Capacitive Sensing of Intercalated H2O Molecules Using Graphene.
Understanding the interactions of ambient molecules with graphene and adjacent dielectrics is of fundamental importance for a range of graphene-based devices, particularly sensors, where such interactions could influence the operation of the device. It is well-known that water can be trapped underneath graphene and its host substrate; however, the electrical effect of water beneath graphene and the dynamics of how the interfacial water changes with different ambient conditions has not been quantified. Here, using a metal-oxide-graphene variable-capacitor (varactor) structure, we show that graphene can be used to capacitively sense the intercalation of water between graphene and HfO2 and that this process is reversible on a fast time scale. Atomic force microscopy is used to confirm the intercalation and quantify the displacement of graphene as a function of humidity. Density functional theory simulations are used to quantify the displacement of graphene induced by intercalated water and also explain the observed Dirac point shifts as being due to the combined effect of water and oxygen on the carrier concentration in the graphene. Finally, molecular dynamics simulations indicate that a likely mechanism for the intercalation involves adsorption and lateral diffusion of water molecules beneath the graphene.
Department of Electrical and Computer Engineering, University of Minnesota-Twin Cities , 200 Union Street SE, Minneapolis, Minnesota 55455, United States.
Eric J
EJ
Olson
Department of Electrical and Computer Engineering, University of Minnesota-Twin Cities , 200 Union Street SE, Minneapolis, Minnesota 55455, United States.
Rui
R
Ma
Department of Mechanical Science and Engineering, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61802, United States.
Tao
T
Sun
Department of Electrical and Computer Engineering, University of Minnesota-Twin Cities , 200 Union Street SE, Minneapolis, Minnesota 55455, United States.
Mona A
MA
Ebrish
Department of Electrical and Computer Engineering, University of Minnesota-Twin Cities , 200 Union Street SE, Minneapolis, Minnesota 55455, United States.
Nazila
N
Haratipour
Department of Mechanical Science and Engineering, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61802, United States.
Kyoungmin
K
Min
Department of Mechanical Science and Engineering, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61802, United States.
Narayana R
NR
Aluru
Department of Electrical and Computer Engineering, University of Minnesota-Twin Cities , 200 Union Street SE, Minneapolis, Minnesota 55455, United States.
Steven J
SJ
Koester
capacitance; graphene; sensor; varactor; water