## 3 Results and Discussion
Figure 4B also displays the surface of the Cu, where a rough coating-like surface is visible, suggesting that more than a monolayer of aminophenyl was present after grafting, also supporting the FT-IR spectrum in Figure 3. Ethylenediamine and _p_-phenylenediamine were both employed to functionalize the metal surface, but due to its electron-rich and electrically conductive nature, _p_-phenylenediamine is preferred. Similarly, a cylindrical structure of vertically oriented CNTs remained attached to the flat Pt surface after removing the encapsulating polymer (Figure 4C), which suggests that the interaction between the CNTs and Pt was also strong. The junction between the Pt  
Figure 4: SEM images of HD-CNTs bonded to a solid Cu and Pt surfaces after removing the encapsulating polymer. (**A**) Low-magnification and (**B**) high-magnification images showing the three-dimensional nature of the CNTs assembled on the Cu surface. (**C**) Low magnification and (**D**) high magnification of CNTs connected to the metal Pt surface. surface and the CNTs is displayed in Figure 4D. Despite the roughness of the Pt metal surface, the pressure applied to the HD-CNTs during the reaction between the amine and carboxylic groups was sufficient to connect the CNTs to the Pt substrate via linker molecules. Additionally, after sonication of the Cu metal substrate with bonded HD-CNTs, some CNT fragments remained on the metal substrate, as observed by SEM (Figure S5). These CNT fragments were located in the area where the HD-CNTs were originally bonded to the Cu substrate, suggesting that the degree of bonding between CNTs was extremely strong, but not all CNTs were chemically bonded to the Cu. The presence of CNTs on the metal surface after sonication was also confirmed by Raman spectroscopy, as the G and D bands typical of CNTs were observed. However, the fact that only small bundles of CNTs remained after sonication suggests non-uniformity among the CNTs bonding to the Cu surface. This was possible due to the roughness of the Cu substrate and lack of atomically flat HD-CNT cross-sections. In a similar experiment with a Pt substrate, it was difficult to locate clean CNTs due to some coating that occurred after sonication. Successful metal-CNT bonding was also confirmed using electrochemical methods. CNT-Cu bonded electrodes were prepared in which only the HD-CNT cross-section was exposed to the electrolyte. Typically, Ru(NH\({}_{3}\))6\({}^{2+/3+}\) is a good indicator for carbon electrode surfaces and electrolyte interactions. The absence of sharp oxidation or reduction peaks in the background cyclic voltammogram (CV) confirmed the inert nature of the tailored electrode surface for oxidation or reduction in the presence of a supporting electrolyte (Figure 5), which is characteristic of CNT cross-sectional electrodes. This observation suggests that electron transfer at the working electrode can only occur through the CNT cross-sections available to the solution. In addition, the interface between the Cu metal and HD-CNTs must be electrically conductive to allow electron transfer between them. Furthermore, the observation of characteristic oxidation and reduction peaks in the cyclic voltammogram of the ruthenium redox couple confirmed the electrically conductive nature of the CNT-Cu bonded electrode, attributable to a stable electrically conductive joint between the CNT cross-section and the metal substrate (Figure 5). As a benchmark, the electrochemical performance of freshly microtomed HD-CNTs connected to a metal surface using colloidal Ag paste was compared with that of CNTs co  
Figure 5: Electrochemical characterization of CNTs bonded to metal surfaces. Cyclic voltammograms of CNTs bonded to Cu as the working electrode: red and black lines = background response in 0.5 M KCl aqueous solution; pink and blue lines (pink barely visible under the blue) = response for 2 mM Ru(NH\({}_{3}\))6\({}^{2+/3+}\) in 0.5 M aqueous KCl solution.