Work functions of self-assembled monolayers on metal surfaces

TL;DR

This study uses first-principles calculations to demonstrate how self-assembled monolayers can significantly modify the work functions of noble metal surfaces, with implications for electronic device engineering.

Contribution

It provides a detailed analysis of how organic monolayers alter metal work functions, highlighting the role of interface dipoles and their dependence on metal type.

Findings

Work function can change by up to 2 eV due to monolayer adsorption.

Adsorption reverses the natural order of work functions among metals.

Interface dipoles are primarily influenced by the metal, not the molecules.

Abstract

Using first-principles calculations we show that the work function of noble metals can be decreased or increased by up to 2 eV upon the adsorption of self-assembled monolayers of organic molecules. We identify the contributions to these changes for several (fluorinated) thiolate molecules adsorbed on Ag(111), Au(111) and Pt(111) surfaces. The work function of the clean metal surfaces increases in this order, but adsorption of the monolayers reverses the order completely. Bonds between the thiolate molecules and the metal surfaces generate an interface dipole, whose size is a function of the metal, but it is relatively independent of the molecules. The molecular and bond dipoles can then be added to determine the overall work function.