Electronic Supporting Information Optical response of monolayer , few-layer and bulk tungsten disul de

It is worth to point out an important property of selected samples prepared by means of mechanical exfoliation, which may signi cantly a ect their PL response. It particularly concerns the large-area akes, which at the fabrication stage are subject to strongly non-uniform eld of tearing force. Acting on thicker akes, such force can locally split them into subunits composed of smaller number of layers, which nonetheless do not stop to interact with one another. For example, within a 3 ML-thick ake a pocket containing a 1 ML patch that is partially detached from its 2 ML-thick companion can be created. If optically probed, it may then give rise to the appearance of mixed PL signal comprising contributions of all three kinds, i.e. the 1 ML-, 2 ML-, and 3 ML-like, of course distorted by interactions between the two subunits. When performing preliminary measurements we experienced such a situation for some of our akes composed of 3 MLs and 4 MLs, whose PL spectra were dominated by a set of prominent features resembling those observed for the monolayer. In order to avoid in uencing our results by this artifact, we then carefully examined all akes under consideration before qualifying them for further optical study.