Quantum Transport Signatures of Gas Sensing in Ultra-Narrow Graphene Nanoribbons: A Platform for Future Gated Devices

Compact, selective gas sensors are crucial for environmental and healthcare monitoring. Using density functional theory + NEGF transport simulations, we investigate the influence of the graphene nanoribbon (GNR) width on the detection of gas molecules such as CO, CO₂, and NH₃. We show that ultra-narrow GNRs produce molecule-specific transmission fingerprints: CO, CO₂, and NH₃ adsorption induce distinct shifts and broadenings of resonant channels. When the ribbon width approaches molecular scales, quantum confinement and interference effects strongly enhance the conductance modulation under finite bias. Among the three molecules, NH₃ produces the highest sensitivity in the ultra-narrow device (Device 3), particularly at bias voltages above ∼2 V, due to its stronger adsorption energy and pronounced charge redistribution, leading to the largest current suppression relative to the pristine ribbon. These geometry-dependent signatures suggest a practical route to gate-tunable selectivity in GNR-based chemical sensors.