Production and processing of graphene and related materials
Journal article, 2020
We present an overview of the main techniques for production and processing of graphene and related materials (GRMs), as well as the key characterization procedures. We adopt a 'hands-on' approach, providing practical details and procedures as derived from literature as well as from the authors' experience, in order to enable the reader to reproduce the results. Section I is devoted to 'bottom up' approaches, whereby individual constituents are pieced together into more complex structures. We consider graphene nanoribbons (GNRs) produced either by solution processing or by on-surface synthesis in ultra high vacuum (UHV), as well carbon nanomembranes (CNM). Production of a variety of GNRs with tailored band gaps and edge shapes is now possible. CNMs can be tuned in terms of porosity, crystallinity and electronic behaviour. Section II covers 'top down' techniques. These rely on breaking down of a layered precursor, in the graphene case usually natural crystals like graphite or artificially synthesized materials, such as highly oriented pyrolythic graphite, monolayers or few layers (FL) flakes. The main focus of this section is on various exfoliation techniques in a liquid media, either intercalation or liquid phase exfoliation (LPE). The choice of precursor, exfoliation method, medium as well as the control of parameters such as time or temperature are crucial. A definite choice of parameters and conditions yields a particular material with specific properties that makes it more suitable for a targeted application. We cover protocols for the graphitic precursors to graphene oxide (GO). This is an important material for a range of applications in biomedicine, energy storage, nanocomposites, etc. Hummers' and modified Hummers' methods are used to make GO that subsequently can be reduced to obtain reduced graphene oxide (RGO) with a variety of strategies. GO flakes are also employed to prepare three-dimensional (3d) low density structures, such as sponges, foams, hydro- or aerogels. The assembly of flakes into 3d structures can provide improved mechanical properties. Aerogels with a highly open structure, with interconnected hierarchical pores, can enhance the accessibility to the whole surface area, as relevant for a number of applications, such as energy storage. The main recipes to yield graphite intercalation compounds (GICs) are also discussed. GICs are suitable precursors for covalent functionalization of graphene, but can also be used for the synthesis of uncharged graphene in solution. Degradation of the molecules intercalated in GICs can be triggered by high temperature treatment or microwave irradiation, creating a gas pressure surge in graphite and exfoliation. Electrochemical exfoliation by applying a voltage in an electrolyte to a graphite electrode can be tuned by varying precursors, electrolytes and potential. Graphite electrodes can be either negatively or positively intercalated to obtain GICs that are subsequently exfoliated. We also discuss the materials that can be amenable to exfoliation, by employing a theoretical data-mining approach. The exfoliation of LMs usually results in a heterogeneous dispersion of flakes with different lateral size and thickness. This is a critical bottleneck for applications, and hinders the full exploitation of GRMs produced by solution processing. The establishment of procedures to control the morphological properties of exfoliated GRMs, which also need to be industrially scalable, is one of the key needs. Section III deals with the processing of flakes. (Ultra)centrifugation techniques have thus far been the most investigated to sort GRMs following ultrasonication, shear mixing, ball milling, microfluidization, and wet-jet milling. It allows sorting by size and thickness. Inks formulated from GRM dispersions can be printed using a number of processes, from inkjet to screen printing. Each technique has specific rheological requirements, as well as geometrical constraints. The solvent choice is critical, not only for the GRM stability, but also in terms of optimizing printing on different substrates, such as glass, Si, plastic, paper, etc, all with different surface energies. Chemical modifications of such substrates is also a key step. Sections IV-VII are devoted to the growth of GRMs on various substrates and their processing after growth to place them on the surface of choice for specific applications. The substrate for graphene growth is a key determinant of the nature and quality of the resultant film. The lattice mismatch between graphene and substrate influences the resulting crystallinity. Growth on insulators, such as SiO2, typically results in films with small crystallites, whereas growth on the close-packed surfaces of metals yields highly crystalline films. Section IV outlines the growth of graphene on SiC substrates. This satisfies the requirements for electronic applications, with well-defined graphene-substrate interface, low trapped impurities and no need for transfer. It also allows graphene structures and devices to be measured directly on the growth substrate. The flatness of the substrate results in graphene with minimal strain and ripples on large areas, allowing spectroscopies and surface science to be performed. We also discuss the surface engineering by intercalation of the resulting graphene, its integration with Si-wafers and the production of nanostructures with the desired shape, with no need for patterning. Section V deals with chemical vapour deposition (CVD) onto various transition metals and on insulators. Growth on Ni results in graphitized polycrystalline films. While the thickness of these films can be optimized by controlling the deposition parameters, such as the type of hydrocarbon precursor and temperature, it is difficult to attain single layer