Some aspects of pulsed laser deposited nanocrystalline LaB6 film:: atomic force microscopy, constant force current imaging and field emission investigations

Nanocrystalline lanthanum hexaboride (LaB6) films have been deposited on molybdenum foil by the pulsed laser deposition (PLD) technique. The as-deposited films were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The XRD pattern shows the cubic crystallinity of the LaB6 film. The AFM studies reveal that the conical shaped LaB6 nanostructures have height 60 nm, base 800 nm, and a typical radius of curvature similar to 20 nm. A comparison of force and in situ current imaging AFM studies reveals that current contrast does not originate from the surface topography of the LaB6 film. Field emission studies have been performed in the planar diode configuration. A current density of 4.4 x 10(-2) A cm(-2) is drawn from the actual emitting area. The Fowler-Nordheim plot is found to be linear, in accordance with the quantum mechanical tunneling phenomenon. The field enhancement factor is estimated to be 3585, indicating that the field emission is from LaB6 nanocrystallites present on the emitter surface, as confirmed by the AFM. The emission current-time plots show current stability to the extent of 5% fluctuation about the average current over a period of 3 h.