## 2 Experimental Framework  
In this study, CNPs are obtained by the pulsed arc discharge method which is done by employing a pulsed high voltage inverter, as shown in Figure 1. To raise the HDPE temperature to the melting point, it is placed inside a quartz tube on top of a heater and the next step is to measure the I-V characteristic with a signal generator together with an oscilloscope. Finally, the presence of DC voltage-transmitted heat by a non-contact thermometer, which is focused on the CNPs, is investigated. In this method, two pointed rods (either steel rods (for results and comparison, see Appendix A) with 0.5 mm diameters or graphite rods with 2 mm diameters are used as electrodes and are placed face to face inside a carbonic source (HDPE), as shown in Figure 2. The HDPE polymer is heated up to its melting point which provides the spark path inside the carbonic polymer that is being used as a carbon source. Figure 1: The schematic presentation of the experimental setup. The potential of a few kV between two electrodes is generated by the high-voltage system when the polymer is melted, which leads to the creation of plasma in the quartz chamber and the ionization of the HDPE carbon source. Therefore, by breaking the molecular bonds of the polymer and separating the carbon atoms, the carbon ions are accumulated on the tips of both electrodes and grow until they are joined to each other, and this process leads to CNP production. Consequently, a complete circuit is created and therefore electric charges can flow. It is notable that all measurements are done in ambient conditions (temperature = 300 K, pressure = 1 atm). Additionally, the produced nanoparticles are surrounded by an HDPE-polymer composite, which makes the fabricated device more stable and increases the strength of the structure [23; 24]. This type of arrangement is known as a metal-semiconductor-metal (MSM) structure, with two back-to-back Schottky diodes. Our sample mainly consists of multiwall CNTs (MWCNTs) that have been previously reported in several analyses by our team to have a size on the nanometer scale [25; 26; 27; 28; 29]. In addition, as shown in Figure 3a, a finger-shaped qualitative surface morphology is identified by scanning electron microscopy (SEM) and in the focused part, the presence of cylindrical nanoparticles a few hundred nanometers in size is revealed (Figure 3b). Figure 3: SEM images of (**a**) a bulk nanoparticle strand and (**b**) a zoomed in image of the marked area in (**a**), which displays the presence of cylindrical nanoparticles in the core of the synthesized strand. Figure 2: The real device (**top**), and its schematic representation (**bottom**). According to the SEM images, the excess MWCNTs that are overlaid by HDPE chains similar to the composites reported by [PERSON] et al. (2018) are realized. Additionally, the nano-focus image of the fabricated CNPs is carried out, as shown in Figure 4, which leads to the estimated size of the particles. As shown in Figure 4 (for high resolution, see Appendix B), on the surface of the carbon strand, the minimum and maximum points are about 240 micrometers away from each other which, based on the SEM image, can be used as a CNP length indicator as well. The surface analysis indicates numerous micro-cracks in the strand which form a mechanically delicate structure in the fabricated strand since the strand structure is covered by a polymer network and the strand is stable for typical electro-thermal element applications. To investigate the performance of the CNP-polymer composite as an electrical heating building block, continuous DC power is applied to the fabricated MSM structure with graphite electrodes. Furthermore, the temperature variation is analyzed by a non-contact infrared thermometer with a 0.1 K accuracy.