Fabrication and Characterization of Iridium Oxide pH Microelectrodes Based on Sputter Deposition Method

Abstract

pH value plays an important role in many fields such as chemistry and biology; therefore, rapid and accurate pH measurement is very important. Because of its advantages in preparation, wide test range, rapid response, and good biocompatibility, iridium oxide material has received more and more attention. In this paper, we present a method for preparing iridium oxide pH microelectrodes based on the sputter deposition method. The sputtering parameters of iridium oxide are also studied and optimized. Open-circuit potential tests show that microelectrodes exhibit near-Nernstian pH response with good linearity (about 60 mV/pH), fast response, high stability (a slight periodic fluctuation of potential change <2.5 mV in 24 h), and good reversibility in the pH range of 1.00-13.00.

Keywords: iridium oxide; long-term stability; near-Nernstian response; pH electrode.

Figure 1

Process diagram showing the preparation of iridium oxide pH microelectrode based on sputter deposition method.

Figure 2

Schematic diagram of electrochemical test.

Figure 3

The surface morphology and EDS of iridium oxide film; insets are the atomic percentage of different elements.

Figure 4

The surface morphology of iridium oxide films prepared at oxygen flow rates of (a) 10 sccm, (b) 20 sccm, (c) 30 sccm, and (d) 40 sccm; the Ar flow rate was maintained at 10 sccm during preparation, and the sputtering time was 15 min.

Figure 5

The sensitivity and response time of iridium oxide films prepared at oxygen flow rates of (a) S1 10 sccm, (b) S2 20 sccm, (c) S3 30 sccm, and (d) S4 40 sccm; the Ar flow rate was maintained at 10 sccm during the sputtering process.

Figure 6

The surface morphology of iridium oxide films prepared with a sputtering time of (a) 1 min, (b) 3 min, (c) 5 min and (d) 15 min; the oxygen and argon flow rates were all maintained at 10 sccm during the sputtering process.

Figure 7

The morphology of an iridium oxide microelectrode under the following parameters: 10 sccm O₂, 10 sccm Ar, and 15 min of sputtering time.

Figure 8

The measurement of pH sensing of iridium oxide pH microelectrodes: (a) response time, (b) potential stability test, (c) potential response to pH changes for acid-to-base and base-to-acid, (d) potential-pH dependence for acid-to-base and base-to-acid.