The influence of nanocrystal size on optical second harmonic generation by para-nitroanaline embedded in electro-spun polymeric fibers
Poly(methyl methacrylate) electro-spun fibers with embedded nanocrystals of the paradigmatic donor–acceptor nonlinear chromophore para-nitroaniline have been recently demonstrated to be efficient generators of second harmonic light. To understand the influence of the size and local strain experienced by the embedded para-nitroaniline nanocrystals, a Williamson−Hall analysis was carried out on the X-ray diffraction intensity. Both the mean crystal size and strain can be tuned by simple changes in the deposition parameters of flow rate and applied voltage. The observed second harmonic signal is well correlated with the ratio of the fiber diameter to the mean para-nitroaniline crystal size suggesting that surface effects are the main source of the strong nonlinear optical response. Adjusting the electro-spinning deposition parameters when producing polymeric fibers doped with strong nonlinear organic chromophores with high dipole moments has the potential to provide a versatile and efficient method for developing second-order nonlinear optical materials.
KeywordsSecond harmonic generation Electro-spun polymeric fibers Nanocrystal size and strain Williamson-Hall analysis Breaking of centrosymmetry Polymer nanocrystal interface
Hugo Gonçalves gratefully acknowledges support from the Portuguese Foundation for Science and Technology (FCT) through the grant PD/BD/111873/2015. The equipment used to characterize the second harmonic response of the electro-spun fibers was acquired within the framework of the Portuguese National Program for Scientific Re-equipment, contract REEQ-25/FIS/2005 with funds from POCI 2010 (FEDER) and FCT. The authors thank Elettra, Trieste, Italy, for beam time and support through the project 20170363.
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The authors declare that they have no conflicts of interest.
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