Optical Properties Of Graphene Research Articles

Design optimization of single and double layer Graphene phase modulators in SOI.

In this paper we report on an electro-refractive modulator based on single or double-layer graphene on top of silicon waveguides. The graphene layers are biased to the transparency condition in order to achieve phase modulation with negligible amplitude modulation. By means of a detailed study of both the electrical and optical properties of graphene and silicon, as well as through optimization of the geometrical parameters, we show that the proposed devices may theoretically outperform existing modulators both in terms of V(π)L and of insertion losses. The overall figures of merit of the proposed devices are as low as 8.5 and 2dB∙V for the single and double layer cases, respectively.

Bio-inspired materials and graphene for electronic applications

Graphene, a very recent rising star, with an atomically thin, 2D honeycomb lattice that consists of sp2-hybridized carbons, exhibits remarkable electronic, thermal, optical, and mechanical properties. Many attempts have been made to demonstrate the applications of graphene and graphene-based materials in several fields, nevertheless the combination of bio-inspired materials with graphene and their related properties have attracted attention only recently. In particular, the electrical and optical properties of graphene with bio-inspired materials could lead to novel graphene-based devices with remarkable performance. This feature article will briefly introduce the recent progress in this direction. The first part of the article will report on some bio-inspired modifications useful to modulate the electrical performance of graphene composites as well as interesting examples with silk, nanocellulose and proteins. In the second part, the recent progress in bio-inspired modification and applications of graphene in photodetection, organic solar cells and photothermal therapy is discussed. From this perspective this field of research is still at an early stage but it might become a hot topic in the near future.

Influence of a gold substrate on the optical properties of graphene

Spectroscopic ellipsometry combined with measurements of electrical characteristics and Kelvin probe force microscopy have been employed to investigate the interaction between graphene and a gold substrate, and the consequent changes of graphene's complex refractive index on gold. A strong blue shift, as much as 350 meV, of the prominent absorption peak (exciton-shifted M-point Van Hove singularity in the ultraviolet range) of graphene has been observed, with respect to the peak position for the sample on an insulating substrate where this peak was observed at about 4.55 eV. The results show that an interaction between graphene and a gold substrate can be characterized through the change of graphene's optical properties. In addition, the effects that a water layer trapped between graphene and gold during the transfer process has on the charge transfer between graphene and the gold substrate have been investigated.

Patterning and tuning of electrical and optical properties of graphene by laser induced two-photon oxidation.

We demonstrate a simple all-optical patterning method for graphene, based on laser induced two-photon oxidation. By tuning the intensity and dose of irradiation, the level of oxidation is controlled, the band gap is introduced and electrical and optical properties are continuously tuned. Complex patterning is performed for air-suspended monolayer graphene and for graphene on substrates. The presented concept allows development of all-graphene electronic and optoelectronic devices with an all-optical method.

A new characteristics matrix method based on conductivity and its application in the optical properties of graphene in THz frequency range

A new characteristics matrix method along with the formulas based on conductivity, which can be used to calculate the optical properties of an ultra-thin conductive composite multilayer dielectric structure, is derived for the first time as faras we know based on the electromagnetic boundary conditions Maxwell's equations required. It can be used to calculate the reflection, transmission, and absorption of light, provided that the conductivity of the conductive body is known, also it can overcom the shortcoming of the traditional transfer matrix method, i.e.it is necessary to know the permittivity and permeability of the material. By using the proposed method, the optical behavior of graphene and composite multilayer structures can be obtained in the THz frequency range.

Coherent resonance of quantum plasmons in the graphene-gold cluster hybrid system.

Noble metal nanoparticles can modify the optical properties of graphene. Here we present a detailed theoretical analysis of the coherent resonance of quantum plasmons in the graphene-gold cluster hybrid system by using time dependent density functional theory (TDDFT). This plasmon coherent effect is mainly attributed to the electromagnetic field coupling between the graphene and the gold cluster. As a result, the optical response of the hybrid system exhibits a remarkably strong, selectable tuning and polarization dependent plasmon resonance enhanced in wide frequency regions. This investigation provides an improved understanding of the plasmon enhancement effect in a graphene-based photoelectric device.

