The Determinants of Crystalline Phase in Bottom-Up Nanocrystal Synthesis

Professor Janet Macdonald of Vanderbilt University is studying how crystal structure can be controlled with manufacturing nanocrystals. The properties of all matter are determined not only by the elements present, but their arrangement in space. This is especially true for nanocrystals, as structure dictates whether a material is a semiconductor for electronics, stores lithium ions in batteries or catalyzes important industrial chemical reactions. For nanocrystal chemists, it is straightforward to select which elements are present but not how they attach to each other. This study will use new families of reagents that can be tailored to change the rate at which they release their atoms to make the nanocrystals. Reactions that happen quickly produce different crystalline structures than those that happen slowly. This method has been successful for controlling the crystalline structure in metal sulfide nanocrystals. Moving forward, the much more synthetically challenging metal selenides, tellurides and phosphides will be tackled. For broader impacts, the research group’s deep knowledge of iron chemistry will be used to rediscover methods for painting the highly resilient rock paintings of the Anishinaabe which has been lost for 200 years. Professor Janet Macdonald of Vanderbilt University is studying the phase control of metal selenides, tellurides and phosphides in nanocrystal manufacturing. The approach is to develop and use families of reagents that control how fast the chalcogen or pnictide is released without changing the underlying chemical mechanism. This way the roles of reaction kinetics can be isolated and relationships between phases discovered. A quantitative metric of similarity between crystal structures will be developed to predict which crystalline phases are most likely to interconvert under synthetic pressures. The goal is to provide the rules that underpin phase selection in colloidal synthesis which will lead to manufacturing guidelines to achieve desired phases, moving the community past serendipity to rational phase control. These synthetic guidelines will aid any technology where crystalline phase of nanoscale materials is important, including earth abundant and active industrial catalysts, photothermal therapy agents, superconductors, supercapacitors, magnetic storage media, and ion storage materials in batteries. Under broader impacts, using established knowledge of iron chalcogen surface chemistry, methods for painting the rock art of the Anishinaabe will be developed using culturally significant plants. The way to make these highly weather resilient paintings have been lost for 200 years. Furthermore, an approach will be developed for testing if indeed plant materials were used for paint deposition based on silicon isotopic ratios and trace element analysis. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.