  Spintronics aims to exploit the spin degree of freedom in solid state devices
for data storage and information processing technologies. The fundamental
spintronic device concepts such as creation, manipulation and detection of spin
polarization has been demonstrated in semiconductors and spin transistor
structures using both the electrical and optical methods. However, an unsolved
challenge in the field is the realization of all electrical methods to control
the spin polarization and spin transistor operation at ambient temperature. For
this purpose, two-dimensional (2D) crystals offer a unique platform due to
their remarkable and contrasting spintronic properties, such as weak spin-orbit
coupling (SOC) in graphene and strong SOC in molybdenum disulfide (MoS$_2$).
Here we combine graphene and MoS$_2$ in a van der Waals heterostructure to
realize the electric control of the spin polarization and spin lifetime, and
demonstrated a spin field-effect transistor (spin-FET) at room temperature in a
non-local measurement geometry. We observe electrical gate control of the spin
valve signal due to pure spin transport and Hanle spin precession signals in
the graphene channel in proximity with MoS$_2$ at room temperature. We show
that this unprecedented control over the spin polarization and lifetime stems
from the gate-tuning of the Schottky barrier at the MoS$_2$/graphene interface
and MoS$_2$ channel conductivity leading to spin interaction with high SOC
material. The all-electrical creation, transport and control of the spin
polarization in a spin-FET device at room temperature is a substantial step in
the field of spintronics. It opens a new platform for the interplay of spin,
charge and orbital degrees of freedom for testing a plethora of exotic physical
phenomena, which can be key building blocks in future device architectures.