Comprehensive study of graphene grown by chemical vapor deposition

Graphene was grown on Cu foil by chemical vapor deposition with CH4 as carbon source, and then was transferred onto various substrates for device applications. The structural and optical properties of graphene were investigated, comprehensively. Raman spectra indicate as-grown and transferred graphene films are homogenous monolayer graphene. Optical microscopy and scanning electron microscopy images reveal wrinkle-free and smooth surface of transferred graphene, confirming the high quality of graphene. In addition, the transferred graphene on glass exhibits excellent transmittances in the visible region (89.3 % at ~500 nm). Therefore, the results present the controllable approaches to achieve as-grown and transferred high quality graphene for the fabrication of multiple nanoelectronic devices.

Reversible Charge-Transfer Doping in Graphene due to Reaction with Polymer Residues

Chemical doping in graphene due to polymer molecules adsorption has attracted much recent interest because of the modification of electrical, magnetic, and optical properties of graphene. We show a reversible charge-transfer doping effect in graphene due to the reaction with poly(methyl methacrylate) (PMMA) residues. By helium ion irradiation and vacuum annealing without introducing an external dopant, reversible shifts in Raman G and 2D bands are observed as well as the change in the relative 2D band intensity to the G band. Chemical bonds between functional groups from PMMA residues and graphene could be formed due to He+ ion irradiation, and the desorption of functional groups from graphene is dominant during the vacuum annealing process. Meanwhile, PMMA residue on the graphene surface is mostly removed and the surface morphology becomes smooth after irradiation and annealing. Both electrical conductance and Raman band shifts show nonmonotonic dependence on the dose density, which remains after anneali...

Tuning Many-Body Interactions in Graphene: The Effects of Doping on Excitons and Carrier Lifetimes

The optical properties of graphene are strongly affected by electron-electron (e-e) and electron-hole (e-h) interactions. Here we tune these many-body interactions through varying the density of free charge carriers. Measurements from the infrared to the ultraviolet reveal significant changes in the optical conductivity of graphene for both electron and hole doping. The shift, broadening, and modification in shape of the saddle-point exciton resonance reflect strong screening of the many-body interactions by the carriers, as well as changes in quasi-particle lifetimes. Ab initio calculations by the GW Bethe-Salpeter equation (GW-BSE), which take into account modification of both the repulsive e-e and the attractive e-h interactions, provide excellent agreement with experiment. Understanding the optical properties and high-energy carrier dynamics of graphene over a wide range of doping is crucial for both fundamental graphene physics and for emerging applications of graphene in photonics.

Preface to Special Issue on Cutting-Edge Research on Optical Properties of Graphene and their Photonic Applications

Preface to Special Issue on Cutting-Edge Research on Optical Properties of Graphene and their Photonic Applications

Snapshots of non-equilibrium Dirac carrier distributions in graphene

The optical properties of graphene are made unique by the linear band structure and the vanishing density of states at the Dirac point. It has been proposed that even in the absence of a bandgap, a relaxation bottleneck at the Dirac point may allow for population inversion and lasing at arbitrarily long wavelengths. Furthermore, efficient carrier multiplication by impact ionization has been discussed in the context of light harvesting applications. However, all of these effects are difficult to test quantitatively by measuring the transient optical properties alone, as these only indirectly reflect the energy- and momentum-dependent carrier distributions. Here, we use time- and angle-resolved photoemission spectroscopy with femtosecond extreme-ultraviolet pulses to directly probe the non-equilibrium response of Dirac electrons near the K-point of the Brillouin zone. In lightly hole-doped epitaxial graphene samples, we explore excitation in the mid- and near-infrared, both below and above the minimum photon energy for direct interband transitions. Whereas excitation in the mid-infrared results only in heating of the equilibrium carrier distribution, interband excitations give rise to population inversion, suggesting that terahertz lasing may be possible. However, in neither excitation regime do we find any indication of carrier multiplication, questioning the applicability of graphene for light harvesting.

Electronic Properties of Boron and Nitrogen Doped Graphene

Graphene is the thinnest 2-D material which can be regarded as a single layer of graphite. The unique electrical, mechanical and optical properties of graphene can be used in many technological applications. 2-D nanomaterials with semiconducting properties are of great interest since they can be applied in electronics industry. Pure graphene is a zerogap semiconductor or semimetal, since the electron states just cross the Fermi energy. However, the electronic properties of graphene can be tuned by doping boron or nitrogen atoms. Understanding the electronic properties in terms of density of states and band structure of doped graphene is of great relevance today. In our work, we have analyzed the electronic properties of boron and nitrogen doped graphene using Density Functional Theory (DFT). The stability and charge analysis of doped structures have been studied. The Local Density Approximation (LDA) calculations have been used to find the total energies of the structures. In addition to the electronics industry, doped graphene also has great potential to adsorb gas molecules. Therefore, we have analyzed the H2 molecule adsorption in pure, B-doped and N-doped graphene.

