A Gold Nano-Urchin-Decorated Quasi-Freestanding Graphene-Based Humidity Sensor with Excellent Responsivity and a Wide Relative Humidity Detection Range for Real-Time Applications

Abstract

Excellent humidity response and detection threshold are essential attributes of a humidity sensor. In this study, quasi-freestanding graphene (QFSG) was grown epitaxially on vicinal silicon carbide via thermal annealing, followed by decoration with hydrophilic gold nano-urchins (AuNUs). The resulting humidity sensor consistently achieved highly effective non-contact humidity-sensing performance, which can be used to monitor breathing and skin moisture. The proposed humidity sensor demonstrated a strong linear response of ~119.98% over a wide relative humidity detection range of 5–96% at a frequency of 1 kHz, outperforming a QFSG-only humidity-sensing device (~11.92% and 22–84% relative humidity, respectively). This 10-fold increase in humidity response and wider detection range is attributed to the hydrophilicity and plasmonic behavior of the AuNUs. It also demonstrated transient impedance response/recovery time of 4.5 and 3.0 s, respectively; low hysteresis of 3.6%; and stability over 25 days, which are key factors for effective humidity sensing. The fast response and sensitivity of the AuNUs/QFSG humidity sensor indicate its suitability for various real-time monitoring applications such as human breathing and non-contact proximity testing.

Keywords: Gold Nano-urchin, QFSG, Vicinal SiC, Responsivity, Wide-range, Humidity sensor