Field emission of Alq3 nanoprotrusions

Quasi-amorphous Alq3 (tris-(8-hydroxyquinoline) aluminium) thin films with nanoprotrusions on the surface were fabricated by vapour condensation under different conditions. The films fabricated under a liquid nitrogen cold trap have a smoother surface with smaller nanoprotrusions and exhibit a turn-on field of 6-9 mu m(-1). The films fabricated without a cold trap, with a rougher surface and larger nanoprotrusions, exhibit a turn-on field of 2-12 V mu m(-1). The electrons are emitted from an effective area on the tip of the nanoprotrusions. Both larger thickness and smaller effective protrusion radius lead to a larger field enhancement. A linear relationship between the effective and measured radii of the nanoprotrusions demonstrates that surface roughness indeed has a significant influence on the field emission efficiency. The nanostructured thin films exhibit a relatively lower emission threshold field than Alq(3) nanowires and most other film emitters.