A research team led by Stephan Link of Rice University Laboratory has found a method to manipulate light dispersed by gold nanorods utilizing liquid crystals. This method paves the way to fabricate metamaterials with unique optical properties, which can be manipulated actively.
The positioning of liquid crystal molecules, which alternatively obstruct and expose the light scattered from the nanoparticles, is finely controlled by utilizing voltage. The findings of the study were published in the Nano Letters, a journal of the American Chemical Society.
Rice University researchers have created a technique to control plasmonic scattering from nanoparticles using liquid crystals. Credit: Jeff Fitlow/Rice University
Stephan Link stated that his research team spent two years to fine-tune the method to the point where the light scattered from the nanoparticles can be fully controlled. He added that the basis of their method is that the liquid crystal molecules coated over each gold nanorod that functions as an optical antenna rotates in-plane. The novel device, a super half wave plate used by the research team is an upgraded version of a standard unit that modifies the light polarization, he said.
The research team believes that its novel equipment can control light transmitted from any nanostructure that includes carbon nanotubes and quantum dots. During the study, the research team placed nanorods that are randomly deposited on a glass slide between a series of alternating electrodes and added a cover slip and liquid crystal bath. A polyimide coating over the top cover slip directed the liquid crystals to arrange themselves in a way parallel to the electrodes.
Liquid crystals in the homogenous phase obstructed light transmitted from nanorods pointed in one direction, while allowing light from nanorods turned in another direction via a polarizer into the detector. During the application of a voltage of 4 V to the electrodes, liquid crystals near the nanorods arrange themselves with the electrical field of the electrodes, while crystals that lie above remained in the same place due to the cover slip coating. The crystals’ new structure is known as a twisted nematic phase.
Link believes that his novel technique has great prospect when utilized with an arrangement of nanoparticles oriented in particular directions, where every nanoparticle can be fully controlled, like a switch.