Supplement Number 1

The supplementary document provides detailed insights into the fabrication, characterization, and experimental evaluation of a hybrid spintronic terahertz emitter (STE) based on a cobalt (Co) layer and a monolayer two-dimensional (2D) semiconductor WSe2. It outlines the synthesis of the WSe2 monolayer via chemical vapor deposition (CVD), subsequent Co deposition using magnetron sputtering under controlled conditions, and protective silicon capping to prevent oxidation. Advanced techniques like Raman spectroscopy and photoluminescence (PL) confirm the structural integrity of WSe2 after processing. The study explores THz emission characteristics through time-domain spectroscopy (THz-TDS), analyzing spin-to-charge conversion effects, polarization control via external magnetic fields, and the influence of pump beam polarization. The results highlight tunable THz polarization states and reduced magnetic anisotropy due to WSe2's crystalline properties, underscoring the emitter's potential for ultrafast optoelectronic applications.