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11 pages, 17591 KiB

Open AccessArticle

Measurement of the Induced Magnetic Polarisation of Rotated-Domain Graphene Grown on Co Film with Polarised Neutron Reflectivity

by Razan Omar M. Aboljadayel, Christy John Kinane, Carlos Antonio Fernandes Vaz, David Michael Love, Marie-Blandine Martin, Andrea Cabrero-Vilatela, Philipp Braeuninger-Weimer, Adrian Ionescu, Andrew John Caruana, Timothy Randall Charlton, Justin Llandro, Pedro Manuel da Silva Monteiro, Crispin Henry William Barnes, Stephan Hofmann and Sean Langridge

Nanomaterials 2023, 13(19), 2620; https://doi.org/10.3390/nano13192620 - 22 Sep 2023

Viewed by 763

Abstract

In this paper, we determine the magnetic moment induced in graphene when grown on a cobalt film using polarised neutron reflectivity (PNR). A magnetic signal in the graphene was detected by X-ray magnetic circular dichroism (XMCD) spectra at the C K-edge. From [...] Read more.

In this paper, we determine the magnetic moment induced in graphene when grown on a cobalt film using polarised neutron reflectivity (PNR). A magnetic signal in the graphene was detected by X-ray magnetic circular dichroism (XMCD) spectra at the C K-edge. From the XMCD sum rules an estimated magnetic moment of 0.3

μ

_B/C atom, while a more accurate estimation of 0.49

μ

_B/C atom was obtained by carrying out a PNR measurement at 300 K. The results indicate that the higher magnetic moment in Co is counterbalanced by the larger lattice mismatch between the Co-C (1.6%) and the slightly longer bond length, inducing a magnetic moment in graphene that is similar to that reported in Ni/graphene heterostructures. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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14 pages, 2824 KiB

Open AccessArticle

Plasma-Induced Surface Modification of Sapphire and Its Influence on Graphene Grown by Plasma-Enhanced Chemical Vapour Deposition

by Miguel Sinusia Lozano, Ignacio Bernat-Montoya, Todora Ivanova Angelova, Alberto Boscá Mojena, Francisco J. Díaz-Fernández, Miroslavna Kovylina, Alejandro Martínez, Elena Pinilla Cienfuegos and Víctor J. Gómez

Nanomaterials 2023, 13(13), 1952; https://doi.org/10.3390/nano13131952 - 27 Jun 2023

Viewed by 1277

Abstract

In this work, we study the influence of the different surface terminations of c-plane sapphire substrates on the synthesis of graphene via plasma-enhanced chemical vapor deposition. The different terminations of the sapphire surface are controlled by a plasma process. A design of experiments [...] Read more.

In this work, we study the influence of the different surface terminations of c-plane sapphire substrates on the synthesis of graphene via plasma-enhanced chemical vapor deposition. The different terminations of the sapphire surface are controlled by a plasma process. A design of experiments procedure was carried out to evaluate the major effects governing the plasma process of four different parameters: i.e., discharge power, time, pressure and gas employed. In the characterization of the substrate, two sapphire surface terminations were identified and characterized by means of contact angle measurements, being a hydrophilic (hydrophobic) surface and the fingerprint of an Al- (OH-) terminated surface, respectively. The defects within the synthesized graphene were analyzed by Raman spectroscopy. Notably, we found that the I_D/I_G ratio decreases for graphene grown on OH-terminated surfaces. Furthermore, two different regimes related to the nature of graphene defects were identified and, depending on the sapphire terminated surface, are bound either to vacancy or boundary-like defects. Finally, studying the density of defects and the crystallite area, as well as their relationship with the sapphire surface termination, paves the way for increasing the crystallinity of the synthesized graphene. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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11 pages, 2272 KiB

Open AccessArticle

A Modified Wet Transfer Method for Eliminating Interfacial Impurities in Graphene

by Dong Jin Jang, Mohd Musaib Haidari, Jin Hong Kim, Jin-Yong Ko, Yoonsik Yi and Jin Sik Choi

Nanomaterials 2023, 13(9), 1494; https://doi.org/10.3390/nano13091494 - 27 Apr 2023

Cited by 1 | Viewed by 1489

Abstract

Graphene has immense potential as a material for electronic devices owing to its unique electrical properties. However, large-area graphene produced by chemical vapor deposition (CVD) must be transferred from the as-grown copper substrate to an arbitrary substrate for device fabrication. The conventional wet [...] Read more.

Graphene has immense potential as a material for electronic devices owing to its unique electrical properties. However, large-area graphene produced by chemical vapor deposition (CVD) must be transferred from the as-grown copper substrate to an arbitrary substrate for device fabrication. The conventional wet transfer technique, which uses FeCl₃ as a Cu etchant, leaves microscale impurities from the substrate, and the etchant adheres to graphene, thereby degrading its electrical performance. To address this limitation, this study introduces a modified transfer process that utilizes a temporary UV-treated SiO₂ substrate to adsorb impurities from graphene before transferring it onto the final substrate. Optical microscopy and Raman mapping confirmed the adhesion of impurities to the temporary substrate, leading to a clean graphene/substrate interface. The retransferred graphene shows a reduction in electron–hole asymmetry and sheet resistance compared to conventionally transferred graphene, as confirmed by the transmission line model (TLM) and Hall effect measurements (HEMs). These results indicate that only the substrate effects remain in action in the retransferred graphene, and most of the effects of the impurities are eliminated. Overall, the modified transfer process is a promising method for obtaining high-quality graphene suitable for industrial-scale utilization in electronic devices. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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9 pages, 2902 KiB

