Hongtao Cong

Fabrication of nano-Al based composites reinforced by single-walled carbon nanotubes

Chinese Acad Sci, Met Res Inst, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China.;Cong, HT (reprint author), Chinese Acad Sci, Met Res Inst, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China;htcong@imr.ac.cn

Semi-continuous synthesis of single-walled carbon nanotubes by a hydrogen arc discharge method

acad sinica, inst met res, state key lab rsa, shenyang 110015, peoples r china. chinese acad sci, natl lab superlattices & microstruct, inst semicond res, beijing 100083, peoples r china.;liu, c (reprint author), acad sinica, inst met res, state key lab rsa, 72 wenhua rd, shenyang 110015, peoples r china

Synthesis of macroscopically long ropes of well-aligned single-walled carbon nanotubes

chinese acad sci, inst met res, int ctr mat phys, shenyang 110015, peoples r china. mit, dept elect engn & comp sci, cambridge, ma 02139 usa. mit, dept phys, cambridge, ma 02139 usa.;cheng, hm (reprint author), chinese acad sci, inst met res, int ctr mat phys, 72 wenhua rd, shenyang 110015, peoples r china

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.

An array of Eiffel-tower-shape AlN nanotips and its field emission properties

An array of Eiffel-tower-shape AlN nanotips has been synthesized and assembled vertically with Si substrate by a chemical vapor deposition method at 700 degrees C. The single-crystalline AlN nanotips along [001] direction, including sharp tips with 10-100 nm in diameter and submicron-sized bases, are distributed uniformly with density of 10(6)-10(7) tips/cm(2). Field emission (FE) measurements show that its turn on field is 4.7 V/mu m, which is comparable to that of carbon nanotubes, and the fluctuation of FE current is as small as 0.74% for 4 h. It is revealed this nanostructure is available to optimize the FE properties and make the array a promising field emitter. (c) 2005 American Institute of Physics.

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.

Double-walled carbon nanotubes synthesized using carbon black as the dot carbon source

Double- walled carbon nanotubes (DWNTs) were synthesized used carbon black as the dot carbon source by a semi-continuous hydrogen arc discharge process. High-resolution transmission electron microscopy (HRTEM) observations revealed that most of the tubes were DWNTs with outer and inner diameters in the range of 2.67 - 4 nm and 1.96 - 3.21 nm, respectively. Most of the DWNTs were in a bundle form of about 10 - 30 nm in diameter with high purity ( about 70%) from thermal gravimetric analysis (TGA), resonant laser Raman spectroscopy, scanning electron microscopy (SEM) and TEM characterizations. It was found that carbon black as the dot carbon source could be easy controlled to synthesize one type of nanotube. A simple process combining oxidation and acid treatment to purify the DWNT bundles was used without damaging the bundles. The structure of carbon black, as the key element for influencing purity, bundle formation and purification of DWNTs, is discussed.

Tuning the coercivity of Fe-filled carbon-nanotube arrays by changing the shape anisotropy of the encapsulated Fe nanoparticles

To tune the coercivity of Fe-filled carbon-nanotube (CNT) arrays, the shape anisotropy of encapsulated Fe nanoparticles (Fe-NPs) was investigated. Four Fe-filled CNT-array samples with different Fe-NP aspect ratios were prepared by catalytic pyrolysis of acetylene using ferrocene as catalyst. The coercivity of the Fe-filled CNT arrays increased from ∼300 to ∼800 Oe at room temperature when the mean aspect ratio of the encapsulated Fe-NPs changed from 1.6 to 6.0. This clear dependence of the coercivity of the Fe-filled CNT arrays on the aspect ratio of the Fe-NPs might be interpreted in terms of the Stoner–Wohlfarth model. This result indicates that changing the shape anisotropy of the encapsulated Fe-NPs is an effective method to tune the coercivity of the Fe-filled CNTs.

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.