Special Issue "Recent Advances in 2D Nanomaterials"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (30 November 2018).

Special Issue Editor

Prof. Dr. Antonio Di Bartolomeo
Website
Guest Editor
Department of Physics E. R. Caianiello, Università di Salerno, Salerno, Italy
Interests: field-effect transistors; tunneling transistors; nonvolatile memories; CMOS technologies; solid-state radiation detectors; field emission; optical and electrical properties of carbon nanotubes, graphene, and 2D materials; semiconductor heterojunctions and their application as photodetectors, solar cells, and chemical sensors; van der Waals heterojunctions of 2D-layered materials
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Special Issue Information

Dear Colleagues,

Graphene, graphene-based and graphene-like materials have been dominating the fundamental and applied research in materials science since 2004. The 2D nanomaterials family, characterized by confinement in one direction, has been growing over the years with the continuous addition of new members that cover a wide variety of electrical, magnetic, optical, thermal, mechanical and chemical properties.

The abundance of properties, combined with the highest achievable surface-to-volume ratio, render 2D nanomaterials suitable for advanced applications in several areas, such as material science, physics, chemistry, engineering, biology, pharmacy, medicine, etcetera.

From the initial mechanical exfoliation, new production methods for large-area and defect-free synthesis, suitable for mass production, have been developed, along with new characterization tools and techniques.

Despite the impressive amount of consolidated knowledge, 2D nanomaterials offer plenty of opportunities to study electronic, optical, thermal, mechanical, vibrational, spin and plasmonic properties. The development of new applications, as well as of novel top-down or bottom-up approaches to create new materials, as it is currently happening for transition-metal carbides or nitrides, is endless. 

The scope of this Special Issue, entitled “The Advances in 2D Nanomaterials” is to provide the state-of-the-art of the research on the properties, the production, the characterization and the applications of 2D nanomaterials, as well as to cover the current challenges related to them.  

This Special Issue aims at collecting experimental or theoretical review articles and leading-edge research papers dealing with graphene, different transition metal chalcogenides, arsenene, stanene, germanene, silicene, black phosphorus, hexagonal boron-nitride, layered 2D compound materials or any other 2D nanomaterials.

As renowned researcher in the field, I would like to invite you to enrich this Special Issue.

Prof. Dr. Antonio Di Bartolomeo
Guest Editor

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • 2D materials properties
  • 2D materials production methods
  • 2D materials characterization tools and techniques
  • 2D materials applications
  • 2D materials devices, sensors and actuators
  • Graphene
  • Transition Metal Dichalcogenides (TMDC)
  • InSe- or Ga- monochalcogenides, Ti, Zn or Hf –trichalcogenides
  • Silicene, Germanene, Arsenene, Stanene, Black phosphorus
  • Niobium disulfide, Vanadium oxide and disulfide
  • MXenes and MAX phases
  • 2D Oxides, Hexagonal Boron Nitride
  • 2D topological insulators
  • Layered 2D compound materials
  • 2D colloidal nanoplatelets

Published Papers (13 papers)

