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Astract: Epitaxial thin-film heterostructures offer a versatile platform for realizing topological surface states (TSSs) that may be emergent and tunable by tailoring the atomic layering in the system. As an experimental demonstration, Sb and Bi₂Te₃ thin films with closely matched in-plane lattice constants are chosen to form two complementary heterostructures: Sb on Bi₂Te₃ and Bi₂Te₃ on Sb, with the overlayer thickness as a tuning parameter. In bulk form, Sb (a semimetal) and Bi₂Te₃ (an insulator) both host TSSs with the same topological order but very different decay lengths and dispersions, whereas ultrathin Sb and Bi₂Te₃ films by themselves are fully-gapped trivial insulators. Angle-resolved photoemission band mappings, aided by theoretical calculations, confirm the formation of emergent TSSs in both heterostructures. The energy position of the topological Dirac point varies as a function of overlayer thickness, but the variation is non-monotonic, indicating nontrivial effects in the formation of composite electronic states. The results illustrate the rich physics of engineered composite topological systems that may be exploited for nanoscale spintronics applications.