Supramolecular Attachment of Metalloporphyrins to Graphene Oxide and its Pyridine‐Containing Derivative

Graphene is a unique material due to its remarkable mechanical, electrical, and optical properties. [1] Although the optical properties of graphene can be exploited in a variety of applications, the use of graphene in transparent electrodes in solar cells or liquid-crystal devices [2] has rarely been explored. Therefore, modulation of its optical properties by chemically functionalizing graphene with optoelectronically active porphyrins could result in interesting multifunctional, nanoscale materials for optical and/or optoelectronic applications. To pursue this goal, enhancement of the solubility of graphene [3] through chemical functionalization is often required. The extended oxidation of graphene, which produces single layers of graphene oxide (GO), has been especially useful in this regard. The resulting water-soluble nanomaterial, which contains hydroxyl, epoxide, and carboxylic groups, [4] offers a platform to explore further functionalization by means of conventional organic reactions. [5] The processability and chemical reactivity of GO allow the functionalization of GO with porphyrins from different perspectives. To date, graphene or graphene oxide porphyrin hybrid materials have been produced by supramolecular interaction of porphyrins with graphene/GO and by covalent attachment of porphyrins to graphene/GO. Following the former strategy, several examples of protoporphyrins containing charged meso-groups have been reported to interact with reduced GO through a combination of ionic and p–p interactions. [6] In addition, neutral proto- and metallopor

Temperature-dependent far-infrared response of epitaxial multilayer graphene

The optical response of pristine and FeCl3-intercalated epitaxial graphene has been studied over the temperature range from 11 K to 296 K. The far-infrared (FIR) Drude conductivity of pristine graphene rises with increasing temperature, opposite to the behavior of intercalated graphene. This is a result of intercalation-induced p-type doping compensating the intrinsic n-doping in epitaxial graphene. Temperature-dependent Drude parameters are obtained by fitting the FIR response. This study demonstrates the influence of temperature variation on the optical properties of graphene, which should be a vital factor to be considered for graphene-based device applications.

Photocurrent in graphene harnessed by tunable intrinsic plasmons

Graphene's optical properties in the infrared and terahertz can be tailored and enhanced by patterning graphene into periodic metamaterials with sub-wavelength feature sizes. Here we demonstrate polarization-sensitive and gate-tunable photodetection in graphene nanoribbon arrays. The long-lived hybrid plasmon-phonon modes utilized are coupled excitations of electron density oscillations and substrate (SiO2) surface polar phonons. Their excitation by s-polarization leads to an in-resonance photocurrent, an order of magnitude larger than the photocurrent observed for p-polarization, which excites electron-hole pairs. The plasmonic detectors exhibit photo-induced temperature increases up to four times as large as comparable two-dimensional graphene detectors. Moreover, the photocurrent sign becomes polarization sensitive in the narrowest nanoribbon arrays owing to differences in decay channels for photoexcited hybrid plasmon-phonons and electrons. Our work provides a path to light-sensitive and frequency-selective photodetectors based on graphene's plasmonic excitations.

Correction to Tuning the Electrical and Optical Properties of Graphene by Ozone Treatment for Patterning Monolithic Transparent Electrodes

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionCorrection to Tuning the Electrical and Optical Properties of Graphene by Ozone Treatment for Patterning Monolithic Transparent ElectrodesJiangtan Yuan, Lai-Peng Ma, Songfeng Pei, Jinhong Du, Yang Su, Wencai Ren, and Hui-Ming Cheng*Cite this: ACS Nano 2013, 7, 6, 5647Publication Date (Web):May 28, 2013Publication History Published online28 May 2013Published inissue 25 June 2013https://doi.org/10.1021/nn402580yCopyright © 2013 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views704Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (42 KB) Get e-AlertsSUBJECTS:Electrodes,Optical properties,Two dimensional materials Get e-Alerts

