The Role of External Defects in Chemical Sensing of Graphene Field-Effect Transistors

Abstract

A fundamental understanding of chemical sensing mechanisms in graphene-based chemical field-effect transistors (chemFETs) is essential for the development of next generation chemical sensors. Here we explore the hidden sensing modalities responsible for tailoring the gas detection ability of pristine graphene sensors by exposing graphene chemFETs to electron donor and acceptor trace gas vapors. We uncover that the sensitivity (in terms of modulation in electrical conductivity) of pristine graphene chemFETs is not necessarily intrinsic to graphene, but rather it is facilitated by external defects in the insulating substrate, which can modulate the electronic properties of graphene. We disclose a mixing effect caused by partial overlap of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of adsorbed gas molecules to explain graphene's ability to detect adsorbed molecules. Our results open a new design space, suggesting that control of external defects in supporting substrates can lead to tunable graphene chemical sensors, which could be developed without compromising the intrinsic electrical and structural properties of graphene.

Chemical sensing with switchable transport channels in graphene grain boundaries

“…In the presence of DMMP, GB is additionally n-doped, as shown by a shifted transmission spectrum down (by B0.05 eV) with respect to E f , assuming that E f stays fixed with respect to the rest of the system (grains transmission spectra shown by green dashed lines). The 0.05 eV shift corresponds to an electron density concentration of B2.5 Â 10 11 cm À 2 , which is compatible with DMMP/graphene experimental values 23 .…”

“…It was shown that the sensitivity of an isolated GB is B300 times higher than that of a single graphene grain and much larger than that of polycrystalline graphene sensors. We have verified that the presence of local transport gaps in GBs together with the local accumulation of gas molecules plays a crucial role in the observed large chemical sensitivity of GBs, so the mechanism differs from the previously reported carrier density modulation in carbon-based sensors 6,7,[23][24][25][26][27][28] . The sensing mechanism is based on a marked closing or opening of local conduction channels through the GB by the adsorbed …”

Graphene nanoelectronic heterodyne sensor for rapid and sensitive vapour detection

“…4, although all devices processed (including thermal oxide growth) in one batch show consistent behaviour. We attribute this to a substrate effect 32 where end terminations may preferentially orient the molecules through hydrogen bonding, but further detailed investigation is needed.…”

A graphene field-effect transistor as a molecule-specific probe of DNA nucleobases

“…Although defects may play a dominant role in the observed shifts, we can exclude that a unique defect or a contamination in our samples is responsible for the sensing mechanism by observing the same results on two different graphene samples from different sources. The SiO 2 substrate can also play an important role in the sensing mechanism of GFETs on SiO 2 as has been proposed recently 50 . Using DFT modelling it has been suggested that the sensitivity of graphene to gas adsorbates can be attributed to external defects in the insulating substrate 50 .…”