Figure 6
Experimental XR curves from a 2 ml bulk NP solution injected onto a 2-inch-diameter sapphire substrate (bulk electron density [\rho_{\rm sa}] = 1.175 e- Å-3) and kept at constant [\Delta T] = 60 mK for ~20 h. The solution contains the NPs necessary to assemble a close-packed NP bilayer covering the entire sapphire wafer after complete solvent evaporation. Up-triangles: NP solution surface 5 h after injection. The oscillatory XR character indicates surface NP accumulation. Squares: (×10-2) same NP solution 8 h after injection. The smaller oscillation amplitude suggests partial NP dissolution into the bulk sub-phase. Diamonds: (×10-4) same NP solution 18 h after injection. The absence of XR oscillations indicates the complete disappearance of the transient surface NP layer. Down-triangles: (×10-8) example of XR measurement at the buried substrate-NP-solution interface. The monotonic XR character indicates the absence of NP accumulation at the buried solid-liquid interface. The solid lines are physical model fits obtained by applying the Parratt recursive method to the electron density profiles reported in inset (a). Inset (b): schematic representation of two core-shell NPs at the toluene-vapour interface, with the parameters involved in the physically motivated model described in §4[link].  [article HTML]