Local Manipulation of the Energy Levels of 2D TMDCs on the Microscale Level via Microprinted Self-Assembled Monolayers

2D transition metal dichalcogenides (TMDCs) are atomically-thick semiconductors with great potential for next-generation optoelectronic applications, such as transistors and sensors. Their large surface-to-volume ratio makes them energy-efficient but also extremely sensitive to the physical-chemical surroundings. The latter must be carefully considered when predicting the electronic behavior, such as their energy level alignment, which ultimately affects the charge carrier injection and transport in devices. Here, local doping is demonstrated and thus adjusting the opto-electronic properties of monolayer TMDCs (WSe2 and MoS2) by chemically engineering the surface of the supporting substrate. This is achieved by decorating the substrate by microcontact printing with patterns of two different self-assembled monolayers (SAMs). The SAMs posses distinct molecular dipoles and dielectric constants, significantly influencing the TMDCs electronic and optical properties. By analyzing (on various substrtates), it is confirmed that these effects arise solely from the interaction between SAMs and TMDCs. Understanding the diverse dielectric environments experienced by TMDCs allows for a correlation between electronic and optical behaviours. The changes primarily involve alteration in the electronic band gap width, which can be calculated using the Schottky-Mott rule, incorporating the dielectric screening of the TMDCs surroundings. This knowledge enables accurate prediction of the (opto-)electronic behavior of monolayer TMDCs for advanced device design.