  The thermal radiative near field transport between vanadium dioxide and
silicon oxide at submicron distances is expected to exhibit a strong dependence
on the state of vanadium dioxide which undergoes a metal-insulator transition
near room temperature. We report the measurement of near field thermal
transport between a heated silicon oxide micro-sphere and a vanadium dioxide
thin film on a titanium oxide (rutile) substrate. The temperatures of the 15 nm
vanadium dioxide thin film varied to be below and above the
metal-insulator-transition, the sphere temperatures were varied in a range
between 100 and 200 Celsius. The measurements were performed using a
vacuum-based scanning thermal microscope with a cantilevered resistive thermal
sensor. We observe a thermal conductivity per unit area between the sphere and
the film with a distance dependence following a power law trend and a
conductance contrast larger than 2 for the two different phase states of the
film.
