Graphene, a two-dimensional, single-layer sheet of sp(2) hybridized carbon atoms, has attracted tremendous attention and research interest, owing to its exceptional physical properties, such as high electronic conductivity, good thermal stability, and excellent mechanical strength. Other forms of graphene-related materials, including graphene oxide, reduced graphene oxide, and exfoliated graphite, have been reliably produced in large scale. The promising properties together with the ease of processibility and functionalization make graphene-based materials ideal candidates for incorporation into a variety of functional materials. Importantly, graphene and its derivatives have been explored in a wide range of applications, such as electronic and photonic devices, clean energy, and sensors. In this review, after a general introduction to graphene and its derivatives, the synthesis, characterization, properties, and applications of graphene-based materials are discussed.

Graphene-Based Materials: Synthesis, Characterization, Properties, and Applications

Owing to their extraordinary electrical, chemical, optical, mechanical and structural properties, graphene and its derivatives have stimulated exploding interests in their sensor applications ever since the first isolation of free-standing graphene sheets in year 2004. This article critically and comprehensively reviews the emerging graphene-based electrochemical sensors, electronic sensors, optical sensors, and nanopore sensors for biological or chemical detection. We emphasize on the underlying detection (or signal transduction) mechanisms, the unique roles and advantages of the used graphene materials. Properties and preparations of different graphene materials, their functionalizations are also comparatively discussed in view of sensor development. Finally, the perspective and current challenges of graphene sensors are outlined (312 references).

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Biological and chemical sensors based on graphene materials

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, a two-dimensional atomically thick carbon atom arranged in a honeycomb lattice, was recently isolated by repeatedly peeling highly oriented pyrolytic graphite (HOPG) using sticky tape. [ 1 ] Since then, outstanding physical properties predicted and measured for graphene have been explored for practical applications such as fi eld-effect transistors, [ 1–4 ] chemical sensors [ 5–7 ] and composite reinforcement. [ 8–10 ] Monolayer graphene possesses high crystallographic quality and ballistic electron transport on the micrometer scale with only 2.3% of light absorption. [ 11 , 12 ] Moreover, the combination of its high chemical and thermal stability, [ 13 , 14 ] high stretchability, [ 15–17 ]

Graphene as Transparent Electrode Material for Organic Electronics

In this review, we discuss the most recent progress on graphene-related nanomaterials, including doped graphene and derived graphene nanoribbons, graphene oxide, graphane, fluorographene, graphyne, graphdiyne, and porous graphene, from both experimental and theoretical perspectives, and emphasize tuning their stability, electronic and magnetic properties by chemical functionalization.

Graphene-related nanomaterials: tuning properties by functionalization

In this Letter, the photoinduced switching of the single nitrogen-vacancy (NV) center between two different charge states, negative (${\mathrm{NV}}^{\ensuremath{-}}$) and neutral (${\mathrm{NV}}^{0}$), is studied under resonant excitation at liquid helium temperature. We show that resonant conversion of ${\mathrm{NV}}^{0}$ to ${\mathrm{NV}}^{\ensuremath{-}}$ significantly improves spectral stability of the ${\mathrm{NV}}^{\ensuremath{-}}$ defect and allows high fidelity initialization of the spin qubit. Based on density functional theory calculations a novel mechanism involving an Auger ionization of ${\mathrm{NV}}^{\ensuremath{-}}$ and charge transfer of an electron from the valence band to ${\mathrm{NV}}^{0}$ is discussed. This study provides further insight into the charge dynamics of the NV center, which is relevant for quantum information processing based on an ${\mathrm{NV}}^{\ensuremath{-}}$ defect in diamond.

Optically Controlled Switching of the Charge State of a Single Nitrogen-Vacancy Center in Diamond at Cryogenic Temperatures

We use local density function theory to study the electronic properties of tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) deposited on a graphene surface. We show that charge transfer of 0.3 holes/molecule between graphene and F4-TCNQ occurs, which makes graphene p-type doped. These results are in agreement with experimental findings on F4-TCNQ.

https://iopscience.iop.org/article/10.1088/0953-8984/21/40/402001/pdf

p-type doping of graphene with F4-TCNQ

Many potential applications of graphene require its precise and controllable doping with charge carriers. Being a two-dimensional material graphene is extremely sensitive to surface adsorbates, so its electronic properties can be effectively modified by deposition of different atoms and molecules. In this paper, we review two mechanisms of graphene doping by surface adsorbates, namely electronic and electrochemical doping. Although, electronic doping has been extensively studied and discussed in the literature, much less attention has been paid to electrochemical doping. This mechanism can, however, explain the doping of graphene by adsorbates for which no charge transfer is expected within the electronic doping model. In addition, electrochemical doping is in the origin of the hysteresis effects often observed in graphene-based field effect transistors when operating in the atmospheric environment.

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Electronic and electrochemical doping of graphene by surface adsorbates.

We distinguish three mechanisms of doping graphene. Density functional theory is used to show that electronegative molecules like tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) and electropositive metals like K dope graphene p- and n- type, respectively. These dopants are expected to lead to a decrease in carrier mobility arising from Coulomb scattering but without any hysteresis effects. Secondly, a novel doping mechanism is exhibited by Au which dopes bilayer graphene but not single layer. Thirdly, electrochemical doping is effected by redox reactions and can result in p-doping by humid atmospheres and n-doping by NH 3 and toluene.

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Mechanisms of doping graphene

The chemical termination of diamond has a dramatic impact on its electrical and chemical properties, where hydrogen and oxygen termination produce negative and positive electron affinities, respectively. However, the impact of halogen termination is not fully understood. We show that for low-index surfaces, 100% fluorinated surfaces exhibit chemically stable positive electron affinities in the 1.17 to 2.63 eV range, whereas 100% chlorination is energetically unfavorable. At lower coverage the positive electron affinity is smaller, being a combination of halogen-terminated and unterminated sites. For mixed halogen and hydrogen termination, a wide range of negative and positive electron affinities can be achieved by varying the relative concentrations of adsorbed species. © 2011 American Physical Society.

H. Pinto

Papers

Optically Controlled Switching of the Charge State of a Single Nitrogen-Vacancy Center in Diamond at Cryogenic Temperatures

p-type doping of graphene with F4-TCNQ

Electronic and electrochemical doping of graphene by surface adsorbates.

Mechanisms of doping graphene

Calculated electron affinity and stability of halogen-terminated diamond