Special Issue "Two-Dimensional Materials beyond Graphene and their Van der Waals Heterostructures"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystal Engineering".

Deadline for manuscript submissions: closed (31 July 2017)

Special Issue Editors

Guest Editor
Dr. Cristina E. Giusca

National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW, UK
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Interests: electronic and optical properties of 2D materials and heterostructures; graphene; scanning probe microscopy; electronic effects in photoexcited materials; surface processes in various environments; nano- and opto-electronic applications of graphene and 2D materials
Guest Editor
Dr. Spyros Yannopoulos

Foundation for Research and Technology – Hellas, Institute of Chemical Engineering Sciences (FORTH/ICE–HT), 1414 Rio-Patras, GR-26504, Greece
Website | E-Mail
Interests: controlled growth of 2D TMDCs materials by CVD; laser assisted growth of graphene; Raman and photoluminescence characterization of 2D crystals; heterostructures of 2D crystals; electrochemical applications of 2D materials; electrodes and counter-electrodes of solar cells

Special Issue Information

Dear Colleagues,

Recently-isolated two-dimensional (2D) atomic crystals provide an attractive material platform for exploring the fundamentals of atomically thin semiconductors, as well as presenting exciting prospects for future advances in fields as diverse as sensors and catalysis, membranes, energy storage/conversion, optoelectronics, spintronics, and valleytronics.

The realm of properties and applications is further enriched by artificially integrating 2D monolayers in vertical and lateral heterostructures, which enable the engineering of novel architectures with a rich combination of properties for multifunctional systems with enhanced performance. Given the astonishing developments in the field, this Special Issue will be dedicated to discussing the very latest research associated with 2D materials and their heterostructures, from fundamentals to applications, and addressing an outlook for emerging advances of the field.

Contributions are invited on 2D materials research-related topics, with special emphasis on (but not limited to):

  • Controlled synthesis of 2D materials (including transition metal dichalcogenides, phosphorene, silicene, germanene, stanene) and heterostructures
  • Advanced characterisation of electronic, optical, mechanical and catalytic properties
  • Surface chemistry and chemical functionalisation of 2D materials, including doping and defect engineering
  • Emerging applications in optoelectronics, spintronics, valleytronics, photonics, energy harvesting and storage, catalysis, sensors,
  • Modelling of properties and devices based on 2D materials and heterostructures

Dr. Cristina E. Giusca
Dr. Spyros Yannopoulos
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 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
  • heterostructures
  • layered crystals
  • 2D heterojunction
  • transition metal dichalcogenides
  • monolayer
  • 2D semiconductors
  • van der Waals epitaxy
  • 2D-material based devices
  • technological applications

Published Papers (9 papers)

