Nanomaterials

Research

11 pages, 2666 KiB

Open AccessArticle

Extracting the Infrared Permittivity of SiO₂ Substrates Locally by Near-Field Imaging of Phonon Polaritons in a van der Waals Crystal

by Patricia Aguilar-Merino, Gonzalo Álvarez-Pérez, Javier Taboada-Gutiérrez, Jiahua Duan, Iván Prieto, Luis Manuel Álvarez-Prado, Alexey Y. Nikitin, Javier Martín-Sánchez and Pablo Alonso-González

Nanomaterials 2021, 11(1), 120; https://doi.org/10.3390/nano11010120 - 7 Jan 2021

Cited by 8 | Viewed by 4237

Abstract

Layered materials in which individual atomic layers are bonded by weak van der Waals forces (vdW materials) constitute one of the most prominent platforms for materials research. Particularly, polar vdW crystals, such as hexagonal boron nitride (h-BN), alpha-molybdenum trioxide (α-MoO₃) or [...] Read more.

Layered materials in which individual atomic layers are bonded by weak van der Waals forces (vdW materials) constitute one of the most prominent platforms for materials research. Particularly, polar vdW crystals, such as hexagonal boron nitride (h-BN), alpha-molybdenum trioxide (α-MoO₃) or alpha-vanadium pentoxide (α-V₂O₅), have received significant attention in nano-optics, since they support phonon polaritons (PhPs)―light coupled to lattice vibrations― with strong electromagnetic confinement and low optical losses. Recently, correlative far- and near-field studies of α-MoO₃ have been demonstrated as an effective strategy to accurately extract the permittivity of this material. Here, we use this accurately characterized and low-loss polaritonic material to sense its local dielectric environment, namely silica (SiO₂), one of the most widespread substrates in nanotechnology. By studying the propagation of PhPs on α-MoO₃ flakes with different thicknesses laying on SiO₂ substrates via near-field microscopy (s-SNOM), we extract locally the infrared permittivity of SiO₂. Our work reveals PhPs nanoimaging as a versatile method for the quantitative characterization of the local optical properties of dielectric substrates, crucial for understanding and predicting the response of nanomaterials and for the future scalability of integrated nanophotonic devices. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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15 pages, 8037 KiB

Open AccessArticle

Role of Graphene in Constructing Multilayer Plasmonic SERS Substrate with Graphene/AgNPs as Chemical Mechanism—Electromagnetic Mechanism Unit

by Lu Liu, Shuting Hou, Xiaofei Zhao, Chundong Liu, Zhen Li, Chonghui Li, Shicai Xu, Guilin Wang, Jing Yu, Chao Zhang and Baoyuan Man

Nanomaterials 2020, 10(12), 2371; https://doi.org/10.3390/nano10122371 - 28 Nov 2020

Cited by 14 | Viewed by 2713

Abstract

Graphene–metal substrates have received widespread attention due to their superior surface-enhanced Raman scattering (SERS) performance. The strong coupling between graphene and metal particles can greatly improve the SERS performance and thus broaden the application fields. The way in which to make full use [...] Read more.

Graphene–metal substrates have received widespread attention due to their superior surface-enhanced Raman scattering (SERS) performance. The strong coupling between graphene and metal particles can greatly improve the SERS performance and thus broaden the application fields. The way in which to make full use of the synergistic effect of the hybrid is still a key issue to improve SERS activity and stability. Here, we used graphene as a chemical mechanism (CM) layer and Ag nanoparticles (AgNPs) as an electromagnetic mechanism (EM) layer, forming a CM–EM unit and constructing a multi-layer hybrid structure as a SERS substrate. The improved SERS performance of the multilayer nanostructure was investigated experimentally and in theory. We demonstrated that the Raman enhancement effect increased as the number of CM–EM units increased, remaining nearly unchanged when the CM–EM unit was more than four. The limit of detection was down to 10⁻¹⁴ M for rhodamine 6G (R6G) and 10⁻¹² M for crystal violet (CV), which confirmed the ultrahigh sensitivity of the multilayer SERS substrate. Furthermore, we investigated the reproducibility and thermal stability of the proposed multilayer SERS substrate. On the basis of these promising results, the development of new materials and novel methods for high performance sensing and biosensing applications will be promoted. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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11 pages, 2620 KiB

Open AccessArticle

Structural and Electronic Properties of Heterostructures Composed of Antimonene and Monolayer MoS₂

by Congcong Zhou, Xiaodan Li and Taotao Hu

Nanomaterials 2020, 10(12), 2358; https://doi.org/10.3390/nano10122358 - 27 Nov 2020

Cited by 5 | Viewed by 2812

Abstract

Antimonene is found to be a promising material for two-dimensional optoelectronic equipment due to its broad band gap and high carrier mobility. The van der Waals heterostructure, as a unique structural unit for the study of photoelectric properties, has attracted great attention. By [...] Read more.

