Intercalation Leads to Inverse Layer Dependence of Friction on Chemically Doped MoS_{2}

Acikgoz, Ogulcan; Guerrero, Enrique Durán; Yanılmaz, Alper; Dagdeviren, Omur E.; Çelebi, Cem; Strubbe, David A.; Baykara, Mehmet Z.

doi:10.48550/arxiv.2007.05805

Cited by 2 publications

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“…48 Drops in Raman intensities of the A 1g peak have been associated with Re-intercalated MoS 2 and may explain frictional losses in many-layered systems through enhanced EPC. 47 In our systems, only the Mo-substituted shows substantial changes in intensities, whereas other sites stay within 10% of the pristine peak.…”

Section: Resultsmentioning

confidence: 58%

“…41 Re doping has been shown to go against this trend-a decreasing layer count decreases friction despite increased electron-phonon interactions measured as a decrease in the A 1g peak height. 47 The importance of the Raman active modes encompasses the identification of structural differences and as a measurement of EPC, 48 we have thus included Raman calculations in our results. Although we find no experimental comparisons of infrared spectroscopy on doped MoS 2 , we found strong unique IR activity related to Ni inclusion so we have included these results as well.…”

Section: Introductionmentioning

confidence: 99%

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Phase Stability and Raman/IR Signatures of Ni-Doped MoS$_2$ from Density-Functional Theory Studies

Guerrero,

Karkee,

Strubbe

2020

Preprint

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Ni-doped MoS 2 is a layered material that is known to have useful tribological, optoelectronic, and catalytic properties. So far, experiment and theory regarding doped MoS 2 has focused mostly on monolayers, small flakes, or nanoparticles, and an understanding of how Ni doping alters properties in bulk is lacking. We use density functional theory calculations to determine the structure, mechanical properties, electronic properties, and formation energies of bulk Ni-doped 2H-MoS 2 as a function of the doping concentration. We find four meta-stable structures of Ni-doped MoS 2 : Mo substitution, S substitution, and tetrahedral (t-site) and octahedral (o-site) intercalation. We compute relative formation energies and create phase diagrams as a function of chemical potential to guide experimental synthesis. A convex hull analysis shows that the t-site intercalation (favored over o-site) is quite stable against phase segregation and compared to other compounds containing Ni, Mo, and S. Intercalation is found not to significantly change the c-parameter due to forming strong covalent bonds between layers. Ni doping creates new states in the electronic density of states in MoS 2 and shifts the Fermi level, which can be of interest for tuning the electronic and optical properties. We calculate the infrared and Raman spectra and find new peaks and shifts in existing peaks that are unique to each dopant site, and therefore may be used to identify the dopant site experimentally, which has been a challenge to do conclusively.Ni doping in bulk 2H-MoS 2 and the effects on materials properties as computed by density functional theory (DFT).Much previous work about MoS 2 , especially doping, has been motivated by catalysis.MoS 2 has properties that are desirable in photo-, electro-, and thermocatalysis. 6 The ease of cleaving means that high surface areas are obtainable. Strong light absorption, favorable bandgap, and a large surface are useful properties for photocatalysis. 6 On its own, however, MoS 2 has poor intrinsic catalytic activity. Defects, especially at edge sites, 9-12 are generally regarded as the active sites for catalysis. A common strategy to enhance the catalytic activity is the introduction of dopants. 13 Group V transition metals (V, Ta, Nb) dopants have been found to create catalyst for the adsorption of small gas molecules. 6,13,14 Co and Ni doping at the edge sites have been studied theoretically 9,15 and experimentally 8,11,16 in some detail for their ability to adsorb hydrogen. These experiments and DFT simulations suggest that Ni replaces Mo at the edge of small MoS 2 flakes and, when it does, the material has an increased efficiency in the hydrogen evolution reaction. While edge sites of MoS 2 have been deemed the most active sites, 12 intercalation by Na, Co, Ni, and Ca has also been shown to increase catalytic activity in 1T-MoS 2 . 17 MoS 2 , especially as a monolayer, shows promise for optoelectronic applications such as photovoltaics 18 or LEDs. 19 As the number of layers is reduced, the bandgap (≈1...

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Section: Resultsmentioning

confidence: 58%

Section: Introductionmentioning

confidence: 99%

Phase Stability and Raman/IR Signatures of Ni-Doped MoS$_2$ from Density-Functional Theory Studies

Guerrero,

Karkee,

Strubbe

2020

Preprint

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“…It is also important in macroscale applications such as solid lubrication. [2,15] In this work, we study both bulk and few-layer systems of Re-doped MoS 2 with particular focus on implications for friction and atomic force microscopy (AFM). a eguerrero23@ucmerced.edu b dstrubbe@ucmerced.edu MoS 2 is an effective solid lubricant owing to the ease of shearing along the basal planes.…”

Section: Introductionmentioning

confidence: 99%

“…[18] Surprising opposite trends in friction have been measured for Re-doped MoS 2 however. [15] The consensus in the literature is that Re in monolayer MoS 2 substitutes for Mo, based on annular dark-field imaging, [9,10] scanning atomic tomography, [13] formation energy calculations, [6] and a general chemical similarity between Mo and Re. In bulk, neighboring layers allow for the possibility of intercalation, and so the favored site is unclear and has not been established by experiments, which are not necessarily able to distinguish between the sites in a multi-layer structures.…”

Section: Introductionmentioning

confidence: 99%

“…In bulk, neighboring layers allow for the possibility of intercalation, and so the favored site is unclear and has not been established by experiments, which are not necessarily able to distinguish between the sites in a multi-layer structures. In particular, there is some experimental evidence of intercalation, [15,19] as well as DFT studies indicating the stability of other transition metals in tetrahedral intercalation, [20,21] making this and other possibilities worth investigating.…”

Section: Introductionmentioning

confidence: 99%

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Structure, friction, and Raman spectroscopy of Re-doped bulk MoS$_2$ from first principles

Guerrero¹,

Strubbe²

2022

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Doping MoS 2 with Re is known to alter the electronic, structural, and tribological properties.Re-doped MoS 2 has been mainly studied in monolayer or few-layer form, but can also be relevant for applications in many-layer or bulk form. In this work, we use density functional theory to explore the phase stability, Raman spectra, and atomic force microscopy (AFM) sliding interactions of bulk Re-doped MoS 2 . We consider the possibility of the Re dopant existing at different locations and provide experimentally distinguishable characteristics of the most likely sites-Mo-substitution and tetrahedral (t-) intercalation. We demonstrate and benchmark an approach to calculate Raman spectra of doped materials with metallic densities of states by using atomic Raman tensors from the pristine material. Applying this method to the metallic Re-doped structures, we find consistent shifts in the Raman-active peaks depending on Re dopant position: redshifts in both A 1g and E 1 2g peaks in the t-intercalated case versus a redshift for A 1g and blueshift for E 1 2g peaks in the Mo-substituted case. AFM friction forces, if the MoS 2 surface remains flat and unpuckered, are increased by Re dopants, similar for Mo-substitution and t-intercalation, and would decrease with the number of layers.

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Intercalation Leads to Inverse Layer Dependence of Friction on Chemically Doped MoS_{2}

Cited by 2 publications

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Phase Stability and Raman/IR Signatures of Ni-Doped MoS$_2$ from Density-Functional Theory Studies

Phase Stability and Raman/IR Signatures of Ni-Doped MoS$_2$ from Density-Functional Theory Studies

Structure, friction, and Raman spectroscopy of Re-doped bulk MoS$_2$ from first principles

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