Microstructure and magneto-optical surface plasmon resonance of Co/Au multilayers

Abstract

Magneto-optical surface plasmon resonance (MOSPR) sensors benefit from a magneto-optic enhancement with respect to surface plasmon resonance (SPR) sensors, making these devices attractive for biosensing applications. Typical design compromises seek to balance magneto-optic effects and optical losses associated with surface plasmon waves extending to the ferromagnetic layer. Here, we demonstrate that Co/Au multilayers can yield sizeable MOSPR improvements in spite of the relative high total Co layer thickness. Co (t Co )/Au (2 nm) multilayers, with 1.2t Co 1.8 nm are prepared and characterized. X-ray analysis shows that the microstructure maintains high layer periodicity and improves upon annealing. The multilayer structures were then modeled to study their SPR/MOSPR sensitivities, suggesting that the MOSPR sensitivity is enhanced by a factor of up to 3 and 4 with respect to the SPR sensitivity when the devices are operated in Air and Water media, respectively. We find that multilayers provide a particular advantage when operating the sensors in Water-based media.

Magneto-Optic Surface Plasmon Resonance Ti/Au/Co/Au/Pc Configuration and Sensitivity

“…ε moCo is the complex magneto-optic constant of Co, also known as off-diagonal tensor component (ε moCo = −0.85 + j0.0006 at λ = 785 nm), obtained from a past paper [5]. For the MO characterizations, the multilayer structure shown in Figure 5 was optically interfaced to a prism in Kretschmann configuration using an index matching fluid (i.e., matching liquid) between the glass substrate and prism surface, similarly to the configuration shown previously [20]. The surface plasmon was excited using TM-polarized (p-polarized) optical radiation at an λ of 785 nm.…”

“…Finally, a 10 nm of Au layer was deposited on top of the Co layer. For further details on the fabrication method, interested readers are referred to my recent paper [20]. Various geometrical and optical parameters are given in Table 2.…”

“…After annealing, the dip in the reflection peaks is further reduced suggesting the improvement of the surface of the buffer layer. For additional information about roughness, I refer interested readers to my prior work [20]. are referred to past papers [24,25].…”

“…I analyze the MO effect using transfer matrix method similar to what has been described in my prior work [20]. Both variations in optical excitation wavelength and probed medium are also taken into consideration in the analysis.…”

Horizontal Plasmonic Ruler Based on the Scattering Far-Field Pattern

“…SPR is an optical phenomenon that results from strong light-matter interaction, thus leading to resonance oscillation of electron charges excited by the incident light at the interface between two materials with different permittivity values. These different positive and negative permittivity values are mostly associated with dielectric and metallic materials [3,4,5,6,7]. At the resonance wavelength, the amplitude of the near-field is enhanced owing to the strong confinement at the interface.…”