Open AccessCommunication

Epitaxial Lateral Overgrowth of GaN on a Laser-Patterned Graphene Mask

by Arūnas Kadys, Jūras Mickevičius, Kazimieras Badokas, Simonas Strumskis, Egidijus Vanagas, Žydrūnas Podlipskas, Ilja Ignatjev and Tadas Malinauskas

Nanomaterials 2023, 13(4), 784; https://doi.org/10.3390/nano13040784 - 20 Feb 2023

Viewed by 1842

Abstract

Epitaxial lateral overgrowth (ELO) of GaN epilayers on a sapphire substrate was studied by using a laser-patterned graphene interlayer. Monolayer graphene was transferred onto the sapphire substrate using a wet transfer technique, and its quality was confirmed by Raman spectroscopy. The graphene layer [...] Read more.

Epitaxial lateral overgrowth (ELO) of GaN epilayers on a sapphire substrate was studied by using a laser-patterned graphene interlayer. Monolayer graphene was transferred onto the sapphire substrate using a wet transfer technique, and its quality was confirmed by Raman spectroscopy. The graphene layer was ablated using a femtosecond laser, which produced well-defined patterns without damaging the underlying sapphire substrate. Different types of patterns were produced for ELO of GaN epilayers: stripe patterns were ablated along the

{[\bar{1} 100]}_{sapphire}

and

{[11 \bar{2} 0]}_{sapphire}

directions, a square island pattern was ablated additionally. The impact of the graphene pattern on GaN nucleation was analyzed by scanning electron microscopy. The structural quality of GaN epilayers was studied by cathodoluminescence. The investigation shows that the laser-ablated graphene can be integrated into the III-nitride growth process to improve crystal quality. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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11 pages, 2617 KiB

Open AccessArticle

Low-Threshold and High-Extinction-Ratio Optical Bistability within a Graphene-Based Perfect Absorber

by Zhengzhuo Zhang, Qiaoge Sun, Yansong Fan, Zhihong Zhu, Jianfa Zhang, Xiaodong Yuan and Chucai Guo

Nanomaterials 2023, 13(3), 389; https://doi.org/10.3390/nano13030389 - 18 Jan 2023

Cited by 2 | Viewed by 1410

Abstract

A kind of graphene-based perfect absorber which can generate low-threshold and high-extinction-ratio optical bistability in the near-IR band is proposed and simulated with numerical methods. The interaction between input light and monolayer graphene in the absorber can be greatly enhanced due to the [...] Read more.

A kind of graphene-based perfect absorber which can generate low-threshold and high-extinction-ratio optical bistability in the near-IR band is proposed and simulated with numerical methods. The interaction between input light and monolayer graphene in the absorber can be greatly enhanced due to the perfect absorption. The large nonlinear coefficient of graphene and the strong light-graphene interaction contribute to the nonlinear response of the structure, leading to relatively low switching thresholds of less than 2.5 MW/cm² for an absorber with a Q factor lower than 1000. Meanwhile, the extinction ratio of bistable states in the absorber reaches an ultrahigh value of 47.3 dB at 1545.3 nm. Moreover, the influence of changing the structural parameters on the bistable behaviors is discussed in detail, showing that the structure can tolerate structural parametric deviation to some extent. The proposed bistable structure with ultra-compact size, low thresholds, high extinction ratio, and ultrafast response time could be of great applications for fabricating high-performance all-optical-communication devices. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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10 pages, 2260 KiB

Open AccessArticle

Cluster Formation Effect of Water on Pristine and Defective MoS₂ Monolayers

by Kangli Wang and Beate Paulus

Nanomaterials 2023, 13(2), 229; https://doi.org/10.3390/nano13020229 - 04 Jan 2023

Cited by 1 | Viewed by 1166

Abstract

The structure and electronic properties of the molybdenum disulfide (MoS₂) monolayer upon water cluster adsorption are studied using density functional theory and the optical properties are further analyzed with the Bethe–Salpeter equation (BSE). Our results reveal that the water clusters are [...] Read more.

The structure and electronic properties of the molybdenum disulfide (MoS₂) monolayer upon water cluster adsorption are studied using density functional theory and the optical properties are further analyzed with the Bethe–Salpeter equation (BSE). Our results reveal that the water clusters are electron acceptors, and the acceptor tendency tends to increase with the size of the water cluster. The electronic band gap of both pristine and defective MoS₂ is rather insensitive to water cluster adsorbates, as all the clusters are weakly bound to the MoS₂ surface. However, our calculations on the BSE level show that the adsorption of the water cluster can dramatically redshift the optical absorption for both pristine and defective MoS₂ monolayers. The binding energy of the excitons of MoS₂ is greatly enhanced with the increasing size of the water cluster and finally converges to a value of approximately 1.16 eV and 1.09 eV for the pristine and defective MoS₂ monolayers, respectively. This illustrates that the presence of the water cluster could localize the excitons of MoS₂, thereby greatly enhance the excitonic binding energy. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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14 pages, 7893 KiB

Open AccessArticle

Adsorption Behavior of Toxic Carbon Dichalcogenides (CX₂; X = O, S, or Se) on β₁₂ Borophene and Pristine Graphene Sheets: A DFT Study

by Mahmoud A. A. Ibrahim, Amna H. M. Mahmoud, Gamal A. H. Mekhemer, Ahmed M. Shawky, Mahmoud E. S. Soliman and Nayra A. M. Moussa

Nanomaterials 2022, 12(19), 3411; https://doi.org/10.3390/nano12193411 - 29 Sep 2022

Cited by 5 | Viewed by 1509

Abstract

The adsorption of toxic carbon dichalcogenides (CX₂; X = O, S, or Se) on β₁₂ borophene (β₁₂) and pristine graphene (GN) sheets was comparatively investigated. Vertical and parallel configurations of CX₂⋯β₁₂/GN complexes [...] Read more.

