Some aspects of pulsed laser deposited nanocrystallineLaB6 film: atomic force microscopy, constant force current imaging and field emissioninvestigations

Abstract

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-raydiffraction (XRD), scanning electron microscopy (SEM) and atomic forcemicroscopy (AFM). The XRD pattern shows the cubic crystallinity of theLaB6 film. The AFM studies reveal that the conical shapedLaB6 nanostructures have height 60 nm, base 800 nm, and a typical radius of curvature∼20 nm. A comparison of force and in situ current imaging AFM studies revealsthat current contrast does not originate from the surface topography of theLaB6 film. Field emission studies have been performed in the planar diode configuration. A current densityof 4.4 × 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 fieldenhancement factor is estimated to be 3585, indicating that the field emission is fromLaB6 nanocrystallites present on the emitter surface, as confirmed by the AFM. The emissioncurrent–time plots show current stability to the extent of 5% fluctuation about the averagecurrent over a period of 3 h.