**1. Introduction**

Nanoimprinting lithography (NIL) has emerged over the last two decades as a high throughput nanofabrication method and is now a consolidated technology [1–3]. The method uses a stamp, brought into physical contact with a polymer, to mold it and transfer the pattern of the stamp into the polymer. Several different approaches can be found for nanoimprinting, being the main ones thermal NIL and UV NIL. In recent years a strong industrially-driven research can be observed, pushing NIL and its applications from purely academic purposes to innovations in data storage, point of care diagnostics, electronic and graphene devices or augmented reality [4–9]. With this shift, new materials need to be developed with properties that are compatible with mass production: fast curing and imprinting, robustness, reproducibility, and patterning on flexible substrates, both, at the micro and nano scale.

NIL was initially used as a purely lithographic method, for pattern transfer [10] as a fast and cheap alternative to electron beam lithography. In recent years, a new trend has emerged towards direct patterning of functional materials, where the imprinted structures are directly used as active elements

in devices. These devices find applications in several different fields, like micro and nanofluidics [11,12], biosensing [13] and DNA analysis [14], optical, nanophotonic [15] and flexible, electrical devices [16]. For example, biocompatible and three dimensional polymer structuring for cell cultivation open a promising field for imprintable polymers as an alternative to conventional processing using photoresists, which need long process times, by offering more flexibility in the processing, higher throughput and incrementing the design freedom [17].

For using patterned surfaces in devices or sensors, the surface of the cured polymer often needs to be chemically modified or activated. The functionalization endows the surface with properties different and independent from the bulk or from other untreated areas of the polymer. However, the process of functionalization often requires an activation, or a two-step modification of the surfaces with strong (and dangerous) chemicals or physical interaction [18,19]. The process is time consuming and not always compatible with the device (e.g. compatibility of biomolecules with temperature changes, chemicals or pH changes). Functional, imprintable polymers with intrinsic and easily modifiable functional groups are very attractive alternatives.

A versatile functional group for surface modifications is the thiol group due to the well-researched "click chemistry" [20] and also its strong affinity to common materials used in micro and nanoengineering, such as gold [21]. Thiols are known to undergo a nucleophilic addition with Michael systems, such as (meth)acrylates or vinyls, at room temperature [22–24], as well as radical additions. Spatially controlled reactions by ink-jet printing or masking could be used for local chemical modification of surfaces and patterns on an imprinted structure.

In this work, we have developed a resist formulation, which has functional thiol groups at the surface and in the bulk. It is easily patternable by UV NIL, both at the micro and nanoscale. In addition, it is possible to etch it selectively and homogeneously by reactive ion etching (RIE) using an oxygen plasma. The surface properties have been characterized by measuring the contact angle for different formulations and curing conditions. The thiol groups have been observed by Raman spectroscopy, confirming their presence at the surface and in the bulk, and also after an O<sup>2</sup> etching. As a first application, we show the possibilities for surface click chemistry on the polymer surface. And, as a second possible application, we show how the polymer, just placed on top of a graphene device, changes its electrical properties and allows for operation at ambient conditions, without ultra-high vacuum.

#### **2. Methods**

## *2.1. Curing of the Material*

Some of the results shown in this work were obtained by curing the polymer with a monochromatic light emitting diode (LED) lamp (365 nm) under a home-made CO<sup>2</sup> flow box. These include those shown in Sections 3.2, 4.2.2 and 4.3.2 (nanometric lines). The rest of the results were obtained using a dedicated UV-NIL equipment (EVG 501, EV Group, Sankt Florian am Inn, Austria), with a controlled atmosphere in the chamber, and a pulsed, broadband xenon lamp (Model LH-810 Spiral Lamp 107-mm, type C spectrum, 190 nm cutoff, power 105 mW/cm<sup>2</sup> , XENON Corporation, Wilmington, MA, USA) for exposure.
