Surface electromagnetic modes in prolate spheroids of gold, aluminum, and copper

Optical absorbance measurements are presented for discontinuous films of gold, aluminum, and copper as a function of wavelength, polarization, and angle. Anomolous peaks in the absorbance spectra are observed for all three metals. Two peaks are detected for gold, and one peak is detected for both aluminum and copper. Comparison with electromagnetic theory is made on the basis that the microstructures can be modeled as prolate spheroids. The theoretical model is tested experimentally for various minor-to-major-axis ratios of the spheroid.