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Research

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Open AccessArticle
2D Material Science: Defect Engineering by Particle Irradiation
Materials 2018, 11(10), 1885; https://doi.org/10.3390/ma11101885 - 02 Oct 2018
Cited by 23
Abstract
Two-dimensional (2D) materials are at the heart of many novel devices due to their unique and often superior properties. For simplicity, 2D materials are often assumed to exist in their text-book form, i.e., as an ideal solid with no imperfections. However, defects are [...] Read more.
Two-dimensional (2D) materials are at the heart of many novel devices due to their unique and often superior properties. For simplicity, 2D materials are often assumed to exist in their text-book form, i.e., as an ideal solid with no imperfections. However, defects are ubiquitous in macroscopic samples and play an important – if not imperative – role for the performance of any device. Thus, many independent studies have targeted the artificial introduction of defects into 2D materials by particle irradiation. In our view it would be beneficial to develop general defect engineering strategies for 2D materials based on a thorough understanding of the defect creation mechanisms, which may significantly vary from the ones relevant for 3D materials. This paper reviews the state-of-the-art in defect engineering of 2D materials by electron and ion irradiation with a clear focus on defect creation on the atomic scale and by individual impacts. Whenever possible we compile reported experimental data alongside corresponding theoretical studies. We show that, on the one hand, defect engineering by particle irradiation covers a wide range of defect types that can be fabricated with great precision in the most commonly investigated 2D materials. On the other hand, gaining a complete understanding still remains a challenge, that can be met by combining advanced theoretical methods and improved experimental set-ups, both of which only now begin to emerge. In conjunction with novel 2D materials, this challenge promises attractive future opportunities for researchers in this field. Full article
(This article belongs to the Special Issue Recent Advances in 2D Nanomaterials)
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Open AccessArticle
Scattering Theory of Graphene Grain Boundaries
Materials 2018, 11(9), 1660; https://doi.org/10.3390/ma11091660 - 08 Sep 2018
Cited by 3
Abstract
The implementation of graphene-based electronics requires fabrication processes that are able to cover large device areas, since the exfoliation method is not compatible with industrial applications. The chemical vapor deposition of large-area graphene represents a suitable solution; however, it has an important drawback [...] Read more.
The implementation of graphene-based electronics requires fabrication processes that are able to cover large device areas, since the exfoliation method is not compatible with industrial applications. The chemical vapor deposition of large-area graphene represents a suitable solution; however, it has an important drawback of producing polycrystalline graphene with the formation of grain boundaries, which are responsible for the limitation of the device’s performance. With these motivations, we formulate a theoretical model of a single-layer graphene grain boundary by generalizing the graphene Dirac Hamiltonian model. The model only includes the long-wavelength regime of the charge carrier transport, which provides the main contribution to the device conductance. Using symmetry-based arguments deduced from the current conservation law, we derive unconventional boundary conditions characterizing the grain boundary physics and analyze their implications on the transport properties of the system. Angle resolved quantities, such as the transmission probability, are studied within the scattering matrix approach. The conditions for the existence of preferential transmission directions are studied in relation with the grain boundary properties. The proposed theory provides a phenomenological model to study grain boundary physics within the scattering approach, and represents per se an important enrichment of the scattering theory of polycrystalline graphene. Moreover, the outcomes of the theory can contribute to understanding and limiting the detrimental effects of graphene grain boundaries, while also providing a benchmark for more elaborate techniques. Full article
(This article belongs to the Special Issue Recent Advances in 2D Nanomaterials)
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Open AccessCommunication
CVD Synthesis of Monodisperse Graphene/Cu Microparticles with High Corrosion Resistance in Cu Etchant
Materials 2018, 11(8), 1459; https://doi.org/10.3390/ma11081459 - 17 Aug 2018
Cited by 4
Abstract
Copper powder has broad applications in the powder metallurgy, heat exchanger, and electronic industries due to its intrinsically high electrical and thermal conductivities. However, the ease of formation of surface oxide or patina layer raises difficulty of storage and handling of copper powder, [...] Read more.
