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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Analysis of Carbon Nanotube Metal-Semiconductor Diode Device

We study recently reported drain current I(sub d)-drain voltage V(sub d) characteristics of a carbon nanotube metal-semiconductor diode device with the gate voltage V(sub g) applied to modulate the carrier density in the nanotube. The diode was kink-shaped at the metal-semiconductor interface. It was shown that (1) larger negative V(sub g) blocked I(sub d) more effectively in the negative V(sub d) region, resulting in the rectifying I(sub d)-V(sub d) characteristics, and that (2) positive V(sub g) allowed I(sub d) in the both V(sub d) polarities, resulting in the non-rectifying characteristics. The negative V(sub d) was the Schottky reverse direction, judging from the negligible I(sub d) behavior for a wide region of -4 V (is less than) V(sub d) (is less than) 0 V, with V(sub g) = -4 V. Such negative V(sub g) would attract positive charges from the metallic electrodes (charge reservoir) to the nanotube and lower the nanotube Fermi energy (E(sub F)). With larger negative V(sub g), the experiment showed that the Schottky forward direction (V(sub d) (is greater than) 0) had a smaller turn-on voltage and the Schottky reverse direction (V(sub d) (is less than) 0) was more resistant to the tunneling breakdown. Therefore, the majority carriers in the transport would be electrons since they can see a lower tunneling barrier (shallower built-in potential) in the forward direction when E(sub F) is lowered, and a thicker tunneling barrier (Schottky barrier) in the reverse direction due to the reduction in the electron density when E(sub F) is lowered.

Yamada, Toshishige↗
NASA NTRS2001

Thermal Expansion and Diffusion Coefficients of Carbon Nanotube-Polymer Composites

Classical molecular dynamics (MD) simulations employing Brenner potential for intra-nanotube interactions and van der Waals forces for polymer-nanotube interface have been used to investigate thermal expansion and diffusion characteristics of carbon nanotube-polyethylene composites. Addition of carbon nanotubes to polymer matrix is found to significantly increase the glass transition temperature Tg, and thermal expansion and diffusion coefficients in the composite above Tg. The increase has been attributed to the temperature dependent increase of the excluded volume for the polymer chains, and the findings could have implications in the composite processing, coating and painting applications.

Wei, Chengyu↗
NASA NTRS2002

Analysis of Carbon Nanotube Metal-Semiconductor Diode Device

We study recently reported drain current Id-drain voltage Vd characteristics of a carbon nanotube metal semiconductor diode device with the gate voltage Vg applied to modulate the carrier density in the nanotube. The diode was kink-shaped at the metal-semiconductor interface. It was shown that (1) larger negative Vg blocked Id more effectively in the negative Vd region, resulting in the rectifying Id-Vd characteristics, and that (2) positive Vg allowed Id in the both Vd polarities, resulting in the non-rectifying characteristics. The negative Vd was the Schottky reverse direction, judging from the negligible Id behavior for a wide region of -4 V less than Vd less than 0 V, with Vg = -4 V. Such negative Vg would attract positive charges from the metallic electrodes (charge reservoir) to the nanotube and lower the nanotube Fermi energy (EF). With larger negative Vg, the experiment showed that the Schottky forward direction (Vd greater than 0) had a smaller turn-on voltage and the Schottky reverse direction (Vd less than 0) was more resistant to the tunneling breakdown. Therefore, the majority carriers in the transport would be electrons since they can see a lower tunneling barrier (shallower built-in potential) in the forward direction when EF is lowered, and a thicker tunneling barrier (Schottky barrier) in the reverse direction due to the reduction in the electron density when EF is lowered.

Yamada, Toshishige↗
NASA NTRS2002

Imaging Carbon Nanotubes in High Performance Polymer Composites via Magnetic Force Microscope

Application of carbon nanotubes as reinforcement in structural composites is dependent on the efficient dispersion of the nanotubes in a high performance polymer matrix. The characterization of such dispersion is limited by the lack of available tools to visualize the quality of the matrix/carbon nanotube interaction. The work reported herein demonstrates the use of magnetic force microscopy (MFM) as a promising technique for characterizing the dispersion of nanotubes in a high performance polymer matrix.

