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10 pages, 1742 KiB

Open AccessArticle

Feasible Structure Manipulation of Vanadium Selenide into VSe₂ on Au(111)

by Chaoqin Huang, Lei Xie, Huan Zhang, Hongbing Wang, Jinping Hu, Zhaofeng Liang, Zheng Jiang and Fei Song

Nanomaterials 2022, 12(15), 2518; https://doi.org/10.3390/nano12152518 - 22 Jul 2022

Cited by 2 | Viewed by 1849

Abstract

Vanadium diselenide (VSe₂), a member of the transition metal dichalcogenides (TMDs), is proposed with intriguing properties. However, a comprehensive investigation of VSe₂ (especially regarding on the growth mechanism) is still lacking. Herein, with the molecular beam epitaxy (MBE) measures frequently [...] Read more.

Vanadium diselenide (VSe₂), a member of the transition metal dichalcogenides (TMDs), is proposed with intriguing properties. However, a comprehensive investigation of VSe₂ (especially regarding on the growth mechanism) is still lacking. Herein, with the molecular beam epitaxy (MBE) measures frequently utilized in surface science, we have successfully synthesized the single-layer VSe₂ on Au(111) and revealed its structural transformation using a combination of scanning tunneling microscopy (STM) and density functional theory (DFT). Initially, formation of the honeycomb structure is observed with the moiré periodicity, which is assigned to VSe₂. Followed by stepwise annealing, defective structures with streaked patterns start to emerge due to the depletion of Se, which can be reversed to the pristine VSe₂ by resupplying Se. With more V than Se deposited, a new compound that has no bulk analogue is discovered on Au(111), which could be transformed back to VSe₂ after providing excessive Se. As the realization of manipulating V selenide phases is subtly determined by the relative ratio of V to Se and post-annealing treatments, this report provides useful insights toward fundamental understanding of the growth mechanism of TMDs and might promote the wide application of VSe₂ in related fields such as catalysis and nanoelectronics. Full article

(This article belongs to the Special Issue Transition Metal Dichalcogenides: From Fundamentals to Nanoelectronics)

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12 pages, 4738 KiB

Open AccessArticle

Synthesis, Characterization, and Supercapacitor Performance of a Mixed-Phase Mn-Doped MoS₂ Nanoflower

by Ismaila T. Bello, Kabir O. Otun, Gayi Nyongombe, Oluwaseun Adedokun, Guy L. Kabongo and Mokhotjwa S. Dhlamini

Nanomaterials 2022, 12(3), 490; https://doi.org/10.3390/nano12030490 - 29 Jan 2022

Cited by 24 | Viewed by 3826

Abstract

The fascinating features of 2D nanomaterials for various applications have prompted increasing research into single and few-layer metal dichalcogenides nanosheets using improved nanofabrication and characterization techniques. MoS₂ has recently been intensively examined among layered metal dichalcogenides and other diverse transition metal-based materials, [...] Read more.

The fascinating features of 2D nanomaterials for various applications have prompted increasing research into single and few-layer metal dichalcogenides nanosheets using improved nanofabrication and characterization techniques. MoS₂ has recently been intensively examined among layered metal dichalcogenides and other diverse transition metal-based materials, that have previously been studied in various applications. In this research, we report mixed-phase Mn-doped MoS₂ nanoflowers for supercapacitor performance studies. The confirmation of the successfully prepared Mn-doped MoS₂ nanoflowers was characterized by XRD, SEM-EDS, RAMAN, and BET research techniques. The mixed-phase of the as-synthesized electrode material was confirmed by the structural changes observed in the XRD and RAMAN studies. The surface area from the BET measurement was calculated to be 46.0628 m²/g, and the adsorption average pore size of the electrode material was 11.26607 nm. The electrochemical performance of the Mn-doped MoS₂ electrode material showed a pseudo-capacitive behavior, with a specific capacitance of 70.37 Fg⁻¹, and with a corresponding energy density of 3.14 Whkg⁻¹ and a power density of 4346.35 Wkg⁻¹. The performance of this metal-doped MoS₂-based supercapacitor device can be attributed to its mixed phase, which requires further optimization in future works. Full article

(This article belongs to the Special Issue Transition Metal Dichalcogenides: From Fundamentals to Nanoelectronics)

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18 pages, 18355 KiB

Open AccessArticle

Positive Magnetoresistance and Chiral Anomaly in Exfoliated Type-II Weyl Semimetal T_d-WTe₂

by Rajdeep Adhikari, Soma Adhikari, Bogdan Faina, Marc Terschanski, Sophie Bork, Claudia Leimhofer, Mirko Cinchetti and Alberta Bonanni

Nanomaterials 2021, 11(10), 2755; https://doi.org/10.3390/nano11102755 - 18 Oct 2021

Cited by 2 | Viewed by 3386

Abstract

Layered van der Waals semimetallic

T_{d}

-WTe

_{2}

, exhibiting intriguing properties which include non-saturating extreme positive magnetoresistance (MR) and tunable chiral anomaly, has emerged as a model topological type-II Weyl semimetal system. Here, ∼45 nm thick mechanically exfoliated flakes of [...] Read more.

