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Application of Kelvin Probe Force Microscopy on Two-Dimensional Structures
Švarc, Vojtěch ; Kunc,, Jan (referee) ; Kolařík, Vladimír (referee) ; Bartošík, Miroslav (advisor)
The presence of water molecules strongly influences the function of solution-based biosensors and ambient operating gas sensors. Water molecules accelerate the charge diffusion on the surface of insulating parts, induce sensor hysteresis, and affect sensors' stability, resistance response, and sensitivity. Therefore, it is essential to understand the behaviour of charge motion influenced by water on the sensor surface. To better understand sensor behaviour and its immediate surroundings under controlled humidity, this study utilizes measurements of transport properties and simultaneous measurement of macroscopic resistance response with mapping of the local surface potential using Kelvin probe force microscopy (KPFM). As a chosen model, the 2D graphene Hall bar structure in the field-effect transistor (FET) architecture was fabricated and optimized. The results indicate that the charge dissipation from the main graphene channel to its insulating surroundings exponentially increases with relative humidity. The amount of this leakage charge can be further tuned by the gate voltage of the FET sensor. Further findings show that the charge diffusing into adjacent SiO2 parts minimally influences the conductivity of the graphene main channel. Simultaneous measurements of resistivity and KPFM on graphene-based sensors deepen the understanding of water's impact on the sensor's active parts and the diffusion of charge on passive insulating parts. These findings could benefit future designs of active graphene parts of the sensor and surface modifications of its insulating parts.
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