**Manuel Müller \*, Rukan Nasri, Lars Tiemann and Irene Fernandez-Cuesta \***

Center for Hybrid Nanostructures (CHyN), Institut für Nanostruktur- und Festkörperphysik (INF), Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany; rukan.nasri@physnet.uni-hamburg.de (R.N.); lars.tiemann@physik.uni-hamburg.de (L.T.)

**\*** Correspondence: mamuelle@physnet.uni-hamburg.de (M.M.); ifernand@physnet.uni-hamburg.de (I.F.-C.)

Received: 22 July 2020; Accepted: 4 September 2020; Published: 14 September 2020

**Abstract:** We present here a novel resist formulation with active thiol groups at the surface. The material is UV curable, and can be patterned at the micro- and nanoscale by UV nanoimprint lithography. The resist formulation development, its processing, patterning and surface characterization are presented here. In addition, a possible application, including its use to modify the electrical properties of graphene devices is shown. The cured material is highly transparent, intrinsically hydrophilic and can be made more hydrophilic following a UV-ozone or an O<sup>2</sup> plasma activation. We evaluated the hydrophilicity of the polymer for different polymer formulations and curing conditions. In addition, a protocol for patterning of the polymer in the micro and nanoscale by nanoimprinting is given and preliminary etching rates together with the polymer selectivity are measured. The main characteristic and unique advantage of the polymer is that it has thiol functional groups at the surface and in the bulk after curing. These groups allow for direct surface modifications with thiol-based chemistry e.g., thiol-ene reactions. We prove the presence of the thiol groups by Raman spectroscopy and perform a thiol-ene reaction to show the potential of the easy "click chemistry". This opens the way for very straightforward surface chemistry on nanoimprinted polymer samples. Furthermore, we show how the polymer improves the electrical properties of a graphene field effect transistor, allowing for optimal performance at ambient conditions.

**Keywords:** nanoimprint lithography; polymer; formulation development; surface chemistry; click chemistry
