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17 pages, 6491 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Electronic Transport Mechanisms Correlated to Structural Properties of a Reduced Graphene Oxide Sponge

by Nicola Pinto, Benjamin McNaughton, Marco Minicucci, Milorad V. Milošević and Andrea Perali

Nanomaterials 2021, 11(10), 2503; https://doi.org/10.3390/nano11102503 - 26 Sep 2021

Viewed by 2353

Abstract

We report morpho-structural properties and charge conduction mechanisms of a foamy “graphene sponge”, having a density as low as ≈0.07 kg/m

^{3}

and a carbon to oxygen ratio C:O ≃ 13:1. The spongy texture analysed by scanning electron microscopy is made of irregularly-shaped [...] Read more.

We report morpho-structural properties and charge conduction mechanisms of a foamy “graphene sponge”, having a density as low as ≈0.07 kg/m

^{3}

and a carbon to oxygen ratio C:O ≃ 13:1. The spongy texture analysed by scanning electron microscopy is made of irregularly-shaped millimetres-sized small flakes, containing small crystallites with a typical size of ≃16.3 nm. A defect density as high as ≃2.6 × 10

^{11}

cm

^{- 2}

has been estimated by the Raman intensity of D and G peaks, dominating the spectrum from room temperature down to ≃153 K. Despite the high C:O ratio, the graphene sponge exhibits an insulating electrical behavior, with a raise of the resistance value at ≃6 K up to 5 orders of magnitude with respect to the room temperature value. A variable range hopping (VRH) conduction, with a strong 2D character, dominates the charge carriers transport, from 300 K down to 20 K. At T < 20 K, graphene sponge resistance tends to saturate, suggesting a temperature-independent quantum tunnelling. The 2D-VRH conduction originates from structural disorder and is consistent with hopping of charge carriers between

s p^{2}

defects in the plane, where

s p^{3}

clusters related to oxygen functional groups act as potential barriers. Full article

(This article belongs to the Special Issue Carbon-Based Materials: Growth, Characterization, and Applications)

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10 pages, 3185 KiB

Open AccessArticle

Holey Graphene: Topological Control of Electronic Properties and Electric Conductivity

by Pavel V. Barkov and Olga E. Glukhova

Nanomaterials 2021, 11(5), 1074; https://doi.org/10.3390/nano11051074 - 22 Apr 2021

Cited by 12 | Viewed by 2348

Abstract

This paper studies holey graphene with various neck widths (the smallest distance between two neighbor holes). For the considered structures, the energy gap, the Fermi level, the density of electronic states, and the distribution of the local density of electronic states (LDOS) were [...] Read more.

This paper studies holey graphene with various neck widths (the smallest distance between two neighbor holes). For the considered structures, the energy gap, the Fermi level, the density of electronic states, and the distribution of the local density of electronic states (LDOS) were found. The electroconductive properties of holey graphene with round holes were calculated depending on the neck width. It was found that, depending on the neck width, holey graphene demonstrated a semiconductor type of conductivity with an energy gap varying in the range of 0.01–0.37 eV. It was also shown that by changing the neck width, it is possible to control the electrical conductivity of holey graphene. The anisotropy of holey graphene electrical conductivity was observed depending on the direction of the current transfer. Full article

(This article belongs to the Special Issue Carbon-Based Materials: Growth, Characterization, and Applications)

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16 pages, 7191 KiB

Open AccessArticle

One-Step Plasma Synthesis of Nitrogen-Doped Carbon Nanomesh

by Alenka Vesel, Rok Zaplotnik, Gregor Primc, Luka Pirker and Miran Mozetič

Nanomaterials 2021, 11(4), 837; https://doi.org/10.3390/nano11040837 - 25 Mar 2021

Cited by 5 | Viewed by 2685

Abstract

A one-step method for plasma synthesis of nitrogen-doped carbon nanomesh is presented. The method involves a molten polymer, which is a source of carbon, and inductively coupled nitrogen plasma, which is a source of highly reactive nitrogen species. The method enables the deposition [...] Read more.

