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A special issue of Nanomaterials (ISSN 2079-4991). This special issue belongs to the section "2D and Carbon Nanomaterials".

Deadline for manuscript submissions: closed (31 July 2023) | Viewed by 16285

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Special Issue Editor

Dr. Ashish Arora

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Guest Editor

1. Department of Physics, Indian Institute of Science Education and Research, Dr. Homi Bhabha Road, Pune 411008, India
2. Institute of Physics and Center for Nanotechnology, University of Münster, 48149 Münster, Germany
Interests: experimental condensed matter physics; 2D materials; layered semiconductors; magneto-optics; high magnetic fields; quantum materials and devices; magnetism at the nanoscale
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The previous decade has witnessed significant research activity in the area of 2D materials such as graphene, transition-metal dichalcogenides (TMDs) of the form MX₂(M = Mo, W, Re; X = S, Se, Te), and 2D magnets such as CrX₃ (X = Cl, Br, I), Cr₂X₂Te₆ (X = Si, Ge), Fe₃GeTe₂, and VSe₂. Simultaneously, a new family of metal phosphorous trichalcogenides (MPT) of the type MPX₃ (M = Mn, Fe, V, Zn, Co, Ni, Cd, Mg; X = S, Se) is emerging, bringing promising semiconductors (band gaps from 1.3 to 3.5 eV) with inherently present antiferromagnetic ordering effects. These materials and their heterostructures hold great potential in fundamental research, where many new low-dimensional phenomena are discovered regularly. Additionally, they hold promise in contributions to the next generation of devices such as spintronics, valleytronics, straintronics, and twistronics.

The present Special Issue aims to publish state-of-the-art manuscripts concerning advancements in the area of 2D semiconductors and magnets research. The topics of the issue tentatively include, but are not limited to:

Synthesis of 2D materials and heterostructures;
Fundamental theoretical and experimental physics of 2D materials and heterostructures;
2D magnetic materials and heterostructures;
Moiré physics in 2D materials-based heterostructures;
Optical and transport properties of 2D materials and heterostructures;
Spintronic and valleytronic advancements based on 2D materials;
Twistronics and straintronics using 2D materials and heterostructures;
2D materials-based devices involving light emission, photovoltaic, excitonic, and polaritonic properties;
Single-photon emission in 2D materials and heterostructures;
Miscellaneous quantum devices based on 2D materials.

Dr. Ashish Arora
Guest Editor

Manuscript Submission Information

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Keywords

2D materials
transition metal dichalcogenides
chromium trihalides
2D heterostructures
moiré physics
spintronics
valleytronics
single-photon emitters
quantum devices
2D ferromagnets
2D antiferromagnets
2D excitons
2D trions
2D biexcitons
interlayer excitons

Published Papers (10 papers)

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Research

14 pages, 7004 KiB

Open AccessArticle

Facile Construction of 2D/2D ZnIn₂S₄-Based Bifunctional Photocatalysts for H₂ Production and Simultaneous Degradation of Rhodamine B and Tetracycline

by Yue Chen, Liezhen Zhu, Youliang Shen, Jing Liu, Jiangbo Xi, Lingfang Qiu, Xun Xu, Dandan Men, Ping Li and Shuwang Duo

Nanomaterials 2023, 13(16), 2315; https://doi.org/10.3390/nano13162315 - 12 Aug 2023

Cited by 4 | Viewed by 1206

Abstract

A two-dimensional/two-dimensional (2D/2D) TiO₂/ZnIn₂S₄ photocatalyst was reasonably proposed and constructed by a two-step oil bath-hydrothermal method. TiO₂ nanosheets uniformly grown on the surface of ZnIn₂S₄ nanosheets and a synergetic effect between the TiO₂ and ZnIn₂S₄ could highly contribute to improving the specific surface area and hydrophilicity of ZnIn₂S₄ as well as accelerating the separation and transfer of photon-generated e⁻-h⁺ pairs, and thus enhancing the visible-light photocatalytic degradation and H₂ evolution performance of ZnIn₂S₄. Rhodamine B (RhB) and tetracycline (TC) were simultaneously selected as the target pollutants for degradation in the work. The optimum photocatalytic RhB and TC degradation properties of TiO₂/ZnIn₂S₄-10 wt% were almost 3.11- and 8.61-fold higher than that of pure ZnIn₂S₄, separately, while the highest photocatalytic hydrogen evolution rate was also observed in the presence of TiO₂/ZnIn₂S₄-10wt% and 4.28-fold higher than that of ZnIn₂S₄. Moreover, the possible photocatalytic mechanisms for enhanced visible-light photocatalytic degradation and H₂ evolution were investigated and proposed in detail. Our research results open an easy pathway for developing efficient bifunctional photocatalysts. Full article