graphene (SLG) across large areas, owing to the simultaneous nucleation/growth and solution/precipitation mechanisms. The differing characteristics of polycrystalline Ni films facilitate the growth of graphitic layers at different rates, resulting in regions with differing numbers of graphitic layers. High-quality films can be grown on Cu. Cu is available in a variety of shapes and forms, such as foils, bulks, foams, thin films on other materials and powders, making it attractive for industrial production of large area graphene films. The push to use CVD graphene in applications has also triggered a research line for the direct growth on insulators. The quality of the resulting films is lower than possible to date on metals, but enough, in terms of transmittance and resistivity, for many applications as described in section V. Transfer technologies are the focus of section VI. CVD synthesis of graphene on metals and bottom up molecular approaches require SLG to be transferred to the final target substrates. To have technological impact, the advances in production of high-quality large-area CVD graphene must be commensurate with those on transfer and placement on the final substrates. This is a prerequisite for most applications, such as touch panels, anticorrosion coatings, transparent electrodes and gas sensors etc. New strategies have improved the transferred graphene quality, making CVD graphene a feasible option for CMOS foundries. Methods based on complete etching of the metal substrate in suitable etchants, typically iron chloride, ammonium persulfate, or hydrogen chloride although reliable, are time- and resource-consuming, with damage to graphene and production of metal and etchant residues. Electrochemical delamination in a low-concentration aqueous solution is an alternative. In this case metallic substrates can be reused. Dry transfer is less detrimental for the SLG quality, enabling a deterministic transfer. There is a large range of layered materials (LMs) beyond graphite. Only few of them have been already exfoliated and fully characterized. Section VII deals with the growth of some of these materials. Amongst them, h-BN, transition metal tri- and di-chalcogenides are of paramount importance. The growth of h-BN is at present considered essential for the development of graphene in (opto) electronic applications, as h-BN is ideal as capping layer or substrate. The interesting optical and electronic properties of TMDs also require the development of scalable methods for their production. Large scale growth using chemical/physical vapour deposition or thermal assisted conversion has been thus far limited to a small set, such as h-BN or some TMDs. Heterostructures could also be directly grown. Section VIII discusses advances in GRM functionalization. A broad range of organic molecules can be anchored to the sp(2) basal plane by reductive functionalization. Negatively charged graphene can be prepared in liquid phase (e.g. via intercalation chemistry or electrochemically) and can react with electrophiles. This can be achieved both in dispersion or on substrate. The functional groups of GO can be further derivatized. Graphene can also be noncovalently functionalized, in particular with polycyclic aromatic hydrocarbons that assemble on the sp(2) carbon network by pi-pi stacking. In the liquid phase, this can enhance the colloidal stability of SLG/FLG. Approaches to achieve noncovalent on-substrate functionalization are also discussed, which can chemically dope graphene. Research efforts to derivatize CNMs are also summarized, as well as novel routes to selectively address defect sites. In dispersion, edges are the most dominant defects and can be covalently modified. This enhances colloidal stability without modifying the graphene basal plane. Basal plane point defects can also be modified, passivated and healed in ultra-high vacuum. The decoration of graphene with metal nanoparticles (NPs) has also received considerable attention, as it allows to exploit synergistic effects between NPs and graphene. Decoration can be either achieved chemically or in the gas phase. All LMs, can be functionalized and we summarize emerging approaches to covalently and noncovalently functionalize MoS2 both in the liquid and on substrate. Section IX describes some of the most popular characterization techniques, ranging from optical detection to the measurement of the electronic structure. Microscopies play an important role, although macroscopic techniques are also used for the measurement of the properties of these materials and their devices. Raman spectroscopy is paramount for GRMs, while PL is more adequate for non-graphene LMs (see section IX.2). Liquid based methods result in flakes with different thicknesses and dimensions. The qualification of size and thickness can be achieved using imaging techniques, like scanning probe microscopy (SPM) or transmission electron microscopy (TEM) or spectroscopic techniques. Optical microscopy enables the detection of flakes on suitable surfaces as well as the measurement of optical properties. Characterization of exfoliated materials is essential to improve the GRM metrology for applications and quality control. For grown GRMs, SPM can be used to probe morphological properties, as well as to study growth mechanisms and quality of transfer. More generally, SPM combined with smart measurement protocols in various modes allows one to get obtain information on mechanical properties, surface potential, work functions, electrical properties, or effectiveness of functionalization. Some of the techniques described are suitable for 'in situ' characterization, and can be hosted within the growth chambers. If the diagnosis is made 'ex situ', consideration should be given to the preparation of the samples to avoid contamination. Occasionally cleaning methods have to be used prior to measurement.
