High Electrical Conductivity and Transparency in Deoxycholate-Stabilized Carbon Nanotube Thin Films

Layer-by-layer (LbL) assembly was used to generate transparent, highly conductive thin films containing carbon nanotubes. Three different types of nanotubes were used, (1) multiwalled carbon nanotubes (MWNTs), (2) a mixture of single, di-, and triwalled nanotubes, also known as few-walled carbon nanotubes, and (3) purified single-walled carbon nanotubes (SWNTs). Thin films, less than 100 nm thick, were created by alternately exposing a substrate to aqueous suspensions of nanotubes stabilized by deoxycholate (DOC) and a solution of poly(diallyldimethylammonium chloride) [PDDA]. SWNTs produced the most transparent (>85%visible light transmittance) and electrically conductive (∼ 150 S/cm) 20 bilayer films with a 41.6 nm thickness. With just two bilayers of PDDA/(SWNT+DOC), these films have an electrical conductivity of 40 S/cm (3.8 nm thick with a sheet resistance of 65 kΩ/sq) and transmittance greater than 97% at 550 nm. MWNT-based films are much thicker and more opaque as a function of PDDA/(MWNT+DOC) bilayers deposited. A 20 bilayer PDDA/(MWNT+DOC) film is approximately 103 nm thick with a conductivity of 36 S/cm having a transmittance of 30% at 550 nm. Ellipsometry and a quartz crystal microbalance were used to measure the linear growth of these films as a function of bilayers deposited, while transmission electron microscopy and scanning electron microscopy were used to visualize the nanostructure of these films. This study demonstrates the ability of the LbL technique to produce highly transparent and conductive nanotube-based thin films. Films with a small number of bilayers are potentially useful for antistatic films, while adding more bilayers could produce transparent, flexible electrodes.