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DOE OSTI2020

Materials Data on Fe(MoS2)2 by Materials Project

FeMo2S4 crystallizes in the monoclinic Cc space group. The structure is three-dimensional. there are four inequivalent Mo+2.50+ sites. In the first Mo+2.50+ site, Mo+2.50+ is bonded to six S2- atoms to form MoS6 octahedra that share corners with six FeS6 octahedra, edges with six MoS6 octahedra, and a faceface with one FeS6 octahedra. The corner-sharing octahedra tilt angles range from 48–56°. There are a spread of Mo–S bond distances ranging from 2.37–2.58 Å. In the second Mo+2.50+ site, Mo+2.50+ is bonded to six S2- atoms to form MoS6 octahedra that share corners with six FeS6 octahedra, edges with six MoS6 octahedra, and a faceface with one FeS6 octahedra. The corner-sharing octahedra tilt angles range from 49–56°. There are a spread of Mo–S bond distances ranging from 2.37–2.59 Å. In the third Mo+2.50+ site, Mo+2.50+ is bonded to six S2- atoms to form distorted MoS6 octahedra that share corners with six FeS6 octahedra, edges with six MoS6 octahedra, and a faceface with one FeS6 octahedra. The corner-sharing octahedra tilt angles range from 49–57°. There are a spread of Mo–S bond distances ranging from 2.37–2.61 Å. In the fourth Mo+2.50+ site, Mo+2.50+ is bonded to six S2- atoms to form distorted MoS6 octahedra that share corners with six FeS6 octahedra, edges with six MoS6 octahedra, and a faceface with one FeS6 octahedra. The corner-sharing octahedra tilt angles range from 50–57°. There are a spread of Mo–S bond distances ranging from 2.37–2.63 Å. There are two inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to six S2- atoms to form FeS6 octahedra that share corners with twelve MoS6 octahedra, edges with two equivalent FeS6 octahedra, and faces with two MoS6 octahedra. The corner-sharing octahedra tilt angles range from 48–57°. There are a spread of Fe–S bond distances ranging from 2.34–2.48 Å. In the second Fe3+ site, Fe3+ is bonded to six S2- atoms to form FeS6 octahedra that share corners with twelve MoS6 octahedra, edges with two equivalent FeS6 octahedra, and faces with two MoS6 octahedra. The corner-sharing octahedra tilt angles range from 49–57°. There are a spread of Fe–S bond distances ranging from 2.34–2.52 Å. There are eight inequivalent S2- sites. In the first S2- site, S2- is bonded in a 5-coordinate geometry to three Mo+2.50+ and two Fe3+ atoms. In the second S2- site, S2- is bonded in a 5-coordinate geometry to three Mo+2.50+ and two Fe3+ atoms. In the third S2- site, S2- is bonded in a 4-coordinate geometry to three Mo+2.50+ and one Fe3+ atom. In the fourth S2- site, S2- is bonded in a 4-coordinate geometry to three Mo+2.50+ and one Fe3+ atom. In the fifth S2- site, S2- is bonded in a 4-coordinate geometry to three Mo+2.50+ and one Fe3+ atom. In the sixth S2- site, S2- is bonded in a 4-coordinate geometry to three Mo+2.50+ and one Fe3+ atom. In the seventh S2- site, S2- is bonded in a 5-coordinate geometry to three Mo+2.50+ and two Fe3+ atoms. In the eighth S2- site, S2- is bonded in a 5-coordinate geometry to three Mo+2.50+ and two Fe3+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Enabling room temperature ferromagnetism in monolayer MoS2 via in situ iron-doping

Abstract Two-dimensional semiconductors, including transition metal dichalcogenides, are of interest in electronics and photonics but remain nonmagnetic in their intrinsic form. Previous efforts to form two-dimensional dilute magnetic semiconductors utilized extrinsic doping techniques or bulk crystal growth, detrimentally affecting uniformity, scalability, or Curie temperature. Here, we demonstrate an in situ substitutional doping of Fe atoms into MoS 2 monolayers in the chemical vapor deposition growth. The iron atoms substitute molybdenum sites in MoS 2 crystals, as confirmed by transmission electron microscopy and Raman signatures. We uncover an Fe-related spectral transition of Fe:MoS 2 monolayers that appears at 2.28 eV above the pristine bandgap and displays pronounced ferromagnetic hysteresis. The microscopic origin is further corroborated by density functional theory calculations of dipole-allowed transitions in Fe:MoS 2 . Using spatially integrating magnetization measurements and spatially resolving nitrogen-vacancy center magnetometry, we show that Fe:MoS 2 monolayers remain magnetized even at ambient conditions, manifesting ferromagnetism at room temperature.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Bioinspired Activation of N 2 on Asymmetrical Coordinated Fe Grafted 1T MoS 2 at Room Temperature