Lillehei, Peter T.↗
NASA NTRS2003

Development of Metal-impregnated Single Walled Carbon Nanotubes for Toxic Gas Contaminant Control in Advanced Life Support Systems

The success of physico-chemical waste processing and resource recovery technologies for life support application depends partly on the ability of gas clean-up systems to efficiently remove trace contaminants generated during the process with minimal use of expendables. Highly purified metal-impregnated carbon nanotubes promise superior performance over conventional approaches to gas clean-up due to their ability to direct the selective uptake gaseous species based both on the nanotube s controlled pore size, high surface area, and ordered chemical structure that allows functionalization and on the nanotube s effectiveness as a catalyst support material for toxic contaminants removal. We present results on the purification of single walled carbon nanotubes (SWCNT) and efforts at metal impregnation of the SWCNT's.

Cinke, Martin↗
NASA NTRS2003

Preparation and Characterization of Space Durable Polymer Nanocomposite Films from Functionalized Carbon Nanotubes

Low color, flexible, space durable polyimide films with inherent, robust electrical conductivity have been under investigation as part of a continuing materials development activity for future NASA space missions involving Gossamer structures. Electrical conductivity is needed in these films to dissipate electrostatic charge build-up that occurs due to the orbital environment. One method of imparting conductivity is through the use of single walled carbon nanotubes (SWNTs). However, the incompatibility and insolubility of the SWNTs severely hampers their dispersion in polymeric matrices. In an attempt to improve their dispersability, SWNTs were functionalized by the reaction with an alkyl hydrazone. After this functionalization, the SWNTs were soluble in select solvents and dispersed more readily in the polymer matrix. The functionalized SWNTs were characterized by Raman spectroscopy and thermogravimetric analysis (TGA). The functionalized nanotubes were dispersed in the bulk of the films using a solution technique. The functionalized nanotubes were also applied to the surface of polyimide films using a spray coating technique. The resultant polyimide nanocomposite films were evaluated for nanotube dispersion, electrical conductivity, mechanical, and optical properties and compared with previously prepared polyimide-SWNT samples to assess the effects of SWNT functionalization.

Delozier, D. M.↗
NASA NTRS2003

Attachment of Single-wall Carbon Nanotubes (SWNTs) on Platinum Surfaces by Self-Assembling Techniques

Single-wall carbon nanotubes (SWNTs) are very interesting materials because of their morphology, electronic and mechanical properties. Its morphology (high length-to-diameter ratio) and electronic properties suggest potential application of SWNTs as anode material for lithium ion secondary batteries. The introduction of SWNTs on these types of sources systems will improve their performance, efficiency, and capacity to store energy. A purification method has been applied for the removal of iron and amorphous carbon from the nanotubes. Unpurified and purified SWNTs were characterized by transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). In order to attach carbon nanotubes on platinum electrode surfaces, a self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP) was deposited over the electrodes. The amino-terminated SAM obtained was characterized by cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and Fourier-transforms infrared (FTIR) spectroscopy. Carbon nanotubes were deposited over the amino-terminated SAM by an amide bond formed between SAM amino groups and carboxylic acid groups at the open ends of the carbon nanotubes.This deposition was characterized using Raman spectroscopy and Scanning Electron microscopy (SEM).

Rosario-Castro, Belinda I.↗
NASA NTRS2004

Growth of Multi-Walled Carbon Nanotubes by Injection CVD Using Cyclopentadienyliron Dicarbonyl Dimer and Cyclooctatetraene Iron Tricarbonyl

Preferential oriented multiwalled carbon nanotubes were prepared by the injection chemical vapor deposition (CVD) method using either cyclopentadienyliron dicarbonyl dimer or cycloctatetraene iron tricarbonyl as the iron catalyst source. The catalyst precursors were dissolved in toluene as the carrier solvent for the injections. The concentration of the catalyst was found to influence both the growth of the nanotubes as well as the amount of iron in the deposited material. As deposited the multiwalled carbon nanotubes contained as little as 2.8% iron by weight. The material was deposited onto tantalum foil and fused silica substrates. The nanotubes were characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and thermogravimetric analysis. This synthetic route provides a simple and scalable method to deposit MWNTs with a low defect density, low metal content and preferred orientation.

