Research

Research at the Haber Group at the Department of Chemistry at Louisiana State University in Baton Rouge focuses on fundamental investigations of nanoparticles and nanomaterials and their interactions with molecules and light. Our research group uses ultrafast spectroscopy and nonlinear spectroscopy, such as time-resolved second harmonic generation (SHG), sum-frequency generation (SFG), and transient absorption (TA) to study processes such as molecular adsorption, molecular structure and orientation, and energy and electron transfer at nanoparticle surfaces, either supported on substrates or in colloidal suspension. We are particularly interested in surface plasmon resonances of metallic nanoparticles, characterized by the coherent oscillations of free electrons under incident light, which provide large optical field enhancements while altering the excited-state energies and relaxation dynamics of nearby molecules. Additionally, our research focuses on potential advances in applications of molecular sensing, nanomedicine, catalysis, and solar energy.

We utilize ultrafast and nonlinear spectroscopy to study the optical and molecular interactions with nanoparticles and nanomaterials. One of our recent publications reports on the molecular adsorption and spectroscopy of different dye molecules at colloidal gold nanoparticle surfaces. Using the surface-specific technique of second harmonic generation, the adsorption isotherms of the triphenylmethane dyes malachite green, brilliant green, and methyl green were measured and the influence of the chemical changes were observed to dramatically influence the free energies of absorption and the adsorbate site densities on the gold nanoparticle surface in water. The spectral interactions between the molecules and the plasmonic gold nanoparticles were also carefully analyzed to obtain new insights on plamonic resonant coupling through polaritons, which has important implications for molecular sensing applications.

 

Additional work has studied other molecular, optical, and physical interactions involving nanoparticle surfaces using advanced spectroscopic techniques. In a recently submitted paper, we have determined the surface charge density of small gold nanoparticles using second harmonic generation for the first time. In another recently submitted paper, we have investigated energy transfer and excited-state relaxation dynamics of nanoparticles composed of organic salts using transient absorption for developing new nanomaterials that are promising candidates for increasing photovoltaic efficiencies. We have ongoing studies on biologically-relevant plasmonic nanoparticles for photothermal cancer therapy and drug delivery using SHG and TA. We are also investigating photocatalysis on nanomaterials through pump-probe vibrational sum-frequency generation spectroscopy experiments. Using ultrafast and nonlinear spectroscopic techniques, our research group provides fundamental measurements on molecular interactions with different types of nanoparticles and nanomaterials for advanced applications in molecular sensing, nanomedicine, catalysis, and solar energy.