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## Raman spectroscopy of temperature induced effects in four carbon allotropes

Joya, M. R.; Zanatta, Antonio Ricardo; Barba-Ortega, J.
Fonte: World Scientific; Singapore Publicador: World Scientific; Singapore
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
56.96%
In this paper, we report strong variations in the Raman spectra of different carbon allotropes samples, for temperatures ranging from 83 K to 1123 K. The temperature dependence of D and G peak frequencies in the Raman spectrum of diamond, graphite, graphene, and carbon nanoparticles (CNPs) with 20 nm dot-size were investigated. These effects caused by temperature can be estimated from the changes in position ( dω/dT )p and in linewidth of peak full width at half maximum (FWHM) G in the Raman spectrum of each sample. The broadening for each allotrope under the same conditions of temperature were: diamond ∼4 cm-1, graphite ∼50 cm-1, graphene ∼5 cm-1 and nanoparticles ∼7 cm-1. We also used scanning electron microscopy (SEM) to study the morphology and determine the size of the samples. According to the experimental data, the residual structural disorder and stress present in the samples are enhanced with temperature and responds for the observed changes in the Raman spectra. We present a systematic study of the temperature-dependent Raman spectra of four carbon allotropes.; CNPq; FAPESP; COLCIENCIAS (RC-N 696-2011); Dirección de Investigación Sede Bogotá (DIB) - Universidad Nacional de Colombia (UNAL)

## A nonzero gap two-dimensional carbon allotrope from porous graphene

Brunetto, Gustavo; Santos, Bruno I.; Autreto, Pedro A. S.; Machado, Leonadro D.; Dos Santos, Ricardo P. B.; Galvao, Douglas S.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 79-84
ENG
Relevância na Pesquisa
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Graphene has been one of the hottest topics in materials science in the last years. Because of its special electronic properties graphene is considered one of the most promising materials for future electronics. However, in its pristine form graphene is a gapless semiconductor, which poses some limitations to its use in some transistor electronics. Many approaches have been tried to create, in a controlled way, a gap in graphene. These approaches have obtained limited successes. Recently, hydrogenated graphene-like structures, the so-called porous graphene, have been synthesized. In this work we show, based on ab initio quantum molecular dynamics calculations, that porous graphene dehydrogenation can lead to a spontaneous formation of a nonzero gap two-dimensional carbon allotrope, called biphenylene carbon (BC). Besides exhibiting an intrinsic nonzero gap value, BC also presents well delocalized frontier orbitals, suggestive of a structure with high electronic mobility. Possible synthetic routes to obtain BC from porous graphene are addressed. © 2012 Materials Research Society.

## Carbon-Binding Designer Proteins that Discriminate between sp2- and sp3-Hybridized Carbon Surfaces

Coyle, Brandon L.; Rolandi, Marco; Baneyx, François
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36.45%
Robust and simple strategies to directly functionalize graphene- and diamond-based nanostructures with proteins are of considerable interest for biologically driven manufacturing, biosensing and bioimaging. Here, we identify a new set of carbon binding peptides that vary in overall hydrophobicity and charge, and engineer two of these sequences (Car9 and Car15) within the framework of E. coli Thioredoxin 1 (TrxA). We develop purification schemes to recover the resulting TrxA derivatives in a soluble form and conduct a detailed analysis of the mechanisms that underpin the interaction of the fusion proteins with carbonaceous surfaces. Although equilibrium quartz crystal microbalance measurements show that TrxA∷Car9 and TrxA∷Car15 have similar affinity for sp2-hybridized graphitic carbon (Kd = 50 and 90 nM, respectively), only the latter protein is capable of dispersing carbon nanotubes. Further investigation by surface plasmon resonance and atomic force microscopy reveals that TrxA∷Car15 interacts with sp2-bonded carbon through a combination of hydrophobic and π-π interactions but that TrxA∷Car9 exhibits a cooperative mode of binding which relies on a combination of electrostatics and weaker π-stacking. Consequently, we find that TrxA∷Car9 binds equally well to sp2- and sp3-bonded (diamond-like) carbon particles...

