Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session L22: Focus Session: Carbon Nanotubes Alignment and Sorting: Device Applications |
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Sponsoring Units: DMP Chair: Mathias Steiner, IBM Room: Portland Ballroom 252 |
Tuesday, March 16, 2010 2:30PM - 3:06PM |
L22.00001: Functional Single-walled Carbon Nanotube Electrodes for Solar Energy Conversion Invited Speaker: In this presentation, we discuss our progress in producing high surface area electrodes from single-walled carbon nanotubes (SWNTs) and the utilization of these electrodes in solar energy conversion devices. SWNTs have several fundamental properties that make them attractive for functional electrodes, including high electron and hole mobilities, a tunable work function with an energy range relevant to many photovoltaic devices, and optical transitions in the visible and near infrared that may be useful for solar driven photochemical reactions. Additionally, they possess numerous properties amenable to practical, scalable, and economic electrode deposition including abundant source material, a natural disposition for solution processing, and high surface area and flexibility. All of these features make them extremely attractive for replacing conventional electrodes, such as tin-doped indium oxide (ITO), which suffer from questionable world supply, high temperature/low pressure deposition requirements, and brittleness. We will present our development of a versatile and scalable ultrasonic spray process for producing SWNT electrodes with high transparency, high conductivity, and very low surface roughness. This method can be adapted for aqueous and organic solvents, allowing SWNT electrodes to be sprayed on a variety of different substrates, including directly on photovoltaic devices. The performance of PV devices incorporating our electrodes is nearly equivalent to devices incorporating traditional transparent conducting oxides. Finally, we demonstrate that this method can be extended to the production of a variety of different functional SWNT electrodes, including bio-hybrid electrodes for the production of hydrogen fuel. These electrodes achieve electrolytic current densities close to that of platinum at a fraction of the cost. We will discuss devices incorporating bulk SWNTs as well as SWNTs enriched in specific electronic structures. [Preview Abstract] |
Tuesday, March 16, 2010 3:06PM - 3:18PM |
L22.00002: Nanotube-graphene interfaces Mitsuhide Takekoshi, Vikram Deshpande, Tony Heinz, James Hone , Philip Kim It is advantageous for carbon nanoelectronics to develop nanotube-graphene hybrid circuits to fully utilize the individual strengths of both materials. In particular, their similarity of lattice parameters and electronic work-function suggests the formation of seamless electrical interfaces between these materials, which is an appealing prospect for this field. Here, we study electrical transport across such interfaces for both exfoliated and CVD-grown graphene. We will present our device fabrication and latest results. [Preview Abstract] |
Tuesday, March 16, 2010 3:18PM - 3:30PM |
L22.00003: Chemically doped, transparent carbon nanotube films and the study of their interface with amorphous silicon Bhupesh Chandra, George Tulevski, Ali Afzali-Ardakani, Teresita Graham Carbon nanotube films are a strong candidate for replacing ITO as transparent electrode in variety of applications such as solar cells, flexible electronics, displays etc. A nanotube film is a network of semiconducting and metallic nanotubes where the electronic properties are dominated mainly by tube-tube interfaces. Chemical doping of nanotubes decreases the tube resistivity and helps in reducing the high barriers present at the tube-tube junctions. However, most of the chemical dopants presently used are very unstable and highly oxidizing in nature, making them less attractive for practical applications. Present work focuses on a novel charge transfer compound which can bring a much stable chemical doping to the nanotube films. Optical and electronic transport measurements on such doped films will be presented. Measurement of interfacial electronic barriers between doped nanotube films and p-doped silicon surface of amorphous silicon solar cell will also be discussed. [Preview Abstract] |
Tuesday, March 16, 2010 3:30PM - 3:42PM |
