Byproduct-Free Route to Aminosiloxane Monolayers on Silicon/Silicon Dioxide

Abstract

The chemisorption of N-methyl-aza-2,2,4-trimethylsilacyclopentane from either the solution or the vapor phase produces monolayer films on silicon (oxide) substrates. The formation of a covalent siloxane linkage to the surface by this adsorbate is accompanied by ring opening, which produces no byproduct. The resulting secondary amine reacts with maleic anhydride to produce a carboxylic acid-terminated surface, accompanied by the formation of a stable amide bond. These reactions and their products were characterized by a combination of optical ellipsometry, contact-angle goniometry, and X-ray photoelectron spectroscopy.

Byproduct‐Free Synthesis, Characterization, and Reactivity of 1, 2‐Diaminosiloxane Monolayers on Silicon/Silicon Dioxide

“…We describe a one‐step synthesis of monolayers terminated by 1, 2‐diamines on Si/SiO 2 by reaction of the cyclic azasilane, N ‐(2‐aminoethyl)‐2, 2, 4‐trimethyl‐1‐aza‐2‐silacyclopentane at the surface. This cyclic azasilane reacts with surface silanols to give a ring‐opened product covalently attached to the surface through a siloxane linkage . Our current studies focused on adsorptions from solution phase, and the Brønsted basicity of the product surface and its potential efficacy as a coupling agent.…”

“…We attribute the peak at 285.0 eV (fixed by calibration) to a combination of photoemission from the aliphatic carbons and those bound to the amine nitrogens . The peak at ∼286.1‐286.2 eV is consistent with carbon bound to protonated amine nitrogens . The photoemission in the N 1s region comprises two peaks, at ∼399.2‐399.9 eV assigned to the unprotonated amines and at ∼401.2‐402.0 eV assigned to protonated or hydrogen‐bonded amines …”

“…Comparison of these results for monolayers containing both primary and secondary amine groups (Figure ) to results for an analogous surface containing only secondary amines with similar steric constraints (OSiMe 2 CH 2 CH (Me)CH 2 NHMe) provides interesting insights . Under the same reaction conditions with maleic anhydride, the surface reported here (primary and secondary amines) reached limiting values of contact angle at high and low pH within 20 min.…”

“…Under the same reaction conditions with maleic anhydride, the surface reported here (primary and secondary amines) reached limiting values of contact angle at high and low pH within 20 min. The secondary amines reported previously, in contrast, required about 6 d to reach a limiting wettability . We infer from this difference that primary amines react at a faster rate than the more sterically hindered secondary amines.…”

“…In addition, organosilanes with amine functional groups have been extensively used as primers in peptide synthesis, immobilization of biomaterials, and the preparation of DNA‐based micro‐arrays on substrates . We have previously reported methods for producing self‐assembled monolayers (SAMs) containing primary amine groups on Si/SiO 2 , and here we have extended this work to include vicinal diamines …”