Demonstration of the key substrate-dependent charge transfer mechanisms between monolayer MoS2 and molecular dopants

Abstract

Tuning the Fermi level (E F ) in two-dimensional transition metal dichalcogenide (TMDC) semiconductors is crucial for optimizing their application in (opto-)electronic devices. Doping by molecular electron acceptors and donors has been suggested as a promising method to achieve E F -adjustment. Here, we demonstrate that the charge transfer (CT) mechanism between TMDC and molecular dopant depends critically on the electrical nature of the substrate as well as its electronic coupling with the TMDC. Using angle-resolved ultraviolet and X-ray photoelectron spectroscopy, we reveal three fundamentally different, substratedependent CT mechanisms between the molecular electron acceptor 1,3,4,5,7,8-hexafluorotetracyano-naphthoquinodimethane (F 6 TCNNQ) and a MoS 2 monolayer. Our results demonstrate that any substrate that acts as charge reservoir for dopant molecules can prohibit factual doping of a TMDC monolayer. On the other hand, the three different CT mechanisms can be exploited for the design of advanced heterostructures, exhibiting tailored electronic properties in (opto-)electronic devices based on two-dimensional semiconductors.

Temperature‐Dependent Electronic Ground‐State Charge Transfer in van der Waals Heterostructures

“…[8,9] Furthermore, it has been recognized that strong molecular electron acceptors and donors can be employed as dopants for numerous 2D semiconductors, particularly for transition metal dichalcogenides (TMDCs). [10][11][12][13][14] This doping, on the one hand, allows controlling the Fermi level (E F ) position and mobile carrier density in the semiconductor, and, on the other hand, enables manipulation of optical quasiparticles, such as charged excitons (positive or negative trions) in TMDC monolayers. [15][16][17][18][19] Such vdW heterostructures can be ideal model systems for exploring intriguing physical phenomena, [20,21] and they can pave the way for a broader class of device applications.…”

Thermally Activated Gold‐Mediated Transition Metal Dichalcogenide Exfoliation and a Unique Gold‐Mediated Transfer

“…The large monolayer areas achieved here allow to study the electronic structure of MoS 2 , in principle on any substrate, using standard photoemission spectroscopy without experiencing issues with sample charging [17] (details in Figure S4, Supporting Information). The lack of Mo 6þ peaks in the Mo3d core-level region indicates the absence of oxidation, [24][25][26] rendering our exfoliation/transfer process a suitable route for high-quality monolayers. Furthermore, the complete etching and removal of gold after transfer were confirmed ( Figure S5, Supporting Information).…”

Breast cancer biomarker detection through the photoluminescence of epitaxial monolayer MoS2 flakes

“…The two main peaks are located at 384 cm −1 and 404 cm −1 , which belong to the main phonon vibrations E 1 2g and A 1g , respectively 23 . The wavenumber difference between these two peaks (20 cm −1 ) is used as a fingerprint of the monolayer character of the material 24 , although some differences can arise from using different excitation lasers 23 or substrates 25,26 . The ratio of the intensities A 1g /E 1 2g is 1.927.…”

“…At the same time, charge transfer mechanisms between MoS 2 monolayer and other molecules (or layers) have been reported recently 43,44 and validated by means of density functional theory computations 45 . Interestingly, this charge transfer mechanism was found to be substrate-dependent too 26 . Therefore, a combination of these two phenomena (change in the dielectric function and charge transfer) can explain the results found.…”