Research

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10 pages, 2425 KiB

Open AccessArticle

Microwave Plasma Formation of Nanographene and Graphitic Carbon Black

by Raju R. Kumal, Akshay Gharpure, Vignesh Viswanathan, Aayush Mantri, George Skoptsov and Randy Vander Wal

C 2020, 6(4), 70; https://0-doi-org.brum.beds.ac.uk/10.3390/c6040070 - 31 Oct 2020

Cited by 5 | Viewed by 3818

Abstract

Aerosol formation of novel carbons offers potential for scale and purity unmatched by condensed phase processes. A microwave driven plasma drives decarbonization of methane to form solid carbon as an aerosol. Dependent upon gas mixture, different forms of carbon are produced: 2D nanographene [...] Read more.

Aerosol formation of novel carbons offers potential for scale and purity unmatched by condensed phase processes. A microwave driven plasma drives decarbonization of methane to form solid carbon as an aerosol. Dependent upon gas mixture, different forms of carbon are produced: 2D nanographene and a 3D graphitic carbon black analogue. TEM reveals the morphological differences and nanostructure. The ability to tune the dominant form is demonstrated by control of the CH₄/Ar ratio. TGA plots reveal the change in products with feed gas composition and quality by oxidation temperature shift. Corresponding Raman analysis illustrates control of graphene content and lamellae quality by peak ratios. To test the origins of the graphitic particles and nanographene, a commercial carbon black was seeded into the microwave reactor, demonstrating a path for graphitic nanostructure evolution and confirming the molecular growth origins for the nanographene. Full article

(This article belongs to the Special Issue Characterization of Disorder in Carbons)

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15 pages, 5052 KiB

Open AccessFeature PaperArticle

Effect of Cellulose Nanocrystals on the Coating of Chitosan Nanocomposite Film Using Plasma-Mediated Deposition of Amorphous Hydrogenated Carbon (a–C:H) Layers

by Torben Schlebrowski, Zineb Kassab, Mounir El Achaby, Stefan Wehner and Christian B. Fischer

C 2020, 6(3), 51; https://0-doi-org.brum.beds.ac.uk/10.3390/c6030051 - 30 Jul 2020

Cited by 3 | Viewed by 2600

Abstract

The substitution of petroleum-based polymers with naturally derived biopolymers may be a good alternative for the conservation of natural fossil resources and the alleviation of pollution and waste disposal problems. However, in order to be used in a wide range of applications, some [...] Read more.

The substitution of petroleum-based polymers with naturally derived biopolymers may be a good alternative for the conservation of natural fossil resources and the alleviation of pollution and waste disposal problems. However, in order to be used in a wide range of applications, some biopolymers’ properties should be enhanced. In this study, biocompatible, non-toxic, and biodegradable chitosan (CS) film and CS reinforced with 10 wt% of cellulose nanocrystals (CN–CS) were coated with amorphous hydrogenated carbon layers (a–C:H) of different thickness. To investigate the effect of the nano-reinforcement on the a–C:H layer applied, mild radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) was used to coat the CS and its CN–CS bio-nanocomposite film. Both the surface characteristics and the chemical composition were analyzed. The surface morphology and wettability were examined by ex-situ atomic force microscopy (AFM) and contact angle measurements (CA), respectively. Hereby, the relationship between sp²/sp³ ratios on a macroscopic scale was also evaluated. For the investigation of the chemical composition, the surface sensitive synchrotron X-ray radiation techniques near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) as well as diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) were used. Full article

(This article belongs to the Special Issue Characterization of Disorder in Carbons)

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11 pages, 443 KiB

Open AccessFeature PaperArticle

Evidence for Glass Behavior in Amorphous Carbon

by Steven Best, Jake B. Wasley, Carla de Tomas, Alireza Aghajamali, Irene Suarez-Martinez and Nigel A. Marks

C 2020, 6(3), 50; https://0-doi-org.brum.beds.ac.uk/10.3390/c6030050 - 30 Jul 2020

Cited by 6 | Viewed by 3604

Abstract

Amorphous carbons are disordered carbons with densities of circa 1.9–3.1 g/cc and a mixture of

s p^{2}

and

s p^{3}

hybridization. Using molecular dynamics simulations, we simulate diffusion in amorphous carbons at different densities and temperatures to investigate the transition between [...] Read more.

