Abstract
Surface plasmon polaritons (SPPs), which are spatially confined electromagnetic modes related to collective electron oscillations, are now attracting substantial interests. Due to the unique characteristics of SPP, two dimensional devices such as SP mirrors, SP beam splitters, SP waveguides, etc. can be found in a broad range of applications including nanophotonics and biological sensing. In this work, SPP excitation and propagation on gold patterns are studied by near-field optical scanning microscopy (NSOM). For constructing the gold patterns, AFM nanomachining is used to create nanowire arrays. On the other hand, e-beam lithography is used to define other patterns. The SPPs are excited by an attenuated total reflection (ATR) configuration with the use of a transverse magnetic polarized laser source (532 nm). The optical distributions on the gold patterns are studied by a commercial NSOM. By illuminating gold microstripes (5 μm in width and 20 μm in length) uniformly, the optical image shows the excitation of SPPs with an obvious interference pattern. The measured wavelength of 480 nm is in good agreement with the calculated wavelength of the surface plasmons (λsp = 471 nm). By illuminating one side of a gold microstripe, SPP propagation and scattering at the other side is observed. A gold nanowire (130 nm in width and 15 μm in length) array is illuminated by focusing a laser beam with two types of incident direction. With the incident direction parallel to the nanowire array, SPPs are excited on one side of the array and propagating to the other side. The measured wavelength of 479 nm is again in good agreement with the calculated wavelength. With the incident direction perpendicular to the nanowire array, the electromagnetic field enhancement on both sides of nanowires is 3.5 times larger than that on the quartz. Finally by applying a voltage between the two sides of a gold microstripe when SPPs are excited, the disturbance of the SPP interference pattern is observed when a current passes through the microstripe.