Antimonene is found to be a promising material for two-dimensional optoelectronic equipment due to its broad band gap and high carrier mobility. The van der Waals heterostructure, as a unique structural unit for the study of photoelectric properties, has attracted great attention. By using ab initio density functional theory with van der Waals corrections, we theoretically investigated the structural and electronic properties of the heterostructures composed of antimonene and monolayer MoS₂. Our results revealed that the Sb/MoS₂ hetero-bilayer is an indirect semiconductor with type-II band alignment, which implies the spatial separation of photogenerated electron–hole pairs. Due to the weak van der Waals interlayer interactions between the adjacent sheets of the hetero-bilayer systems, the band structures of isolated antimonene and monolayer MoS₂ are preserved. In addition, a tunable band gap in Sb/MoS₂ hetero-bilayer can be realized by applying in-plane biaxial compressing/stretching. When antimonene and monolayer MoS₂ are stacked into superlattices, the indirect semiconductors turn into direct semiconductors with the decreased band gaps. Our results show that the antimonene-based hybrid structures are good candidate structures for photovoltaic devices. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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12 pages, 4501 KiB

Open AccessArticle

Making van der Waals Heterostructures Assembly Accessible to Everyone

by Sergey G. Martanov, Natalia K. Zhurbina, Mikhail V. Pugachev, Aliaksandr I. Duleba, Mark A. Akmaev, Vasilii V. Belykh and Aleksandr Y. Kuntsevich

Nanomaterials 2020, 10(11), 2305; https://doi.org/10.3390/nano10112305 - 21 Nov 2020

Cited by 16 | Viewed by 6391

Abstract

Van-der Waals heterostructures assembled from one or few atomic layer thickness crystals are becoming increasingly more popular in condensed matter physics. These structures are assembled using transfer machines, those are based on mask aligners, probe stations or are home-made. For many laboratories it [...] Read more.

Van-der Waals heterostructures assembled from one or few atomic layer thickness crystals are becoming increasingly more popular in condensed matter physics. These structures are assembled using transfer machines, those are based on mask aligners, probe stations or are home-made. For many laboratories it is vital to build a simple, convenient and universal transfer machine. In this paper we discuss the guiding principles for the design of such a machine, review the existing machines and demonstrate our own construction, that is powerful and fast-in-operation. All components of this machine are extremely cheap and can be easily purchased using common online retail services. Moreover, assembling a heterostructure out of exfoliated commercially available hexagonal boron nitride and tungsten diselenide crystals with a pick-up technique and using the microphotolumenescence spectra, we show well-resolved exciton and trion lines, as a results of disorder suppression in WSe

_{2}

monolayer. Our results thus show that technology of the two-dimensional materials and heterostructures becomes accessible to anyone. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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17 pages, 8330 KiB

Open AccessArticle

Electron Density and Its Relation with Electronic and Optical Properties in 2D Mo/W Dichalcogenides

by Pingping Jiang, Marie-Christine Record and Pascal Boulet

Nanomaterials 2020, 10(11), 2221; https://doi.org/10.3390/nano10112221 - 8 Nov 2020

Cited by 10 | Viewed by 3023

Abstract

Two-dimensional MX₂ (M = Mo, W; X = S, Se, Te) homo- and heterostructures have attracted extensive attention in electronics and optoelectronics due to their unique structures and properties. In this work, the layer-dependent electronic and optical properties have been studied by [...] Read more.

