<p>Nanotwinned copper (NT-Cu) has emerged as a critical material for advanced packaging interconnects due to its unique combination of high strength and superior electrical conductivity. In this study, we systematically investigated the two-dimensional nucleation and growth mechanism of selectively oriented NT-Cu through additive-mediated electrodeposition. The synergistic effects of Cl⁻ and gelatin additives were found to critically influence the crystallographic orientation evolution during direct current (DC) electroplating. Experimental results demonstrated that Cl⁻ ions induced a (110)-oriented growth pattern by accelerating Cu²⁺ reduction kinetics through depolarization effects, achieving a 96.68% (110) texture dominance with columnar twin structures (average thickness: 437&#xa0;nm). Conversely, the combined use of Cl⁻ and gelatin promoted (111)-oriented growth through geometric shielding effects, attaining a 97.92% (111) texture preference with refined twin lamellae (14.6&#xa0;nm thickness). Electrochemical analysis revealed that Cl⁻ reduced charge transfer resistance by 21% while gelatin increased Warburg impedance significantly, establishing a dynamic balance between nucleation and growth rates. Cross-scale characterization through FIB, EBSD, and TEM confirmed that (110) orientation resulted from a growth-dominated mode under low overpotential, whereas (111) orientation resulted from a nucleation-dominated growth mode characterized by lateral step advancement. These findings provide critical insights into crystallographic control strategies for fabricating orientation-engineered NT-Cu.</p> Graphical abstract <p></p>