Patchwork field emission properties of lanthanum sulfide thin films

The field emission (FE) properties of lanthanum monosulfide (LaS) films, deposited on Si and InP substrates by pulsed laser deposition, have been thoroughly analyzed via the scanning anode field emission microscopy technique (SAFEM, Fig. 1) at different surface locations and at different temperatures. For one location, the full set of measured I-V characteristics (total measured current versus applied voltage) for different values of Z, the distance between the cathode surface and the probe ball, were then analyzed in order to extract the current density J versus actual applied field F (J-F data), within the approximation that the LaS surface is a plane. A characteristic J-F variation is shown in Fig. 2. The work function of the LaS thin film has been extracted from the slope of the plot ln(J/F²) vs 1/F, by using the conventional Fowler-Nordheim relation, leading to a value of ∼0.65 eV which is in agreement with the onset of the electric field needed to observe an emission current density of 1 mA/cm² at an applied electric field across the vacuum gap around 230 V/μm.