Magnesium film-over-nanospheres (FONs) for surface-enhanced Raman scattering

Understanding interfacial interactions at the native oxide surface of Mg is important for catalytic and biomedical applications. Recent advancements in plasmonic Mg research led to its use for surface-enhanced Raman scattering (SERS), a vibrational spectroscopy particularly sensitive to molecules bound to the enhancing substrate. Here, novel Mg film-over-nanospheres (FONs) are fabricated and used as SERS substrates to study molecular binding on Mg surfaces, augmenting previous results on 4-mercaptobenzoic acid (4-MBA) and 4-nitrothiophenol (4-NTP) by revealing the binding of 4-nitrophenol (4-NP) and 5,5'-dithiobis (2-nitrobenzoic acid) (DTNB). Through a systematic study of a total of 17 molecules with various functional groups, a pK_a-related trend is unravelled: binding on natively oxidised Mg requires the adsorbate to dissociate and have a pK_a between ∼4.5 and 7.5, however diselenides and ditellurides do not appear to follow this trend. The results pave the way for chemical functionalisation of Mg surfaces for plasmonic and other applications.