## Structural, vibrational and thermodynamic properties of carbon allotropes from first-principles : diamond, graphite, and nanotubes

Mounet, Nicolas (Nicolas Frank)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 104 p.; 4519769 bytes; 4524067 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
46.63%
The structural, dynamical, and thermodynamic properties of different carbon allotropes are computed using a combination of ab-initio methods: density-functional theory for total-energy calculations and density-functional perturbation theory for lattice dynamics. For diamond, graphite, graphene, and armchair or zigzag single-walled nanotubes we first calculate the ground-state properties: lattice parameters, elastic constants and phonon dispersions and density of states. Very good agreement with available experimental data is found for all these, with the exception of the c/a ratio in graphite and the associated elastic constants and phonon dispersions. Agreement with experiments is recovered once the experimental c/a is chosen for the calculations. Results for carbon nanotubes confirm and expand available, but scarce, experimental data. The vibrational free energy and the thermal expansion, the temperature dependence of the elastic moduli and the specific heat are calculated using the quasi-harmonic approximation. Graphite shows a distinctive in-plane negative thermal-expansion coefficient that reaches its lowest value around room temperature, in very good agreement with experiments. The predicted value for the thermal-contraction coefficient of narrow single-walled nanotubes is half that of graphite...

## Dissolution, processing and fluid structure of graphene and carbon nanotube in superacids: The route toward high performance multifunctional materials.

Behabtu, Natnael
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
46.44%
Carbon allotropes have taken central stage of nanotechnology in the last two decades. Today, fullerenes, carbon nanotubes (CNTs), and graphene are essential building blocks for nanotechnology. Their superlative electrical, thermal and mechanical properties make them desirable for a number of technological applications ranging from lightweight strong materials to electrical wires and support for catalysts. However, transferring the exceptional single molecule properties into macroscopic objects has presented major challenges. This thesis demonstrates that carbon nanotubes and graphite dissolve in superacids and these solution can processed into macroscopic objects. Chapter 2 reviews neat CNT fiber literature. Specifically, the two main processing methods —solid– state and solution spinning — are discussed. CNT aspect ratio and fibers structure are identified as the main variables affecting fiber properties. Chapter 3 shows that graphite can be exfoliated into single-layer graphene by spontaneous dissolution in chlorosulfonic acid. The dissolution is general and can be applied to various forms of graphite, including graphene nanoribbons. Dilute solutions of graphene can be used to form transparent conductive films. At high concentration...

## Magnetic Properties of Novel Carbon Allotropes

Rode, Andrei V; Christy, Andrew; Gamaly, Eugene G; Hyde, Stephen; Luther-Davies, Barry
Fonte: Elsevier Publicador: Elsevier
Tipo: Parte de Livro
Relevância na Pesquisa
46.56%
This chapter elaborates the magnetic properties of novel carbon allotropes. The polyhedral molecules of fullerene, C60, undergo cross-linking reactions when annealed at pressures to form a variety of crystalline polymers with layered structures. These pol

## Superhard sp3 carbon allotropes with odd and even ring topologies

Selli, Daniele; Baburin, Igor A.; Martoňák, Roman; Leoni, Stefano
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 23/06/2012
Relevância na Pesquisa
46.67%
Four sp3 carbon allotropes with six, eight, and 16 atoms per primitive cell have been derived using a combination of metadynamics simulations and topological scan. A chiral orthorhombic phase oC16 (C2221) was found to be harder than monoclinic M-carbon and shows excellent stability in the high-pressure range. A second orthorhombic phase of Cmmm symmetry, by \sim 0.028 eV/atom energetically lower than W-carbon, can be formed from graphite at \sim 9 GPa. In general, the mechanical response under pressure was found to depend on the structure topology, which reflects the way rings are formed from an initial graphene layer stacking.; Comment: 5 pages, 5 figures

## Superstructures of Cubic and Hexagonal Diamonds Comprising a Family of Novel $sp^3$ Superhard Carbon Allotropes

Cui, Hui-Juan; Sheng, Xian-Lei; Yan, Qing-Bo; Zheng, Qing-Rong; Su, Gang
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/10/2013
Relevância na Pesquisa
46.7%
Superstructures of cubic and hexagonal diamonds (h- and c-diamond) comprising a family of stable diamond-like $sp^3$ hybridized novel carbon allotropes are proposed, which are referred to as U$_n$-carbon where $n \geq 2$ denotes the number of structural layers in a unit cell. The conventional h- and c-diamond are included in this family as members with $n=2$ and 3, respectively. U$_n$-carbon ($n=4-6$), which are unveiled energetically and thermodynamically more stable than h-diamond and possess remarkable kinetic stabilities, are shown to be insulators with indirect gaps of $5.6 \sim 5.8$ eV, densities of $3.5 \sim 3.6$ g/cm$^3$, bulk modulus of $4.3 \sim 4.4 \times 10^{2}$ GPa, and Vickers hardness of $92.9 \sim 97.5$ GPa even harder than h- and c-diamond. The simulated x-ray diffraction and Raman spectra are presented for experimental characterization. These new structures of carbon would have a compelling impact in physics, chemistry, materials science and geophysics.