Copper powder has broad applications in the powder metallurgy, heat exchanger, and electronic industries due to its intrinsically high electrical and thermal conductivities. However, the ease of formation of surface oxide or patina layer raises difficulty of storage and handling of copper powder, particularly in the case of Cu microparticles. Here, we developed a thermal chemical vapor deposition chemical vapor deposition (CVD) process for large-scale synthesis of graphene coatings on Cu microparticles, which importantly can remain monodisperse without aggregation after graphene growth at high temperature by using removal spacers. Compared to other protective coating methods, the intrinsic electrical and thermal properties of Cu powder would not be degraded by uniform growth of low defect few-layer graphene on each particle surface. As a result, when the anticorrosion performance test was carried out by immersing the samples in Cu etchant, the corrosion rate of graphene/Cu microparticles was significantly improved (ca three times slower) compared to that of pristine Cu powder, also showing a comparable anticorrosion ability to commercial CuZn30 alloy. Full article
(This article belongs to the Special Issue Recent Advances in 2D Nanomaterials)
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Open AccessFeature PaperArticle
Effect of Graphene Flakes Modified by Dispersion in Surfactant Solutions on the Fluorescence Behaviour of Pyridoxine
Materials 2018, 11(6), 888; https://doi.org/10.3390/ma11060888 - 25 May 2018
Cited by 3
Abstract
The influence of graphene (G) dispersions in different types of surfactants (anionic, non-ionic, and cationic) on the fluorescence of vitamin B6 (pyridoxine) was studied. Scanning electron microscopy (SEM) was used to evaluate the quality of the G dispersions via measuring their flake [...] Read more.
The influence of graphene (G) dispersions in different types of surfactants (anionic, non-ionic, and cationic) on the fluorescence of vitamin B6 (pyridoxine) was studied. Scanning electron microscopy (SEM) was used to evaluate the quality of the G dispersions via measuring their flake thickness. The effect of surfactant type and concentration on the fluorescence intensity was analyzed, and fluorescence quenching effects were found for all of the systems. These turn out to be more intense with increasing both surfactant and G concentrations, albeit they do not depend on the G/surfactant weight ratio. For the same G concentration, the magnitude of the quenching follows the order: cationic > non-ionic ≥ anionic. The cationic surfactants, which strongly adsorb onto G via electrostatic attraction, are the most effective dispersing agents and they enable a stronger interaction with the zwitterionic form of the vitamin; the dispersing power improves with increasing the surfactant chain length. The fit of the experimental data to the Stern-Volmer equation suggests either a static or dynamic quenching mechanism for the dispersions in non-ionic surfactants, while those in ionic surfactants show a combined mechanism. The results that were obtained herein have been compared to those that were reported earlier for the quenching of another vitamin, riboflavin, to elucidate how the change in the vitamin structure influences the interactions with G in the surfactant dispersions. Full article
(This article belongs to the Special Issue Recent Advances in 2D Nanomaterials)
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Open AccessArticle
Control of the Nucleation Density of Molybdenum Disulfide in Large-Scale Synthesis Using Chemical Vapor Deposition
Materials 2018, 11(6), 870; https://doi.org/10.3390/ma11060870 - 23 May 2018
Cited by 6
Abstract
Atmospheric pressure chemical vapor deposition (CVD) is presently a promising approach for preparing two-dimensional (2D) MoS2 crystals at high temperatures on SiO2/Si substrates. In this work, we propose an improved CVD method without hydrogen, which can increase formula flexibility by [...] Read more.
Atmospheric pressure chemical vapor deposition (CVD) is presently a promising approach for preparing two-dimensional (2D) MoS2 crystals at high temperatures on SiO2/Si substrates. In this work, we propose an improved CVD method without hydrogen, which can increase formula flexibility by controlling the heating temperature of MoO3 powder and sulfur powder. The results show that the size and coverage of MoS2 domains vary largely, from discrete triangles to continuous film, on substrate. We find that the formation of MoS2 domains is dependent on the nucleation density of MoS2. Laminar flow theory is employed to elucidate the cause of the different shapes of MoS2 domains. The distribution of carrier gas speeds at the substrate surface leads to a change of nucleation density and a variation of domain morphology. Thus, nucleation density and domain morphology can be actively controlled by adjusting the carrier gas flow rate in the experimental system. These results are of significance for understanding the growth regulation of 2D MoS2 crystals. Full article
(This article belongs to the Special Issue Recent Advances in 2D Nanomaterials)
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Open AccessArticle
Effect of the Channel Length on the Transport Characteristics of Transistors Based on Boron-Doped Graphene Ribbons
