Density gradient ultracentrifugation (DDU) of 2D material containing solution further allows the separation of single layers from few layers. This technique was first successfully applied to separate single layer graphene oxide using sodium cholate as intercalating agent (surfactant) from the solution [182]. Buoyant density difference of mono and few layer nanosheets separate single layer, few layers and bulk crystals. Despite the large scale production ability of this method, mechanical exfoliation remains the preferred choice for layered 2D materials due to the less destructive nature as well as mono layers of size up to 10 µm have been peeled off on a variety of substrates [131, 183].