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17 pages, 4744 KiB

Open AccessArticle

Nature of Excitons in Bidimensional WSe₂ by Hybrid Density Functional Theory Calculations

by Hongsheng Liu, Paolo Lazzaroni and Cristiana Di Valentin

Nanomaterials 2018, 8(7), 481; https://doi.org/10.3390/nano8070481 - 29 Jun 2018

Cited by 11 | Viewed by 7408

Abstract

2D tungsten diselenide (2D-WSe₂) is one of the most successful bidimensional materials for optoelectronic and photonic applications, thanks to its strong photoluminescence properties and to a characteristic large exciton binding energy. Although these optical properties are widely recognized by the scientific [...] Read more.

2D tungsten diselenide (2D-WSe₂) is one of the most successful bidimensional materials for optoelectronic and photonic applications, thanks to its strong photoluminescence properties and to a characteristic large exciton binding energy. Although these optical properties are widely recognized by the scientific community, there is no general understanding of the atomistic details of the excitonic species giving rise to them. In this work, we present a density functional theory investigation of excitons in 2D-WSe₂, where we compare results obtained by standard generalized gradient approximation (GGA) methods (including spin-orbit coupling) with those by hybrid density functionals. Our study provides information on the size of the self-trapped exciton, the number and type of atoms involved, the structural reorganization, the self-trapping energy, and the photoluminescence energy, whose computed value is in good agreement with experimental measurements in the literature. Moreover, based on the comparative analysis of the self-trapping energy for the exciton with that for isolated charge carriers (unbound electrons and holes), we also suggest a simplified approach for the theoretical estimation of the excitonic binding energy, which can be compared with previous estimates from different approaches or from experimental data. Full article

(This article belongs to the Special Issue Synthesis, Structure and Applications of 2D Nanomaterials)

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13 pages, 12523 KiB

Open AccessArticle

Aerosol Synthesis of N and N-S Doped and Crumpled Graphene Nanostructures

by Francesco Carraro, Mattia Cattelan, Marco Favaro and Laura Calvillo

Nanomaterials 2018, 8(6), 406; https://doi.org/10.3390/nano8060406 - 6 Jun 2018

Cited by 10 | Viewed by 5912

Abstract

Chemically modified graphene–based materials (CMG) are currently attracting a vast interest in their application in different fields. In particular, heteroatom-doped graphenes have revealed great potentialities in the field of electrocatalysis as substitutes of fuel cell noble metal–based catalysts. In this work, we investigate [...] Read more.

Chemically modified graphene–based materials (CMG) are currently attracting a vast interest in their application in different fields. In particular, heteroatom-doped graphenes have revealed great potentialities in the field of electrocatalysis as substitutes of fuel cell noble metal–based catalysts. In this work, we investigate an innovative process for doping graphene nanostructures. We optimize a novel synthetic route based on aerosol preparation, which allows the simultaneous doping, crumpling, and reduction of graphene oxide (GO). Starting from aqueous solutions containing GO and the dopant precursors, we synthesize N- and N,S-dual-doped 3D graphene nanostructures (N-cGO and N,S-cGO). In the aerosol process, every aerosol droplet can be considered as a microreactor where dopant precursors undergo thermal decomposition and react with the GO flakes. Simultaneously, thanks to the relatively high temperature, GO undergoes crumpling and partial reduction. Using a combination of spectroscopic and microscopic characterization techniques, we investigate the morphology of the obtained materials and the chemical nature of the dopants within the crumpled graphene sheets. This study highlights the versatility of the aerosol process for the design of new CMG materials with tailored electrocatalytic properties. Full article

(This article belongs to the Special Issue Synthesis, Structure and Applications of 2D Nanomaterials)

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11 pages, 3398 KiB

Open AccessArticle

Self-Assembled Ag-Cu₂O Nanocomposite Films at Air-Liquid Interfaces for Surface-Enhanced Raman Scattering and Electrochemical Detection of H₂O₂

by Li Wang, Huan Qi, Lei Chen, Yantao Sun and Zhuang Li

Nanomaterials 2018, 8(5), 332; https://doi.org/10.3390/nano8050332 - 15 May 2018

Cited by 9 | Viewed by 4392

Abstract

We employ a facile and novel route to synthesize multifunctional Ag-Cu₂O nanocomposite films through the self-assembly of nanoparticles at an air-liquid interface. In the ethanol-water phase, AgNO₃ and Cu(NO₃)₂ were reduced to Ag-Cu₂O nanoparticles by [...] Read more.

