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Abstract: Hierarchically structured CaCO3 films were synthesized at atmospheric conditions (room temperature and 1atm) without the use of templates or amphiphilic molecules in this process. The resulting CaCO3 film was formed by self-organization between Ca(OH)2 and aqueous CO2. The building blocks of the CaCO3 film were thought to be CaCO3 primary nanoparticles that aligned to build higher level structures with greater size, called mesocrystals, depending on the additives. The soluble additives played a key role in the control of the morphology, crystallinity, and polymorphism of the CaCO3 film, and the effects strongly depended on the type of additive and their concentrations. The additives used in this study decreased the crystallinity of CaCO3 (calcite) film in the order of glucose>aspartic acid>serine in a manner inversely proportional to the concentration of the additives. In addition, Mg2+, K+, and Na+ ion additives led to the formation of an aragonite phase, the proportion of which increased with the concentration of ions. The threshold concentrations of these ions for the formation of the aragonite phase in CaCO3 film were found to be in the order of Na+ >K+ >Mg2+. [ABSTRACT FROM AUTHOR]