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Research

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Open AccessArticle Algebraic Theory of Crystal Vibrations: Localization Properties of Wave Functions in Two-Dimensional Lattices
Crystals 2017, 7(8), 246; doi:10.3390/cryst7080246
Received: 14 July 2017 / Revised: 2 August 2017 / Accepted: 3 August 2017 / Published: 7 August 2017
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Abstract
The localization properties of the wave functions of vibrations in two-dimensional (2D) crystals are studied numerically for square and hexagonal lattices within the framework of an algebraic model. The wave functions of 2D lattices have remarkable localization properties, especially at the van Hove
[...] Read more.
The localization properties of the wave functions of vibrations in two-dimensional (2D) crystals are studied numerically for square and hexagonal lattices within the framework of an algebraic model. The wave functions of 2D lattices have remarkable localization properties, especially at the van Hove singularities (vHs). Finite-size sheets with a hexagonal lattice (graphene-like materials), in addition, exhibit at zero energy a localization of the wave functions at zigzag edges, so-called edge states. The striped structure of the wave functions at a vHs is particularly noteworthy. We have investigated its stability and that of the edge states with respect to perturbations in the lattice structure, and the effect of the boundary shape on the localization properties. We find that the stripes disappear instantaneously at the vHs in a square lattice when turning on the perturbation, whereas they broaden but persist at the vHss in a hexagonal lattice. For one of them, they eventually merge into edge states with increasing coupling, which, in contrast to the zero-energy edge states, are localized at armchair edges. The results are corroborated based on participation ratios, obtained under various conditions. Full article
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Open AccessArticle Graphene-Hexagonal Boron Nitride Heterostructure as a Tunable Phonon–Plasmon Coupling System
Crystals 2017, 7(2), 49; doi:10.3390/cryst7020049
Received: 31 December 2016 / Revised: 30 January 2017 / Accepted: 4 February 2017 / Published: 10 February 2017
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Abstract
The layered van der Waals (vdW) heterostructure, assembled from monolayer graphene, hexagonal boron nitride (h-BN) and other atomic crystals in various combinations, is emerging as a new paradigm with which to attain desired electronic and optical properties. In this paper, we study theoretically
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The layered van der Waals (vdW) heterostructure, assembled from monolayer graphene, hexagonal boron nitride (h-BN) and other atomic crystals in various combinations, is emerging as a new paradigm with which to attain desired electronic and optical properties. In this paper, we study theoretically the mid-infrared optical properties of the vdW heterostructure based on the graphene–h-BN system. The light–matter interaction of this heterostructure system is described by the hyperbolic phonon–plasmon polaritons which originate from the coupling modes of surface plasmon polaritons (SPPs) in graphene with hyperbolic phonon polaritons (HPPs) in h-BN. By numerical simulation, we find that the coupling modes are governed by the Fermi level of monolayer graphene, the thickness of the h-BN slab and the mode excitation sequence of SPPs and HPPs. Moreover, the response of the coupling modes of the graphene–h-BN heterostructure on a noble metal layer is also proposed in this paper. Full article
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Open AccessArticle The Effect of Twin Grain Boundary Tuned by Temperature on the Electrical Transport Properties of Monolayer MoS2
Crystals 2016, 6(9), 115; doi:10.3390/cryst6090115
Received: 30 June 2016 / Revised: 14 August 2016 / Accepted: 7 September 2016 / Published: 14 September 2016
Cited by 1 | PDF Full-text (4597 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Theoretical calculation and experimental measurement have shown that twin grain boundary (GB) of molybdenum disulphide (MoS2) exhibits extraordinary effects on transport properties. Precise transport measurements need to verify the transport mechanism of twin GB in MoS2. Here, monolayer molybdenum
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Theoretical calculation and experimental measurement have shown that twin grain boundary (GB) of molybdenum disulphide (MoS2) exhibits extraordinary effects on transport properties. Precise transport measurements need to verify the transport mechanism of twin GB in MoS2. Here, monolayer molybdenum disulphide with a twin grain boundary was grown in our developed low-pressure chemical vapor deposition (CVD) system, and we investigated how the twin GB affects the electrical transport properties of MoS2 by temperature-dependent transport studies. At low temperature, the twin GB can increase the in-plane electrical conductivity of MoS2 and the transport exhibits variable-range hopping (VRH), while at high temperature, the twin GB impedes the electrical transport of MoS2 and the transport exhibits nearest-neighbor hopping (NNH). Our results elucidate carrier transport mechanism of twin GB and give an important indication of twin GB in tailoring the electronic properties of MoS2 for its applications in next-generation electronics and optoelectronic devices. Full article
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Review

