Interface effects on the phase transition of MnS nanocrystal

Abstract

Abstract Phase stability of nanocrystals and its targeted transition is of great significance for the controllable synthesis of nanocrystals with particular properties and uitilizations. Crystal size and surface environment are generally regarded as two critical factors with the relative phase stability, whereas the thermodynamic realtionship between them are still unclear. Herein, we utilized MnS nanocystal of 9-nm as a probe, to study the phase stability and transition of nanocrystals under different surface environments, one of which with a strong surfactant of mercaptoethanol and the other with pure H2O, respectively. Combining analysis including X-ray diffraction, transmission electron microscopy and scanning electron microscopy indicated that the critical size of MnS transforming from wurtzite phase to rock-salt phase was ~ 200\xa0nm in pure H2O. However, this value decreased to 13\xa0nm in mercaptoethanol, which was more than 15 times smaller than that in pure H2O. Thermodynamic analysis further demonstrated a decreasing trend of critical size for phase transformation when the surface of nano MnS was covered by strong surfactant, which was caused by the decreasing of surface free energy. This is probably due to more active coordination sites of rock-salt MnS owing to octahedral configuration of Mn with S. This study provided a critical evidence to prove the fundamental influence of surface environment on phase stability, which may provide a novel thought on regulating phase transition of crystals in nanoscale.