This proposal requests funding to design, build and commission a femtosecond SFG scattering instrument. Once commissioned it will be used to examine the structure of molecules at interfaces (liquid/solid, air/solid, air/liquid). The scattering patterns generated by this instrument from particles in solution provide insight into the size and shape of the particles. The spectra generated by this instrument provide information about the structure of molecules bound to these particles. A femtosecond SFG scattering instrument is ideal for in situ characterization of nanoparticles (NPs) in complex solutions and will provide important, new information about those NPs, molecules bound to the NPs, and solvent molecules interacting with the NPs. This instrument will be integrated into the National ESCA and Surface Analysis Center for Biomedical Problems (NESA/BIO), allowing a wide range of researchers access to this novel instrument.
In the past 10-15 years there has been an explosion of interest and activity in the synthesis and applications of novel nanomaterials. In most nanomaterial research areas, especially for nanomaterials dispersed in complex solutions and other matrices (soil, biological fluids, etc.), methods to provide in situ characterization of the nanomaterial surface chemistry and structure is lacking. Non-linear optical methods have the potential to probe the surface structure of nanomaterials in these complex environments. The non-linear process requires two high intensity laser beams to be overlapped in time and space at the interface of interest (liquid/solid, liquid/air or solid/air). To date nearly all non-linear optical experiments done in the sum frequency generation mode have focused on obtaining vibrational spectra from large, flat interfaces. The new state-of-the-art femtosecond sum frequency instrument designed and constructed in this project can do sum frequency experiments in the scattering mode on nanomaterials dispersed in solutions. The results provided by the new femtosecond sum frequency scattering instrument will advance our understanding of nanomaterial surface chemistry and structure, as well as how these nanomaterials interact with their surrounding environment. This information in turn can be used to design and engineer new, higher performance nanomaterials. In addition to operation in scattering mode, the instrument can also be operated in the reflection mode to provide vibrational spectra from flat interfaces. The tunability of the both the visible and infrared laser beams allows the ability to significantly increase the sum frequency signals by matching the wavelengths of these two incidence laser beams to resonances in the materials being investigated.