  Using long-distance lateral devices, spin transport near the interface of Si
and its native oxide (SiO2) is studied by spin-valve measurements in an
in-plane magnetic field and spin precession measurements in a perpendicular
magnetic field at 60K. As electrons are attracted to the interface by an
electrostatic gate, we observe shorter average spin transit times and an
increase in spin coherence, despite a reduction in total spin polarization.
This behavior, which is in contrast to the expected exponential depolarization
seen in bulk transport devices, is explained using a transform method to
recover the empirical spin transit-time distribution and a simple two-stage
drift-diffusion model. We identify strong interface-induced spin depolarization
(reducing the spin lifetime by over two orders of magnitude from its bulk
transport value) as the consistent cause of these phenomena.
