As an extension to the previous self-assembly on the liquid-liquid interface, Park et al.

developed a new strategy to in situ coat long-chain alkanethiol on the nanoparticles which are entrapped at the interface. The coating of amphiphilic molecules render the nanoparticles to closely packed with each other, forming large-scale and ordered packing. Such method can be extended to particles with larger size63 (25

This method was further extended to fabricate plasmonic nanosheets on the hexane-water interface from anisotropic core-shell [email protected] NCs and NBs (Figure 2.3a).64 The assembly process starts with mixing the particle colloid solution of [email protected] NC or [email protected] NB with the same amount of hexane with DDT. Then nanoparticles spontaneously self-assembled at the water/hexane interface and the mirror-like sheets began to appear and become larger with the injection of ethanol.  During this process, ethanol facilitated the ligand exchanges between DDT and CTAC surfactants (capped during the early-synthesis procedure) by reducing the interfacial surface tension. Since the weak binding CTAC is replaced by strong binding DDT, the particles are rendered to be hydrophobic, resulting in the deposition of nanoparticles at the interfaces.

Finally, the fluid interface is all covered with a mirror-like membrane that is as large as ?13 cm2 as shown in Figure 2.3e. After the hexane fully evaporated and the self-assembly completed, the assembled nanosheets were transferred to Poly(dimethylsiloxane) (PDMS) via horizontal lifting. 2.2.

4 Langmuir-Blodgett technique As an air-water interfacial assembly method, Langmuir–Blodgett (LB) technique has been widely used as a versatile method to fabricate plasmonic monolayers due to its ability in controlling the interparticle distance, particle density, and arrangement in a monolayer. During this process, nanoparticles that dispersed in an immiscible solvent was spread on a water surface, forming a thin Langmuir layer. This thin film can be compressed or expended moving a solid barrier that is vertical to the air-water interface, leading to the formation of nanoparticle arrays with controlled spacing and ordering (Figure 2.4a-b).

65 The obtained nanoparticle monolayer is normally large scale and is able to be transferred to solid or soft surface by either Langmuir-Schaefer technique or dip-coating. 

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