Harris, Jerry D.↗
NASA NTRS2005

Pyrolytic Synthesis of Carbon Nanotubes from Sucrose on a Mesoporous Silicate

Multiwall carbon nanotubes were synthesized from sucrose by a pyrolytic technique using mesoporous MCM-41 silicate templates without transition metal catalysts. The Nanotubes were examined in the carbon/silicate composite and after dissolution of the silicate. High resolution transmission electron microscopy study of the multiwall nanotubes showed them to be 15 nm in diameter, 200 nm in length and close-ended. There was variation in crystallinity with some nanotubes showing disordered wall structures.

Abdel-Fattah, Tarek↗
NASA NTRS2003

Silicon Carbide Nanotube Synthesized

Carbon nanotubes (CNTs) have generated a great deal of scientific and commercial interest because of the countless envisioned applications that stem from their extraordinary materials properties. Included among these properties are high mechanical strength (tensile and modulus), high thermal conductivity, and electrical properties that make different forms of single-walled CNTs either conducting or semiconducting, and therefore, suitable for making ultraminiature, high-performance CNT-based electronics, sensors, and actuators. Among the limitations for CNTs is their inability to survive in high-temperature, harsh-environment applications. Silicon carbon nanotubes (SiCNTs) are being developed for their superior material properties under such conditions. For example, SiC is stable in regards to oxidation in air to temperatures exceeding 1000 C, whereas carbon-based materials are limited to 600 C. The high-temperature stability of SiCNTs is envisioned to enable high-temperature, harsh-environment nanofiber- and nanotube-reinforced ceramics. In addition, single-crystal SiC-based semiconductors are being developed for hightemperature, high-power electronics, and by analogy to CNTs with silicon semiconductors, SiCNTs with single-crystal SiC-based semiconductors may allow high-temperature harsh-environment nanoelectronics, nanosensors, and nanoactuators to be realized. Another challenge in CNT development is the difficulty of chemically modifying the tube walls, which are composed of chemically stable graphene sheets. The chemical substitution of the CNTs walls will be necessary for nanotube self-assembly and biological- and chemical-sensing applications. SiCNTs are expected to have a different multiple-bilayer wall structure, allowing the surface Si atoms to be functionalized readily with molecules that will allow SiCNTs to undergo self-assembly and be compatible with a variety of materials (for biotechnology applications and high-performance fiber-reinforced ceramics).

Lienhard, Michael A.↗
NASA NTRS2006

Carbon Nanotube-enhanced Carbon-phenolic Ablator Material

Phenolic impregnated carbon ablator (PICA) is a thermal protection system (TPS) material developed at NASA Ames Research Center in the mid-90 s for Discovery missions. It was used on the Stardust return capsule heat shield which successfully executed the highest speed Earth entry to date on January 15, 2006. PICA is a porous fibrous carbon insulation infiltrated with phenolic resin, and is an excellent ablator that is effective for heating rates up to 1000 W/sq cm. It is one of several candidate TPS materials for the next generation of crewed spacecraft for Lunar and Mars missions. We will describe an ongoing research effort at NASA to improve mechanical properties of the phenolic matrix with carbon nanotubes. The aim is two-fold: to increase overall TPS strength during reentry and to improve Micrometeoroid/Orbital Debris (MMOD) protection in space. The former requires at least a good dispersion of nanotubes in phenolic, while the latter also requires covalent bonding between them to couple and transfer impact energy effectively from matrix to nanotubes. We will discuss the required chemical functionalization of nanotubes, processing issues and test results.

Nikolaev, P.↗
NASA NTRS2005

Influence of the Gas Pressure on Single-wall Carbon Nanotubes Formation

Experiments and modeling have been performed to predict the effect of gas pressure on species distribution and nanotube growth rate under specific conditions of synthesis of singlewall carbon nanotubes (SWCNTs) by arc discharge. Numerical results were compared with experiments in order to find a consistent correlation between the nanotube growth and the pressure. We used argon and helium as buffer gases with a total pressure varied between 0.1 and 1 bar. We experimentally observed that both the anode erosion rate and the Brunauer-Emmett-Teller (BET) surface area of the as produced nanotube soot material are very sensitive to the total gas pressure in the reactor

