  Strain engineering vanadium dioxide thin films is one way to alter this
material's characteristic first order transition from semiconductor to metal.
In this study we extend the exploitable strain regime by utilizing the very
large lattice mismatch of 8.78 % occurring in the VO$_2$/RuO$_2$ system along
the c axis of the rutile structure. We have grown VO$_2$ thin films on single
domain RuO$_2$ islands of two distinct surface orientations by atomic
oxygen-supported reactive MBE. These films were examined by spatially resolved
photoelectron and x-ray absorption spectroscopy, confirming the correct
stoichiometry. Low energy electron diffraction then reveals the VO$_2$ films to
grow indeed fully strained on RuO$_2$(110), exhibiting a previously unreported
($2\times2$) reconstruction. On TiO$_2$(110) substrates, we reproduce this
reconstruction and attribute it to an oxygen-rich termination caused by the
high oxygen chemical potential. On RuO$_2$(100) on the other hand, the films
grow fully relaxed. Hence, the presented growth method allows for simultaneous
access to a remarkable strain window ranging from bulk-like structures to
massively strained regions.
