ABSTRACT

This EAGER award supports a postdoctoral student to assist in the development of methods to fabricate appropriately shaped, nanometer scale, tips of abiogenic and biogenic carbonates using a focused ion beam (FIB) for subsequent compositional analysis using atom probe tomography (APT). APT was developed for the analysis of synthesized conducting materials for process control in the semiconductor industry and sub-nanoscale/atomic scale spatially resolved analysis of elemental distributions in other synthesized materials (e.g., ceramics). The PI, a mineralogist/geochemist who specializes in studies of biogenic mineralization processes seeks to employ the extant FIB-SEM and APT instruments housed in the Central Analytical Facility (CAF) at the University of Alabama. APT technology uses pulsed laser evaporation of extremely delicate nanoscale materials tips followed by time-of-flight mass spectrometry (TOF-MS) to image individual atom distributions in sample tips. Application of APT to studies of carbonates is in its infancy and presents major challenges to successful analysis for potential application to understanding mineralization and diagenetic processes at the atomic scale. Fabrication of tips from brittle biogenic carbonates minerals requires extremely careful ion milling and tip loads into the APT instrument and the PI has thus far only achieved a single successful analysis of a biogenic carbonate tip with limited analytical precision. A goal of this EAGER is to first try to improve methods to ion mill tips of abiogenic carbonates for subsequent APT analysis and then to attempt to extrapolate those processes to ion milling of natural biogenic carbonate minerals. A second goal is develop optimal analysis protocols to determine if the relative abundances of major, minor, and trace elements of carbonate minerals can be successfully imaged at the atomic scale. The technique, should it be successful, could prove transformative for studies of microbially mediated carbonate mineralization processes and paleorecords research but it presents considerable risk, hence the EAGER proposal mechanism.

Carbonate rocks are present in large parts of the sedimentary continental crust of the Earth and thus are of great significance in geological studies. Furthermore, much of the current development of geochemical techniques and applications is for studies in paleoclimate and paleoenvironmental reconstructions in which the analysis of biogenic carbonate minerals plays a crucial role. The potential use of atom probe could contribute advanced knowledge of: 1) diffusion kinetics (volume, grain-boundary, trace elements, etc.); 2) element partitioning; 3) mineral dissolution and recrystallization; and 4) transformation of transient amorphous phases into crystalline counterparts. Proposed new analytical developments could encourage new approaches to geochemistry research and mineral analysis and promote interdisciplinary research. Should the technique development prove successful, the APT and FIB instruments in the Central Analytical Facility (CAF) of The University of Alabama could be opened for outside community use. The proposal will engage a postdoctoral scientist and results will be disseminated through talks at topical workshops, scientific conferences and through scholarly publication.

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