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Michael L Simpson - One of the best experts on this subject based on the ideXlab platform.

  • reversible electrowetting of vertically aligned superhydrophobic Carbon Nanofibers
    Langmuir, 2006
    Co-Authors: Manjeet Dhindsa, And Neil R Smith, J Heikenfeld, Philip D Rack, Jason D Fowlkes, Mitchel J Doktycz, And Anatoli V Melechko, Michael L Simpson
    Abstract:

    Reversible electrostatically induced wetting (electrowetting) of vertically aligned superhydrophobic Carbon Nanofibers has been investigated. Carbon Nanofibers on a 5 × 5 μm pitch were grown on Si substrates, electrically insulated with a conformal dielectric, and hydrophobized with fluoropolymer. This nanostructured scaffold exhibited superhydrophobic behavior for saline (θ ≈ 160°). Electrowetting induced a contact angle reduction to θ ≈ 100°. Competitive two-liquid (dodecane/saline) electrowetting exhibited reversibility on the same nanostructured scaffold. Without applied bias, ultra-fine-point tip (∼25 nm radius) Nanofibers result in effectively zero capacitance with the overlying saline layer. Complete electrowetting of the substrate is confirmed as capacitance values increase by several orders of magnitude with increased wetting. These results demonstrate the applicability of reversible electrowetting on nanostructured scaffolds and use of nanofabricated structures that can be integrated with variou...

  • initial growth of vertically aligned Carbon Nanofibers
    Applied Physics Letters, 2004
    Co-Authors: X Yang, Michael L Simpson, D H Lowndes, M Varela
    Abstract:

    Samples of vertically aligned Carbon Nanofibers (VACNFs) were viewed transverse to the growth direction and studied using both scanning and transmission electron microscopy. The VACNFs are composed of graphite layers nearly parallel to the substrate at their bottom end, gradually formed graphite “cups” in the main body, and a catalyst particle on the tip. The formation of such structure is due to the corresponding transformation of the shape of the catalyst particle during initial VACNF growth. A model for their initial growth is proposed.

  • four probe charge transport measurements on individual vertically aligned Carbon Nanofibers
    Applied Physics Letters, 2004
    Co-Authors: Lan Zhang, D H Lowndes, Derek W Austin, Vladimir I Merkulov, Anatoli V Meleshko, K L Klein, Michael A Guillorn, Michael L Simpson
    Abstract:

    We report four-probe I–V measurements on individual vertically aligned Carbon Nanofibers (VACNFs). These measurements were enabled by the fabrication of multiple Ti/Au ohmic contacts on individual fibers that exhibited resistance of only a few kilohms. These measurements demonstrate that VACNFs exhibit linear I–V behavior at room temperature, with a resistivity of approximately 4.2×10−3 Ω cm. Our measurements are consistent with a dominant transport mechanism of electrons traveling through intergraphitic planes in the VACNFs.

  • controlled alignment of Carbon Nanofibers in a large scale synthesis process
    Applied Physics Letters, 2002
    Co-Authors: Vladimir I Merkulov, Michael L Simpson, D H Lowndes, A V Melechko, M A Guillorn, J H Whealton, R J Raridon
    Abstract:

    Controlled alignment of catalytically grown Carbon Nanofibers (CNFs) at a variable angle to the substrate during a plasma-enhanced chemical vapor deposition process is achieved. The CNF alignment is controlled by the direction of the electric field lines during the synthesis process. Off normal CNF orientations are achieved by positioning the sample in the vicinity of geometrical features of the sample holder, where bending of the electric field lines occurs. The controlled growth of kinked CNFs that consist of two parts aligned at different angles to the substrate normal also is demonstrated.