Tuning the Electrical and Optical Properties of Graphene by Ozone Treatment for Patterning Monolithic Transparent Electrodes

Tunable electrical and optical properties of graphene are vital to promote its use as film electrodes in a variety of devices. We developed an etching-free ozone treatment method to continuously tune the electrical resistance and optical transmittance of graphene films by simply varying the time and temperature of graphene exposure to ozone. Initially, ozone exposure dramatically decreases the electrical resistance of graphene films by p-doping, but this is followed by increases in the resistance and optical transmittance as a result of surface oxidation. The rate of resistance increase can be significantly increased by raising the treatment temperature. The ozone-oxidized graphene is not removed but is gradually transformed to graphene oxide (GO). On the basis of such effects of ozone treatment, we demonstrate a well-defined graphene pattern by using ozone photolithography, in which the ozone-treated graphene electrodes are monolithic but separated by insulating GO regions. Such a monolithic graphene pattern shows low optical contrast, a clean and more hydrophilic surface, indicating the promising use of ozone treatment to achieve high-performance graphene-based optoelectronic devices.

Electronic and optical properties of graphene and graphitic ZnO nanocomposite structures

Electronic and optical properties of graphene and graphitic ZnO (G/g-ZnO) nanocomposites have been investigated with density functional theory. Graphene interacts overall weakly with g-ZnO monolayer via van der Waals interaction. There is no charge transfer between the graphene and g-ZnO monolayer, while a charge redistribution does happen within the graphene layer itself, forming well-defined electron-hole puddles. When Al or Li is doped in the g-ZnO monolayer, substantial electron (n-type) and hole (p-type) doping can be induced in graphene, leading to well-separated electron-hole pairs at their interfaces. Improved optical properties in graphene/g-ZnO nanocomposite systems are also observed, with potential photocatalytic and photovoltaic applications.

Tuning the electronic and optical properties of graphene and boron-nitride quantum dots by molecular charge-transfer interactions: a theoretical study

Spin-polarized first-principles calculations have been performed to tune the electronic and optical properties of graphene (G) and boron-nitride (BN) quantum dots (QDs) through molecular charge-transfer using tetracyanoquinodimethane (TCNQ) and tetrathiafulvalene (TTF) as dopants. From our results, based on the formation energy and the distance between QDs and dopants, we infer that both the dopants are physisorbed on the QDs. Also, we find that GQDs interact strongly with the dopants compared to the BNQDs. Interestingly, although the dopants are physisorbed on QDs, their interactions lead to a decrement in the HOMO-LUMO gap of QDs by more than half of their original value. We have found a spin-polarized HOMO-LUMO gap in certain QD-dopant complexes. Mülliken population analysis, generation of density of states (DOS) and projected DOS (pDOS) plots, and optical conductivity calculations have been performed to support and understand the reasons behind our findings.

Ab initio optical study of graphene on hexagonal boron nitride and fluorographene substrates

The fascinating optical properties of graphene are usually concluded in theory under the assumption that graphene is freestanding. However, in experimentally realizable devices, graphene is usually supported by a substrate, which may influence the optical properties of the graphene. Choosing the right substrate is therefore critical for graphene electromagnetic (EM) devices. In this paper, we studied the influence of two types of two-dimensional (2D) insulating substrates, hexagonal boron nitride (h-BN) and fluorographene (FG), on the graphene optical properties at room temperature. Our work shows that both substrates can preserve well the optical properties of graphene from 0.6 eV to 3.5 eV and the FG substrate can retain graphene’s original properties much better than the h-BN substrate when the photon energy is 3.5 eV. Besides, by analyzing the Kubo formula, the relaxation time of non-freestanding graphene, which can reflect the substrate–graphene interaction, is highly dependent on the substrate type and its stacking pattern. A THz graphene surface plasmonic modulator is used to further explain the substrate effect on graphene EM device design. Our results demonstrate that the h-BN substrate may degrade or fail the performance of THz ( 0.2 eV) can overcome the performance degradation. Finally, the substrate effects on graphene properties are also studied by examining the electronic properties of double-layer structures. Our results on the sensitivity issue that are caused by the stacking pattern and inter-layer distance may provide a reasonable explanation on the inconsistency of substrate-induced bandgap opening in graphene/h-BN heterostructures discussed in recent experimental and theoretical studies.