The Experts below are selected from a list of 14859 Experts worldwide ranked by ideXlab platform
Fong-cheng Tai - One of the best experts on this subject based on the ideXlab platform.
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The separation of different conducting multi-walled carbon nanotubes by AC Dielectrophoresis
Diamond and Related Materials, 2008Co-Authors: Chehung Wei, Ting-you Wei, Cheng-hao Liang, Fong-cheng TaiAbstract:A microfluidic device was fabricated to separate different conducting parts of multi-walled carbon nanotubes (MWCNTs). The device consists of a curing PDMS fluidic-flow chamber covered on electrode coated glass. The electrode was designed to generate non-uniform electric field by patterning via lithography. A range of frequencies with low applied voltage was utilized to induce different sign of Dielectrophoresis force. Two different separation schemes based on positive and negative Dielectrophoresis were employed to separate different conducting parts in unsorted MWCNTs. From Raman spectroscopy, conducting MWCNTs collected by positive Dielectrophoresis showed little variation in the intensities of D-band and G-band ratio while the less conducting MWCNTs collected by negative Dielectrophoresis showed decreasing intensities in these positions. The ID/IG ratio in the samples collected by both separation schemes is decreasing compared to the unsorted samples. The electric properties of the samples were characterized by a Dielectrophoresis frequency spectra method. The conductance in positive Dielectrophoresis collected sample is the greatest while the conductance in negative Dielectrophoresis collected sample is the smallest. The trend in the conductance in unsorted and sorted samples is confirmed by current-voltage measurements.
Chehung Wei - One of the best experts on this subject based on the ideXlab platform.
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The separation of different conducting multi-walled carbon nanotubes by AC Dielectrophoresis
Diamond and Related Materials, 2008Co-Authors: Chehung Wei, Ting-you Wei, Cheng-hao Liang, Fong-cheng TaiAbstract:A microfluidic device was fabricated to separate different conducting parts of multi-walled carbon nanotubes (MWCNTs). The device consists of a curing PDMS fluidic-flow chamber covered on electrode coated glass. The electrode was designed to generate non-uniform electric field by patterning via lithography. A range of frequencies with low applied voltage was utilized to induce different sign of Dielectrophoresis force. Two different separation schemes based on positive and negative Dielectrophoresis were employed to separate different conducting parts in unsorted MWCNTs. From Raman spectroscopy, conducting MWCNTs collected by positive Dielectrophoresis showed little variation in the intensities of D-band and G-band ratio while the less conducting MWCNTs collected by negative Dielectrophoresis showed decreasing intensities in these positions. The ID/IG ratio in the samples collected by both separation schemes is decreasing compared to the unsorted samples. The electric properties of the samples were characterized by a Dielectrophoresis frequency spectra method. The conductance in positive Dielectrophoresis collected sample is the greatest while the conductance in negative Dielectrophoresis collected sample is the smallest. The trend in the conductance in unsorted and sorted samples is confirmed by current-voltage measurements.
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The Application of Dielectrophoresis on the Characterization of Electric property in Multi Walled Carbon Nanotubes
Carbon Nanotubes and Associated Devices, 2008Co-Authors: Chehung Wei, Cheng-hou Liang, Ting-you WeiAbstract:Carbon nanotubes have been extensively studied due to their unique property and potential application like field emission. For successful implementation, it is essential to know the properties of carbon nanotubes. In this work, we propose a simple method to estimate the electric property of multi walled carbon nanotubes (MWCNTs) by ac Dielectrophoresis. Dielectrophoresis is a phenomenon resulted from the inhomogeneous electric field and has been used to sort out colloids with different dielectric properties. When applied ac Dielectrophoresis, the movement of the colloids depends on the polarizability of the colloids relative to the medium as well as the applied frequency. In certain frequency, the direction of Dielectrophoresis force will change and this crossover frequency is related to the electric property of colloids. Since the crossover frequency is a function of the particle’s dielectric property, as a result, if the crossover frequency can be obtained, then the electric property of MWCNTs can be estimated. In a preliminary experiment, NanoAmor MWCNTs (95+%, core diameter: 5-10 nm, outside diameter 20-40 nm, length 5-15µ m) mixed with alcohol, DI water and the surfactant was injected onto a Dielectrophoresis microfluidic chip to measure the crossover frequency. These MWCNTs were under negative Dielectrophoresis (repelled from high electric field) for frequencies over 12 KHz, and were under positive Dielectrophoresis (attracted to the high electric field) for frequencies under 1 KHz. These results were compared with the CM factor frequency spectrum with known electric properties. The results show that for positive Dielectrophoresis in low frequency and negative Dielectrophoresis in high frequency is a characteristic of conducting materials which indicates that these MWCNTs are conducting in nature. One application of this technique is the characterization of electric property of SWCNT which is currently under investigation.
