## 3 Results and Discussion
### Electrical and Optical Properties of Graphene/AgNPs-Based Films  
Hybrid suspensions manufactured in this work were used to obtain transparent films on glass substrates. Although comparison of the results of numerous studies suggest that the technology of film preparation greatly affects film properties, especially for carbon [77, 78], metallic nanoparticles [77] and their hybrids [79, 80], we used simple drop-casting in order to ascertain the effect of composition on structure-dependent properties formation. Electrical properties were evaluated via analysis of the I-V curves measured using direct current and a 4-probe technique. Typical V-I curves are shown in Figure 8. It can be seen that all of the films behaved as linear resistors (as can be seen from the symmetric linear shape of the curve around zero point), which is consistent with TCE and contact track working conditions. It is noteworthy that concentration of the initial suspension seriously affects both the slope of the V-I curve around 0 V and the range of linearity, which generally tends to decrease at lower AgNP concentrations from \(\pm\)6 V at 15 wt.% FLG down to less than \(\pm\)1 V at 85 wt.%  
Although the range of linearity is a very important property for microelectronics, sheet resistance is usually considered as a figure of merit for electrode-related applications [77, 78, 79, 80]. In the current study, sheet resistance was estimated from resistance data defined as V-I curve slope around 0 V. It can be seen from Figure 9 that the plot is quite complex. Minimal resistance is seen for the pure AgNP film, which had poor optical properties. With an increase in FLG content (pure FLG film had the highest sheet resistance), one can observe a pronounced minimum once again around 65 wt.% of FLG content, which suggests that quantitative effects of AgNPs bridging FLG particles in the optimal concentration range hold true both in suspensions and in films. Figure 7: Optical transmission for FLG/AgNP-hybrid suspensions at different component ratios (wavelength—see legend). Figure 8: V-I curves of hybrid FLG/ AgNPs films at 15 (**a**), 35 (**b**), 50 (**c**) and 85 wt.% (**d**) of FLG content. Figure 9: Sheet resistance of hybrid FLG/ AgNPs films at different component ratios. Figure 10 shows typical optical absorption spectra for different suspension compositions. Leaving aside the absolute values for transmission that may be attributed to technological aspects of film manufacturing, one can see that at least several spectra (e.g., for 65, 85 wt.% FLG) have pronounced SPR absorption; in this case, however, the overall absorption is significantly less than it is for pure AgNPs (0% FLG). Minimal absorption for hybrid suspensions (pure FLG was not considered) was observed for 50 and 75 wt.% of FLG. It can be concluded that, although it is close to the optimal value for suspensions (65 wt.%), interactions with light in hybrid thin films probably have certain differences as compared to suspensions, at least as long as interactions with an electromagnetic field are considered. Moreover, for films the SPR peak of AgNPs can be distinguished in most spectra. Both these effects may be attributed to two main reasons. First, sintering leads to an increase in AgNP size and a subsequent change of optical properties. Second, interparticle interactions and network structure are most probably not equal in suspensions and films. Moreover, a simplistic film deposition technique can also affect the properties of the films; therefore, more advanced deposition techniques, such as the Langmuir-Blodgett [71], or spray-coating coupled with substrate pre-treatment, are suggested to test whether optimal FLG concentration in hybrid suspensions coincides with that in films as far as optical properties are examined.