Amorphous carbons are disordered carbons with densities of circa 1.9–3.1 g/cc and a mixture of

s p^{2}

and

s p^{3}

hybridization. Using molecular dynamics simulations, we simulate diffusion in amorphous carbons at different densities and temperatures to investigate the transition between amorphous carbon and the liquid state. Arrhenius plots of the self-diffusion coefficient clearly demonstrate that there is a glass transition rather than a melting point. We consider five common carbon potentials (Tersoff, REBO-II, AIREBO, ReaxFF and EDIP) and all exhibit a glass transition. Although the glass-transition temperature (

T_{g}

) is not significantly affected by density, the choice of potential can vary

T_{g}

by up to 40%. Our results suggest that amorphous carbon should be interpreted as a glass rather than a solid. Full article

(This article belongs to the Special Issue Characterization of Disorder in Carbons)

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23 pages, 1394 KiB

Open AccessArticle

Bonding States of Hydrogen in Plasma-Deposited Hydrocarbon Films

by Wolfgang Jacob, Thomas Dürbeck, Thomas Schwarz-Selinger and Udo von Toussaint

C 2020, 6(1), 3; https://0-doi-org.brum.beds.ac.uk/10.3390/c6010003 - 09 Jan 2020

Cited by 6 | Viewed by 2357

Abstract

We applied temperature-programmed desorption (TPD) spectroscopy to study the bonding of hydrogen in amorphous hydrogenated carbon (a–C:H) films. Typical hard plasma-deposited a–C:H films with an initial hydrogen content (H/(H+C)) of about 30% were used as samples. About 85% of the initial hydrogen content [...] Read more.

We applied temperature-programmed desorption (TPD) spectroscopy to study the bonding of hydrogen in amorphous hydrogenated carbon (a–C:H) films. Typical hard plasma-deposited a–C:H films with an initial hydrogen content (H/(H+C)) of about 30% were used as samples. About 85% of the initial hydrogen content is released in the form of H₂, the rest in the form of hydrocarbons. Using a temperature ramp of 15 K/min, release of hydrogen starts at about 600 K with a first peak at about 875 K and a broad shoulder around 1050 K. The peak positions depend on the temperature ramp. This fact was exploited to determine the pre-exponential factor for an analytic analysis of the release spectra. This analysis revealed a pre-exponential factor of

ν = 1 \times 10^{16}

1/s, which deviates significantly from the frequently assumed prefactor

1 \times 10^{13}

1/s. This higher prefactor leads to a shift in the determined binding energies by about +0.5 eV. Standard TPD measurements with linear temperature ramps up to 1275 K were complemented by so-called “ramp and hold” experiments with linear ramps up to certain intermediate temperatures and holding the samples for different times at these temperatures. Such experiments provide valuable additional data for investigation of the thermal behavior of the investigated films. Our experiments prove that the width of the hydrogen release spectrum is determined by a distribution of binding energies rather than release kinetics or diffusive effects. This binding energy distribution has a peak at about 3.1 eV and a shoulder at higher energies extending from about 3.6 to 3.9 eV. Full article

(This article belongs to the Special Issue Characterization of Disorder in Carbons)

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12 pages, 1348 KiB

Open AccessCommunication

Investigating the Possible Origin of Raman Bands in Defective sp²/sp³ Carbons below 900 cm⁻¹: Phonon Density of States or Double Resonance Mechanism at Play?

by Cedric Pardanaud, Gilles Cartry, Luc Lajaunie, Raul Arenal and Josephus Gerardus Buijnsters

C 2019, 5(4), 79; https://0-doi-org.brum.beds.ac.uk/10.3390/c5040079 - 29 Nov 2019

Cited by 23 | Viewed by 3624

Abstract

Multiwavelength Raman spectroscopy (325, 514, 633 nm) was used to analyze three different kinds of samples containing sp² and sp³ carbons: chemical vapor deposited diamond films of varying microstructure, a plasma-enhanced chemical vapor deposited hydrogenated amorphous carbon film heated at 500 [...] Read more.

Multiwavelength Raman spectroscopy (325, 514, 633 nm) was used to analyze three different kinds of samples containing sp² and sp³ carbons: chemical vapor deposited diamond films of varying microstructure, a plasma-enhanced chemical vapor deposited hydrogenated amorphous carbon film heated at 500 °C and highly oriented pyrolytic graphite exposed to a radio-frequent deuterium plasma. We found evidence that the lower part of the phonon density of states (PDOS) spectral region (300–900 cm⁻¹) that rises when defects are introduced in crystals can give more information on the structure than expected. For example, the height of the PDOS, taken at 400 cm⁻¹ and compared to the height of the G band, depends on the sp² content, estimated by electron energy-loss spectroscopy. This ratio measured with 633 nm laser is more intense than with 514 nm laser. It is also correlated for diamond to the relative intensity ratio between the diamond band at 1332 cm⁻¹ and the G band at ≈1500–1600 cm⁻¹ when using 325 nm laser. Moreover, it is found that the shape of the PDOS of the exposed graphite samples is different when changing the wavelength of the laser used, giving evidence of a double resonance mechanism origin with the rise of the associated D₃, D₄ and D₅ bands, which is not the case for a-C:H samples. Full article

