On columnar thin films as platforms for surface-plasmonic-polaritonic optical sensing: Higher-order considerations

Surface-plasmon-polariton (SPP) waves, guided by the planar interface of an infiltrated columnar thin film (CTF) and a thin layer of metal, may be harnessed to detect substances that penetrate the void regions in between the columns of a CTF. This scenario was investigated theoretically using a higher-order homogenization technique, based on an extended version of the second-order strong-permittivity-fluctuation theory, which takes into account the size of the component particles which make up the infiltrated CTF and the statistical distribution of these particles. Our numerical studies revealed that as the size of the component particles increases and as the correlation length that characterizes their distribution increases: (i) the phase speed of the SPP wave decreases and the SPP wave's attenuation increases: (ii) the SPP wave's penetration into the CTF decreases; (iii) the angle of incidence required to excite the SPP wave in a modified Kretschmann configuration increases; (iv) the sharpness of the SPP trough in the graph of reflectance versus the angle of incidence increases; and (v) the sensitivity to changes in refractive index of the infiltrating fluid decreases. The performance parameters of the infiltrated CTF, as revealed by the implementation of our particularly sophisticated theoretical approach, suggest that these structures are promising platforms for SPP-based optical sensing. (C) 2012 Elsevier ay. All rights reserved.