Is the Enhanced Adhesion of PEDOT Thin Films on Electrodes Due to Sulfur - Gold Interaction? - An XPS Study

Abstract

Electrode materials obtained through electropolymerization of 3,4-ethylenedioxythiophene (EDOT) have sparked interest toward applications in neuroscience and neuroprosthetics due to their favorable electrochemical properties and their biocompatibility. However, insufficient mechanical stability had been an unresolved issue and hindered practical applications, until recent research by our group demonstrated proper adhesion of poly(3,4ethylenedioxythiophene) (PEDOT) to a gold surface. In the present study, X-ray photoelectron spectroscopy (XPS) was employed and in particular the chemical shift of the S2p band, which is indicative of binding between sulfur and gold, was used to assess the degree of interaction between 3,4-ethylenedioxythiophene (EDOT), thiophene, and 3thiophenecarboxylic acid (thiophene-COOH), with the gold surface. The results of the XPS investigations indicate a covalent bond between EDOT and gold, which should indeed contribute to improved adhesion.

New One-Step Thiol Functionalization Procedure for Ni by Self-Assembled Monolayers

“…3 The third and less intense peak observed at 168.0 eV confirms the presence of a small amount of oxidized sulfur. 23 These three structures are well consistent with the overall picture of the monolayer structure, with some thiophenic sulfurs or cysteine S terminals that interact strongly with the surface. The presence of some oxidized sulfur can be explained by taking into account the relative fragility of the side chain cysteine Boc protected moiety (See Chart 1), which can undergo oxidation reactions.…”

“…The main peak at 163.5 eV is associated to sulfur in the thiophene rings -or to unbound S, while the one at 161.0 eV gives a strong indication of the presence of some level of reaction between S and the substrate, with the formation possible molecular fragments from reacted thiophene units and chemisorbed sulfur. 23 The bonding between S in the cysteine groups with the substrate can also contribute to the low binding energy feature. 3 The third and less intense peak observed at 168.0 eV confirms the presence of a small amount of oxidized sulfur.…”

Binding Interactions of Keratin-Based Hair Fiber Extract to Gold, Keratin, and BMP-2

“…In the S2p region, a 163.6-eV peak was recorded for KTN groups, representing the free thiols (C-SH)[ 49 ] in KTN species. The 162.5 eV signal for gold-bound thiol (R-S-Au)[ 50 – 52 ] was partially buried in the free thiol curve. The bare gold surface generated two expected peaks at 87.3 and 83.6 eV for Au electron signals in the 4f5 and 4f7 orbitals, respectively.…”

Computational study of Polymerization, Crystallization and Mechanical Properties of Conducting Polymers

“…36,37 The stability of PEDOT is attributed to the positive mesomeric effect of ethylenedioxy group that stabilizes the positive charges of oxidized PEDOT. 34,38 In addition, a number of well-established polymerization methods make PEDOT attractive such as Vapor Phase Polymerization (VPP), [39][40][41] Chemical Vapor Deposition (CVD), 42 Electrochemical Polymerization, 43,44 and Insitu Chemical Polymerization. 29,45,46 Owing to these superior properties and facile polymerization methods, PEDOT is used for a range of organic electric devices such as supercapacitors, [47][48][49][50] ion-pumps, 51,52 thermoelectric modulus, 43,[53][54][55] solar cells, 56,57 fuel cells, [58][59][60] electrochromic display, 61 light-emit diodes, 62 field effect transistors [63][64][65] and devices for bioelectronics.…”