The adsorption of toxic carbon dichalcogenides (CX₂; X = O, S, or Se) on β₁₂ borophene (β₁₂) and pristine graphene (GN) sheets was comparatively investigated. Vertical and parallel configurations of CX₂⋯β₁₂/GN complexes were studied herein via density functional theory (DFT) calculations. Energetic quantities confirmed that the adsorption process in the case of the parallel configuration was more desirable than that in the vertical analog and showed values up to −10.96 kcal/mol. The strength of the CX₂⋯β₁₂/GN complexes decreased in the order CSe₂ > CS₂ > CO₂, indicating that β₁₂ and GN sheets showed significant selectivity for the CSe₂ molecule with superb potentiality for β₁₂ sheets. Bader charge transfer analysis revealed that the CO₂⋯β₁₂/GN complexes in the parallel configuration had the maximum negative charge transfer values, up to −0.0304 e, outlining the electron-donating character of CO₂. The CS₂ and CSe₂ molecules frequently exhibited dual behavior as electron donors in the vertical configuration and acceptors in the parallel one. Band structure results addressed some differences observed for the electronic structures of the pure β₁₂ and GN sheets after the adsorption process, especially in the parallel configuration compared with the vertical one. According to the results of the density of states, new peaks were observed after adsorbing CX₂ molecules on the studied 2D sheets. These results form a fundamental basis for future studies pertaining to applications of β₁₂ and GN sheets for detecting toxic carbon dichalcogenides. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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14 pages, 2346 KiB

Open AccessArticle

Reduced Graphene Oxide Derived from Low-Grade Coal for High-Performance Flexible Supercapacitors with Ultrahigh Cyclability

by Yi-Ming Wang and Chun-Hua Zhang

Nanomaterials 2022, 12(17), 2989; https://doi.org/10.3390/nano12172989 - 29 Aug 2022

Cited by 6 | Viewed by 1451

Abstract

Preparation of reduced graphene oxide (RGO) from abundant and inexpensive low-grade coal is regarded as one of the most promising methods for utilizing this resource in a high-value and environmentally sustainable manner. As the main precursor for the fabrication of RGO, graphene oxide [...] Read more.

Preparation of reduced graphene oxide (RGO) from abundant and inexpensive low-grade coal is regarded as one of the most promising methods for utilizing this resource in a high-value and environmentally sustainable manner. As the main precursor for the fabrication of RGO, graphene oxide (GO) can be extracted from low-grade coal such as lignite, but its size is just in the range of tens to hundreds of nanometers, which limits its practical application. Herein, we demonstrate that large-size RGO sheets can be prepared in large quantities by the pretreatment of lignite using the high temperature–high pressure (HTHP) method. The RGO electrode after the reduction reaction by 50 mM NaBH₄ at 105 °C features porosity and high conductivity, which can facilitate high electrochemical reaction efficiency. Thus, we also demonstrate the use of lignite-derived RGO for supercapacitor electrode materials with high performance. The lignite-derived RGO supercapacitor can deliver outstanding volumetric capacitance (30.6 F cm⁻³), high energy density (4.2 mW h cm⁻³), excellent flexibility (79.5% retention of the initial capacitance at 180° bending), and a long lifespan (112.3% retention of the initial capacitance after 20,000 cycles). It is believed that the proposed large-size RGO based on reasonable optimization of inferior lignite will offer a new prospect for next-generation energy storage applications. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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13 pages, 4941 KiB

Open AccessArticle

Graphene-Delivered Insecticides against Cotton Bollworm

by Zhiwen Chen, Jianguo Zhao, Zehui Liu, Xiuli Bai, Weijia Li, Zhifang Guan, Ming Zhou and Hongwei Zhu

Nanomaterials 2022, 12(16), 2731; https://doi.org/10.3390/nano12162731 - 09 Aug 2022

Cited by 3 | Viewed by 2128

Abstract

Nanopesticides can facilitate controlled release kinetics and efficiently enhance the permeability of active ingredients to reduce the dosage and loss of pesticides. To clarify the synergistic mechanism of graphene–insecticide nanocarriers against cotton bollworm, treatment groups, namely, control, graphene (G), insecticide (lambda-cyhalothrin (Cyh) and [...] Read more.

