Manipulation of Conducting Polymer Hydrogels with Different Shapes and Related Multifunctionality.

Maneuver of conducting polymers (CPs) into lightweight hydrogels can improve their functional performances in energy devices, chemical sensing, pollutant removal, drug delivery, etc. Current approaches for the manipulation of CP hydrogels are limited, and they are mostly accompanied by harsh conditions, tedious processing, compositing with other constituents, or using unusual chemicals. Herein, a two-step route is introduced for the controllable fabrication of CP hydrogels in ambient conditions, where gelation of the shape-anisotropic nano-oxidants followed by in-situ oxidative polymerization leads to the formation of polyaniline (PANI) and polypyrrole hydrogels. The method is readily coupled with different approaches for materials processing of PANI hydrogels into varied shapes, including spherical beads, continuous wires, patterned films, and free-standing objects. In comparison with their bulky counterparts, lightweight PANI items exhibit improved properties when those with specific shapes are used as electrodes for supercapacitors, gas sensors, or dye adsorbents. The current study therefore provides a general and controllable approach for the implementation of CP into hydrogels of varied external shapes, which can pave the way for the integration of lightweight CP structures with emerging functional devices.

Surface-restrained growth of vertically aligned carbon nanotube arrays with excellent thermal transport performance.

A vertically aligned carbon nanotube (VACNT) array is a promising candidate for a high-performance thermal interface material in high-power microprocessors due to its excellent thermal transport property. However, its rough and entangled free tips always cause poor interfacial contact, which results in serious contact resistance dominating the total thermal resistance. Here, we employed a thin carbon cover to restrain the disorderly growth of the free tips of a VACNT array. As a result, all the free tips are seamlessly connected by this thin carbon cover and the top surface of the array is smoothed. This unique structure guarantees the participation of all the carbon nanotubes in the array in the heat transport. Consequently the VACNT array grown on a Cu substrate shows a record low thermal resistance of 0.8 mm2 K W-1 including the two-sided contact resistances, which is 4 times lower than the best result previously reported. Remarkably, the VACNT array can be easily peeled away from the Cu substrate and act as a thermal pad with excellent flexibility, adhesive ability and heat transport capability. As a result the CNT array with a thin carbon cover shows great potential for use as a high-performance flexible thermal interface material.

Selective Growth of Metal-Free Metallic and Semiconducting Single-Wall Carbon Nanotubes.

A major obstacle for the use of single-wall carbon nanotubes (SWCNTs) in electronic devices is their mixture of different types of electrical conductivity that strongly depends on their helical structure. The existence of metal impurities as a residue of a metallic growth catalyst may also lower the performance of SWCNT-based devices. Here, it is shown that by using silicon oxide (SiOx ) nanoparticles as a catalyst, metal-free semiconducting and metallic SWCNTs can be selectively synthesized by the chemical vapor deposition of ethanol. It is found that control over the nanoparticle size and the content of oxygen in the SiOx catalyst plays a key role in the selective growth of SWCNTs. Furthermore, by using the as-grown semiconducting and metallic SWCNTs as the channel material and source/drain electrodes, respectively, all-SWCNT thin-film transistors are fabricated to demonstrate the remarkable potential of these SWCNTs for electronic devices.

Preparation of high purity ZnO nanobelts by thermal evaporation of ZnS.

High purity one-dimensional ZnO nanobelts were synthesized by thermally evaporating commercial ZnS powders in a hydrogen-oxygen mixture gas at 1050 degrees C. It was found that these ZnO nanobelts had a single crystal hexagonal wurtzite structure growing along the [0001] direction. They had a rectangle-shaped cross-section with typical widths of 20 to 100 nanometers and lengths of up to hundreds of micrometers with lattice constants of a = 0.325 nm and c = 0.520 nm. The self-catalytic hydrogen-oxygen assisted growth of ZnO nanobelt is discussed. The photoluminescence (PL) characterization of the ZnO nanobelts shows strong near-band UV emission (about 383 nm) and one broad peak at 501 nm, which indicates that the ZnO nanobelts have good potential application in optoelectronic devices.

Growth of semiconducting single-wall carbon nanotubes with a narrow band-gap distribution.

The growth of high-quality semiconducting single-wall carbon nanotubes with a narrow band-gap distribution is crucial for the fabrication of high-performance electronic devices. However, the single-wall carbon nanotubes grown from traditional metal catalysts usually have diversified structures and properties. Here we design and prepare an acorn-like, partially carbon-coated cobalt nanoparticle catalyst with a uniform size and structure by the thermal reduction of a [Co(CN)6](3-) precursor adsorbed on a self-assembled block copolymer nanodomain. The inner cobalt nanoparticle functions as active catalytic phase for carbon nanotube growth, whereas the outer carbon layer prevents the aggregation of cobalt nanoparticles and ensures a perpendicular growth mode. The grown single-wall carbon nanotubes have a very narrow diameter distribution centred at 1.7 nm and a high semiconducting content of >95%. These semiconducting single-wall carbon nanotubes have a very small band-gap difference of ∼0.08 eV and show excellent thin-film transistor performance.

