Two-dimensional lattice anchoring strategy for the synthesis of atomically thin Mo_0.92Er_0.08S₂ rare-earth materials

Two-dimensional rare-earth (2D RE) materials have attracted significant research interest in fields such as electronics and optoelectronics, owing to their abundant 4f electron transitions and diverse luminescent properties. Currently, the preparation of RE-doped MoS2 has been achieved through strategies such as pre-deposition of RE precursors, controlled release of RE precursors, and pulsed laser deposition. Furthermore, the properties of these two-dimensional systems, such as upconversion luminescence resulting from the modulated 4f energy levels, were thoroughly investigated. Nevertheless, the synthesis of large-area and atomically thick 2D RE materials, which are essential for logic operations and imaging chips, remains a significant challenge. Herein, we report a 2D lattice anchoring strategy, which enables the anchoring of erbium (Er) atoms into the MoS2 lattice for the synthesis of high-quality, large-area monolayer Mo0.92Er0.08S2, thereby facilitating the investigation of its electrical and photoelectronic properties. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) confirmed that Er atoms are uniformly anchored into the MoS2 host lattice by directly substituting for Mo atoms. The Er doping concentration in the material was determined employing X-ray Photoelectron Spectroscopy (XPS) and STEM. By controlling the anchoring temperature and the concentration of the erbium precursor, the Er anchoring ratio within the lattice was tuned from 0.2% to 8%. A high growth temperature enables the overcoming of lattice strain induced by RE doping and facilitates an increase in the doping concentration. In addition, NaCl acts as a catalyst to lower the melting point of the rare-earth precursor and facilitates the lateral epitaxial growth of Mo0.92Er0.08S2. And, the structurally stable porous molecular sieve at high temperatures provides favorable channels for the controlled release of the RE precursor. The synergistic strategy employing high growth temperature, NaCl and molecular sieves is therefore pivotal in realizing high-concentration Er doping within monolayer MoS2. Interestingly, as the Er doping concentration increases, the sample morphology evolves from regular triangles to irregular circular shapes. This is likely attributed to the disruption of the pristine MoS2’s threefold symmetry by the high-concentration Er doping. Compared to pristine MoS2 monolayer, the monolayer Mo0.92Er0.08S2 device exhibited a significantly enhanced carrier mobility and photoresponse rate. This effect originates from the rich 4f electronic states of rare-earth dopants, functioning as highly effective light absorbers. Consistent with previous studies on RE hybrid materials, this effect enhances the photoconversion efficiency of the intrinsic MoS2, imparting superior photocurrent and response speed. In our rare-earth-doped materials, the charge transfer efficiency of non-radiative transitions between the rare-earth ions and the host matrix is enhanced, thereby serving as the proposed key mechanism for the improved photoelectronic performance. Our work provides a novel approach for creating large-area 2D RE materials, thereby paving the way for the industrial development of RE-based electronics and optoelectronics.