High-resolution surface plasmon imaging of gold nanoparticles by energy-filtered transmission electron microscopy

We demonstrate the imaging capabilities of energy-filtered transmission electron microscopy at high-energy resolution in the low-energy-loss region, reporting the direct image of a surface plasmon of an elongated gold nanoparticle at energies around 1 eV. Using complimentary model calculations performed within the boundary element method approach we can assign the observed results to the plasmon eigenmodes of the metallic nanoparticle.

Figure 1

(Color online) (a) TEM bright field image of rod-shaped gold nanoparticle, with approximately 400 nm length and 75 nm diameter. The markers indicate pixel positions at which EELS spectra in Fig. 2 have been extracted. [(b)–(d)] EFTEM images at given energy-loss values. Image intensities have been normalized with respect to the maximum intensity of panel (b). We use pseudocolor for better visibility. The EFTEM maps show the electromagnetic eigenmodes of the gold nanorod.

Figure 2

(Color online) (a) Single-pixel extracted EELS spectra from EFTEM data at positions indicated in Fig. 1a. (b) STEM EELS spectra acquired at the same sample positions. The arrows in the lower parts of the panels indicate the energy resolution of the data.

Figure 3

(Color online) Results of BEM simulation. (a) Triangulated surface of rod-shaped nanoparticle and EFTEM maps as computed according to the prescription of Ref. 26. The maps at the energies of 1.08, 1.85, and 2.29 eV have been displayed in pseudocolor scaled to match the data range of the 1.08 eV map. The loss rates for the 2.29 eV map have been multiplied by a factor of 5 for better visibility. The lines indicate the direction of the electron beam. (b) Energy-loss probability at the positions indicated in panel (a).