Carbon nanotubes (CNTs) have captured the interest of scientist due to their large aspect ratios, remarkable optical, electrical and mechanical properties. A recent breakthrough has produced highly aligned nanotube films. Although these films are tightly packed, mono-domain and wafer-scale, their conductivity is lower than that of the theoretical maximum of single-wall CNTs or CNT fibers produced by wet spinning. Conductivity can be enhanced in these films via chemical doping. Chemical doping increases conductivity by decreasing the the resistance across tube-tube junctions and increasing intra-tube conductivity. In this study, we investigated the potency and stability of six different dopants using terahertz time-domain spectroscopy. The results show that common high-redox potential acid dopants, such as nitric acid, are potent but volatile in stability. Dopants such as AuCl3 (gold chloride) and F4-CNTQ (a popular p-type dopant for hole-only devices) are more effective and stable when used with CNT films.
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