## 3 Results and Discussion
Further, the FT-IR results show that the addition of HQ to BQ/MeOH solution increased the O-H peak intensity up to the 1:1 ratio with BQ. This is because the oxidation potential of HQ in MeOH is \(\sim\)0.29 V [21], and this is lower than that of MeOH itself of \(\sim\)0.38 V [22]. Therefore, when HQ co-exists with BQ in MeOH, HQ acts as a strong reducing agent for BQ, replacing the role of MeOH as an H\({}^{+}\) donor as shown in Figure 4c, so that a higher fraction of MeOH molecules retain their H\({}^{+}\). As a result, the overall absorbance of solution from O-H bonds gradually re-gained its intensity as HQ ratio increased. Above a 1 to 1 ratio the intensity of the O-H peaks at both 3390 and 1400 cm\({}^{-1}\) became saturated, which is evidence that only a limited amount of HQ will react with BQ. This is because the BQ-HQ redox system is known to produce a stabilized intermediate molecule of semiquinone (SQ) radical by exchanging one H\({}^{+}\) in a non-aqueous and weak hydrogen bonding agent like MeOH [17; 23]. Figure 3: High-resolution tapping mode atomic force microscope (HR-AFM) images of (**a**) pure BQ; (**b**) BQ:HQ = 1:0.5; (**c**) BQ:HQ = 1:1; and (**d**) BQ:HQ = 1:1.5 mixture ratios (scan scale = 200 nm \(\times\) 200 nm; scale bar = 50 nm). From the report by [PERSON] et al. it was confirmed the final molecular formation bonding with Si surface is the SQ molecule [24]. In Figure 5, the schematic illustration is shown for SQ and Si surface dangling bonds to produce Si-SQ bond for passivation. For SQ formation, only one H\({}^{+}\) exchange is required; therefore, a 1 to 1 interaction between BQ and HQ should be the maximum reaction ratio, which indicates that excess HQ above the 1:1 ratio with BQ will remain un-reacted in the solution. It was shown that HQ alone is not involved in the passivation reaction (Figure 2). Based on the HR-AFM images in Figure 3d, we assumed that the un-reacted HQ had hindered an intimate interaction between the passivation molecule and Si surface dangling-bond states followed by deteriorated uniformity of the passivation layer. To further clarify the role of HQ, TUNA was used to provide surface conductivity mapping with high current sensitivity (<1 pA). With a TUNA scan the densely packed molecular area and non-passivated area can be distinguished because of the high resistivity of native oxide formed on the non-passivated surface, in contrast with the passivation area. (Note: it is known that the densely packed  
Figure 4: (**a**) Fourier transform infrared spectroscopy (FT-IR) results of BQ (black-solid line), HQ (black-dash line), and various HQ mixture ratios into fixed BQ in MeOH (green, blue, red-solid line) and pure MeOH (orange-solid line); (**b**) reducing reaction of BQ into one SQ in BQ/MeOH; and (**c**) effect of HQ to produce two SQs formation in QHY (BQ:HQ = 1:1)/MeOH. Figure 5: Schematic illustration for Si–SQ formation. packed molecule area on the Si surface delays formation of native oxide) [25; 26]. The TUNA scan results with various HQ mixture ratios with BQ are shown in Figure 6. From the TUNA image of the excess 1.5 HQ ratio (Figure 6c), a large number of dark areas (white circle) on the surface were observed, which indicates that the excess mixture ratio of HQ would hinder formation of a uniform passivation layer followed by sparse oxidation for non-passivated areas; however, with lower HQ ratios of 0.5 (Figure 6a) and 1.0 (Figure 6b), fewer dark areas were revealed. The large contrast between 0.5 HQ and 1.0 HQ also can be explained by the different density of SQ produced by H\({}^{+}\) exchange between BQ and HQ because SQ is the actual molecule passivating the Si surface, as confirmed by [PERSON] et al. [24]. From the HR-AFM and TUNA results, it is clear that HQ affects the uniformity and coverage of the passivation layer on the Si surface. The dipping time effect of passivation was also investigated in both pure BQ and BQ:HQ = 1:1 (QHY) in MeOH with \(\tau_{\text{eff}}\) measurements.