A 15-nm-thick GdOx membrane in an electrolyte-insulator-semiconductor (EIS) structure shows a higher pH sensitivity of 54.2 mV/pH and enzyme-free hydrogen peroxide (H2O2) detection than those of the bare SiO2 and 3-nm-thick GdOx membranes for the first time. Polycrystalline grain and higher Gd content of the thicker GdOx films are confirmed by transmission electron microscopy (TEM) and X-ray photo-electron spectroscopy (XPS), respectively. In a thicker GdOx membrane, polycrystalline grain has lower energy gap and Gd2+ oxidation states lead to change Gd3+ states in the presence of H2O2, which are confirmed by electron energy loss spectroscopy (EELS). The oxidation/reduction (redox) properties of thicker GdOx membrane with higher Gd content are responsible for detecting H2O2 whereas both bare SiO2 and thinner GdOx membranes do not show sensing. A low detection limit of 1 μM is obtained due to strong catalytic activity of Gd. The reference voltage shift increases with increase of the H2O2 concentration from 1 to 200 μM owing to more generation of Gd3+ ions, and the H2O2 sensing mechanism has been explained as well.
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