from ASML Holding [43], SiPix Imaging, Inc. in 2003 [44], and Hwang et al. from Korea University [26]. Albeit selleck screening library the more complicated mechanism as compared to roll coating, the usage of spray/valve jet mechanism allows very efficient usage of resist during the NIL process; in the work of Maury and the team [43], a resist amount as little as 5 ml was reported for imprinting 50 copies of a 6-in. wafer

consisting of active-matrix organic light-emitting diode (AMOLED) transistor designs using the valve jet resist dispensing. Figure 11 A thermal R2R NIL process with gravure-based resist coating [42] . Figure 12 Spray coating illustration diagram. Additionally, for thermal R2R NIL, the process may also be conducted without the need for continuous resist coating mechanism, where the patterns are imprinted directly onto a heated polymer substrate as shown MAPK inhibitor in Figure 13 [45], similar to their R2P counterpart by Song et al. [36] and Lim et al. [37]. Using this method, the process is further simplified as the need for control of resist coating uniformity is not required.

It was reported by Mäkelä et al. [45] that grating structures of 10 μm and 400 nm have been successfully imprinted on a cellulose-acetate film at speeds between 0.2 and 15 m/min. Nagato and the team from The University of Tokyo [46], on the other hand, have proposed an iterative roller imprint mechanism capable of producing multilayered nanostructures on a PMMA film as shown in Figure 14. The process introduced is capable of producing multilayered nanogaps and thin-film materials as shown in Figure 15. In imprint lithography, self-alignment is possible for a multilayer product, called self-aligned imprint lithography (SAIL). SAIL works by encoring multiple patterns and alignment

into thickness modulations of a monolithic masking structure. In recent development, R2R NIL is no longer limited in polymer substrates. In the work of Ahn et al. from Yonsei University [47], a continuous R2R NIL system was also proposed for rigid substrates such as glass. FER A gap control system was also introduced to cater for variable substrate thickness as shown in Figure 16. Figure 13 Photo of the thermal R2R NIL system for direct polymer film imprinting from [45] . Figure 14 Schematic of the R2R NIL system for multilayered structures from [46] . Figure 15 Process flow to produce (a) multilayered nanogaps and (b) multilayered thin-film materials. Using the R2R NIL system shown in Figure 16 as observed in [46]. Figure 16 Schematic of R2R NIL for a rigid substrate by Ahn et al. from Yonsei University [47] . Despite the advantages, it is noted that there are several challenges in realizing the continuous R2R NIL process. One of the main challenges is the fabrication of the special flexible mold, which will be discussed in further sections.