Electronic Coupling in Metallophthalocyanine-Transition Metal Dichalcogenide Mixed-Dimensional Heterojunctions.

Amsterdam, Samuel H; Stanev, Teodor K; Zhou, Qunfei; Lou, Alexander J-T; Bergeron, Hadallia; Darancet, Pierre; Hersam, Mark C; Stern, Nathaniel P et al. · ACS Nano · 2019

basic_science · Level V

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Abstract

Mixed-dimensional heterojunctions, such as zero-dimensional (0D) organic molecules deposited on two-dimensional (2D) transition metal dichalcogenides (TMDCs), often exhibit interfacial effects that enhance the properties of the individual constituent layers. Here we report a systematic study of interfacial charge transfer in metallophthalocyanine (MPc) - MoS<sub>2</sub> heterojunctions using optical absorption and Raman spectroscopy to elucidate M core (M = first row transition metal), MoS<sub>2</sub> layer number, and excitation wavelength effects. Observed phenomena include the emergence of heterojunction-specific optical absorption transitions and strong Raman enhancement that depends on the M identity. In addition, the Raman enhancement is tunable by excitation laser wavelength and MoS<sub>2</sub> layer number, ultimately reaching a maximum enhancement factor of 30x relative to SiO<sub>2</sub> substrates. These experimental results, combined with density functional theory (DFT) calculations, indicate strong coupling between nonfrontier MPc orbitals and the MoS<sub>2</sub> band structure as well as charge transfer across the heterojunction interface that varies as a function of the MPc electronic structure.