Two-dimensional MX₂ (M = Mo, W; X = S, Se, Te) homo- and heterostructures have attracted extensive attention in electronics and optoelectronics due to their unique structures and properties. In this work, the layer-dependent electronic and optical properties have been studied by varying layer thickness and stacking order. Based on the quantum theory of atoms in molecules, topological analyses on interatomic interactions of layered MX₂ and WX₂/MoX₂, including bond degree (BD), bond length (BL), and bond angle (BA), have been detailed to probe structure-property relationships. Results show that M-X and X-X bonds are strengthened and weakened in layered MX₂ compared to the counterparts in bulks. X-X and M-Se/Te are weakened at compressive strain while strengthened at tensile strain and are more responsive to the former than the latter. Discordant BD variation of individual parts of WX₂/MoX₂ accounts for exclusively distributed electrons and holes, yielding type-II band offsets. X-X BL correlates positively to binding energy (E_b), while X-X BA correlates negatively to lattice mismatch (lm). The resulting interlayer distance limitation evidences constraint-free lattice of vdW structure. Finally, the connection between microscopic interatomic interaction and macroscopic electromagnetic behavior has been quantified firstly by a cubic equation relating to weighted BD summation and static dielectric constant. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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16 pages, 5799 KiB

Open AccessEditor’s ChoiceArticle

Structure-Property Relationships of 2D Ga/In Chalcogenides

by Pingping Jiang, Pascal Boulet and Marie-Christine Record

Nanomaterials 2020, 10(11), 2188; https://doi.org/10.3390/nano10112188 - 2 Nov 2020

Cited by 2 | Viewed by 2232

Abstract

Two-dimensional MX (M = Ga, In; X = S, Se, Te) homo- and heterostructures are of interest in electronics and optoelectronics. Structural, electronic and optical properties of bulk and layered MX and GaX/InX heterostructures have been investigated comprehensively using density functional theory (DFT) [...] Read more.

Two-dimensional MX (M = Ga, In; X = S, Se, Te) homo- and heterostructures are of interest in electronics and optoelectronics. Structural, electronic and optical properties of bulk and layered MX and GaX/InX heterostructures have been investigated comprehensively using density functional theory (DFT) calculations. Based on the quantum theory of atoms in molecules, topological analyses of bond degree (BD), bond length (BL) and bond angle (BA) have been detailed for interpreting interatomic interactions, hence the structure–property relationship. The X–X BD correlates linearly with the ratio of local potential and kinetic energy, and decreases as X goes from S to Te. For van der Waals (vdW) homo- and heterostructures of GaX and InX, a cubic relationship between microscopic interatomic interaction and macroscopic electromagnetic behavior has been established firstly relating to weighted absolute BD summation and static dielectric constant. A decisive role of vdW interaction in layer-dependent properties has been identified. The GaX/InX heterostructures have bandgaps in the range 0.23–1.49 eV, absorption coefficients over 10⁻⁵ cm⁻¹ and maximum conversion efficiency over 27%. Under strain, discordant BD evolutions are responsible for the exclusively distributed electrons and holes in sublayers of GaX/InX. Meanwhile, the interlayer BA adjustment with lattice mismatch explains the constraint-free lattice of the vdW heterostructure. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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12 pages, 4280 KiB

Open AccessArticle

Sensitivity-Enhanced SPR Sensor Based on Graphene and Subwavelength Silver Gratings

by Lu Kong, Jiangtao Lv, Qiongchan Gu, Yu Ying, Xiaoxiao Jiang and Guangyuan Si

Nanomaterials 2020, 10(11), 2125; https://doi.org/10.3390/nano10112125 - 26 Oct 2020

Cited by 26 | Viewed by 3015

Abstract

A novel surface plasmon resonance (SPR) sensor with graphene and subwavelength gratings is proposed to improve the sensing performance. A series of numerical analyses were performed to investigate the effect of structural parameters on the sensing performance, such as minimum reflectance at resonance [...] Read more.

A novel surface plasmon resonance (SPR) sensor with graphene and subwavelength gratings is proposed to improve the sensing performance. A series of numerical analyses were performed to investigate the effect of structural parameters on the sensing performance, such as minimum reflectance at resonance (MRR), full width at half maximum (FWHM), and resonance angle. The results indicated that near-zero MRR (2.9 × 10⁻⁶) and narrow FWHM (about 3.5 deg) could be obtained by optimizing the geometrical parameters. Moreover, the influence of the number of graphene layers on sensitivity was also studied. The maximum sensitivity of the designed sensor could reach 192 deg/refractive index unit (RIU), which is a great enhancement compared to the silver-only SPR sensor. In addition, ethylene glycol solutions with different refractive indices were detected. The results showed that the sensitivity of the sensor could reach 220.67 deg/RIU, and the proposed sensor had excellent linearity between the resonance angle and refractive index, enabling extensive potential practical sensing applications. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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24 pages, 7599 KiB