(This article belongs to the Special Issue 2D Semiconductor Nanomaterials and Heterostructures)

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13 pages, 4335 KiB

Open AccessArticle

Controllable Doping Characteristics for WS_xSe_y Monolayers Based on the Tunable S/Se Ratio

by Chen Ji, Yung-Huang Chang, Chien-Sheng Huang, Bohr-Ran Huang and Yuan-Tsung Chen

Nanomaterials 2023, 13(14), 2107; https://doi.org/10.3390/nano13142107 - 19 Jul 2023

Cited by 1 | Viewed by 931

Abstract

Transition metal dichalcogenides (TMDs) have attracted much attention because of their unique characteristics and potential applications in electronic devices. Recent reports have successfully demonstrated the growth of 2-dimensional MoS_xSe_y, Mo_xW_yS₂, Mo_xW_ySe₂, and WS_xSe_y monolayers that exhibit tunable band gap energies. However, few works have examined the doping behavior of those 2D monolayers. This study synthesizes WS_xSe_y monolayers using the CVD process, in which different heating temperatures are applied to sulfur powders to control the ratio of S to Se in WS_xSe_y. Increasing the Se component in WS_xSe_y monolayers produced an apparent electronic state transformation from p-type to n-type, recorded through energy band diagrams. Simultaneously, p-type characteristics gradually became clear as the S component was enhanced in WS_xSe_y monolayers. In addition, Raman spectra showed a red shift of the WS₂-related peaks, indicating n-doping behavior in the WS_xSe_y monolayers. In contrast, with the increase of the sulfur component, the blue shift of the WSe₂-related peaks in the Raman spectra involved the p-doping behavior of WS_xSe_y monolayers. In addition, the optical band gap of the as-grown WS_xSe_y monolayers from 1.97 eV to 1.61 eV is precisely tunable via the different chalcogenide heating temperatures. The results regarding the doping characteristics of WS_xSe_y monolayers provide more options in electronic and optical design. Full article

(This article belongs to the Special Issue 2D Semiconductor Nanomaterials and Heterostructures)

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17 pages, 5597 KiB

Open AccessArticle

Highly Selective NH₃ Sensor Based on MoS₂/WS₂ Heterojunction

by Min Zhang and Jinzhu Zhang

Nanomaterials 2023, 13(12), 1835; https://doi.org/10.3390/nano13121835 - 10 Jun 2023

Cited by 4 | Viewed by 1474

Abstract

In this paper, the heterostructure of MoS₂/WS₂ was prepared by a hydrothermal method; the n-n heterostructure was demonstrated using TEM combined with Mott-Schottky analysis. The valence and conduction band positions were further identified by the XPS valence band spectra. The NH₃-sensing properties were assessed at room temperature by changing the mass ratio of the MoS₂ and WS₂ components. The 50 wt%-MoS₂/WS₂ sample exhibited the best performance, with a peak response of 23643% to NH₃ at a concentration of 500 ppm, a minimum detection limit of 20 ppm, and a fast recovery time of 2.6 s. Furthermore, the composites-based sensors demonstrated an excellent humidity immune property with less than one order of magnitude in the humidity range of 11–95% RH, revealing the practical application value of these sensors. These results suggest that the MoS₂/WS₂ heterojunction is an intriguing candidate for fabricating NH₃ sensors. Full article

(This article belongs to the Special Issue 2D Semiconductor Nanomaterials and Heterostructures)

