The possibility of imaging metal-water systems at high spatial and chemical resolution would provide unique and critical information on the interfacial phenomena controlling the behavior and degradation of catalytic and structural alloy systems while under service conditions. Existing approaches to these questions currently focus on developing in-situ TEM holders or spectroscopy techniques that can provide real time information. However these techniques generally lack spatial and chemical resolutions that are necessary to quantify the interfacial phenomena down to the atomic level. The objective of this project is to develop a unique method to image metal/water interfaces in three dimensions and at the nanoscale through unique cryo-preparation and cryo-imaging capabilities at the University of California, Berkeley and at the University of Michigan, respectively. It involves the development of specimen preparation from samples of ice that are suitable for examination by atom probe tomography (APT); focused ion beam (FIB) milling is the specimen-preparation method of choice. The high pay-off of the proposed approach resides in the versatility of the method that will allow not only metal-water systems to be studied, but will also be applicable to interfaces between hard and soft materials.
NON-TECHNICAL SUMMARY: This project will develop a novel technique for imaging frozen solid-liquid interfaces. First, miniature needles will be machined out of a frozen specimen. Secondly, the frozen needle will be analyzed atom by atom to form a 3D image of the local chemistry and atomic arrangement. The technique will be able to analyze solid-liquid interfaces important for many scientific and industrial technologies. For instance, this technique can address corrosion phenomena important for alloy development that are currently understood only at a phenomenological level because of the lack of high resolution characterization techniques such as the one proposed here. The methods are expected to impact a large number of research areas relevant to the development of energy materials (such as structural materials for power plants, battery materials, nanoparticles for catalysis, and organic electronic devices). An integrated research and education plan will employ one or more undergraduate students to work with a post-doctoral researcher and leverage existing University programs that emphasize the recruitment of women and under-represented minorities.
Atom probe tomography (APT) is a technique used to image hard materials at the atomic scale. It provides three dimensional reconstructions of the analyzed volumes by identifying and positioning atoms present in the analyzed material. Specimens for this technique are required to be in the form of very sharp needles with typical apex diameters of 200nm. An outstanding challenge is the application of this technique to liquids and biological samples. This objective of this EAGER project was to demonstrate the feasibility of analyzing ice and more specifically vitreous ice which is an amorphous form of ice routinely used in biology. The ability to spatially and chemically resolve structures embedded in vitreous ice at sub-nanometer length scales will lend itself to the study of ionic transport and corrosion phenomena at liquid/metal interfaces, solution based nanostructured synthesis, and biological materials. In addition it will also facilitate the analysis of structures that would otherwise be too small to be formed into a sample, such as core/shell metallic nanoparticles, by using the ice as a suspension matrix (as done routinely in cryo microscopy for biological applications). During this 2-year project, a post-doctoral researcher was mentored at UCB and an undergraduate student at UM performed research over the course of two year and successfully applied for graduate school. The technical outcomes are the design of a cryo-plunge device for needle-shaped specimens and transfer to the APT instrument, the development of a cryo-focused ion beam milling technique for reproducible cryogenic sample preparation and transfer to an electron microscope, demonstration of ice analysis by APT. A number of difficulties related to contamination and design flaws of the cryo-transfer system originally designed for a scanning electron microscope and adapted to the APT instrument by the manufacturer had to be overcome. It led to design ideas for successful contamination free specimen transfer systems and APT analysis.
