Surface properties and interfacial interactions of nanomaterials directly impact the widespread application of these systems by mediating essential processes including light emission and electron transfer. Directly probing and characterizing these surface states, however, remains a complex research goal. Conventional techniques, such as UV-Vis and photoluminescence, struggle to address the electronic structure of nanomaterial surfaces because they tend to be obscured in bulk ensemble measurements due to a broad range of sites, chemical environments, and surface dissimilarities. To circumvent these limitations, we report the use of an electronic sum frequency generation (eSFG) widefield microscope to provide a direct absorption-like measurement with enhanced surface sensitivity on a limited number of nanoparticles. In addition, by performing eSFG measurements with broadband excitation in the visible regime, a complete characterization of the transitions corresponding to the core and potential surface states that lie below the band gap is possible simultaneously. Our preliminary results on CdSe quantum dots reveal transitions corresponding to core state sand show signatures of surface trap states at energies below the band gap. Modification of the surfaces via oxidation allows the interfacial character of these observed transitions to be explored in more depth. The approach and results of this work provide a new methodology to directly characterize these and other nanomaterial interfaces.<br/>

Probing the surfaces of CdSe quantum dots using sum frequency generation

253rd National Meeting (2017)

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