## 3 Results and Discussion
The measured \(\tau_{\text{eff}}\) values for samples dipped in the solutions from 10 to 180 min (Figure 7a) show a dramatic increase of \(\tau_{\text{eff}}\) with QHY/MeOH compared with pure BQ/MeOH for dipping times less than 50 min. This rapid increase of \(\tau_{\text{eff}}\) can be explained by the higher density of SQ in QHY/MeOH accelerating the passivation reaction between SQ and the Si surface as discussed earlier in relation to Figure 4. However, after 50 min a gradual decrease of \(\tau_{\text{eff}}\) with QHY/MeOH was observed, but the \(\tau_{\text{eff}}\) from BQ/MeOH continued to increase. From repeated \(\tau_{\text{eff}}\) measurements for various dipping times, 1 h and 3 h were determined to be the optimal treatment times for QHY/MeOH and BQ/MeOH, respectively. To help understand the negative effects of over-treatment, HR-AFM images of the sample surfaces from various treatment times were obtained (Figure 7b-e). After 180-min passivation in QHY/MeOH (Figure 7c), the scan shows highly severe molecular aggregations compared with that of pure BQ (Figure 7e). The QHY/MeOH passivation is known to induce positive surface charge on the Si surface by the strong dipole moment of the SQ molecule producing Si surface band-bending (field effect passivation) [24]; therefore, the molecular aggregation after excess dipping time weakened the molecular dipole moment [12]. This is because, although dipole moment is a vector quantity produced by charge asymmetry within molecules, random stacking of molecules would encourage \(\pi\)-\(\pi\) interaction between stacked molecules, thereby reducing charge asymmetry and consequently producing a weaker dipole moment within the molecular layer [27]. To clarify the relationship between \(\tau_{\text{eff}}\) and passivation layer morphology, surface potential voltage (SPV) was also measured with two different dipping times, 1 h and 3 h, for QHY, BQ, and HQ/MeOH solutions. The measured SPV results (Table 1) show that QHY with 1 h dipping produced a stronger SPV and an increased \(\tau_{\text{eff}}\) (317 meV and 2813 \(\upmu\)s) compared with 3 h dipping (249 meV and 2195 \(\upmu\)s). In contrast, for BQ, 3 h dipping produced a stronger SPV with a longer \(\tau_{\text{eff}}\) (357 meV and 3398 \(\upmu\)s) compared with 1 h dipping (317 meV and 1522 \(\upmu\)s). These SPV results strongly support the relationship between dipping time and \(\tau_{\text{eff}}\) that was described in relation to Figure 7. In addition, as shown in Table 1, HQ/MeOH barely produces SPV on the Si surface, thereby supporting the contention that HQ itself provides no passivation effect for Si, as noted earlier. Figure 6: Tunneling mode atomic force microscope (TUNA) images of (**a**) 0.5 HQ; (**b**) 1.0 HQ; and (**c**) 1.5 HQ mixture ratios with 10 mM of BQ in MeOH. (scan scale = 200 nm \(\times\) 200 nm; scale bar - 50 nm). From the results of SPV, AFM, and \(\tau_{\text{eff}}\) measurements, the molecular contribution of \(\mathrm{BQ}\) and \(\mathrm{HQ}\) for Si surface passivation was clarified with \(\mathrm{BQ}\) shown as a passivation agent and \(\mathrm{HQ}\) shown as accelerating the passivation process after donating \(\mathrm{H}^{+}\) to \(\mathrm{BQ}\). However, even though \(\mathrm{HQ}\) offers a shorter passivation time, it has a significant effect on passivation layer uniformity, which might be a crucial factor to passivate a complex Si surface. In this paper, therefore, we also performed QHY/MeOH and \(\mathrm{BQ}\)/MeOH passivation for a nanostructured Si surface (Figure 8a). The nanostructured Si surface was fabricated with a reactive ion etching (RIE) process by using silica nanospheres as a mask material, which was developed as a silica nanosphere lithography (SNL) technique in our previous report [28]. The nanostructures were fabricated on a 2-inch diameter round Si wafer with a 310 nm period. After nanostructure fabrication, the wafer was cut for passivation to offer an identical nanostructure environment for each passivation condition.