Excited State Imaging and STM Characterization of Nanomaterials

In an effort to spatially resolve excited state properties of nanomaterials with sub-nm resolution, our group has developed an excited state imaging technique known as single-molecule absorption scanning tunneling microscopy (SMA-STM). This technique allows us to probe changes in tunneling associated with laser excitation, creating an image that maps the excited state electronic structure of nanomaterials. We have applied this technique widely to study excited state properties of quantum dots (QDs) and carbon nanotubes (CNTs) and will discuss results surrounding the interaction of optically excited QDs with CNTs. Our results show a distant-dependent transverse polarization of CNTs in the presence of an excited QD, while semiquantitative tight-binding calculations performed on an analogous system allow us to model the observed interaction. We will also discuss our preliminary work with traditional STM on carbon nanothreads and their variants, which aims to characterize the ground state electronic properties of these carbon materials. Initial results show highly variable band gaps of aggregate structures likely due to varied ordering and defects, while techniques allowing for investigation of individual threads will ultimately position us for excited state characterization.