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Electron-Phonon Interaction in Organic/2D-Transition Metal Dichalcogenide Heterojunctions: A Temperature-Dependent Raman Spectroscopic Study.

ABSTRACT: The heterojunctions of organic/two-dimensional transition metal dichalcogenides (TMDs) have the potential to be used in the next-generation optoelectronic and photonic devices. Herein, we have systemically investigated the temperature-dependent Raman spectroscopy to elucidate the phonon shift and thermal properties of the semiconducting TMD nanosheets grafted by a conjugated polymer (PG-MoS₂ and PG-MoSe₂) forming heterojunctions. Our results reveal that softening of Raman modes of PG-TMDs as temperature increases from 77 to 300 K is due to the negative temperature coefficient (TC) and anharmonicity. The TCs of E¹ _2g and A_1g modes of PG-MoS₂ nanosheets and A_1g mode of PG-MoSe₂ were found to be -0.015, -0.010, and -0.010 cm^-1 K^-1, respectively. The origin of negative TCs is explained on the basis of a double resonance process, which is more active in single- and few-layer MoS₂ and MoSe₂. Interestingly, the temperature-dependent behavior of the phonon modes of PG-MoS₂ and PG-MoSe₂ is similar to that of pristine nanosheets. Grafting by conjugated polymer does not affect the electron-phonon (e-p) interaction in the semiconducting (2H-phase) TMDs, hinting the application potential of such materials in field-effect electronic devices.

SUBMITTER: Sarkar AS

PROVIDER: S-EPMC6641913 | biostudies-literature | 2017 Aug

REPOSITORIES: biostudies-literature

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Publications

Electron-Phonon Interaction in Organic/2D-Transition Metal Dichalcogenide Heterojunctions: A Temperature-Dependent Raman Spectroscopic Study.

Sarkar Abdus Salam AS Pal Suman Kalyan SK

ACS omega 20170808 8

The heterojunctions of organic/two-dimensional transition metal dichalcogenides (TMDs) have the potential to be used in the next-generation optoelectronic and photonic devices. Herein, we have systemically investigated the temperature-dependent Raman spectroscopy to elucidate the phonon shift and thermal properties of the semiconducting TMD nanosheets grafted by a conjugated polymer (PG-MoS<sub>2</sub> and PG-MoSe<sub>2</sub>) forming heterojunctions. Our results reveal that softening of Raman m ...[more]

PMID: 31457725

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Project description:High-entropy (HE) metal chalcogenides are a class of materials that have great potential in applications such as thermoelectrics and electrocatalysis. Layered 2D transition-metal dichalcogenides (TMDCs) are a sub-class of high entropy metal chalcogenides that have received little attention to date as their preparation currently involves complicated, energy-intensive, or hazardous synthetic steps. To address this, a low-temperature (500 °C) and rapid (1 h) single source precursor approach is successfully adopted to synthesize the hexernary high-entropy metal disulfide (MoWReMnCr)S2 . (MoWReMnCr)S2 powders are characterized by powder X-ray diffraction (pXRD) and Raman spectroscopy, which confirmed that the material is comprised predominantly of a hexagonal phase. The surface oxidation states and elemental compositions are studied by X-ray photoelectron spectroscopy (XPS) whilst the bulk morphology and elemental stoichiometry with spatial distribution is determined by scanning electron microscopy (SEM) with elemental mapping information acquired from energy-dispersive X-ray (EDX) spectroscopy. The bulk, layered material is subsequently exfoliated to ultra-thin, several-layer 2D nanosheets by liquid-phase exfoliation (LPE). The resulting few-layer HE (MoWReMnCr)S2 nanosheets are found to contain a homogeneous elemental distribution of metals at the nanoscale by high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) with EDX mapping. Finally, (MoWReMnCr)S2 is demonstrated as a hydrogen evolution electrocatalyst and compared to 2H-MoS2 synthesized using the molecular precursor approach. (MoWReMnCr)S2 with 20% w/w of high-conductivity carbon black displays a low overpotential of 229 mV in 0.5 M H2 SO4 to reach a current density of 10 mA cm-2 , which is much lower than the overpotential of 362 mV for MoS2 . From density functional theory calculations, it is hypothesised that the enhanced catalytic activity is due to activation of the basal plane upon incorporation of other elements into the 2H-MoS2 structure, in particular, the first row TMs Cr and Mn.

Dataset Information

Electron-Phonon Interaction in Organic/2D-Transition Metal Dichalcogenide Heterojunctions: A Temperature-Dependent Raman Spectroscopic Study.

Publications

Electron-Phonon Interaction in Organic/2D-Transition Metal Dichalcogenide Heterojunctions: A Temperature-Dependent Raman Spectroscopic Study.

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