Recently developed metal nanoshells are ideal building blocks for metal-dielectric photonic crystals operating in visible and near-infrared spectrum. We applied silica coating to screen the van der Waals force and also added a dispersant to increase the electrostatic repulsive force. We also stabilized the gold nanoshell sterically by using a surfactant. With the use of tetrasodium pyrophosphate as a dispersant and Tween as a surfactant, we successfully obtained highly stable colloidal solution of gold nanoshells and subsequently self-assembled them into highly ordered opal structures. We observed well-defined diffraction pattern in the fast Fourier Transform spectra and optical spectra that match well the theoretical photonic band structure.
A novel micro-electro-optic filter formed by integrating photonic crystals with photodiodes on a silicon substrate is demonstrated in this paper. P-n diodes were fabricated on a Silicon wafer using standard processes. Reactive ion etching (RIE) was used to form trenches into the diodes to contain and position photonic crystals. The wafer was then immersed vertically into a slowly evaporating colloidal suspension of silica mircrospheres to assemble the photonic crystal over the photodiodes. Spectral measurements using a grating monochrometer confirmed that a dip exists in the photocurrent response of the photonic crystal filter-photodetectors at the predicted wavelength of 600 nm. We performed a series of measurements using several different sphere sizes and light incidence angles to further characterize the filters, and evaluated the use of device as a wavelength selective detector. Since silica has a low coefficient of thermal expansion, the wavelength selective characteristics of the device are expected to be insensitive to ambient temperatures.