Humidity dependence of electrical resistivity of bucky papers with different crystallinity

抄録

A bucky paper (BP), which consists of a large amount of carbon nanotubes (CNTs), is a potential candidate for electrical devices due to its high electrical conductivity and flexibility. BP devices are often used in the atmosphere. Although, the effect of water vapor on the resistivity of BPs has been observed, there is little agreement on its physical origin [1, 2]. The effect of water vapor on the resistivity of CNTs has also been discussed for individual SWCNTs. First-principles calculations have shown that charge transfer occurs between an individual CNT and adsorbed water molecules [3]. In this study, we measure the electrical resistivity of different types of BPs in a wide range of humidity and clarify the physical origin.

We prepared two types of BPs with different crystallinity. One was prepared by super-growth (SG) methods and dispersed in ethanol (SG-E), while the other was prepared by eDIPS methods and dispersed in denatured alcohol (eDIPS-D). SG-E consisted of low-crystallinity CNTs with low G/D ratio. e-DIPS consisted of high-crystallinity CNTs with high G/D ratio. First, we measured the resistivity by the four-terminal measurement method under controlled humidity at RH = 20, 40, 60, 80 % and at constant temperature T ~ 24℃ as shown in Fig. 1 (a,b). Second, we focused on charge transfer as the cause of the decrease in electrical resistivity with increasing humidity. For this reason, we performed Raman measurement to observe the presence of G-band shift as shown in Fig. 1 (c,d). The resistivity of SG-E decreased with increasing the humidity as shown in Fig. 1 (a), while that of eDIPS-D was almost unchanged as shown in Fig. 1 (b). The G-band shift was not observed in SG-E, while a shift of about 2 cm^-1 shift from 1532 cm^-1 was observed in eDIPS-D. This shift suggests charge transfer from water molecules to CNT by humidification. Consequently, the G-band shift was observed only in the samples where the resistivity was almost unchanged with increasing humidity. In the presentation, we will discuss about these unexpected results of the G-band shift. Furthermore, we will investigate the carriers and their mobility of BP by Hall effect measurements and discuss the effect of charge transfer on the humidity dependence of resistivity.

[1] A. Zahab et al., PHYSICAL REVIEW, 62, 15, 10000 (2000).

[2] Y. Kakogi et al., Meeting abstract of IVC (2022).

[3] D. Iwasaki et al., Appl. Phys. Express 10, 045101 (2017).