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Open AccessReview Recent Advances in Two-Dimensional Materials with Charge Density Waves: Synthesis, Characterization and Applications
Crystals 2017, 7(10), 298; doi:10.3390/cryst7100298
Received: 10 August 2017 / Revised: 25 September 2017 / Accepted: 26 September 2017 / Published: 3 October 2017
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Abstract
Recently, two-dimensional (2D) charge density wave (CDW) materials have attracted extensive interest due to potential applications as high performance functional nanomaterials. As other 2D materials, 2D CDW materials are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into layers
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Recently, two-dimensional (2D) charge density wave (CDW) materials have attracted extensive interest due to potential applications as high performance functional nanomaterials. As other 2D materials, 2D CDW materials are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into layers of single unit cell thickness. Although bulk CDW materials have been studied for decades, recent developments in nanoscale characterization and device fabrication have opened up new opportunities allowing applications such as oscillators, electrodes in supercapacitors, energy storage and conversion, sensors and spinelectronic devices. In this review, we first outline the synthesis techniques of 2D CDW materials including mechanical exfoliation, liquid exfoliation, chemical vapor transport (CVT), chemical vapor deposition (CVD), molecular beam epitaxy (MBE) and electrochemical exfoliation. Then, the characterization procedure of the 2D CDW materials such as temperature-dependent Raman spectroscopy, temperature-dependent resistivity, magnetic susceptibility and scanning tunneling microscopy (STM) are reviewed. Finally, applications of 2D CDW materials are reviewed. Full article
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Open AccessReview Interfacing 2D Semiconductors with Functional Oxides: Fundamentals, Properties, and Applications
Crystals 2017, 7(9), 265; doi:10.3390/cryst7090265
Received: 29 July 2017 / Revised: 24 August 2017 / Accepted: 28 August 2017 / Published: 31 August 2017
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Abstract
Two-dimensional semiconductors, such as transition-metal dichalcogenides (TMDs) and black phosphorous (BP), have found various potential applications in electronic and opto-electronic devices. However, several problems including low carrier mobility and low photoluminescence efficiencies still limit the performance of these devices. Interfacing 2D semiconductors with
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Two-dimensional semiconductors, such as transition-metal dichalcogenides (TMDs) and black phosphorous (BP), have found various potential applications in electronic and opto-electronic devices. However, several problems including low carrier mobility and low photoluminescence efficiencies still limit the performance of these devices. Interfacing 2D semiconductors with functional oxides provides a way to address the problems by overcoming the intrinsic limitations of 2D semiconductors and offering them multiple functionalities with various mechanisms. In this review, we first focus on the physical effects of various types of functional oxides on 2D semiconductors, mostly on MoS2 and BP as they are the intensively studied 2D semiconductors. Insulating, semiconducting, conventional piezoelectric, strongly correlated, and magnetic oxides are discussed. Then we introduce the applications of these 2D semiconductors/functional oxides systems in field-effect devices, nonvolatile memory, and photosensing. Finally, we discuss the perspectives and challenges within this research field. Our review provides a comprehensive understanding of 2D semiconductors/functional oxide heterostructures, and could inspire novel ideas in interface engineering to improve the performance of 2D semiconductor devices. Full article
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Open AccessReview Material and Device Architecture Engineering Toward High Performance Two-Dimensional (2D) Photodetectors
Crystals 2017, 7(5), 149; doi:10.3390/cryst7050149
Received: 1 April 2017 / Revised: 4 May 2017 / Accepted: 10 May 2017 / Published: 22 May 2017
Cited by 1 | PDF Full-text (5701 KB) | HTML Full-text | XML Full-text
Abstract
Photodetectors based on two-dimensional (2D) nanostructures have led to a high optical response, and a long photocarrier lifetime because of spatial confinement effects. Since the discovery of graphene, many different 2D semiconductors have been developed and utilized in the ultrafast and ultrasensitive detection
