Self‐assembled monolayers of octadecylphosphonic acid and polymer films: Surface chemistry and chemical structures studied by time‐of‐flight secondary ion mass spectrometry

Abstract

With the ever-decreasing thickness of functional organic thin films, surface sensitive analytical techniques are required to probe surface/interface chemistry and structural changes of ultra-thin organic films such as self-assembled monolayers (SAMs) of amphiphilic molecules and polymeric coatings. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) fits this requirement because it is extremely surface sensitive and provides rich chemical information. In this article prepared for celebrating the 35th anniversary of our lab as a surface analysis service provider and a surface science research center, we highlight our TOF-SIMS studies on exploring the surface chemistry of SAMs of octadecylphosphonic acid. Due to our contribution to developing the fast growth method of delivering octadecylphosphonic acid SAMs via the use of solvents having a dielectric constant of 3 to 5, we will review the formation mechanisms of SAMs. We will also review our recent results that demonstrated the feasibility of using the ion intensity ratio between C 6 H À and C 4 H À to differentiate the chemical structures of several polymers and depth profiling the cross-linking degree of a polymer. In this article, we show results from principal component analysis on numerous C n H À intensity data from multiple spectra obtained from polyethylene, polypropylene, polyisoprene, and polystyrene. This multivariate analysis method allowed us to better understand the relationships between the polymers and between C n H À , as well as verify the rationale for the selection of C 4 H À as the reference ion for normalization. We demonstrate that together with principal component analysis, TOF-SIMS is unique in differentiating chemical structures of polymers.

Area-Selective Atomic Layer Deposition on Chemically Similar Materials: Achieving Selectivity on Oxide/Oxide Patterns

“…In addition, the properties of solvents can affect the quality of the SAM structure. Studies have shown that when a nonpolar solvent is used, the hydrophilic ODPA headgroups are more likely to escape from the nonpolar solution and align at the solution–substrate interface, which can facilitate the formation of good quality SAMs. , In contrast, a polar solvent may help dissolve the hydrophilic ODPA headgroups, which prevents the alignment of the ODPA headgroup at the solution–substrate interface. Polar solvents also have a higher tendency to adsorb on substrate surfaces, ,, which can introduce more barriers for ODPA molecule adsorption.…”

Superhydrophobic Self-Assembled Silane Monolayers on Hierarchical 6082 Aluminum Alloy for Anti-Corrosion Applications

“…However, only the polar solvents have been extensively used under the consideration that they dissolve the molecules well. Recently, Nie [42] demonstrated experimentally that the dielectric constant of the solvent has a great role in producing the self-assembled monolayers because it measures the ability of dissolving or separating charged particles. Thus, not only the polar solvent but also the apolar solvent with an appropriate dielectric constant is able to align and concentrate the polar head-groups of the molecules on its surface.…”

Parameters controlling octadecyl phosphonic acid self-assembled monolayers on titanium dioxide for anti-fouling biomedical applications

“…The researchers also showed that full coverage and well-ordered SAMs of ODPA were formed specifically in non-polar solvents with dielectric constants between 3 and 5 [20]. Interestingly, the use of these specific non-polar solvents significantly decreased deposition times from days and hours to minutes and seconds [20,21]. Furthermore the ability to form SAMs using environmentally friendly solvents such as anisole (dielectric constant of 4.3) has also been demonstrated for aluminium films [18].…”

“…Importantly, for titanium modification, differences between water and toluene have been shown to affect not only the binding mechanism of propylphosphonic acid and the close packing of the molecules but the solvent of choice has also been shown to influence the impact of other processing conditions, such as temperature and ODPA concentration, on the successful development of a SAM [17]. Nie and co-authors discovered that well-ordered SAMs of ODPA only formed on the surface of silicon wafers and aluminium films when using non-polar solvents whilst use of polar solvents resulted in low quality SAMs [18][19][20][21]. The researchers also showed that full coverage and well-ordered SAMs of ODPA were formed specifically in non-polar solvents with dielectric constants between 3 and 5 [20].…”

“…Nie and co-authors discovered that well-ordered SAMs of ODPA only formed on the surface of silicon wafers and aluminium films when using non-polar solvents whilst use of polar solvents resulted in low quality SAMs [18][19][20][21]. The researchers also showed that full coverage and well-ordered SAMs of ODPA were formed specifically in non-polar solvents with dielectric constants between 3 and 5 [20]. Interestingly, the use of these specific non-polar solvents significantly decreased deposition times from days and hours to minutes and seconds [20,21].…”