Figure 1

The surface-plasmon pattern can be imprinted on the material. (a) Scanning electron microscopy (SEM) image of $G$-shaped nanostructures made of Ni, before illumination. (b) Upon illumination with 800 nm light, second harmonic microscopy reveals localized field enhancements due to plasmons. The color-coded intensities increase from black through purple to pink and the white arrow indicates the direction of the incident light polarization. (c) SEM images after illumination show that the plasmonic pattern has been imprinted on the structures. (d) AFM images confirm that this imprint (plasmonic hotspot decorations) is of structural nature rather than electron specific. (e) Energy dispersive spectroscopy (EDS) shows that the decorations in (d) are made of Ni, most likely oxidized. The EDS was performed along the red segment $A,B$ in (c).Reuse & Permissions

Figure 2

Better mapping: higher laser power reveals additional features of the plasmonic pattern. (a) Theoretical simulation of the electric currents in the nickel nanostructures. The highest electric field enhancements are indicated with full white circles. The simulation also reveals that there are two other regions with high field enhancement, indicated with dashed white circles. (b) For a laser power of 0.98 mW, SHG microscopy shows the highest field enhancements. The white arrow indicates the direction of the incident light polarization. Upon increasing the laser power to 1.23 mW (c), the SHG microscopy also reveals the enhancements within the dashed white circles. Although these additional hotspots are well resolved in terms of shape and contrast, they are rather large. Consequently, pinpointing the plasmon excitation on the nanostructures remains a challenge. However, upon examining the imprint on the structures with AFM (d), the regions of field enhancements are very well resolved and correspond perfectly to the simulation results.Reuse & Permissions

Figure 3

Hotspot decoration beyond nickel: palladium. An AFM image of the nonilluminated unit cell of the palladium nanostructures array  (a). It is a mirror image of the unit cell used for nickel. (b) SHG microscopy of the palladium nanostructures reveals the local field enhancements. The white arrow indicates the direction of the incident light polarization. Following the illumination, the hotspots are imprinted on the palladium nanostructures as evidenced by the AFM image (c).Reuse & Permissions

Figure 4

Hotspot decoration beyond the $G$-shaped geometry: nanobricks. (a) An array of nickel nanobricks (rectangular hexahedrons), 40 nm thick, with increasing length in steps of 50 nm. (b) Under the direction of light polarization, indicated with the white arrow, two local field enhancements form on the edges of each structure. SHG microscopy starts to resolve these field enhancements for structure lengths of approximately 650 nm. (c) Numerical simulations of the electric currents in the three encircled nanostructures indicate that there are two hotspots at the edges. (d) AFM images demonstrate that the plasmon imprinting perfectly resolves the local field enhancements even in the smallest structures.Reuse & Permissions