Nanoscale Refractive Index Tuning of Siloxane-Based Self-Assembled Electro-Optic Superlattices

Abstract

The refractive indices of self-assembled organic electro-optic superlattices can be tuned by intercalating high-Z optically transparent group 13 metal oxide sheets into the structures during the self-assembly process. Microstructurally regular acentricity and sizable electro-optic responses are retained in this straightforward synthetic procedure. This ªone-potº all wet-chemistry approach involves: i) layer-by-layer covalent self-assembly of intrinsically acentric multilayers of high-hyperpolarizability chromophores on inorganic oxide substrates, ii) protecting group cleavage to generate a large density of reactive surface hydroxyl sites, iii) self-limiting capping of each chromophore layer with octachlorotrisiloxane, iv) deposition of metal oxide sheets derived from THF solutions of Ga(O i C 3 H 7 ) 3 or In(O i C 3 H 7 ) 3 , and v) covalent capping of the resulting superlattices. Scheme 2. Schematic representation of the layer-by-layer self-assembly of 1-based chromophoric superlattices with incorporation of refractive index modifying group 13 oxide layers. 394

Specular x-ray reflectivity study of ordering in self-assembled organic and hybrid organic–inorganic electro-optic multilayer films

“…In the present study, substrate cleaning procedures, chromophore synthesis, and film analyses were similar to those previously reported. 6,13,14,26,27 All reactions were carried out under inert atmosphere in a nitrogen filled glovebox or using standard Schlenk techniques. Solvents were dried over Na/K alloy, distilled and degassed before use.…”

“…Here b i is the atomic scattering factor for the ith atom 35 ͑the summation is carried out over all atoms͒, N A is Avogadro's number, M is the molar mass, and d is the physical density of the substance. Assuming that Ga and In in the films are present in the form of Ga 2 O 3 (dϭ5.88 g/cm 3 ) and In 2 O 3 (d ϭ7.18 g/cm 3 ), 14 we calculate electron densities for these compounds: Ga 2 O 3 ϭ2.2 and In 2 O 3 ϭ2.7. Comparing these values with those experimentally obtained by XRR for the Ga-and In-based SA films, 1.30 and 1.65, we conclude that the mass contribution of the inorganic part in the Ga-and In-based SAS multilayers is about 50%.…”

“…36,37 This result is in agreement with the twofold greater thickness of the repeat distances in the hybrid films as compared to the pure organic ones, based on the summed thicknesses of the chromophore and two capping layers ͑ϳ30 Å͒. 13,14,27 The fitting procedures also indicate a good fit to the XRR data based on the average electron density of the multilayer films that results from the relative roughness of the individual layers in comparison with their thickness.…”

“…The unique layer-bylayer modularity of the building block incorporation process has raised the intriguing issue of whether other functional ͑e.g., optical, magnetic, mechanical͒ constituents can be intercalated during the self-assembly process. In a recent study 13,14 we reported an all-''wet-chemical'' approach to the self-assembled superlattice ͑SAS͒ refractive index tuning achieved by intercalating layers of gallium or indium oxide while retaining matrix acentricity, large electro-optic responses, and microstructural regularity ͑Fig. 1͒.…”

Electric-field-induced layer-by-layer fabrication of inorganic–organic hybrid second-order nonlinear optical films

“…The poor temporal or mechanical stability of the poled polymer systems and LB films restrict their potential applications [17,18]. Chemical reaction in covalent self-assembly is tedious and the reaction condition is always rigorous [19][20][21][22][23][24]. The layer-by-layer (LbL) assembly technique which utilizes electrostatic interaction as the driving force for film construction is a versatile and convenient method for the construction of layered ultrathin films with precise control of film thickness and composition [25][26][27][28][29][30][31][32][33].…”