Molecular Edge-Layer Engineering Suppresses Nanoscale Dissipation at Graphitic Step Interfaces

Abstract

Atomic step edges are dominant sources of nanoscale energy dissipation on graphitic surfaces, including well-defined model interfaces and graphitic defect regions in carbon-based sliding contacts. Here, we show that treatment with linear n-alcohols provides a chain-length-dependent route to suppress step-associated lateral response at graphitic interfaces. Atomic force microscopy measurements on alcohol-treated highly oriented pyrolytic graphite reveal that lateral responses remain localized near step edges, whereas the apparent step height remains nearly unchanged after treatment. In contrast, the integrated step-associated lateral-response index decreases systematically with increasing alkyl-chain length, demonstrating that the local molecular environment at the step can regulate dissipative coupling without measurably altering the underlying carbon morphology. Reactive molecular dynamics simulations using controlled edge-associated alcohol-layer models reproduce the decreasing trend and identify how molecular-layer compliance and orientation can attenuate step-localized resistance. Longer chains suppress both step-up and step-down resistive responses by increasing interfacial compliance, aligning more readily with the scan direction, and reducing scan-direction strain accumulation in the silica tip. Short-lived tip–molecule/step interactions occur during step traversal and contribute a secondary, phase-dependent force component, but the dominant chain-length effect arises from molecular-layer mechanics and geometric buffering of the tip–step contact. These results establish molecular edge-layer compliance and orientation as descriptors for reducing nanoscale dissipation at graphitic step interfaces, while the applicability to real carbon-based coatings depends on defect structure, molecular retention, wear, and tribochemical regime.