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21 pages, 1430 KiB

Open AccessArticle

Effects of Coulomb Blockade on the Charge Transport through the Topological States of Finite Armchair Graphene Nanoribbons and Heterostructures

by David M. T. Kuo

Nanomaterials 2023, 13(11), 1757; https://doi.org/10.3390/nano13111757 - 29 May 2023

Cited by 2 | Viewed by 1865

Abstract

In this study, we investigate the charge transport properties of semiconducting armchair graphene nanoribbons (AGNRs) and heterostructures through their topological states (TSs), with a specific focus on the Coulomb blockade region. Our approach employs a two-site Hubbard model that takes into account both intra- and inter-site Coulomb interactions. Using this model, we calculate the electron thermoelectric coefficients and tunneling currents of serially coupled TSs (SCTSs). In the linear response regime, we analyze the electrical conductance (

G_{e}

), Seebeck coefficient (S), and electron thermal conductance (

κ_{e}

) of finite AGNRs. Our results reveal that at low temperatures, the Seebeck coefficient is more sensitive to many-body spectra than electrical conductance. Furthermore, we observe that the optimized S at high temperatures is less sensitive to electron Coulomb interactions than

G_{e}

and

κ_{e}

. In the nonlinear response regime, we observe a tunneling current with negative differential conductance through the SCTSs of finite AGNRs. This current is generated by electron inter-site Coulomb interactions rather than intra-site Coulomb interactions. Additionally, we observe current rectification behavior in asymmetrical junction systems of SCTSs of AGNRs. Notably, we also uncover the remarkable current rectification behavior of SCTSs of 9-7-9 AGNR heterostructure in the Pauli spin blockade configuration. Overall, our study provides valuable insights into the charge transport properties of TSs in finite AGNRs and heterostructures. We emphasize the importance of considering electron–electron interactions in understanding the behavior of these materials. Full article

(This article belongs to the Special Issue 2D Semiconductor Nanomaterials and Heterostructures)

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13 pages, 2946 KiB

Open AccessArticle

Thickness-Dependent Evolutions of Surface Reconstruction and Band Structures in Epitaxial β–In₂Se₃ Thin Films

by Qinghao Meng, Fan Yu, Gan Liu, Junyu Zong, Qichao Tian, Kaili Wang, Xiaodong Qiu, Can Wang, Xiaoxiang Xi and Yi Zhang

Nanomaterials 2023, 13(9), 1533; https://doi.org/10.3390/nano13091533 - 3 May 2023

Cited by 1 | Viewed by 2002

Abstract

Ferroelectric materials have received great attention in the field of data storage, benefiting from their exotic transport properties. Among these materials, the two-dimensional (2D) In₂Se₃ has been of particular interest because of its ability to exhibit both in-plane and out-of-plane ferroelectricity. In this article, we realized the molecular beam epitaxial (MBE) growth of β–In₂Se₃ films on bilayer graphene (BLG) substrates with precisely controlled thickness. Combining in situ scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) measurements, we found that the four-monolayer β–In₂Se₃ is a semiconductor with a (9 × 1) reconstructed superlattice. In contrast, the monolayer β–In₂Se₃/BLG heterostructure does not show any surface reconstruction due to the interfacial interaction and moiré superlattice, which instead results in a folding Dirac cone at the center of the Brillouin zone. In addition, we found that the band gap of In₂Se₃ film decreases after potassium doping on its surface, and the valence band maximum also shifts in momentum after surface potassium doping. The successful growth of high-quality β–In₂Se₃ thin films would be a new platform for studying the 2D ferroelectric heterostructures and devices. The experimental results on the surface reconstruction and band structures also provide important information on the quantum confinement and interfacial effects in the epitaxial β–In₂Se₃ films. Full article

(This article belongs to the Special Issue 2D Semiconductor Nanomaterials and Heterostructures)

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12 pages, 3291 KiB

Open AccessArticle

Prediction and Control of Thermal Transport at Defective State Gr/h-BN Heterojunction Interfaces

by Mingjian Zhou, Liqing Liu, Jiahao Liu and Zihang Mei

Nanomaterials 2023, 13(9), 1462; https://doi.org/10.3390/nano13091462 - 25 Apr 2023

