Cerium hexaboride is a well-known material for the filaments of electron microscopes due to its field emission properties (high brightness electron source) and its long service life. The synthesis of cerium hexaboride (and most other borides) normally requires very high temperatures (1500 C-1700 C) and high pressures. Thus, the low temperature synthesis of cerium hexaboride at ambient pressure is a challenge. The present study highlights the synthesis of vertically aligned cerium hexaboride nanorods which offer better field emission properties with the highest field enhancement factor reported so far. The optimization of the process for obtaining vertically aligned cerium hexaboride nanorods involves three different stages. First, the low temperature synthesis of polycrystalline cerium hexaboride; second, the fabrication of cerium hexaboride films having vertically oriented nanorods (by spin coating and slow evaporation) and third, the enhancement of the field emission properties. The synthesis of cerium hexaboride nanorods has been carried out by a low temperature borothermal reduction process using a cerium precursor (synthesized via a reverse micellar route and a hydrothermal route) and boron as the starting materials. The borothermal reduction of the cerium precursors has been carried out at low temperature ($1300 C) and ambient pressure in an inert atmosphere. The field emission studies of the vertically aligned nanorods of diameter 30 nm and 200 nm show a field enhancement factor of 3863 and 3658, respectively, which is nearly seven-fold higher than the maximum field enhancement factor known so far.

The field emission (FE) properties of nickel nanoparticles embedded in thin silica matrix irradiated with 100 MeV Au+7 ions at various fluences are studied here. A large increase in FE current density is observed in the irradiated films as compared to their as deposited counterpart. The dependence of FE properties on irradiation fluence is correlated with surface roughness, density of states of valence band and size distribution of nanoparticles as examined with atomic force microscope, X-ray photoelectron spectroscopy, and grazing incidence small angle x-ray scattering. A current density as high as 0.48 mA/cm2 at an applied field 15 V/μm has been found for the first time for planar field emitters in the film irradiated with fluence of 5.0 × 1013 ions/cm2. This significant enhancement in the current density is attributed to an optimized size distribution along with highest surface roughness of the same. This new member of field emission family meets most of the requirements of cold cathodes for vacuum micro/nanoelectronic devices.

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Detailed results from field emission studies of lanthanum hexaboride (LaB 6) coated multiwalled carbon nanotube (MWCNT) films, pristine LaB 6 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 LaB 6-coated MWCNTs compared to pristine MWCNT and pristine LaB 6 films. Surface morphology of the films has been examined by scanning electron microscopy. Introduction of LaB 6 nanoparticles on the outer walls of CNTs LaB 6-coated MWCNTs films is confirmed by transmission electron microscopy. The presence of LaB 6 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 LaB 6 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 LaB 6-coated MWCNT with respect to its pristine counterpart. The enhanced field emission properties in LaB 6-coated MWCNT films are correlated with a change in microstructure and work function.