Imaging excited-state dynamics of individual nanoparticles using single-molecule absorption scanning tunneling microscopy

Characterizing the unique optical phenomena of nanomaterials has been a central theme in understanding how we can leverage these materials for applications in fields including photocatalysis and renewable energy. However, techniques often used to probe optical properties of these materials rely on detection of bulk material properties. Given the significant population of defects or structural variations that are innate to most nanomaterial syntheses, understanding precisely how heterogeneity affects the properties of these materials is critical, and requires single-particle techniques capable of probing both the structural and excited state electronic properties on the nm scale. To measure excited-state dynamics of single nanoparticles with spatial sub-nm resolution and temporal sub-ps resolution, our group employs an excited state imaging technique known as single-molecule absorption scanning tunneling microscopy (SMA-STM). We will discuss applications of this technique and preliminary STM data for characterizing the excited state structure and energy transfer dynamics of carbon dots to understand their fluorescence mechanism and quantum dots designed for triplet energy transfer.