  • control mechanisms for the growth of isolated vertically aligned Carbon Nanofibers
    Journal of Physical Chemistry B, 2002
    Co-Authors: Vladimir I Merkulov, D H Lowndes, A V Melechko, M A Guillorn, D K Hensley, Michael L Simpson
    Abstract:

    Isolated vertically aligned Carbon Nanofibers (VACNFs) have been grown using dc plasma-enhanced chemical vapor deposition, and the effects of the growth conditions on VACNF morphology and composition have been determined in substantial detail. The dependence of the growth rate, tip and base diameters, and chemical composition of isolated VACNFs on the growth parameters is described, including the effects of plasma power and gas mixture. Phenomenological models explaining the observed growth behavior are presented. The results indicate the importance of plasma control for the deterministic growth of isolated VACNFs, which are promising elements for the fabrication of practical nanoscale devices.

Jianming Jiang - One of the best experts on this subject based on the ideXlab platform.

  • microwave absorption enhancement of porous Carbon fibers compared with Carbon Nanofibers
    Journal of Physical Chemistry C, 2012
    Co-Authors: Tianshi Xie, Shenglin Yang, Junhong Jin, Jianming Jiang
    Abstract:

    Porous Carbon fibers (pores of: 0.1–3 μm in diameter) and Carbon Nanofibers (∼100 nm in diameter) were prepared from polyacrylonitrile/polymethyl methacrylate (PAN/PMMA) blend fibers with 70/30 and 30/70 weight ratio, respectively, as precursors. The composites containing 2–6 wt % porous Carbon fibers or Carbon Nanofibers as microwave absorbents were fabricated. The complex permittivity of these composites was measured, and the microwave absorption properties were stimulated based on a model for a single-layer plane wave absorber. We found that composites filled with the porous Carbon fibers exhibited a much better performance in microwave absorption than those containing the Carbon Nanofibers. Composites containing 6 wt % porous Carbon fibers or Carbon Nanofibers showed the lowest reflection loss of −31 dB at 9.7 GHz and −12.2 dB at 10.7 GHz, respectively. The bandwidth with reflection loss below −5 dB covered the whole X band (4.2 GHz) in the former case, whereas it was only 2.6 GHz in the latter case, ...

  • microwave absorption enhancement of porous Carbon fibers compared with Carbon Nanofibers
    Journal of Physical Chemistry C, 2012
    Co-Authors: Tianshi Xie, Shenglin Yang, Junhong Jin, Jianming Jiang
    Abstract:

    Porous Carbon fibers (pores of: 0.1–3 μm in diameter) and Carbon Nanofibers (∼100 nm in diameter) were prepared from polyacrylonitrile/polymethyl methacrylate (PAN/PMMA) blend fibers with 70/30 and...

D H Lowndes - One of the best experts on this subject based on the ideXlab platform.

  • initial growth of vertically aligned Carbon Nanofibers
    Applied Physics Letters, 2004
    Co-Authors: X Yang, Michael L Simpson, D H Lowndes, M Varela
    Abstract:

    Samples of vertically aligned Carbon Nanofibers (VACNFs) were viewed transverse to the growth direction and studied using both scanning and transmission electron microscopy. The VACNFs are composed of graphite layers nearly parallel to the substrate at their bottom end, gradually formed graphite “cups” in the main body, and a catalyst particle on the tip. The formation of such structure is due to the corresponding transformation of the shape of the catalyst particle during initial VACNF growth. A model for their initial growth is proposed.

  • four probe charge transport measurements on individual vertically aligned Carbon Nanofibers
    Applied Physics Letters, 2004
    Co-Authors: Lan Zhang, D H Lowndes, Derek W Austin, Vladimir I Merkulov, Anatoli V Meleshko, K L Klein, Michael A Guillorn, Michael L Simpson
    Abstract:

    We report four-probe I–V measurements on individual vertically aligned Carbon Nanofibers (VACNFs). These measurements were enabled by the fabrication of multiple Ti/Au ohmic contacts on individual fibers that exhibited resistance of only a few kilohms. These measurements demonstrate that VACNFs exhibit linear I–V behavior at room temperature, with a resistivity of approximately 4.2×10−3 Ω cm. Our measurements are consistent with a dominant transport mechanism of electrons traveling through intergraphitic planes in the VACNFs.

