Gas Adsorption Thermodynamics
Deduced from the Electrical
Responses in Gas-Gated Field-Effect Nanosensors
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Abstract
Understanding
the underlying physical chemistry governing the nanomaterial-based
electrical gas sensing process is pivotal for the rational design
of high-performance gas sensors. Herein, using a remarkable ppb-level
NO<sub>2</sub>-gated field-effect nanosensor that is based on a reduced
graphene oxide rGO/TiO<sub>2</sub> nanoparticle heterojunction, as
an exploratory platform, we have established a generic physical chemistry
model to quantitatively gain insight into the correlation between
the measured source-drain (S-D) current and the gas sorption thermodynamics
in this NO<sub>2</sub> nanosensor. Based on thin-film field-effect
transistor theory, the measured S-D current leads to the solution
to the gas-induced gate voltage, which further solves the surface
charge density using the Graham surface potential vs surface charge
density function. Consequently, based on the Van’t Hoff equation,
key thermodynamic information can be obtained from this model including
adsorption equilibrium constants and adsorption enthalpy of NO<sub>2</sub> on TiO<sub>2</sub> nanoparticles. The acquisition of gas
adsorption enthalpy provides a generic and nonspecific method to identify
the nature of the adsorbed molecules