Production and processing of graphene and related materials
Creators: name: Backes, Claudia
name: Abdelkader, Amr M
name: Alonso, Concepción
name: Andrieux-Ledier, Amandine
name: Arenal, Raul
name: Azpeitia, Jon
name: Balakrishnan, Nilanthy
name: Banszerus, Luca
name: Barjon, Julien
name: Bartali, Ruben
name: Bellani, Sebastiano
name: Berger, Claire
name: Berger, Reinhard
name: Ortega, M M Bernal
name: Bernard, Carlo
name: Beton, Peter H
name: Beyer, André
name: Bianco, Alberto
name: Bøggild, Peter
name: Bonaccorso, Francesco
name: Barin, Gabriela Borin
name: Botas, Cristina
name: Bueno, Rebeca A
name: Carriazo, Daniel
name: Castellanos-Gomez, Andres
name: Christian, Meganne
name: Ciesielski, Artur
name: Ciuk, Tymoteusz
name: Cole, Matthew T
name: Coleman, Jonathan
name: Coletti, Camilla
name: Crema, Luigi
name: Cun, Huanyao
name: Dasler, Daniela
name: De Fazio, Domenico
name: Díez, Noel
name: Drieschner, Simon
name: Duesberg, Georg S
name: Fasel, Roman
name: Feng, Xinliang
name: Fina, Alberto
name: Forti, Stiven
name: Galiotis, Costas
name: Garberoglio, Giovanni
name: García, Jorge M
name: Garrido, Jose Antonio
name: Gibertini, Marco
name: Gölzhäuser, Armin
name: Gómez, Julio
name: Greber, Thomas
name: Hauke, Frank
name: Hemmi, Adrian
name: Hernandez-Rodriguez, Irene
name: Hirsch, Andreas
name: Hodge, Stephen A
name: Huttel, Yves
name: Jepsen, Peter U
name: Jimenez, Ignacio
name: Kaiser, Ute
name: Kaplas, Tommi
name: Kim, HoKwon
name: Kis, Andras
name: Papagelis, Konstantinos
name: Kostarelos, Kostas
name: Krajewska, Aleksandra
name: Lee, Kangho
name: Li, Changfeng
name: Lipsanen, Harri
name: Liscio, Andrea
name: Lohe, Martin R
name: Loiseau, Annick
name: Lombardi, Lucia
name: Francisca López, Maria
name: Martin, Oliver
name: Martín, Cristina
name: Martínez, Lidia
name: Martin-Gago, Jose Angel
name: Ignacio Martínez, José
name: Marzari, Nicola
name: Mayoral, Álvaro
name: McManus, John
name: Melucci, Manuela
name: Méndez, Javier
name: Merino, Cesar
name: Merino, Pablo
name: Meyer, Andreas P
name: Miniussi, Elisa
name: Miseikis, Vaidotas
name: Mishra, Neeraj
name: Morandi, Vittorio
name: Munuera, Carmen
name: Muñoz, Roberto
name: Nolan, Hugo
name: Ortolani, Luca
name: Ott, Anna K
name: Palacio, Irene
name: Palermo, Vincenzo
name: Parthenios, John
name: Pasternak, Iwona
name: Patane, Amalia
name: Prato, Maurizio
name: Prevost, Henri
name: Prudkovskiy, Vladimir
name: Pugno, Nicola
name: Rojo, Teófilo
name: Rossi, Antonio
name: Ruffieux, Pascal
name: Samorì, Paolo
name: Schué, Léonard
name: Setijadi, Eki
name: Seyller, Thomas
name: Speranza, Giorgio
name: Stampfer, Christoph
name: Stenger, Ingrid
name: Strupinski, Wlodek
name: Svirko, Yuri
name: Taioli, Simone
name: Teo, Kenneth B K
name: Testi, Matteo
name: Tomarchio, Flavia
name: Tortello, Mauro
name: Treossi, Emanuele
name: Turchanin, Andrey
name: Vazquez, Ester
name: Villaro, Elvira
name: Whelan, Patrick R
name: Xia, Zhenyuan
name: Yakimova, Rositza
name: Yang, Sheng
name: Yazdi, G Reza
name: Yim, Chanyoung
name: Yoon, Duhee
name: Zhang, Xianghui
name: Zhuang, Xiaodong
name: Colombo, Luigi
name: Ferrari, Andrea C
name: Garcia-Hernandez, Mar
Publisher: name: Universität Ulm
Year: 2020
Subjects: subject: processing of layered materials
subject: inks of layered materials
subject: characterization of layered materials
subject: functionalization of layered materials
subject: synthesis of graphene and related materials
subject: growth of layered materials
subject: DDC 620 / Engineering &amp; allied operations
subject: Graphene
subject: Nanoröhre

description: Abstract 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 sp2 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 sp2 carbon network by π–π 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.