Two-dimensional (2D) materials have emerged as a central focus in condensed matter physics since the discovery of graphene, owing to their atomic-scale confinement, mechanical flexibility, and tunable electronic structures. The interplay between reduced dimensionality and nontrivial band topology gives rise to a range of exotic phenomena, including 2D magnetism, 2D topological phases, and 2D superconductivity. Topological semimetals, such as Dirac and Weyl systems, host gapless excitations that are protected by both crystalline symmetry and topology. These states, described by relativistic chiral fermion models, provide a condensed-matter platform to explore particle physics analogs and open new opportunities for spintronics and quantum computation. Unlike their three-dimensional counterparts, truly 2D Dirac and Weyl systems are rare due to the stringent symmetry and dimensional constraints required for their realization. In addition to intrinsic 2D materials, interfacial systems—where electronic states are strongly modified by coupling and proximity effects—offer an alternative route to engineer novel quantum phases. Interfacial topological superconductivity (TSC), formed at the interface between a topological layer and a superconducting layer, exemplifies such emergent behavior. TSC has garnered significant attention as a robust platform for realizing Majorana-bound states—zero-energy quasiparticles with non-Abelian statistics that form the foundation for fault-tolerant quantum computation.  In this work, molecular beam epitaxy (MBE) is employed to synthesize high-quality 2D and interfacial systems, which are then characterized using in-situ scanning tunneling microscopy (STM), spin- and angle-resolved photoemission spectroscopy (SARPES), and first-principles calculations to elucidate their structural, electronic, and topological properties. Three 2D systems will be discussed: (1) unpinned 2D Dirac states in α-Sb, (2) 2D Weyl states in monolayer Bi, and (3) interfacial topological superconductivity in Fe(Te,Se)/Bi₂Te₃ heterostructures.