Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Z20: Carbon Nanotubes: Fundamentals and Applications |
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Sponsoring Units: FIAP Chair: Yuriy Bozme, Duke University Room: C120-122 |
Friday, March 19, 2010 11:15AM - 11:27AM |
Z20.00001: Tuning Circular Carbon Nanotubes into Regular Polygons via Selective Hydrogenation Guangfen Wu, Jinlan Wang, Feng Ding Using density functional theory approach, we study the selective hydrogenation of single walled carbon nanotubes (SWNTs). We confirmed that fully hydrogenated SWNT (FH-SWNT) is energetically more favorable than partially hydrogenated ones. Previous studies have revealed polygonization of bare carbon nanotubes (CNTs) through plasticity and buckling. Different from those traditional mechanical methods, we found that the curvature energy of a FH-SWNT can be significantly relaxed by the breaking of its cylindrical symmetry through a chemical pathway with low energetic compensation. Flipping a few rows of H over the FH-SWNT wall significantly reduces the tube curvature energy and leads to more stable configurations with polygonal (triangle, square etc) cross-sections. [Preview Abstract] |
Friday, March 19, 2010 11:27AM - 11:39AM |
Z20.00002: Synthesis, Characterization and Adaptability of Carbon Nanotube-Based Solid Lubricants Amelia Church, Xianfeng Zhang, Brandon Luster, Punit Kholi, Samir Aoaudi, Saikat Talapatra We report on the experimental investigations of the tribological properties of carbon nanotube (CNT) based composites. Two different CNT composites were obtained by electro-depositing molybdenum disulfide (MoS$_{2})$ and silver (Ag) on vertically aligned assemblies of CNTs. Both of the CNT based composites, CNT-MoS$_{2,}$ as well as CNT-Ag, showed substantially lower values of friction coefficients and wear rates than traditional thin films of MoS$_{2,}$ and Ag. The adaptabilities of these composites under humid and non-humid conditions for CNT-MoS$_{2,}$ and high temperature cycling in the case of CNT-Ag composites, were also tested and will be presented. Our results indicate that the CNT-MoS$_{2}$ composites were able to sustain their lubricating properties under humid/non-humid cycling, whereas the CNT-Ag composites showed degradation of their frictional properties under high temperature cycling. [Preview Abstract] |
Friday, March 19, 2010 11:39AM - 11:51AM |
Z20.00003: Phase behavior of SWNT-superacid solutions and fabrication of aligned macrostructures Budhadipta Dan, Matteo Pasquali Single-wall carbon nanotubes (SWNTs) are carbon based molecules which possess very high aspect ratio, high persistence length and behave as rigid rods when dispersed in a liquid phase. Superacids (oleum, chlorosulfonic acid etc) have been shown as one of the most effective solvents for dispersing and dissolving SWNTs. The SWNT-superacid systems exhibit a very rich phase behavior with well defined isotropic, bi-phasic and liquid crystalline phases, and controlled by factors like the SWNT concentration, SWNT length and strength of the acid (solvent). We report the fabrication of SWNT macrostructures with high degree of alignment by self assembly and exploiting the phase behavior of SWNT-superacid solutions. Phase transitions were induced in SWNT-superacid solutions in a controlled manner by gradually changing the strength of the acid solvent. This resulted in the precipitation of SWNT flakes and fibrils which exhibit a high degree of alignment. Detailed characterization of these macrostructures was performed using Raman spectroscopy and polarized optical microscopy. The above method presents a self-assembly based route for fabrication of aligned SWNT based structures from SWNT-superacid systems. [Preview Abstract] |
Friday, March 19, 2010 11:51AM - 12:03PM |
Z20.00004: An ab initio realization of the transport in molecular junctions with armchair carbon-nanotube leads Yiing-Rei Chen, Hsin-Han Lee We perform an ab initio study for the system of molecular junctions with armchair carbon-nanotube leads. The transport behavior of the different 2-polyene junction cases shows remarkable agreement with the expected interference effect we predict with tight binding model which greatly simplified and omitted realistic parameters. Moreover, the slight disagreements between the ab initio study and the analytic study could be well understood with the parameter tests in the tight binding model. [Preview Abstract] |
Friday, March 19, 2010 12:03PM - 12:15PM |
Z20.00005: Nematic Anchoring on Carbon Nanotubes Rajratan Basu, Germano Iannacchione A$^{ }$dilute suspension of carbon nanotubes (CNTs) in a nematic liquid$^{ }$crystal (LC) does not disturb the LC director. Due to$^{ }$a strong LC-CNT anchoring energy and structural symmetry matching, CNT$^{ }$long axis follows the director field, possessing enhanced dielectric anisotropy$^{ }$of the LC media. This strong anchoring energy stabilizes local \textit{pseudonematic} domains, resulting in nonzero dielectric anisotropy in the isotropic$^{ }$phase. These anisotropic domains respond to external electric fields and$^{ }$show intrinsic frequency response. The presence of these domains makes$^{ }$the isotropic phase electric field-responsive, giving rise to a large$^{ }$dielectric hysteresis effect. [Preview Abstract] |
Friday, March 19, 2010 12:15PM - 12:27PM |
