PNNL

Abstract

Polyoxometalates (POMs) with localized radical or open-shell metal sites have the potential to be used as transformative electronic spin based molecular qubits (MQs) for quantum computing (QC). For practical applications, MQs have to be immobilized in electronically or optically addressable arrays which introduces interactions with supports as well as neighboring POMs. How these interactions influence the spin-lattice relaxation time (T1) for an excited spin to relax back to its ground state remains insufficiently understood, particularly in the quest to design supported MQ arrays with long decoherence times (?100 µs). Herein, we synthesized Keggin POMs with both tungsten (W) and vanadium (V) addenda atoms. Ion soft landing, a highly-controlled surface modification technique, was used to deliver mass-selected V-doped POMs to different self-assembled monolayer surfaces on gold (SAMs) without the solvent, counterions, and contaminants that normally accompany deposition from solution. Alkylthiol, perfluorinated, and carboxylic-acid terminated monolayers were employed as representative model supports on which different POM-surface and POM-POM interactions were characterized. We obtained insights into the vibrational properties of supported V-doped POMs and how they are perturbed by interactions with specific functional groups using infrared reflection absorption and scattering-type scanning near-field optical microscopy, as well as tip enhanced Raman spectroscopy. The electronic structure of the V-doped POMs was determined in the gas phase using negative ion photoelectron spectroscopy and on surfaces with scanning Kelvin probe microscopy. The geometric and electronic structure of the POMs were also interrogated using density functional theory. Our joint experimental and theoretical findings provide insight into how V substitution as well as POM-surface and POM-POM interactions influence the vibrational properties of POMs which are known to govern the spin-lattice decoherence rates of MQs used in QC applications. O.M.P., S.T., D.Z., B.T.O., and E.T.B acknowledge support from the Laboratory Directed Research and Development Program at PNNL. G.E.J., V.P., and V.-A.G. were partially supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, project 72353 (Interfacial Structure and Dynamics in Separations). P.Z.E., X.-B.W., and W.C. were partially supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences (Chemical Kinetics and Dynamics at Interfaces). Part of this work was performed using EMSL, a National Scientific User Facility sponsored by the DOE’s Office of Biological and Environmental Research and located at the Pacific Northwest National Laboratory (PNNL). PNNL is a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy under contract DE-AC05-76RL01830. Computer resources were provided by Research Computing at the PNNL and the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science User Facility operated under contract DE-AC02-05CH11231.