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A popular 2D active material, molybdenum disulfide (MoS₂), just got a platinum upgrade at an atomic level. A study led by researchers from the University of Vienna and Vienna University of Technology embedded individual platinum (Pt) atoms onto an ultrathin MoS₂ monolayer and, for the first time, pinpointed their exact positions within the lattice with atomic precision.

The study, in the journal Nano Letters, achieved this feat with an innovative approach that integrates targeted defect creation in the MoS₂ monolayer, controlled platinum deposition, and a high-contrast computational microscopic imaging technique—ptychography.

The researchers believe that this new strategy for ultra-precise doping and mapping offers new pathways for understanding and engineering atomic-scale features in 2D systems.

2D monolayer MoS₂, an intrinsic direct band gap semiconductor, thanks to its large surface-to-volume ratio, has garnered particular attention and is being widely explored as the active component in next-generation catalysts and gas sensors. However, its potential is constrained by the inherent chemical inertness of its flat surface, which significantly limits catalytic activity.

Studies have shown that material engineering strategies, such as substitutional doping—a single heteroatom replaces one or more lattice atoms—can be a simple and effective method to overcome this issue. This technique of material design creates active centers on the material surface that act as tiny chemical reactors where reactants combine, or gas molecules can dock at predetermined locations.

Substitution at sulfur (S) sites in MoS₂ has been demonstrated for more than half of the periodic table, but atomic-scale confirmation of where and where the substitutions occur remains limited.

Although theoretical predictions strongly support Pt substitution as a means to create catalytically active sites and boost sensing capabilities, experimental exploration of Pt-doped MoS₂ has been minimal.

The researchers of this study initiated their three-step process to incorporate and map Pt on a 2D MoS₂ surface with defect engineering.

They irradiated the material's surface with a stream of low-energy helium ions to produce controlled microscopic defects in the form of atomic vacancies for the Pt atoms to occupy.

The second step involved evaporating Pt atoms onto the samples, filling in the vacancies created. The next step was detecting the exact location of doping.

Since conventional microscopic techniques often fail to distinguish between different types of defects, the researchers chose single-sideband ptychography (SSB), a high-resolution and high-contrast imaging method that relies on electron diffraction patterns.

Using SSB, the researchers were able to pinpoint both the dopants and contaminants like carbon. The results revealed that Pt atoms preferentially occupied sulfur vacancy sites, with over 80% of the incorporated atoms at V_1S defects, while the remaining atoms settled at V_2s (12%) and V_Mo (8%) sites. Once incorporated onto MoS₂, the Pt atoms exhibited high stability even at room temperature.

The study successfully demonstrated the ability to engineer materials at the atomic level, presenting new avenues for designer functional materials.

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