Layered van der Waals semimetallic

T_{d}

-WTe

_{2}

, exhibiting intriguing properties which include non-saturating extreme positive magnetoresistance (MR) and tunable chiral anomaly, has emerged as a model topological type-II Weyl semimetal system. Here, ∼45 nm thick mechanically exfoliated flakes of

T_{d}

-WTe

_{2}

are studied via atomic force microscopy, Raman spectroscopy, low-T/high-

μ_{0} H

magnetotransport measurements and optical reflectivity. The contribution of anisotropy of the Fermi liquid state to the origin of the large positive transverse

{MR}_{⊥}

and the signature of chiral anomaly of the type-II Weyl Fermions are reported. The samples are found to be stable in air and no oxidation or degradation of the electronic properties is observed. A transverse

{MR}_{⊥}

∼1200 % and an average carrier mobility of 5000 cm

^{2}

V

^{- 1}

s

^{- 1}

at

T = 5 K

for an applied perpendicular field

μ_{0} H_{⊥} = 7 T

are established. The system follows a Fermi liquid model for

T \leq 50 K

and the anisotropy of the Fermi surface is concluded to be at the origin of the observed positive MR. Optical reflectivity measurements confirm the anisotropy of the electronic behaviour. The relative orientation of the crystal axes and of the applied electric and magnetic fields is proven to determine the observed chiral anomaly in the in-plane magnetotransport. The observed chiral anomaly in the WTe

_{2}

flakes is found to persist up to

T = 120 K

, a temperature at least four times higher than the ones reported to date. Full article

(This article belongs to the Special Issue Transition Metal Dichalcogenides: From Fundamentals to Nanoelectronics)

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11 pages, 3909 KiB

Open AccessArticle

One-Pot Synthesis of Chlorophyll-Assisted Exfoliated MoS₂/WS₂ Heterostructures via Liquid-Phase Exfoliation Method for Photocatalytic Hydrogen Production

by I-Wen P. Chen, Yan-Ming Lai and Wei-Sheng Liao

Nanomaterials 2021, 11(9), 2436; https://doi.org/10.3390/nano11092436 - 18 Sep 2021

Cited by 8 | Viewed by 2501

Abstract

Developing strategies for producing hydrogen economically and in greener ways is still an unaccomplished goal. Photoelectrochemical (PEC) water splitting using photoelectrodes under neutral electrolyte conditions provides possibly one of the greenest routes to produce hydrogen. Here, we demonstrate that chlorophyll extracts can be [...] Read more.

Developing strategies for producing hydrogen economically and in greener ways is still an unaccomplished goal. Photoelectrochemical (PEC) water splitting using photoelectrodes under neutral electrolyte conditions provides possibly one of the greenest routes to produce hydrogen. Here, we demonstrate that chlorophyll extracts can be used as an efficient exfoliant to exfoliate bulk MoS₂ and WS₂ to form a thin layer of a MoS₂/WS₂ heterostructure. Thin films of solution-processed MoS₂ and WS₂ nanosheets display photocurrent densities of −1 and −5 mA/cm², respectively, and hydrogen evolution under simulated solar irradiation. The exfoliated WS₂ is significantly more efficient than the exfoliated MoS₂; however, the MoS₂/WS₂ heterostructure results in a 2500% increase in photocurrent densities compared to the individual constituents and over 12 h of PEC durability under a neutral electrolyte. Surprisingly, in real seawater, the MoS₂/WS₂ heterostructure exhibits stable hydrogen production after solar illumination for 12 h. The synthesis method showed, for the first time, how the MoS₂/WS₂ heterostructure can be used to produce hydrogen effectively. Our findings highlight the prospects for this heterostructure, which could be coupled with various processes towards improving PEC efficiency and applications. Full article

(This article belongs to the Special Issue Transition Metal Dichalcogenides: From Fundamentals to Nanoelectronics)

