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.