## 3 Results and Discussion
Aside from CNT open-end functionalization, suitable functional groups at the metal surface are needed in order to chemically link CNTs to metal surfaces. Metal surface functionalization was accomplished using organic radical metal reactions, also known as grafting. To realize bond formation between a carboxylic functionalized CNT tip and a metal, the metal surface was functionalized with the amine groups (Figure 2A,B). Amine functionalization of the Cu surface was achieved using a spontaneous reaction between a \(p\)-aminobenzenediazonium cation and Cu metal, which left the chemically bonded aminophenyl group on the Cu surface in a similar manner to that reported by [PERSON] et al. [60]. In contrast, the Pt surface was electrografted by short ethylamine groups with ethylenediamine as described in the experimental section. Then, to promote bond formation between the CNTs and the organic groups grafted on the metal surfaces, functionalized open-ended CNTs were pressed against the metal surfaces using small magnetic discs during the reaction while the temperature was increased. The electrografted organics on metals acted as linkers to join the open-ended CNTs. This type of metal functionalization using reactive organic molecules is a topic of intense research. Several metals, including stainless steel, Ni, Au, and polycrystalline Cu, have been functionalized using aryl diazonium cations (R-N\({}_{2}\)+). Anthracene, anthraquinone, and hydroquinone have been covalently bonded to metal surfaces, presumably through the formation of carbides and nitrides [73]. As shown by the reaction mechanism in Figure 2A, upon reduction, the diazonium salts generated strong radical species that could bond to metal and carbon surfaces [74]. \(p\)-Phenylenediamine reacted with NaNO\({}_{2}\) and HCl to generate the \(p\)-aminobenzenediazonium cation in situ as described by [PERSON] et al., which was spontaneously grafted onto the Cu surface to generate aminophenyl groups [75]. Spontaneous grafting will occur if the surface of the substrate is sufficiently reduced to convert the diazonium salt to a radical that can react with the same surface. In addition, there is the potential to be applied to promote a reaction between \(p\)-aminobenzenediazonium cations and metals such as Pt and Au [76]. The grafted aminophenyl groups on the Cu surface reacted with the carboxylic groups on the CNT open ends, which were obtained by CNT oxidation. Although the amine-carboxylic coupling reactions employed in this work were aimed at covalent bond formation between functional groups at the metal surface and open-end CNTs, the nature of the resulting bonding was not possible to determine. As a result of those challenges, \"chemical bond\" is used throughout the text instead of covalent bonding. The expected amide formation resulting from amine-carboxylic coupling is localized between macro- and micro-structures, where the access is limited. Covalent bonding of ethylenediamine on the Pt surface was accomplished via electrografting (Figure 2B). The highly reactive ethylenediamine radical is known to attack metal surfaces, leaving an amine functional group available for subsequent reactions. Similar bonding has been reported by [PERSON] et al., and a mechanism of bond formation between metals and organic moieties has been reported [73]. Upon the electrochemical oxidation of primary amines using Pt metal as a working electrode, bond formation and the growth of a continuous film was observed. Unfortunately, due to the polymerization of ethylenediamine on the working electrode surface, more than a monolayer buildup was observed, which resulted in an electrical passivation of the metal surface. Although further investigations to identify the thickness of the interface between Pt and the CNTs are pending, bonding of ethylenediamine has been confirmed by several other researchers. FT-IR spectral analysis on the functionalized Cu supported the organic moiety grafting to the Cu surface.