  The progress of semiconductor electronics toward ever-smaller length scales
and associated higher power densities brings a need for new high-resolution
thermal microscopy techniques. Traditional thermal microscopy is performed by
detecting infrared radiation with far-field optics, where the resolution is
limited by the wavelength of the light. By adopting a serial, local-probe
approach, near-field and scanned-probe microscopies can surpass this limit but
sacrifice imaging speed. In the same way that electron microscopy was invented
to overcome the resolution limits of light microscopy, we here demonstrate a
thermal imaging technique that uses an electron microscope to overcome the
limits of infrared thermal microscopy, without compromising imaging speed. With
this new technique, which we call electron thermal microscopy, temperature is
resolved by detecting the liquid-solid transition of arrays of nanoscale
islands, producing thermal maps in real-time (30 thermal images per second over
a 16um^2 field-of-view). The experimental demonstration is supported by
combined electrical and thermal modeling.
