In Situ Study of the Deposition of (Ultra)thin Organic Phosphonic Acid Layers on the Oxide of Aluminum

Abstract

The interest in self-assembling monolayer deposition on various oxide substrate surfaces is steeply increasing in the last decades. Although many studies are being performed, literature does not come with a general insight in the adsorption of these layers on oxide surfaces. Also for the deposition of phosphonic acids on aluminum oxides, there is no global consensus. In this paper, we present an original in situ analysis in order to eludicate the real layer formation mechanism. First of all, the state of the phosphonic acid molecules was determined using DOSY NMR, making sure that no structures other than free molecules were present at the concentration used. With in situ atomic force microscopy and in situ visual ellipsometry, multilayers of phosphonic acids, showing 3D island growth, were determined. It was shown that using the variation of the in situ obtained roughness and bearing ratio, together with the equivalent thickness modeled by ellipsometry, the growth of the layers occurs in situ in three different stages. They consist of increasing number of islands growth, followed by filling up the gaps between islands. At last, within the adsorption time frame measured, the islands grow further in dimensions but not in numbers. This closely corresponds with the behavior of the octylphosphonic acid films analyzed by ex situ techniques.

Effect of time and deposition method on quality of phosphonic acid modifier self-assembled monolayers on indium zinc oxide

“…PAs on Al2O3 are also relevant systems. Atomic force microscopy (AFM) and ellipsometry data for PA-modified Al2O3 surfaces were reported by Hauffman et al 30,31 In situ AFM shows fast island formation at the beginning of deposition followed by gap filling. The islands then grow further before the monolayer fully covers the surface.…”

Observation of self‐assembled layers of alkyl phosphonic acid on aluminum using low‐voltage scanning electron microscopy and AFM

“…Aluminum and its alloys are important practical metallic materials and are usually used after suitable surface treatments, such as anodizing and conversion coating. The formation of SAMs has been investigated as a new surface treatment of aluminum for various applications, including improving adhesion between substrates and paints, and biocompatibilities . SAMs are also introduced on oxidized aluminum surfaces with nanotextures for superhydrophobicity and superoleophobicity .…”

“…It was reported that an anodized aluminum surface coated with fluorinated alkyl phosphonic acids showed higher contact angles for water and organic liquids in comparison with the alkylsilanes with the same alkyl groups, although the reason was not clarified . Although there are some advantages of phosphonic acids for formation of SAMs on aluminum and several studies on phosphonic acid‐based SAMs on aluminum have been carried out, the formation of SAMs has not been fully understood. Recent in situ analysis revealed island growth of phosphonic acid molecules on aluminum oxide, suggesting that a monolayer is not always formed.…”

Self‐assembling behavior of TDPA molecules on inhomogeneous surface of 2024 aluminum alloy

“…However, Hauffman et al . observed multilayer of phosphonic acid molecules on the Al surface deposited from water solution by AFM and ellipsometry, shown by three growth zones including island growth, island coalescence and new island growth. In addition, on the polar mica surface which is similar to oxide film of aluminum, it is possible to deposit self‐assembled vertical bilayers of simple linear phosphonic acid molecules by spread coating technique, where a solution droplet is deposited on a surface and blow dried with an inert gas .…”