A novel form of carbon nitrides: Well-aligned carbon nitride nanotubes and their characterization
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A novel form of carbon nitrides: Well-aligned carbon nitride nanotubes and their characterization S.L. Sung, S.H. Tsai, X.W. Liu, and H.C. Shiha) Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 300, Taiwan, Republic of China (Received 12 April 1999; accepted 30 November 1999)
Well-aligned carbon nitride nanotubes were prepared with a porous alumina membrane as a template when using electron cyclotron resonance (ECR) plasma in a mixture of C2H2 and N2 as the precursor with an applied negative bias to the graphite sample holder. The hollow structure and good alignment of the nanotubes were verified by field-emission scanning electron microscopy. Carbon nitride nanotubes were transparent when viewed by transmission electron microscopy, which showed that the nanotubes were hollow with a diameter of about 250 nm and a length of about 50–80 m. The amorphous nature of the nanotubes was confirmed by the absence of crystalline phases arising from selected-area diffraction patterns. Both Auger electron microscopy and x-ray photoelectron spectroscopy spectra indicated that these nanotubes are composed of nitrogen and carbon. The total N/C ratio is 0.72, which is considerably higher than other forms of carbon nitrides. No free-carbon phase was observed in the amorphous carbon nitride nanotubes. The absorption bands between 1250 and 1750 cm−1 in Fourier transform infrared spectroscopy provided direct evidence for nitrogen atoms, effectively incorporated within the amorphous carbon network. Such growth of well-aligned carbon nitride nanotubes can be controlled by tuning the ECR plasma conditions and the applied negative voltage to the alumina template.
I. INTRODUCTION
The electron field emitters of carbon-related materials have rapidly become the focus of worldwide attention as new electron sources for flat-panel displays, electronic devices, and so on.1–3 Electron field emissions from bulk materials, such as diamond,4 – 6 nitrogenated diamond,7 caesiated diamond,8 and amorphous carbon,9,10 have been reported at moderately low electric fields. One of the major factors that has contributed to the low electron field emission at low fields is the low electron affinity of carbon films.11,12 Also, the space-charge-induced band bending of the carbon films could be important in both amorphous carbon9,13 and diamond films8,14 for the field-emission enhancement. In 1991 one-dimensional nanostructured materials, carbon nanotubes, were synthesized.15 Due to their onedimensional nature and high aspect ratio, carbon nanotubes constitute a novel structure for the field-emission electron source.16–19 Table I shows the obvious improvement of emission parameters for the one-dimensional nanostructured materials, carbon nanotubes, compared
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J. Mater. Res., Vol. 15, No. 2, Feb 2000 Downloaded: 14 Mar 2015
with the traditional bulk materials.20 We have also successfully synthesi
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