characterization of layered materials
functionalization of layered materials
synthesis of graphene and related materials
processing of layered materials
growth of layered materials
inks of layered materials
Author
Claudia Backes
Heidelberg University
Trinity College Dublin
Amr M. Abdelkader
University of Cambridge
Concepcion Alonso
Autonomous University of Madrid
Amandine Andrieux-Ledier
University Paris-Saclay
Raul Arenal
Fundación ARAID
University of Zaragoza
Jon Azpeitia
Spanish National Research Council (CSIC)
Nilanthy Balakrishnan
University of Nottingham
Luca Banszerus
RWTH Aachen University
Julien Barjon
University Paris-Saclay
Ruben Bartali
Fondazione Bruno Kessler (FBK)
Sebastiano Bellani
Istituto Italiano di Tecnologia
Claire Berger
Georgia Institute of Technology
Grenoble Alpes University
Reinhard Berger
Technische Universität Dresden
M. M. Bernal Ortega
Polytechnic University of Turin
Carlo Bernard
University of Zürich
Peter H. Beton
University of Nottingham
Andre Beyer
Bielefeld University
Alberto Bianco
University of Strasbourg
Peter Boggild
Technical University of Denmark (DTU)
Francesco Bonaccorso
BeDimensional
Istituto Italiano di Tecnologia
Gabriela Borin Barin
Swiss Federal Laboratories for Materials Science and Technology (Empa)
Cristina Botas
CIC EnergiGUNE
Rebeca A. Bueno
Spanish National Research Council (CSIC)
Daniel Carriazo
CIC EnergiGUNE
Basque Foundation for Science (Ikerbasque)
Andres Castellanos-Gomez
Spanish National Research Council (CSIC)
Meganne Christian
National Research Council of Italy (CNR)
Artur Ciesielski
University of Strasbourg
Tymoteusz Ciuk
Lukasiewicz Research Network - Institute of Microelectronics and Photonics (LUKASIEWICZ-IMIF)
Matthew T. Cole
University of Bath
Jonathan Coleman
Trinity College Dublin
Camilla Coletti
Istituto Italiano di Tecnologia
Luigi Crema
Fondazione Bruno Kessler (FBK)
Huanyao Cun
University of Zürich
Daniela Dasler
University of Erlangen-Nuremberg (FAU)
Domenico De Fazio
University of Cambridge
Noel Diez
CIC EnergiGUNE
Simon Drieschner
Technical University of Munich
Georg S. Duesberg
Bundeswehr University Munich
Roman Fasel
University of Bern
Swiss Federal Laboratories for Materials Science and Technology (Empa)
Xinliang Feng
Technische Universität Dresden
Alberto Fina
Polytechnic University of Turin
Stiven Forti
Istituto Italiano di Tecnologia
Costas Galiotis
Universityof Patras
Foundation for Research and Technology Hellas (FORTH)
Giovanni Garberoglio
National Institute for Nuclear Physics
European Centre for Theoretical Studies in Nuclear Physics and Related Areas
Jorge M. Garcia
Spanish National Research Council (CSIC)
Jose Antonio Garrido
Catalan Institute of Nanoscience and Nanotechnology (ICN2)
Marco Gibertini
Swiss Federal Institute of Technology in Lausanne (EPFL)
Armin Goelzhaeuser
Bielefeld University
Julio Gomez
Avanzare Innovacion Tecnologica Sl
Thomas Greber
University of Zürich
Frank Hauke
University of Erlangen-Nuremberg (FAU)
Adrian Hemmi
University of Zürich
Irene Hernandez-Rodriguez
Spanish National Research Council (CSIC)
Andreas Hirsch
University of Erlangen-Nuremberg (FAU)
Stephen A. Hodge
University of Cambridge
Yves Huttel
Spanish National Research Council (CSIC)
Peter U. Jepsen
Technical University of Denmark (DTU)
Ignacio Jimenez
Spanish National Research Council (CSIC)
Ute Kaiser
University of Ulm
Tommi Kaplas
University of Eastern Finland
HoKwon Kim
Swiss Federal Institute of Technology in Lausanne (EPFL)
Andras Kis
Swiss Federal Institute of Technology in Lausanne (EPFL)
Konstantinos Papagelis
Aristotle University of Thessaloniki
Foundation for Research and Technology Hellas (FORTH)
Kostas Kostarelos
University of Manchester
Consorzio Nazionale Interuniversitario per le Telecomunicazioni (CNIT)
Aleksandra Krajewska
Polish Academy of Sciences
Lukasiewicz Research Network - Institute of Microelectronics and Photonics (LUKASIEWICZ-IMIF)
Kangho Lee
Bundeswehr University Munich
Changfeng Li
Aalto University
Harri Lipsanen
Aalto University
Andrea Liscio
National Research Council of Italy (CNR)
Martin R. Lohe
