Microplasma emission performances dependent on silicon nanowires morphologies

Abstract

Silicon nanowires (SiNWs) are introduced into microdischarge to improve microplasma properties due to its field emission electrons and field enhancement effect. The geometrical arrangement and dimensional features of SiNWs have desicive influence on field emission properties, thus the dependence of microplasma emission performances on the SiNWs morphologies is investigated in this paper. The different morphologies of SiNWs can be prepared by electrocatalytic metal-assisted chemical etching with varied etching currents. With the increase of etching current from 3 mA to 30 mA (AgNO3:HF:H2O2 = 0.02:4.6:0.1 mol l−1, deposition time 1 min and etching time 10 min), the field emission current density J of the SiNWs prepared at 20 mA etching current is the largest ∼0.28 mA cm−2 at a field 4.5 V μm−1, and turn-on field is the lowest of 3.52 V μm−1. Accordingly, the microplasma in the device fabricated on the SiNWs-decorated substrate (etching current at 20 mA) has the strongest average emission intensity of ∼11 565 a.u., the minimal relative standard deviation of emission intensity 4.9% and the fastest propagation velocity of 471 km s−1. The field emission electrons of SiNWs could inject more seed electrons into microcavity which causes higher electron collision probability, and the field enhancement effect at tips of SiNWs can provide more energy for the charged particles, which are helpful to the microdischarge. The most difficulty is to balance the distance of emitters and the percentage of SiNWs in entire emission region because the shielding effect will reduce while the surface emitter numbers will decrease when the distance of emitters increases. Here, a ‘proper percentage of SiNWs’ of 19.3% is obtained what indicates that if SiNWs percentage is greater than the threshold, field enhancement factor β eff is weakened by the decrease of aspect ratio and the increase of percentage. When SiNWs percentage is less than 19.3%, β eff will increase and be dominated by the percentage of SiNWs. The results are significant for the application of SiNWs in microdischarge devices.