The nanoscale fabrication of modern nanotechnology is mostly based on photolithographic techniques due to its versatility to produce a wide variety of patterns. Incorporation of lithographic techniques into self-assembly processes provides great flexibility in the variability of the nanoscale organization. Lithography can be used to fabricate patterned templates of nanoscale architectures for colloidal nanoparticle assembly. The patterns for self-assembly can be composed of a soft mold (such as PDMS) or they can also be engraved onto the substrate. As shown in Figure (a), the fabrication of a soft PDMS template first requires the fabrication of a topographically structured Si master template. The inverted pyramid patterned Si template in this case was produced by a direct laser writing lithography technique. The final soft PDMS mold facilitates the assembly of the colloidal Au nanoparticles into pyramidal clusters on a glass substrate. A concentrated Au nanoparticle colloid was drop-casted on the mold before covering with the glass substrate for the drying of the solvent phase. Similarly, Matricardi et al. prepared 2D Au nanoparticle assemblies by a similar procedure using PDMS soft molds, Figure ). Importantly, since the nanoparticles are welldispersed in an aqueous phase, the substrate required hydrophilization by plasma treatment in order to enhance the nanoparticle-substrate affinity. Instead of using soft molds, the substrate itself can also be patterned. Flauraud et al. showed that nanorods can be trapped in trenches patterned on a Si substrate during a capillary self-assembly procedure. As shown in Figure (c), a concentrated control volume of Au nanorod colloidal solution was confined between a top plate and the low wetting patterned substrate so that a receding solvent/vapor interface is formed upon sliding the top plate. By heating of the substrate, solvent evaporation is induced at the wedge-shaped receding interface which also results in convective flow that drags the nanoparticles from the bulk to the interface. The flow induces concentration of nanoparticles in the wedge-shaped region and dynamically sustains the concentration against nanoparticle back-diffusion. The receding contact line drags the concentrated colloid zone over the substrate, and the nanoparticles escape the colloidal meniscus to get trapped in the trenches as shown in the inset. As shown in Figure (d), this technique is quite efficient in producing complex patterns of nanoparticles. In the assembly of anisotropic nanoparticles such as nanorods, the orientation of the particles is also important, especially in the case of plasmonic nanoparticles. As shown by Hanske et al., colloidal destabilization by varying the solvent composition leads to enhanced surface activity and partial aggregation of gold nanoparticles, which can be advantageous for creating homogeneous AuNR arrays. In the formation of nanorod clusters in soft PDMS molds, the presence of ethanol in the solvent promoted horizontal orientation of the nanorods in the clusters, Figure (e). Also, the average cluster height increases with an increasing concentration of the surfactant CTAB. Complete filling of the PDMA mold voids could be possible only above a minimum surfactant concentration. Interestingly, the height of the assembly could also be controlled by the variation of the surfactant concentration. As shown in Figure (f), by increasing the CTAB concentration from 20 µM to 500 µM, the height of the assembly could be increased from 40 to 120 nm. An alternative approach can also be through photolithographic patterning on a self-assembled film. It has been shown that photolithography on a silica nanoparticle film followed by reactive-ion etching can produce different patterns . In the combination of self-assembly and lithography, one is complimentary to the other as each technique has its merits and drawbacks. While self-assembly provides access to small and complex colloidal nanostructures, lithography enables the formation of complex patterns with a high degree of control. The SEM image shows the pyramidal assemblies. Reprinted with permission © 2017, American Chemical Society (b) 2D nanoparticle clusters from a soft PDMS mold. Reprinted with permission © 2018, American Chemical Society (c) Capillary assembly processes of nanoparticles in nanoscale trenches engraved on substrate. (d) Accuracy of the capillary assembly process in obtaining complex structures.(c-d) Reprinted with permission ©2017 Nature publishing group (e) Presence of ethanol in the colloid resulted in more ordered clustering of nanorods in a soft PDMS mold. (f) Increasing surfactant (CTAB) concentration increases the cluster height (red: 20 µM, green: 100 µM, blue: 500 µM of CTAB).(e-f) © 2019 CC-BY 4.0.