  We show that functionalized micromechanical bilayer levers can be used as
sensitive probes to accurately measure radiative heat flux in vacuum between
two materials at the micro scale. By means of calibration to one material these
measurements can be made quantitative for radiative heat flux or for either
temperature or material emissivity. We discuss issues and opportunities for our
method and provide ample technical details regarding its implementation and
demonstrate good correspondence with the Stefan Boltzman law. We use this
system to probe the phase transition of VO2 and find that radiative heat
transfer in farfield between VO2 and glass can be reversibly modulated by a
factor of 5.