L22.00004: Single-Walled Carbon Nanotube Transparent Electrodes Jeremy D. Bergeson, Jeffrey L. Blackburn, Patrick R. Brown, Brian A. Larsen, Matthew O. Reese, Teresa M. Barnes Transparent conducting electrodes made from thin-film networks of single-walled carbon nanotubes (SWCNTs) are an alternative to transparent conducting oxides in many optoelectronic device applications. However, we have shown the electrical conductivity of SWCNT electrodes is limited by energy barriers at the nanotube-nanotube interfaces throughout the thin-film network [Barnes, et al., ACS Nano 2, 1968 (2008)]. We investigate various fabrication and treatment conditions to improve the electrical and optical properties of these SWCNT films. One potential pathway to improvement is to change the distribution of metallic-to-semiconducting tube types within the SWCNT network. We report the thorough characterization of SWCNT network electrodes with highly enriched metallic or semiconducting tube content through optical transmission and electrical transport measurements, as well as their performance in both organic and inorganic thin-film photovoltaic devices. [Preview Abstract] |
Tuesday, March 16, 2010 3:42PM - 4:18PM |
L22.00005: Synthesis and application of CNT arrays Invited Speaker: High mobilities and other attractive features of single-walled carbon nanotubes (SWNTs), create interest in their use in high speed or unusual (i.e. flexible, stretchable) forms of electronics. Growth strategies that use chemical vapor deposition onto crystalline quartz substrates yield nearly perfectly linear, perfectly aligned, horizontal arrays of individual SWNTs. Such configurations are ideally suited to integration into planar device technologies. This talk describes our research in this area, and highlights (1) fundamental theoretical and experimental studies of the alignment process, (2) some strategies for achieving high density arrays and for removing metallic SWNTs, and (3) device and circuit implementations, including high mobility transistors with GHz switching speeds and their integration into carbon nanotube transistor radios. [Preview Abstract] |
Tuesday, March 16, 2010 4:18PM - 4:30PM |
L22.00006: Wafer-scale Meniscus Alignment of Carbon Nanotubes Joshua Wood, Vineet Nazareth, Joseph Lyding Making single-walled carbon nanotubes (SWNTs) a possible next-generation transistor nanotechnology requires control of their chirality, length, placement, and alignment. We develop a method for controlled placement and alignment of SWNTs using mechanical meniscus action. In this technique, we suspend surfactant-coated SWNTs in aqueous solution and place the solution between two surfaces of differing hydrophobicity, forming a meniscus. We drag this meniscus across the bottom substrate, causing SWNT alignment in the meniscus drag direction by torque. Alignment critically depends on the meniscus velocity and the substrate's contact angle, parameters that we determine from Monte Carlo simulation. On the H-passivated Si(111) surface, our SWNTs align with at an angle of 4.35$\pm $37.94\r{ } relative to the meniscus direction, indicating good alignment. We place SWNTs in densities of up to $\sim $30 SWNTs/$\mu $m$^{2}$, with the density exponentially dependent on the number of meniscus passes. In comparison to aligning SWNTs during growth or by dielectrophoresis, our technique aligns SWNTs on the wafer-scale while controlling SWNT density and using chirally pure SWNTs. [Preview Abstract] |
Tuesday, March 16, 2010 4:30PM - 4:42PM |
L22.00007: Structural Control of Carbon Nanotube Networks for High-Performance Devices Juhun Park, Minbaek Lee, Hyungwoo Lee, Seunghun Hong, Young-Kyun Kwon, Meg Noah, June Park, Maeng-Je Seong In recent years, single walled carbon nanotube (swCNT)-based network devices were extensively studied for various practical applications such as transistors, sensors, etc. However, `random' network-based devices have been suffering from various limitations such as poor on-off ratio, decreased mobility and conductivity with reduced channel width. Herein, we report a simple but efficient strategy to significantly improve the performance of network-based devices by controlling the `network structures'. In this method, self-assembly monolayer was utilized to control the structures of CNT networks with desired connectivity. For example, as the channels of swCNT-based transistors became narrower, swCNTs aligned in the channels, which resulted in the enhancement of their on--off ratios. Significantly, the aligned network channels exhibited enhanced conductivity and mobility with reduced line width, which is a completely opposite behavior to randomly oriented swCNT networks or even conventional silicon-based devices. Furthermore, we could also improve the sensitivity of swCNT network-based sensors by aligning swCNTs in the networks. [Preview Abstract] |
