Approaches, Derivatives and Applications Vasilios Georgakilas,† Michal Otyepka,‡ Athanasios B. Bourlinos,‡ Vimlesh Chandra, Namdong Kim, K. Christian Kemp, Pavel Hobza,‡,§,⊥ Radek Zboril,*,‡ and Kwang S. Kim* †Institute of Materials Science, NCSR “Demokritos”, Ag. Paraskevi Attikis, 15310 Athens, Greece ‡Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University Olomouc, 17. listopadu 12, 771 46 Olomouc, Czech Republic Center for Superfunctional Materials, Department of Chemistry, Pohang University of Science and Technology, San 31, Hyojadong, Namgu, Pohang 790-784, Korea Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, v.v.i., Flemingovo naḿ. 2, 166 10 Prague 6, Czech Republic

Functionalization of Graphene: Covalent and Non-Covalent Approaches, Derivatives and Applications

Recently, a lot of effort has been focused on improving the performance and exploring the electric properties of graphene. This article presents a summary of chemical doping of graphene aimed at tuning the electronic properties of graphene. p-Type and n-type doping of graphene achieved through surface transfer doping or substitutional doping and their applications based on doping are reviewed. Chemical doping for band gap tuning in graphene is also presented. It will be beneficial to designing high performance electronic devices based on chemically doped graphene.

Chemical doping of graphene

Graphene-based materials exhibit remarkable electronic, optical, and mechanical properties, which has resulted in both high scientific interest and huge potential for a variety of applications. Furthermore, the family of graphene-based materials is growing because of developments in preparation methods. Raman spectroscopy is a versatile tool to identify and characterize the chemical and physical properties of these materials, both at the laboratory and mass-production scale. This technique is so important that most of the papers published concerning these materials contain at least one Raman spectrum. Thus, here, we systematically review the developments in Raman spectroscopy of graphene-based materials from both fundamental research and practical (i.e., device applications) perspectives. We describe the essential Raman scattering processes of the entire first- and second-order modes in intrinsic graphene. Furthermore, the shear, layer-breathing, G and 2D modes of multilayer graphene with different stacking orders are discussed. Techniques to determine the number of graphene layers, to probe resonance Raman spectra of monolayer and multilayer graphenes and to obtain Raman images of graphene-based materials are also presented. The extensive capabilities of Raman spectroscopy for the investigation of the fundamental properties of graphene under external perturbations are described, which have also been extended to other graphene-based materials, such as graphene quantum dots, carbon dots, graphene oxide, nanoribbons, chemical vapor deposition-grown and SiC epitaxially grown graphene flakes, composites, and graphene-based van der Waals heterostructures. These fundamental properties have been used to probe the states, effects, and mechanisms of graphene materials present in the related heterostructures and devices. We hope that this review will be beneficial in all the aspects of graphene investigations, from basic research to material synthesis and device applications.

/pdf/raman-spectroscopy-of-graphene-based-materials-and-its-3g29xwkxmv.pdf

Raman spectroscopy of graphene-based materials and its applications in related devices.

A stoichiometric derivative of graphene with a fluorine atom attached to each carbon is reported Raman, optical, structural, micromechanical, and transport studies show that the material is qualitatively different from the known graphene-based nonstoichiometric derivatives Fluorographene is a high-quality insulator (resistivity >10(12) Omega) with an optical gap of 3 eV It inherits the mechanical strength of graphene, exhibiting a Young's modulus of 100 N m(-1) and sustaining strains of 15% Fluorographene is inert and stable up to 400 degrees C even in air, similar to Teflon

/pdf/fluorographene-a-two-dimensional-counterpart-of-teflon-2eoe4l6d9z.pdf

Fluorographene: A Two‐Dimensional Counterpart of Teflon

The density functional theory method (M05-2X/6-31G(d)) was used to investigate reaction mechanisms for deoxygenation of graphene oxides (GOs) with hydrazine or heat treatment. Three mechanisms were identified as reducing epoxide groups of GO with hydrazine as a reducing agent. No reaction path was found for the hydrazine-mediated reductions of the hydroxyl, carbonyl, and carboxyl groups of GO. We instead discovered the mechanisms for dehydroxylation, decarbonylation, and decarboxylation using heat treatment. The hydrazine de-epoxidation and thermal dehydroxylation of GO have opposite dependencies on the reaction temperature. In both reduction types, the oxygen functionalities attached to the interior of an aromatic domain in GO are removed more easily, both kinetically and thermodynamically, than those attached at the edges of an aromatic domain. The hydrazine-mediated reductions of epoxide groups at the edges are suspended by forming hydrazino alcohols. We provide atomic-level elucidation for the deoxyge...

Hydrazine and Thermal Reduction of Graphene Oxide: Reaction Mechanisms, Product Structures, and Reaction Design

We report the synthesis and evidence of graphene fluoride, a two-dimensional wide bandgap semiconductor derived from graphene. Graphene fluoride exhibits hexagonal crystalline order and strongly insulating behavior with resistance exceeding $10\text{ }\text{G}\ensuremath{\Omega}$ at room temperature. Electron transport in graphene fluoride is well described by variable range hopping in two dimensions due to the presence of localized states in the band gap. Graphene obtained through the reduction of graphene fluoride is highly conductive, exhibiting a resistivity of less than $100\text{ }\text{k}\ensuremath{\Omega}$ at room temperature. Our approach provides a pathway to reversibly engineer the band structure and conductivity of graphene for electronic and optical applications.