Open AccessArticle

EMI Shielding of the Hydrophobic, Flexible, Lightweight Carbonless Nano-Plate Composites

by Kanthasamy Raagulan, Jin Soo Ghim, Ramanaskanda Braveenth, Moon Jai Jung, Sang Bok Lee, Kyu Yun Chai, Bo Mi Kim and Joonsik Lee

Nanomaterials 2020, 10(10), 2086; https://doi.org/10.3390/nano10102086 - 21 Oct 2020

Cited by 11 | Viewed by 3027

Abstract

The cost-effective spray coated composite was successfully synthesis and characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction techniques. The one step synthetic strategy was used for the synthesis of nanoplates that have a crystalline nature. The composites are [...] Read more.

The cost-effective spray coated composite was successfully synthesis and characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction techniques. The one step synthetic strategy was used for the synthesis of nanoplates that have a crystalline nature. The composites are amorphous and hydrophobic with micron thickness (<400 μm). The maximum contact angle showed by composite is 132.65° and have wetting energy of −49.32 mN m⁻¹, spreading coefficient −122.12 mN m⁻¹, and work of adhesion 23.48 mN m⁻¹. The minimum thickness of synthesized nanoplate is 3 nm while the maximum sheet resistance, resistivity, and electrical conductivity of the composites are 11.890 ohm sq⁻¹, 0.4399 Ω.cm⁻¹, and 8.967 S.cm⁻¹, respectively. The cobalt nanoplate coated non-woven carbon fabric (CoFC) possesses excellent sheet resistance, hydrophobic nature, and EMI shielding efficiency of 99.99964%. The composite can block above 99.9913% of incident radiation (X band). Hence, the composite can be utilized in application areas such as medical clothes, mobile phones, automobiles, aerospace, and military equipment. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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11 pages, 3856 KiB

Open AccessArticle

Tunable Electronic Properties of Type-II SiS₂/WSe₂ Hetero-Bilayers

by Yue Guan, Xiaodan Li, Ruixia Niu, Ningxia Zhang, Taotao Hu and Liyao Zhang

Nanomaterials 2020, 10(10), 2037; https://doi.org/10.3390/nano10102037 - 15 Oct 2020

Cited by 9 | Viewed by 3762

Abstract

First-principle calculations based on the density functional theory (DFT) are implemented to study the structural and electronic properties of the SiS₂/WSe₂ hetero-bilayers. It is found that the AB-2 stacking model is most stable among all the six SiS₂/WSe [...] Read more.

First-principle calculations based on the density functional theory (DFT) are implemented to study the structural and electronic properties of the SiS₂/WSe₂ hetero-bilayers. It is found that the AB-2 stacking model is most stable among all the six SiS₂/WSe₂ heterostructures considered in this work. The AB-2 stacking SiS₂/WSe₂ hetero-bilayer possesses a type-II band alignment with a narrow indirect band gap (0.154 eV and 0.738 eV obtained by GGA-PBE and HSE06, respectively), which can effectively separate the photogenerated electron–hole pairs and prevent the recombination of the electron–hole pairs. Our results revealed that the band gap can be tuned effectively within the range of elastic deformation (biaxial strain range from −7% to 7%) while maintaining the type-II band alignment. Furthermore, due to the effective regulation of interlayer charge transfer, the band gap along with the band offset of the SiS₂/WSe₂ heterostructure can also be modulated effectively by applying a vertical external electric field. Our results offer interesting alternatives for the engineering of two-dimensional material-based optoelectronic nanodevices. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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9 pages, 2019 KiB

Open AccessArticle

Influence of SERS Activity of SnSe₂ Nanosheets Doped with Sulfur

by Yuan Tian, Haonan Wei, Yujie Xu, Qianqian Sun, Baoyuan Man and Mei Liu

Nanomaterials 2020, 10(10), 1910; https://doi.org/10.3390/nano10101910 - 24 Sep 2020

Cited by 16 | Viewed by 3645

Abstract

The application of 2D semiconductor nanomaterials in the field of SERS is limited due to its weak enhancement effect and the unclear enhancement mechanism. In this study, we changed the surface morphology and energy level structure of 2D SnSe₂ nanosheets using different [...] Read more.

