Surface properties of SnO2 nanolayers prepared by spin-coating and thermal oxidation.

In this work, comparative studies of the surface morphology and surface chemistry of SnO2 nanolayers prepared by spin coating with subsequent thermal oxidation (SCTO) in the temperature range of 400-700 °C using scanning electron microscopy (SEM), atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS) methods, are presented. The SEM images show that SCTO SnO2 nanolayers contain partly connected irregular structures strongly dependent on the final oxidation temperature, with interconnected single grains of longitudinal shape and size, resulting in a flatter surface morphology with respect to the commonly used three-dimensional (3D) SnO2 thin films. In turn, AFM studies additionally confirm that SCTO SnO2 nanolayers after post-oxidation annealing at higher temperatures contain isolated grains of average lateral dimensions in the range of 20-50 nm having a rather flat surface morphology of average surface roughness defined by the root mean square factor at the level of ∼2 nm. From the XPS experimental research it can be concluded that, for our SCTO SnO2 samples, a slight surface nonstoichiometry defined by the relative [O]/[Sn] concentration at the level of 1.8-1.9 is observed, also depending on the final post-oxidation temperature, being an evident contradiction to recently published literature using x-ray diffraction data. Moreover, XPS experiments show that there is also a permanent small amount of carbon contamination present at the surface of internal grains of our SCTO SnO2 nanolayers, creating an undesired potential barrier for interactions with gaseous species when they are used as the active materials for gas sensing devices.

Application of scanning thermal microscopy for investigation of thermal boundaries in multilayered photonic structures.

In current work the application of modified Scanning Thermal Microscopy (SThM) technique for thermal imaging of multilayered periodic photonic structures is presented. The measurements were carried out using non-standard operation mode of the SThM. The thermal probe was driven by the sum of DC and small AC currents. The main advantages of presented approach are mechanical stability of the probe during measurements and high sensitivity of AC signal detection by the use of lock-in amplifier. The amplitude and phase components of probe response signal are used for visualization and analysis of the thermal properties of the layer interfaces. Basing on topographic and thermal signals the thermal boundaries between layers were revealed and the periodicity of the structure was analyzed. Presented experiment indicates that the proposed method provides spatial resolution at least about 30% better than 100 nm, which is considered for standard nanofabricated thermal probes. Therefore, proposed technique may be successfully used for the thermal boundaries mapping, as well as for the high-resolution nanoscale imaging of thermal properties distribution. The results prove that thermal imaging provides additional information to that obtained by standard AFM imaging.