Enhancing the response of NH3 graphene-sensors by using devices with different graphene-substrate distances

TL;DR

This study investigates how the substrate material beneath graphene influences its ammonia sensing capabilities, revealing that substrate choice affects charge transfer, response times, and adsorption processes, thus guiding improved sensor design.

Contribution

The paper provides experimental and theoretical evidence that substrate distance and material significantly impact graphene's ammonia sensing performance, highlighting substrate engineering as a key factor.

Findings

Graphene on hBN shows the smallest substrate distance and fastest recovery.

Sensor response depends on both top and bottom adsorption sites.

Substrate choice influences charge transfer and sensor recovery times.

Abstract

Graphene (G) is a two-dimensional material with exceptional sensing properties. In general, graphene gas sensors are produced in field effect transistor configuration on several substrates. The role of the substrates on the sensor characteristics has not yet been entirely established. To provide further insight on the interaction between ammonia molecules (NH3) and graphene devices, we report experimental and theoretical studies of NH3 graphene sensors with graphene supported on three substrates: SiO2, talc and hexagonal boron nitride (hBN). Our results indicate that the charge transfer from NH3 to graphene depends not only on extrinsic parameters like temperature and gas concentration, but also on the average distance between the graphene sheet and the substrate. We find that the average distance between graphene and hBN crystals is the smallest among the three substrates, and that graphene-ammonia gas sensors based on a G/hBN heterostructure exhibit the fastest recovery times for NH3 exposure and are slightly affected by wet or dry air environment. Moreover, the dependence of graphene-ammonia sensors on different substrates indicates that graphene sensors exhibit two different adsorption processes for NH3 molecules: one at the top of the graphene surface and another at its bottom side close to the substrate. Therefore, our findings show that substrate engineering is crucial to the development of graphene-based gas sensors and indicate additional routes for faster sensors.