A Synthesis of Molybdenum Trioxide and their applications.

Abstract

After the introduction of graphene, two-dimensional (2D) materials turned into very interesting topics for research because of their excellent electronic, chemical, and mechanical properties [1]. Like other two-dimensional (2D) materials, Transition-metal oxides (TMOs) can be stacked as heterostructures for 2D electronics [2]. Transition metal oxides contain a massive family of materials that performance a variety of extraordinary properties that are attractive for many applications [3]. Transition metal oxides (TMOs) such as MoO₃ have been researched for so many years due to their stunning applications in electronics, gas sensors, Light-emitting diode  (LEDs), photo, electrochromic materials, and so on. In this work, we have carried out two types of synthesis on nanostructures of molybdenum trioxides. Molybdenum trioxide (MoO₃) can be appeared in varied crystal structures like orthorhombic (α-MoO₃), monoclinic (β- MoO₃) and hexagonal (h- MoO₃). When compared with other phases, Orthorhombic (α-MoO₃) is more stable thermodynamically also maintains a unique layered structure and in each of its layers, the octahedra MoO₆ consists of two sub-layers interconnected in (101) direction [4]. β- MoO₃ is the metastable phase that is transformed into the α-phase by heating above 673K. The unit cell parameters of α- MoO₃ a=0.37 nm, b=0.36 nm, c=1.229 nm (α=β=δ=90⁰) and for β-MoO₃ is a=0.77 nm, b=0.74 nm, c=1.09 nm (α=β= 90⁰, δ=120⁰) [5]. We can use a hot plate and chemical vapor deposition. This method will give multilayers of MoO₃ on graphene/SiO₂ and graphene/glass as a substrate with temperature variations. Hot plate and Chemical vapor deposition (CVD) can be done in ambient conditions.

The chemical vapor deposition (CARBOLITE GERO 30-3000⁰C) was utilized to grow α-MoO₃. The deposited Mo thin films on Sputtering are used as a source and place graphene/SiO₂ as a substrate upside down to source in Quartz tube. The detailed information of tube is 1m length and inner diameter 5.5 cm and outer diameter 5.9 cm containing 0.2 cm thickness of tube in the furnace. We have three zones in CVD, in that three zones, the middle zone has gas flow parameters of Argon (Ar), Oxygen (O₂), Carbon dioxide (CO₂), Nitrogen (N₂). First, MoO₃ form on the source and become like α-MoO₃. Later α-MoO₃ will be evaporated from temp 650⁰C. Fig.1 shows the arrangement of the source and substrate in a quartz tube, and how it forms on the substrate in CVD. Argon and Oxygen gases pursuing with 1L/min and 2L/min held for 30mins at 650⁰C. We get α-MoO₃ nanosheets on Substrate.

An alternate method to grow α-MoO₃ is a hotplate. (iStir HP 550⁰C) was utilized to grow α-MoO₃. In this case, also, we have used the sputter-deposited Mo film as the source of Molybdenum. It was observed that the Hotplate method produced a large area and faster growth compared to CVD-grown samples.

The characterization of α-MoO₃ was studied in X-ray diffraction (XRD), Glancing incidence  X-ray diffraction (GIXRD), UV-VIS bandgap, Raman spectroscopy, Impedance spectroscopy, Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Atomic force microscopy (AFM), X-Ray photoelectron spectroscopy (XPS), may give the information of crystal structure, impedance, orientation, surface morphology, bandgap and optical images of α-MoO₃. Our synthesis method can also be generalized to other transition metal oxides (WO₃) for future flexible electronic devices.