Controlled clustering in metal nanorod arrays leads to strongly enhanced field emission characteristics

We show that controlled clustering in electrochemically grown silver nanorods results in up to 50% enhancement in their field emission performance. Larger cluster size and nanorod length lead to a lower turn-on electric field, a higher current density and a larger enhancement factor. However, beyond a critical length (≈30 µm), the nanorods begin to form disordered ridges instead of well separated conical clusters and the field emission performance proceeds to deteriorate. With the help of finite element modelling, we show that a larger cluster size indeed leads to an enhanced electric field at the cluster edges, effectively reducing screening effects and thereby enhancing the field emission performance. Though our present work pertains to silver nanorods, a similar clustering of nanorods is observed in many types of electrochemically grown nanorods, and even in carbon nanotubes and Si nanowires grown by other techniques. Hence, we expect this study to have general applicability in the design of better nanorod-based field emitters.