Surface Chemistry of Mercaptan and Growth of Pyridine Short-Chain Alkoxy Silane Molecular Layers

Abstract

The use of molecular layers to modify the surface and interfaces of solid-state materials while retaining their bulk properties offers great potential. Despite the widespread interest, little work has been undertaken to characterize the growth and surface chemistry of the short-chain alkoxy silane molecular layers. Variable angle spectroscopic ellipsometry, contact angle goniometry, and X-ray photoelectron spectroscopy are used to undertake the work in the present study. Results indicate that 3-mercaptopropyltrimethoxysilane and 2-(trimethoxysilylethyl)pyridine are both unique among the short-chain alkoxy silanes and grow multilayer films in a toluene solution on hydroxylated SiO2 surfaces. In particular, the mercaptan molecular layers show evidence of a changing surface chemistry as a function of growth time. Further, added surface moisture on mercaptan molecular layers yields thicker films of a higher density with more reduced surface sulfur when subsequent growth is resumed as compared to a control sample. Further, the pyridine molecular layers possess negative optical birefringence much like the parylene polymers, polyimides, and phthalocyanine Langmuir-Blodgett films undertaken by previous researchers. In previous cases, the presence of a phenyl group with a large anisotropic molecular polarizability caused the large in-plane polarizability. Further, the pyridine molecular layers exhibited a high index of refraction of 1.567 ( 0.005 explaining its superior properties as a metallic diffusion barrier at dielectric/metal interfaces from previous research.

Effects of Tailored Surface Chemistry on Desorption Electrospray Ionization Mass Spectrometry: a Surface-Analytical Study by XPS and AFM

“…The C 1s/O 1s (533.8 eV) ratio was found to be 5.9, which is consistent with previous hypotheses. In addition, the ratio of C 1s/S 2p was found to be 5.0, consistent with the hypothesis of the multilayered adsorption of silanes, involving ethanesulfonic acid or ethylmercaptan elimination as the multilayer mercaptan grows [35]. These findings support ARXPS observations, which showed a thickness double that expected from a monolayer of MTES molecules.…”

“…Starting from g-MTES, three major peaks are identified in the C 1 s spectrum (Figure 4a). The peak centered at 285.0 eV was ascribed to C-C and C-Si bonds [35][36][37], whereas carbon atoms bonded to sulfur and oxygen appear at 286.3 eV [38,39]. A third minor peak, found at about 288 eV, may be due to an oxygen-containing compound adsorbed on the sample surface.…”

“…A further confirmation of the effectiveness of the functionalization was from Si 2p, where the high-resolution spectrum signal was found to contain contributions at 103.0 and 103.7 eV (Figure 4d) ascribable to Si of g-MTES and Si-O of glass [40], respectively. The high-resolution spectrum of S 2p was fitted with two doublets whose maxima in their 2p 3/2 components were at 164 and about 168 eV, assigned to the presence of well-ordered MTES layers having thiol groups at the top of the surface [41], and to a minor contribution from oxidized sulfur [35,42,43] (Supporting Information). For g-OTES, similarly to what was observed for g-MTES, C 1 s showed three major contributions at 285, 286.5, and 288 eV ( Figure 4b) and two components for the Si 2p signal at 103.0 and 103.8 eV, ascribed to Si-C and glass (Figure 4e).…”

Molecular Layer Chemistry via Parylenes

“…[2] However, unless the surface is carefully treated and the alkyl chain is long, these SAMs tend to form disordered monolayers, which do not pack well. [3,4] Unlike SAMs, which pack based on the all trans configuration of the alkyl chain, the repeat unit of the parylenes (the monomer) interact with each other based on the high polarizability of the phenyl ring. These molecular layers are significantly more robust than alkyl-based SAMs, with a conformal vapor deposition process, superior thermal stability, [5] selectivity versus transition metals, [6,7] and functionalizability.…”

Selective nanoshaving of self-assembled monolayers of 2-(4-pyridylethyl)triethoxysilane

“…The complications that need to be avoided in the selective mechanical "shearing" process are the removal or displacement of all of the adsorbate species (as opposed to shaving off a portion of the molecule), or the mechanical canting or "tipping" the orientation of the adsorbate species. Layers made from alkoxy silane species, with various end group ligands, have unique merits as these molecular complexes form strong bonds with an oxide surface and can be used to modify both the dielectric properties and the optical properties of the surface [13]. In this paper we focus on 2-(4-pyr idylethyl)triethoxysilane molecules, schematically shown in Figure 1, to demonstrate a selective mechanical cutting of molecular layers on SiO 2 .…”