NSOM Investigations of the Spectroscopy and Morphology of Self-Assembled Multilayered Thin Films

Abstract

Near-field scanning optical microscopy (NSOM) and atomic force microscopy (AFM) have been employed to spatially resolve the complex nanoscale morphologies, spectroscopy, and energy-transfer efficiencies of self-assembled multilayered structures composed of alternating layers of R-zirconium phosphate [R-Zr(HPO 4 ) 2 ] (ZrP) and dye-labeled poly(allylamine hydrochloride) (dye-PAH) (where dye ) Fluorescein (FL), Rhodamine B (RhB), or Texas Red (TR)). Two types of multilayer films have been investigated, namely, glass/anchor/ ZrP/dye-PAH and glass/anchor/ZrP/dye-PAH/ZrP/dye-PAH, which were formed by the sequential layer-bylayer adsorption of the charged polyelectrolyte component layers. High-and low-coverage films were investigated. The glass/anchor/ZrP assemblies were shown to consist of a densely packed "tiled" motif of ZrP sheets which lie flat on the surface and cover more than 95% of the area, with average plate sizes of height ) 13 (7) Å, width ≈ 150 nm. The dye-labeled polymer layers in glass/anchor/ZrP/dye-PAH and glass/ anchor/ZrP/dye-PAH/ZrP/dye-PAH were shown to adhere to the surface of the ZrP sheets and fill in the cracks between the sheets to a lesser extent. The measured heights of these polymer-coated multilayer films are 26(9) and 48(15) Å, respectively. These heights are consistent with theoretical estimates of ideally packed ionic films (28 and 48 Å, respectively). Dual-wavelength fluorescence NSOM imaging at 580 nm and >610 nm and near-field photobleach experiments were used to spatially resolve nanoscopic regions that display energy transfer between the layers.

Ultrathin polymer coatings by complexation of polyelectrolytes at interfaces: suitable materials, structure and properties

“…Besides exfoliated smektite-type clays, some other intrinsically charged inorganic sheets have been employed for ESA such as exfoliated a-zirconium phosphate 119,200,206,207,255,274,277,289,291,322,323) , niobates 206,207,277,296,322) , tungstates 121) , MoS 2 150, 284) , SnS 2 284) or graphite oxide 150,195,287,294,321,324,325) . In addition to synthetic polymers and charged nanoobjects, natural polyelectrolytes have been used for ESA such as nucleic acids, proteins, and polysaccharides, as well as certain charged supramolecular biological assemblies such as virus 326) , or membrane fragments [327][328][329][330] .…”

“…Not surprisingly, layer-by-layer deposition gives rise to polymer films with alternating surface properties, such as contact angle 30,187,273,363,394,398,400,436) , chemical composition 35,227,239,383,398,437) , or f-potential 32, 34-41, 46, 92, 353) . Prepared films are typically not birefringent 15,32,58,80,81,88,89,110,135,138,254,255,431) , i. e. they are isotropic in the film plane (for an exception, see ref. 93) ), and very smooth 20,29,237,270,431) .…”

“…Still, trans-cis isomerization upon irradiation with polarized light enables to induce birefringence into the layers, and thus to create orientation layers for liquid crystals or to potentially serve for optical storage 88,120,144) . Other studies look at photo-bleaching 255) or photo-ablation 19,26) to create patterns in the films. The majority of photo reactions studied in ESA-films are, however, focused on photo polymerizations or on crosslinking reactions to improve stability of the films 87,96,99,103,104,113,114,141,212,213,414) .…”

Photocatalytic Water Oxidation in a Buffered Tris(2,2‘-bipyridyl)ruthenium Complex-Colloidal IrO2 System

“…5 The preparation of amine-derivatized silica has been described elswhere. 13 A portion, 0.1 g, of amine-derivatized silica was stirred for 1 h in 80 mL of 6.2 × 10 -4 M colloidal IrO 2 . The amount of adsorbed colloid was estimated to be 5.0 × 10 -4 mol/g from UV-vis spectra of a colloidal IrO 2 solution (which has a broad absorption band between 500 and 700 nm 8 ) before and after adsorption.…”

Electrochemical behavior of Ag+ intercalated layered oxides

“…The pH of the resultant solution was around 12. The deposition of the intercalated layered oxide films on platinum substrates was carried out by layer-by-layer self assembly (LBL) method [11,[43][44][45]. LBL method allows sequential deposition of oppositely charged species on a substrate.…”