Abstract
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•Presents capacitive sensor on micro-fabricated Si substrate to sense soil moisture.•Sensing demonstrated in three different soil groups with four different materials.•In-situ FTIR and KPFM are performed to understand the sensing mechanism.•These capacitive soil moisture sensors are durable, re-generable, and selective.•MoS2 based sensor exhibits an excellent sensitivity than the other three materials.
The development of in-situ soil moisture sensors (SMS) with advanced materials is the requirement of the future autonomous agriculture industry. However, an open challenge for these sensors is to control changes in the capacitance rather than resistance while attaining reliability, high performance, scalability and stability. In this work, a series of materials such as Graphite oxide (GO), Molybdenum disulfide (MoS2), Vanadium oxide (V2O5), and Molybdenum oxide (MoO3) are tested in realizing a receptor layer that can efficiently sense soil moisture. Here, we found that MoS2 offers the sensitivity, which is nearly three times higher (1200 pF) than in the case of V2O5 for any given range of soil-moisture content outperforming both GO and MoO3 materials. The corresponding increase in the sensitivities for MoO3, GO, MoS2, and V2O5 are ∼13 %, ∼11 %, ∼30 %, and ∼9 % respectively, for a variety of temperature up to 45 °C. A temperature variation of 25 °C to 50 °C showed a minimal increase in the sensitivity response for all the devices. We further demonstrated a record sensitivity of 540 % with MoS2 in black soil and the corresponding response time was 65 s. Finally, the recovery time for the MoS2 sensor is 27 s, which is quite fast.