Shapes and shape transformations of solution-phase metal particles in the sub-nanometer to nanometer size range: Progress and challenges

Metal nanocrystals figure prominently in many current technologies, and they will play an important role in enabling a host of future applications. Since many of the beneficial properties of nanocrystals arise from their shape, achieving shape control is important yet still elusive in many instances. Shape control begins with seed crystals-nanometer- or sub-nanometersized particles that grow postnucleation and that may fluctuate through several shapes prior to achieving a set of shapes that act as templates for growth of the final nanocrystals. In this Perspective, we discuss experimental and theoretical progress in understanding the shapes of monometallic nanocrystal seeds. With the confluence of promising new applications, rapidly developing capabilities in electron microscopy in both vacuum and the liquid phase, and new theoretical developments in quantum and statistical mechanics, there are many exciting prospects for advancing this field. We delineate a few areas that are ripe for progress.