(589b) Directly Measuring the Diamond Nucleation Landscape to Test Classical Nucleation Theory

Nucleation is a core scientific concept describing the formation of new phases and materials. While classical nucleation theory is applied in many fields, experimental nucleation rates often greatly exceed classical predictions, and nucleation energy landscapes have never been directly measured, particularly at the nanoscale. I will present a method for directly measuring the nucleation energy landscape of diamond, a previously inaccessible regime in a core physical process. Using a series of diamondoid molecules as atomically-defined proto-nuclei, we find that 26 carbon atom clusters, which do not contain a single bulk atom, are post-critical nuclei and measure the nucleation barrier to be four orders of magnitude lower than prior bulk estimates. These data support both classical and non-classical ideas for multi-step nucleation and growth during the gas phase synthesis of solid materials, and I will discuss insights to guide the growth of nanomaterials for bio-imaging and molecular sensing. More broadly, we provide direct experimental evidence to support recent theoretical proposals of multi-step nucleation pathways with metastable critical nuclei that fundamentally differ from the final bulk phase in processes ranging from cloud formation to nanoparticle synthesis.