Ionomigratively Pumped Salt Micro/Nanolenses along a Cation-Specific 1D Nanochannel

Abstract

A micro/nanolens of hygroscopic salt with tunable refractive indices provides unique opportunities in molecular spectroscopy and nanotechnology. Forming salt lenses and arranging them in a well-defined manner, however, has been challenging. Here we demonstrate that the exterior of single-walled carbon nanotubes (SWNTs) is a cation-specific 1D nanochannel, which facilitates formation of such lenses via ionomigration driven by momentum transfer from ion flux under electric field. Ionomigration is assisted by strong cation-π interaction, enabling spatiotemporally non-uniform transport of charges along SWNTs. The lens is stable in ambient conditions indefinitely, non-invasively amplifies Raman scattering of various molecular species and SWNTs, by up to two orders of magnitude, optically visualizes individual nanotubes, and can be easily rinsed off. The cation-specific 1D channel has broad implications in spectroscopy, charge-specific chemistry in 1D space, single-molecule transport and detection, and novel charge storage devices.