Nanopesticides can facilitate controlled release kinetics and efficiently enhance the permeability of active ingredients to reduce the dosage and loss of pesticides. To clarify the synergistic mechanism of graphene–insecticide nanocarriers against cotton bollworm, treatment groups, namely, control, graphene (G), insecticide (lambda-cyhalothrin (Cyh) and cyfluthrin (Cyf)), and graphene-delivered insecticide groups were used to treat the third-instar larvae of cotton bollworm. The variations in phenotypes, namely, the body length, body weight, and mortality of the cotton bollworm, were analyzed. The results show that graphene enhances the insecticidal activity of lambda-cyhalothrin and cyfluthrin against cotton bollworm. The two graphene-delivered insecticides with optimal compositions (3:1) had the strongest inhibitory effects and the highest mortality rates, with the fatality rates for the 3/1 Cyh/G and Cyf/G mixture compositions being 62.91% and 38.89%, respectively. In addition, the 100 μg/mL Cyh/G mixture had the greatest inhibitory effect on cotton bollworm, and it decreased the body length by 1.40 mm, decreased the weight by 1.88 mg, and had a mortality rate of up to 61.85%. The 100 and 150 μg/mL Cyh/G mixtures achieved the same mortality rate as that of lambda-cyhalothrin, thus reducing the use of the insecticide by one-quarter. The graphene-delivered insecticides could effectively destroy the epicuticle spine cells of the cotton bollworm by increasing the permeability and, thus, the toxicity of the insecticides. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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16 pages, 31436 KiB

Open AccessArticle

Borophene and Pristine Graphene 2D Sheets as Potential Surfaces for the Adsorption of Electron-Rich and Electron-Deficient π-Systems: A Comparative DFT Study

by Mahmoud A. A. Ibrahim, Amna H. M. Mahmoud, Kamal A. Soliman, Gamal A. H. Mekhemer, Muhammad Naeem Ahmed, Ahmed M. Shawky, Mohammed A. S. Abourehab, Eslam B. Elkaeed, Mahmoud E. S. Soliman and Nayra A. M. Moussa

Nanomaterials 2022, 12(6), 1028; https://doi.org/10.3390/nano12061028 - 21 Mar 2022

Cited by 7 | Viewed by 3824

Abstract

The versatility of striped borophene (sB), β₁₂ borophene (β₁₂), and pristine graphene (GN) to adsorb π-systems was comparatively assessed using benzene (BNZ) and hexafluorobenzene (HFB) as electron-rich and electron-deficient aromatic π-systems, respectively. Using the density functional theory (DFT) method, [...] Read more.

The versatility of striped borophene (sB), β₁₂ borophene (β₁₂), and pristine graphene (GN) to adsorb π-systems was comparatively assessed using benzene (BNZ) and hexafluorobenzene (HFB) as electron-rich and electron-deficient aromatic π-systems, respectively. Using the density functional theory (DFT) method, the adsorption process of the π-systems on the investigated 2D sheets in the parallel configuration was observed to have proceeded more favorably than those in the vertical configuration. According to the observations of the Bader charge transfer analysis, the π-system∙∙∙sB complexes were generally recorded with the largest contributions of charge transfer, followed by the π-system∙∙∙β₁₂ and ∙∙∙GN complexes. The band structures of the pure sheets signaled the metallic and semiconductor characters of the sB/β₁₂ and GN surfaces, respectively. In the parallel configuration, the adsorption of both BNZ and HFB showed more valence and conduction bands compared to the adsorption in the vertical configuration, revealing the prominent preferentiality of the anterior configuration. The density-of-states (DOSs) results also affirmed that the adsorption process of the BNZ and HFB on the surface of the investigated 2D sheets increased their electrical properties. In all instances, the sB and β₁₂ surfaces demonstrated higher adsorptivity towards the BNZ and HFB than the GN analog. The findings of this work could make a significant contribution to the deep understanding of the adsorption behavior of aromatic π-systems toward 2D nanomaterials, leading, in turn, to their development of a wide range of applications. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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15 pages, 4940 KiB

Open AccessArticle

High-Yield Production of Selected 2D Materials by Understanding Their Sonication-Assisted Liquid-Phase Exfoliation

by Freskida Goni, Angela Chemelli and Frank Uhlig

Nanomaterials 2021, 11(12), 3253; https://doi.org/10.3390/nano11123253 - 30 Nov 2021

Cited by 12 | Viewed by 3062

Abstract

Liquid-phase exfoliation (LPE) is a widely used and promising method for the production of 2D nanomaterials because it can be scaled up relatively easily. Nevertheless, the yields achieved by this process are still low, ranging between 2% and 5%, which makes the large-scale [...] Read more.

Liquid-phase exfoliation (LPE) is a widely used and promising method for the production of 2D nanomaterials because it can be scaled up relatively easily. Nevertheless, the yields achieved by this process are still low, ranging between 2% and 5%, which makes the large-scale production of these materials difficult. In this report, we investigate the cause of these low yields by examining the sonication-assisted LPE of graphene, boron nitride nanosheets (BNNSs), and molybdenum disulfide nanosheets (MoS₂ NS). Our results show that the low yields are caused by an equilibrium that is formed between the exfoliated nanosheets and the flocculated ones during the sonication process. This study provides an understanding of this behaviour, which prevents further exfoliation of nanosheets. By avoiding this equilibrium, we were able to increase the total yields of graphene, BNNSs, and MoS₂ NS up to 14%, 44%, and 29%, respectively. Here, we demonstrate a modified LPE process that leads to the high-yield production of 2D nanomaterials. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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12 pages, 1336 KiB

Open AccessArticle

Role Played by Edge-Defects in the Optical Properties of Armchair Graphene Nanoribbons

by Thi-Nga Do, Godfrey Gumbs, Danhong Huang, Bui D. Hoi and Po-Hsin Shih

Nanomaterials 2021, 11(12), 3229; https://doi.org/10.3390/nano11123229 - 28 Nov 2021

Cited by 3 | Viewed by 1824

Abstract

We explore the implementation of specific optical properties of armchair graphene nanoribbons (AGNRs) through edge-defect manipulation. This technique employs the tight-binding model in conjunction with the calculated absorption spectral function. Modification of the edge states gives rise to the diverse electronic structures with [...] Read more.

