  The control of chemical exchange across heterointerfaces formed between
ultra-thin functional transition-metal oxide layers provides an effective route
to manipulate the electronic properties of these systems. We show that cationic
exchange across the interface between the Mott insulator, LaTiO$_3$(LTO) grown
epitaxially on SrTiO$_3$(STO)-buffered Silicon by molecular beam epitaxy
depends strongly on the surface termination of the strained STO buffer. Using a
combination of temperature-dependent transport and synchrotron X-ray crystal
truncation rods and reciprocal space mapping, an enhanced conductivity in
STO/LTO/SrO- terminated STO buffers compared to heterostructures with
TiO$_2$-terminated STO buffers is correlated with La/Sr exchange and the
formation of metallic La$_{1-x}$Sr$_x$TiO$_3$. La/Sr exchange effectively
reduces the strain energy of the system due to the large lattice mismatch
between the nominal oxide layers and the Si substrate.