  • controlled alignment of Carbon Nanofibers in a large scale synthesis process
    Applied Physics Letters, 2002
    Co-Authors: Vladimir I Merkulov, Michael L Simpson, D H Lowndes, A V Melechko, M A Guillorn, J H Whealton, R J Raridon
    Abstract:

    Controlled alignment of catalytically grown Carbon Nanofibers (CNFs) at a variable angle to the substrate during a plasma-enhanced chemical vapor deposition process is achieved. The CNF alignment is controlled by the direction of the electric field lines during the synthesis process. Off normal CNF orientations are achieved by positioning the sample in the vicinity of geometrical features of the sample holder, where bending of the electric field lines occurs. The controlled growth of kinked CNFs that consist of two parts aligned at different angles to the substrate normal also is demonstrated.

  • control mechanisms for the growth of isolated vertically aligned Carbon Nanofibers
    Journal of Physical Chemistry B, 2002
    Co-Authors: Vladimir I Merkulov, D H Lowndes, A V Melechko, M A Guillorn, D K Hensley, Michael L Simpson
    Abstract:

    Isolated vertically aligned Carbon Nanofibers (VACNFs) have been grown using dc plasma-enhanced chemical vapor deposition, and the effects of the growth conditions on VACNF morphology and composition have been determined in substantial detail. The dependence of the growth rate, tip and base diameters, and chemical composition of isolated VACNFs on the growth parameters is described, including the effects of plasma power and gas mixture. Phenomenological models explaining the observed growth behavior are presented. The results indicate the importance of plasma control for the deterministic growth of isolated VACNFs, which are promising elements for the fabrication of practical nanoscale devices.

Vladimir I Merkulov - One of the best experts on this subject based on the ideXlab platform.

  • four probe charge transport measurements on individual vertically aligned Carbon Nanofibers
    Applied Physics Letters, 2004
    Co-Authors: Lan Zhang, D H Lowndes, Derek W Austin, Vladimir I Merkulov, Anatoli V Meleshko, K L Klein, Michael A Guillorn, Michael L Simpson
    Abstract:

    We report four-probe I–V measurements on individual vertically aligned Carbon Nanofibers (VACNFs). These measurements were enabled by the fabrication of multiple Ti/Au ohmic contacts on individual fibers that exhibited resistance of only a few kilohms. These measurements demonstrate that VACNFs exhibit linear I–V behavior at room temperature, with a resistivity of approximately 4.2×10−3 Ω cm. Our measurements are consistent with a dominant transport mechanism of electrons traveling through intergraphitic planes in the VACNFs.

  • controlled alignment of Carbon Nanofibers in a large scale synthesis process
    Applied Physics Letters, 2002
    Co-Authors: Vladimir I Merkulov, Michael L Simpson, D H Lowndes, A V Melechko, M A Guillorn, J H Whealton, R J Raridon
    Abstract:

    Controlled alignment of catalytically grown Carbon Nanofibers (CNFs) at a variable angle to the substrate during a plasma-enhanced chemical vapor deposition process is achieved. The CNF alignment is controlled by the direction of the electric field lines during the synthesis process. Off normal CNF orientations are achieved by positioning the sample in the vicinity of geometrical features of the sample holder, where bending of the electric field lines occurs. The controlled growth of kinked CNFs that consist of two parts aligned at different angles to the substrate normal also is demonstrated.

  • control mechanisms for the growth of isolated vertically aligned Carbon Nanofibers
    Journal of Physical Chemistry B, 2002
    Co-Authors: Vladimir I Merkulov, D H Lowndes, A V Melechko, M A Guillorn, D K Hensley, Michael L Simpson
    Abstract:

    Isolated vertically aligned Carbon Nanofibers (VACNFs) have been grown using dc plasma-enhanced chemical vapor deposition, and the effects of the growth conditions on VACNF morphology and composition have been determined in substantial detail. The dependence of the growth rate, tip and base diameters, and chemical composition of isolated VACNFs on the growth parameters is described, including the effects of plasma power and gas mixture. Phenomenological models explaining the observed growth behavior are presented. The results indicate the importance of plasma control for the deterministic growth of isolated VACNFs, which are promising elements for the fabrication of practical nanoscale devices.