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14 pages, 3409 KiB

Open AccessArticle

Enhancement of Photodetective Properties on Multilayered MoS₂ Thin Film Transistors via Self-Assembled Poly-L-Lysine Treatment and Their Potential Application in Optical Sensors

by Seung Gi Seo, Jae Hyeon Ryu, Seung Yeob Kim, Jinheon Jeong and Sung Hun Jin

Nanomaterials 2021, 11(6), 1586; https://doi.org/10.3390/nano11061586 - 17 Jun 2021

Cited by 2 | Viewed by 2361

Abstract

Photodetectors and display backplane transistors based on molybdenum disulfide (MoS₂) have been regarded as promising topics. However, most studies have focused on the improvement in the performances of the MoS₂ photodetector itself or emerging applications. In this study, to suggest [...] Read more.

Photodetectors and display backplane transistors based on molybdenum disulfide (MoS₂) have been regarded as promising topics. However, most studies have focused on the improvement in the performances of the MoS₂ photodetector itself or emerging applications. In this study, to suggest a better insight into the photodetector performances of MoS₂ thin film transistors (TFTs), as photosensors for possible integrated system, we performed a comparative study on the photoresponse of MoS₂ and hydrogenated amorphous silicon (a-Si:H) TFTs. As a result, in the various wavelengths and optical power ranges, MoS₂ TFTs exhibit 2~4 orders larger photo responsivities and detectivities. The overall quantitative comparison of photoresponse in single device and inverters confirms a much better performance by the MoS₂ photodetectors. Furthermore, as a strategy to improve the field effect mobility and photoresponse of the MoS₂ TFTs, molecular doping via poly-L-lysine (PLL) treatment was applied to the MoS₂ TFTs. Transfer and output characteristics of the MoS₂ TFTs clearly show improved photocurrent generation under a wide range of illuminations (740~365 nm). These results provide useful insights for considering MoS₂ as a next-generation photodetector in flat panel displays and makes it more attractive due to the fact of its potential as a high-performance photodetector enabled by a novel doping technique. Full article

(This article belongs to the Special Issue Transition Metal Dichalcogenides: From Fundamentals to Nanoelectronics)

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12 pages, 1723 KiB

Open AccessArticle

Optical Constants and Structural Properties of Epitaxial MoS₂ Monolayers

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

Nanomaterials 2021, 11(6), 1411; https://doi.org/10.3390/nano11061411 - 27 May 2021

Cited by 17 | Viewed by 4030

Abstract

Two-dimensional layers of transition-metal dichalcogenides (TMDs) have been widely studied owing to their exciting potential for applications in advanced electronic and optoelectronic devices. Typically, monolayers of TMDs are produced either by mechanical exfoliation or chemical vapor deposition (CVD). While the former produces high-quality [...] Read more.

Two-dimensional layers of transition-metal dichalcogenides (TMDs) have been widely studied owing to their exciting potential for applications in advanced electronic and optoelectronic devices. Typically, monolayers of TMDs are produced either by mechanical exfoliation or chemical vapor deposition (CVD). While the former produces high-quality flakes with a size limited to a few micrometers, the latter gives large-area layers but with a nonuniform surface resulting from multiple defects and randomly oriented domains. The use of epitaxy growth can produce continuous, crystalline and uniform films with fewer defects. Here, we present a comprehensive study of the optical and structural properties of a single layer of MoS₂ synthesized by molecular beam epitaxy (MBE) on a sapphire substrate. For optical characterization, we performed spectroscopic ellipsometry over a broad spectral range (from 250 to 1700 nm) under variable incident angles. The structural quality was assessed by optical microscopy, atomic force microscopy, scanning electron microscopy, and Raman spectroscopy through which we were able to confirm that our sample contains a single-atomic layer of MoS₂ with a low number of defects. Raman and photoluminescence spectroscopies revealed that MBE-synthesized MoS₂ layers exhibit a two-times higher quantum yield of photoluminescence along with lower photobleaching compared to CVD-grown MoS₂, thus making it an attractive candidate for photonic applications. Full article

(This article belongs to the Special Issue Transition Metal Dichalcogenides: From Fundamentals to Nanoelectronics)

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15 pages, 2043 KiB

Open AccessArticle

Synergic Effect of Novel WS₂ Carriers Holding Spherical Cobalt Ferrite @cubic Fe₃O₄ (WS₂/s-CoFe₂O₄@c-Fe₃O₄) Nanocomposites in Magnetic Resonance Imaging and Photothermal Therapy for Ocular Treatments and Investigation of Corneal Endothelial Cell Migration

by Shadie Hatamie, Po-Jen Shih, Bo-Wei Chen, I-Jong Wang, Tai-Horng Young and Da-Jeng Yao

