  The preservation and manipulation of a spin state mainly depends on the
strength of the spin-orbit interaction. For pristine graphene, the intrinsic
spin-orbit coupling (SOC) is only in the order of few ueV, which makes it
almost impossible to be used as an active element in future electric field
controlled spintronics devices. This stimulates the development of a systematic
method for extrinsically enhancing the SOC of graphene. In this letter, we
study the strength of SOC in weakly fluorinated graphene devices. We observe
high non-local signals even without applying any external magnetic field. The
magnitude of the signal increases with increasing fluorine adatom coverage.
From the length dependence of the non-local transport measurements, we obtain
SOC values of ~ 5.1 meV and ~ 9.1 meV for the devices with ~ 0.005% and ~ 0.06%
fluorination, respectively. Such a large enhancement, together with the high
charge mobility of fluorinated samples (u~4300 cm2/Vs - 2700 cm2/Vs), enables
the detection of the spin Hall effect even at room temperature.