We employ a facile and novel route to synthesize multifunctional Ag-Cu₂O nanocomposite films through the self-assembly of nanoparticles at an air-liquid interface. In the ethanol-water phase, AgNO₃ and Cu(NO₃)₂ were reduced to Ag-Cu₂O nanoparticles by NaBH₄ in the presence of cinnamic acid. The Ag-Cu₂O nanoparticles were immediately trapped at the air-liquid interface to form two-dimensional nanocomposite films after the reduction reaction was finished. The morphology of the nanocomposite films could be controlled by the systematic regulation of experimental parameters. It was found that the prepared nanocomposite films serving as the substrates exhibited strong surface-enhanced Raman scattering (SERS) activity. 4-aminothiophenol (4-ATP) molecules were used as the test probes to examine the SERS sensitivity of the nanocomposite films. Moreover, the nanocomposite films synthesized by our method showed enhanced electrocatalytic activity towards hydrogen peroxide (H₂O₂) and therefore could be utilized to fabricate a non-enzymatic electrochemical H₂O₂ sensor. Full article

(This article belongs to the Special Issue Synthesis, Structure and Applications of 2D Nanomaterials)

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10 pages, 2550 KiB

Open AccessArticle

Transport and Field Emission Properties of MoS₂ Bilayers

by Francesca Urban, Maurizio Passacantando, Filippo Giubileo, Laura Iemmo and Antonio Di Bartolomeo

Nanomaterials 2018, 8(3), 151; https://doi.org/10.3390/nano8030151 - 8 Mar 2018

Cited by 75 | Viewed by 6632

Abstract

We report the electrical characterization and field emission properties of

{MoS}_{2}

bilayers deposited on a

{SiO}_{2} / Si

substrate. Current–voltage characteristics are measured in the back-gate transistor configuration, with

Ti

contacts patterned by electron beam lithography. We confirm the n-type character [...] Read more.

We report the electrical characterization and field emission properties of

{MoS}_{2}

bilayers deposited on a

{SiO}_{2} / Si

substrate. Current–voltage characteristics are measured in the back-gate transistor configuration, with

Ti

contacts patterned by electron beam lithography. We confirm the n-type character of as-grown

{MoS}_{2}

and we report normally-on field-effect transistors. Local characterization of field emission is performed inside a scanning electron microscope chamber with piezo-controlled tungsten tips working as the anode and the cathode. We demonstrate that an electric field of

~ 200 V / μ m

is able to extract current from the flat part of

{MoS}_{2}

bilayers, which can therefore be conveniently exploited for field emission applications even in low field enhancement configurations. We show that a Fowler–Nordheim model, modified to account for electron confinement in two-dimensional (2D) materials, fully describes the emission process. Full article

(This article belongs to the Special Issue Synthesis, Structure and Applications of 2D Nanomaterials)

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2080 KiB

Open AccessArticle

Raman Enhancement and Photo-Bleaching of Organic Dyes in the Presence of Chemical Vapor Deposition-Grown Graphene

by Jiaxin Weng, Shichao Zhao, Zhiting Li, Karen B. Ricardo, Feng Zhou, Hyojeong Kim and Haitao Liu

Nanomaterials 2017, 7(10), 337; https://doi.org/10.3390/nano7100337 - 19 Oct 2017

Cited by 9 | Viewed by 4675

Abstract

Fluorescent organic dyes photobleach under intense light. Graphene has been shown to improve the photo-stability of organic dyes. In this paper, we investigated the Raman spectroscopy and photo-bleaching kinetics of dyes in the absence/presence of chemical vapor deposition (CVD)-grown graphene. We show that [...] Read more.

Fluorescent organic dyes photobleach under intense light. Graphene has been shown to improve the photo-stability of organic dyes. In this paper, we investigated the Raman spectroscopy and photo-bleaching kinetics of dyes in the absence/presence of chemical vapor deposition (CVD)-grown graphene. We show that graphene enhances the Raman signal of a wide range of dyes. The photo-bleaching of the dyes was reduced when the dyes were in contact with graphene. In contrast, monolayer hexagonal boron nitride (h-BN) was much less effective in reducing the photo-bleaching rate of the dyes. We attribute the suppression of photo-bleaching to the energy or electron transfer from dye to graphene. The results highlight the potential of CVD graphene as a substrate for protecting and enhancing Raman response of organic dyes. Full article

(This article belongs to the Special Issue Synthesis, Structure and Applications of 2D Nanomaterials)

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Review

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40 pages, 5904 KiB

Open AccessReview

Properties, Preparation and Applications of Low Dimensional Transition Metal Dichalcogenides

by Lei Yang, Chenggen Xie, Juncheng Jin, Rai Nauman Ali, Chao Feng, Ping Liu and Bin Xiang

Nanomaterials 2018, 8(7), 463; https://doi.org/10.3390/nano8070463 - 26 Jun 2018

Cited by 44 | Viewed by 7210

Abstract

Low-dimensional layered transition metal dichalcogenides (TMDs) have recently emerged as an important fundamental research material because of their unique structural, physical and chemical properties. These novel properties make these TMDs a suitable candidate in numerous potential applications. In this review, we briefly summarize [...] Read more.

