant circuit design for NAND and NOR was proposed and demonstrated to guarantee the correct operation of logic circuit, regardless of the presence of mis-aligned or mis-positioned nanotubes. [Preview Abstract] |
Monday, March 16, 2009 1:03PM - 1:15PM |
B36.00010: A Novel Fabrication Method for Pristine Suspended Carbon Nanotube Devices Vinod Sangwan, Vincent Ballarotto, Michael Fuhrer, Ellen Williams A simple and scalable method has been developed to fabricate suspended carbon nanotube (CNT) field effect transistors using as-grown CNTs without subsequent chemical processing.\footnote{\textit{V. K. Sangwan} et al, APL \textbf{93}, 113112 (2008)} A printing process is used to transfer CVD-grown CNTs onto specially configured electrode (Au) sets fabricated on SiO$_{2}$. The versatility of the technique is demonstrated by controlling the number of suspended CNTs per device, and by re-using the same electrode set multiple times to produce the desired device characteristics. The quality of suspended CNTs is characterized by electrical transport as well as 1/f noise measurements. Standard resist-processed CNTs on SiO$_{2}$ substrates show p-type behavior and strong hysteresis associated with doping by the SiO$_{2}$ surface and charge trapping in the SiO$_{2}$, respectively. In contrast, suspended CNTs show ambipolar behavior with negligible hysteresis. Low frequency noise measurements on suspended CNT show 1$/f$ behavior with Hooge's constant 2.6 x 10$^{-3}$, around 20 times less than that of CNTs lying on SiO$_{2}$, consistent with reduced effect of the SiO$_{2}$ charge traps, responsible for the bulk of the noise in CNTs on SiO$_{2}$. [Preview Abstract] |
Monday, March 16, 2009 1:15PM - 1:27PM |
B36.00011: As-Grown Single-Walled Carbon Nanotube Diodes Govind Mallick, Shashi Karna, Sarah Lastella, Sangeeta Sahoo, Pulickel Ajayan We present the observation of unidirectional electric current through as-grown single-walled carbon nanotubes (SWNTs) grown by catalytic chemical vapor deposition (CCVD) process. Long strands of as-grown SWNTs were utilized to fabricate multiple arrays of switching devices with the channel length of 3, 5, 7 and 10 $\mu $m on a 15 mm x 15 mm SiO$_{2}$ on Si substrate. Of the fabricated devices, $\sim $ 34{\%} exhibited electrical activity. Of the active devices, about 70{\%} exhibited diode-like unidirectional current, not observed previously in CCVD grown SWNTs. High resolution atomic force microscopic (AFM) analysis of the device structure and surface topology of SWNTs suggests the observed unidirectional current to result from surface irregularities and change in the chirality along the tube axis. [Preview Abstract] |
Monday, March 16, 2009 1:27PM - 1:39PM |
B36.00012: Gate Controlled Negative Differential Resistance and Photoconductivity Enhancement in Carbon Nanotube Intra-connects Seon Woo Lee, Slava Rotkin, Andrei Sirenko, Haim Grebel Field effect transistors were fabricated using carbon nanotubes (CNT). Gate-controlled, N-shaped negative differential resistance (NDR) has been demonstrated. In addition, a large photoconductance effect was associated with the NDR. The intra-connects -- bridges spanning across planar electrodes and contain individual tube or in a small bundle -- were grown using chemical vapor deposition (CVD) precisely between very sharp metal tips on the pre-fabricated electrodes. NDR was observed for intra-connects exhibiting either, ohmic or, non-ohmic contacts. Yet, the enhanced photoconductivity was more pronounced for intra-connects exhibiting ohmic contact at zero gate bias. [Preview Abstract] |
Monday, March 16, 2009 1:39PM - 1:51PM |
B36.00013: Magnetic Carbon Nanotubes: Materials Development and Property Characterization Dereje Seifu, Shashi Karna A versatile chemical method was used to fill multi-wall carbon nanotubes (MWCNTs) with ferromagnetic nanoparticles [1]. For the first time, pulsed laser deposition and magnetron DC sputtering were used to fill vertically aligned MWCNTs. The later approaches gave high-yield nanoparticle filling of MWCNTs. Samples were characterized by Electron Microscopy, Energy Dispersive Spectroscopy, M\"{o}ssbauer Spectroscopy, and magnetization measurements. M\"{o}ssbauer measurements on chemically impregnated MWCNTs clearly show the presence of atomic Fe as well as mixed phases of Fe nano-particles inside the tubes. Magnetization measurements on PLD-filled vertically aligned MWCNTs indicate reasonable coercivity. However, the magnetic anisotropy appears to be randomly oriented, suggesting polycrystalline sample. \newline Acknowledgement: The research at Morgan State University was partially supported by the US ARL-WMRD (W1813LT-5006-7056). \newline [1] D. Seifu, Y. Hijji, G. Hirsch, and S. P. Karna, \textit{J. Magn. Magn. Mat.} \textbf{320}, 312 (2008). [Preview Abstract] |
Monday, March 16, 2009 1:51PM - 2:03PM |
B36.00014: Electrical and Thermal Properties of Orientated Multiwall Carbon Nanotube Bulk Materials Keqin Yang, Jian He, Zhe Shu, Apparao Rao Millimeter long vertically oriented multiwall carbon nanotube (MWNT) arrays with typical tube diameter around 30-50 nm were grown on Si substrates using thermal chemical vapor deposition. The arrays were realigned and densified using a spark plasma sintering process to form oriented MWNT bulk samples. Electron microscopy studies on the as-prepared bulk samples corroborate that the MWNTs are fairly well aligned and the pristine tubular morphology of the MWNTs is preserved during the sintering. The temperature dependent electrical, thermopower and thermal conductivity measurements were performed along different directions relative to the preferred orientation of MWNTs. In particular, the longitudinal and transverse thermal conductivity at 300 K are found to be about 35 W/(mK) and 1 W/(mK), respectively. In the temperature regime between 10 -- 300 K, the electrical resistivity is on the order of few m$\Omega $cm and exhibits a thermal excitation type temperature dependence, while the Seebeck coefficient is on the order of few uV/K and exhibits a weak temperature dependence. These results give new insights into the unique electrical and thermal transport mechanisms in and between MWNTs. [Preview Abstract] |
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