Abstract
Silicon nanoparticles encapsulated in carbon shells (Si@C) were synthesized via polymer-derived carbonization and subsequently fluorinated by gas-phase treatment to tailor their interfacial electronic properties. The resulting Si@C–F core–shell nanostructures were investigated as chemiresistive sensors for ammonia detection at room temperature. The fluorinated hybrids exhibit a 2–2.5-fold enhancement in response toward NH3 in the 1–20 ppm range, while maintaining linear behavior (R2>0.99) at low concentrations. The enhanced performance is attributed to fluorination induced modulation of interfacial electronic states and the barrier height at the Si/SiOx/C:F heterojunction. The introduction of electron-withdrawing C–F groups increases the work function of the carbon shell and strengthens interfacial dipole fields, leading to amplified resistance modulation under NH3 adsorption. Owing to the nanoscale dimensions of the silicon cores (20–40 nm), comparable to the Debye length, surface charge variations significantly influence charge transport. The sensors demonstrate high selectivity toward ammonia over alcohol vapors (ppm-normalized selectivity >104) and stable operation under moderate humidity. These findings establish fluorination as an effective strategy for engineering interfacial charge transfer in Si–C hybrids for room-temperature gas sensing. Keywords: Si@C hybrids; fluorinated carbon; ammonia sensing; coreshell nanostructures; chemiresistive gas sensor.