Synthesis and structural characterization of MoS₂ micropyramids

Two-dimensional (2D) materials based on molybdenum sulfide (MoS₂) have shown promising applications in semiconductors, optoelectronics, and catalysis. The variety of applications implies a controlled manipulation of purity, shape, and phase of such materials. This work elaborates on the structural characterization of MoS₂ micro-assemblies produced in a chemical vapor deposition (CVD) system with emphasis on the pyramidal structures formed at high temperature and low gas rate, on a silicon dioxide (SiO₂) substrate. A precise control of temperature and gas rate in the CVD process prompts the growth of pyramidal and other micron-size arrangements of MoS₂ layers. An integrative set of high-resolution and analytical electron microscopy techniques, in conjunction with Raman and X-ray photoelectron spectroscopy (XPS), revealed the structural features of the MoS₂ microstructures. Raman and XPS confirmed the presence of MoS₂ and some residual oxide phases. Ultra-high-resolution scanning electron microscopy provided direct observation of the distinctive stacking of layers forming the pyramidal microstructures. Cross section samples from selected structures were done using focused ion beam. An extent of transmission electron microscopy and Cs-corrected scanning transmission electron microscopy (Cs-corrected STEM) results is discussed. This approach allowed to understand the growth mechanism of the triangular MoS₂ microstructures through spiral grow around a screw dislocation, initiated at the center of the assembly.