The application of 2D semiconductor nanomaterials in the field of SERS is limited due to its weak enhancement effect and the unclear enhancement mechanism. In this study, we changed the surface morphology and energy level structure of 2D SnSe₂ nanosheets using different amounts of S dopant. This caused the vibration coupling of the substrate and the adsorbed molecules and affects the SERS activities of the SnSe₂ nanosheets. SERS performance of the 2D semiconductor substrate can effectively be improved by suitable doping, which can effectively break the limitation of 2D semiconductor compounds in SERS detection and will have very important significance in the fields of chemical, biological, and materials sciences. In this work, the intensities of SERS signals for R6G molecules on SnSe_0.93S_0.94 are 1.3 to 1.7 times stronger than those on pure SnSe₂ substrate. It not only provides a new way to effectively improve the SERS activity of a semiconductor SERS substrates but also helps to design more efficient and stable semiconductor SERS substrates for practical application. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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14 pages, 2182 KiB

Open AccessArticle

Tunable Photodetectors via In Situ Thermal Conversion of TiS₃ to TiO₂

by Foad Ghasemi, Riccardo Frisenda, Eduardo Flores, Nikos Papadopoulos, Robert Biele, David Perez de Lara, Herre S. J. van der Zant, Kenji Watanabe, Takashi Taniguchi, Roberto D’Agosta, Jose R. Ares, Carlos Sánchez, Isabel J. Ferrer and Andres Castellanos-Gomez

Nanomaterials 2020, 10(4), 711; https://doi.org/10.3390/nano10040711 - 9 Apr 2020

Cited by 18 | Viewed by 3982

Abstract

In two-dimensional materials research, oxidation is usually considered as a common source for the degradation of electronic and optoelectronic devices or even device failure. However, in some cases a controlled oxidation can open the possibility to widely tune the band structure of 2D [...] Read more.

In two-dimensional materials research, oxidation is usually considered as a common source for the degradation of electronic and optoelectronic devices or even device failure. However, in some cases a controlled oxidation can open the possibility to widely tune the band structure of 2D materials. In particular, we demonstrate the controlled oxidation of titanium trisulfide (TiS₃), a layered semicon-ductor that has attracted much attention recently thanks to its quasi-1D electronic and optoelectron-ic properties and its direct bandgap of 1.1 eV. Heating TiS₃ in air above 300 °C gradually converts it into TiO₂, a semiconductor with a wide bandgap of 3.2 eV with applications in photo-electrochemistry and catalysis. In this work, we investigate the controlled thermal oxidation of indi-vidual TiS₃ nanoribbons and its influence on the optoelectronic properties of TiS₃-based photodetec-tors. We observe a step-wise change in the cut-off wavelength from its pristine value ~1000 nm to 450 nm after subjecting the TiS₃ devices to subsequent thermal treatment cycles. Ab-initio and many-body calculations confirm an increase in the bandgap of titanium oxysulfide (TiO_2-xS_x) when in-creasing the amount of oxygen and reducing the amount of sulfur. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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10 pages, 2390 KiB

Open AccessArticle

Electrical Phase Control Based on Graphene Surface Plasmon Polaritons in Mid-infrared

by Yindi Wang, Hongxia Liu, Shulong Wang, Ming Cai, Haifeng Zhang and Yanbin Qiao

Nanomaterials 2020, 10(3), 576; https://doi.org/10.3390/nano10030576 - 22 Mar 2020

Cited by 9 | Viewed by 2813

Abstract

Phase modulation of light is the core of many optoelectronic applications, such as electro-optic switch, sensors and modulators. Graphene Surface plasmon polaritons (SPPs) exhibit unique properties in phase modulation including dynamic tunability, a small driving voltage and small device size. In this paper, [...] Read more.

Phase modulation of light is the core of many optoelectronic applications, such as electro-optic switch, sensors and modulators. Graphene Surface plasmon polaritons (SPPs) exhibit unique properties in phase modulation including dynamic tunability, a small driving voltage and small device size. In this paper, the novel phase modulation capability of graphene SPPs in mid-infrared are confirmed through theory and simulation. The results show that graphene SPPs can realize continuous tuning of the phase shift at multiple wavelengths in mid-infrared, covering the phase range from 0° to 360°. Based on these results, a sandwich waveguide structure of dielectric–graphene–dielectric with a device length of 800 nm is proposed, which shows up to 381° phase modulation range at an operating wavelength of 6.55 µm, given a 1 V driving voltage. In addition, the structure size is much shorter than the wavelength in mid-infrared and can realize sub-wavelength operation. This work paves the way to develop graphene-based tunable devices for mid-infrared wave-front control. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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14 pages, 3717 KiB

