So far, we have shown the effect of DHF pretreatment on the shape and morphology of subsequent Au deposition on nanoclusters. We now consider what happens if DHF processing occurs after Au deposition. There are many papers dealing with the dynamic coalescence of metal nanoparticles in liquids. In previous work, we have found that silver nanoparticles undergo Smoluchowski maturation in DHF solutions by increasing their size and decreasing their surface density. For the case of gold nanoparticles on Si, we expect more complex cases due to the stronger interaction between gold and silicon and the formation of quasi-heteroepitaxial layers. Figure 3 reports the AFM of a Si sample with AuNP (in a tapping mode with a silicon tip having a radius of curvature of 10-15 nm) before and after 70 seconds of hydrofluoric acid deposition treatment (Figure 3a) and thereafter (Figure 3b) Observed morphology.

Post-deposition treatment by hydrofluoric acid apparently resulted in a flatter surface morphology than untreated samples. This effect can be quantified by calculating the root mean square (RMS) roughness from two 1x1 [mu] m scans in Figure 3, shown in the untreated sample, decreasing the RMS value from 2.53 nm to 1.16 nm after hydrofluoric acid treatment . This indicates a more uniform height distribution of clusters relative to the substrate after the post-deposition process. To better illustrate this aspect, the histograms of the z-values extracted from the two AFM images (in terms of deviations from the mean height) are also reported in Figure 3c, showing a broad distribution in the deposited sample, The tail extends to a lower z value, while a much narrower distribution is observed after hydrofluoric acid treatment.