Pd-Functionalized, Suspended Graphene Nanosheet for Fast, Low-Energy Multimolecular Sensors

Abstract

To demonstrate the feasibility of a fast, low-energy breath diagnosis method, hydrogen sensors utilizing Joule self-heating were developed. The sensors consisted of suspended graphene films functionalized with Pd nanoparticles as sensing layers and utilized self-heating to achieve fast responses and humidity robustness with low energy consumption. Thanks to nanoscale point contacts between the graphene and Au electrodes, heat dissipation to the electrodes was greatly suppressed. The application of an appropriate voltage bias increased the graphene temperature to 180 °C with a low power consumption per unit graphene width of 0.93 mW/μm. Because of the temperature increase caused by the Joule self-heating of the graphene, the sensors responded to parts per million level H2, and a response time of 15 s was achieved at a H2 concentration of 100 ppm. At temperatures over 100 °C, the sensor response realized by self-heating was lower than that by heating using an external heater. The response reduction was due to suppressed charged-carrier scatterings with H-induced potentials under high electric fields in the self-heated graphene. Finally, we demonstrated voltage-controlled multimolecular detection by self-heating. At a two-terminal voltage difference of 0.1 V, Pd-functionalized graphene responded not to H2 but to humidity. Meanwhile, at 0.9 V, the sensor responded to 10 ppm of H2 despite great humidity variations in the background. Temperature change by self-heating is much faster and requires less energy than that by heating using an external heater. Fast, low-energy multimolecule detection realized by self-heating paves the way for mobile, low-power, real-time molecular sensors for use in health diagnosis applications.