Paper AS-ThP14
Probing the Chemical-State of Zinc centers in unknown Environments: A Comparison of Conventional and Core-core-core Auger Parameter Analyses

Thursday, November 2, 2017, 6:30 pm, Room Central Hall

Citrus greening is a major problem for the agricultural community in the United States. Afflicted trees typically die within a few years of infection and produce fruit that is green, misshapen, and bitter to the taste. To mitigate the deleterious effects of this epidemic, a Florida-based team of researchers have developed a spray-dispersible bactericide known as Zinkicide^TM, which consists of zinc-containing nanoparticles capable of entering and freely traversing the phloem-containing vascular system of infected trees to selectively kill bacteria within infected cells. While controlling the size of the particles is of key importance to their membrane transverability, the chemical-state of the zinc centers is believed to be of key importance to controlling the resultant chemical interactions with the bacteria.

Having demonstrated proof-of-concept utility with laboratory-scale quantities of bactericides created from reagent-grade precursors, TradeMark Nitrogen has since begun scale-up efforts using agricultural-grade precursors. Given the importance of chemical-state on the bacteriacidal properties of the nanoparticulates, detailed characterization of the powders is of great importance. Unfortunately, traditional core-level XPS analysis of zinc centers is not sufficient for such characterization due to the relative insensitivity of the most intense transition (Zn 2p), which results in shifts too small to distinguish Zn in chemical compositions as disparate as Zn⁰ and ZnO for example.

Due to this core-level insensitivity, most reported photoemission analysis of Zn makes use of an associated Auger transition to allow for Wagner plot comparisons to libraries of Zn in known compositions. Such analysis allows for peak assignments through both qualitative and quantitative comparisons with reference data, but is limited in its ability to disambiguate the chemical-states of Zn in environments not perfectly reproducing those of previously measured control samples due to the non-extrapolatable nature of Auger parameter measurements incorporating core-valence-valence transitions. By contrast, appropriately chosen combinations of core-level XPS and core-core-core Auger lines have been shown to provide more reliable estimates of final-state contributions to XPS peak shifts, thereby allowing for direct initial-state interpretation of those shifts (i.e. direct correlation between the extent of the final-state corrected XPS shifts and the degree of oxidation). In this talk, we will present XPS and Auger data sufficient to compare results from both types of analyses on both reference and various Zinkicide^TM samples made available for analysis by TradeMark Nitrogen.