Effects of ultrathin ZnO and ZnS interlayers on Ag wetting and adhesion behaviors

초록

Ultrathin, continuous Ag layers are promising alternatives to oxide-based transparent electrodes for flexible optoelectronic devices. However, their practical use is limited by their poor wetting and weak adhesion to nonmetallic substrates. Here, we report the first systematic comparison of the effect of ultrathin ZnO and ZnS interlayers on Ag wetting and adhesion, revealing that wetting and adhesion, which have been long assumed to be intrinsically coupled, can be independently tuned. We find that both 1.5-nm-thick interlayers suppress the intrinsic three-dimensional granular growth of Ag, improving wetting and morphological continuity. However, abrasion tests establish a clear adhesion hierarchy of ZnS > ZnO > Ti, showing that the stronger adhesion does not necessarily yield superior wetting. Notably, Ag layers exhibit strong, thickness-independent adhesion on ZnS with failure at 30 N, whereas Ag layers show thickness-dependent improvement on ZnO. The Ag layer withstands >20 N with a 3-nm-thick ZnO, approaching the strength of ZnS. This difference stems from distinct interfacial chemistries as graded S diffusion across the Ag-ZnS interface reduces chemical discontinuity and strengthens adhesion. By contrast, limited O availability and weaker O diffusion at the Ag-ZnO interface result in its lower adhesion. Device-level Joule-heating tests confirm the practical durability of this system, as 9-nm-thick Ag layers on either interlayer tolerate >600 K thermal loads and >10,000 bending cycles without dewetting or delamination. These results outline a simple, metallic-interlayer-free route to fabricate thermally and mechanically robust Ag-based electrodes by independently tuning wetting and adhesion using interlayers.

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