Microscopic observation of catalytically etched channels and pits in MoS ₂ flakes

With a growing interest in two-dimensional transition metal dichalcogenide (TMD), etching the structure of TMD for further application is a challenge due to its thermal stability by a high melting point. Here, we report on diverse etched structures in MoS ₂ flakes based on the catalytic oxidation using a Co catalyst. After impregnated with a Co precursor, MoS ₂ flakes were oxidized in air by induction heating to obtain an etched structure. As a result, microscopic observation revealed that diverse etched structures in the shape of a channel and a pit were created in the MoS ₂ flakes. Especially, the catalytic etching by CoO nanoparticles produced two types of channels which have an angle of 120° and 150° respectively. Also, a pit with a depth of approximately 3 nm was found on the oxidized surface of MoS ₂ flakes. Our results open a new perspective to control the edge site of TMD flakes including S element as well as MoS ₂ flakes.