## 3 Results and Discussion  
Before processing the electrode structure, we first tried to solder the entire CNT to the metal surface. MWCNTs were deposited on a gold surface with a thickness of 60 nm, then irradiated by laser. The laser energy density was approximately 23.810 mJ/cm\({}^{2}\). The results of several experiments showed that the MWCNTs were embedded and welded into the metal surface after laser irradiation, and only part of the end of the CNTs were exposed. Figure 2a shows a typical scanning electron microscope (SEM) image of comparison of the laser irradiated and un-irradiated areas, with the lower half being the un-irradiated area and the upper half being the laser irradiated area with significant differences between the two areas. Figure 2b is a high-resolution SEM image before laser irradiation. It shows that the MWCNTs loosely stay on the surface of metal electrode, and the CNTs can be clearly observed. Figure 2c is a high resolution SEM image after laser irradiation, in which the arrows indicate MWCNTs embedded in the gold surface and the highlights are part of the exposed CNTs. Figure 2: SEM images of the surface after welding a large number of MWCNTs onto Au at a laser energy density of 23.810 mJ/cm\({}^{2}\); (**a**) Surface topography of the irradiation (upper side) and non-irradiation (lower side) areas; (**b**) A view in which the partial area is enlarged in the un-irradiation area. The arrows in (**c**) indicate that some of the short ends of the MWCNTs protrude from the solder substrate. After that, we tried to connect the SWCNTs with the metal electrodes. Figure 3a shows a SEM image of CNTs deposited on the surface of the electrodes before laser irradiation. The morphology of the CNTs and the electrode surface can be clearly seen in the figure. At this time, the CNTs are only lying on the surface, and thus, there is a large contact resistance with the surface of the electrodes. Figure 3b shows a topographical view after laser irradiation. A certain degree of morphological change occurred on the surface of the electrodes which can be clearly observed, and the ends of CNTs were buried in the metal electrodes so that the ends of the CNTs were almost invisible in the SEM image. A partial topographical view of the CNTs-to-electrode connection is shown in Figure 3c, in which it can be clearly observed that the SWNCTs is embedded in the metal electrode. The mechanism of the laser-induced connection is explained as follows. Femtosecond (fs) laser illumination combines high pulse intensity with ultrashort pulse duration, the metal and surrounding surface Plasmon resonance (SPR) in the irradiated region can be excited by appropriate power  
Figure 3: (**a,b**) SEM image before laser irradiation at the same position and after irradiation with a laser having an energy density of 13.810m/cm\({}^{2}\). It can be observed that the ends of the SWCNT can be clearly seen on the surface of the electrodes before irradiation, and the end of the SWCNTs is hardly visible after irradiation. At this time, SWCNTs are connected to the Ni electrodes; (**c**) A high-resolution SEM image of the SWCNTs connected to the electrode, the SWCNTs embedded in the electrode are marked. irradiation [33; 34]. Due to the Ohmic thermal effect of the metal, SPR will only generate local electric field enhancement in a small area (sub-wavelength) [35]. When the oscillation frequency of the electron coincides with the frequency of the incident light wave, resonance will occur [36; 37]. In the resonance state, the energy of the electromagnetic field transforms effectively into the collective vibrational energy of free electrons on the metal surface, thereby accelerating the electron diffusion of the contact surface between the CNTs and the metal electrodes [38]. At the same time, the surface of the electrode and the ends of CNT form a stronger local thermal field than other regions under the femtosecond laser irradiation, so that the surface at the edge of the metal electrode is slightly melted to form a molten pool [13].