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Tantalum Thin Film Electrochemical pH Sensor

"Tantalum Thin Film Electrochemical pH Sensor"


Table 1 Comparison of work performed on Ta thin films for pH sensing using several techniques

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Table 2 Process parameters of Ta coating thin film

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Due to the good adhesion and chemical stability of Ta film, Ta film was prepared on glass substrate by tantalum vapor deposition technique. The structure, roughness and surface morphology of these films were further characterized using XRD, CCI and SEM techniques, respectively.

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Figure1 XRD data of Ta film and after exposure to harsh solvent (HCl) for different time

 

The Ta film thickness of 1 μm soaked in pH 1.0 solution for 15 minutes showed a thickness similar to that before use.

Based on the XRD patterns and thickness measurement data, it can be said that the material maintained its structure during the experiments in low pH solution, which confirmed its stability.

The roughness of the Ta film was measured using the CCI technique and found to be 0.3 nm (Figure 2), which shows better film quality.

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Figure2 CCI surface image and roughness map of Ta film

 

Figure 3(a) and (b) show the cross-section and 2D surface morphology of the electrode material before the sensing study. However, Figures 3(c) and (d) represent the cross-section and 2D surface morphology of the electrode material after immersion in 1.0 pH solution for 15 min. It again confirmed that the electrode material did not dissolve in solution and remained stable during the study.

 

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Figure4 (a) SEM image of bare Ta film, (b) SEM image of cross-section of bare Ta film, (c) SEM image of used Ta film, (d) SEM image of cross-section of used Ta film image

 

In the case of Ta thin film surfaces, the relocation of electric potential and charge will occur during the interaction of the two different surfaces (ie, solid and liquid).

 

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Figure4 Current responses of ta/glass substrates in 112 pH solutions

 

Linear Sweep Voltammetry (LSV) performed LSV studies at a constant scan rate of 10 mV/s over a potential range of 0.5 to 0.5 V using solutions at pH 1.0 to 12.0. The resistive response was measured as a function of current and the results are shown in Figure 5. As the potential was increased, a sudden decrease in current was observed and the current was found to saturate at higher potentials. These electrochemical findings identify the presence of electroactive species in solution.

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Figure5 LSV curves of coated substrates in different pH ranges from 1 to 12

 

Cyclic voltammetry (CV) experiments were also performed using the three-electrode configuration used in earlier studies. Solutions of various pH (1.012.0) were used as electrolytes and the scan rate was 10 mV/s. Receive data for all pH levels. Data for lower and higher pH (2.0 and 11.0) are shown in Figure 6. For other pH values, CV data were recorded and provided as supplementary data in this manuscript.

The reproducible CV curves represent the stability of the films and thus show better electrocatalytic activity.

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Figure6 Cyclic voltammograms of coated substrates in 2.0 and 11.0 pH solutions

 

ta/glass substrates were used as pH sensing electrodes. The resistance responses of the electrodes in various pH solutions were recorded, and the data are shown in Figure 7.

Figure 7 shows that the resistance of the electrode decreases in the pH range of 1.07.0. On the other hand, in the case of high pH (8.01.4.0), the response of the electrode was found to increase with increasing pH. In pH solutions of 9.014.0, the resistance increases steadily but slowly. The experiment was repeated 5 times with fresh electrodes and pH solution and a similar response was observed. Data are provided as supplementary data.

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Figure 7 Effect of pH on Coated Electrode Resistance for (a) 1.0 to 7.0 and (b) 8.0 to 12.0

 

The reliability of the fabricated sensor was verified with ordinary water samples, also using a similar technique previously used for a series of controlled pH solutions, and the data received are shown in Figures 8(a) to (c). Comparing these results with previously received results for various pH solutions, it can be said that the presence of other ions does not affect the performance of the Ta-based sensor.

Five water samples were collected from different sources and their pH was measured using the ta2/glass electrodes fabricated in this study and a standard pH measurement system. These values are compared and shown in Table 3. The results show that the error is less than 2%, indicating the reliability of the sensing material.

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Figure 8 (a) Linear sweep voltammogram (b) time response and (c) cyclic voltammogram of tap water

 

Table 3 pH comparison of water samples collected from different sources using ta/glass electrodes and pH meter

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