In Situ TEM Observations on the Sulfur-Assisted Catalytic Growth of Single-Wall Carbon Nanotubes.

The effect of sulfur on the catalytic nucleation and growth of single-wall carbon nanotubes (SWCNTs) from an iron catalyst was investigated in situ by transmission electron microscopy (TEM). The catalyst precursor of ferrocene and growth promoter of sulfur were selectively loaded inside of the hollow core of multiwall CNTs with open ends, which served as a nanoreactor powered by applying a voltage inside of the chamber of a TEM. It was found that a SWCNT nucleated and grew perpendicularly from a region of the catalyst nanoparticle surface, instead of the normal tangential growth that occurs with no sulfur addition. Our in situ TEM observation combined with CVD growth studies suggests that sulfur functions to promote the nucleation and growth of SWCNTs by forming inhomogeneous local active sites and modifying the interface bonding between catalysts and precipitated graphitic layers, so that carbon caps can be lifted off from the catalyst particle.

High-quality, highly concentrated semiconducting single-wall carbon nanotubes for use in field effect transistors and biosensors.

We developed a simple and scalable selective synthesis method of high-quality, highly concentrated semiconducting single-wall carbon nanotubes (s-SWCNTs) by in situ hydrogen etching. Samples containing ~93% s-SWCNTs were obtained in bulk. These s-SWCNTs with good structural integrity showed a high oxidation resistance temperature of ~800 °C. Thin-film transistors based on the s-SWCNTs demonstrated a high carrier mobility of 21.1 cm(2) V(-1) s(-1) at an on/off ratio of 1.1 × 10(4) and a high on/off ratio of 4.0 × 10(5) with a carrier mobility of 7.0 cm(2) V(-1) s(-1). A biosensor fabricated using the s-SWCNTs had a very low dopamine detection limit of 10(-18) mol/L at room temperature.

In situ assembly of multi-sheeted buckybooks from single-walled carbon nanotubes.

We report a simple approach for the direct and nondestructive assembly of multi-sheeted single-walled carbon nanotube book-like macrostructures (buckybooks) with good control of the nanotube diameter, the sheet packing density, and the book thickness during the floating catalytic growth process. The promise of such buckybooks is highlighted by demonstrating their high capacitance and high-efficiency molecular separation by directly using them as a binder-free electrode and as a filter, respectively. Our approach also provides a flexible and reliable way to easily assemble various other types of nanotubes into book-like or even more sophisticated sandwich-like hybrid macrostructures, realizing the shape-engineering of one-dimensional nanostructures to macroscopic well-defined architectures for various applications.

Diameter-selective growth of single-walled carbon nanotubes with high quality by floating catalyst method.

High-quality single-walled carbon nanotubes (SWNTs) with tunable diameters were synthesized by an improved H(2)/CH(4)-based floating catalyst method. Transmission electron microscopy observations and Raman results demonstrated the overall quality of the as-synthesized samples with finely tailored large diameters at 1.28, 1.62, 1.72, 1.91, and 2.13 nm, depending on the experimental conditions. In addition, Raman analysis revealed that the abundance of specific (n, m) SWNTs could be selectively enriched simultaneously along with the diameter modulation. It was found that the selective etching effects of high hydrogen flow stabilized the decomposition of ultralow CH(4) flow and considerably suppressed the deposition of amorphous carbon and small nanotubes, leading to very pure samples with high structural homogeneity suitable for further applications in practical electronic systems.

A simple solution route to controlled synthesis of ZnS submicrospheres, nanosheets and nanorods.

ZnS nanostructures with different morphologies of submicrospheres, nanosheets and nanorods were synthesized by solution precipitation of thiourea with Zn(NO(3))(2) in the presence of block copolymer at low temperature. The sizes and morphologies of ZnS can be controlled simply by changing the processing parameters. The results show that the ZnS submicrospheres are of 250-500 nm in diameter, nanosheets are 2.5 µm × 5.5 µm with an estimated thickness of 20-30 nm, and nanorods are 2-5 nm in diameter and 10-30 nm in length. Keeping the precursor system in an autoclave at 105 °C results in the formation of ZnS submicrospheres; ultrasonication and keeping the system at room temperature leads to the formation of ZnS nanosheets; and long-time continuous ultrasonication and keeping the system in an autoclave at 105 °C induces the formation of uniform ZnS nanorods. We argue that the reaction temperature and P123 may play crucial roles in the formation of three ZnS structures in this work. The morphologically controllable synthesis strategies may be extended to the shape-controlled production of nanostructures of other inorganic materials.