In scanning thermal microscopy, but also in scanning tunneling microscopy, the thermal contact between tip and sample plays an important role. The heat transfer across the vacuum gap between two parallel metallic surfaces, if the gap width is decreased below several microns, has been investigated. At these distances propagating electromagnetic modes die out but simultaneously a transfer of nonpropagating surface modes across the gap becomes more probable. The heat conductance of the vacuum gap should become distance dependent and larger than that given by the Stefan–Boltzmann law; however, the experimental results and theoretical considerations indicate that the heat transfer, based on the discussed proximity mechanism, is very small, smaller than predicted by the theory of Polder and Van Hove [Phys. Rev. B 4, 3303 (1971)].

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If there is a temperature difference between tip and sample of a scanning tunneling microscope a thermovoltage is generated which is very sensitive to the electronic states involved in the tunneling process. This has been used, e.g., to distinguish between different metals of a heterogeneous metallic surface. To demonstrate the capability of this method it has been applied to copper islands on a Ag(111) surface. Knowing the thermopower for chemically homogeneous silver and copper surfaces of −45 and −15 μV/K, respectively, islands of copper on the silver substrate can be well identified with a lateral resolution of 1 nm.

Planar thermocouples designed for investigation of heat transfer in scanning tunneling microscopy and scanning thermal microscopy are described. The limit of sensitivity to local thermal power can be as small as 10 nW. The devices are based on two different thin films formed as a cross on a thin glass substrate. Heat fluxes in the cross point can be detected by measuring the thermoelectric signal from two ends of the cross. As described elsewhere planar thermocouples of this type have been successfully used to detect the energy which is deposited by tunneling electrons and to measure the heat which is coupled across a submicron vacuum gap between two metals by the fluctuating fields of electromagnetic surface modes.