Materials 2018, 11(5), 667; https://doi.org/10.3390/ma11050667 - 25 Apr 2018
Cited by 6
Abstract
Substitutional boron doping of devices based on graphene ribbons gives rise to a unipolar behavior, a mobility gap, and an increase of the ION/IOFF ratio of the transistor. Here we study how this effect depends on [...] Read more.
Substitutional boron doping of devices based on graphene ribbons gives rise to a unipolar behavior, a mobility gap, and an increase of the I O N / I O F F ratio of the transistor. Here we study how this effect depends on the length of the doped channel. By means of self-consistent simulations based on a tight-binding description and a non-equilibrium Green’s function approach, we demonstrate a promising increase of the I O N / I O F F ratio with the length of the channel, as a consequence of the different transport regimes in the ON and OFF states. Therefore, the adoption of doped ribbons with longer aspect ratios could represent a significant step toward graphene-based transistors with an improved switching behavior. Full article
(This article belongs to the Special Issue Recent Advances in 2D Nanomaterials)
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Open AccessArticle
Morphological Evolution of Vertically Standing Molybdenum Disulfide Nanosheets by Chemical Vapor Deposition
Materials 2018, 11(4), 631; https://doi.org/10.3390/ma11040631 - 20 Apr 2018
Cited by 3
Abstract
In this study, we demonstrated the chemical vapor deposition (CVD) of vertically standing molybdenum disulfide (MoS2) nanosheets, with an unconventional combination of molybdenum hexacarbonyl (Mo(CO)6) and 1,2-ethanedithiol (C2H6S2) as the novel kind of [...] Read more.
In this study, we demonstrated the chemical vapor deposition (CVD) of vertically standing molybdenum disulfide (MoS2) nanosheets, with an unconventional combination of molybdenum hexacarbonyl (Mo(CO)6) and 1,2-ethanedithiol (C2H6S2) as the novel kind of Mo and S precursors respectively. The effect of the distance between the precursor’s outlet and substrates (denoted as d) on the growth characteristics of MoS2, including surface morphology and nanosheet structure, was investigated. Meanwhile, the relationship between the structure characteristics of MoS2 nanosheets and their catalytic performance for hydrogen evolution reaction (HER) was elucidated. The formation of vertically standing nanosheets was analyzed and verified by means of an extrusion growth model. The crystallinity, average length, and average depth between peak and valley (Rz) of MoS2 nanosheets differed depending on the spatial location of the substrate. Good crystalized MoS2 nanosheets grown at d = 5.5 cm with the largest average length of 440 nm, and the highest Rz of 162 nm contributed to a better HER performance, with a respective Tafel slope and exchange current density of 138.9 mV/decade, and 22.6 μA/cm2 for raw data (127.8 mV/decade and 19.3 μA/cm2 for iR-corrected data). Full article
(This article belongs to the Special Issue Recent Advances in 2D Nanomaterials)
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Open AccessCommunication
Label-Free Electrochemical Detection of Vanillin through Low-Defect Graphene Electrodes Modified with Au Nanoparticles
Materials 2018, 11(4), 489; https://doi.org/10.3390/ma11040489 - 25 Mar 2018
Cited by 9
Abstract
Graphene is an excellent modifier for the surface modification of electrochemical electrodes due to its exceptional physical properties and, for the development of graphene-based chemical and biosensors, is usually coated on glassy carbon electrodes (GCEs) via drop casting. However, the ease of aggregation [...] Read more.
Graphene is an excellent modifier for the surface modification of electrochemical electrodes due to its exceptional physical properties and, for the development of graphene-based chemical and biosensors, is usually coated on glassy carbon electrodes (GCEs) via drop casting. However, the ease of aggregation and high defect content of reduced graphene oxides degrade the electrical properties. Here, we fabricated low-defect graphene electrodes by catalytically thermal treatment of HPHT diamond substrate, followed by the electrodeposition of Au nanoparticles (AuNPs) with an average size of ≈60 nm on the electrode surface using cyclic voltammetry. The Au nanoparticle-decorated graphene electrodes show a wide linear response range to vanillin from 0.2 to 40 µM with a low limit of detection of 10 nM. This work demonstrates the potential applications of graphene-based hybrid electrodes for highly sensitive chemical detection. Full article
(This article belongs to the Special Issue Recent Advances in 2D Nanomaterials)
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Open AccessCommunication
Highly Sensitive and Selective Potassium Ion Detection Based on Graphene Hall Effect Biosensors
Materials 2018, 11(3), 399; https://doi.org/10.3390/ma11030399 - 07 Mar 2018
Cited by 9
Abstract
Potassium (K+) ion is an important biological substance in the human body and plays a critical role in the maintenance of transmembrane potential and hormone secretion. Several detection techniques, including fluorescent, electrochemical, and electrical methods, have been extensively investigated to selectively [...] Read more.
