Multifunctional Properties of Two-Dimensional Materials, VxWyMo1−x−yS2zSe2(1−z): First-Principles Study

Abstract

First principles calculations were employed to study the multifunctional properties including structural, phonon, electronic, thermal and optical of two dimensional materials, VxWyMo1−x−yS2zSe2(1−z) incorporating both the periodic substitutions and randomly doped structures. The structural analysis reveals that the incorporation of vanadium, sulfur and tungsten alters the bond lengths, bond angles and lattice constants of the pristine of two dimensional, hexagonal molybdenum diselenide (2H-MoSe2). Phonon dispersion spectra confirmed the dynamic stability of the materials with higher frequency modes attributed to smaller atomic mass of sulfur and shorter metal-sulfur bonds. The thermodynamic results indicated substitution and/or doping raises the Helmholtz free energy at low temperatures while enhancing the entropy and specific heat capacity at high temperatures. The modifications enhance thermal performance underscoring the suitability of the substituted or doped systems for optoelectronic and thermal management applications at higher temperature. Electronic structure calculations show at higher vanadium composition, the material exhibits degenerate semiconductor behavior caused by localized 3d states, while at lower doping compositions retains its normal semiconductor properties. In contrast, all substitutions or dilute doping compositions of tungsten preserve the semiconductor character of the material due to the presence of isoelectronic behavior between tungsten and molybdenum atoms. Among all studied compositions, the W0.5Mo0.5S1.5Se0.5 has the smaller band-gap, and the MoS0.125Se1.875 the larger. The dielectric function is computed within the independent particle approximation and considering non-zero dipole matrix elements and energy conservation reveals a strong sensitivity of the optical response to chemical substitution. In general, the findings indicate tuning the types and composition of dopants precise control the material’s properties and enhancing its suitability for infrared optoelectronic and thermal management applications at higher temperature.