We explore the implementation of specific optical properties of armchair graphene nanoribbons (AGNRs) through edge-defect manipulation. This technique employs the tight-binding model in conjunction with the calculated absorption spectral function. Modification of the edge states gives rise to the diverse electronic structures with striking changes in the band gap and special flat bands at low energy. The optical-absorption spectra exhibit unique excitation peaks, and they strongly depend on the type and period of the edge extension. Remarkably, there exist the unusual transition channels associated with the flat bands for selected edge-modified systems. We discovered the special rule governing how the edge-defect influences the electronic and optical properties in AGNRs. Our theoretical prediction demonstrates an efficient way to manipulate the optical properties of AGNRs. This might be of importance in the search for suitable materials designed to have possible technology applications in nano-optical, plasmonic and optoelectronic devices. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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11 pages, 9926 KiB

Open AccessArticle

Epitaxial Growth of Uniform Single-Layer and Bilayer Graphene with Assistance of Nitrogen Plasma

by Shaoen Jin, Junyu Zong, Wang Chen, Qichao Tian, Xiaodong Qiu, Gan Liu, Hang Zheng, Xiaoxiang Xi, Libo Gao, Can Wang and Yi Zhang

Nanomaterials 2021, 11(12), 3217; https://doi.org/10.3390/nano11123217 - 26 Nov 2021

Cited by 7 | Viewed by 2167

Abstract

Graphene was reported as the first-discovered two-dimensional material, and the thermal decomposition of SiC is a feasible route to prepare graphene films. However, it is difficult to obtain a uniform single-layer graphene avoiding the coexistence of multilayer graphene islands or bare substrate holes, [...] Read more.

Graphene was reported as the first-discovered two-dimensional material, and the thermal decomposition of SiC is a feasible route to prepare graphene films. However, it is difficult to obtain a uniform single-layer graphene avoiding the coexistence of multilayer graphene islands or bare substrate holes, which give rise to the degradation of device performance and becomes an obstacle for the further applications. Here, with the assistance of nitrogen plasma, we successfully obtained high-quality single-layer and bilayer graphene with large-scale and uniform surface via annealing 4H-SiC(0001) wafers. The highly flat surface and ordered terraces of the samples were characterized using in situ scanning tunneling microscopy. The Dirac bands in single-layer and bilayer graphene were measured using angle-resolved photoemission spectroscopy. X-ray photoelectron spectroscopy combined with Raman spectroscopy were used to determine the composition of the samples and to ensure no intercalation or chemical reaction of nitrogen with graphene. Our work has provided an efficient way to obtain the uniform single-layer and bilayer graphene films grown on a semiconductive substrate, which would be an ideal platform for fabricating two-dimensional devices based on graphene. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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12 pages, 2840 KiB

Open AccessArticle

Atomic Defect Induced Saturable Absorption of Hexagonal Boron Nitride in Near Infrared Band for Ultrafast Lasing Applications

by Chen Cheng, Ziqi Li, Ningning Dong, Rang Li, Jun Wang and Feng Chen

Nanomaterials 2021, 11(12), 3203; https://doi.org/10.3390/nano11123203 - 26 Nov 2021

Cited by 1 | Viewed by 1984

Abstract

Defect-induced phenomena in 2D materials has received increasing interest among researchers due to the novel properties correlated with precise modification of materials. We performed a study of the nonlinear saturable absorption of the boron-atom-vacancy defective hexagonal boron nitride (h-BN) thin film at a [...] Read more.

Defect-induced phenomena in 2D materials has received increasing interest among researchers due to the novel properties correlated with precise modification of materials. We performed a study of the nonlinear saturable absorption of the boron-atom-vacancy defective hexagonal boron nitride (h-BN) thin film at a wavelength of ~1 μm and its applications in ultrafast laser generation. The h-BN is with wide band gap of ~6 eV. Our investigation shows that the defective h-BN has a wide absorption band from visible to near infrared regimes. First-principle calculations based on density functional theory (DFT) indicate that optical property changes may be attributed to the boron-vacancy-related defects. The photoluminescence spectrum shows a strong emission peak at ~1.79 eV. The ultrafast Z-scan measurement shows saturable absorbance response has been detected for the defective h-BN with saturation intensity of ~1.03 GW/cm² and modulation depth of 1.1%. In addition, the defective h-BN has been applied as a new saturable absorber (SA) to generate laser pulses through the passively Q-switched mode-locking configuration. Based on a Nd:YAG waveguide platform, 8.7 GHz repetition rate and 55 ps pulse duration of the waveguide laser have been achieved. Our results suggest potential applications of defective h-BN for ultrafast lasing and integrated photonics. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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14 pages, 9420 KiB

Open AccessArticle

Temperature-Induced Plasmon Excitations for the

α

–

T_{3}

Lattice in Perpendicular Magnetic Field

by Antonios Balassis, Godfrey Gumbs and Oleksiy Roslyak

Nanomaterials 2021, 11(7), 1720; https://doi.org/10.3390/nano11071720 - 29 Jun 2021

Cited by 2 | Viewed by 1719

Abstract

We have investigated the

α

–

T_{3}

model in the presence of a mass term which opens a gap in the energy dispersive spectrum, as well as under a uniform perpendicular quantizing magnetic field. The gap opening mass term plays the role [...] Read more.

