A challenge to investigate the physical properties in μm-size crystals
It is important to study the properties of high quality single crystal in order to resolve the issue of an interesting material that certain debatable fundamental properties exist. However, it is unfortunate that sizable single crystal for experimental measurements is not always available. NbN is one of the examples, it has attracted scientific and engineering interests due to its diverse physical properties and a variety of structural phases. Until now superconductivity is only observed in cubic δ- and tetragonal γ- NbN but not in hexagonal ε-NbN. Recently, Zou et. al. reported the observation of superconductivity with TC~11.6 K in a hexagonal ε-NbN based on the measurement on a multi-phase powder specimen. In order to resolve the issue, the work used the Electron Back-Scattering Diffraction (EBSD) technique to characterize phases of micron-size NbN crystals from commercial powders and measure their transport properties. Our results unambiguously confirm that the hexagonal ε-NbN phase is not superconducting. Furthermore, I will also show you how to develop an innovative nano-calorimeter use to study the thermodynamic properties in um-size crystals.