A dual surface roughening scheme to improve the sensitivity of pH sensors based on hydrothermally grown nickel oxide nanosheets on KOH-etched Si substrates

A dual surface roughening scheme using a KOH-etched Si (100) substrate for the hydrothermal growth (HTG) of NiO nanosheets (NSs) to improve pH sensing performance is demonstrated. The effects of the KOH etching conditions and the HTG time for the synthesis of NSs on the pH sensing response are discussed. The NiO NS sensing electrode (SE) based on a KOH-etched Si substrate showed a near-perfect linearity of 0.999 and a near-Nernstian response of 56.5 mV pH^-1. As compared with an NS-type SE based on planar Si (53.64 mV pH^-1) and an SE based on sputtering NiO on a KOH-etched Si substrate (52.87 mV pH^-1), an enhancement in pH sensitivity of 5.33% and 6.87% was achieved, respectively. It is attributed to the fact that the dual surface roughening scheme greatly increased the sensing area and the number of surface sites for ion adsorption.