20 August 2009 Investigation of ultrafast carrier dynamics in ZnO rods using two-photon emission and second harmonic generation microscopy
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The demand for novel optoelectronic and photonic technologies has fueled an intense research effort to synthesize and characterize nanostructured semiconductor materials with unique properties that lend themselves to technological innovation. Zinc Oxide has emerged as an attractive candidate for a variety of applications, due in part to a large second order nonlinear susceptibility, its wide band-gap and large exciton binding energy. We have used time-resolved nonlinear two-photon emission and second harmonic generation microscopy to characterize the optical properties and excited state dynamics of individual rods. Ultrafast emission microscopy is used to follow the trapping dynamics of photoexcited charge carriers. Our results show a time-dependent red-shift in the trap emission band that is interpreted as arising from carrier percolation through trap states. In a second series of experiments, second harmonic generation (SHG) microscopy illustrates the connection between the optical mode structure of the object and its nonlinear mixing efficiency. Images show a periodic modulation in the SHG efficiency that is symmetrically situated relative to the rod midpoint. This phenomenon arises when the fundamental optical field couples into standing wave resonator modes of the structure and is a direct manifestation of the tapered shape of the rod.
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Ralph L. House, Ralph L. House, Brian P. Mehl, Brian P. Mehl, Chuan Zhang, Chuan Zhang, Justin R. Kirschbrown, Justin R. Kirschbrown, Scott C. Barnes, Scott C. Barnes, John M. Papanikolas, John M. Papanikolas, } "Investigation of ultrafast carrier dynamics in ZnO rods using two-photon emission and second harmonic generation microscopy", Proc. SPIE 7396, Physical Chemistry of Interfaces and Nanomaterials VIII, 73960G (20 August 2009); doi: 10.1117/12.826064; https://doi.org/10.1117/12.826064

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