The effect of formation temperature and flexo-chemical strains on the electrophysical properties of the molybdenum-disulfide-oxide nanoflakes

• Main Authors: Pylypchuk, Oleksandr S, Vainberg, Victor V, Poroshin, Vladimir N, Terebilenko, Anastasyia V, Nikolenko, Andrii S, Popenko, Vadym I, Tolochko, Anatolyi S, Olenchuk, Maryna V, Bezkrovnyi, Oleksii, Dovbeshko, Galina I, Sabov, Tomash, Romanyuk, Boris M, Morozovska, Anna N, Kolotilov, Sergey V
• Format: Journal Article
• Language: English
• Published: 01-11-2024
• Subjects: Physics - Materials Science; Physics - Mesoscale and Nanoscale Physics
• DOI: 10.48550/arxiv.2411.00603

We synthesized the powder of molybdenum-disulfide-oxide nanoflowers
consisting of self-assembled 10-20 nm thin nanoflakes by reaction of
(NH4)6Mo7O24 with thiourea in aqueous solution at temperatures from 130oC to
180oC in hydrothermal conditions. The detailed analysis of the XPS, EDX and
Raman spectroscopy results reveal the significant amount of the molybdenum
oxides, sulfides and sulfates in the molybdenum disulfide nanoflakes, which
allows to consider the "effective" formulae MoSxOy for their chemical
composition. The MoSxOy nanoflakes reveal unusual electric transport features
interesting for material science and promising for applications. The chemical
composition and microstructure of the nanoflakes, which are determined by the
temperature of synthesis, is shown to be responsible for the electro-conduction
mechanism. Namely, the current-voltage characteristics (I-V curves) grow
monotonically with the applied voltage for the samples, synthesized at the
temperatures T_s<<150oC and T_s>>150oC, being non-ohmic and hysteretic at lower
voltages and becoming close to the ohmic at higher voltages. The I-V curves
acquire N-like shape with a strongly pronounced negative differential
resistivity part at T_s=150oC. Both with and without N-shape, the I-V curves
manifest hysteretic behavior with the difference between increasing and
decreasing voltage sweeps, and the hysteresis loop parameters are determined by
the temperature of synthesis. Important, that the studied nanoflakes manifest
very long living deep charging and discharging after the voltage switching "on"
and "off".Considering that the presence of oxygen non-stoichiometry and bending
can create strong flexo-chemical strains in the nanoflakes, we proposed the
flexo-chemical model of the polar and electro-transport properties of the
pressed MoSxOy nanoflakes, which describes the observed I-V curves.