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Two-Dimensional Transition Metal Dichalcogenides

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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Chemical and Molecular Sciences".

Deadline for manuscript submissions: closed (31 July 2016) | Viewed by 59600

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Special Issue Editor

Dr. Andres Castellanos-Gomez

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Guest Editor

Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), E-28049 Madrid, Spain
Interests: two-dimensional materials; nanomechanics; strain-engineering; optoelectronics; molybdenum disulfide (MoS₂); transition metal dichalcogenides; black phosphorus
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Special Issue Information

Dear Colleagues,

The isolation of graphene opened the gate to a vast field devoted to the study of inorganic two-dimensional materials. Among the different two-dimensional materials beyond graphene, the family of transition metal dichalcogenides has recently attracted the interest of the scientific community as a large variety of electronic behaviors, ranging from wide band gap semiconductors to superconductors, is exhibited by the different members of this large family of two-dimensional materials.

This Special Issue aims to cover the entire range of fundamental, applied and practical subjects associated with the synthesis, characterization and development of transition metal dichalcogenide-based devices.

Dr. Andres Castellanos-Gomez
Guest Editor

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Keywords

Transition metal dichalcogenides
Molybdenum disulfide MoS2
Molybdenum diselenide MoSe2
Tungsten disulfide WS2
Tungsten diselenide WSe2
Niobium diselenide NbSe2
Rhenium disulfide ReS2
Rhenium diselenide ReSe2
Tantalum disulfide TaS2
Tantalum diselenide TaSe2
Hafnium disulfide HfS2
Hafnium diselenide HfSe2
Properties: electronic, optical, thermal, mechanical
Optoelectronics
Thermoelectrics
Nanodevices
Nano-electromechanical systems

Published Papers (6 papers)

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Research

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1441 KiB

Open AccessFeature PaperArticle

Electronic Band Structure of Transition Metal Dichalcogenides from Ab Initio and Slater–Koster Tight-Binding Model

by Jose Ángel Silva-Guillén, Pablo San-Jose and Rafael Roldán

Appl. Sci. 2016, 6(10), 284; https://0-doi-org.brum.beds.ac.uk/10.3390/app6100284 - 01 Oct 2016

Cited by 59 | Viewed by 13194

Abstract

Semiconducting transition metal dichalcogenides present a complex electronic band structure with a rich orbital contribution to their valence and conduction bands. The possibility to consider the electronic states from a tight-binding model is highly useful for the calculation of many physical properties, for which first principle calculations are more demanding in computational terms when having a large number of atoms. Here, we present a set of Slater–Koster parameters for a tight-binding model that accurately reproduce the structure and the orbital character of the valence and conduction bands of single layer MX

_{2}

, where

M =

Mo, W and

X =

S, Se. The fit of the analytical tight-binding Hamiltonian is done based on band structure from ab initio calculations. The model is used to calculate the optical conductivity of the different compounds from the Kubo formula. Full article

(This article belongs to the Special Issue Two-Dimensional Transition Metal Dichalcogenides)

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Figure 1

9339 KiB

Open AccessCommunication

Raman Spectra of ZrS₂ and ZrSe₂ from Bulk to Atomically Thin Layers

by Samuel Mañas-Valero, Víctor García-López, Andrés Cantarero and Marta Galbiati

Appl. Sci. 2016, 6(9), 264; https://0-doi-org.brum.beds.ac.uk/10.3390/app6090264 - 15 Sep 2016

Cited by 74 | Viewed by 13838

Abstract

In the race towards two-dimensional electronic and optoelectronic devices, semiconducting transition metal dichalcogenides (TMDCs) from group VIB have been intensively studied in recent years due to the indirect to direct band-gap transition from bulk to the monolayer. However, new materials still need to be explored. For example, semiconducting TMDCs from group IVB have been predicted to have larger mobilities than their counterparts from group VIB in the monolayer limit. In this work we report the mechanical exfoliation of ZrX₂ (X = S, Se) from bulk down to the monolayer and we study the dimensionality dependence of the Raman spectra in ambient conditions. We observe Raman signal from bulk to few layers and no shift in the peak positions is found when decreasing the dimensionality. While a Raman signal can be observed from bulk to a bilayer for ZrS₂, we could only detect signal down to five layers for flakes of ZrSe₂. These results show the possibility of obtaining atomically thin layers of ZrX₂ by mechanical exfoliation and represent one of the first steps towards the investigation of the properties of these materials, still unexplored in the two-dimensional limit. Full article

(This article belongs to the Special Issue Two-Dimensional Transition Metal Dichalcogenides)

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Figure 1

4619 KiB

Open AccessArticle

Local Oxidation Nanolithography on Metallic Transition Metal Dichalcogenides Surfaces

by Elena Pinilla-Cienfuegos, Samuel Mañas-Valero, Efrén Navarro-Moratalla, Sergio Tatay, Alicia Forment-Aliaga and Eugenio Coronado

Appl. Sci. 2016, 6(9), 250; https://0-doi-org.brum.beds.ac.uk/10.3390/app6090250 - 08 Sep 2016

