Electrospray mass spectrometry of semiconductor nanoclusters: comparative analysis of positive and negative ion mode

There has been a substantial growth in the application of mass spectrometry (MS) methods for the analysis of inorganic materials, due to the inherent sensitivity of mass spectrometry ionization to the specific composition and structure of the analyzed materials. To date, few mass spectrometry studies have focused on metal-chalcogenide materials, an important class of semiconductor materials at the nanoscale, that exhibit interesting optical and electronic properties as a function of size. In this study, we report the application of a correlated electrospray mass spectrometry (ESMS) study between negative-ion and positive-ion mode under low-cone voltage to probe size, composition, and stability of metal-chalcogenide materials at the <1 nm scale. This correlation approach provides insight into the ionization behavior and thermodynamic stability of clusters in the <1.0 nm size domain of the form [Zn4(SPh)10][Me4N]2, [Cd4(SPh)10][Me4N]2, [E4Zn10(SPh)16][Me4N]4, [E4Cd10(SPh)16][Me4N]4 (E = S, Se). It is demonstrated that application of low-cone voltage ESMS can be a useful technique for the rapid analysis of intact solid state nanomaterials when both negative and positive ionic modes are analyzed, with a potential for extrapolation to other classes of nanoscale materials.