5 to 1.1 k Ω/sq. It is also worthy to mention that the sheet resistance of the compressed CNTF seems to be the same as that of the as-sprayed CNTF at the room temperature compression, which implies that the heat plays an important role in the reduction of sheet resistance under the thermal compression. Figure 5 shows the sheet resistance against the compression duration for the 230-nm-thick CNTFs under the compression force of 100 N. The sheet resistance decreases with the increasing of the compression duration. For the compression duration of 60 min, the sheet

resistance of CNTF at the compression temperature of 400°C selleck compound is lower than that of the one compressed at 200°C. The initial sheet resistance for the 230-nm-thick learn more CNTFs is 17 k Ω/sq, and the sheet resistances with the compression duration of 60 min are about 3.3 k Ω/sq for the CNTF compressed at 200°C and 0.9 k Ω/sq for the one compressed at 400°C.

Although the decreasing of sheet resistance seems to be saturated after 50 min, it is suspected that the sheet resistance of CNTF can be further decreased if the compression temperature increases. A possible mechanism for the enhanced conductivity of CNTF after the thermal compression is therefore proposed. At first, there are some defects created on the surface of CNTs after the acid treatment, and the CNTs in the as-sprayed CNTF are distributed arbitrarily with the wire shape, which these CNTs contact each other at the joints without any chemical bonds, as illustrated in Figure 6a. As we know, the carriers in the length-limited CNTs need to cross a lot of junctions from one CNT to another, and then the CNTF generally attained an unsatisfied conductivity mainly attributed to the existences of these junctions at the joints of CNTs. After the thermal compression, for instance, under the compression force of 100 N at 200°C, a high pressure, close to 1 GPa at the joints of CNTs in our case, acts on CNTs, and the CNTs are squeezed and deformed, as shown in Figure 6b. With the assistance of heat, the carbon

atoms around the defect sites start to bond with the neighbor carbon atoms that require a lower reaction energy. While the compression force, duration, and temperature are quite enough for the reaction, the linking of CNTs proceeds entirely, and then the CNTs are twined into a continuous film, as depicted in Figure 6c. Therefore, the carrier transports with a Carnitine palmitoyltransferase II high conductivity after thermal compression are obtained due to the lower junction barrier at the joints of linked CNTs. Figure 3 The Raman spectra of the as-sprayed CNTF and thermally compressed ones, accordingly. Figure 4 Sheet resistance versus the compression temperature for the 110-nm-thick and 230-nm-thick CNTFs. Sheet resistance under the compression force of 100 N for 50 min. Figure 5 Sheet resistance against the compression duration for the 230-nm-thick CNTFs. Sheet resistance under the compression force of 100 N at 200°C and 400°C, accordingly.