## New Superhard Carbon Phases Between Graphite and Diamond

He, Chaoyu; Sun, L. Z.; Zhang, C. X.; Zhang, K. W.; Peng, Xiangyang; Zhong, Jianxin
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Two new carbon allotropes (H-carbon and S-carbon) are proposed, as possible candidates for the intermediate superhard phases between graphite and diamond obtained in the process of cold compressing graphite, based on the results of first-principles calculations. Both H-carbon and S-carbon are more stable than previously proposed M-carbon and W-carbon and their bulk modulus are comparable to that of diamond. H-carbon is an indirect-band-gap semiconductor with a gap of 4.459 eV and S-carbon is a direct-band-gap semiconductor with a gap of 4.343 eV. The transition pressure from cold compressing graphite is 10.08 GPa and 5.93 Gpa for H-carbon and S-carbon, respectively, which is in consistent with the recent experimental report.; Comment: 5pages,4figures,submitted to Phys.Rev.Lett on 18Jan12, transfer to Phys.Rev.B on 25Mar12; Solid State Communications(2012), http://dx.doi.org/10.1016/j.ssc.2012.05.022

## Four superhard carbon allotropes: First-principle study

He, Chaoyu; Sun, L. Z.; Zhang, C. X.; Zhang, K. W.; Peng, Xiangyang; Zhong, Jianxin
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.98%
Using a generalized genetic algorithm, we propose four new sp3 carbon allotropes with 5-6-7 (5-6-7-type Z-ACA and Z-CACB) or 4-6-8(4-6-8-type Z4-A3B1 and A4-A2B2) carbon rings. Their stability, mechanical and electronic properties are systematically studied using first-principles method. We find that all these four carbon allotropes show amazing stability in comparison with recently proposed carbon phases. Both ZACA and Z-CACB are direct-band-gap semiconductors with band gaps of 2.261 eV and 4.196 eV, respectively. Whereas Z4-A3B1 and A4-A2B2 are indirect-band-gap semiconductors with band gaps of 3.105 eV and 3.271 eV, respectively. Their mechanical properties reveal that all these four carbon allotropes are superhard materials comparable to diamond.; Comment: 6 pages, 4 figures, submit to PCCP on 21-Feb-2012

## Hexagon Preserving Carbon Nanofoams

Seifert, Gotthard; Kuc, Agnieszka; Heine, Thomas
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 29/06/2011
Relevância na Pesquisa
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Carbon foams are hypothetical carbon allotropes that contain graphite-like (sp$^2$ carbon) segments, connected by sp$^3$ carbon atoms, resulting in porous structures. In this work the DFTB (Density Functional based Tight-Binding) method with periodic boundary conditions (PBC) was employed to study energetics, the stability and electronic properties of this unusual class of carbon systems. Concerning the most stable phases of carbon (graphite and diamond), foams show high structural stability at very low mass density. The electronic band structure and electronic DOS (density of states) of foams indicate a similar size dependence as carbon nanotubes. The calculated bulk moduli are in the range between that of graphite (5.5 GPa) and diamond (514 GPa). These structures may represent novel stable carbon modifications with sp$^2$+sp$^3$ hybridization.; Comment: Book chapter in the book entitled "Computer based modelling of novel carbon systems and their properties", published in L. colombo and A. Fasolino (eds.). The original publication is available at www.springerlink.com

## RF plasma cleaning of optical surfaces: A study of cleaning rates on different carbon allotropes as a function of RF powers and distances

Cuxart, M. González; Reyes-Herrera, J.; Šics, I.; Goñi, A. R.; Fernandez, H. Moreno; Carlino, V.; Pellegrin, E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.67%
An extended study on an advanced method for the cleaning of carbon contaminations on large optical surfaces using a remote inductively coupled low pressure RF plasma source (GV10x downstream asher) is reported in this work. Technical as well as scientific features of this scaled up cleaning process are analyzed, such as the cleaning efficiency for different carbon allotropes (amorphous and diamond-like carbon) as a function of feedstock gas composition, RF power (ranging from 30 to 300W), and source-object distances (415 to 840 mm). The underlying physical phenomena for these functional dependences are discussed.; Comment: 16 pages, 9 figures

