Excited State Imaging and STM Characterization of Materials on the Nanoscale

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 nanomaterials including quantum dots (QDs) and carbon nanotubes (CNTs), and will discuss results surrounding the interactions of optically excited QDs and CNTs. This work will focus on semi-quantitative modeling of our experiments showing the distant-dependent transverse polarization of CNTs in the presence of an excited QD and modeling energy transfer between materials. We will also discuss 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.