Potassium (K+) ion is an important biological substance in the human body and plays a critical role in the maintenance of transmembrane potential and hormone secretion. Several detection techniques, including fluorescent, electrochemical, and electrical methods, have been extensively investigated to selectively recognize K+ ions. In this work, a highly sensitive and selective biosensor based on single-layer graphene has been developed for K+ ion detection under Van der Pauw measurement configuration. With pre-immobilization of guanine-rich DNA on the graphene surface, the graphene devices exhibit a very low limit of detection (≈1 nM) with a dynamic range of 1 nM–10 μM and excellent K+ ion specificity against other alkali cations, such as Na+ ions. The origin of K+ ion selectivity can be attributed to the fact that the formation of guanine-quadruplexes from guanine-rich DNA has a strong affinity for capturing K+ ions. The graphene-based biosensors with improved sensing performance for K+ ion recognition can be applied to health monitoring and early disease diagnosis. Full article
(This article belongs to the Special Issue Recent Advances in 2D Nanomaterials)
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Open AccessArticle
Current Modulation of a Heterojunction Structure by an Ultra-Thin Graphene Base Electrode
Materials 2018, 11(3), 345; https://doi.org/10.3390/ma11030345 - 27 Feb 2018
Cited by 6
Abstract
Graphene has been proposed as the current controlling element of vertical transport in heterojunction transistors, as it could potentially achieve high operation frequencies due to its metallic character and 2D nature. Simulations of graphene acting as a thermionic barrier between the transport of [...] Read more.
Graphene has been proposed as the current controlling element of vertical transport in heterojunction transistors, as it could potentially achieve high operation frequencies due to its metallic character and 2D nature. Simulations of graphene acting as a thermionic barrier between the transport of two semiconductor layers have shown cut-off frequencies larger than 1 THz. Furthermore, the use of n-doped amorphous silicon, (n)-a-Si:H, as the semiconductor for this approach could enable flexible electronics with high cutoff frequencies. In this work, we fabricated a vertical structure on a rigid substrate where graphene is embedded between two differently doped (n)-a-Si:H layers deposited by very high frequency (140 MHz) plasma-enhanced chemical vapor deposition. The operation of this heterojunction structure is investigated by the two diode-like interfaces by means of temperature dependent current-voltage characterization, followed by the electrical characterization in a three-terminal configuration. We demonstrate that the vertical current between the (n)-a-Si:H layers is successfully controlled by the ultra-thin graphene base voltage. While current saturation is yet to be achieved, a transconductance of ~230 μ S was obtained, demonstrating a moderate modulation of the collector-emitter current by the ultra-thin graphene base voltage. These results show promising progress towards the application of graphene base heterojunction transistors. Full article
(This article belongs to the Special Issue Recent Advances in 2D Nanomaterials)
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Open AccessArticle
High Temperature Growth of Graphene from Cobalt Volume: Effect on Structural Properties
Materials 2018, 11(2), 257; https://doi.org/10.3390/ma11020257 - 07 Feb 2018
Cited by 11
Abstract
Several transition metals other than the largely used Cu and Ni can be, in principle, employed to catalyze carbon precursors for the chemical vapor deposition of graphene, because the thermodynamics of their alloying with carbon is well known. For example, the wealth of [...] Read more.
Several transition metals other than the largely used Cu and Ni can be, in principle, employed to catalyze carbon precursors for the chemical vapor deposition of graphene, because the thermodynamics of their alloying with carbon is well known. For example, the wealth of information in the Co-C phase diagram can be used to predict the properties of graphene grown in this way. It is, in fact, expected that growth occurs at a temperature higher than in Ni, with beneficial consequences to the mechanical and electronic properties of the final product. In this work, the growth of graphene onto Co film is presented together with an extensive Raman characterization of the structural properties of the material so far obtained. Previous results reporting the full coverage with negligible defective areas, in spite of discontinuities in the underlying metal, are confirmed, together with the occurrence of strain in the graphene sheet. Strain is deeply investigated in this work, in view of possible employment in engineering the material properties. The observed strain is ascribed to the high thermal mismatch with the substrate, even if an effect of the crystallographic transition of Co cannot be excluded. Full article
(This article belongs to the Special Issue Recent Advances in 2D Nanomaterials)
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Review

