Since ∆ƒ is the convolution of the gradient of the conservative force Fcons with weighting by displacement over a vibration cycle and the Fcons is the gradient of its potential, the oscillation of ∆ƒ indicates a similar oscillation of Fcons and the corresponding potential. To convert the Fcons distribution to the density distribution of low-molecular-weight compounds such as water, the solvent tip approximation (STA) has been used. Although it cannot be directly applied to polymer melts because of the molecular size of the polymer (length > 100 nm), the periodic distribution in the tip potential qualitatively indicates the existence of corresponding periodic density distribution with approximately the same period. Therefore, it can be concluded that PDMS molecules formed a layered density distribution with a period of 0.7-0.9 nm near the mica surface, which suggests that the main chains of PDMS molecules near the mica surface were oriented parallel to the solid surface. This result is well consistent with a previous static-mode AFM study performed on a 480 mPa•s PDMS/SiO2 interface 9 and our previous qPlus FM-AFM study performed on a 970 mPa•s PDMS/mica interface. Furthermore, the curves acquired during the tip approach (red) and retraction (blue) were well consistent. Generally, in Δƒ-z curve measurements and 2D Δƒ mapping at solid-liquid interfaces, the tip perturbs the liquid distribution when approaching the tip. Therefore, the result that the curves coincided during the approach and retraction suggests that the layered structure on the interface was stable or metastable. . Both approaching and retracting curve fluctuated with a period of 0.9 to 1.4 nm, and these curves were not consistent. This period was larger than that obtained on the 29 h-settling sample. The disordered structure and the inconsistency between the two curves can be regarded as an incomplete state before reaching the layered structure observed on the 29 h-settling sample. This result suggests the following two possibilities. The first one is that the formation of the layered distribution takes more than 25 h. As shown in Figure (a), a layered distribution was observed in 29 h, and the difference in time was not significant. Another possibility is that the in-plane distribution was not uniform. That is, at 25-29 h after spin coating, both regions with the layered distribution and the disordered regions exist. However, as shown in Figures ) and 2(d), the ∆ƒ-z curves obtained on the layered structure during the approach and the retraction were well consistent, whereas the curves obtained on the disordered region were not. This suggests that the layered structure is metastable or stable. Also, the fact that the layered structure observed after a longer settling time (Figure ) is reasonable from the viewpoint that a more stable structure would be formed by increasing the settling time.