Inspired by the nitrogen fixation process on MoFe nitrogenase, asymmetrical coordinated Fe grafted onto 1T MoS 2 were successfully synthesized. The unique electron -rich structure with asymmetrical coordination made the 1T Fe 0.1 Mo 0.9 S 2 layered material actively react with water and dinitrogen at room temperature and atmosphere pressure. Subsequently, ammonia can be produced with a yield of 800 pmol (NH 4 + ) g -1 (12.5% yield in mole). The activation, fixation and reduction of dinitrogen were confirmed by isotopically labeled experiments. The location and the specific coordination environment of grafted Fe in Fe-Mo-S were further determined by X-ray absorption spectroscopy analysis. Our work demonstrates that the nitrogen fixation and reduction for ammonia at room temperature without any chemical and electrochemical assistance is distinctly different from traditional bionic -inspired nitrogen fixation process. The mechanism of the activation and reduction of N 2 was further investigated by density functional theory calculation and Raman spectra. Compared with 1T MoS 2 , the enriched electron nature and asymmetrical coordination of Fe in Fe-Mo-S materials play a critical role in the bioinspired activation of N 2 at ambient condition.

1T MoS2↗

DOE OSTI2022

Effect of Support on Oxygen Reduction Reaction Activity of Supported Iron Porphyrins

In this work, we report the oxygen reduction reaction (ORR) activity in acid of an Fe porphyrin on different supports. While the activity is high (E 1/2 = 0.34 V vs RHE with n = 3.8) when the Fe porphyrin is adsorbed on XC72 (a graphitic carbon), this activity is much lower when the porphyrin is adsorbed on either MoS 2 (E 1/2 = -0.15 V vs RHE with n = 2.2) or g-C 3 N 4 (E 1/2 = -0.24 V vs RHE with n = 3.1). Electron paramagnetic resonance (EPR), X-ray absorption fine structure (XAFS), and magnetometry measurements show the electronic structure around the Fe center is the same for all three supports. Only the Fe porphyrin supported on XC72 exhibits a pH dependence in its ORR activity. This observation, coupled with the increased hydrophilicity of XC72 relative to the other supports, suggests that the support-electrolyte interaction controls the ORR activity. Modification of MoS 2 to increase its hydrophilicity results in a more active ORR catalyst.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Crystal structure and shape selection in the growth of 3D metallic crystallites on layered materials: Fe on MoS 2

Nucleation and growth of supported 3D metal clusters or crystallites during deposition on MoS 2 , or on other weakly-adhering layered materials, can potentially produce diverse growth shapes, and even crystal structures differing from the bulk metal. For Fe deposition on MoS 2 , SEM and AFM observations reveal three distinct crystallite shapes. By comparison with atomistic structure models incorporating realistic Fe-MoS 2 interface structures, here we conclude that these are: triangular fcc(111) pyramids with sloped {100} side facets; bcc(110) A-frame tents with sloped {100} side facets; and bcc(110) mesas with vertical {100} and {110} side facets. The following picture is proposed for the competitive formation of clusters and crystallites with different structures: (i) small nanoclusters formed at the onset of deposition exhibit facile fluxional dynamics allowing sampling of different crystal structures and shapes; (ii) sufficient fluxionality implies a Boltzmann distribution of sampled structures, and thus coexistence of different structures follows from the demonstrated similar energies for those structures; (iii) growing clusters reach a threshold size above which the characteristic time scale for restructuring exceeds that for cluster growth. Thereafter, clusters are locked-in to a specific crystal structure and shape as revealed by imaging of larger crystallites. Despite a penalty for fcc(111) over bcc(111) pyramids based on bulk energetics, favorable surface and interface energies makes them preferable for smaller sizes.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Dilute magnetic impurity-induced effective phonon magnetic moment in Fe-doped monolayer MoS 2

Realization of large effective phonon magnetic moment in monolayer MoS 2 has established an important route for exploring intriguing magnetic phenomena in a nonmagnetic material. The sizable coupling between the orbital transition and the circularly polarized phonon results in the large effective phonon magnetic moment. In this work, using magneto-Raman spectroscopy, we investigate substitutional doping of magnetic atoms as a tuning knob of the electronic and phononic properties of MoS 2 . We show that Fe-doping polarizes the spin of the conduction bands and introduces a localized Fe band underneath the conduction band. As a result, an additional orbital transition between the Mo 4d and Fe 3d states emerges, producing an orbital-phonon hybridized mode at 283 cm −1 . Our magnetic field dependent measurements demonstrate that this new mode carries 2.8 $\mu_{\mathrm{B}}$ effective phonon magnetic moment, which is comparable to that of the undoped MoS 2 . Moreover, even though a long-range magnetic order is absent in Fe-doped MoS 2 , the local magnetic moment of Fe modifies the nature of the spin fluctuation, producing monotonically increasing quasielastic scattering spectral weight as temperature decreases. Our results highlight two-dimensional dilute magnetic semiconductors synthesized by substitutional doping as a promising material platform to manipulate the phonon magnetic moment through orbital-phonon coupling.

36 MATERIALS SCIENCE↗