Hybrid anion and cation ion sensors with samarium oxide sensing membrane treated by nitrogen plasma immersion ion implantation

For hybrid anion and cation ion sensing, an electrolyte–insulator–semiconductor (EIS) device with a samarium oxide (Sm2O3) sensing membrane treated by nitrogen plasma immersion ion implantation (PIII) was proposed. The N+ and N2+ ions were implanted into the Sm2O3 membranes to form the positive charges of NO and NON bonds, which were investigated by the X-ray photoelectron spectroscopy (XPS). The observed positive charges were then correlated with the resulting anion and cation ion sensing performances. The EIS device with the pure Sm2O3 membrane exhibited the mean potassium and calcium ion sensitivity of 36.71 mV/pK and 21.27 mV/pCa respectively because of the main surface sites of O− groups generated under the pH 8.0 Tris/HCl buffer solution. A high chloride ion sensitivity of 47.92 mV/pCl was obtained from the EIS device with nitrogen PIII treated Sm2O3 membrane. This result is attributed to the reaction of OH2+ group surface sites with chloride ions by the plasma induced positive charges within the membrane. The drift rate of less than 2.22 mV/h for the Sm2O3-EIS device was achieved and suitable for future biosensing use.