Vertically aligned nanorods of lanthanum hexaboride with efficient field emission properties

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

“…A comparative emission current density (J) versus applied field (E) plot for the pristine MWCNT film, pristine LaB 6 film, 23 and LaB 6 -coated MWCNT film is shown in Figure 6. At a constant electric field of 4.0 V/lm, the maximum emission current density of LaB 6 coated MWCNT is (918.9978 6 0.0001) lA/cm 2 , which shows a 4.5-fold increase in comparison to that of the pristine MWCNT film ((198.5960 6 0.0001) lA/cm 2 ) and a 25 fold increase in comparison to that for pristine LaB 6 film ((37.4014 6 0.0001) lA/cm 2 ).…”

“…At a constant electric field of 4.0 V/lm, the maximum emission current density of LaB 6 coated MWCNT is (918.9978 6 0.0001) lA/cm 2 , which shows a 4.5-fold increase in comparison to that of the pristine MWCNT film ((198.5960 6 0.0001) lA/cm 2 ) and a 25 fold increase in comparison to that for pristine LaB 6 film ((37.4014 6 0.0001) lA/cm 2 ). 23 Due to the LaB 6 -coating on the MWCNT film, the turn-on field (applied field needed to get an emission current of 10.0 lA/cm 2 ) is observed to reduce to (2.3 6 0.2) V/lm from (2.7 6 0.2) V/lm for pristine MWCNT film and the threshold field (field needed to be applied to get an emission current of 100.0 lA/cm 2 ) is observed to reduce to (3.0 6 0.2) V/lm from (3.60 6 0.15) V/lm for the pristine MWCNT film. The maximum current density for LaB 6 never achieved 100.0 lA/cm 2 within experimental conditions, which limited the calculation of the threshold field for this sample.…”

“…So, the enhancement factor (b) is calculated at higher electric field side by determining the slope value of the FN plot, which amounts to 2471 for the LaB 6 coated MWCNT film, 3565 for the pristine MWCNT film, and 1988 for the pristine LaB 6 film. 23 Kirley et al shown that the total available charge in LaB 6 is directly proportional to the thickness of the film. These charges diffuse through barrier and the residual charges causes screening to the external field.…”

“…Lanthanum hydroxide precursor, synthesized by the reverse micellar route, was used as a precursor (for details see our earlier work 23 ) and boron as starting material to synthesize lanthanum hexaboride (LaB 6 ). Finally, polycrystalline LaB 6 solution (0.05 g of the as-obtained pure polycrystalline LaB 6 , dispersed in 2.0 ml of ethanol: ethylene glycol mixture (1:1 volume ratio)) was spin coated (3000 rpm for 60 s) on a MWCNT film followed by a slow drying process (at 200 C at a rate of 20 C/h) in Ar atmosphere to obtain the LaB 6 -CNT composite.…”

“…Lanthanum hexaboride (LaB 6 ), a rare earth and low work function ($2.6 eV) thermionic material, has already been used as vacuum stable, high density electron source in electron microscopes due to its high melting point of 2500 C, 17 high electrical conductivity, 18 and low vapor pressure at high temperature. 19 Recently, field emission studies of LaB 6 nanowires [20][21][22] and nanorods 23 clearly indicate that this material can also be used as an efficient FE electron source for microscopes. Attempts have also been made to grow lanthanum hexaboride (LaB 6 )-multiwalled CNT (MWCNT) nanocomposite films 24 as well as LaB 6 decorated MWCNT films 25 for field emission studies.…”