2015-3

121110-3 Nasir et al. Appl. Phys. Lett. 107, 121110 (2015)
FIG. 1. (a) Schematics of the metamaterial based on a nanorod array. (b) SEM image of porous alumina synthesized in selenic acid at 48 V (sample B). (c)
Comparison of sulphuric and selenic acid molecules. (d) SEM image of the nanorods after removal of alumina matrix (sample B). Please note that disorder is
introduced in the nanorod array after the matrix removal due to the reduced self-supporting properties of thin nanorods. (e) The effect of nanorod concentration
on the extinction of the metamaterial (the Au nanorods in AAO matrix, p-polarized light, 40 angle of incidence).
light polarised perpendicular to the nanorod axes, while the
strong long-wavelength absorption near the effective plasma
frequency takes place for incident light polarised along the
nanorod axes. 30 These two resonances, of a different nature,
remain separated even when the AAO is removed, when for
the samples with higher nanorod concentrations they typically
overlap. For smaller nanorod diameters with the same
period, the peak in the ENZ region is shifted further in the
FIG. 2. Extinction spectra of metamaterials (a–c) A (nanorods of 40 nm diameter, 115 nm period, and 200 nm height, embedded in AAO matrix) and (d–f)
B (nanorods of 25 nm diameter, 115 nm period, and 350 nm height, embedded in AAO matrix) at different angles of light incidence: (a) and (d) experiment,
(b) and (e) full-vectorial microscopic modelling, (c) and (f) EMT modelling. For sample A an electron mean free path restriction of 23 nm was used for electrochemical
Au; 18 the metamaterial has a 7 nm thick Au underlayer and a 700 nm thick AAO overlayer. For sample B, the electron mean free path restriction is
8 nm for electrochemical Au; the metamaterial has a 7 nm thick Au underlayer and a 650 nm thick AAO overlayer.