For more than 30 years, scanning thermal microscopy (SThM) has been used for thermal imaging and quantitative thermal measurements. It has proven its usefulness for investigations of the thermal transport in nanoscale devices and structures. However, because of the complexity of the heat transport phenomena, a quantitative analysis of the experimental results remains a non-trivial task. This paper shows the SThM state-of-art, beginning with the equipment and methodology of the measurements, through its theoretical background and ending with selected examples of its applications. Every section concludes with considerations on the future development of the experimental technique. Nowadays, SThM has passed from its childhood into maturity from the development stage to its effective practical use in materials research.

Scanning thermal microscopy (SThM) is the only method for thermal measurements providing spatial resolution in the nanometer range. The method combines the topographical imaging of atomic force microscopy (AFM) with the thermal characterization of samples by the use of specially designed AFM probes having a temperature sensor near the apex. Measurements can be carried out in two modes: the temperature contrast (or passive) mode and the conductance contrast (or active) mode. In the first mode, the probe is not heated and the temperature distribution on the sample surface is measured. In the second mode, there are no heat sources in the sample and the probe is heated. The probe temperature depends on the thermal conductance for the heat exchange between the probe and the sample. This thermal conductance depends on the sample thermal conductivity and probe-sample interfacial thermal resistance. If the latter is constant, the distribution of the thermal conductivity on the sample surface can be obtained. The principle of qualitative SThM is quite simple. However, quantitative measurements require rigorous analysis of temperature distribution and heat fluxes in the probe-sample system. This paper provides basic information about SThM starting from first principles, through instrumentation, characterization of probes used for measurements, general theory of the temperature, and the thermal conductivity measurements, to a few examples of practical applications of this method. Finally, perspectives and challenges for SThM based measurements are discussed.

The thermal diffusivity and the thermal conductivity of compressed expanded graphite (CEG) samples were investigated by photothermal measurements in two geometries differing by a place of temperature disturbance detection. This disturbance can be detected on a surface opposite to the one at which the disturbance was generated (rear detection) or on the same surface (front detection). A measurement based on the rear detection allowed us to determine the effective thermal diffusivity of the sample, while the method with front detection gives the possibility of analysis of homogeneity of the sample. It is shown that the thermal diffusivity of CEG strongly depends on its apparent density. Moreover, CEG samples reveal anisotropy of the thermal properties. The thermal diffusivity in the direction parallel to the compacting axis is lower than the one in the direction perpendicular to it. The parallel thermal diffusivity decreases with growing apparent density, while the perpendicular thermal diffusivity significantly grows when the apparent density grows. The perpendicular thermal conductivity exhibits the same behavior as the perpendicular thermal diffusivity. The parallel thermal conductivity slightly grows with growing density and then reaches a plateau. The anisotropy of CEG samples grows with growing apparent density and vanishes for low-density samples. The photothermal measurement with front signal detection revealed that the CEG samples are non-homogeneous in the direction of the compacting axis and can be modeled by a two-layer system.

Quantitative thermal measurements with spatial resolution allowing the examination of objects of submicron dimensions are still a challenging task. The quantity of methods providing spatial resolution better than 100 nm is very limited. One of them is scanning thermal microscopy (SThM). This method is a variant of atomic force microscopy which uses a probe equipped with a temperature sensor near the apex. Depending on the sensor current, either the temperature or the thermal conductivity distribution at the sample surface can be measured. However, like all microscopy methods, the SThM gives only qualitative information. Quantitative measuring methods using SThM equipment are still under development. In this paper, a method based on simultaneous registration of the static and the dynamic electrical resistances of the probe driven by the sum of dc and ac currents, and examples of its applications are described. Special attention is paid to the investigation of thin films deposited on thick substrates. The influence of substrate thermal properties on the measured signal and its dependence on thin film thermal conductivity and film thickness are analyzed. It is shown that in the case where layer thicknesses are comparable or smaller than the probe–sample contact diameter, a correction procedure is required to obtain actual thermal conductivity of the layer. Experimental results obtained for thin SiO\(_{\mathrm {2}}\) and BaTiO\(_{\mathrm {3 }}\)layers with thicknesses in the range from 11 nm to 100 nm are correctly confirmed with this approach.