Hao Fong - One of the best experts on this subject based on the ideXlab platform.

  • A review: Carbon Nanofibers from electrospun polyacrylonitrile and their applications
    Journal of Materials Science, 2014
    Co-Authors: Lifeng Zhang, Alex Aboagye, Ajit Kelkar, Chuilin Lai, Hao Fong
    Abstract:

    Carbon Nanofibers with diameters that fall into submicron and nanometer range have attracted growing attention in recent years due to their superior chemical, electrical, and mechanical properties in combination with their unique 1D nanostructures. Unlike catalytic synthesis, electrospinning polyacrylonitrile (PAN) followed by stabilization and Carbonization has become a straightforward and convenient route to make continuous Carbon Nanofibers. This paper is a comprehensive and state-of-the-art review of the latest advances made in development and application of electrospun PAN-based Carbon Nanofibers. Our goal is to demonstrate an objective and overall picture of current research work on both functional Carbon Nanofibers and high-strength Carbon Nanofibers from the viewpoint of a materials scientist. Strategies to make a variety of Carbon nanofibrous materials for energy conversion and storage, catalysis, sensor, adsorption/separation, and biomedical applications as well as attempts to achieve high-strength Carbon Nanofibers are addressed.

  • development of Carbon Nanofibers from aligned electrospun polyacrylonitrile nanofiber bundles and characterization of their microstructural electrical and mechanical properties
    Polymer, 2009
    Co-Authors: Zhengping Zhou, Lifeng Zhang, Yong Qian, Darrell H Reneker, Hao Fong
    Abstract:

    Abstract Carbon Nanofibers with diameters of 200–300 nm were developed through stabilization and Carbonization of aligned electrospun polyacrylonitrile (PAN) nanofiber bundles. Prior to the oxidative stabilization in air, the electrospun PAN nanofiber bundle was tightly wrapped onto a glass rod, so that tension existed during the stabilization. We also investigated several Carbonization procedures by varying final Carbonization temperatures in the range from 1000 to 2200 °C. The study revealed that: (1) with increase of the final Carbonization temperature, the Carbon Nanofibers became more graphitic and structurally ordered; (2) the Carbon nanofiber bundles possessed anisotropic electrical conductivities, and the differences between the parallel and perpendicular directions to the bundle axes were over 20 times; and (3) the tensile strengths and Young's moduli of the prepared Carbon nanofiber bundles were in the ranges of 300–600 MPa and 40–60 GPa, respectively.

  • Carbon Nanofibers from polyacrylonitrile and mesophase pitch
    Journal of Advanced Materials, 1999
    Co-Authors: Iksoo Chun, Darrell H Reneker, Hao Fong, Xiaoyan Fang, Joseph M. Deitzel, Nora Beck Tan, K. Kearns
    Abstract:

    Carbon Nanofibers were produced from both polyacrylonitrile and mesophase pitch. Stabilization and Carbonization processes were used to convert as-spun Nanofibers to Carbon fibers. The Nanofibers are arbitrarily long, although a way to make Nanofibers less than a millimeter long, with high aspect ratios, was found. The diameters of typical Carbon Nanofibers are in the range from 100 nanometer to a few microns. A log normal distribution provides a good representation of the measured distribution of diameters. The Carbon Nanofibers were observed by polarized optical microscopy, scanning electron microscopy, transmission electron microscopy, and wide angle x-ray diffraction. As-spun mesophase pitch fibers are transparent, red or orange in transmitted light, and birefringent. Electron diffraction patterns were obtained from individual Carbon Nanofibers. The interplane spacing of (002) planes of mesophase pitch based Carbon Nanofibers was measured using wide angle x-ray diffraction. Nanofibers provide a higher ratio of surface area to mass than Carbon fibers ordinarily used in composites. Carbon Nanofibers can be useful in filters, as a support for catalysts in high temperature reactions, in composites to improve mechanical properties, or for thermal management in semiconductor devices. Nanopores in Carbon fibers were produced using nitrogen gas saturated with water vapor.