Z20.00006: A Multi-scale Approach to Nano-Composite Nickel-Based Materials Angela Wilson, Jamal Uddin, Thomas Cundari The behavior of nano-composite materials that are formed by incorporating aligned carbon nanotubes (CNTs) into a bulk nickel matrix have been considered. Mechanical properties of these novel materials have been predicted and strain-stress relationships have been investigated by atomistic calculations with interactions derived from the modified embedded-atom method (MEAM). The mechanical stability has been assessed, with consideration of Young's modulus both within and beyond the small elastic deformation regime. Comparisons have been made between Ni/CNTs, the pure FCC nickel matrix, and pristine CNTs. Both single-walled and multi-walled nanotube systems have been considered. [Preview Abstract] |
Friday, March 19, 2010 12:27PM - 12:39PM |
Z20.00007: Physical Properties of Carbon Nanotube Sheets Dry-Drawn from Tall MWCNT Forests Julia Bykova, William Holmes, Anvar Zakhidov Highly aligned MWCNT forests can by grown by catalytic CVD process in a dry-spinable highly oriented form which allows to draw CNT sheets and twist spin yarns [1,2]. However the sheet resistance of such transparent CNT sheets with average height of 300 um is quite high: 500-700 Ohm/sq. Motivation of our study is to grow taller forests with optimal interbundle connectivity [3] which may result in lower sheet resistance of CNT sheets and higher optical transparency by optimized control of CCVD conditions. We have succeeded to grow tall CNT forest with h=1 $\mu$m and resulting sheet resistance about 200 Ohm/sq. To find the correlation between properties of CNT forests and CNT sheets we conducted SEM analysis combined with Raman, AFM and small-angle X-ray scattering. This study shows how the number, geometry, and mechanical strength of interconnects between bundles are related to the physical properties of CNT sheets. \\[4pt] [1] M.Zhang, S.Fang et al., Science, V.309 (2005) 1215 \\[0pt] [2] M.Zhang, K.Atkinson, R.Baughman, Science, V.306 (2004) 1358 \\[0pt] [3] A.Kuznetsov, A.Fonseca et al., Adv.Mat., (submitted) [Preview Abstract] |
Friday, March 19, 2010 12:39PM - 12:51PM |
Z20.00008: Isosteric heat of adsorption and uptake of gases in open and closed individual carbon nanotubes Mamadou Mbaye, Silvina Gatica We compute by the method of Grand Canonical Monte Carlo the adsorption of argon, methane and hydrogen in the interior and exterior of a single carbon nanotube. The isosteric heat of adsorption is calculated, and the steps observed in the computed adsorption isotherms are interpreted as the formation of cylindrical layers. Our simulations are compared with novel experimental results obtained recently for adsorption in individual carbon nanotubes. [Preview Abstract] |
Friday, March 19, 2010 12:51PM - 1:03PM |
Z20.00009: Characterisation of Carbon Nano-Materials with the Confocal Raman AFM Klaus Weishaupt, Jiangyong Yang, Thomas Dieing, Ute Schmidt Carbon is known to exist in a number of allotropes which range from single crystalline diamond - the hardest of all known materials, to the soft, mainly amorphous graphite. The recently discovered carbon nano- materials such as nanotubes and graphene gain more attention in the field of material science due to their light weight, unique electrical and optical properties and mechanical strength. The implementation of such carbon nano-materials into electrical devices or as fillers in polymeric matrixes requires characterization techniques suited for the nanometer range. Due to the unique optical properties of carbon nano-materials, Raman microscopy can be used to characterize single walled carbon nanotubes (SWCNT) with a diameter far below the optical resolution limit in the nano-meter range. Furthermore, the distribution of such nanotubes in polymeric matrixes can be visualized structurally as well as chemometrically. Raman spectroscopy is a well-suited tool to characterize graphene with its unique optical properties, similar to those of CNTs, as a two-dimensional model system. The correlation of spectral data with the number of grapheme layers can be achieved by combining Raman microscopy with AFM. [Preview Abstract] |
Friday, March 19, 2010 1:03PM - 1:15PM |
Z20.00010: Characterization of the junction between single-walled carbon nanotube films and silicon substrates Nischal Arkali Radhakrishna, Ashkan Behnam, Jason Johnson, Ant Ural We experimentally characterize the junction between single-walled carbon nanotube (CNT) films and both $n$-type and $p$-type Si substrates. We prepare CNT films by vacuum filtration, transfer them onto Si substrates and pattern them by photolithography and reactive ion etching. We also fabricate control samples, in which the CNT film is replaced with a Ti/Au metal stack for comparison. We characterize these devices by dark and photo $I-V$ and $C-V$ measurements at various temperatures. Our dark $I-V$ measurements reveal that the CNT film forms a Schottky contact with an average barrier height of 0.44 $\pm $ 0.03 eV and 0.6 $\pm $ 0.02 eV on $p$-type and $n$-type Si, respectively. Average ideality factors and series resistances (normalized with area) are also extracted for both the $n$- and $p$-type CNT film-Si junctions. Furthermore, photocurrent measurements at reverse bias result in responsivity and normalized photo to dark current ratio of 0.197 A/W and 7.11 $\times $ 10$^{4}$ mW$^{-1}$ respectively at a bias of 3 volts. $C-V$ measurements verify the barrier heights extracted from $I-V $measurements. These results extract the important parameters of CNT film-Si junctions and facilitate the application of CNT films as Schottky electrodes in conventional semiconductor electronic and optoelectronic devices. [Preview Abstract] |
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