Dendrimer-Modified Silicon Oxide Surfaces as Platforms for the Deposition of Gold and Silver Colloid Monolayers:  Preparation Method, Characterization, and Correlation between Microstructure and Optical Properties

Abstract

We describe a novel approach for Au and Ag colloid monolayer formation on different silicon oxide surfaces such as glass, silicon, and ITO. The preparation method is simple and yields monolayers with easily controlled spacing within the monolayer without aggregation of metal particles. The colloid monolayers are prepared in two steps: (1) modification of the substrates with starburst dendrimers and (2) noble metal colloid deposition onto the dendrimer layer. Different Au and Ag colloids, ranging from 15 to 80 nm in particle diameter, have been deposited onto the dendrimer-modified surfaces. The structure and properties of the resulting particle arrays have been studied by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, and surface-enhanced Raman scattering (SERS). XPS data show that the dendrimers spontaneously adsorb to various silicon oxide surfaces. The thickness of the dendrimer overlayer has been calculated and lies in the d ) 14-25 Å range. SEM and AFM data show that the colloids spontaneously form continuous films on the dendrimermodified surfaces. The noble metal particles are well isolated and confined to a single layer, and aggregation does not occur on the surface. The interparticle spacing (74-829 nm) and surface coverage can be controlled over a wide range by colloid size, colloid concentration, and immersion time. UV-vis spectroscopic data show that the microstructure directly controls the optical properties of the layer. Finally, we demonstrate that the prepared substrates provide a useful platform for SERS studies of materials adsorbed on the metal particles.

A Spectroscopic Study of Mercury Vapor Adsorption on Gold Nanoparticle Films

“…The similarity of the N(1s) binding energy for APTMS (400.7 eV) and the PAMAM dendrimer (401.0 eV) indicates that both layers contain nitrogen atoms in a similar chemical state (i.e., -NH 2 ). Our determination of the N(1s) binding energy for the dendrimer sample is in very good agreement with a previous XPS study (400.7 eV) (16). The N(1s) binding energy for PDAC is higher than for the other two adhesion layers, which reflects the formal positive charge on the quaternary nitrogen atom in the polymer.…”

“…The thickness of the APTMS film indicates that the alkyl chains are nearly perpendicular to the oxide surface. The dendrimer, in agreement with Bar's observation, is compressed on the surface relative to its diameter in solution of ∼4 nm (16). The morphology of PDAC on the surface is difficult to determine from just a thickness determination, but based on the measured thickness, its morphology can be assumed to be typical of cationic polymers on surfaces (27).…”

“…In one strategy a bifunctional organic molecule is anchored to a substrate through one end group and the other, such as -SH, -NH 2 , or -CN, is used to bind the nanoparticles (12)(13)(14)(15). In another approach, purely electrostatic interactions between a charged adhesion layer (usually a polymeric film) and a colloidal particle can facilitate the adsorption process (16)(17)(18). Alternatively, nanoparticles can be transferred to a solid substrate through the Langmuir-Blodgett technique (19).…”

Poly(N-isopropylacrylamide)-grafted silica as a support of platinum colloids: Preparation method, characterization, and catalytic properties in hydrogenation

“…10,11 Stable noble metal colloids in aqueous solution can be easily and reproducible prepared in a wide range of sizes by different methods. 12 The catalytic properties of noble metal particles depend on the preparation method, the capping agent, and particularly the size and shape. 13 We have reported the formation of platinum nanoparticles in a ethanol-water mixture by ethanol reduction of ionic platinum in the presence of poly(N-isopropylacrylamide) (PNIPAAm).…”

Gold-Containing dendrimers: A new class of macromolecules

“…Step 1 Dendrimers Colloids Figure 4 Schematic representation of the synthetic route for colloid monolayer preparation (adapted from reference 23) …”