Fabrication of Micrometer-Sized Conical Field Emitters Using Femtosecond Laser-Assisted Etching of Silicon

We produce quasi-ordered arrays of sharp, conical microstructures by structuring the surface of a silicon wafer using femtosecond laser-assisted etching. Analysis of the arrays shows high, stable field emission without any further processing. The sharp, micrometer-sized conical structures result from irradiation of a silicon surface with hundreds of femtosecond-laser pulses in an atmosphere of SF6. These conical microstructures have sharp tips with a radius of curvature of about 250 nm and a subtended angle of less than 20°. They are 10–14 µm tall, have tip-to-tip separations of 6–10 µm, and form in the direction of the incoming radiation. Without any processing beyond the laser irradiation required to form our microstructures, we obtain emission currents comparable with current standards and suitable for applications. The field required to produce an emission current density of 1 nA/mm2, is 8 V/mm. We have obtained emission currents up to 20 µA/mm2 at an applied field of 40 V/mm. Lifetime testing of emission of a sample over 24 hours at an anode-cathode spacing of 40 mm shows that after an initial drop in emission current to 75% in the first half hour, the emission current remains steady. The structures are very robust and continue to produce field emission after being left in air for several weeks.