Silane coupling agents can act as bonding intermediates at the interface of two dissimilar materials by altering surface properties. In this study, (3-aminopropyl) trimethoxysilane (APTMS) was used as a silane precursor for vapor-phase deposition on organosilane-grafted moisture-crosslinked polyethylene (Si-XLPE) substrate. Chemical vapor deposition (CVD) and plasma-facilitated in situ grafting methods (grafting-from and grafting-onto) were employed to graft APTMS, and the consequent effects on surface of Si-XLPE were evaluated. In-depth analysis was done to determine the assembly behavior of the fabricated APTMS layers and their influences on the surface properties. Characterizations were based on the assessment of surface chemistry (by XPS, EDX, and ATR-FTIR), morphology (by AFM and FESEM), and wettability (by contact angle measurement). The results showed that APTMS molecules inclined to form multilayer structures instead of monolayers. Height of the formed layers ranged approximately 5-30 nm. Also, it was deduced that crosslinking of deposited layers happened through different siloxane configurations in siloxane polyhedral networks on the surface. The arrangement of APTMS molecules led to the creation of hydrophobic surfaces (water contact angle >= 100 degrees) implying prevailing attachment of APTMS molecules from amino groups to the substrates. Findings confirmed that the plasma grafting-from approach possessed the highest APTMS attachment efficiency.