  Ultrathin topological insulator membranes are building blocks of exotic
quantum matter. However, traditional epitaxy of these materials does not
facilitate stacking in arbitrary orders, while mechanical exfoliation from bulk
crystals is also challenging due to the non-negligible interlayer coupling
therein. Here we liberate millimeter-scale films of topological insulator
Bi$_2$Se$_3$, grown by molecular beam epitaxy, down to 3 quintuple layers. We
characterize the preservation of the topological surface states and quantum
well states in transferred Bi$_{2}$Se$_{3}$ films using angle-resolved
photoemission spectroscopy. Leveraging the photon-energy-dependent surface
sensitivity, the photoemission spectra taken with $6$ eV and $21.2$ eV photons
reveal a transfer-induced migration of the topological surface states from the
top to the inner layers. By establishing clear electronic structures of the
transferred films and unveiling the wavefunction relocation of the topological
surface states, our work paves the physics foundation crucial for the future
fabrication of artificially stacked topological materials with single-layer
precision.
