Characterization and Field Emission Properties of Lanthanum Monosulfide Nanodot and Nanowire Arrays Deposited by Pulsed Laser Deposition on Self-assembled Nanoporous Al2O3 Matrix

Successful growth of lanthanum monosulfide (LaS) nanodot and nanowire arrays has been performed by pulsed laser deposition (PLD) using self-assembled nanoporous alumina templates containing pores about 50 nm wide and 200-300 nm deep. The arrays were characterized by X-ray diffraction, atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM) and scanning anode field emission microscopy (SAFEM). The array of LaS nanodots grows selectively at boundaries between different regions of the alumina film with local hexagonal symmetry of pores. The density of these dots is about 10⁹ /cm². Cross sectional FE-SEM showed that LaS nanowires also grow inside the pores with a density of 10¹⁰/cm² , which is equal to the pore density of the templates. The field emission properties of the LaS nanodots grown on top of the alumina templates were measured using SAFEM. A typical current-voltage characteristic is shown. Using the conventional Fowler-Nordheim relation, the work function of the LaS nanodots has been extracted from the slope of the plot ln(J/F²) vs 1/F, where J is the field emission current density and F is the local applied field. This leads to an outstanding, reproducible effective work function value of ~1 eV for the LaS nanodots. The threshold for an emission current density of 1 mA/cm² occurs around a 150 V/mum which is considerably lower than the 230 V/mum threshold value reported recently for LaS thin films