Tuesday, March 16, 2010 4:42PM - 4:54PM |
L22.00008: Enhanced electromodulation of infrared transmittance in semitransparent films of large diameter semiconducting single-walled carbon nanotubes Feihu Wang, Mikhail Itkis, Robert Haddon We report a comprehensive study of the gate induced electromodulated transmittance of infrared light by single-walled carbon nanotube (SWNT) thin films. The observed electromodulation is significantly enhanced by utilizing large diameter SWNTs, increasing the ratio of semiconducting to metal SWNTs and by decreasing the SWNT film thickness. The amplitude of the effect reported herein is more than an order of magnitude larger than in previous SWNT thin film solid state devices. [Preview Abstract] |
Tuesday, March 16, 2010 4:54PM - 5:06PM |
L22.00009: Selection of Single-Walled Carbon Nanotubes According to both Their Diameter and Chirality via Nanotweezers Jing Zhou, Hong Li, Jing Lu, Guangfu Luo, Lin Lai, Rui Qin, Lu Wang, Zhengxiang Gao, Dapeng Yu, Shigeru Nagase, Wai-Ning Mei, Guangping Li, Stefano Sanvito Diameter- and chirality-dependent interaction between the aromatic molecule-based nanotweezers (NTs) and single-walled carbon nanotubes (SWNTs) is revealed for the first time by using the density functional theory. We found the threshold diameter of selected SWNTs is determined by the end-to-end distance of the NTs. Large-diametered SWNTs are preferred by the NTs with an obtuse folding angle, whereas small-diametered SWNTs are favored by the one with an acute folding angle. The adsorption can be further stabilized by the orientational alignment of the hexagonal ring between the NTs and SWNT sidewall. Therefore, by taking advantage of the supramolecular recognition ability of the NTs, SWNTs can be enriched with both controllable diameter and chirality. [Preview Abstract] |
Tuesday, March 16, 2010 5:06PM - 5:18PM |
L22.00010: Chirality Separation in Larger Diameter Nanotubes Jeffrey Fagan, Ji Yeon Huh, Angela Walker, Erik Hobbie Separation of carbon nanotubes by their chiral vector becomes increasingly difficult as the diameter of the nanotube, and thus the number of combinatorial possibilities, increases. Here the separation of laser ablation and electric arc synthesized SWCNTs by the apparent chiral angle, but not diameter, of the SWCNTs is reported. Separation is achieved through ultracentrifugation, and non-intuitively works under the experimental conditions only for larger diameter SWCNTs. Characterization of the resulting fractions was performed through resonant Raman, NIR photoluminescence and UV-vis-NIR absorbance spectroscopies. [Preview Abstract] |
Tuesday, March 16, 2010 5:18PM - 5:30PM |
L22.00011: Selective Isolation of Single-Walled Carbon Nanotubes Using Density Gradient Ultracentrifugation Pei Zhao, Georgia Lagoudas, Erik Einarsson, Junichiro Shiomi, Shigeo Maruyama We present a protocol to selectively isolate single-walled carbon nanotubes (SWNTs) using density gradient ultracentrifugation (DGU). Starting with SWNTs synthesized by the alcohol catalytic chemical vapor deposition (ACCVD) method and using sodium deoxycholate (DOC) and sodium dodecyl sulfate (SDS) as co-surfactant encapsulating agents we achieved isolation of SWNTs with different properties. By changing the order in which surfactants were added, SWNTs could be separated into colorful layers containing different chiralities or diameters, such as (6,5) in a violet layer. However, if the co-surfactants are both added to disperse SWNTs, subsequent DGU results in the simultaneous selection of (6,5) nanotubes and separation of semiconducting/metallic nanotubes. Various optical spectroscopies, such as optical absorbance and photoluminescence excitation (PLE) were used to characterize the SWNTs before and after DGU. A time-dependent sequence of the simultaneous selection and separation shows that three main portions---corresponding to semiconducting, metallic, and (6,5) nanotubes---clearly have different moving behavior during the DGU process. This method illustrates the potential for nanotube isolation and separation, and we believe that further refinement of this process can lead to higher purity extractions of SWNTs. [Preview Abstract] |
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