The impact of morphological structure and flexo-chemical strains on the electric transport mechanisms in the molybdenum-disulfide-oxide nanoflakes

Electric conduction mechanisms are studied in the pressed nanoflake powder of the molybdenum-disulfide-oxide (MoSxOy) depending on their content and structure. The MoSxOy nanoflakes were prepared by reaction of (NH4)6Mo7O24 with thiourea in aqueous solution followed by aerial oxidation. The sintered nanoflakes are 10-20 nm thick and self-assembled in the "nanoflower"-shape aggregates forming powder particles. The chemical composition and structure of the powders were studied by XPS, EDS and Raman spectroscopy, which show that the powders have different chemical composition and structure depending on the preparation conditions. These studies revealed the existence of different forms of MoS2 and its oxides in the powders. These features are impactful on electric transport properties. The current-voltage (I-V) curves of the pressed MoSxOy nanoflakes reveal hysteresis-like behavior; at that the loop width depends on the chemical composition and structure. The negative differential conductivity is observed for the highest content of Mo in oxide/sulfoxide form. The I-V curves of all MoSxOy nanoflake samples manifest the three-state resistive switching and the long-lasting transient charge/discharge on switching "on/off" the voltage across the sample, which evidences the role of interface charges in their conductivity. To describe theoretically the observed I-V curves, polar and electric-transport properties of the pressed MoSxOy nanoflakes, the Landau-Cahn-Hilliard approach considering flexo-chemical field has been used. The revealed experimentally and explained theoretically features of resistive switching and charge accumulation look promising for applications in memristors and high-performance supercapacitors.