Graphene-TiS$_3$ heterojunction for selective polar vapor sensing at room temperature

In this work, the room temperature polar vapor sensing behavior of two dimentional (2D) heterojunction Graphene-TiS3 materials and TiS3 nanoribbons is investigated. TiS3 nanoribbons were synthesized via chemical vapor transport (CVT) and their structure was investigated by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X- ray spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy and Fourier transform infrared spectroscopy (FT-IR) analysis. The gas sensing performance of the TiS3 nanoribbons was assessed through the observed changes in their electronic behavior. Sensing devices were fabricated with gold contacts and with lithographically patterned graphene (Gr) electrodes in a 2D heterojunction Gr-TiS3-Gr architecture.. It is observed that the gold contacted TiS3 device has a rather linear I-V behavior while the Gr-TiS3-Gr heterojunction forms a contact with a higher Schottky barrier (250 meV). I-V responses of the sensors were recorded at room temperature with a relative humidity of 55% and for different ethanol vapor concentrations (varying from 2 to 20 ppm). I-V plots indicated an increase in the resistance of Gr-TiS3-Gr by the adsorption of water and ethanol molecules with relatively high sensing response (~3353% at 2 ppm). Our results reveal that selective and stable responses to a low concentration of ethanol vapor (2 ppm) can be achieved at room temperature with transient response and recovery times of around 6 s and 40 s, respectively. Our proposed design demonstrate a new approach for selective molecular recognition using polar interactions between analyte vapors and heterojunctions of 2D-materials.