Field-emission properties of multihead silicon cone arrays coated with cesium

Field emission from multihead silicon (Si) cones was substantially improved by cesium (Cs) coating. Increasing the Cs coating lowered the emission turn-on field (for $\text{10\hspace{0.17em}μ}{\mathrm{A/cm}}^2)$ from 25 V/μm to a saturated value of 13 V/μm, while the threshold field (for $\text{10\hspace{0.17em}}{\mathrm{mA/cm}}^2)$ decreased by 30%, dropping from 27 V/μm for Si cones coated with 1.8 monolayers (ML) of Cs to a saturated value of 19 V/μm with 4.1 ML of Cs. The Cs-treated Si cones could give an emission current density that was three to ten times that delivered by bare Si cones. The work function reduced by a factor of 1.43 for Si cones coated with 4.9 ML of Cs with reference to the untreated Si cones. From the slope of Fowler–Nordheim plot, the field enhancement factor β was found to increase by a factor of 2.02 for Si cones coated with 2.5 ML of Cs and then reduce to 1.57 after the 4.9 ML of Cs deposition. Reduction of the factor β might occur because of a thick Cs layer, which could flatten the sharp cone features. Stability test showed that no current decay was observed at a current density of $\text{0.8\hspace{0.17em}}{\mathrm{mA/cm}}^2$ under a constant applied field of 16 V/μm during the 10 h investigation.