Technische Universität Dresden
Annick Loiseau
University Paris-Saclay
Lucia Lombardi
University of Cambridge
Maria Francisca Lopez
Spanish National Research Council (CSIC)
Oliver Martin
University of Erlangen-Nuremberg (FAU)
Cristina Martin
University of Castilla, La Mancha
Lidia Martinez
Spanish National Research Council (CSIC)
Jose Angel Martin-Gago
Spanish National Research Council (CSIC)
Jose Ignacio Martinez
Spanish National Research Council (CSIC)
Nicola Marzari
Swiss Federal Institute of Technology in Lausanne (EPFL)
Alvaro Mayoral
University of Zaragoza
ShanghaiTech University
John McManus
Trinity College Dublin
Manuela Melucci
National Research Council of Italy (CNR)
Javier Mendez
Spanish National Research Council (CSIC)
Cesar Merino
Grupo Antolin
Pablo Merino
Spanish National Research Council (CSIC)
Andreas P. Meyer
University of Erlangen-Nuremberg (FAU)
Elisa Miniussi
University of Zürich
Vaidotas Miseikis
Istituto Italiano di Tecnologia
Neeraj Mishra
Istituto Italiano di Tecnologia
Vittorio Morandi
National Research Council of Italy (CNR)
Carmen Munuera
Spanish National Research Council (CSIC)
Roberto Munoz
Spanish National Research Council (CSIC)
Hugo Nolan
Trinity College Dublin
Luca Ortolani
National Research Council of Italy (CNR)
Anna K. Ott
University of Exeter
University of Cambridge
Irene Palacio
Spanish National Research Council (CSIC)
Vincenzo Palermo
Institute for organic syntheses and photoreactivity (ISOF-CNR)
Chalmers, Industrial and Materials Science, Materials and manufacture
John Parthenios
Foundation for Research and Technology Hellas (FORTH)
Iwona Pasternak
Lukasiewicz Research Network - Institute of Microelectronics and Photonics (LUKASIEWICZ-IMIF)
Warsaw University of Technology
Amalia Patane
University of Nottingham
Maurizio Prato
University of Trieste
Basque Foundation for Science (Ikerbasque)
Centro de Investigación Cooperativa en Biomateriales CIC biomaGUNE
Henri Prevost
University Paris-Saclay
Vladimir Prudkovskiy
Grenoble Alpes University
Nicola Pugno
Queen Mary University of London
Edoardo Amaldi Foundation
University of Trento
Teofilo Rojo
University of the Basque Country (UPV/EHU)
CIC EnergiGUNE
Antonio Rossi
Istituto Italiano di Tecnologia
Pascal Ruffieux
Swiss Federal Laboratories for Materials Science and Technology (Empa)
Paolo Samori
University of Strasbourg
Leonard Schue
University Paris-Saclay
Eki Setijadi
Fondazione Bruno Kessler (FBK)
Thomas Seyller
Technische Universität Chemnitz
Giorgio Speranza
Fondazione Bruno Kessler (FBK)
Christoph Stampfer
RWTH Aachen University
Ingrid Stenger
University Paris-Saclay
Wlodek Strupinski
Lukasiewicz Research Network - Institute of Microelectronics and Photonics (LUKASIEWICZ-IMIF)
Warsaw University of Technology
Yuri Svirko
University of Eastern Finland
Simone Taioli
National Institute for Nuclear Physics
Charles University
European Centre for Theoretical Studies in Nuclear Physics and Related Areas
Kenneth B. K. Teo
Aixtron
Matteo Testi
Fondazione Bruno Kessler (FBK)
Flavia Tomarchio
University of Cambridge
Mauro Tortello
Polytechnic University of Turin
Emanuele Treossi
National Research Council of Italy (CNR)
Andrey Turchanin
Friedrich Schiller University Jena
Ester Vazquez
University of Castilla, La Mancha
Elvira Villaro
InterQuimica
Patrick R. Whelan
Technical University of Denmark (DTU)
Zhenyuan Xia
Institute for organic syntheses and photoreactivity (ISOF-CNR)
Chalmers, Industrial and Materials Science, Materials and manufacture
Rositza Yakimova
Linköping University
Sheng Yang
Technische Universität Dresden
G. Reza Yazdi
Linköping University
Chanyoung Yim
Bundeswehr University Munich
Duhee Yoon
University of Cambridge
Xianghui Zhang
Bielefeld University
Xiaodong Zhuang
Technische Universität Dresden
Luigi Colombo
University of Texas at Dallas
Andrea C. Ferrari
University of Cambridge
Mar Garcia-Hernandez
Spanish National Research Council (CSIC)
2D Materials
2053-1583 (eISSN)
Vol. 7 2 022001Subject Categories
Materials Engineering
Materials Chemistry
Condensed Matter Physics
DOI
10.1088/2053-1583/ab1e0a