2D Molybdenum disulfide (2D-MoS2) is easily synthesized in its semiconducting 2H phase. In contrast, the metallic-phase 1T-MoS2 is a highly sensitive, metastable, and complex phase that is not naturally occurring. The interest for the metallic phase combined with its instability have resulted in a widespread misrepresentation in academic literature. Based on our current work presented here, we can uphold that many Raman investigations incorrectly identify the spectrum of MoO3 as 1T-MoS2 due to the oxidation of MoS2 samples when exposed to laser irradiation in the presence of air, as commonly performed in Raman measurements. 

The present work focuses on conducting a comprehensive Raman analysis of 1T-MoS2 by investigating the impact of oxidizing atmosphere, laser power, irradiation time, and temperature changes on the sample. Controlling the Raman conditions has allowed to detect a novel spectrum that hints to a new phase triggered by laser heating. This has led to further confusion in the identification of the metallic MoS2 polymorphs. This study seeks to expose the current challenges in characterizing the metallic phase of MoS2, especially when using Raman spectroscopy, which, until now, is considered the most reliable technique for this purpose. These results provide guidance to the next experimental Raman studies as well as possible practical applications for materials engineering.

2D Molybdenum disulfide (2D-MoS2) is easily synthesized in its semiconducting 2H phase. In contrast, the metallic-phase 1T-MoS2 is a highly sensitive, metastable, and complex phase that is not naturally occurring. The interest for the metallic phase combined with its instability have resulted in a widespread misrepresentation in academic literature. Based on our current work presented here, we can uphold that many Raman investigations incorrectly identify the spectrum of MoO3 as 1T-MoS2 due to the oxidation of MoS2 samples when exposed to laser irradiation in the presence of air, as commonly performed in Raman measurements. 

The present work focuses on conducting a comprehensive Raman analysis of 1T-MoS2 by investigating the impact of oxidizing atmosphere, laser power, irradiation time, and temperature changes on the sample. Controlling the Raman conditions has allowed to detect a novel spectrum that hints to a new phase triggered by laser heating. This has led to further confusion in the identification of the metallic MoS2 polymorphs. This study seeks to expose the current challenges in characterizing the metallic phase of MoS2, especially when using Raman spectroscopy, which, until now, is considered the most reliable technique for this purpose. These results provide guidance to the next experimental Raman studies as well as possible practical applications for materials engineering.