Effect of Pt Decoration on the Optical Properties of Pristine and Defective MoS₂: An Ab-Initio Study

Using structural relaxation calculations and first-principles molecular dynamics (FPMD), we performed numerical simulations to explore the interaction of a 2D MoS₂ surface and a platinum atom, calculating the optical properties of the resulting material. We explored three initial positions for the interaction of the Pt atom and the pristine MoS₂ surface, plus another position between Pt and the MoS₂ surface with a sulfur vacancy V_S. The surface absorbed the Pt atom in all cases considered, with absorption energies ranging from -2.77 eV to -5.83 eV. We calculated the optical properties and band structure of the two cases with the largest absorption energies (-3.45 eV and -5.83 eV). The pristine MoS₂ is a semiconductor with a gap of around 1.80 eV. With the adsorption of the Pt atom (the -3.45 eV case), the material reduces its band gap to 0.95 eV. Additionally, the optical absorption in the visible range is greatly increased. The energy band structure of the 2D MoS₂ with a sulfur vacancy V_S shows a band gap of 0.74 eV, with consequent changes in its optical properties. After the adsorption of Pt atoms in the V_S vacancy, the material has a band gap of 1.06 eV. In this case, the optical absorption in the visible range increases by about eight times. The reflectivity in the infrared range gets roughly doubled for both situations of the Pt-absorbed atom considered. Finally, we performed two FPMD runs at 300 K to test the stability of the cases with the lowest and highest absorption energies observed, confirming the qualitative results obtained with the structural relaxations.