N‐Heterocyclic Carbene Based Nanolayer for Copper Film Oxidation Mitigation

Abstract

The wide use of copper is limited by its rapid oxidation. Main oxidation mitigation approaches involve alloying or surface passivation technologies. However, surface alloying often modifies the physical properties of copper, while surface passivation is characterized by limited thermal and chemical stability. Herein, we demonstrate an electrochemical approach for surfaceanchoring of an N-heterocyclic carbene (NHC) nanolayer on a copper electrode by electro-deposition of alkyne-functionalized imidazolium cations. Water reduction reaction generated a high concentration of hydroxide ions that induced deprotonation of imidazolium cations and self-assembly of NHCs on the copper electrode. In addition, alkyne group deprotonation enabled on-surface polymerization by coupling surfaceanchored and solvated NHCs, which resulted in a 2 nm thick NHC-nanolayer. Copper film coated with a NHCnanolayer demonstrated high oxidation resistance at elevated temperatures and under alkaline conditions.

Functionalized N-Heterocyclic Carbene Monolayers on Gold for Surface-Initiated Polymerizations

“…Thus, the newly developed radical initiator NHC15AZO SAMs with hairpin conformations on the surface of gold provide convenient platforms for growing surface-initiated polymers in which the film thickness can be tuned simply by adjusting the reaction time. Importantly, the growth of these films can be tuned to give markedly greater polymer thicknesses than those generated using other NHC-based adsorbates (e.g., 250 nm vs 2 nm). , …”

“…In fact, the Crudden group found that SAMs generated from NHCs are more chemically, thermally, and electrochemically stable than thiol-derived SAMs on gold . Despite these attractive features, the major drawback to forming SAMs on gold via carbene adsorption is the contamination of residual amines from the strong bases (e.g., KHMDS) used to produce free carbenes; such residues limit the formation of well-ordered SAMs because these residual amines can bind strongly to the metal surface. , The most successful efforts to overcome this disadvantage have been concentrated on using “masked NHCs”, which can generate free carbenes without the use of strong bases . Specifically, the Crudden group reported the preparation and deposition of benzimidazolium hydrogen carbonate salts, which are “masked NHCs”, on gold surfaces. ,, In these studies, bench-stable NHC bicarbonate-based adsorbates were prepared via ion-exchange.…”

“…Gold slides were then immersed into solutions of the NHC bicarbonate-based adsorbates under an ambient atmosphere, which led to self-assembly of the adsorbates into thin films on the gold surfaces. However, the studies related to NHC-based SAMs on flat gold surfaces thus far have mostly focused on the configurations of NHC adsorbates on gold surfaces using experimental and computational methods. − Until now, there have been only limited examples of functionalized NHC SAMs and their applications, including biosensors, , microprinting, organic electronics, − photoswitches, and polymerization. , …”

“…30−35 Until now, there have been only limited examples of functionalized NHC SAMs and their applications, 22 including biosensors, 36,37 microprinting, 38 organic electronics, 39−41 photoswitches, 42 and polymerization. 25,26 In this study, we report a new method for the direct formation of functionalized NHC-based monolayers on gold and utilized azo-initiated NHC SAMs for growing polymer brushes from gold surfaces based on this newly developed method. This method includes three steps: (i) development of the bench-stable benzimidazole methanesulfonate-based adsorbates and optimization of their SAM formation on gold, (ii) generation and characterization of azo-initiator NHC SAMs on gold, and (iii) surface-initiated polymerizations from the azoradical initiated NHC monolayers.…”

Covalent Adsorption of N-Heterocyclic Carbenes on a Copper Oxide Surface

“…Among these metals, copper, an abundant and inexpensive first-row transition metal, is historically one of the most commonly employed in the development of technological applications. The functionalization of oxidized copper surfaces is challenging because the attachment of organic molecules leads to reduction. − At the same time, many efforts have been made to avoid further oxidation of copper using thiols or, recently, NHC ligands. − In photocatalysis, copper oxide is a widely used material and the attachment of organic molecules can be very beneficial …”