We have investigated the

α

–

T_{3}

model in the presence of a mass term which opens a gap in the energy dispersive spectrum, as well as under a uniform perpendicular quantizing magnetic field. The gap opening mass term plays the role of Zeeman splitting at low magnetic fields for this pseudospin-1 system, and, as a consequence, we are able to compare physical properties of the the

α

–

T_{3}

model at low and high magnetic fields. Specifically, we explore the magnetoplasmon dispersion relation in these two extreme limits. Central to the calculation of these collective modes is the dielectric function which is determined by the polarizability of the system. This latter function is generated by transition energies between subband states, as well as the overlap of their wave functions. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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8 pages, 1220 KiB

Open AccessCommunication

Size-Dependent Ion Adsorption in Graphene Oxide Membranes

by Xiaoheng Jin, Xinyue Wen, Sean Lim and Rakesh Joshi

Nanomaterials 2021, 11(7), 1676; https://doi.org/10.3390/nano11071676 - 25 Jun 2021

Cited by 5 | Viewed by 2306

Abstract

Graphene oxide (GO)-based materials have demonstrated promising potential for adsorption and purification applications. Due to its amphiphilic nature, GO offers the possibility of removing various kinds of contaminants, including heavy metal ions and organic pollutants from aqueous environments. Here, we present size-selective ion [...] Read more.

Graphene oxide (GO)-based materials have demonstrated promising potential for adsorption and purification applications. Due to its amphiphilic nature, GO offers the possibility of removing various kinds of contaminants, including heavy metal ions and organic pollutants from aqueous environments. Here, we present size-selective ion adsorption in GO-based laminates by directly measuring the weight uptake of slats. Adsorption studies were conducted in graphene oxide purchased from Nisina Materials Japan prepared using a controlled method. We tuned the interlayer spacing of GO membranes via cationic control solutions using intercalation of very small salts ions (i.e., K⁺, Na⁺, Cl⁻) very precisely to facilitate the adsorption of larger ions such as [Fe(CN)₆]⁴⁻ and [Fe(CN)₆]³⁻. This study demonstrates that if the opening of nanocapillaries within the laminates is bigger than the hydrated diameter of ions, the adsorption occurs within the membranes while for smaller opening, with no ion entrance the sorption occurs on the surface of the membranes. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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18 pages, 35053 KiB

Open AccessArticle

Efficient ReSe₂ Photodetectors with CVD Single-Crystal Graphene Contacts

by Bruna Silva, João Rodrigues, Balaji Sompalle, Chun-Da Liao, Nicoleta Nicoara, Jérôme Borme, Fátima Cerqueira, Marcel Claro, Sascha Sadewasser, Pedro Alpuim and Andrea Capasso

Nanomaterials 2021, 11(7), 1650; https://doi.org/10.3390/nano11071650 - 23 Jun 2021

Cited by 9 | Viewed by 3748

Abstract

Rhenium-based 2D transition metal dichalcogenides such as ReSe₂ are suitable candidates as photoactive materials for optoelectronic devices. Here, photodetectors based on mechanically exfoliated ReSe₂ crystals were fabricated using chemical vapor deposited (CVD) graphene single-crystal (GSC) as lateral contacts. A “pick & [...] Read more.

Rhenium-based 2D transition metal dichalcogenides such as ReSe₂ are suitable candidates as photoactive materials for optoelectronic devices. Here, photodetectors based on mechanically exfoliated ReSe₂ crystals were fabricated using chemical vapor deposited (CVD) graphene single-crystal (GSC) as lateral contacts. A “pick & place” method was adopted to transfer the desired crystals to the intended position, easing the device fabrication while reducing potential contaminations. A similar device with Au was fabricated to compare contacts’ performance. Lastly, a CVD hexagonal boron nitride (hBN) substrate passivation layer was designed and introduced in the device architecture. Raman spectroscopy was carried out to evaluate the device materials’ structural and electronic properties. Kelvin probe force measurements were done to calculate the materials’ work function, measuring a minimal Schottky barrier height for the GSC/ReSe₂ contact (0.06 eV). Regarding the electrical performance, I-V curves showed sizable currents in the GSC/ReSe₂ devices in the dark and under illumination. The devices presented high photocurrent and responsivity, along with an external quantum efficiency greatly exceeding 100%, confirming the non-blocking nature of the GSC contacts at high bias voltage (above 2 V). When introducing the hBN passivation layer, the device under white light reached a photo-to-dark current ratio up to 10⁶. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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13 pages, 5994 KiB

Open AccessArticle

Optical Constants of Chemical Vapor Deposited Graphene for Photonic Applications

by Marwa A. El-Sayed, Georgy A. Ermolaev, Kirill V. Voronin, Roman I. Romanov, Gleb I. Tselikov, Dmitry I. Yakubovsky, Natalia V. Doroshina, Anton B. Nemtsov, Valentin R. Solovey, Artem A. Voronov, Sergey M. Novikov, Andrey A. Vyshnevyy, Andrey M. Markeev, Aleksey V. Arsenin and Valentyn S. Volkov

Nanomaterials 2021, 11(5), 1230; https://doi.org/10.3390/nano11051230 - 07 May 2021

Cited by 26 | Viewed by 4130

Abstract

Graphene is a promising building block material for developing novel photonic and optoelectronic devices. Here, we report a comprehensive experimental study of chemical-vapor deposited (CVD) monolayer graphene’s optical properties on three different substrates for ultraviolet, visible, and near-infrared spectral ranges (from 240 to [...] Read more.

