## 3 Results
### Effect of BSA Step on Interfacial Adhesion Between the ENM and Cu Layer  
The interfacial adhesion between the ENM and the Cu layer was evaluated using a 90\({}^{\circ}\) peel test (Figure 3a). In the peel strength-displacement curves, the ENMH exhibited a sharp increase in peel strength after approximately 10 mm, maintaining a steady peel strength in the range of 0.073-0.096 N/mm up to around 30 mm (Figure 3b). In contrast, the ENMH(-BSA step) displayed a lower maximum peel strength of 0.053-0.076 N/mm over the same displacement range, with a relatively stable curve. Although the ENMH maintained a higher peel strength overall, the curve showed more frequent minor fluctuations across the displacement range. In addition, the larger area under the curve for the ENMH indicates that greater peel strength was sustained during the peeling process, reflecting stronger interfacial adhesion. Transmission electron microscopy (TEM) analysis provided insight into the morphology of Pd nanoparticles. Low-magnification images revealed small, irregularly shaped spherical Pd nanoparticles, several tens of nanometers in diameter, appearing as high-contrast dark spots embedded within a relatively large, low-contrast BSA matrix (Figure 3c). The Pd nanoparticles were uniformly dispersed throughout the BSA layer. High-resolution TEM images showed clear lattice fringes with an interplanar spacing of approximately 2.25 A, corresponding to the (111) planes of Pd [37] (Figure 3d). Selected area electron diffraction (SAED) patterns exhibited ring-shaped diffraction features, indicative of a polycrystalline structure [38]. Elemental mapping by energy-dispersive X-ray spectroscopy (EDS) confirmed the presence of C, N, O, S, and Pd elements (Figure 3e). The Pd signal was uniformly distributed, while the C, N, O, and S signals were consistent with the elemental composition of BSA [39]. Scanning electron microscopy (SEM) images of the peeled tape surfaces further supported the adhesion results. The ENMH showed minimal residual Cu particles on the tape, with Cu signals confined to a few localized regions in the corresponding elemental map (Figure 3f). In contrast, the ENMH(-BSA step) displayed a broader distribution of residual Cu particles across the tape surface, with widespread Cu signal coverage. Photographic images of the peeled tape surfaces (Figure S3) provided visual confirmation of this disparity. To assess interfacial durability, up to five peel cycles were performed, and the Cu coverage on the tape surface was quantitatively analyzed after each cycle using a fresh piece of tape (Figure 3g). As the number of cycles increased, both ENMH and ENMH(-BSA step) showed gradual increases in Cu residue. This trend is attributed to the progressive degradation of interfacial bonding caused by the accumulation of micro-damage and stress during repeated peeling. In particular, the ENMH(-BSA step), which lacks the interfacial reinforcement provided by the BSA layer, exhibited a more rapid deterioration, resulting in a Cu coverage of 64.6% after the fifth cycle--more than 2.5 times higher than that of the ENMH (25.9%). Throughout all cycles, the ENMH consistently maintained a lower level of Cu transfer, indicating superior interfacial stability. In addition to differences in average values, the ENMH(-BSA step) group exhibited large standard deviations even at the first cycle, indicating non-uniform delamination behavior. In contrast, the ENMH group showed a sharp increase in both residue fraction and variability from the third cycle onward, suggesting stress-induced interfacial degradation. Figure 3: Adhesion analysis between the ENM and the deposited Cu layer. (**a**) Schematic illustration of the 90\({}^{\circ}\)peel test. (**b**) Peel strength comparison for ENMH and ENMH(\(-\)BSA step). TEM characterizations of Pd nanoparticles crosslinked by BSA on ENMH: (**c**) TEM image illustrating the overall morphology and particle dispersion. (**d**) High-resolution TEM image and corresponding SAED pattern of a representative particle.