# Processing of Single-Walled Carbon Nanotubes with Femtosecond Laser Pulses
## 1 Introduction  
In recent years, the femtosecond laser appeared as a powerful technique to investigate laser matter interactions for micromachining, surface modification, laser surgery, nanostructure generation, structural evolutions, etc. [1, 2]. Particularly, femtosecond laser assisted nano-joining has received great attention due to its critical role in the technological development of microelectronics, MEMS, and nano-devices among various applications [3, 4]. Several studies were performed on the joining of different materials with a laser beam in the form of bulk, as well as powder, at the nano and micron scales [2, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]. For instance, [PERSON] et al. joined Al and Fe nanoparticles by exposing them to multiple femtosecond laser pulses [15]. The authors suggested that bonding is attributed to intermixing within a region of high field intensity among particles [15]. Similarly, [PERSON] and coworkers reported a scalable technique by demonstrating fast and robust joining of clear glass to glass surface, which contained randomly distributed and embedded spherical silver nanoparticles through the irradiationof a nanosecond pulsed laser [16]. They reported a joint strength of 12.5 MPa by applying a laser fluence of only \(\sim\)0.13 J/cm\({}^{2}\) and a scanning speed of 10 mm/s [16]. Among carbon allotropes, single wall carbon nanotubes (SWCNTs) are one of the amazing high aspect ratio nanostructures that possess remarkable electrical, mechanical, thermal, and optical properties with extreme flexibility. Therefore, they have a great potential for nanoscale device applications [17]. An individual nanotube acts as a genuine quantum wire and demonstrates a perfect one-dimensional (1D) nature of conducting modes. Furthermore, the electron motion without backscattering in metallic nanotubes results in perfect conduction, even in the presence of scatters [18]. Therefore, SWCNTs are an excellent candidate for power and signal interconnection due to their ability to conduct large current densities, as the conventional metallic interconnects have severe limitations due to feature size shrinkage [19; 20]. Despite their immense significance, there are substantial challenges in synthesizing techniques for their broad range applications. For instance, it is difficult to fabricate the electrically homogenous SWCNTs by controlling the chirality, diameter, and length in a scalable and high-speed manner [21]. Furthermore, SWCNTs are usually grown in the form of a mixture of semiconducting and metallic nanotubes that hinders the broadened application of nanotubes in electronics [22]. Regardless of these challenges, there is an interest to fully exploit their exceptional properties for real-world applications by joining them in networks or bundles while keeping intact their exceptional properties [23]. Based on their amazing electronic transport properties, the microbundle array of carbon nanotubes are showing a promising application in field emission devices [24]. Consequently, it is highly desirable to establish true joints between SWCNTs, having the same order of magnitude of mechanical/electronic properties that is retained by an individual single wall nanotube [23]. In general, few studies were conducted on the joining of low dimensional carbon allotropes. For example, in a novel experiment, stable crosslinks between neighboring carbon nanotubes within bundles were formed by moderate electron beam irradiation and reported improved intertube bridging [25]. Moreover, multiwall carbon nanotubes joining were reported by continuous fiber laser irradiation on silicon and silica substrate [26]. The nanoscale welding of MWCNTs for three-second irradiation was attributed to the breaking of C-C bonds and the formation of new graphene layers [26]. Recently, [PERSON] and coworkers formed a cross-stacked CNT architecture and reported joining through sp\({}^{3}\) covalent bonding under high pressure and temperature through laser heating [14].