ToF‐SIMS study of stages in the electrochemical growth of insulating poly(o‐aminophenol) films

Abstract

Previous XPS investigations of insulating poly(o‐aminophenol) (PoAP), electrosynthesized by cyclic voltammetry on Pt substrates, revealed the formation of a thin film of about 7 nm of thickness, firmly adherent onto the electrode surface and stable even under Ultra High Vacuum (UHV) conditions. A constant repeat formula made of alternating quinoneimine and monomer units was derived with polymer chains terminating as carbonyl‐type groups. Based on these findings, we have continued our investigation on insulating PoAP by employing time‐of‐flight SIMS whose superior surface sensitivity is well‐known. The aim was to corroborate the polymer structure with particular reference to the top surface layers in view of possible bio‐applications and to understand the possible way of interaction with the underlying platinum electrode surface. In order to do this, we analyzed PoAP films grown at different levels of the electrochemical synthesis (1, 5, and 20 scan cycles) and the platinum substrate itself. The individuation of the main characteristic fragments and the behavior of their intensity by varying the stage of the electropolymerization allowed to confirm the polymer structure and the presence of terminating carbonyl groups. Remarkably, from the analysis of the PoAP/Pt interface at the early stage of the polymer formation, it was possible to discern that polymer chains tend to interact with the electrode surface preferentially by the nitrogen atom of the oxidized monomers. Copyright © 2016 John Wiley & Sons, Ltd.

In Situ Electrochemical–AFM and Cluster-Ion-Profiled XPS Characterization of an Insulating Polymeric Membrane as a Substrate for Immobilizing Biomolecules

“…It has a monomer-like ratio in agreement with our previous ToF-SIMS results. 8 In conclusion, the distribution of water molecules in the structure is good evidence of the alignment of PoAP chains perpendicular to the substrate. The observation made feasible by the use of cluster ion etching provides a useful example of the etching efficiency of an argon gas cluster ion source: the preservation of chemical PoAP features through the profile is a typical indicator of the minimal damage effects from the MAGCIS source.…”

“…The majority of the research on the PoAP structure and morphology has been based on ex situ experiments after washing, drying, or treatment under vacuum on the polymeric films. 1,2,4,8,9,19 Here, an in situ EC−AFM investigation of the stages of its electrochemical deposition on platinum electrodes was attempted because it affords fundamental insight into the simultaneous study of the surface morphology and growth mechanism. 25 PoAP was electrochemically synthesized on Pt as described in the Experimental Section, and two different approaches for the morphological image registration were adopted.…”

“…XPS and, more recently, time-of-flight secondary ion mass spectrometry (ToF-SIMS) investigations have led to the hypothesis that the film composition consisted of short chains, on average 7 nm, made of alternating quinoneimine and oAP units and containing water molecules. , XPS results from smaller numbers of cycles showed that the PoAP composition is the same at any number of cycles . Thus, the progressive coverage of the platinum sites with each cycle was postulated and confirmed by use of the electrochemical oxidation of potassium ferrocyanide to measure the remaining exposed surface as a function of the number of cycles.…”

“…9 Thus, the progressive coverage of the platinum sites with each cycle was postulated and confirmed by use of the electrochemical oxidation of potassium ferrocyanide to measure the remaining exposed surface as a function of the number of cycles. The most recent work 8 by ToF-SIMS analysis of the PoAP/Pt interface in the early stage of polymer formation showed that polymer chains tend to interact with the electrode surface preferentially through the nitrogen atom of the oxidized monomers. ToF-SIMS as a function of the number of cycles through to full passivity showed that the nitrogen-containing fragment attached to Pt decreases with increasing surface coverage, as it becomes masked by the clustering of polymeric molecules progressively adsorbed on neighboring platinum sites.…”

“…As this basal fragment decreases in intensity, with coverage, fragments associated with the outer terminal groups increase in intensity. 8 Some questions left unanswered concern the growth orientation of polymer chains. Because of its very small thickness, the vertical alignment of polymer chains was deduced only from indirect evidence.…”