Annealing-induced morphological evolution and underlying atomic-scale mechanism of magnetron-sputtered carbon films on Ti substrates

Titanium (Ti) substrates are commonly used as current collectors or functional supports in all-solid-state batteries and related thin-film devices, but their surface and interfacial state can affect subsequent functional-layer construction and device stability. Carbon films, as carbon-based functional layers, can regulate the interfacial properties of Ti surfaces and provide potential conductive pathways. However, the morphological evolution of magnetron-sputtered carbon films on Ti substrates and its formation mechanism remain unclear. This work combines experimental characterization with molecular dynamics (MD) simulations to investigate the deposition and annealing behavior of carbon films on Ti substrates. Experimental results showed that annealing transformed the carbon film from relatively uniform coverage into a distinct island-like distribution. MD simulations revealed that metastable regions within the carbon film evolved toward more stable configurations through bond breaking, bond formation, and local rearrangement, accompanied by local contraction and densification. Under the combined effects of substrate constraint and interfacial interactions, these structural changes further induced hole expansion and nonuniform coverage, ultimately leading to island-like morphology formation. These results indicate that annealing-induced island formation is not merely surface roughening, but a consequence of thermally driven local contraction, structural densification, and stress relaxation, showing features of early-stage solid-state dewetting. This study clarifies the atomic-scale mechanism of island formation in Ti/C systems and provides guidance for thermal-treatment design of carbon layers on Ti substrates and functional-interface design in high-performance all-solid-state batteries.