A process for depositing a metal on a substrate involves the use of two reduction reactions in a bottom-up based tandem manner starting from a substrate surface and working upward. A first reduction reaction starts on the substrate surface at ambient temperature, and a second reduction reaction, which is initiated by the reaction heat of the first reduction reaction, occurs in a reactive ink solution film coated on top, which becomes solid after the reaction. Gas and other small molecules generated from the reduction reactions, and the solvent, can readily escape through the upper surface of the film before the solid metal layer is formed or during post-treatment, with no or few voids left in the metal film. Thus, the process can be used to form highly conductive films and features at ambient temperature on various substrates.