Nanomaterials 2020, 10(12), 2555; https://doi.org/10.3390/nano10122555 - 19 Dec 2020

Cited by 8 | Viewed by 2764

Abstract

The design of novel materials to use simultaneously in an ocular system for driven therapeutics and wound healing is still challenging. Here, we produced nanocomposites of tungsten disulfide carriers with spherical cobalt ferrite nanoparticles (NPs) as core inside a cubic iron oxide NPs [...] Read more.

The design of novel materials to use simultaneously in an ocular system for driven therapeutics and wound healing is still challenging. Here, we produced nanocomposites of tungsten disulfide carriers with spherical cobalt ferrite nanoparticles (NPs) as core inside a cubic iron oxide NPs shell (WS₂/s-CoFe₂O₄@c-Fe₃O₄). Transmission electron microscopy (TEM) confirmed that 10 nm s-CoFe₂O₄@c-Fe₃O₄ NPs were attached on the WS₂ sheet surfaces. The cytotoxicity of the WS₂ sheets and nanocomposites were evaluated on bovine cornea endothelial cells (BCECs) using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay for a duration of three days. The MTT assay results showed low toxicity of the WS₂ sheets on BCECs by 67% cell viability at 100 μg/mL in 24 h, while the nanocomposites show 50% cell viability in the same conditions. The magnetic resonance imaging (MRI) of nanocomposites revealed the excellent T₂-weighted imaging with an r₂ contrast of 108 mM⁻¹ S⁻¹. The in vitro photothermal therapy based on WS₂ sheets and WS₂/s-CoFe₂O₄ @c-Fe₃O₄ nanocomposites using 808 nm laser showed that the maximum thermal energy dispatched in medium at different applied power densities (1200 mw, 1800, 2200, 2600 mW) was for 0.1 mg/mL of the sample solution. The migration assay of BCECs showed that the wound healing was approximately 20% slower for the cell exposed by nanocomposites compared with the control (no exposed BCECs). We believe that WS₂/s-CoFe₂O₄@c-Fe₃O₄ nanocomposites have a synergic effect as photothermal therapy agents for eye diseases and could be a target in an ocular system using MRI. Full article

(This article belongs to the Special Issue Transition Metal Dichalcogenides: From Fundamentals to Nanoelectronics)

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Review

Jump to: Research

25 pages, 3129 KiB

Open AccessReview

Interfacial Coupling and Modulation of van der Waals Heterostructures for Nanodevices

by Kun Zhao, Dawei He, Shaohua Fu, Zhiying Bai, Qing Miao, Mohan Huang, Yongsheng Wang and Xiaoxian Zhang

Nanomaterials 2022, 12(19), 3418; https://doi.org/10.3390/nano12193418 - 29 Sep 2022

Cited by 6 | Viewed by 1695

Abstract

In recent years, van der Waals heterostructures (vdWHs) of two-dimensional (2D) materials have attracted extensive research interest. By stacking various 2D materials together to form vdWHs, it is interesting to see that new and fascinating properties are formed beyond single 2D materials; thus, [...] Read more.

In recent years, van der Waals heterostructures (vdWHs) of two-dimensional (2D) materials have attracted extensive research interest. By stacking various 2D materials together to form vdWHs, it is interesting to see that new and fascinating properties are formed beyond single 2D materials; thus, 2D heterostructures-based nanodevices, especially for potential optoelectronic applications, were successfully constructed in the past few decades. With the dramatically increased demand for well-controlled heterostructures for nanodevices with desired performance in recent years, various interfacial modulation methods have been carried out to regulate the interfacial coupling of such heterostructures. Here, the research progress in the study of interfacial coupling of vdWHs (investigated by Photoluminescence, Raman, and Pump–probe spectroscopies as well as other techniques), the modulation of interfacial coupling by applying various external fields (including electrical, optical, mechanical fields), as well as the related applications for future electrics and optoelectronics, have been briefly reviewed. By summarizing the recent progress, discussing the recent advances, and looking forward to future trends and existing challenges, this review is aimed at providing an overall picture of the importance of interfacial modulation in vdWHs for possible strategies to optimize the device’s performance. Full article

(This article belongs to the Special Issue Transition Metal Dichalcogenides: From Fundamentals to Nanoelectronics)

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