Cited by 14 | Viewed by 6882

Abstract

The integration of atomically-thin layers of two dimensional (2D) materials in nanodevices demands for precise techniques at the nanoscale permitting their local modification, structuration or resettlement. Here, we present the use of Local Oxidation Nanolithography (LON) performed with an Atomic Force Microscope (AFM) for the patterning of nanometric motifs on different metallic Transition Metal Dichalcogenides (TMDCs). We show the results of a systematic study of the parameters that affect the LON process as well as the use of two different modes of lithographic operation: dynamic and static. The application of this kind of lithography in different types of TMDCs demonstrates the versatility of the LON for the creation of accurate and reproducible nanopatterns in exfoliated 2D-crystals and reveals the influence of the chemical composition and crystalline structure of the systems on the morphology of the resultant oxide motifs. Full article

(This article belongs to the Special Issue Two-Dimensional Transition Metal Dichalcogenides)

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1472 KiB

Open AccessArticle

The Positive Effects of Hydrophobic Fluoropolymers on the Electrical Properties of MoS₂ Transistors

by Somayyeh Rahimi, Rudresh Ghosh, Seohee Kim, Ananth Dodabalapur, Sanjay Banerjee and Deji Akinwande

Appl. Sci. 2016, 6(9), 236; https://0-doi-org.brum.beds.ac.uk/10.3390/app6090236 - 23 Aug 2016

Cited by 2 | Viewed by 6152

Abstract

We report the improvement of the electrical performance of field effect transistors (FETs) fabricated on monolayer chemical vapor deposited (CVD) MoS₂, by applying an interacting fluoropolymer capping layer (Teflon-AF). The electrical characterizations of more than 60 FETs, after applying Teflon-AF cap, show significant improvement of the device properties and reduced device to device variation. The improvement includes: 50% reduction of the average gate hysteresis, 30% reduction of the subthreshold swing and about an order of magnitude increase of the current on-off ratio. These favorable changes in device performance are attributed to the reduced exposure of MoS₂ channels to the adsorbates in the ambient which can be explained by the polar nature of Teflon-AF cap. A positive shift in the threshold voltage of all the measured FETs is observed, which translates to the more desirable enhancement mode transistor characteristics. Full article

(This article belongs to the Special Issue Two-Dimensional Transition Metal Dichalcogenides)

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1886 KiB

Open AccessArticle

Optical and Transport Properties of Ni-MoS₂

by Tsung-Shine Ko, Cheng-Ching Huang and Der-Yuh Lin

Appl. Sci. 2016, 6(8), 227; https://0-doi-org.brum.beds.ac.uk/10.3390/app6080227 - 12 Aug 2016

Cited by 12 | Viewed by 4823

Abstract

In this paper, MoS₂ and Ni-MoS₂ crystal layers were fabricated by the chemical vapor transport method with iodine as the transport agent. Two direct band edge transitions of excitons at 1.9 and 2.1 eV were observed successfully for both MoS₂ and Ni-MoS₂ samples using temperature-dependent optical reflectance (R) measurement. Hall effect measurements were carried out to analyze the transport behavior of carriers in MoS₂ and Ni-MoS₂, which indicate that the Ni-MoS₂ sample is n-type and has a higher resistance and lower mobility than the MoS₂ sample has. A photoconductivity spectrum was performed which shows an additional Ni doping level existing at 1.2 eV and a higher photocurrent generating only for Ni-MoS₂. The differences between MoS₂ and Ni-MoS₂ could be attributed to the effect of Ni atoms causing small lattice imperfections to form trap states around 1.2 eV. The temperature-dependent conductivity shows the presence of two shallow levels with activation energies (84 and 6.7 meV in MoS₂; 57 and 6.5 meV in Ni-MoS₂). Therefore, the Ni doping level leads to high resistance, low mobility and small activation energies. A series of experimental results could provide useful guidance for the fabrication of optoelectronic devices using MoS₂ structures. Full article

(This article belongs to the Special Issue Two-Dimensional Transition Metal Dichalcogenides)

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Review

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7082 KiB

Open AccessReview

Optoelectronic Devices Based on Atomically Thin Transition Metal Dichalcogenides

by Andreas Pospischil and Thomas Mueller

Appl. Sci. 2016, 6(3), 78; https://0-doi-org.brum.beds.ac.uk/10.3390/app6030078 - 10 Mar 2016

Cited by 101 | Viewed by 13427

Abstract

We review the application of atomically thin transition metal dichalcogenides in optoelectronic devices. First, a brief overview of the optical properties of two-dimensional layered semiconductors is given and the role of excitons and valley dichroism in these materials are discussed. The following sections review and compare different concepts of photodetecting and light emitting devices, nanoscale lasers, single photon emitters, valleytronics devices, as well as photovoltaic cells. Lateral and vertical device layouts and different operation mechanisms are compared. An insight into the emerging field of valley-based optoelectronics is given. We conclude with a critical evaluation of the research area, where we discuss potential future applications and remaining challenges. Full article

(This article belongs to the Special Issue Two-Dimensional Transition Metal Dichalcogenides)

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