Design of Liquid Crystalline Sensor for Carbon Nanotube Agglomerations

Abstract

Carbon nanotube (CNT)-based transistor has been considered as a promising substitute for silicon-based transistor due to low power consumption and propagation delay time.[1] In the preparation of CNT thin film, it has been shown that CNTs naturally bundle together forming agglomerations. Because the CNT agglomerations play as defect sites impeding electron flow,[2] the detection of CNT agglomerations is required for the design of CNT-based devices. Due to their nanoscale size, however, they were detected by Scanning Electron Microscope (SEM) that is time consuming and can only be applied to nano-to-micro scale area. In this work, we propose a facile and generalized method to instantaneously detect the surface defects in large area by leveraging anisotropic properties (elasticity and birefringence) and long range molecular ordering of liquid crystals (LCs). We prepared LC injected non-agglomeration and agglomeration-rich samples and compared them by POM image. (Fig 1) While the non-agglomeration sample shows a black texture, the agglomeration-rich sample shows a distinct bright dot texture in POM image. The dark texture is caused by vertical ordering of LCs. The bright texture is caused by tilted long range ordering of LCs against the substrate magnifying the nanoscale defect to the visible scale texture. The proposed method enables fast and whole-area detection of CNT agglomerations possible. Furthermore, this method can be used to detect general surface defect.1