• Affannoukoué, Kévin
• Canulescu, Stela
• Döbeli, Max
• Schou, Jørgen

Abstract

Two-dimensional transition metal dichalcogenides (2D-TMDCs), such as MoS2, have emerged as a<br/>new class of semiconducting materials with distinct optical and electrical properties. The availability<br/>of 2D-TMDCs with distinct band gaps allows for unlimited combinations of TMDC monolayers<br/>(MLs) and enables engineering of van der Waals (vdW) heterostructures with characteristics<br/>fundamentally different compared to the conventional 3D-covalently bounded heterostructures.<br/>Although various 2D materials have been successfully synthesized by mechanical exfoliation or<br/>chemical vapor deposition (CVD), a strategy for the fabrication of 2D heterostructures must be<br/>developed. Here we demonstrate a novel approach for the bottom-up synthesis of TMDC monolayers, namely Pulsed Laser Deposition (PLD) combined with a sulfur evaporation beam. PLD relies on the use of a pulsed laser (ns pulse duration) to induce material transfer from a solid source (such as a sintered target of MoS2) to a substrate (such as Si or sapphire). The deposition rate in PLD is typically much less than a monolayer per pulse, meaning that the number of MLs can be controlled by a careful selection of the number of laser pulses. In the paper, we will discuss the growth of high-quality MoS2 in the form of one or several MLs over large areas and several substrates, such as sapphire, SiO2/Si and indium tin oxide (ITO). This approach allows the synthesis of 2D-TMDCs without the use of catalyst and with a good control of the sulfur vacancies. We have found that the absorption spectra of the MoS2 films exhibit distinct excitonic peaks at ~1.8 and ~2 eV when grown in the presence of a sulfur evaporation beam as compared to those deposited in vacuum. The structure of the PLD-grown MoS2 films will be further discussed based Raman spectroscopy analysis, photoluminescence, as composition/thickness determined by Rutherford backscattering (RBS). Some challenging issues and future directions on the use of PLD for the synthesis of complex heterostructures by PLD will be discussed.

Topics

• impedance spectroscopy
• photoluminescence
• laser emission spectroscopy
• two-dimensional
• tin
• pulsed laser deposition
• Raman spectroscopy
• evaporation
• chemical vapor deposition
• Rutherford backscattering spectrometry
• Indium