Enhanced field emission from lanthanum hexaboride coated multiwalled carbon nanotubes: correlation with physical properties

Abstract

Detailed results from field emission studies of lanthanum hexaboride (LaB₆) coated multiwalled carbon nanotube (MWCNT) films, pristine LaB₆ films, and pristine MWCNT films are reported. The films have been synthesized by a combination of chemical and physical deposition processes. An impressive increase in field enhancement factor and temporal stability as well as a reduction in turn-on field and threshold field are observed in LaB₆-coated MWCNTs compared to pristine MWCNT and pristine LaB₆ films. Surface morphology of the films has been examined by scanning electron microscopy. Introduction of LaB₆ nanoparticles on the outer walls of CNTs LaB₆-coated MWCNTs films is confirmed by transmission electron microscopy. The presence of LaB₆ was confirmed by X-ray photoelectron spectroscopy results and further validated by the Raman spectra. Raman spectroscopy also shows 67% increase in defect concentration in MWCNTs upon coating with LaB₆ and an upshift in the 2D band that could be attributed to p-type doping. Ultraviolet photoelectron spectroscopy studies reveal a reduction in the work function of LaB₆-coated MWCNT with respect to its pristine counterpart. The enhanced field emission properties in LaB₆-coated MWCNT films are correlated with a change in microstructure and work function.