The effect of I- ions on the threshold voltages of the electrolyte-solution-gate diamond field-effect transistors (SGFETs) in KI solution is investigated. The threshold voltages of hydrogen-terminated (H-terminated) diamond SGFETs shift in the KI concentration range of 10-6-10-1 M in aqueous solutions. The sensitivity of the H-terminated diamond surface to I- ions is higher than that to Cl- or Br- ions. However, the sensitivity to I- ions of the partially oxygen-terminated (O-terminated) diamond surface drastically decreases with ozone treatment. The mechanisms of these phenomena can be explained by the surface charge and the adsorbability of I- ions on the H-terminated and O-terminated diamond surfaces.
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