Carving Plasmon Modes in Silver Sierpiński Fractals

Abstract

The surface plasmon resonance (SPR) modes of the first three generations of a Sierpinski fractal triangle are investigated using electron energy loss spectroscopy (EELS) complemented with finite difference time domain simulations. The Sierpinski fractal geometry is created in a subtractive manner, by carving triangular apertures into the triangular prism of the previous fractal generation. The ability of the fractal antenna to efficiently utilize space in coupling to long wavelength excitations is confirmed on the single nanostructure level via redshifting of the primary dipole mode as the fractal generation is increased. Through application of the Babinet principle, it is demonstrated that this spectral shift is caused by coupling of two degenerate orthogonal dipolar modes of a single triangle with two degenerate orthogonal dipole modes of the triangular aperture occupying the center of the first generation fractal. It is also shown that the spectral position and strength of the dipole mode can be tuned ...