A one-step method for plasma synthesis of nitrogen-doped carbon nanomesh is presented. The method involves a molten polymer, which is a source of carbon, and inductively coupled nitrogen plasma, which is a source of highly reactive nitrogen species. The method enables the deposition of the nanocarbon layer at a rate of almost 0.1 µm/s. The deposited nanocarbon is in the form of randomly oriented multilayer graphene nanosheets or nanoflakes with a thickness of several nm and an area of the order of 1000 nm². The concentration of chemically bonded nitrogen on the surface of the film increases with deposition time and saturates at approximately 15 at.%. Initially, the oxygen concentration is up to approximately 10 at.% but decreases with treatment time and finally saturates at approximately 2 at.%. Nitrogen is bonded in various configurations, including graphitic, pyridinic, and pyrrolic nitrogen. Full article

(This article belongs to the Special Issue Carbon-Based Materials: Growth, Characterization, and Applications)

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15 pages, 4305 KiB

Open AccessArticle

Large Optical Nonlinearity of the Activated Carbon Nanoparticles Prepared by Laser Ablation

by Yasin Orooji, Hamed Ghanbari Gol, Babak Jaleh, Mohammad Reza Rashidian Vaziri and Mahtab Eslamipanah

Nanomaterials 2021, 11(3), 737; https://doi.org/10.3390/nano11030737 - 15 Mar 2021

Cited by 17 | Viewed by 3145

Abstract

Carbon nanoparticles (CNPs) with high porosity and great optical features can be used as a luminescent material. One year later, the same group investigated the NLO properties CNPs and boron-doped CNPs by 532 nm and 1064 nm laser excitations to uncover the underlying [...] Read more.

Carbon nanoparticles (CNPs) with high porosity and great optical features can be used as a luminescent material. One year later, the same group investigated the NLO properties CNPs and boron-doped CNPs by 532 nm and 1064 nm laser excitations to uncover the underlying physical mechanisms in their NLO response. Hence, a facile approach, laser ablation technique, was employed for carbon nanoparticles (CNPs) synthesis from suspended activated carbon (AC). Morphological properties of the prepared CNPs were studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). UV-Vis and fluorescence (FL) spectra were used to optical properties investigation of CNPs. The size distribution of nanoparticles was evaluated using dynamic light scattering (DLS). The nonlinear optical (NLO) coefficients of the synthesized CNPs were determined by the Z-scan method. As a result, strong reverse saturable absorption and self-defocusing effects were observed at the excitation wavelength of 442 nm laser irradiation. These effects were ascribed to the presence of delocalized π-electrons in AC CNPs. To the best of our knowledge, this is the first study investigating the NLO properties of the AC CNPs. Full article

(This article belongs to the Special Issue Carbon-Based Materials: Growth, Characterization, and Applications)

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14 pages, 23359 KiB

Open AccessArticle

Terahertz Broadband Polarization Conversion for Transmitted Waves Based on Graphene Plasmon Resonances

by Anqi Yu, Dahai Yu, Zhenyu Yang, Xuguang Guo, Yuxiang Ren, Xiaofei Zang, Alexei V. Balakin, Alexander P. Shkurinov and YiMing Zhu

Nanomaterials 2021, 11(1), 56; https://doi.org/10.3390/nano11010056 - 28 Dec 2020

Cited by 7 | Viewed by 2559

Abstract

We applied the harmonic oscillator model combined with the transfer matrix method to study the polarization conversion for transmitted waves in metallic grating/plasmon-excitation layer/metallic grating structure in the terahertz (THz) region. By comparing the calculated spectra and the simulated (by the finite-difference-time-domain method) [...] Read more.

We applied the harmonic oscillator model combined with the transfer matrix method to study the polarization conversion for transmitted waves in metallic grating/plasmon-excitation layer/metallic grating structure in the terahertz (THz) region. By comparing the calculated spectra and the simulated (by the finite-difference-time-domain method) ones, we found that they correspond well with each other. Both methods show that the Drude background absorption and the excited plasmon resonances are responsible for polarization conversion. The transmission is close to 0 when the distance between the top/bottom metallic gratings and gated graphene is an integer multiple of half the wavelength of the incident wave (in the dielectrics), at which points the plasmon resonances are greatly suppressed by the destructive interference between the backward/forward electromagnetic waves and that reflected by the top/bottom metallic gratings. Away from these points, the transmission can be higher than 80%. The electron density and the excitation efficiency of the plasmon-excitation layer were found to be important for the bandwidth of the polarization conversion window, while the scattering rate was found to influence mainly the polarization conversion rate. Multi-broadband polarization conversion is realized by exciting plasmon modes between the 0 transmission points in the THz region. Full article

(This article belongs to the Special Issue Carbon-Based Materials: Growth, Characterization, and Applications)

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19 pages, 3256 KiB

Open AccessArticle

Introducing the Novel Mixed Gaussian-Lorentzian Lineshape in the Analysis of the Raman Signal of Biochar

by Alberto Tagliaferro, Massimo Rovere, Elisa Padovano, Mattia Bartoli and Mauro Giorcelli

Nanomaterials 2020, 10(9), 1748; https://doi.org/10.3390/nano10091748 - 3 Sep 2020

Cited by 56 | Viewed by 5141

Abstract

In this research, an innovative procedure is proposed to elaborate Raman spectra obtained from nanostructured and disordered solids. As a challenging case study, biochar, a bio-derived carbon based material, was selected. The complex structure of biochar (i.e., channeled surface, inorganic content) represents a [...] Read more.

