surface hole doped with NO$_{2}$ at a temperature T = 10 K. Figures 4(c) and (d) illustrate that the charge neutral point-like FS (Fig. 4(a)) is robust up to room temperature ( T = 300 K) over days long measurement times. A density of states that decreases linearly to zero at the Dirac point energy at 300 K (Fig. 4(f)) is further evidence that the low energy properties of Bi$_{1}$$_{.}$$_{9975}$Ca$_{0}$$_{.}$$_{0025}$Se$_{3}$.NO$_{2}$ are dominated by a novel ground state that features massless helical Dirac fermions with nearly 100% spin polarization. This also confirms a non-trivial π Berrys phase on the surface due to the spin-momentum locking pattern that we observe, which is similar to the robust Berrys phase previously observed in the Bi-Sb system [14] (Fig. 1). Helical nodal Dirac fermions are forbidden from acquiring a mass through band gap formation because they are located around time-reversal invariant (Kramers’) momenta k$_{T}$ = ¯ Γ or ¯ M (Fig. 4(h)). This makes them fundamentally different from chiral Dirac fermions such as those found in graphene, which are located at ¯ K and not topologically protected (Fig. 4(g)). The helical Dirac fermion on the surface of Bi$_{2}$Se$_{3}$ owes its existence to a non-zero topological number ν$_{0}$ given by (-1) ν 0 = Π$_{k}$$_{T}$ Π N m $_{=1}$ξ$_{2}$$_{m}$ ( k$_{T}$ ), where ξ$_{2}$$_{m}$ ( k$_{T}$ ) is the parity eigenvalue of the bulk wavefunction at the 3D Kramers’ point k$_{T}$ and N is the number of occupied bulk bands [4]. Because Ca dopants are present in only trace quantities in Bi$_{1}$$_{.}$$_{9975}$Ca$_{0}$$_{.}$$_{0025}$Se$_{3}$.NO$_{2}$, the values of ξ$_{2}$$_{m}$ ( k$_{T}$ ) do not deviate from those of pure Bi$_{2}$Se$_{3}$, as evidenced by the persistence of a single gapless surface band in both Bi$_{2}$Se$_{3}$ and Bi$_{1}$$_{.}$$_{9975}$Ca$_{0}$$_{.}$$_{0025}$Se$_{3}$. Both Ca 2+ and NO 2 − are non-magnetic and so do not break time- reversal symmetry, therefore the same topological number ( ν$_{0}$ = 1) applies even in the Dirac transport regime (Fig. 4) realized by our method shown here, which is stable with both time and temperature. Our direct demonstration of spin-polarized edge channels and room temperature operability of chemically gated stoichiometric Bi$_{2}$Se$_{3}$ or Bi$_{2}$$_{−}$$_{δ}$Ca$_{δ}$Se$_{3}$, not achieved in purely 2D topological systems such as Hg(Cd)Te quantum wells [29], enables exciting future room temperature experiments on surface helical Dirac fermions that carry a non-trivial π Berry’s phase. Our demonstration of topological order at room temperature opens up possibilities of us- ing quantum Hall-like phenomena and spin-polarized protected edge channels for spintronic or computing device applications without the traditional requirements of high magnetic fields and delicate cryogenics. A direct detection of surface-edge states would be possible in stoichiometric Bi$_{2}$Se$_{3}$ or Bi$_{2}$$_{−}$$_{δ}$Ca$_{δ}$Se$_{3}$, using transport methods which will bear signatures of weak anti-localization and thus exhibit anomalous magneto-optic effects. Here we envisage 8