Determining In-plane and Thru-plane Percolation Thresholds for Carbon Nanotube Thin Films Deposited on Paper Substrates
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Determining In-plane and Thru-plane Percolation Thresholds for Carbon Nanotube Thin Films Deposited on Paper Substrates Using Impedance Spectroscopy Rachel L. Muhlbauer1and Rosario A. Gerhardt1 1 Georgia Institute of Technology, 771 Ferst Dr. Atlanta, GA 30332, USA ABSTRACT Concentration- and layer-dependent percolation thresholds can be determined for carbon nanotube (CNT) films deposited from aqueous dispersions on paper substrates at both the surface of the deposited film (in-plane) and through the thickness of the paper (thru-plane) using impedance spectroscopy. By analyzing the impedance spectra as a function of the number of layers (solution concentration is constant) or the solution concentration (number of layers is constant), the electrical properties and percolation thresholds for CNT-paper composites can be determined. In-plane measurements show that percolation occurs at 4 layers when 1 mg/mL solution concentration is used. In the thru-plane direction, the films are already percolated at 1 mg/mL concentration, which is confirmed by varying the concentration of the solution used to deposit 1 layer films. A second percolation event happens between 8 and 12 layers due to an increased number of interconnections of CNTs within the paper substrate. The lowest sheet resistance achieved was 100 / . INTRODUCTION In recent years, paper electronics have soared in popularity due to the low-cost, widespread availability, and flexible nature of paper [1]. At the same time, research into the use of carbon nanotubes (CNTs) as an electronic conducting material has grown due to the exceptional theoretical properties exhibited by CNTs. Printing as a film deposition method for CNTs onto flexible paper substrates has been shown previously to be a cost effective method of creating electronically conductive films for a variety of applications [2-4]. If the application does not require complex shapes, it is possible to print highly conductive films of non-surface modified multiwalled carbon nanotubes (MWNTs) from an aqueous dispersion on paper substrates using only a few printed layers by using a vacuum filtration-aided dropcasting technique [5,6]. Additionally, it can be shown how the electrical properties evolve both on the surface (in-plane) and through the thickness (thru-plane) of the paper through the use of impedance spectroscopy. Impedance spectroscopy is an AC electrical characterization technique which is used to determine frequency dependent electrical behavior in films. AC electrical techniques are more sensitive to individual electronic processes present in films making it possible to separate contributions of these different electronic processes from the overall electrical behavior of the film [5-7]. While we will not discuss each electrical process found in the films in detail in this paper, we will show how we can use the data found by impedance spectroscopy to determine percolation thresholds for these MWNT-paper films made as described. EXPERIMENT Aqueous dispersions of multiwalled carbon nanotubes (MWNT) obta
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