Zhaoxia Jin

Controlling growth and field emission property of aligned carbon nanotubes on porous silicon substrates

An aligned and well-distributed carbon nanotubes array was produced by pyrolysis of hydrocarbons catalyzed by nickel nanoparticles embedded in porous silicon (PS) substrates. Scanning electron microscope images show that the nanotubes form an aligned array approximately perpendicular to the surface of the PS substrate and the diameters of most of the tubes within the array are 10–30 nm. High-magnification transmission electron microscopy images confirmed that the nanotubes are well graphitized and typically consist of about 15 concentric shells of carbon sheets. Furthermore, the strong field emission from the aligned carbon nanotubes emitter by pyrolysis of hydrocarbons was observed.

High yield synthesis and growth mechanism of carbon nanotubes

Abstract With Y 2 O 3 /carbon composite rods, Carbon nanotube bundles were synthesized in high yield by d.c. arc-vaporizing method. The carbon nanotube bundles and carbon nanotubes were observed by optical microscope, scan electron microscope and high-resolution transmission electron microscope. According to our observations, a new model is proposed to account for the growth of cathode deposit with nanotube bundles.

Growth and structure of C60 thin films on NaCl, glass and mica substrates

Abstract We studied the growth and structure of C60 thin film condensed on NaCl, glass and mica substrates by transmission electron microscopy. Highly ordered, (111) textured and epitaxial thin films were obtained on (001) NaCl and mica respectively. Various deposition parameters including different substrate temperatures, deposition rates and film thicknesses were experimented with. The orientational order and nature of defects present in the films were assessed by electron diffraction, bright and dark field images. We ascribe the abnormal reflections in the electron diffraction patterns which had been thought by some workers to belong to the diffraction of an h.c.p. structure phase to the existence of stacking disorder in the f.c.c. structure.

Study of microstructure and anomalous variation of resistivity in metal-C60 multilayer thin films

Abstract The structure and electrical transport properties of C60 thin films and some metal-C60 multilayer thin films were studied. We find the resistance decreases sharply when adding C60 on some specific metal layers. There are two possible explainations: one is the formation of a conduction layer of metal doped C60, the other is the bonding interfacial interaction between the metal and C60 layers, which may result a better continuous metal layer.

Study of microstructure of epitaxial fullerenes films

Abstract A comprehensive study was made on the structure of epitaxial thin films of C 60 and C 70 by means of transmission electron microscopy. Both the films show similar face-centered cubic structure and are epitaxial on (001) mica with close-packed plane parallel to the substrate surface. Two main kinds of defects-stacking faults and twins-were observed and are discussed. The effect of the remaining C 70 impurity on the crystal orientation of C 60 films was studied by comparing different samples made from high-purity fullerene and C 60 /C 70 mixtures. The results show that there is a higher density of planar defects in the films containing larger amounts of impurities: moreover, some faint anomalous reflections located at so-called 2a 0 fcc reciprocal lattice points were also detected, probably as a result of C 70 contamination. Finally, it is found that stacking disorders can be easily increased by keeping the high-quality pure C 60 film in air at room temperature for a few weeks, implying the instability of the crystal orientation of the epitaxial fullerene films.

Surface enhanced electronic transport. A new method to probe the possible interactions between C60 and non-alkali metals

Abstract By measuring the resistance in situ during the deposition of C 60 on ultrathin metal layers in a UHV system, we find the resistance decreases sharply in most cases. This enhanced electronic transport in metal—C 60 multilayers (bilayers), may be related to charge transfer from the metal to C 60 and surface bonding effects, and hence can be used as a new possible approach for probing the interfacial interactions between C 60 and metals.

Epitaxial thin films of C70: Growth and structure characterization

Abstract Epitaxial thin films of C 70 have been grown on (001) mica substrate by resistive evaporation at a vacuum pressure of about 10 -3 Pa. The orientational ordering and the nature of the defects presented in the films were assessed by transmission electron diffraction and electron microscopy. The fundamental structure of the C 70 crystals is face-centered cubic with the lattice parameter a 0 = 1.50 nm, but forbidden reflections resulted from hcp stacking were also detected which are usually appeared in the prior study of alloys with low stacking fault energy and the solid C 60 . Furthermore, we also studied the films deposited on (001) NaCl and Si single crystals and the results show these substrates promoted polycrystal growth under the same evaporation conditions where epitaxy was observed on mica.

A possible interaction between nonalkali metals and C60 thin films

By measuring the resistance in situ during the deposition of metals-C60 multilayer thin films on sapphire substrates at room temperature, the authors find that the resistance decreases sharply when adding C60 on some metal layers. There are two possible explanations: one is the formation of a conduction layer of metal- (Sn-, Ba-, Ga-) doped C60; the other is a bonding interfacial interaction between the metal and C60 layers, which may result in a better continuous metal layer.

In situ electronic transport measurement as a tool for investigating the 2D doping in metal-C60 interfacial systems

The two-dimensional doping by charge transfer and/or diffusion of metal atoms into C60 has been studied by in situ electronic transport measurements during the deposition of metal-C60 ultrathin bilayers. The results show that the transport properties of these interfacial systems are significantly altered by such doping processes. Some useful information about the charge transfer from metal to C60 and the electronic transport properties of the metal-doped-monolayer C60 can be obtained after careful analysis.

Synthesis of K3C60 single crystal thin films with high critical currents

Abstract High quality K3C60 single crystal thin films have been synthesized on (001) mica substrates. The normal state electrical resistivity shows classic metallic temperature dependence and can be fit to a functional form of ϱ(T)=a+bT2. The film has a sharp transition to superconductivity near 22K, with a 10% to 90% width less than 700 mK. The experimental data near Tc have poor agreements with the Aslmozov-Larkin type fluctuation. Furthermore, critical current density up to 50 000 A/cm2 has been obtained at 4.7 K by continuous DC measurements, the preliminary analysis indicate that Jc is proportional to 1-(T/Tc)3.