Therefore, the exact nature of the responsible mechanism for the G-band up-shift on these substrates is still unclear so far. Figure 4 shows the results of the temperature dependence of the electrical resistance (normalized to its value at 300 K) of the two SWNTs measured with an electrical current of 10 nA. For SWNT1, the resistance CP673451 chemical structure decreases with decreasing temperature from room temperature down to about 120 K and then it increases by decreasing temperature

down to 2 K. At the lowest temperature of 2 K, the resistance reaches about four times its room temperature value of 181 kΩ. On the other hand, the resistance of SWNT2 shows an increase with decreasing temperature from room temperature all the way down to 2 K. OICR-9429 purchase However, at 2 K, the AZD2281 cost normalized resistance reaches about 280 times its value at room temperature of 1.46 MΩ, which is more than 2 orders of magnitude higher than that in the case of SWNT1. Figure 4 Temperature dependence of the

electrical resistance of the samples. (a) SWNT1 and (b) SWNT2. Insets show the resistance in the low temperatures range. The electrical current is 10 nA in all measurements. Natural logarithm of the resistance versus 1/T for samples (c) SWNT1 and (d) SWNT2 is shown. The solid lines are fits to a thermal activation formula R ~ exp (U/k B T), where U is an energy barrier (see text). First, the values of the resistance at room temperature are considered. The

intrinsic resistance of a SWNT in the diffusive this website regime (non-ballistic) can be estimated from the formula R = R c + R Q (L/l + 1), where R c , R Q = h/4e 2 ~ 6.45 kΩ, L, and l are the contact resistance between SWNT and the electrodes, the quantum resistance of a SWNT, the measured length of the SWNT, and the electron’s mean free path, respectively [32]. By comparing the 2 and 4-terminal resistances of our samples, and using L = 4 μm (distance between the inner voltage terminals), R c and l are estimated to be 8 and 19 kΩ, and 148 and 18 nm, for SWNT1 and SWNT2, respectively. The deduced mean free paths for SWNT1 and SWNT2 at 300 K are within the range of reported values for SWNTs [18, 33, 34]. Nevertheless, it is very difficult to compare directly with our samples because most of the published electrical transport properties data either do not define the chirality of the measured SWNTs or it is about SWNTs with larger diameters than ours. In general, the SWNT’s resistance at high temperatures is theoretically attributed to inelastic scattering between electrons and acoustic phonons within the SWNT [35]. However, the experimentally measured mean free paths of our SWNTs and others [18, 33, 34] are smaller by an order of magnitude than the theoretical calculations [35]. Recently, this discrepancy has been successfully addressed by introducing the effect of surface polar phonons (SPPs) from the substrate [36, 37].