This study presents a novel method based on the electrochemical co-reduction of two aryldiazonium salts, enabling the synthesis of controlled two-component monolayer thin films on carbon in a single step. By introducing a 12-carbon alkyl chain as a spacer between the aryldiazonium function and the functional group, precise control over film thickness and composition was achieved. The alkyl chain effectively standardizes the reduction potential, enabling the equalization of reactivity and precise stoichiometric control. Experimental results from spectroscopic, electrochemical, and X-ray photoelectron spectroscopy analyses validate the effectiveness of the method in controlling the composition of the mixed layers.