H V Lohneysen - One of the best experts on this subject based on the ideXlab platform.
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simultaneous deposition of metallic bundles of single walled carbon nanotubes using ac Dielectrophoresis
Nano Letters, 2003Co-Authors: Ralph Krupke, Frank Hennrich, Heiko B Weber, Manfred M Kappes, H V LohneysenAbstract:A simple and scalable scheme based on alternating current (ac-) Dielectrophoresis is used for the simultaneous and site-selective deposition of single bundles of single-walled carbon nanotubes (SWNTs) onto a large number of contacts requiring only one bond wire. This allows for a large number of transport measurements that show that the deposited bundles contain at least one metallic SWNT dominating the transport. With high-voltage pulses, metallic bundles are transformed into Schottky-barrier-type field-effect transistors with p-type, ambipolar, or n-type behavior. From a simple electromechanical model, we derive the fact that ac-Dielectrophoresis selectively deposits bundles containing metallic tubes.
Peter Bøggild - One of the best experts on this subject based on the ideXlab platform.
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Dielectrophoresis of carbon nanotubes using microelectrodes: a numerical study
Nanotechnology, 2004Co-Authors: Maria Dimaki, Peter BøggildAbstract:Single-walled carbon nanotubes are candidates for a number of electronics and sensing applications, provided nanotubes with semiconducting and metallic band structure can be separated. Dielectrophoresis has recently been demonstrated as a route towards the separation of metallic nanotubes from semiconducting nanotubes, and is moreover a method for controlled assembly of the nanotubes on microstructures that has the possibility to be scaled to wafer-level manufacturing. In this paper we will present numerical calculations of carbon nanotubes subjected to Dielectrophoresis, drag force and Brownian motion induced by application of an ac voltage to a set of microelectrodes in a microliquid channel. We calculate the probability of capturing various types of carbon nanotubes, the time frame for the assembly and the efficiency of separation, for different experimental parameters. Our results suggest that relatively low frequencies, where both semiconducting and metallic nanotubes are subject to positive Dielectrophoresis, may be optimal for separation, due to large differences in the magnitude of the dielectrophoretic force.
Howard K Schmidt - One of the best experts on this subject based on the ideXlab platform.
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Dielectrophoresis field flow fractionation of single walled carbon nanotubes
Journal of the American Chemical Society, 2006Co-Authors: Haiqing Peng, Noe T Alvarez, Carter Kittrell, Robert H Hauge, Howard K SchmidtAbstract:We report a study on Dielectrophoresis Field Flow Fractionation of Single-Wall Carbon Nanotubes (SWNTs). SWNTs, individually suspended in 1% SDBS solution, were separated by type when they passed a Dielectrophoresis field flow fractionation device where 1 MHz AC voltage was supplied and the field strength was well below 1 V per μm. Furthermore, we uniquely observed enrichment of semiconductive SWNTs based on their band gap. In addition to Raman spectrum, UV−vis absorption and NIR fluorescence spectra were used for solution samples for characterization.