Estudo da interação do hidrogênio molecular com dispositivo de grafeno e sua aplicação em sensores de gás

Abstract

This work aims to study the interaction of molecular hydrogen with graphene field effect transistors. We show that H2 generates a local doping in graphene in the vicinity of the heterojunction formed by graphene-contact. Moreover, this interaction is strongly dependent on the characteristics of the metal-graphene interface. When investigating different types of metal contacts, being these Au, Au / Cr, Au / TiOx and Au /Cr2O3, it is observed that they can be both strongly and weakly coupled to electrostatically graphene. Thus, for contacts strongly coupled to graphene, the exposure to hydrogen generates an inversion in the asymmetry of the resistance curves as a function of the gate voltage. The asymmetry in the curves in the absence of H2 is observed for all cases studied in which the contacts are projected on graphene in the invasive geometry. Its origin comes from the local doping generated by the difference between the work functions of the graphene and contact, in addition to the electrostatic doping generated by the application of the gate voltage. The hydrogen, in this case, acts modulating the pn junction formed at the interface, causing the inversion of the observed asymmetry. While for contacts weakly coupled to graphene, exposure to hydrogen manifests itself with the formation of a second charge neutrality point. We propose in this work that this phenomenon happens due to the decoupling between the work functions of graphene and metallic contacts, such that the carrier density in both the conduction channel region and the region of the metal contacts can be modulated by applying the gate potential, generating the two charge neutrality points. We studied the relationship of this phenomenon with the geometry of the device, also with the hydrogen concentration and exposure temperature. The results indicate a completely reversible gas induced doping under all interfaces conditions under study. This behavior indicating a controlled way of creating a p-n junction in graphene, generating a significant variation of resistance that will be explored in the development of high-performance hydrogen sensors.