In this research, an innovative procedure is proposed to elaborate Raman spectra obtained from nanostructured and disordered solids. As a challenging case study, biochar, a bio-derived carbon based material, was selected. The complex structure of biochar (i.e., channeled surface, inorganic content) represents a serious challenge for Raman characterization. As widely reported, the Raman spectra are closely linked to thermal treatments of carbon material. The individual contributions to the Raman spectra are difficult to identify due to the numerous peaks that contribute to the spectra. To tackle this problem, we propose a brand new approach based on the introduction, on sound theoretical grounds, of a mixed Gaussian-–Lorentzian lineshape. As per the experimental part, biochar samples were carbonized in an inert atmosphere at various temperatures and their respective spectra were successfully decomposed using the new lineshape. The evolution of the structure with carbonization temperature was investigated by Raman and XRD analysis. The results of the two techniques fairly well agree. Compared to other approaches commonly reported in the literature this method (i) gives a sounder basis to the lineshape used in disordered materials, and (ii) appears to reduce the number of components, leading to an easier understanding of their origin. Full article

(This article belongs to the Special Issue Carbon-Based Materials: Growth, Characterization, and Applications)

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Review

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34 pages, 3827 KiB

Open AccessReview

An Overview of Recent Advances in the Synthesis and Applications of the Transition Metal Carbide Nanomaterials

by Saba Ahmad, Iffat Ashraf, Muhammad Adil Mansoor, Syed Rizwan and Mudassir Iqbal

Nanomaterials 2021, 11(3), 776; https://doi.org/10.3390/nano11030776 - 18 Mar 2021

Cited by 47 | Viewed by 5054

Abstract

Good stability and reproducibility are important factors in determining the place of any material in their respective field and these two factors also enable them to use in various applications. At present, transition metal carbides (TMCs) have high demand either in the two-dimensional [...] Read more.

Good stability and reproducibility are important factors in determining the place of any material in their respective field and these two factors also enable them to use in various applications. At present, transition metal carbides (TMCs) have high demand either in the two-dimensional (2D) form (MXene) or as nanocomposites, nanoparticles, carbide films, carbide nano-powder, and carbide nanofibers. They have shown good stability at high temperatures in different environments and also have the ability to show adequate reproducibility. Metal carbides have shown a broad spectrum of properties enabling them to engage the modern approach of multifacet material. Several ways have been routed to synthesize metal carbides in their various forms but few of those gain more attention due to their easy approach and better properties. TMCs find applications in various fields, such as catalysts, absorbents, bio-sensors, pesticides, electrogenerated chemiluminescence (ECL), anti-pollution and anti-bacterial agents, and in tumor detection. This article highlights some recent developments in the synthesis methods and applications of TMCs in various fields. Full article

(This article belongs to the Special Issue Carbon-Based Materials: Growth, Characterization, and Applications)

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15 pages, 2823 KiB

Open AccessReview

Kinetics of Carbon Nanotubes and Graphene Growth on Iron and Steel: Evidencing the Mechanisms of Carbon Formation

by Luís Sousa Lobo and Sónia A. C. Carabineiro

Nanomaterials 2021, 11(1), 143; https://doi.org/10.3390/nano11010143 - 8 Jan 2021

Cited by 10 | Viewed by 2963

Abstract

Carbon formation on steel has recently become an active research area with several important applications, using either carbon nanotubes (CNTs) or graphene structures. The production of vertically aligned CNT (VACNT) forests with combined metals has been explored with important results. Detailed kinetics is [...] Read more.

Carbon formation on steel has recently become an active research area with several important applications, using either carbon nanotubes (CNTs) or graphene structures. The production of vertically aligned CNT (VACNT) forests with combined metals has been explored with important results. Detailed kinetics is the best approach to understand a mechanism. The growth behavior seems complex but can be simplified through the knowledge of the three more common alternative reaction mechanisms/routes. The time required to optimize the production and properties might be reduced. The mechanistic proposal reported in 1971 was better explained recently. The volcano shape Arrhenius plot reported is observed only when Fe, Co, and Ni are used as reaction catalysts. Other metals are catalytically active at higher temperatures, following a different route, which does not require surface catalysis decomposition of the reactive gas. C₂H₂ and low olefins react well, but CH₄ is not reactive via this surface catalysis route. Optimizing production of CNTs, research work is usually based on previous experience, but solid-state science-based studies are available. Full article

(This article belongs to the Special Issue Carbon-Based Materials: Growth, Characterization, and Applications)

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