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Photodetectors based on two-dimensional (2D) nanostructures have led to a high optical response, and a long photocarrier lifetime because of spatial confinement effects. Since the discovery of graphene, many different 2D semiconductors have been developed and utilized in the ultrafast and ultrasensitive detection of light in the ultraviolet, visible, infrared and terahertz frequency ranges. This review presents a comprehensive summary of recent breakthroughs in constructing high-performance photodetectors based on 2D materials. First, we give a general overview of 2D photodetectors based on various single-component materials and their operating wavelength (ultraviolet to terahertz regime). Then, we summarize the design and controllable synthesis of heterostructure material systems to promote device photoresponse. Subsequently, special emphasis is put on the accepted methods in rational engineering of device architectures toward the photoresponse improvements. Finally, we conclude with our personal viewpoints on the challenges and promising future directions in this research field. Full article
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Open AccessReview Dirac Cones in Graphene, Interlayer Interaction in Layered Materials, and the Band Gap in MoS2
Crystals 2016, 6(11), 143; doi:10.3390/cryst6110143
Received: 15 June 2016 / Revised: 14 October 2016 / Accepted: 4 November 2016 / Published: 10 November 2016
Cited by 4 | PDF Full-text (1054 KB) | HTML Full-text | XML Full-text
Abstract
The 2D outlook of graphene and similar layers has initiated a number of theoretical considerations of electronic structure that are both interesting and exciting, but applying these ideas to real layered systems, in terms of a model 2D system, must be done with
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The 2D outlook of graphene and similar layers has initiated a number of theoretical considerations of electronic structure that are both interesting and exciting, but applying these ideas to real layered systems, in terms of a model 2D system, must be done with extreme care. In the present review, we will discuss the applicability of the 2D concept with examples of peculiarities of electronic structures and interactions in particular layered systems: (i) Dirac points and cones in graphene; (ii) van der Waals interaction between MoS2 monolayers; and (iii) the issue of a 2D screening in estimates of the band gap for MoS2 monolayers. Full article
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Open AccessReview Van Der Waals Heterostructures between Small Organic Molecules and Layered Substrates
Crystals 2016, 6(9), 113; doi:10.3390/cryst6090113
Received: 16 July 2016 / Revised: 27 August 2016 / Accepted: 30 August 2016 / Published: 9 September 2016
Cited by 6 | PDF Full-text (5821 KB) | HTML Full-text | XML Full-text
Abstract
Two dimensional atomic crystals, like grapheme (G) and molybdenum disulfide (MoS2), exhibit great interest in electronic and optoelectronic applications. The excellent physical properties, such as transparency, semiconductivity, and flexibility, make them compatible with current organic electronics. Here, we review recent progress
[...] Read more.
Two dimensional atomic crystals, like grapheme (G) and molybdenum disulfide (MoS2), exhibit great interest in electronic and optoelectronic applications. The excellent physical properties, such as transparency, semiconductivity, and flexibility, make them compatible with current organic electronics. Here, we review recent progress in the understanding of the interfaces of van der Waals (vdW) heterostructures between small organic molecules (pentacene, copper phthalocyanine (CuPc), perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), and dioctylbenzothienobenzothiophene (C8-BTBT)) and layered substrates (G, MoS2 and hexagonal boron nitride (h-BN)). The influences of the underlying layered substrates on the molecular arrangement, electronic and vibrational properties will be addressed. Full article
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Open AccessReview Graphene-Like ZnO: A Mini Review
Crystals 2016, 6(8), 100; doi:10.3390/cryst6080100
Received: 2 August 2016 / Revised: 18 August 2016 / Accepted: 18 August 2016 / Published: 22 August 2016
Cited by 3 | PDF Full-text (9847 KB) | HTML Full-text | XML Full-text
Abstract
The isolation of a single layer of graphite, known today as graphene, not only demonstrated amazing new properties but also paved the way for a new class of materials often referred to as two-dimensional (2D) materials. Beyond graphene, other 2D materials include h-BN,
[...] Read more.
The isolation of a single layer of graphite, known today as graphene, not only demonstrated amazing new properties but also paved the way for a new class of materials often referred to as two-dimensional (2D) materials. Beyond graphene, other 2D materials include h-BN, transition metal dichalcogenides (TMDs), silicene, and germanene, to name a few. All tend to have exciting physical and chemical properties which appear due to dimensionality effects and modulation of their band structure. A more recent member of the 2D family is graphene-like zinc oxide (g-ZnO) which also holds great promise as a future functional material. This review examines current progress in the synthesis and characterization of g-ZnO. In addition, an overview of works dealing with the properties of g-ZnO both in its pristine form and modified forms (e.g., nano-ribbon, doped material, etc.) is presented. Finally, discussions/studies on the potential applications of g-ZnO are reviewed and discussed. Full article
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