Self-Assembled Polystyrene Beads for Templated Covalent Functionalization of Graphitic Substrates Using Diazonium Chemistry

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.

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.

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.

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.

A chemisorbed interfacial layer for seeding atomic layer deposition on graphite

The integration of graphene, and more broadly two-dimensional materials, into devices and hybrid materials often requires the deposition of thin films on their usually inert surface. As a result, strategies for the introduction of surface reactive sites have been developed but currently pose a dilemma between robustness and preservation of the graphene properties. A method is reported here for covalently modifying graphitic surfaces, introducing functional groups that act as reactive sites for the growth of high quality dielectric layers. Aryl diazonium species containing tri-methoxy groups are covalently bonded (grafted) to highly oriented pyrolytic graphite (HOPG) and graphene, acting as seeding species for atomic layer deposition (ALD) of Al₂O₃, a high-κ dielectric material. A smooth and uniform dielectric film growth is confirmed by scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrical measurements. Raman spectroscopy showed that the aryl groups gradually detach from the graphitic surface during the Al₂O₃ ALD process at 150 °C, with the surface reverting back to the original sp²-hybridized state and without damaging the dielectric layer. Thus, the grafted aryl groups can act as a sacrificial seeding layer after healing the defects of the graphitic surface with annealing treatment.

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.

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

A convenient covalent functionalization approach and nanopatterning method of graphite and graphene is developed. In contrast to expectations, electrochemically activated dediazotization of a mixture of two aryl diazonium compounds in aqueous media leads to a spatially inhomogeneous functionalization of graphitic surfaces, creating covalently modified surfaces with quasi-uniform spaced islands of pristine graphite or graphene, coined nanocorrals. Cyclic voltammetry and chronoamperometry approaches are compared. The average diameter (45-130 nm) and surface density (20-125 corrals/μm²) of these nanocorrals are tunable. These chemically modified nanostructured graphitic (CMNG) surfaces are characterized by atomic force microscopy, scanning tunneling microscopy, Raman spectroscopy and microscopy, and X-ray photoelectron spectroscopy. Mechanisms leading to the formation of these CMNG surfaces are discussed. The potential of these surfaces to investigate supramolecular self-assembly and on-surface reactions under nanoconfinement conditions is demonstrated.

Vapor Annealing and Colloid Lithography: An Effective Tool To Control Spatial Resolution of Surface Modification

Colloid lithography represents a simple and efficient method for creation of a large-scale template for subsequent surface patterning, deposition of regular metal nanostructures, or periodical surface structures. However, this method is significantly restricted by its ability to create only a limited number of structures with confined geometry and symmetry features. To overcome this limitation, different techniques, such as plasma treatment or tilting angle metal deposition, have been proposed. In this paper, an alternative method based on the vapor annealing of ordered single polystyrene (PS) microspheres layer, followed by the surface grafting with arenediazonium tosylates is proposed. Application of vapor treatment before surface grafting allows effective control of the area screened by PS microspheres. Pristine and vapor-annealed microsphere arrays on the gold substrate were electrochemically modified using ADTs. Subsequent removal of the PS microsphere mask enabled to prepare well-defined nanostructures with controllable surface features. In particular, prepared periodic arrangements were achieved by the grafting of OFGs to the empty interspaces between nanopore arrays. The process of sample preparation was controlled, and the properties of prepared structures were characterized by various techniques, including atomic force microscopy (AFM), conductive AFM, scanning electron microscopy energy-dispersive X-ray spectrometry, Raman spectroscopy, and voltammetry.