Structural modification of MgO/Au thin films by aluminum Co-doping and related studies on secondary electron emission

The secondary electron emission (SEE) has the potential applications in electron multiplication, mass spectrometer, scanning electron microscope, photomultiplier tubes and so on. Among these, the electron multiplier (EM) based on MgO/Au thin film has attracted great attention over the past few years. Here, we design a new kind of MgO thin film by co-doping of gold and aluminum elements based on the structural modification through reactive magnetron sputtering method. The doping of Al into MgO/Au film gives a rise to the maximum SEE coefficient (δ_max) between 9.02 and 10.23 while the optimal decay rate is around 10.4 % after 2 h of consistent electron bombardment. Herein, we also improved the stability of the film stored in air by sputtering Al₂O₃ layer on it. For the sample sputtered with the protecting layer Al₂O₃, its SEE coefficient (δ) at the incident electron energy of 200 eV still kept at a relatively high level that exceed 4.5 after stored in air for 72 h. The film properties after Al and Au co-doping are investigated in detail by the SEM, AFM, XPS and UV-VIS spectroscopy. Our results provide a new candidate for SEE layer in the application of long lifespan vacuum electron devices.