Covalent Grafting of Polyoxometalate Hybrids onto Flat Silicon/Silicon Oxide: Insights from POMs Layers on Oxides

TL;DR

This study reports the covalent grafting of polyoxometalate hybrids onto silicon oxide surfaces, characterizing the interface and electronic properties to enhance applications in catalysis and molecular electronics.

Contribution

It introduces a novel covalent grafting method for POM hybrids onto Si/SiO2, with detailed interface characterization and analysis of electronic transport properties.

Findings

POM layers are covalently anchored via specific modes at the oxide interface.

Electronic properties are dominated by POM LUMO levels regardless of tether or anchoring group.

The molecular junctions exhibit electron transport influenced primarily by POM electronic features.

Abstract

Immobilization of polyoxometalates (POMs) onto oxides is relevant to many applications in the fields of catalysis, energy conversion/storage or molecular electronics. Optimization and understanding the molecule/oxide interface is crucial to rationally improve the performance of the final molecular materials. We herein describe the synthesis and covalent grafting of POM hybrids with remote carboxylic acid functions onto flat Si/SiO2 substrates. Special attention has been paid to the characterization of the molecular layer and to the description of the POM anchoring mode at the oxide interface through the use of various characterization techniques, including ellipsometry, AFM, XPS and FTIR. Finally, electron transport properties were probed in a vertical junction configuration and energy level diagrams have been drawn and discussed in relation with the POM molecular electronic features inferred from cyclic-voltammetry, UV-visible absorption spectra and theoretical calculations. The electronic properties of these POM-based molecular junctions are driven by the POM LUMO (d-orbitals) whatever the nature of the tether or the anchoring group.