In macroscopic photothermal measurement techniques inhomogeneous thermal waves are used to probe thermal properties of materials on a macroscopic scale. The same principle has been adapted to a high-resolution scanning thermal microscope. Heating the thermal probe periodically results in an amplitude and a phase signal which can be referred to the dynamical thermal behavior of the sample. This measurement mode allows the investigation of the thermal diffusivity of samples in contrast to experiments known from static scanning thermal microscopy which so related to the thermal conductivity. The photothermal scanning thermal microscope technique was used to investigate grains of thin polycrystalline diamond films. For topography measurements the thermal probes were additionally employed for scanning tunneling microscopy.