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.
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