Hinkov, I.↗
NASA NTRS2007

Developing Carbon Nanotube Standards at NASA

Single wall carbon nanotubes (SWCNTs) are currently being produced and processed by several methods. Many researchers are continuously modifying existing methods and developing new methods to incorporate carbon nanotubes into other materials and utilize the phenomenal properties of SWCNTs. These applications require availability of SWCNTs with known properties and there is a need to characterize these materials in a consistent manner. In order to monitor such progress, it is critical to establish a means by which to define the quality of SWCNT material and develop characterization standards to evaluate of nanotube quality across the board. Such characterization standards should be applicable to as-produced materials as well as processed SWCNT materials. In order to address this issue, NASA Johnson Space Center has developed a protocol for purity and dispersion characterization of SWCNTs (Ref.1). The NASA JSC group is currently working with NIST, ANSI and ISO to establish purity and dispersion standards for SWCNT material. A practice guide for nanotube characterization is being developed in cooperation with NIST (Ref.2). Furthermore, work is in progress to incorporate additional characterization methods for electrical, mechanical, thermal, optical and other properties of SWCNTs.

Nikolaev, Pasha↗
NASA NTRS2007

Carbon Nanotube-based Sensor and Method for Continually Sensing Changes in a Structure

A sensor has a plurality of carbon nanotube (CNT)-based conductors operatively positioned on a substrate. The conductors are arranged side-by-side, such as in a substantially parallel relationship to one another. At least one pair of spaced-apart electrodes is coupled to opposing ends of the conductors. A portion of each of the conductors spanning between each pair of electrodes comprises a plurality of carbon nanotubes arranged end-to-end and substantially aligned along an axis. Because a direct correlation exists between resistance of a carbon nanotube and carbon nanotube strain, changes experienced by the portion of the structure to which the sensor is coupled induce a change in electrical properties of the conductors.

Jordan, Jeffry D.↗
NASA NTRS2007

Templated Growth of Carbon Nanotubes

A method of growing carbon nanotubes uses a synthesized mesoporous si lica template with approximately cylindrical pores being formed there in. The surfaces of the pores are coated with a carbon nanotube precu rsor, and the template with the surfaces of the pores so-coated is th en heated until the carbon nanotube precursor in each pore is convert ed to a carbon nanotube.

Siochik Emilie J.↗
NASA NTRS2007

Developing Carbon Nanotube Standards at NASA

Single wall carbon nanotubes (SWCNTs) are currently being produced and processed by several methods. Many researchers are continuously modifying existing methods and developing new methods to incorporate carbon nanotubes into other materials and utilize the phenomenal properties of SWCNTs. These applications require availability of SWCNTs with known properties and there is a need to characterize these materials in a consistent manner. In order to monitor such progress, it is critical to establish a means by which to define the quality of SWCNT material and develop characterization standards to evaluate of nanotube quality across the board. Such characterization standards should be applicable to as-produced materials as well as processed SWCNT materials. In order to address this issue, NASA Johnson Space Center has developed a protocol for purity and dispersion characterization of SWCNTs. The NASA JSC group is currently working with NIST, ANSI and ISO to establish purity and dispersion standards for SWCNT material. A practice guide for nanotube characterization is being developed in cooperation with NIST. Furthermore, work is in progress to incorporate additional characterization methods for electrical, mechanical, thermal, optical and other properties of SWCNTs.

Nikolaev, Pasha↗
NASA NTRS2008

Single Wall Nanotube Type-Specific Functionalization and Separation

Metallic single-wall carbon nanotubes were selectively solubilized in THF and separated from semiconducting nanotubes. Once separated, the functionalized metallic tubes were de-functionalized to restore their metallic band structure. Absorption and Raman spectroscopy of the enriched samples support conclusions of the enrichment of nanotube samples by metallic type. A scalable method for enriching nanotube conductive type has been developed. Raman and UV-Vis data indicate SWCNT reaction with dodecylbenzenediazonium results in metallic enrichment. It is expected that further refinement of this techniques will lead to more dramatic separations of types and diameters.

Boul, Peter↗
NASA NTRS2008

Polymer composites containing nanotubes

The present invention relates to polymer composite materials containing carbon nanotubes, particularly to those containing singled-walled nanotubes. The invention provides a polymer composite comprising one or more base polymers, one or more functionalized m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers and carbon nanotubes. The invention also relates to functionalized m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers, particularly to m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers having side chain functionalization, and more particularly to m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers having olefin side chains and alkyl epoxy side chains. The invention further relates to methods of making polymer composites comprising carbon nanotubes.

Bley, Richard A.↗