University of Texas at Austin, Austin, Texas
December 5, 2014 @ 4:00pm in Robert Lee Moore* Hall Room 5.104 (*now Physics, Math, and Astronomy Building)
Nonlinear Optical Spectroscopy of Silicon Nanocrystals
Brandon J. Furey1
1University of Texas at Austin
My current project is second-harmonic generation (SHG) and two-photon absorption (TPA) spectroscopy of ligand-stabilized silicon nanocrystals (ncSi), a new form of free-standing mono-disperse ncSi developed recently in Professor Brian Korgel’s chemical engineering group that can be dispersed in various liquid solvents, including water. Silicon nanocrystals embedded in solid oxides have been of interest to silicon photonics for many years because, unlike other forms of silicon, they luminesce efficiently. However, the microscopic mechanisms of luminescence remain controversial, in part because the difficult-to-characterize nano-interface of the ncSi plays an important role. A previous Downer student (Junwei Wei, PhD 2012) carried out a SHG study of oxide-embedded ncSi that revealed nano-interface-specific spectroscopic signatures that contributed to better understanding of this elusive nano-interface.
My proposed work aims in part to provide a comparative SHG study of ligand-stabilized free-standing ncSi. Raman spectroscopy by Korgel’s group and ours has already shown that absence of interface strain in free-standing ncSi causes important changes in their vibrational spectra, compared to their highly-strained, oxide-embedded counterparts. My proposed SHG study will probe corresponding differences in the electronic structure of the nano-interfaces.
A second scientific interest of free-standing ncSi is bio-imaging. Since ligand-stabilized ncSi are non-toxic, they can be attached to living organelles, which can be imaged via their photoluminescence. Unfortunately, the upper luminescing states must usually be excited by UV light, which damages cells and is not easily transmitted through tissue. For in-situ applications, I therefore propose to excite these states via TPA using near-infrared femtosecond light pulses, which are non-ionizing and much more readily transmitted through biological samples.
I will present details of the experimental procedure and preliminary results.
Link to host department: https://ph.utexas.edu/
Brandon J. Furey 