Fig. 2. Fabrication of arrays of site-specific functionalized nanocrescents. (i) A thin layer of titanium (1 nm, as adhesion promoter) and gold (20 nm) are evaporated at an angle of 30° with respect to the surface normal (red arrow) to deposit gold underneath the masking particles. (ii) A second layer of gold is deposited at a different azimuthal angle γ, indicated by the blue arrow in the cartoon. This angle defines the overlap of the gold layers underneath the particle, and by this increases the contour of the crescent. (iii) Reactive ion etching along the surface normal (pink arrow) is used to remove material not covered by the shadow of the particle. (iv) Evaporation of a thin layer of titanium (5 nm) at half the previous azimuthal angle (γ/2) to passivate the central area of the crescent. The deposition of titanium with an azimuthal angle in between the two gold azimuthal angles (green arrow) ensures that the tips of the crescent remain uncovered. (v) Removal of the particle mask using adhesive tape. (vi) Oxidation of titanium to titania and removal of residuals of the particle mask by oxygen plasma. (vii) Selective functionalization of the uncovered region using thiol chemistry. (viii) Site-selective deposition by electrostatic attraction of negatively charged gold nanoparticles onto the tip region functionalized with positively charged cysteamine molecules.