Effect of the thickness of thallium deposits on the values of EQCM sensitivity constant

Abstract

Three methods were used to obtain values of the sensitivity constant (C_f) of an electrochemical quartz crystal microbalance (EQCM) using solutions of Tl⁺ ions: chronoamperometry, chronopotentiometry and cyclic voltammetry. The results obtained by these three methods showed that the C_f values were very sensitive to experimental conditions used to form deposits and the three techniques revealed that C_f is markedly influenced by the roughness of thallium films. For example, if the thickness is low or too high, the relative error of C_f with respect to the theoretical value is in the order of −20% due to its roughness and mechanical stress produced by the difference in atomic size. On the contrary, if the thicknesses are intermediate, the C_f values approach the theoretical value with errors that may be below +5%. Furthermore, the electrodes employed in this determination can be used again without important modifications in their surface composition.