## Two semiconducting three-dimensional all-sp2 carbon allotropes

He, Chaoyu; Sun, L. Z.; Zhang, C. X.; Zhong, J. X.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 30/06/2012
Relevância na Pesquisa
46.91%
Using first-principles method, we investigate the energetic stability, dynamic stability and electronic properties of two three-dimensional (3D) all-sp2 carbon allotropes, sp2-diamond and cubic-graphite. The cubic-graphite was predicted by Michael O'Keeffe in 1992 (Phys. Rev. Lett., 68, 15, 1992.) possessing space group of Pn-3m (224), whereas the sp2-diamond with the space group Fd-3m (227) same as that of diamond has not been reported before. Our results indicate that sp2-diamond is more stable than previously proposed K4-carbon and T-carbon, and cubic-graphite is even more stable than superhard M-carbon, W-carbon and Z-carbon.The calculations on vibrational properties show that both structures are dynamically stable. Interestingly, both sp2-diamond and cubic-graphite behave as semiconductors which are contrary to previously proposed all-sp2 carbon allotropes. The sp2-diamond is a semiconductor with a direct band gap of 1.66 eV, and cubic-graphite is an indirect semiconductor with band gap of 2.89 eV. The very lower densities and entirely sp2 configures of sp2-diamond and cubic-graphite can be potentially applied in hydrogen-storage, photocatalysts and molecular sieves.; Comment: 5 pages, 5 figures

## Novel Two-dimensional Carbon Allotrope with Strong Electronic Anisotropy

Su, Cong; Jiang, Hua; Feng, Ji
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.63%
Two novel two-dimensional carbon allotropes comprised of octagons and pentagons are proposed based on the first-principles calculations. The two carbon allotropes, named OPG-L and OPG-Z, are found to have distinct properties. OPG-L is metallic, while OPG-Z is a gapless semimetal. Remarkably, OPG-Z exhibits pronounced electronic anisotropy with highly anisotropic Dirac points at the Fermi level. A tight-binding model is suggested to describe the low-energy quasiparticles, which clarifies the origin of the anisotropic Dirac points. Such an anisotropic electronic characteristic of OPG-Z is expected to have wide implications in nano-electronics.; Comment: 6 pages, 5 figures (accepted by Physical Review B)

## Electronic and optical properties of novel carbon allotropes

Wang, Zhanyu; Zhang, R. J.; Zheng, Y. X.; Chen, L. Y.; Wang, S. Y.; Wang, C. Z.; Ho, K. M.; Fan, Yuan-Jia; Jin, Bih-Yaw; Su, Wan-Sheng
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 27/08/2015
Relevância na Pesquisa
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The phonon properties, electronic structures and optical properties of novel carbon allotropes, such as monolayer penta-graphene (PG), double-layer PG and T12-carbon, were explored by means of first-principles calculations. Results of phonon calculations demonstrate that these exotic carbon allotropes are dynamically stable. In addition, the bulk T12 phase is an indirect-gap semiconductor having a bandgap of ~4.89 eV. Whereas the bulk material transforms to a 2D phase, the monolayer and double-layer PG become quasi-direct gap semiconductors with smaller band gaps of ~2.64 eV and ~3.27eV, respectively. Furthermore, the partial charge density analysis indicates that the 2D phases retain part of the electronic characteristics of the T12 phase. The linear photon energy-dependent dielectric functions and related optical properties including refractive index, extinction coefficient, absorption spectrum, reflectivity, and energy loss spectrum were also computed and discussed. The structural estimation obtained as well as other findings are in agreement with existing theoretical data. The calculated results are beneficial to the practical applications of these exotic carbon allotropes in optoelectronics and electronics.

## Families of superhard crystalline carbon allotropes induced via cold-compressed graphite and nanotubes

Niu, Haiyang; Chen, Xing-Qiu; Wang, Shibing; Li, Dianzhong; Mao, Wendy L.; Li, Yiyi
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 13/03/2012
Relevância na Pesquisa
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We report a general scheme to systematically construct two classes of structural families of superhard sp3 carbon allotropes of cold compressed graphite through the topological analysis of odd 5+7 or even 4+8 membered carbon rings stemmed from the stacking of zigzag and armchair chains. Our results show that the previously proposed M, bct-C4, W and Z allotropes belong to our currently proposed families and that depending on the topological arrangement of the native carbon rings numerous other members are found that can help us understand the structural phase transformation of cold-compressed graphite and carbon nanotubes (CNTs). In particular, we predict the existence of two simple allotropes, R- and P-carbon, which match well the experimental X-ray diffraction patterns of cold-compressed graphite and CNTs, respectively, display a transparent wide-gap insulator ground state and possess a large Vickers hardness comparable to diamond.; Comment: 5 pages, 4 figures, accepted by Phys. Rev. Lett

