Application of work function measurements to the characterization of thin films and solid surfaces

Abstract

Two different methods of electron work function measurements, the diode and the onset method, which can easily be incorporated in existing analytical equipment are described. For the diode method the sample is used as the anode of a diode arrangement, and the work function changes of the specimen are obtained from the shift of the break points of characteristic retarding field lines. The onset method uses the shift of the onset of the secondary electron energy distribution due to work function changes. Both methods were applied to Ta2O5 layers of 500 A thickness which were produced by electrochemical oxidation of polycrystalline tantalum substrates. In particular, bombardment induced work function changes during sputter removal of these layers have been investigated. The onset method was also applied to differently oriented grains of a polycrystalline Ta specimen. Work function differences of 0.1 eV between two different grain surfaces were safely detectable. In addition, a work function difference of 0.5 eV between Au and Mo was determined which agrees well with literature values.