Assessing quality and purity of MoS2 nanosheets by diffuse reflectance IR spectroscopy

Liquid-phase processing is increasingly used to produce thin films and composites from nanomaterials, including 2D nanosheets derived from van der Waals crystals. However, an inherent problem is the exposure of the nanomaterial to organic compounds from the environment—solvents, intercalants, and stabilizers—which can adsorb and potentially degrade device performance, especially at electrode interfaces. For conventional washing methods it is often challenging to confirm complete removal, as these residues are difficult to detect spectroscopically. Here, we use diffuse reflectance infrared (IR) Fourier transform spectroscopy to analyze freeze-dried 2D MoS2 nanosheets produced via various exfoliation methods. First-principles calculations predict IR spectral shifts corresponding to nanosheet thickness in the few-layer regime (