Showing papers by "Zhifeng Ren published in 2001"
TL;DR: A review of recent advances in carbon nanotubes and their composites can be found in this article, where the authors examine the research work reported in the literature on the structure and processing of carbon Nanotubes.
4,709 citations
TL;DR: In this article, the growth mechanism of carbon nanotube Y junctions has been discussed based on the analysis on the structure of the Y junction and the fact that all the Y-joints grow in a similar way may be very important in the development of nanoelectronic devices.
Abstract: Carbon nanotube junctions are of great interest in the fundamental research and nanoelectronic applications. Identical carbon nanotube Y junctions have been successfully synthesized by pyrolysis of methane over cobalt supported on magnesium oxide. The Y junctions have very straight arms with uniform diameters, and the angles between the three arms are close to 120°. Based on the analysis on the structure of the Y junctions the growth mechanism has been discussed. The fact that all the Y junctions grow in a similar way may be very important in the development of nanoelectronic devices.
117 citations
TL;DR: In this article, the growth of carbon nanotubes on patterned nickel nanodots and uniform thin films was studied by electron microscopy and it was found that the growth pattern of carbon nano-tubes on uniform thin film is different.
Abstract: Microstructures of well-aligned multiwall carbon nanotubes grown on patterned nickel nanodots and uniform thin films by plasma-enhanced chemical vapor deposition have been studied by electron microscopy. It was found that growth of carbon nanotubes on patterned nickel nanodots and uniform thin films is different. During growth of carbon nanotubes, a nickel particle sits at the tip of each nanotube, and its [220] is preferentially oriented along the plasma direction, which can be explained by a channeling effect of ions coming into nickel particles in plasma. The alignment of nanotubes is induced by the electrical field direction relative to substrate surface.
70 citations
TL;DR: In this article, the effects of mixing time and fiber draw ratios on dispersion and alignment of carbon nanotubes in thermoplastic polymers such as polycarbonate have been investigated.
Abstract: Dispersion and alignment of carbon nanotubes in thermoplastic polymers such as polycarbonate have been studied. Dispersion was accomplished by mixing in a conical twin-screw extruder and alignment was carried out using a fiber spinning apparatus. The effects of mixing time and fiber draw ratios on dispersion and alignment were investigated. Uniform dispersions were produced with relatively short residence times in the extruder. Excellent alignment of carbon nanotubes in nanocomposite filaments was obtained when the fiber draw ratio was greater than 7. The ability to closely control the dispersion and alignment of carbon nanotubes in polymers is expected to lead to the development of nanocomposites with desirable electronic and structural properties.
26 citations
TL;DR: GdSr 2 Cu 2 RuO 8 superconducts at an onset temperature T c ≈45 K, and exhibits a low-field magnetic resonance, which the evidence suggests is due to magnetically ordered Cu.
Abstract: GdSr 2 Cu 2 RuO 8 superconducts at an onset temperature T c ≈45 K, and exhibits a low-field magnetic resonance, which the evidence suggests is due to magnetically ordered Cu. Since Bernhard et al. [Phys. Rev. B 59 (1999) 1409] have shown that the magnetism and the superconductivity are homogeneous, it follows that if the cuprate planes are homogeneously magnetic, the superconductivity must be located, not in the cuprate planes, but in the SrO layers. Alternatively there are magnetically ordered Cu impurities on Ru sites, with a locally inhomogeneous magnetization.
6 citations
TL;DR: In this article, an off-axis radiofrequency magnetron sputtering and post-deposition annealing with slow cooling was used to synthesize Tl 2 Ba 2 CuO 6+ δ (Tl-2201) thin films with single superconducting transition temperatures as low as 1.5 K (zero resistance).
Abstract: Heavily overdoped epitaxial superconducting Tl 2 Ba 2 CuO 6+ δ (Tl-2201) thin films with single superconducting transition temperatures as low as 1.5 K (zero resistance) have been successfully synthesized. The films were made by “off-axis” radiofrequency magnetron sputtering and post-deposition annealing with slow cooling. Our investigations showed that the achievement of a single transition can be attributed to an off-axis configuration during sputter deposition, whereas the reduced T c results from a slow-cooling process immediately after annealing at high temperature. Transmission electron microscopy reveals that the films are pure 2201 phase with good crystallinity and modulated structure. Such samples are very much desired for detailed investigations of upper critical magnetic fields using conventional laboratory superconducting magnets, or the dc facilities at National Laboratories.
2 citations