High Sensitivity of Extended-Gate Field-Effect Transistors Based on 1-D ZnO:Ag Nanomaterials through a Cheap Photochemical Synthesis as pH Sensors at Room Temperature

We investigated an extended-gate field-effect transistor (EG-FET) as a pH sensor in this work. It was based on low-temperature hydrothermally grown one-dimensional (1-D) zinc oxide (ZnO) nanorod (NR) arrays. Additionally, silver nanoparticles (Ag NPs) were successfully synthesized on the surfaces of nanostructures through a simple photochemical synthesis process under ultraviolet (UV) light illumination at room temperature. The surface morphology, crystalline nature, elemental content, optical property, and electrical performance of both samples were explored and studied by field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) system, energy-dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectrometer, UV-visible spectroscopy, and a Keithley 2410 semiconductor parameter analyzer with a personal computer. FE-SEM pictures, HR-TEM patterns, and XRD results indicated that the growth of all nanostructures preferentially oriented along the c-axis resulted in hexagonal wurtzite crystals, and the 1-D NRs grew vertically on the ZnO seed layer-coated substrate. The Z@Ag-1 samples were composed of Ag (2.64 atom %), Zn (58.17 atom %), and O (39.19 atom %) in the EDX result. HR-TEM elemental mappings, EDX images, and XPS spectra demonstrated that Ag NPs existed on the surface of the 1-D ZnO NR arrays. The optical characteristics of PL analysis and UV-visible spectroscopy showed two emissions, including UV and the visible region. In the electrical section, all pH sensors showed good pH stability properties and remarkable repeatability. After Ag NP decoration, the 1-D Z@Ag-1 samples exhibited superior pH-sensing response characteristics (59.06 mV/pH, 45.65 mu A/pH) with good linearity (0.996, 0.998). Meanwhile, the hysteresis effect was only 1.49 mV as the pH of the solution changed in the following order: pH 7 -> pH 4 -> pH 7 -> pH 10 -> pH 7. The designed 1-D Z@Ag-1 pH sensors will be remarkably useful in pH-sensing fields and can be combined with Internet-of-Things applications, particularly in industrial, agricultural, medical, and military fields.