## 3 Results and Discussion  
The microwave-assisted hydrothermal synthesis method was used for the direct growth of MoS\({}_{2}\) nanostructures on cellulose paper substrates due to the ease of the technique's application, as well as its ability to change synthesis parameters to optimize the produced structures [29; 30; 31]. The growth was carried out using a two-step process, where the synthesis is performed on a substrate with a thin layer of deposited seeds. For construction of NIR photodetectors, a layer of interdigital silver electrodes was deposited on the layer of the MoS\({}_{2}\) nanostructures using the screen-printing technique. Further details on the growth of nanostructures and the construction of the devices can be found in the Experimental Section. Figure 1 shows a diagram of the MoS\({}_{2}\) nanostructures synthesis and the photodetector production. Figure 2 shows SEM images of the samples synthesized with a synthesis temperature of 220 \({}^{\circ}\)C at different times. Figure 1: Scheme of the synthesis process of the molybdenum disulfide (MoS\({}_{2}\)) nanostructures in paper substrates by the microwave-assisted hydrothermal method, and the production of infrared radiation photodetectors. Figure 2: Scanning electron microscopy (SEM) images of the MoS\({}_{2}\) nanostructures grown directly on cellulose paper substrates with a synthesis temperature of 220 \({}^{\circ}\)C and time of: (**a**) 05 min, (**b**) 15 min, (**c**) 30 min, (**d**) 45 min, (**e**) 60 min, and (**f**) 120 min. Microscopy images show that the beginning of the growth process is characterized by the formation of vertically aligned MoS\({}_{2}\) nanosheets on the paper surface (see also Figure S1 in the Supplementary File), while the paper fibers are not fully covered. For longer synthesis times, the surface of the paper becomes completely covered by vertically aligned MoS\({}_{2}\) nanosheets, regardless the temperature. The effect of temperature is noticed on the time required to observe the first nanosheets on the paper surface. Such a result is expected since, for lower temperatures, the solution is exposed to lower energies during the synthesis process, requiring a longer time for nanomaterial formation. At 190 \({}^{\circ}\)C, it is possible to observe that, even for the longest synthesis time (120 min), the profile of the paper fibers is still perceived, indicating that it was not possible to form a thick and uniform nanostructure layer. On the other hand, at 200 \({}^{\circ}\)C the fibers are uniformly coated with a thick layer of MoS\({}_{2}\) nanosheets. It is important to note that the samples synthesized at this temperature had a more uniform surface profile than the samples produced by the conventional hydrothermal method reported in the literature [28; 33; 35], which generally have agglomerations of MoS\({}_{2}\) nanosheets in microspherical profile. A surface totally covered with nanostructures is also observed in the samples synthesized at 220 \({}^{\circ}\)C. However, at this temperature, it is possible to observe that, for longer synthesis times, the sample surface has regions with a spherical profile very similar to those synthesized by the conventional hydrothermal method [28; 32]. This indicates that there was the production of a large number of nanostructures during the synthesis process, where they tend to agglomerate in spherical shape, microflowers, formed by nanosheets. The growth kinetics of MoS\({}_{2}\) nanostructures on cellulose paper and other flexible substrates was recently discussed by [PERSON] et al. [28] through classical nucleation and growth theory. These spherical structures are formed when there is excessive nanosheets growth, which generally occurs for longer synthesis times or for MoS\({}_{2}\) synthesis without the presence of the substrate [26]. In the synthesis with direct growth on substrate, the excess of grown nanostructures ends up detaching from the paper surface and agglomerating into spherical particles to decrease the surface energy.