Hydrothermal and solvothermal synthesis of nanorods and 3D (micro/nano) V2O5 on macro PSi substrate for pH-EGFET sensors

Abstract

Macro porous silicon (PSi) with porosity of 36.3%, depth of 12 μm, and average pore diameter of 1.38 μm was fabricated by electrochemically etching a p-type single crystal silicon wafer. Two different morphologies of vanadium pentoxide (V2O5), V2O5 nanorods and 3D (micro/nano) V2O5 spheres, were grown on the surface and wall of the prepared macro PSi by hydrothermal and solvothermal methods using deionized water and ethanol as solvents, respectively. The morphology and crystallinity of the as-prepared and annealed V2O5/macro PSi were characterized using different analytical techniques that include field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray (EDX), and ultraviolet–visible-near infrared spectroscopy (UV–VIS-NIR) for optical properties. After annealing and improving their crystal structure, EGFETs based on the V2O5 nanorods/macro PSi and 3D (micro/nano) V2O5/macro PSi were fabricated and examined for pH sensor applications. The sensitivity of the sensor was significantly improved when ethanol was preferably used as a solvent in place of water. The {3D (micro/nano) V2O5/macro PSi} based EGFET sensor exhibited perfect sensitivity and linearity of 91.1 mV/pH and 99.67%, respectively, in the range of pH 2–12. The work reports the conditions under which the pH sensitivity of pH-EGFET sensor can be significantly enhanced. The results show that by using (micro/nano) structures of V2O5 as a pH-EGFET sensor, the sensor displays considerably higher sensitivity that surpass the Nernst limit, which is regarded as an important performance of the prepared pH sensor. Considering the benefits of the fabrication method and distinct characteristics of micro/nano V2O5 spheres and PSi, 3D (micro/nano) V2O5 spheres grown on PSi can be considered as a potential candidate for pH sensor applications.