NaCl substrates for high temperature processing and transfer of ultrathin materials

Ultrathin materials often require high temperatures for growth and processing, which cannot be withstood by the substrate underneath. For example, polymers are widely used as a supporting layer but unfortunately have low strain-point temperatures. This is the case of polyethylene terephthalate (PET) which has glass transition and melting temperatures of 76 and 250 °C, respectively. In this paper we propose to use polished salt, a material that can withstand high temperatures during fabrication and, at the same time, can be sacrificed during the transfer onto the final substrates. More specifically, we demonstrate thermal dewetting of Au ultrathin metal films and growth of MoS₂ on NaCl at 750 and 650 °C, respectively, and subsequent transfer onto PET films, after which the salt is easily dissolved by water. We believe that the proposed technique can be extended to fabrication of other ultrathin materials, e.g. graphene, as well as final substrates for a wide range of applications, including flexible electronic and optoelectronic devices.