Antimony (Sb), an element with strong spin-orbit coupling, is predicted to undergo a topological phase transition from a topological semimetal to a topological insulator as its dimensionality approaches the two-dimensional limit, driven by the quantum confinement effect. In this study, we investigate this transition in Sb thin films grown by molecular beam epitaxy, employing electrical transport measurements and angle-resolved photoemission spectroscopy (ARPES). Electrical transport measurements revealed signatures of a modified electronic band structure, including a Hall response with multiple carrier types, a decreasing carrier concentration, and a transition in the curvature of the longitudinal resistance from quadratic to linear with decreasing film thickness. Temperature-dependent magnetoresistance further showed weak antilocalization below 16 K, indicating strong spin-orbit coupling and suggesting the presence of nontrivial topological states. Analysis of the WAL characteristics revealed a single coherent conducting channel and a thickness-dependent change in the phase decoherence mechanism. Complementary ARPES measurements confirmed that reducing the film thickness lifts the conduction band at the M point, consistent with the emergence of a band gap. These findings support theoretical predictions of a thickness-dependent band structure evolution driven by the quantum confinement effect, providing a foundation for further exploration of topological phase transitions in Sb as well as $\mathrm{B}{\mathrm{i}}_{1–x}\mathrm{S}{\mathrm{b}}_x$. The realization of an elemental topological material with simplified stoichiometry and semiconductor compatibility presents a promising avenue for next-generation hybrid systems and applications in spintronics and quantum technologies.

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• Electrical properties
• Topological phase transition
• Weak antilocalization
• Thin films
• Topological materials
• Angle-resolved photoemission spectroscopy
• Molecular beam epitaxy