Electrochemical Covalent Functionalization of Graphene-on-Cu(111) : Substrate Effect & Reaction Mechanism Study

Abstract

Graphene exhibits remarkable thermal, mechanical, and electronic characteristics. Its applications span diverse fields, including electronics, energy storage, composite materials sensors, and wearable devices, highlighting its significant potential for advancing next-generation technologies. Since its initial report in 2004, extensive research has explored functionalization strategies for this two-dimensional material, broadly categorized into covalent and noncovalent approaches. Covalent functionalization of graphene enables deliberate modification of its electronic structure, including Fermi-level tuning and band-gap opening, initiation of polymerization on the basal plane, and immobilization of catalysts and biomolecules. A range of covalent functionalization strategies exists, including diazo-coupling via radicals from diazonium salts, photochemical reactions at lattice defects with peroxides under intense irradiation14, Diels–Alder cycloadditions, hydrogenation and halogenation, reductive functionalization with organic halides using alkali metal alloys to form graphenide, and electrochemical modification. Because both the identity and coverage of functional groups determine the various properties of graphene, controllability for the degree of functionalization and scope of the available reagents are important. Diazo-coupling is difficult to control degree of functionalization, and reductive functionalization requires harsh conditions. Since transferred graphene was used in most cases, which includes intrinsic heterogeneity from wrinkles, folds, and grain boundaries, as well as polymer contamination and transfer-induced defects, studying inherent graphene’s behavior was not performed properly. Electrochemical methods offer precise control of potential and current, and quantitative analyses with simple procedures. Prior works showed that charge passed in cyclic voltammetry can quantify surface coverage on epitaxial graphene and that redox probes report higher activity on the basal plane than at defects. In this dissertation, I show that the 4-iodoaniline was functionalized on single-crystal graphene on Cu(111)(Gr/Cu(111) with parametric study, with the substrate effect on the reactivity of graphene by comparing the graphene on Cu(111) and Cu(115). Additionally, I test availability of various types ofaryl and alkyl molecules to this method, and study distinct onset potentials of the reagents and reaction mechanisms. In Chapter 1, I report how electrochemical parameters (applied potential, reaction time) and crystallographic orientation of the substrate affect graphene reactivity. The availability of single-crystal copper foils and growth of monolayer graphene on Cu(111) and Cu/Ni(111) enable systematic analysis of the behavior of graphene during the electrochemical reaction. Electrochemical functionalization of monolayer single-crystal Gr/Cu(111) without transfer was performed, which minimizes contamination and extrinsic defects. Under cathodic electric potential, Gr/Cu(111) exhibits graphenide-like reactivity with well-defined potential levels. This approach avoids hazardous reagents and uses precise potential control to manipulate the degree of functionalization. As a model reaction I functionalize Gr/Cu(111) with 4-iodoaniline and quantify coverage versus applied potential and reaction time by Raman spectroscopy. I observe distinct potential threshold and reaction extents on Gr/Cu(111) versus Gr/Cu(115), a common twin facet within Cu(111) foils. I analyze ripple morphology, orientation, work function, and step bunching to rationalize these differences and use density functional theory (DFT) calculations to probe electronic structure, work function, and adsorption energies for epitaxial graphene on Cu(111) and Cu(115). In Chapter 2, I extended scope of the reagent with various phenyl and alkyl iodides. Using graphene-on-Cu(111) enable avoiding external factors including substrate effect and transfer-related impurities and defects. I assess reactivity difference of the reagents at room temperature using Raman spectroscopy and compare onset potentials focusing on 4 chosen reagents that show distinctive reactivity differe1nce. Additionally, possible mechanism was proposed with differential pulse voltammetry (DPV) analysis and DFT calculation. I further probe selectivity using distinctly separated onset potentials. The goal of this work is to establish a framework for understanding and controlling electrochemical functionalization of graphene and to expand the range of tunable properties accessible with this platform.