Graphene is a promising building block material for developing novel photonic and optoelectronic devices. Here, we report a comprehensive experimental study of chemical-vapor deposited (CVD) monolayer graphene’s optical properties on three different substrates for ultraviolet, visible, and near-infrared spectral ranges (from 240 to 1000 nm). Importantly, our ellipsometric measurements are free from the assumptions of additional nanometer-thick layers of water or other media. This issue is critical for practical applications since otherwise, these additional layers must be included in the design models of various graphene photonic, plasmonic, and optoelectronic devices. We observe a slight difference (not exceeding 5%) in the optical constants of graphene on different substrates. Further, the optical constants reported here are very close to those of graphite, which hints on their applicability to multilayer graphene structures. This work provides reliable data on monolayer graphene’s optical properties, which should be useful for modeling and designing photonic devices with graphene. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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16 pages, 4203 KiB

Open AccessArticle

Graphene Oxide/Reduced Graphene Oxide Enhanced Noniridescent Structural Colors Based on Silica Photonic Spray Paints with Improved Mechanical Robustness

by Jiali Yu, Cheng-Hao Lee and Chi-Wai Kan

Nanomaterials 2021, 11(4), 949; https://doi.org/10.3390/nano11040949 - 08 Apr 2021

Cited by 4 | Viewed by 2257

Abstract

In contrast to traditional pigment colors, structural colors have developed a great potential in practical applications, thanks to their unique nonfading and color tunable properties; especially amorphous photonic structures with noniridescent structural colors have attracted considerable attention and their applications have expanded to [...] Read more.

In contrast to traditional pigment colors, structural colors have developed a great potential in practical applications, thanks to their unique nonfading and color tunable properties; especially amorphous photonic structures with noniridescent structural colors have attracted considerable attention and their applications have expanded to more fields. Herein, graphene oxide (GO) and reduced graphene oxide (RGO) enhanced noniridescent structural colors with excellent mechanical robustness were established by a time-saving approach named spray coating, which allows for rapid fabrication of angular independent structural colors by spraying different photonic spray paints (PSPs) to ensure color multiplicity that was adjusted by the silica nanoparticles (SiO₂ NPs) sizes onto the substrates. The incorporation of poly(methyl methacrylate-butyl acrylate) (PMB) improved the adhesion existing among SiO₂ inter-nanoparticles and between SiO₂ NPs and the substrates, taking advantages of the low glass transition temperature (

T_{g}

) of butyl acrylate derivative polymer and made PMB embedded PSPs coated patterns being imparted with good mechanical robustness and abrasive resistance. The peculiar light adsorption of GO and RGO across visible light spectrum facilitate higher color saturation. The improvement in color saturation of GO and RGO doped PSPs is expected to boost the promising applications in structurally colored paintings, inks and other color-related optical fields. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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7 pages, 367 KiB

Open AccessArticle

The Degree of Oxidation of Graphene Oxide

by Alexandra Carvalho, Mariana C. F. Costa, Valeria S. Marangoni, Pei Rou Ng, Thi Le Hang Nguyen and Antonio H. Castro Neto

Nanomaterials 2021, 11(3), 560; https://doi.org/10.3390/nano11030560 - 24 Feb 2021

Cited by 33 | Viewed by 3877

Abstract

We show that the degree of oxidation of graphene oxide (GO) can be obtained by using a combination of state-of-the-art ab initio computational modeling and X-ray photoemission spectroscopy (XPS). We show that the shift of the XPS C1s peak relative to pristine graphene, [...] Read more.

We show that the degree of oxidation of graphene oxide (GO) can be obtained by using a combination of state-of-the-art ab initio computational modeling and X-ray photoemission spectroscopy (XPS). We show that the shift of the XPS C1s peak relative to pristine graphene,

Δ E_{C 1 s}

, can be described with high accuracy by

Δ E_{C 1 s} = A {(c_{O} - c_{l})}^{2} + E_{0}

, where

c_{0}

is the oxygen concentration,

A = 52.3

eV,

c_{l} = 0.122

, and

E_{0} = 1.22

eV. Our results demonstrate a precise determination of the oxygen content of GO samples. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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11 pages, 3264 KiB

Open AccessArticle

Scanning Probe Spectroscopy of WS₂/Graphene Van Der Waals Heterostructures

by Franco Dinelli, Filippo Fabbri, Stiven Forti, Camilla Coletti, Oleg V. Kolosov and Pasqualantonio Pingue

Nanomaterials 2020, 10(12), 2494; https://doi.org/10.3390/nano10122494 - 11 Dec 2020

Cited by 4 | Viewed by 2688

Abstract

In this paper, we present a study of tungsten disulfide (WS₂) two-dimensional (2D) crystals, grown on epitaxial Graphene. In particular, we have employed scanning electron microscopy (SEM) and µRaman spectroscopy combined with multifunctional scanning probe microscopy (SPM), operating in peak force–quantitative [...] Read more.

