Traditional color filters use organic dyes or chemical pigments that can degrade with light and temperature exposure, and require accurate lithographic alignment to pattern each color pixel over a large area. While nanoplasmonic color filters—fabricated to achieve tunable color transmission by adjusting the geometric parameters of nanohole structures (periodicity, shape, and hole size)—are environmentally rugged and simple to fabricate, their low transmission efficiency (30% at visible wavelengths) has, up until now, limited commercial applications. Researchers at Lehigh University (Bethlehem, PA) have since solved the transmission problem through a plasmonic subtractive color filtering (SCF) scheme that increases peak transmission to 60–70%.
In plasmonic SCF, specific colors (cyan, magenta, and yellow) are generated by removing their complementary components (red, green, and blue) from the visible spectrum by varying the period of nanopatterns fabricated (via focused ion beam milling) in single-layer, ultrathin silver (Ag) films on a transparent glass substrate. Unlike plasmonic additive color filtering (ACF) schemes, the transmission through the ultrathin nanopatterned Ag film at resonance wavelengths is actually lower than for unpatterned Ag films, resulting in strong suppression of specific colors. Away from the resonance wavelength, the transmission through the nanogratings increases significantly as highly reflective Ag is removed by patterning of the ultrathin Ag film, leading to the record-high transmission peaks. The filters can be used in miniature spectroscopy, multispectral imaging, and transparent display applications. Contact Filbert J. Bartoli at [email protected].
