Clear Revelation of Topological Surface States in Bi$_{2}$Se$_{3}$ Thin Films by \textit{in situ} Al Passivation

We report that \textit{in situ} aluminum (Al) passivation of Bi$_{2}$Se$_{3}$ can inhibit the degradation process and clearly reveal the massless, Dirac-like topological surface states. In this work, an 8 quintuple layers Bi$_{2}$Se$_{3}$ film was passivated with 2 nm Al, immediately after the MBE growth, which prevents native oxide (BiO$_{x})$ formation, isolates the film from ambient $n$-type doping or contaminations in the subsequent fabrication process. Dual evidences from both Shubnikov-de Hass (SdH) oscillations and weak antilocalization (WAL) effect, originated from the $\pi $ Berry phase of the nontrivial surface states, were clearly revealed in the sample with \textit{in situ} Al passivation. In contrast, we show that the two dimensional carrier density was increased 39.2{\%} for the un-passivated control samples. Also, the SdH oscillations were completely absent and a large deviation from the WAL was observed