Layer-by-Layer Assembly of Nanotube-Polymer Thin Films with High Electrical Conductivity and Transparency
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1205-L08-03
Layer-by-Layer Assembly of Nanotube-Polymer Thin Films with High Electrical Conductivity and Transparency Yong Tae Park1, Aaron Y. Ham1 and Jaime C. Grunlan1,2 1 Department of Mechanical Engineering and 2Materials Science and Engineering Program Texas A&M University, College Station, TX 77843-3123, U.S.A. ABSTRACT Layer-by-layer (LbL) assembly was used to deposit transparent, highly conductive thin films using aqueous solutions of nanotubes stabilized by deoxycholate (DOC) and poly(diallyldimethylammonium chloride) (PDDA). Three different types of carbon nanotubes (CNTs) were used: (1) multi-walled carbon nanotubes (MWNTs), (2) a mixture of single, di- and tri-walled nanotubes (XM grade) and (3) purified HiPCO single-walled carbon nanotubes (SWNTs). SWNTs produced the most transparent (> 85 %T across visible spectrum) and electrically conductive (~ 150 S/cm) 20-bilayer films with 42 nm thickness. Moreover, optoelectronic performance of SWNT-based thin films was improved with heat treatment due to the removal of PDDA. A 20-bilayer SWNT LbL film achieved a conductivity of 369 S/cm with a 5 min exposure to 400 ºC. This study demonstrates the ability of the LbL technique to produce highly transparent and conductive nanotube-based thin films, which may be useful for a variety of large area electronics applications. INTRODUCTION Carbon nanotubes (CNTs) are unique nanoparticles that have been thoroughly examined due to their extraordinary physical properties such as chemical, electrical, mechanical, structural, and thermal properties [1-3]. Recently, CNT-based thin films have been studied in electronic applications including, sensors [4], solar cells [5], integrated circuits [6], and transparent conductive films [7-16]. In the field of optoelectronics, these CNT thin films could eventually replace the current inorganic electrodes in flexible displays and touch screens, which require high transparency and electrical conductivity (≥ 85 % transmittance and ≤ 1 kΩ/sq sheet resistance). There are significant problems with alternative films that include brittle indium tin oxide [17], relatively low conductivity antimony tin oxide/polymer thin films [18], and relatively low transparency poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) films [19]. In this study, three types of CNTs (SWNT, XM, and MWNT) are used to make CNT thin films using a technique known as layer-by-layer (LbL) assembly. LbL is a powerful coating technique widely used in the laboratories to fabricate thin films in a homogeneous and controlled manner [20-22], which can be used to tailor the transmittance and electrical conductivity of CNT-based thin films. Using this method, thin films grow through electrostatic interactions by alternately exposing a substrate to positively and negatively charged aqueous solutions at room temperature, as shown in Figure 1. This study focuses on improving the transparency and conductivity by depositing CNTs as a thin film with a transparent polycation and a stabilizer, which exfoliate individual nanotubes in w
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