Work-function modification of PEG(thiol) adsorbed on the Au(111) surface: A first-principles study

TL;DR

This study uses first-principles calculations to show how PEG(thiol) monolayers modify the work function of Au(111), revealing a length-dependent and odd-even effect driven by interfacial dipoles.

Contribution

It provides a detailed first-principles analysis of how PEG(thiol) SAMs alter electrode work functions, highlighting the length and odd-even effects.

Findings

PEG(thiol) reduces Au(111) work function

The reduction depends on PEG chain length

An odd-even effect influences the dipole moment

Abstract

The possibility of modifying the work function of electrodes is important for optimizing the energy barriers for charge-injection (extraction) at the interface to an organic material. In this study, we perform density-functional-theory calculations to investigate the impact of dithiol-terminated polyethylene glycol (PEG(thiol)) based self-assembled monolayers (SAMs) with different numbers of PEG repeat units on the work function of the Au(111) surface. We find that a monolayer of PEG(thiol) decreases the work function of the Au(111) surface, where the magnitude of this reduction strongly depends on the length of the PEG backbone. The main contribution arises from the dipole due to the adsorption-induced charge rearrangement at the interface. Our work reveals a pronounced odd-even effect, which can be traced back to the dipole moment of the PEG(thiol) layer.