Title: Atom-scale covalent electrochemical modification of single-layer graphene on SiC substrates by diaryliodonium salts

Abstract

Owing to its high conductivity, graphene holds promise as an electrode for energy devices such as batteries and photovoltaics. However, to this end, the work function and doping levels in graphene need to be precisely tuned. One promising route for modifying graphene’s electronic properties is via controlled covalent electrochemical grafting of molecules. We show that by employing diaryliodonium salts instead of the commonly used diazonium salts, spontaneous functionalization is avoided. This then allows for precise tuning of the grafting density. Moreover, by employing bis(4-nitrophenyl)iodonium(III) tetrafluoroborate (DNP) salt calibration curves, the surface functionalization density (coverage) of glassy carbon was controlled using cyclic voltammetry in varying salt concentrations. These electro-grafting conditions and calibration curves translated directly over to modifying single layer epitaxial graphene substrates (grown on insulating 6H-SiC (0 0 0 1)). In addition to quantifying the functionalization densities using electrochemical methods, samples with low grafting densities were characterized by low-temperature scanning tunneling microscopy (LT-STM). We show that the use of buffer-layer free graphene substrates is required for clear observation of the nitrophenyl modifications. Furthermore, atomically-resolved STM images of single site modifications were obtained, showing no preferential grafting at defect sites or SiC step edges as supposed previously in the literature. Mostmore » of the grafts exhibit threefold symmetry, but occasional extended modifications (larger than 4 nm) were observed as well.« less

Authors:

Gearba, Raluca I. ^[1]; Mueller, Kory M. ^[1]; Veneman, Peter A. ^[1]; Holliday, Bradley J. ^[1]; Chan, Calvin K. ^[2]; Stevenson, Keith J. ^[1]

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+ Show Author Affiliations

1. Univ. of Texas, Austin, TX (United States)
2. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Publication Date:

Sat May 09 00:00:00 EDT 2015

Research Org.:

Energy Frontier Research Centers (EFRC) (United States). Understanding Charge Separation and Transfer at Interfaces in Energy Materials (CST); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1140350

Alternate Identifier(s):

OSTI ID: 1252823

Report Number(s):

SAND2014-0150J
Journal ID: ISSN 1572-6657; PII: S1572665715002301; TRN: US1600351

Grant/Contract Number:  

AC04-94AL85000

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Electroanalytical Chemistry

Additional Journal Information:

Journal Volume: 753; Journal Issue: C; Journal ID: ISSN 1572-6657

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

74 ATOMIC AND MOLECULAR PHYSICS; epitaxial graphene; electrochemical modification; functionalization; iodonium salts; STM