Alkaline niobate nanowires as opto-mechanical probes

Abstract

Perovskite alkaline niobate (XNbO₃) nanowires are attracting lots of attention having a variety of interesting properties such as significant nonlinear optical response, pronounced birefringence, considerable piezoelectric, pyroelectric, photorefractive, and photocatalytic response, as well as superior mechanical and chemical stability. Their ability to efficiently generate second harmonic signals (SHG) and their birefringence allow the use of these nanostructures as local mechano-optical probes for single molecule detection. To assess which type of nanowires is suitable for specific application, we performed a comparative study on the nonlinear optical response of the different types of chemically synthesized alkaline niobate nanowires: sodium niobate (NaNbO₃), potassium niobate (KNbO₃) and lithium niobate (LiNbO₃) nanowires. An optical trap setup has been used to demonstrate the possibility to steadily trap the nanowires, their ability to generate high second harmonic signals, to waveguide this signal and to be rotated under a highly focused laser beam with changing polarization. Different applications are suggested for the three materials, such as LiNbO₃ nanowires as imaging markers, while KNbO₃ and NaNbO₃ nanowires for trapping and torque experiments and NaNbO₃ nanowires to waveguide SHG light. Functionalization of the XNbO₃ nanowires has been studied and successfully implemented. This is a first crucial step toward their use in biomedical imaging and single molecule applications.