Size-dependent optical response of few-layered WS2 nanosheets produced by liquid phase exfoliation

Liquid phase exfoliation is a promising and scalable approach to produce high quality WS2 nanosheets. However, dispersions are polydisperse and precise control over lateral size and thickness is still challenging. Here, gradient centrifugation is used to separate the nanosheets into different sizes. Atomic force microscopy and dynamic light scattering measurements confirm reasonable size separation of WS2 nanosheets. UV-vis spectroscopy is also utilized to study exfoliated nanosheets of various dimensions. The absorption spectra show a well-defined dependence on size and thickness distributions of nanosheets. An obvious blueshift of A-exciton with decreasing thickness is observed. This results demonstrate the capability of UV-vis spectroscopy as a powerful tool in preparing dispersions with pre-determined sizes. Such size-dependent optical response removes the need to use costly and time-consuming microscopy techniques.