Figure 4

PEEM images of an array of Au dimer structures. (a) An MP-PEEM image showing the irradiation of the NIR femtosecond pulses only. (b) A PEEM image resulting from simultaneous irradiation with the NIR femtosecond pulses and the mercury lamp. The multiphoton photoemission excited by the laser yielded the LSPR-assisted hot spots, while the one-photon photoemission by the mercury lamp provided the surface morphology of the gold structures. Thus, the PEEM image (b) allowed the precise determination of the hot spot locations. The inset of (a) provides an SEM image of a single dimer structure; the scale bar is 100 nm. MP-PEEM, multiphoton photoemission electron microscopy; NIR, near-infrared; SEM, scanning electron microscopy.