Single-layer MoS2is a direct-gap semiconductor whose band edges character is dominated by the d-orbitals of the Mo atoms. It follows that substitutional doping of the Mo atoms has a significant impact on the material’s electronic properties, namely the size of the band gap and the position of the Fermi level. Here, density functional theory is used along with the G0W0method to examine the effects of substituting Mo with four different transition metal dopants: Nb, Tc, Ta, and Re. Nb and Ta possess one less valence electron than Mo does and are therefore p-type dopants, while Re and Tc are n-type dopants, having one more valence electron than Mo has. Four types of substitutional structures are considered for each dopant species: isolated atoms, lines, three-atom clusters centered on a S atom (c3s), and three-atom clusters centered on a hole (c3h). The c3h structure is found to be the most stable configuration for all dopant species. However, electronic structure calculations reveal that isolated dopants are preferable for efficient n- or p-type performance. Lastly, it is shown that photoluminescence measurements can provide valuable insight into the atomic structure of the doped material. Understanding these properties of substitutionally-doped MoS2can allow for its successful implementation into cutting-edge solid state devices.
Internal magnetic moments induced by magnetic dopants in MoS2monolayers are shown to serve as a new means to engineer valley Zeeman splitting (VZS). Specifically, successful synthesis of monolayer MoS2doped with the magnetic element Co is reported, and the magnitude of the valley splitting is engineered by manipulating the dopant concentration. Valley splittings of 3.9, 5.2, and 6.15 meV at 7 T in Co‐doped MoS2with Co concentrations of 0.8%, 1.7%, and 2.5%, respectively, are achieved as revealed by polarization‐resolved photoluminescence (PL) spectroscopy. Atomic‐resolution electron microscopy studies clearly identify the magnetic sites of Co substitution in the MoS2lattice, forming two distinct types of configurations, namely isolated single dopants and tridopant clusters. Density functional theory (DFT) and model calculations reveal that the observed enhanced VZS arises from an internal magnetic field induced by the tridopant clusters, which couples to the spin, atomic orbital, and valley magnetic moment of carriers from the conduction and valence bands. The present study demonstrates a new method to control the valley pseudospin via magnetic dopants in layered semiconducting materials, paving the way toward magneto‐optical and spintronic devices.
more » « less- Award ID(s):
- 1729787
- NSF-PAR ID:
- 10455099
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 32
- Issue:
- 11
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract In recent years, there has been a substantial surge in the investigation of transition‐metal dichalcogenides such as MoS2as a promising electrochemical catalyst. Inspired by denitrification enzymes such as nitrate reductase and nitrite reductase, the electrochemical nitrate reduction catalyzed by MoS2with varying local atomic structures is reported. It is demonstrated that the hydrothermally synthesized MoS2containing sulfur vacancies behaves as promising catalysts for electrochemical denitrification. With copper doping at less than 9% atomic ratio, the selectivity of denitrification to dinitrogen in the products can be effectively improved. X‐ray absorption characterizations suggest that two sulfur vacancies are associated with one copper dopant in the MoS2skeleton. DFT calculation confirms that copper dopants replace three adjacent Mo atoms to form a trigonal defect‐enriched region, introducing an exposed Mo reaction center that coordinates with Cu atom to increase N2selectivity. Apart from the higher activity and selectivity, the Cu‐doped MoS2also demonstrates remarkably improved tolerance toward oxygen poisoning at high oxygen concentration. Finally, Cu‐doped MoS2based catalysts exhibit very low specific energy consumption during the electrochemical denitrification process, paving the way for potential scale‐up operations.
-
We report a comprehensive study on the effects of rhenium doping on optical properties and photocarrier dynamics of MoS 2 monolayer, few-layer, and bulk samples. Monolayer and few-layer samples of Re-doped (0.6%) and undoped MoS 2 were fabricated by mechanical exfoliation, and were studied by Raman spectroscopy, optical absorption, photoluminescence, and time-resolved differential reflection measurements. Similar Raman, absorption, and photoluminescence spectra were obtained from doped and undoped samples, indicating that the Re doping at this level does not significantly alter the lattice and electronic structures. Red-shift and broadening of the two phonon Raman modes were observed, showing the lattice strain and carrier doping induced by Re. The photoluminescence yield of the doped monolayer is about 15 times lower than that of the undoped sample, while the photocarrier lifetime is about 20 times shorter in the doped monolayer. Both observations can be attributed to diffusion-limited Auger nonradiative recombination of photocarriers at Re dopants. These results provide useful information for developing a doping strategy of MoS 2 for optoelectronic applications.more » « less
-
more » « less
Abstract The ability to control the density and spatial distribution of substitutional dopants in semiconductors is crucial for achieving desired physicochemical properties. Substitutional doping with adjustable doping levels has been previously demonstrated in 2D transition metal dichalcogenides (TMDs); however, the spatial control of dopant distribution remains an open field. In this work, edge termination is demonstrated as an important characteristic of 2D TMD monocrystals that affects the distribution of substitutional dopants. Particularly, in chemical vapor deposition (CVD)‐grown monolayer WS2, it is found that a higher density of transition metal dopants is always incorporated in sulfur‐terminated domains when compared to tungsten‐terminated domains. Two representative examples demonstrate this spatial distribution control, including hexagonal iron‐ and vanadium‐doped WS2monolayers. Density functional theory (DFT) calculations are further performed, indicating that the edge‐dependent dopant distribution is due to a strong binding of tungsten atoms at tungsten‐zigzag edges, resulting in the formation of open sites at sulfur‐zigzag edges that enable preferential dopant incorporation. Based on these results, it is envisioned that edge termination in crystalline TMD monolayers can be utilized as a novel and effective knob for engineering the spatial distribution of substitutional dopants, leading to in‐plane hetero‐/multi‐junctions that display fascinating electronic, optoelectronic, and magnetic properties.
-
more » « less
Abstract The electrochemical CO2reduction reaction (CO2RR) is a promising approach to achieving sustainable electrical‐to‐chemical energy conversion and storage while decarbonizing the emission‐heavy industry. The carbon‐supported, nitrogen‐coordinated, and atomically dispersed metal sites are effective catalysts for CO generation due to their high activity, selectivity, and earth abundance. Here, we discuss progress, challenges, and opportunities for designing and engineering atomic metal catalysts from single to dual metal sites. Engineering single metal sites using a nitrogen‐doped carbon model was highlighted to exclusively study the effect of carbon particle sizes, metal contents, and M−N bond structures in the form of MN4moieties on catalytic activity and selectivity. The structure‐property correlation was analyzed by combining experimental results with theoretical calculations to uncover the CO2to CO conversion mechanisms. Furthermore, dual‐metal site catalysts, inheriting the merits of single‐metal sites, have emerged as a new frontier due to their potentially enhanced catalytic properties. Designing optimal dual metal site catalysts could offer additional sites to alter the surface adsorption to CO2and various intermediates, thus breaking the scaling relationship limitation and activity‐stability trade‐off. The CO2RR electrolysis in flow reactors was discussed to provide insights into the electrolyzer design with improved CO2utilization, reaction kinetics, and mass transport.
