Investigation of structural, optical and thermoelectric properties of 2H–MoTe2 and MoO3–TeO2 thin films

Abstract

Easy synthesis of two-dimensional chalcogenide materials sach as MoTe2 and WTe2 is an important challenge for researchers. In this paper, we are showed that using Mo and Te oxides percursors as inexpensive initial materials and spray pyrolysis method, the MoO3–TeO2 thin film binary compounds, and the important two-dimensional structure of 2H–MoTe2 are prepared. . In this method, through the preparation of thin films of the MoO3–TeO2 binary composition by changing the molar concentration of Mo and Te in a solid-state reaction process, with molar ratios (a) MoO3 (0.05 M) -TeO2 (0.15 M), (b) MoO3 (0.1 M) -TeO2 (0.1 M) and (c) MoO3 (0.15 M) -TeO2 (0.05 M), we can obtain the 2H–MoTe2 phase. After synthesis of MoO3–TeO2 and 2H–MoTe2 compounds, structural and optical characterization of thin films, as well as thermoelectric properties of the prepared thin films were studied before and after annealing at T = 500 °C. X-ray diffraction results showed that the structure of thin films before annealing is amorphous structure, and after annealing at T = 500 °C for synthesis c: MoO3 (0.15 M) -TeO2 (0.05 M), the two-dimensional structure of 2H–MoTe2 was formed. The images of the field emittion scanning electron microscope (FE-SEM) showed that the morphology of the nanoparticles is the pseudo-spherical shape, rod and polygon, indicating the presence of particles in different phases at before annealing and flat – like form after annealing. The results of UV–Vis spectrometry showed that the energy gap of thin films varied in the range of 2.3–2.87 eV. The nanoparticle bonding structure was also studied by FT-IR spectroscopy. Studies on the thermoelectric properties of thin films before and after annealing showed that for synthsis (c): MoO3 (0.15 M) -TeO2 (0.05 M) with formation of the 2-H-MoTe2 phase, the seebeck coefficient was larger than other samples, and the majority carrier are holes. Also, ZT increases with decreasing molar concentration of TeO2 and reached to 1.32 at room temperature for synthesis c: MoO3 (0.15 M) -TeO2 (0.05 M).