Síntese por deposição química de fase vapor e caracterização estrutural do dissulfeto de molibdênio

Abstract

Advances in research on nanoscale two-dimensional (2D) materials are receiving continuous stimulus and benefiting of the knowledge acquired since the isolation of graphene in 2004. Graphene is composed of a sheet of carbon atoms with a single atomic layer of thickness, has several possibilities of applications in the areas of electronics due the wealth of its mechanical, electrical, thermal and optical properties. However, it is a material that does not have a band gap, which difficult its application in electronics devices. Therefore, new families of nanomaterials with properties similar to graphene are being studied as, for example, the Transition Metal Dichalcogenides (TMDCs). TMDCs are materials that have an energy gap that can be modulated to thickness. This property enables the application of these materials in the areas of electronics and optoelectronics, and can be exploited even in the manufacture of flexible and/or transparent electronics devices. In this work, the growth of molybdenum disulphide (MoS2) was carried out, as well as the study of its structural and optical properties, aiming to obtain the structural quality necessary for its future application in electronics devices. The syntheses were performed using the Chemical Vapor Deposition, a technique that allows large area continuous films to grow under controlled pressure and temperature conditions. MoS2 samples were grown in an inert atmosphere containing Ar gas under atmospheric pressure, with precursor reagents S and MoO3 placed in oven independent regions and subjected to different heating rates. The obtained samples presented different morphologies such as MoS2 growth in the form of films covering large regions of the substrate and triangular regions. Subsequently, the obtained films were characterized by Raman spectroscopy technique, which identifies the number of layers of MoS2 films with monolayer, bilayer, trilayer and bulk characteristics. Under all the different conditions established for obtaining the samples, MoS2 films with monolayer characteristic were obtained. Photoluminescence spectroscopy of MoS2 allowed us to study the optical properties of the synthesized samples. The photoluminescence spectrum showed the transition of gap to the monolayer, bilayer and bulk, by means of the differences of intensities between the peaks. Other technique used for the characterization of the films was scanning electron microscopy/energy dispersive spectroscopy (EDS), which allowed us to observe the morphology of the sample and its chemical compositions. Molybdenum Dioxide (MoO2) was also synthesized, a material from the family of Transition Metal Oxides (TMOs) which has attracted interest due to its optical and electronic properties, used in chemical sensors and electrodes for batteries. MoO2 films present different optical contrasts, and may provide an indication of different numbers of layers. The characterization of the crystals of MoO2 was done by Raman Spectroscopy, which enabled to identify the material, through the characteristics of the peaks. Our results showed that it was possible to grow MoS2 from different morphologies on what the gas flow variation and the amount of MoO3 are factors that influence the growth process CVD.