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Open AccessReview
Emergence of Nanoplatelet Light-Emitting Diodes
Materials 2018, 11(8), 1376; https://doi.org/10.3390/ma11081376 - 08 Aug 2018
Cited by 16
Abstract
Since 2014, nanoplatelet light-emitting diodes (NPL-LEDs) have been emerged as a new kind of LEDs. At first, NPL-LEDs are mainly realized by CdSe based NPLs. Since 2016, hybrid organic-inorganic perovskite NPLs are found to be effective to develop NPL-LEDs. In 2017, all-inorganic perovskite [...] Read more.
Since 2014, nanoplatelet light-emitting diodes (NPL-LEDs) have been emerged as a new kind of LEDs. At first, NPL-LEDs are mainly realized by CdSe based NPLs. Since 2016, hybrid organic-inorganic perovskite NPLs are found to be effective to develop NPL-LEDs. In 2017, all-inorganic perovskite NPLs are also demonstrated for NPL-LEDs. Therefore, the development of NPL-LEDs is flourishing. In this review, the fundamental concepts of NPL-LEDs are first introduced, then the main approaches to realize NPL-LEDs are summarized and the recent progress of representative NPL-LEDs is highlighted, finally the challenges and opportunities for NPL-LEDs are presented. Full article
(This article belongs to the Special Issue Recent Advances in 2D Nanomaterials)
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Open AccessReview
Research Progress in Application of 2D Materials in Liquid-Phase Lubrication System
Materials 2018, 11(8), 1314; https://doi.org/10.3390/ma11081314 - 30 Jul 2018
Cited by 11
Abstract
Two-dimensional (2D) materials are ultra-thin crystals with layered structures that have a monolayer and multiple layers of atomic thickness. Due to excellent performance, 2D materials represented by graphene have caused great interest from researchers in various fields, such as nano-electronics, sensors, solar cells, [...] Read more.
Two-dimensional (2D) materials are ultra-thin crystals with layered structures that have a monolayer and multiple layers of atomic thickness. Due to excellent performance, 2D materials represented by graphene have caused great interest from researchers in various fields, such as nano-electronics, sensors, solar cells, composite materials, and so on. In recent years, when graphite was used for liquid phase lubrication, there have been many disadvantages limiting its lubrication properties, such as stable dispersion, fluidity and so on. Therefore, 2D materials have been used as high-performance liquid-phase lubricant additives, which become a perfect entry point for high-performance nano-lubricants and lubrication applications. This review describes the application of 2D materials as additives in the field of liquid-phase lubrication (such as lubricating oil and water lubrication) in terms of experimental content, lubrication performance, and lubrication mechanism. Finally, the challenges and prospects of 2D materials in the lubrication field were also proposed. Full article
(This article belongs to the Special Issue Recent Advances in 2D Nanomaterials)
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