Ultrasensitive chemiresistive humidity sensor based on gold functionalized WS2 nanosheets

An ultrasensitive, low power humidity sensor based on Au nanoparticle-functionalized WS₂ nano-sheets (NS) has been demonstrated in this work. Liquid phase exfoliation of bulk WS₂ was incorporated to prepare this material, followed by its decoration with Au nanoparticles (NPs) using a wet chemical approach. The compositional and nano-structuralproperties of the as-prepared Au-functionalized WS₂ NS have been characterized using microscopic (Transmission Electron Microscopy (TEM)), and spectroscopic (Raman spectroscopy and X-Ray Photoelectron Spectroscopy (XPS)) techniques. The humidity sensing characteristics of Au-functionalized WS₂ NS based sensors and pristine WS₂ NS based sensors have been studied over an extensive relative humidity range, RH(25 %–75 %) at room temperature. The sensing results of Au-functionalized WS₂ NS showed an ultrasensitive response, rapid response/recovery behaviour and excellent repeatability. A giant two orders of magnitude enhancement in humidity sensing response was observed in functionalized nanosheets as compared to the pristine ones (70,000 versus 1000). The sensitivity derived from linear regime of operation in the higher RH% range (55 %–75 %) further suggests two orders of dramatic increase, the values being 3007.9 per RH% for the Au-functionalized device and 44.3 per RH% for pristine WS₂ NS based device. An appreciable improvement in the response/recovery time has been observed; 107s and 13s (at 65 % RH) being the response and recovery time respectively for Au-functionalized WS₂, whereas the corresponding values for pristine WS₂ were found to be 228s and 29s respectively. A probable mechanism for the humidity sensing of Au-functionalized WS₂ NS has also been suggested in this work.