(This article belongs to the Special Issue Characterization of Disorder in Carbons)

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14 pages, 51882 KiB

Open AccessArticle

Micrometric Growth Defects of DLC Thin Films

by Thibault Maerten, Cédric Jaoul, Roland Oltra, Patrice Duport, Christophe Le Niniven, Pascal Tristant, Frédéric Meunier and Olivier Jarry

C 2019, 5(4), 73; https://0-doi-org.brum.beds.ac.uk/10.3390/c5040073 - 14 Nov 2019

Cited by 3 | Viewed by 3384

Abstract

Defects in diamond-like carbon coatings deposited on corrosion sensitive 100Cr6 steel have been studied. Diamond-like carbon (DLC) thin films are promising for corrosion protection due to chemical inertness and low electrical conductivity. Nevertheless, the performance of these coating is highly sensitive to the [...] Read more.

Defects in diamond-like carbon coatings deposited on corrosion sensitive 100Cr6 steel have been studied. Diamond-like carbon (DLC) thin films are promising for corrosion protection due to chemical inertness and low electrical conductivity. Nevertheless, the performance of these coating is highly sensitive to the presence of uncoated areas. These defects represent the primary way of substrate degradation in aggressive environments. An in situ optical microscopy coupled to an electrochemical activation was developed to reveal micrometric growth defects and observe that they were at the origin of corrosion. A square wave voltammetry was applied to increase the sensitivity of electrochemical techniques based on the detection of the dissolution of the bare metal surface triggered by the presence of uncoated spots. This method can be utilized to quantify defect density arising from vapor deposition processes. Full article

(This article belongs to the Special Issue Characterization of Disorder in Carbons)

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20 pages, 3077 KiB

Open AccessFeature PaperArticle

Analyzing the Raman Spectra of Graphenic Carbon Materials from Kerogens to Nanotubes: What Type of Information Can Be Extracted from Defect Bands?

by Pascal Puech, Mariem Kandara, Germercy Paredes, Ludovic Moulin, Elsa Weiss-Hortala, Anirban Kundu, Nicolas Ratel-Ramond, Jérémie-Marie Plewa, Roland Pellenq and Marc Monthioux

C 2019, 5(4), 69; https://doi.org/10.3390/c5040069 - 01 Nov 2019

Cited by 121 | Viewed by 8344

Abstract

Considering typical spectra of a broad range of carbonaceous materials from gas-shale to nanotubes, various ways by which defects show up in Raman spectra are exampled and discussed. The position, resonance behavior, and linewidth of both the D and G bands are compared, [...] Read more.

Considering typical spectra of a broad range of carbonaceous materials from gas-shale to nanotubes, various ways by which defects show up in Raman spectra are exampled and discussed. The position, resonance behavior, and linewidth of both the D and G bands are compared, even if in some cases obtaining accurate information on the materials from the fitting parameters is a difficult task. As a matter of fact, even if a full picture is unreachable, defining parameter trends is one acceptable option. Two ways to determine the linewidth, either graphically and or by fitting are proposed in order to be able to compare literature data. The relationship between the crystallite size obtained from the linewidth and from X-ray diffraction, which is complementary to the Tuinstra and Koenig law, is examined. We show that a single approach is not possible unless modeling is performed and therefore that analysis of Raman spectra should be adapted to the specificities of each sample series, i.e., a minimum of knowledge about the materials is always required. Full article

(This article belongs to the Special Issue Characterization of Disorder in Carbons)

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Review

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14 pages, 2669 KiB

Open AccessFeature PaperReview

Interstellar Carbon Dust

by Emmanuel Dartois

C 2019, 5(4), 80; https://0-doi-org.brum.beds.ac.uk/10.3390/c5040080 - 02 Dec 2019

Cited by 10 | Viewed by 3402

Abstract

In the ranking of cosmic abundance of the elements, carbon is the second element, after oxygen, able to form multiple bonds propagating the formation of a network, thus playing an essential role in the formation of nanometer- to micrometer-sized interstellar dust grains. Astrophysical [...] Read more.

In the ranking of cosmic abundance of the elements, carbon is the second element, after oxygen, able to form multiple bonds propagating the formation of a network, thus playing an essential role in the formation of nanometer- to micrometer-sized interstellar dust grains. Astrophysical spectroscopic observations give us remote access to the composition of carbonaceous and organic interstellar grains. Their presence and abundances from spectroscopic observations and the phases of importance for the Galactic carbon budget are considered in this article. Full article

(This article belongs to the Special Issue Characterization of Disorder in Carbons)

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