Determining the thickness of aliphatic alcohol monolayers covalently attached to silicon oxide surfaces using angle-resolved X-ray photoelectron spectroscopy

Abstract

The thickness of alcohol based monolayers on silicon oxide surfaces were investigated using angle-resolved X-ray photoelectron spectroscopy (ARXPS). Advantages of using alcohols as building blocks for the formation of monolayers include their widespread availability, ease of handling, and stability against side reactions. Recent progress in microwave assisted reactions demonstrated the ease of forming uniform monolayers with alcohol based reagents. The studies shown herein provide a detailed investigation of the thickness of monolayers prepared from a series of aliphatic alcohols of different chain lengths. Monolayers of 1-butanol, 1-hexanol, 1octanol, 1-decanol, and 1-dodecanol were each successfully formed through microwave assisted reactions and characterized by ARXPS techniques. The thickness of these monolayers consistently increased by ~1.0 Å for every additional methylene (CH2) within the hydrocarbon chain of the reagents. Tilt angles of the molecules covalently attached to silicon oxide surfaces were estimated to be ~35° for each type of reagent. These results were consistent with the observations reported for thiol based or silane based monolayers on either gold or silicon oxide surfaces, respectively. The results of this study also suggest that the alcohol based monolayers are uniform at a molecular level.

An electrochemical comparison of thiolated self‐assembled monolayer (SAM) formation and stability in solution on macro‐ and nanoelectrodes

“…Establishing what area is available is key to properly understanding the surface coverage and inspiring confidence in the data reported in this work. [ 9b ]…”

“…The current state of the art theory is that the thiols (RSH) thioesters (RSR) and disulfides (RSSR), deposited from the solution undergo a two‐step binding process to the electrode surface. [ 7c,9 ] There is an initial physisorption step followed by chemisorption in which covalent Au‐S bonds are formed. [ 8b ] During this second step, there is a rearrangement of the surface as pits form in the electrode and the SAMs aggregate to form islands.…”