Towards optimisation of epitaxially grown graphene based sensors for highly sensitive gas detection

Epitaxially grown single-layer and many-layer (10 atomic layers thick) resistive graphene devices were fabricated and compared for response towards NO₂. Single-layer devices showed far greater sensitivity. The many-layer devices reduced in resistance on exposure to electron withdrawing NO₂ demonstrating a majority hole carriers (p-type), whereas the single-layer device demonstrated an increase in resistance upon NO₂ exposure demonstrating a majority of electron carriers (n type). An n-p shift is observed for the single-layer device upon exposure to increasing concentrations of NO₂. This shift is thought to be due to the reduction of electrons in the conduction band upon adsorption of electron-withdrawing NO₂ making holes the majority carriers.