In brief, the substrates were floated on the top of the precursor solution mixture (same recipe as mixing Solution A and B) for the same preparation time at room temperatures. This method was designed to mimic the limited mass transport of the precursor mixtures on the substrates in the hand sprayer-based method. These immersion-route-made oxide coatings (i.e. the IOC series) following the spike-addition manner are denoted as CoMn-IOC (two metal case), CoMnCu-IOC (three metal case), CoMnCuZn-IOC (four metal case), and CoMnCuZnAg-IOC (five metal case).