Aminopropylsilatrane Linkers for Easy and Fast Fabrication of High-Quality 10 nm Thick Gold Films on SiO₂ Substrates

Abstract

Fabricating smooth and contamination-free sub-10 nm thick gold layers on dielectric substrates is of interest for a number of applications, including plasmonics, metamaterials, and nanoelectronics. Metallic adhesion layers are often used to facilitate good adhesion between gold and substrates, but at the cost of interfacial alloying and subsequent deterioration of the optical and electrical properties of the thin films. Another approach for promoting adhesion between gold and SiO 2 substrates is the use of self-assembled organosilane monolayer linkers, such as (3aminopropyl)trimethoxysilane (APTMS). APTMS, however, is a corrosive chemical, and its monolayer preparation is highly sensitive to ambient conditions. Here, we introduce an easy and fast immersion process using (3-aminopropyl)-silatrane (APS) for achieving smooth and high-purity gold films and compare its performance to APTMS. Our APS recipe is water based, does not require environmental considerations, and has approximately 6 times faster deposition time than APTMS (30 min vs 3 h). The results demonstrate that both organic molecules promote the formation of continuous and smooth 10 nm thick gold films, without leading to considerable chemical intermixing at the interface. Monitoring the growth evolution of the gold layer indicates a threshold thickness of 6−7 nm for obtaining continuous films. Overall, the ease of use, faster processing time and low toxicity of APS make it an attractive choice for fabricating high-quality ultrathin gold films on SiO 2 substrates.

Polymer Brushes on Silica Nanostructures Prepared by Aminopropylsilatrane Click Chemistry: Superior Antifouling and Biofunctionality

“…After functionalizing the surface with APS, the C 1s spectrum in Figure B was similar to that for the cleaned substrate with a minor contribution at 286.43 eV attributed to C–N. Also, a clear signal appeared in the N 1s spectrum showing (at least) two peaks, which we attribute to freely available amines (−NH 2 ) and hydrogen bonded (--NH 2 ) or protonated (−NH 3 + ) amines (Figure B), in agreement with observations of APTES-functionalized SiO 2 . ,− However, Heinig et al observed a single -NH 2 peak for XPS measurements on polished silicon wafers (0.2 nm RMS roughness) incubated with APS in water for 30 min. We point out that the amount of --NH 2 and −NH 3 + in relation to −NH 2 is expected to vary in the dry state depending on available surface charges and hydroxyl groups.…”

“…(Although the presence of APS on the surface was qualitatively confirmed, the surface coverage was not quantified in any way in those studies.) After binding, the APS layer should ideally be cured by heating to 75 °C to make it stable toward hydrolysis in water (Figures S4 and S5), similarly to films formed by silanes. ,− Note that this refers to stability after surface binding: APS is perfectly stable in the presence of water while in the solution phase, in contrast to conventional silanes such as APTES. For sulfo-SMCC, hydrolysis may occur in aqueous environments, and the molecule is not easily soluble at high salt concentration, while the hydroxysuccinimidyl group requires a pH of 7–9 for efficient reaction with primary amines.…”

“…However, for silica, such protocols have so far almost exclusively relied on silanes (e.g., triethoxysilane groups), which are widely known to be unreliable due to their susceptibility to hydrolysis and self-polymerization. This results in nonuniform coatings on silica and poor reproducibility in the film properties. − We note that Gidi et al recently presented a protocol for passivating silica with PEG-silanes, but the antifouling performance was only evaluated with respect to a few selected biomolecules, not a real biological fluid like serum. In fact, for grafting-to methods there appears to be a trend of not thoroughly testing the antifouling performance, while this seems to be an established procedure when it comes to grafting-from. , We also note that compatibility with nanochannels or nanopores is normally not demonstrated, neither for grafting-to nor grafting-from approaches.…”

“…A class of molecules that could overcome the limitations of conventional silanes is so-called silatranes. , The closed and compact silatrane group is stable in the presence of water, while still being able to form covalent bonds with silica. ,, Yet, to date silatrane compounds have not been used for grafting polymers to silica. In this work, we present a simple and generic method to make silica highly antifouling and/or bioselective, using aminopropylsilatrane and click chemistry for attaching thiolated poly­(ethylene glycol) (PEG).…”

Curing, thermal, tensile and flammability characteristics of sepiolite/ethylene propylene diene monomer rubber composites with glut palmitate salt and silane coupling agents

“…The amino-silanes are frequently used as coupling or crosslinking agents due to the alkoxy groups performing hydrolysis and polycondensation processes in the presence of water. [37,38] The organosilanes that include the amine (NH 2 ) group are hydrolysed almost instantly in water, generating stable aqueous solutions. Besides, they could serve as linking units in attaching other functional groups.…”