Measuring the Work Function of Carbon Nanotubes with Thermionic Method

Abstract

The work function of carbon nanotubes might depend on their diameters and the number of walls, and be different for their tips and sidewalls. Here we report the work function measurement of single-walled, double-walled, and multiwalled carbon nanotubes by investigating the thermionic emission from the middle of their bundles. It is found that the sidewall work functions of the three kinds of carbon nanotubes are all around 4.7-4.9 eV; the diameter and the numbers of walls have no obvious influence on their work functions. For the carbon nanotube bundle with some tips appearing in the middle, the measured work function is smaller than without tips, indicating that the work function of tips is smaller than that of the sidewalls. This tip effect also results in a difference in the thermionic emission characteristic, implying non-uniform work function distribution along the bundle.

Microwave purification of large-area horizontally aligned arrays of single-walled carbon nanotubes

“…Intrinsic s-SWNTs have a Fermi level at the middle bandgap level B4.78 eV (ref. 53). In practice, s-SWNT often are unintentionally doped (for example, oxygen or water) 17,51 , in a way that shifts the Fermi level towards the valence band, to favour hole transport (schematic of band diagram in Supplementary Fig.…”

Field emission from single-, double-, and multi-walled carbon nanotubes chemically attached to silicon

“…Values of b were calculated from the slope of the F-N plots following previously described methods (l ¼ 1.9 eV, U ¼ 4.8 eV). 33,34 There is a clear correlation between FE properties with CNT diameter. The lowest diameter SWCNTs exhibit the highest b and lowest E to , whereas the largest diameter MWCNTs showed the lowest b and highest E to .…”

Thermionic emission properties of novel carbon nanostructures.

“…Zhao et al performed one of the first studies of the work function of single wall carbon nanotubes and SWNT bundles using first-principles methods [32]. Authors considered the models of the semiconducting and metallic tubes and investigated the dependence of ϕ on the chirality and tube diameter.…”

“…A thorough description of the thermionic emission from the CNT bundles and yarns as well as determination of the value of the work function was presented by Peng Liu et al [32,33].…”

“…There has been a wealth of results on experimental measurements (by different methods and theoretical calculations of the work function of carbon nanotubes [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. We will present some of the reported results on work function values of the carbon nanotubes, first by shortly discussing various methods such as photoelectron emission (PEE), photoemission electron microscopy (PEEM) ultraviolet photoelectron spectroscopy (UPS) and contact potential difference (CPD).…”