Graphite and Graphene Fairy Circles: A Bottom-Up Approach for the Formation of Nanocorrals

Micro-patterning of C-C covalently-bound grafts by mechanochemical imprint lithography

A simple, inexpensive and versatile patterned removal of C-C grafts has been realized for scalable multicomponent micropatterned functionalization.

STM studies on porphyrins and phthalocyanines at the liquid/solid interface for molecular-scale electronics

Porphyrins and phthalocyanines are promising candidates for single-molecule electronics. Among the many characterization tools, scanning tunneling microscopy (STM) represents a very powerful one to gain insight into the electronic properties at the molecular level, by correlating the charge transport behaviours of π-conjugated molecules with ultrahigh resolution imaging. In view of the sophistication of molecular self-assembly in the presence of a solution phase, in this frontier, we focus on STM studies on porphyrins and phthalocyanines at the liquid/solid interface, placing emphasis on the electronic and magnetic properties, as well as the switching behaviour of surface-confined or surface-anchored molecules. Furthermore, we have also addressed the topics of potential that can be exploited in this area.

On the role of functional groups in the formation of diazonium based covalent attachments: dendritic vs. layer-by-layer growth

Multilayered growth is often observed upon electrografting aryl diazonium derivatives on graphitic substrates due to the reactive nature of aryl radicals. The mechanism of the multilayer formation has been investigated either by measuring the thickness of the grafted layer, the charge transfer, or via simulations. Spectroscopy and in particular microscopy approaches are underrepresented. Herein, we demonstrate a comparative characterization of the multilayer growth of two diazonium derivatives on highly oriented pyrolytic graphite using a combination of cyclic voltammetry, atomic force microscopy, and scanning tunneling microscopy. While dendritic growth is observed for 4-nitro phenyl diazonium (4-NBD), 4-carboxy phenyl diazonium (4-CBD) shows layer-by-layer growth upon increasing the molecular concentration, revealing the impact of the functional groups on the growth mechanism.

Spatially Controlled Aryl Radical Grafting of Graphite Surfaces Guided by Self-Assembled Molecular Networks of Linear Alkane Derivatives: The Importance of Conformational Dynamics

The covalent functionalization of carbon surfaces with nanometer-scale precision is of interest because of its potential in a range of applications. We herein report the controlled grafting of graphite surfaces using electrochemically generated aryl radicals templated by self-assembled molecular networks (SAMNs) of bisalkylurea derivatives. A bisalkylurea derivative having two butoxy units acts as a template for the covalent functionalization of aryl groups in between self-assembled rows of this molecule. In contrast, grafting occurs without a spatial order when an SAMN of bis(tetradecyl)urea was used as a template. This indicates that a degree of dynamics at the alkyl termini is required to favor controlled covalent attachment, a situation that is suppressed by strong intrarow intermolecular interactions resulting from the hydrogen bonding of the urea groups, but favored by terminal short alkoxy groups. The present information is useful for understanding the mechanism of the template-guided aryl radical grafting and the molecular design of new generations of template molecules.

The Covalent Functionalization of Surface-Supported Graphene: An Update

In the last decade, the use of graphene supported on solid surfaces has broadened its scope and applications, and graphene has acquire a promising role as a major component of high-performance electronic devices. In this context, the chemical modification of graphene has become essential. In particular, covalent modification offers key benefits, including controllability, stability, and the facility to be integrated into manufacturing operations. In this Review, we critically comment on the latest advances in the covalent modification of supported graphene on substrates. We analyze the different chemical modifications with special attention to radical reactions. In this context, we review the latest achievements in reactivity control, tailoring electronic properties, and introducing active functionalities. Finally, we extended our analysis to other emerging 2D materials supported on surfaces, such as transition metal dichalcogenides, transition metal oxides, and elemental analogs of graphene.

Covalent transfer of chemical gradients onto a graphenic surface with 2D and 3D control

Control over the functionalization of graphenic materials is key to enable their full application in electronic and optical technologies. Covalent functionalization strategies have been proposed as an approach to tailor the interfaces’ structure and properties. However, to date, none of the proposed methods allow for a covalent functionalization with control over the grafting density, layer thickness and/or morphology, which are key aspects for fine-tuning the processability and performance of graphenic materials. Here, we show that the no-slip boundary condition at the walls of a continuous flow microfluidic device offers a way to generate controlled chemical gradients onto a graphenic material with 2D and 3D control, a possibility that will allow the sophisticated functionalization of these technologically-relevant materials.

Covalent modification is an essential chemical method for altering the physicochemical properties of material interfaces. Here, the authors show that the no-slip conditions in microfluidic devices grant spatiotemporal control over molecular grafting.