Open AccessArticle

Facile and Reliable Thickness Identification of Atomically Thin Dichalcogenide Semiconductors Using Hyperspectral Microscopy

by Yu-Chung Chang, Yu-Kai Wang, Yen-Ting Chen and Der-Yuh Lin

Nanomaterials 2020, 10(3), 526; https://doi.org/10.3390/nano10030526 - 14 Mar 2020

Cited by 8 | Viewed by 3437

Abstract

Although large-scale synthesis of layered two-dimensional (2D) transition metal dichalcogenides (TMDCs) has been made possible, mechanical exfoliation of layered van der Waals crystal is still indispensable as every new material research starts with exfoliated flakes. However, it is often a tedious task to [...] Read more.

Although large-scale synthesis of layered two-dimensional (2D) transition metal dichalcogenides (TMDCs) has been made possible, mechanical exfoliation of layered van der Waals crystal is still indispensable as every new material research starts with exfoliated flakes. However, it is often a tedious task to find the flakes with desired thickness and sizes. We propose a method to determine the thickness of few-layer flakes and facilitate the fast searching of flakes with a specific thickness. By using hyperspectral wild field microscopy to acquire differential reflectance and transmittance spectra, we demonstrate unambiguous recognition of typical TMDCs and their thicknesses based on their excitonic resonance features in a single step. Distinct from Raman spectroscopy or atomic force microscopy, our method is non-destructive to the sample. By knowing the contrast between different layers, we developed an algorithm to automatically search for flakes of desired thickness in situ. We extended this method to measure tin dichalcogenides, such as SnS₂ and SnSe₂, which are indirect bandgap semiconductors regardless of the thickness. We observed distinct spectroscopic behaviors as compared with typical TMDCs. Layer-dependent excitonic features were manifested. Our method is ideal for automatic non-destructive optical inspection in mass production in the semiconductor industry. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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14 pages, 3804 KiB

Open AccessArticle

Effect of Compressive Prestrain on the Anti-Pressure and Anti-Wear Performance of Monolayer MoS₂: A Molecular Dynamics Study

by Ning Kong, Boyu Wei, Yuan Zhuang, Jie Zhang, Hongbo Li and Bo Wang

Nanomaterials 2020, 10(2), 275; https://doi.org/10.3390/nano10020275 - 6 Feb 2020

Cited by 8 | Viewed by 2978

Abstract

The effects of in-plane prestrain on the anti-pressure and anti-wear performance of monolayer MoS₂ have been investigated by molecular dynamics simulation. The results show that monolayer MoS₂ observably improves the load bearing capacity of Pt substrate. The friction reduction effect depends [...] Read more.

The effects of in-plane prestrain on the anti-pressure and anti-wear performance of monolayer MoS₂ have been investigated by molecular dynamics simulation. The results show that monolayer MoS₂ observably improves the load bearing capacity of Pt substrate. The friction reduction effect depends on the deformation degree of monolayer MoS₂. The anti-pressure performance of monolayer MoS₂ and Pt substrate is enhanced by around 55.02% when compressive prestrain increases by 4.03% and the anti-wear performance is notably improved as well. The improved capacities for resisting the in-plane tensile and out-of-plane compressive deformation are responsible for the outstanding lubrication mechanism of monolayer MoS₂. This study provides guidelines for optimizing the anti-pressure and anti-wear performance of MoS₂ and other two-dimension materials which are subjected to the in-plane prestrain. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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12 pages, 2241 KiB

Open AccessArticle

Nanotip Contacts for Electric Transport and Field Emission Characterization of Ultrathin MoS₂ Flakes

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

Nanomaterials 2020, 10(1), 106; https://doi.org/10.3390/nano10010106 - 4 Jan 2020

Cited by 27 | Viewed by 3706

Abstract

We report a facile approach based on piezoelectric-driven nanotips inside a scanning electron microscope to contact and electrically characterize ultrathin MoS2 (molybdenum disulfide) flakes on a SiO2/Si (silicon dioxide/silicon) substrate. We apply such a method to analyze the electric transport and field emission [...] Read more.