In this paper, we present a study of tungsten disulfide (WS₂) two-dimensional (2D) crystals, grown on epitaxial Graphene. In particular, we have employed scanning electron microscopy (SEM) and µRaman spectroscopy combined with multifunctional scanning probe microscopy (SPM), operating in peak force–quantitative nano mechanical (PF-QNM), ultrasonic force microscopy (UFM) and electrostatic force microscopy (EFM) modes. This comparative approach provides a wealth of useful complementary information and allows one to cross-analyze on the nanoscale the morphological, mechanical, and electrostatic properties of the 2D heterostructures analyzed. Herein, we show that PF-QNM can accurately map surface properties, such as morphology and adhesion, and that UFM is exceptionally sensitive to a broader range of elastic properties, helping to uncover subsurface features located at the buried interfaces. All these data can be correlated with the local electrostatic properties obtained via EFM mapping of the surface potential, through the cantilever response at the first harmonic, and the dielectric permittivity, through the cantilever response at the second harmonic. In conclusion, we show that combining multi-parametric SPM with SEM and µRaman spectroscopy helps to identify single features of the WS₂/Graphene/SiC heterostructures analyzed, demonstrating that this is a powerful tool-set for the investigation of 2D materials stacks, a building block for new advanced nano-devices. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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17 pages, 2472 KiB

Open AccessArticle

Functionalized Graphene Derivatives and TiO₂ for High Visible Light Photodegradation of Azo Dyes

by Álvaro Pérez-Molina, Sergio Morales-Torres, Francisco J. Maldonado-Hódar and Luisa M. Pastrana-Martínez

Nanomaterials 2020, 10(6), 1106; https://doi.org/10.3390/nano10061106 - 03 Jun 2020

Cited by 12 | Viewed by 2575

Abstract

Functionalized graphene derivatives including graphene oxide (GO), reduced graphene oxide (rGO), and heteroatom (nitrogen/sulphur (N/S) or boron (B))-doped graphene were used to synthesize composites with TiO₂ (T). The photocatalytic performance of composites was assessed for the degradation of Orange G dye (OG) [...] Read more.

Functionalized graphene derivatives including graphene oxide (GO), reduced graphene oxide (rGO), and heteroatom (nitrogen/sulphur (N/S) or boron (B))-doped graphene were used to synthesize composites with TiO₂ (T). The photocatalytic performance of composites was assessed for the degradation of Orange G dye (OG) under simulated solar light. All the prepared graphene derivatives—TiO₂ composites showed better photocatalytic performance than bare TiO₂. A higher photocatalytic activity was found for the composites containing GO and N/S co-doped rGO (k_app = 109.2 × 10⁻³ and 48.4 × 10⁻³ min⁻¹, for GO-T and rGONS-T, respectively). The influence of both initial solution pH and the reactive species involved in the OG degradation pathway were studied. The photocatalytic activity of the samples decreased with the increase of the initial pH (from 3.0 to 10.0) due to the occurrence of electrostatic repulsive forces between the photocatalysts surface and the molecules of OG, both negatively charged. The use of selective scavengers showed that although the photogenerated holes dominate the degradation mechanism, radicals and singlet oxygen also participate in the OG degradation pathway. In addition, reutilization experiments indicated that the samples were stable under the reaction conditions used. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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Review

Jump to: Research

24 pages, 3381 KiB

Open AccessReview

Graphene Biosensors—A Molecular Approach

by Mónica Machado, Alexandra M. L. Oliveira, Gabriela A. Silva, Diogo B. Bitoque, Joana Tavares Ferreira, Luís Abegão Pinto and Quirina Ferreira

Nanomaterials 2022, 12(10), 1624; https://doi.org/10.3390/nano12101624 - 10 May 2022

Cited by 12 | Viewed by 2519

Abstract

Graphene is the material elected to study molecules and monolayers at the molecular scale due to its chemical stability and electrical properties. The invention of scanning tunneling microscopy has deepened our knowledge on molecular systems through imaging at an atomic resolution, and new [...] Read more.

Graphene is the material elected to study molecules and monolayers at the molecular scale due to its chemical stability and electrical properties. The invention of scanning tunneling microscopy has deepened our knowledge on molecular systems through imaging at an atomic resolution, and new possibilities have been investigated at this scale. Interest on studies on biomolecules has been demonstrated due to the possibility of mimicking biological systems, providing several applications in nanomedicine: drug delivery systems, biosensors, nanostructured scaffolds, and biodevices. A breakthrough came with the synthesis of molecular systems by stepwise methods with control at the atomic/molecular level. This article presents a review on self-assembled monolayers of biomolecules on top of graphite with applications in biodevices. Special attention is given to porphyrin systems adsorbed on top of graphite that are able to anchor other biomolecules. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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20 pages, 1860 KiB

Open AccessReview

Graphene Oxide Thin Films with Drug Delivery Function

by Alexandra M. L. Oliveira, Mónica Machado, Gabriela A. Silva, Diogo B. Bitoque, Joana Tavares Ferreira, Luís Abegão Pinto and Quirina Ferreira

Nanomaterials 2022, 12(7), 1149; https://doi.org/10.3390/nano12071149 - 30 Mar 2022

Cited by 32 | Viewed by 4505

Abstract

Graphene oxide has been used in different fields of nanomedicine as a manager of drug delivery due to its inherent physical and chemical properties that allow its use in thin films with biomedical applications. Several studies demonstrated its efficacy in the control of [...] Read more.

Graphene oxide has been used in different fields of nanomedicine as a manager of drug delivery due to its inherent physical and chemical properties that allow its use in thin films with biomedical applications. Several studies demonstrated its efficacy in the control of the amount and the timely delivery of drugs when it is incorporated in multilayer films. It has been demonstrated that oxide graphene layers are able to work as drug delivery or just to delay consecutive drug dosage, allowing the operation of time-controlled systems. This review presents the latest research developments of biomedical applications using graphene oxide as the main component of a drug delivery system, with focus on the production and characterization of films, in vitro and in vivo assays, main applications of graphene oxide biomedical devices, and its biocompatibility properties. Full article

(This article belongs to the Special Issue Graphene and Related 2D Materials)

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