Understanding how Substrate and Intermolecular Interactions Influence the Properties of Supported Polyoxometalate Spin Qubits

Polyoxometalates (POMs) with localized spins have potential as molecular qubits for quantum computing applications. POMs may incorporate magnetic atoms such as V in their structures, producing novel molecules with promising electro/magneto-optical properties. Nevertheless, for eventual applications, molecular qubits need to be arranged in optically-addressable arrays which imposes unavoidable interactions with underlying supports and adjacent POMs. Specifically, spin-lattice (phonon) coupling is an influential decoherence mechanism that remains insufficiently understood for supported molecular qubits. Herein, we synthesized W-based POMs with different numbers of V atoms and transferred them into the gas phase using electrospray ionization. Ion soft landing, a versatile surface modification technique, was used to deliver mass-selected POMs with predetermined V-composition to different self-assembled monolayer surfaces. Alkylthiol, hydrophobic perfluorinated alkylthiol, and hydrophilic carboxylic-acid terminated surfaces on gold were selected as well-defined model supports with which to characterize POM-substrate and POM-POM interactions. Infrared reflection absorption spectroscopy, scattering-type scanning near-field optical microscopy (s-SNOM), and density functional theoretical calculations provide insight into the properties of supported POMs, how they are influenced by V-doping, and how they are perturbed by interaction with the different supports. Spatially-resolved s-SNOM results reveal the VPOM distribution on the supports and the effect of surface coverage on the POM-SAM and POM-POM interactions. The electronic properties of the bare POMs are determined by negative ion photoelectron spectroscopy and cyclic voltammetry, while the supported POMs are investigated by electrostatic force microscopy and scanning Kelvin probe microscopy. Our results provide fundamental insight into how substrate and intermolecular interactions influence the properties of supported molecular qubits, which is central to manipulating their coherence times for quantum computing applications.