  The thermoelectric properties of a nanoscale germanium segment connected by
aluminium nanowires are studied using scanning thermal microscopy. The
germanium segment of 168\,nm length features atomically sharp interfaces to the
aluminium wires and is surrounded by an Al$_2$O$_3$ shell. The temperature
distribution along the self-heated nanowire is measured as a function of the
applied electrical current, for both Joule and Peltier effects. An analysis is
developed that is able to extract the thermal and thermoelectric properties
including thermal conductivity, the thermal boundary resistance to the
substrate and the Peltier coefficient from a single measurement. Our
investigations demonstrate the potential of quantitative measurements of
temperature around self-heated devices and structures down to the scattering
length of heat carriers.
