Figure 2: SERS spectra taken from a single Ag nanobar at two wavelengths and different orientations relative to the laser polarization. (a) SEM image of a typical Ag nanobar of 150 nm in length ( ) and 75 nm in width ( ) supported on a Si wafer. The 514 or 785 nm laser was propagating perpendicular to the Si substrate and the polarization angle (θ) with respect to the nanobar was varied from 0° to 180°. (b) SERS intensity as a function of θ, with the fit to cos4(θ). ((c), (d)) SERS spectra for 1, 4-BDT are plotted for 514 and 785 nm lasers at different polarization angles. The peak at ~980  was from the Si substrate. The 1, 4-BDT peaks at 1562  are highlighted in gray. ((e), (f)) Enhancement factors of individual nanobars calculated from the peaks of 1, 4-BDT for transverse (circles) and longitudinal (squares) polarizations, and with 514 nm (green) and 785 nm (red) excitations. Reprinted with permission from [37]. Copyright 2007 American Chemical Society.