Menaka Jha

Vertically aligned cerium hexaboride nanorods with enhanced field emission properties

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.

Enhanced field emission from cerium hexaboride coated multiwalled carbon nanotube composite films: A potential material for next generation electron sources

Intensified field emission (FE) current from temporally stable cerium hexaboride (CeB6) coated carbon nanotubes (CNTs) on Si substrate is reported aiming to propose the new composite material as a potential candidate for future generation electron sources. The film was synthesized by a combination of chemical and physical deposition processes. A remarkable increase in maximum current density, field enhancement factor, and a reduction in turn-on field and threshold field with comparable temporal current stability are observed in CeB6-coated CNT film when compared to pristine CeB6 film. The elemental composition and surface morphology of the films, as examined by scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray measurements, show decoration of CeB6 nanoparticles on top and walls of CNTs. Chemical functionalization of CNTs by the incorporation of CeB6 nanoparticles is evident by a remarkable increase in intensity of the 2D band in Raman spectrum of coated films as c...

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

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. U...

Investigation of the growth mechanism of the formation of ZnO nanorods by thermal decomposition of zinc acetate and their field emission properties

In the present work, we have explored the growth of ZnO nanorods from a zinc acetate precursor by a thermal decomposition process at 300 °C. Our key observation indicates that a lower heating rate favors the formation of ZnO nanorods while faster heating rates favor the formation of a mixture of ZnO nanorods and nanoparticles. Further, the fabrication of films using dispersions of these nanostructures has been carried out by a low cost spin coating route, which leads to formation of vertically oriented nanorods. The field emission studies of the ZnO film consisting of pure ZnO nanorods show a field enhancement factor of 18 990 while ZnO films containing a mixture of rods and particles show a field enhancement factor in the range of 8571–8829. The field enhancement factor of ZnO nanorods is significantly higher than the previous reports on ZnO nanorods grown by complex physical routes. We have shown a one-step process which results in the formation of high quality ZnO nanorods which is very important for making high end optical and electronic devices.

Enhancement of photocatalytic efficiency using heterostructured SiO2–Ta2O5 thin films

Fabrication of controlled layered structured thin films with tunable physical properties is an important area of research as thin film technology holds potential for a variety of industrial applications. In the present work, we have demonstrated the process for fabrication of multilayer films of silica and tantalum oxide by Langmuir–Blodgett film fabrication technique and investigated their photocatalytic degradation efficiency for organic dye (Rhodamine B) under UV radiation. The photocatalytic degradation of RhB in presence of SiO2–Ta2O5 exhibited remarkably enhanced photocatalytic activity than pure Ta2O5. This is because of the high separation efficiency of photo-generated electron–hole pair due to the Lewis acidity of silica and the greater contact area between these two layers. The SiO2–Ta2O5 system was optimized for the number of self-assembled layers of silica and tantalum oxide, and it has been found that 10S–15T–10S–15T–10S–15T (where S and T represents SiO2 and Ta2O5 respectively) pattern has been found to have maximum photocatalytic degradation efficiency of 71% (with 18% degradation per unit area of the film) which is 3.5 fold higher than pure Ta2O5 under identical experimental condition. Also, the photocatalytic activity of these films was also proved to be sensitive to the sequence of silica and tantalum oxide layers when the film area of all the samples was kept constant (3.75 cm2). Further analysis confirms that the degradation of dye molecules has been largely promoted by the photo generated holes, rather than the super oxide radical anions.