Dispersion and origin of surface optical-like waves in a two-dimensional antidot-patterned structure with a soft intervening layer

Abstract

The phonon dispersion of a square-lattice antidot-patterned Ni 80Fe20 film on a bottom-anti-reflective coating (BARC)/Si substrate has been investigated by Brillouin spectroscopy and finite element simulations. Band structures, measured along Γ-M and Γ-X, exhibit Bragg gap openings, surface optical-like and acoustic-like waves, and an acoustically isolating feature arising from the soft BARC layer. A qualitative explanation of the origin of the optical-like waves is presented, by mapping their displacement fields onto reciprocal space. Interestingly, these waves can be frequency shifted, almost independently of the acoustic-like mode frequencies, by varying one of the dimensions of the patterned array on the Ni80Fe20 film. © 2014 AIP Publishing LLC.