Abstract
Quasi-amorphous Alq 3 (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 V μm -1 . The films fabricated without a cold trap, with a rougher surface and larger nanoprotrusions, exhibit a turn-on field of 2-12 V μm -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. © IOP Publishing Ltd.