Near-Nernstian pH Sensors Based on Hydrothermally Grown NiO Nanosheets on Hierarchically Roughened Si Substrates

Abstract

Introduction: Recently, the use of high surface-to-volume ratio sensing materials, such as TiO 2 , ZnO, and NiO nanostructures, used for pH sensing were demonstrated [ 1 – 4 ]. High response over 44.5 mV/pH was obtained, which was explained as being attributed to increase ion adsorption sites of sensing electrodes (SEs). In this work, pH SEs with improved sensing performance based on hydrothermal growth (HTG) of NiO NSs on Hierarchically roughened Si substrates, which could significantly increase the ion adsorption sites, are proposed and demonstrated. A dual roughening scheme to form pyramidal cones and Si nanowires (Si NWs) consecutively is employed. For comparison, pH sensing performance of SEs with a different combination of the Si NWs, KOH-etched Si substrates, and HTG NiO NSs are also investigated and the benefit of the nanostructures is analyzed. Possible mechanism governing the enhancement in pH sensing response is also proposed and discussed.