Reversible fluorination of graphene: Evidence of a two-dimensional wide bandgap semiconductor

Results are presented from an experimental and theoretical study of the electronic properties of back-gated graphene field effect transistors (FETs) on Si/SiO2 substrates. The excess charge on the graphene was observed by sweeping the gate voltage to determine the charge neutrality point in the graphene. Devices exposed to laboratory environment for several days were always found to be initially p-type. After ∼20 h at 200 °C in ∼5 × 10−7 Torr vacuum, the FET slowly evolved to n-type behavior with a final excess electron density on the graphene of ∼4 × 1012 e/cm2. This value is in excellent agreement with our theoretical calculations on SiO2, where we have used molecular dynamics to build the SiO2 structure and then density functional theory to compute the electronic structure. The essential theoretical result is that the SiO2 has a significant surface state density just below the conduction band edge that donates electrons to the graphene to balance the chemical potential at the interface. An electrostati...

n-Type behavior of graphene supported on Si/SiO(2) substrates.

Graphene is an excellent conductor, while graphene fluoride is a wide band-gap semiconductor. We propose the formation of graphene channels embedded in graphene fluoride as a method to induce quantum confinement of charge carriers in graphene. In particular, we study the electronic structure of graphene channels drawn on the fluoride along two high-symmetry directions: the armchair and zigzag orientations. The zigzag channels are found to have dispersive one-dimensional edge bands, contrary to the case of ribbons and channels drawn on graphane, where the edge state is flat close to the Fermi level and has a very large effective mass. The effective mass of this one-dimensional edge state can be controlled by electrostatic interactions at the edge of the channel. This result indicates that the mobility of these channels can be controlled by a localized gate voltage. The armchair channel is found to be metallic or semiconducting depending on the width of the channel, in agreement with ribbons and hydrogen-limited channels.

/pdf/dispersion-of-edge-states-and-quantum-confinement-of-1xv4s2rfde.pdf

Dispersion of edge states and quantum confinement of electrons in graphene channels drawn on graphene fluoride

The narrow bandgap of near-infrared (NIR) polymers is a major barrier to improving the performance of NIR phototransistors. The existing technique for overcoming this barrier is to construct a bilayer device (channel layer/bulk heterojunction (BHJ) layer). However, acceptor phases of the BHJ dissolve into the channel layer and are randomly distributed by the spin-coating method, resulting in turn-on voltages (Vo) and off-state dark currents remaining at a high level. In this work, a diffusion interface layer is formed between the channel layer and BHJ layer after treating the film transfer method (FTM)-based NIR phototransistors with solvent vapor annealing (SVA). The newly formed diffusion interface layer makes it possible to control the acceptor phase distribution. The performance of the FTM-based device improves after SVA. Vo decreases from 26 V to zero, and the dark currents decrease by one order of magnitude. The photosensitivity (Iph/Idark) increases from 22 to 1.7 × 107. 

https://www.nature.com/articles/s41467-022-28922-4.pdf

Diffusion interface layer controlling the acceptor phase of bilayer near-infrared polymer phototransistors with ultrahigh photosensitivity

Because quantum spin Hall (QSH) insulators with dissipative electron transport properties have broad application prospect in the field of quantum devices, QSH insulators have aroused great research enthusiasm and many ideal QSH insulators are predicted successfully. Based on density functional calculations, we predict that new families of functionalized InBi monolayers, H–InBi-X (X = F, Cl, Br, I), to be QSH insulators. We find that the pristine InBi monolayer that is simultaneously hydrogenated and halogenated has a maximum band gap of 0.49 eV while preserving the untrivial topological properties, which is large enough for room-temperature applications. Because of the absence of inversion symmetry, the Rashba SOC effect occurs in the band structure and the SOC not only opens the bandgaps but also leads to the band inversion. In addition, the topological properties of these monolayers can survive a wide range of external strain from −6% to 6%. Our findings enrich the inversion-asymmetry topological materials and provide a reliable reference for designing QSH insulators at room temperature. • Functionalization can help stabilize two-dimensional structure, enlarge topological band gaps. • Passivating the upper and lower surface of pure InBi film with halogen and hydrogen atoms leads to larger band gaps. • The coexistence of the Rashba SOC effect and the nontrivial topological phase may have potential research significance in spintronics. 

Ning Shen

Papers

Reversible fluorination of graphene: Evidence of a two-dimensional wide bandgap semiconductor

n-Type behavior of graphene supported on Si/SiO(2) substrates.

Dispersion of edge states and quantum confinement of electrons in graphene channels drawn on graphene fluoride

Diffusion interface layer controlling the acceptor phase of bilayer near-infrared polymer phototransistors with ultrahigh photosensitivity

New families of quantum spin Hall insulators with rashba effect in functionalized InBi monolayers