Plasma Polymerized Multi-Layered Photonic Films

A multilayer optical interference film has been developed using plasma-enhanced chemical vapor deposition (PECVD) of different organic precursor materials. A relatively large refractive index contrast for polymers (>0.2) is achieved by sequential plasma polymerization (PP) of octafluorocyclobutane (OFCB) and benzene. Gas-phase molecules of both precursors, excited by an argon plasma in a flowing afterglow reaction chamber, are deposited on a variety of substrates to form dense, pinhole-free, cross-linked polymer films. The PP-OFCB film yields a refractive index of 1.40, whereas PP-benzene exhibits a refractive index of 1.61 at 500 nm. We report here on the chemical (FTIR and XPS), optical (variable angle spectroscopic ellipsometry and UV−Vis spectrometry), and morphological (scanning electron microscopy) characterization of individually polymerized films of each component. These data are used to design a multilayer film with a notch at ∼1 μm. A ten-bilayer stack (alternating high and low refractive index) was fabricated by sequential deposition of high and low refractive index layers at approximately 1 / 4 λ optical thickness. Optical spectra of the experimental stack exhibit a notch wavelength within several nanometers of the design wavelength indicating good thickness control.