Affecting an Ultra‐High Work Function of Silver

Abstract

Efficient control of the work function (WF) of metals and their increase to ultra‐high values are crucial for their applications in functional devices applying interfacial charge transport processes. We report an ultra‐high increase in the WF of silver, from 4.26 to 7.42 eV, that is, an increase of up to ~3.1 eV. This, apparently, highest WF on record for metals supports and is supported by recent computational studies which predict the potential ability to affect an increase of the WF of metals by more than 4 eV. We achieved the ultra‐high increase by a new approach: Rather than using the common method of 2D adsorption of polar molecules layers on the metal surface, we have incorporated WF modifying components ‐ L‐cysteine and Zn(OH) 2 ‐ within the metal, resulting in a 3D architecture. Detailed material characterization by a large array of analytical methods was carried out (XRD, SEM, EDS mapping, TGA/MS, synchrotron X‐ray absorption, inelastic neutron scattering, Raman spectroscopy) the combination of which points to a WF enhancement mechanism which is based on affecting directly the charge transfer ability of the metal separately by cysteine and hydrolyzed zinc(II), and synergistically by the combination of the two components through the known Zn‐cysteine finger redox trap effect. Some additional properties include the ability to fine‐tune the WF from the pure silver values and up; the conductivity of the doped silver remains practically unaffected; the WF is stable beyond 3 months of storage; and it is heat resistant up to 150 o C. The ability to tailor WF changes from the standard value of silver and up over a wide range, will certainly find its applications wherever tuning of the WF is needed for the design of charge transport devices.