A graphene/TiS heterojunction for resistive sensing of polar vapors at room temperature.

The room temperature polar vapor sensing behavior of a graphene-TiS heterojunction material and TiS nanoribbons is described. The nanoribbons were synthesized via chemical vapor transport (CVT) and their structure was investigated by scanning electron microscopy, high resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Raman and Fourier transform infrared spectroscopies. The gas sensing performance was assessed by following the changes in their resistivities. Sensing devices were fabricated with gold contacts and with lithographically patterned graphene (Gr) electrodes in a heterojunction Gr-TiS-Gr. The gold contacted TiS device has a rather linear I-V behavior while the Gr-TiS-Gr heterojunction forms a contact with a higher Schottky barrier (250 meV). The I-V responses of the sensors were recorded at room temperature at a relative humidity of 55% and for different ethanol vapor concentrations (varying from 2 to 20 ppm). The plots indicate an increase in the resistance of Gr-TiS-Gr due to adsorption of water and ethanol with a relatively high sensing response (~495% at 2 ppm). The results reveal that stable responses to 2 ppm concentrations of ethanol are achieved at room temperature. The response and recovery times are around 8 s and 72 s, respectively. Weaker responses are obtained for methanol and acetone. Graphical abstract Schematic representation of resistance sensor for detection of low concentration of ethanol vapor. The graphene and TiS nanoribbons were synthesized using chemical vapor deposition and chemical vapor transport technique respectively. The 2D graphene/TiS heterojunction device was fabricated to make a high response sensor due to their synergy effect.