Work function measurements of Gd/W(111) with and without silicon interface layers: field emission study

Abstract

The adsorption of gadolinium on the (111) plane of tungsten field emitters with and without silicon precovered layers has been investigated. Gd and Si depositions and work function measurements were made at the room substrate temperature. The “thickness” of silicon interface layers has ranged from a fraction of a monolayer (ML) to 1ML, whereas Gd was condensed up to the stabilization of the adsystem work function. With the silicon precoverage increasing (from 0 to 1ML), the dependence of work function on the Gd concentration was modified from the pronounced non-monotonic dependence to a monotonic one, the adsystem final work function was increased from 2.6eV to 3.05eV, and the Gd film growth mode was changed from the layer-by-layer mode (the Frank–van der Merwe mechanism) to the three-dimensional (3D) cluster formation (the Volmer–Weber one). In addition, it was observed that the monolayer coverage of Si effectively passivates the W(111) surface. The mixing and the chemical reaction between the coadsorbed Si and Gd atoms were not found. In all cases of Gd and Si atom adsorption, as well as of their coadsorption, the changes in Fowler–Nordheim pre-exponential with coverage were calculated and their behaviour was discussed.