Vapor Deposited Electro-Optic Films Self-Assembled Through Hydrogen Bonding (22107/22065)
Northwestern researchers created a new family of designed molecular chromophores that afford acentric films essential to non-linear electro-optic applications. These novel materials exhibit excellent physical and non-linear optical properties for waveguiding modulator applications. Intermolecular hydrogen bonding is utilized to produce stable non-centrosymmetric films with unique orientation normal to the substrate plane. Vapor film deposition supports scalable device manufacture.
ADVANTAGES: New chromophoric materials of this invention afford stable non-centrosymmetric films for non-linear optical (NLO) device applications, including modulators, waveguides, switches, emitters and detectors. The fabrication process overcomes limitations of current acentric film forming methods and is well suited for efficient device fabrication.
SUMMARY: Molecule based photonic materials promise significant advances in electro-optic modulators for greatly increased rates of information transmission. Non-centrosymmetric materials are basic to these applications. Current methods to achieve acentric molecular orientation include electric-field (EF) poling, Langmuir-Blodgett (LB) film transfer and layer-by-layer self-assembly (SA). However each has important limitations of orientation stability (EF, LB), variable NLO response (EF, LB), and slow fabrication rate (SA).
Hydrogen bonding has been employed to impart molecular orientation in solids and films. However the requisite perpendicular to substrate orientation, essential for maximum EO response in wave guide applications utilizing H-bonding has not been reported. The present invention employs specially designed constructs that incorporate H-bond donor and acceptor functions in a single NLO active chromophore. These features force the molecules to align in the desired direction from vapor phase to solid film, normal to the substrate plane. Stable non-centrosymmetric microstructures in the deposited film with intrinsic acentricity, good film strength and smoothness are realized. The chromophores are thermally stable, insensitive to moisture, and the films are easy to process. Vapor deposition techniques are rapid, yielding micrometer thick films within hours. The base layer is chemically anchored to glass, quartz, silicon or ITO type substrates.
A representative 1.2 ?m film prepared on ITO glass substrate exhibited layer-by-layer structure with 9.1Å repeat distance and rms roughness of only 1.7 nm. Second harmonic generation measurements at ?0=1064 nm displayed a quadratic dependence at 532 nm light output intensity versus film thickness. A d33 of 0.15 pm/V and d31 of 0.25 pm/V was determined.
STATUS: US patent 7, 291,293 has issued.
Peiwang Zhu and Tobin J. Marks
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