Symmetry and spacing controls in periodic covalent functionalization of graphite surfaces templated by self-assembled molecular networks

We herein present the periodic covalent functionalization of graphite surfaces, creating a range of patterns of different symmetries and pitches at the nanoscale. Self-assembled molecular networks (SAMNs) of rhombic-shaped bis(dehydrobenzo[12]annulene) (bisDBA) derivatives having alkyl chain substituents of different lengths were used as templates for covalent grafting of electrochemically generated aryl radicals. Scanning tunneling microscopy (STM) observations at the 1,2,4-trichlorobenzene/graphite interface revealed that these molecules form a variety of networks that contain pores of different shapes and sizes. The covalently functionalized surfaces show hexagonal, oblique, and quasi-rectangular periodicities. This is attributed to the favorable aryl radical addition at the pore(s). We also confirmed the successful transmission of chirality information from the SAMNs to the alignment of the grafted aryls. In one case, the addition of a guest molecule was used to switch the SAMN symmetry and periodicity, leading to a change in the functionalized surface periodicity from oblique to hexagonal in the presence of the guest molecule. This contribution highlights the potential of SAMNs as templates for the controlled formation of nanopatterned carbon materials.

Electrochemical modification of carbon nanotube fibres

Covalent modification of the surface of carbon nanotube fibres (CNTFs) through electrochemical reduction of para-substituted phenyldiazonium salts and electrochemical oxidation of an aliphatic diamine is described. Following these strategies, diverse surface functionalities have been introduced while preserving the fibre bulk properties. The corresponding modified CNTFs were fully characterised by Raman spectroscopy, X-ray photoelectron spectroscopy, energy dispersive X-Ray, scanning electron microscopy and electrochemical impedance spectroscopy, exhibiting different surface properties from those of the unmodified CNTFs.

Covalent Patterning of Graphene for Controllable Functionalization from Microscale to Nanoscale: A Mini-Review

Covalent patterning of graphene opens many application possibilities in the field of photonics, electronics, sensors, and catalysis due to order-dependent optical properties, band structure engineering, and processibility and reactivity improvement. Owing to the low reactivity of the graphene basal plane, harsh reagents (e.g., radicals) used for covalent functionalization normally result in poor spatial control, which largely compromises the intrinsic properties of graphene. Therefore, precisely spatial control on covalent patterning of graphene is of great importance. Herein, we summarize recent advances for covalent patterning of graphene from the microscale to nanoscale resolution using different techniques such as laser or electrochemical writing, template-directed growth, and tip-induced nanoshaving.

2D Self-assembled molecular networks and on-surface reactivity under nanoscale lateral confinement

Supramolecular self-assembly at surfaces provides a pathway for building chemically customized interfaces. Over the last three decades, research on the role of key parameters such as temperature, solute concentration, and molecular design has enabled a steady increase in the complexity of self-assembled molecular networks (SAMNs) that can thus be created. However, the structure and quality of SAMNs is often determined during the early stages of nucleation and growth. To study and influence self-assembly processes at this deterministic length scale, spatial confinement of molecular adsorbates to well-defined surface patterns with nanoscale lateral dimensions offers exciting possibilities. The aim of this tutorial review is to give an overview of the various ways in which confinement impacts SAMN formation, and how we can use that knowledge to direct assemblies towards desired structures. The possibility to exploit confinement for improved control over on-surface reactions is also contemplated.

Understanding and controlling the covalent functionalisation of graphene

Chemical functionalisation is one of the most active areas of graphene research, motivated by fundamental science, the opportunities to adjust or supplement intrinsic properties, and the need to assemble materials for a broad array of applications. Historically, the primary consideration has been the degree of functionalisation but there is growing interest in understanding how and where modification occurs. Reactions may proceed preferentially at edges, defects, or on graphitic faces; they may be correlated, uncorrelated, or anti-correlated with previously grafted sites. A detailed collation of existing literature data indicates that steric effects play a strong role in limiting the extent of reaction. However, the pattern of functionalisation may have important effects on the resulting properties. This article addresses the unifying principles of current graphene functionalisation technologies, with emphasis on understanding and controlling the locus of functionalisation.

Iodide mediated reductive decomposition of diazonium salts: towards mild and efficient covalent functionalization of surface-supported graphene

Covalent functionalization of graphene is highly sought after, not only in view of the potential applications of the chemically modified material, but also because it brings fundamental insight into the chemistry of graphene. Thus, strategies that yield chemically modified graphene with densely grafted films of aryl groups via simple experimental protocols have been the focus of intense research. Here we report a mild, straightforward and efficient approach to graphene/graphite functionalization using iodide mediated reductive dediazoniation of aryldiazonium salts. The experimental protocol employs aqueous solutions of the reagents. The reaction proceeds rapidly at room temperature without the need of any environmental or electrochemical control. The covalently modified surfaces were characterized at the nanometer scale using a combination of complementary surface analytical techniques. The degree of covalent functionalization, and the morphology, as well as the thickness of the grafted films were studied at the molecular level using Raman spectroscopy and scanning probe microscopy, respectively. Furthermore, solution phase UV-Vis spectroscopy was employed to understand the mechanistic aspects. This work demonstrates a facile and scalable covalent modification method compatible for both bulk and monolayer functionalization of graphene.