Christian Tessarek, Oleg Gridenco, Martin Wiesing, Jan Müssener, Stephan Figge, Kathrin Sebald, Jürgen Gutowski, Martin Eickhoff

ACS Applied Nano Materials (2020) 3, 7490-7498

http://doi.org/10.1021/acsanm.0c01104

Laser-thinning of 2D materials such as MoS₂ is a promising approach for a local reduction of the number of multilayers down to a monolayer. For a precise control of the thinning process real-time monitoring is required. In this work, short-wavelength lasers emitting at 325 or 406 nm respectively are used for laser-thinning and simultaneous Raman or photoluminescence spectroscopy of MoS₂. The time evolution of the Raman and photoluminescence bands during the process shows a layer-by-layer thinning of MoS₂ and a transformation into amorphous MoO_x in an oxygen-containing atmosphere. In addition to the E_2g¹ and A_1g Raman modes, the E_1g, B_2g¹, and second-order modes are analyzed by using the 325 nm laser for excitation to achieve a more accurate determination of the number of layers. As a promising alternative, photoluminescence spectroscopy is used to monitor the thinning progress by analysis of the emission energy and intensity of the direct as well as the indirect band gap transition. Atomic force microscopy measurements show an increased total height of the laser-treated region after thinning of MoS₂ due to the presence of transformed MoO_x. Local micropatterning of a bilayer is also demonstrated by laser-thinning down to a monolayer at selected positions. The results show a new monitoring approach for controlled fabrication of 2D monolayers.