Abstract
The only known approach to fabricate large, uniform arrays of 4-Å single wall carbon nanotubes (SWNTs) is by using zeolite crystals as the template, in which the nanotubes are formed by chemical vapor deposition inside the linear channels of the AlPO4-5 (AFI for short) zeolite. However, up to now the pore filling factor has been very low, as evidenced by the weight percentage of carbon in thermal gravimetric analysis (TGA) measurements. In this work, we show that by using a new, micro-platelet AFI crystals as the template, combined with the use of a new CVD process, we can increase the TGA result to 22.5wt%, which translates to a pore filling factor of 91%. We have observed one dimensional (1D) superconductivity in such samples. The temperature dependence of resistance shows a smooth decreasing trend below 60 K, and the differential resistance displays a gap that disappears above the 1D superconducting initiation temperature. The observed behaviour is shown to agree very well with the theoretical predictions of 1D superconductivity.
Highlights
The discovery of carbon nanotubes[1,2] has propelled a tremendous amount of study on their electrical,[3,4] optical[5,6] and mechanical properties,[7,8] attendant with an increasingly diverse portfolio of applications.[9,10,11,12] With a very large length-to-diameter ratio, carbon nanotubes constitute an ideal one-dimensional material
More recently we have succeeded in synthesizing micro-platelet AFI crystals, which are only 2 microns thick and 5-6 microns in their lateral dimensions. These new AFI crystals have good quality as they contain fewer defects, and the short length of the straight pores, 2 microns, means that the permeability is greatly enhanced for the carbon source(s) in the chemical vapour deposition (CVD) processes. These factors are crucial for achieving the high pore filling factor of 4 Å single wall carbon nanotubes (SWNTs)
We measure the Raman spectra of Angstrom SWNTs embedded in AFI template
Summary
The discovery of carbon nanotubes[1,2] has propelled a tremendous amount of study on their electrical,[3,4] optical[5,6] and mechanical properties,[7,8] attendant with an increasingly diverse portfolio of applications.[9,10,11,12] With a very large length-to-diameter ratio, carbon nanotubes constitute an ideal one-dimensional material. Theoretical calculations[13,14] have predicted stability for carbon nanotube diameters as small as 4 Angstroms, and such small carbon nanotubes were found experimentally.[15,16] Arrays of the 4 Å single wall carbon nanotubes (SWNTs) were synthesized inside the linear channels of zeolite crystals They have been experimentally characterized by polarized and resonant Raman scattering,[17] optical absorption spectra,[18] as well as visualized by transmission electron microscope images.[16] By comparing the experimental observations with first principle calculations,[19] three types of 4 Å SWNTs were identified: (5,0), (3,3), (4,2). Such a high initiation temperature is attributed to the high pore filling factor and the resulting effective dielectric screening of electron-electron interaction as shown theoretically.[24]
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