## Thermal Properties of Graphene, Carbon Nanotubes and Nanostructured Carbon Materials

Balandin, Alexander A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/06/2011
Relevância na Pesquisa
36.46%
Recent years witnessed a rapid growth of interest of scientific and engineering communities to thermal properties of materials. Carbon allotropes and derivatives occupy a unique place in terms of their ability to conduct heat. The room-temperature thermal conductivity of carbon materials span an extraordinary large range - of over five orders of magnitude - from the lowest in amorphous carbons to the highest in graphene and carbon nanotubes. I review thermal and thermoelectric properties of carbon materials focusing on recent results for graphene, carbon nanotubes and nanostructured carbon materials with different degrees of disorder. A special attention is given to the unusual size dependence of heat conduction in two-dimensional crystals and, specifically, in graphene. I also describe prospects of applications of graphene and carbon materials for thermal management of electronics.; Comment: Review Paper; 37 manuscript pages; 4 figures and 2 boxes

## Cohesion Energetics of Carbon Allotropes : Quantum Monte Carlo Study

Shin, Hyeondeok; Kang, Sinabro; Koo, Jahyun; Lee, Hoonkyung; Kim, Jeongnim; Kwon, Yongkyung
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.7%
We have performed quantum Monte Carlo calculations to study the cohesion energetics of carbon allotropes, including $sp^3$-bonded diamond, $sp^2$-bonded graphene, $sp$-$sp^2$ hybridized graphynes, and $sp$-bonded carbyne. The computed cohesive energies of diamond and graphene are found to be in excellent agreement with the corresponding values determined experimentally for diamond and graphite, respectively, when the zero-point energies, along with the interlayer binding in the case of graphite, are included. We have also found that the cohesive energy of graphyne decreases systematically as the ratio of $sp$-bonded carbon atoms increases. The cohesive energy of $\gamma$-graphyne, the most energetically-stable graphyne, turns out to be 6.766(6) eV/atom, which is smaller than that of graphene by 0.698(12) eV/atom. Experimental difficulty in synthesizing graphynes could be explained by their significantly smaller cohesive energies. Finally we conclude that the cohesive energy of a newly-proposed graphyne can be accurately estimated with the carbon-carbon bond energies determined from the cohesive energies of graphene and three different graphynes considered here.; Comment: 18 pages, 4 figures

## Systematic search for low-enthalpy sp3 carbon using evolutionary metadynamics

Zhu, Qiang; Zeng, Qingfeng; Oganov, Artem R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.01%
We present a systematic search for low-energy metastable superhard carbon allotropes by using the recently developed evolutionary metadynamics technique. It is known that cold compression of graphite produces an allotrope at 15-20 GPa. Here we look for all low-enthalpy structures accessible from graphite. Starting from 2H- or 3R-graphite and applying the pressure of 20 GPa, a large variety of intermediate $sp^3$ carbon allotropes were observed in evolutionary metadynamics simulation. Our calculation not only found all the previous proposed candidates for `superhard graphite', but also predicted two allotropes (\emph{X}-carbon and \emph{Y}-carbon) showing novel 5+7 and 4+8 topologies. These superhard carbon allotropes can be classified into five families based on 6 (diamond/lonsdaleite), 5+7 (\emph{M/W}-carbon), 5+7 (\emph{X}-carbon), 4+8 (bct C$_4$), and 4+8 (\emph{Y}-carbon) topologies. This study shows evolutionary metadynamics is a powerful approach both to find the global minima and systematically search for low-energy metastable phases reachable from given starting materials.; Comment: 6 pages, 7 figures

## Nanoengineering Carbon Allotropes from Graphene

Lusk, Mark T.; Carr, L. D.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.98%
Monolithic structures can be built into graphene by the addition and subsequent re-arrangement of carbon atoms. To this end, ad-dimers of carbon are a particularly attractive building block because a number of emerging technologies offer the promise of precisely placing them on carbon surfaces. In concert with the more common Stone-Wales defect, repeating patterns can be introduced to create as yet unrealized materials. The idea of building such allotropes out of defects is new, and we demonstrate the technique by constructing two-dimensional carbon allotropes known as haeckelite. We then extend the idea to create a new class of membranic carbon allotropes that we call \emph{dimerite}, composed exclusively of ad-dimer defects.; Comment: 5 pages, 5 figures