  VO2 is a much-discussed material for oxide electronics and neuromorphic
computing applications. Here, heteroepitaxy of vanadium dioxide (VO2) was
realized on top of oxide nanosheets that cover either the amorphous silicon
dioxide surfaces of Si substrates or X-ray transparent silicon nitride
membranes. The out-of-plane orientation of the VO2 thin films was controlled at
will between (011)M1/(110)R and (-402)M1/(002)R by coating the bulk substrates
with Ti0.87O2 and NbWO6 nanosheets, respectively, prior to VO2 growth.
Temperature dependent X-ray diffraction and automated crystal orientation
mapping in microprobe TEM mode (ACOM-TEM) characterized the high phase purity,
the crystallographic and orientational properties of the VO2 films. Transport
measurements and soft X-ray absorption in transmission are used to probe the
VO2 metal-insulator transition, showing results of a quality equal to those
from epitaxial films on bulk single-crystal substrates. Successful local
manipulation of two different VO2 orientations on a single substrate is
demonstrated using VO2 grown on lithographically-patterned lines of Ti0.87O2
and NbWO6 nanosheets investigated by electron backscatter diffraction. Finally,
the excellent suitability of these nanosheet-templated VO2 films for advanced
lensless imaging of the metal-insulator transition using coherent soft X-rays
is discussed.