We report a facile approach based on piezoelectric-driven nanotips inside a scanning electron microscope to contact and electrically characterize ultrathin MoS2 (molybdenum disulfide) flakes on a SiO2/Si (silicon dioxide/silicon) substrate. We apply such a method to analyze the electric transport and field emission properties of chemical vapor deposition-synthesized monolayer MoS₂, used as the channel of back-gate field effect transistors. We study the effects of the gate-voltage range and sweeping time on the channel current and on its hysteretic behavior. We observe that the conduction of the MoS₂ channel is affected by trap states. Moreover, we report a gate-controlled field emission current from the edge part of the MoS₂ flake, evidencing a field enhancement factor of approximately

200

and a turn-on field of approximately

40 V / μ m

at a cathode–anode separation distance of

900 nm

. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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11 pages, 2760 KiB

Open AccessArticle

High-Efficiency Production of Large-Size Few-Layer Graphene Platelets via Pulsed Discharge of Graphite Strips

by Xin Gao, Tomomasa Hiraoka, Shunsuke Ohmagari, Shigeru Tanaka, Zemin Sheng, Kaiyuan Liu, Meng Xu, Pengwan Chen and Kazuyuki Hokamoto

Nanomaterials 2019, 9(12), 1785; https://doi.org/10.3390/nano9121785 - 16 Dec 2019

Cited by 10 | Viewed by 3698

Abstract

The synthesis of large-size graphene materials is still a central focus of research into additional potential applications in various areas. In this study, large-size graphene platelets were successfully produced by pulsed discharge of loose graphite strips with a dimension of 2 mm × [...] Read more.

The synthesis of large-size graphene materials is still a central focus of research into additional potential applications in various areas. In this study, large-size graphene platelets were successfully produced by pulsed discharge of loose graphite strips with a dimension of 2 mm × 0.5 mm × 80 mm in distilled water. The graphite strips were made by pressing and cutting well-oriented expanded graphite paper. The recovered samples were characterized by various techniques, including TEM, SEM, optical microscopy (OM), atomic force microscopy (AFM), XRD and Raman spectroscopy. Highly crystalline graphene platelets with a lateral dimension of 100–200 μm were identified. The high yield of recovered graphene platelets is in a range of 90–95%. The results also indicate that increasing charging voltage improves the yield of graphene platelets and decreases the number of graphitic layers in produced graphene platelets. The formation mechanism of graphene platelets was discussed. This study provides a one-step cost-effective route to prepare highly crystalline graphene platelets with a sub-millimeter lateral size. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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10 pages, 4340 KiB

Open AccessArticle

The Electronic and Optical Properties of InSe-GeTe Heterobilayer via Applying Biaxial Strain

by Guofeng Yang, Rui Sun, Yan Gu, Feng Xie, Yu Ding, Xiumei Zhang, Yueke Wang, Bin Hua, Xianfeng Ni, Qian Fan and Xing Gu

Nanomaterials 2019, 9(12), 1705; https://doi.org/10.3390/nano9121705 - 28 Nov 2019

Cited by 7 | Viewed by 3433

Abstract

A comprehensive insight into the electronic and optical properties of small-lattice-mismatched InSe-GeTe heterobilayer (HBL) is performed based on the density functional theory (DFT) with van der Waals corrections from first-principles perspective. The optimization of most stable geometric stacking mode for the InSe-GeTe HBL [...] Read more.

A comprehensive insight into the electronic and optical properties of small-lattice-mismatched InSe-GeTe heterobilayer (HBL) is performed based on the density functional theory (DFT) with van der Waals corrections from first-principles perspective. The optimization of most stable geometric stacking mode for the InSe-GeTe HBL is demonstrated. In addition, it is found that the InSe-GeTe HBL forms a type-II heterostructure of staggered-gap band alignment, resulting in an indirect band gap of 0.78 eV, which could be employed as a separator for electron-hole pairs. Moreover, the influence of biaxial strain on the electronic and optical properties of the InSe-GeTe HBL are systematically explored by calculating the band structures, density of states (PDOS), electron density differences, and optical absorption spectra of InSe-GeTe HBL under compressive and tensile biaxial strains. The results indicate that the electronic structures and optical performance of InSe-GeTe HBL could be modulated by changing the biaxial strain conveniently. Our findings provide new opportunities for the novel InSe-GeTe HBL to be applied in the electronic and optoelectronic fields. Full article

(This article belongs to the Special Issue 2D Materials and Their Heterostructures and Superlattices)

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