Low-dimensional layered transition metal dichalcogenides (TMDs) have recently emerged as an important fundamental research material because of their unique structural, physical and chemical properties. These novel properties make these TMDs a suitable candidate in numerous potential applications. In this review, we briefly summarize the properties of low-dimensional TMDs, and then focus on the various methods used in their preparation. The use of TMDs in electronic devices, optoelectronic devices, electrocatalysts, biosystems, and hydrogen storage is also explored. The cutting-edge future development probabilities of these materials and numerous research challenges are also outlined in this review. Full article

(This article belongs to the Special Issue Synthesis, Structure and Applications of 2D Nanomaterials)

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23 pages, 6395 KiB

Open AccessReview

Nanostructured Graphene: An Active Component in Optoelectronic Devices

by Chang-Hyun Kim

Nanomaterials 2018, 8(5), 328; https://doi.org/10.3390/nano8050328 - 14 May 2018

Cited by 8 | Viewed by 6229

Abstract

Nanostructured and chemically modified graphene-based nanomaterials possess intriguing properties for their incorporation as an active component in a wide spectrum of optoelectronic architectures. From a technological point of view, this aspect brings many new opportunities to the now well-known atomically thin carbon sheet, [...] Read more.

Nanostructured and chemically modified graphene-based nanomaterials possess intriguing properties for their incorporation as an active component in a wide spectrum of optoelectronic architectures. From a technological point of view, this aspect brings many new opportunities to the now well-known atomically thin carbon sheet, multiplying its application areas beyond transparent electrodes. This article gives an overview of fundamental concepts, theoretical backgrounds, design principles, technological implications, and recent advances in semiconductor devices that integrate nanostructured graphene materials into their active region. Starting from the unique electronic nature of graphene, a physical understanding of finite-size effects, non-idealities, and functionalizing mechanisms is established. This is followed by the conceptualization of hybridized films, addressing how the insertion of graphene can modulate or improve material properties. Importantly, it provides general guidelines for designing new materials and devices with specific characteristics. Next, a number of notable devices found in the literature are highlighted. It provides practical information on material preparation, device fabrication, and optimization for high-performance optoelectronics with a graphene hybrid channel. Finally, concluding remarks are made with the summary of the current status, scientific issues, and meaningful approaches to realizing next-generation technologies. Full article

(This article belongs to the Special Issue Synthesis, Structure and Applications of 2D Nanomaterials)

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26 pages, 4438 KiB

Open AccessReview

A Perspective on the Application of Spatially Resolved ARPES for 2D Materials

by Mattia Cattelan and Neil A. Fox

Nanomaterials 2018, 8(5), 284; https://doi.org/10.3390/nano8050284 - 27 Apr 2018

Cited by 53 | Viewed by 12725

Abstract

In this paper, a perspective on the application of Spatially- and Angle-Resolved PhotoEmission Spectroscopy (ARPES) for the study of two-dimensional (2D) materials is presented. ARPES allows the direct measurement of the electronic band structure of materials generating extremely useful insights into their electronic [...] Read more.

In this paper, a perspective on the application of Spatially- and Angle-Resolved PhotoEmission Spectroscopy (ARPES) for the study of two-dimensional (2D) materials is presented. ARPES allows the direct measurement of the electronic band structure of materials generating extremely useful insights into their electronic properties. The possibility to apply this technique to 2D materials is of paramount importance because these ultrathin layers are considered fundamental for future electronic, photonic and spintronic devices. In this review an overview of the technical aspects of spatially localized ARPES is given along with a description of the most advanced setups for laboratory and synchrotron-based equipment. This technique is sensitive to the lateral dimensions of the sample. Therefore, a discussion on the preparation methods of 2D material is presented. Some of the most interesting results obtained by ARPES are reported in three sections including: graphene, transition metal dichalcogenides (TMDCs) and 2D heterostructures. Graphene has played a key role in ARPES studies because it inspired the use of this technique with other 2D materials. TMDCs are presented for their peculiar transport, optical and spin properties. Finally, the section featuring heterostructures highlights a future direction for research into 2D material structures. Full article

(This article belongs to the Special Issue Synthesis, Structure and Applications of 2D Nanomaterials)

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19 pages, 4623 KiB

Open AccessReview

Recent Advances in Nanoporous Membranes for Water Purification

by Zhuqing Wang, Aiguo Wu, Lucio Colombi Ciacchi and Gang Wei

Nanomaterials 2018, 8(2), 65; https://doi.org/10.3390/nano8020065 - 25 Jan 2018

Cited by 169 | Viewed by 13316

Abstract

Nanoporous materials exhibit wide applications in the fields of electrocatalysis, nanodevice fabrication, energy, and environmental science, as well as analytical science. In this review, we present a summary of recent studies on nanoporous membranes for water purification application. The types and fabrication strategies [...] Read more.

Nanoporous materials exhibit wide applications in the fields of electrocatalysis, nanodevice fabrication, energy, and environmental science, as well as analytical science. In this review, we present a summary of recent studies on nanoporous membranes for water purification application. The types and fabrication strategies of various nanoporous membranes are first introduced, and then the fabricated nanoporous membranes for removing various water pollutants, such as salt, metallic ions, anions, nanoparticles, organic chemicals, and biological substrates, are demonstrated and discussed. This work will be valuable for readers to understand the design and fabrication of various nanoporous membranes, and their potential purification mechanisms towards different water pollutants. In addition, it will be helpful for developing new nanoporous materials for quick, economic, and high-performance water purification. Full article

(This article belongs to the Special Issue Synthesis, Structure and Applications of 2D Nanomaterials)

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