Cited by 1 | Viewed by 1139

Abstract

The control of interfacial thermal conductivity is the key to two−dimensional heterojunction in semiconductor devices. In this paper, by using non−equilibrium molecular dynamics (NEMD) simulations, we analyze the regulation of interfacial thermal energy transport in graphene (Gr)/hexagonal boron nitride (h-BN) heterojunctions and reveal the variation mechanism of interfacial thermal energy transport. The calculated results show that 2.16% atomic doping can effectively improve interfacial heat transport by more than 15.6%, which is attributed to the enhanced phonon coupling in the mid−frequency region (15–25 THz). The single vacancy in both N and B atoms can significantly reduce the interfacial thermal conductivity (ITC), and the ITC decreases linearly with the increase in vacancy defect concentration, mainly due to the single vacancy defects leading to an increased phonon participation rate (PPR) below 0.4 in the low-frequency region (0–13 THz), which shows the phonon the localization feature, which hinders the interfacial heat transport. Finally, a BP neural network algorithm is constructed using machine learning to achieve fast prediction of the ITC of Gr/h-BN two-dimensional heterogeneous structures, and the results show that the prediction error of the model is less than 2%, and the method will provide guidance and reference for the design and optimization of the ITC of more complex defect-state heterogeneous structures. Full article

(This article belongs to the Special Issue 2D Semiconductor Nanomaterials and Heterostructures)

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9 pages, 2140 KiB

Open AccessArticle

Interfacial Charge Transfer and Ultrafast Photonics Application of 2D Graphene/InSe Heterostructure

by Jialin Li, Lizhen Wang, Yuzhong Chen, Yujie Li, Haiming Zhu, Linjun Li and Limin Tong

Nanomaterials 2023, 13(1), 147; https://doi.org/10.3390/nano13010147 - 28 Dec 2022

Cited by 2 | Viewed by 1887

Abstract

Interface interactions in 2D vertically stacked heterostructures play an important role in optoelectronic applications, and photodetectors based on graphene/InSe heterostructures show promising performance nowadays. However, nonlinear optical property studies based on the graphene/InSe heterostructure are insufficient. Here, we fabricated a graphene/InSe heterostructure by mechanical exfoliation and investigated the optically induced charge transfer between graphene/InSe heterostructures by taking photoluminescence and pump–probe measurements. The large built-in electric field at the interface was confirmed by Kelvin probe force microscopy. Furthermore, due to the efficient interfacial carrier transfer driven by the built-in electric potential (~286 meV) and broadband nonlinear absorption, the application of the graphene/InSe heterostructure in a mode-locked laser was realized. Our work not only provides a deeper understanding of the dipole orientation-related interface interactions on the photoexcited charge transfer of graphene/InSe heterostructures, but also enriches the saturable absorber family for ultrafast photonics application. Full article

(This article belongs to the Special Issue 2D Semiconductor Nanomaterials and Heterostructures)

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14 pages, 2839 KiB

Open AccessArticle

Effective Low-Energy Hamiltonians and Unconventional Landau-Level Spectrum of Monolayer C₃N

by Mohsen Shahbazi, Jamal Davoodi, Arash Boochani, Hadi Khanjani and Andor Kormányos

Nanomaterials 2022, 12(24), 4375; https://doi.org/10.3390/nano12244375 - 8 Dec 2022

Cited by 2 | Viewed by 1331

Abstract

We derive low-energy effective

k \cdot p

Hamiltonians for monolayer C

_{3}

N at the

Γ

and M points of the Brillouin zone, where the band edge in the conduction and valence band can be found. Our analysis of the electronic band symmetries [...] Read more.

We derive low-energy effective

k \cdot p

Hamiltonians for monolayer C

_{3}

N at the

Γ

and M points of the Brillouin zone, where the band edge in the conduction and valence band can be found. Our analysis of the electronic band symmetries helps to better understand several results of recent ab initio calculations for the optical properties of this material. We also calculate the Landau-level spectrum. We find that the Landau-level spectrum in the degenerate conduction bands at the

Γ

point acquires properties that are reminiscent of the corresponding results in bilayer graphene, but there are important differences as well. Moreover, because of the heavy effective mass, n-doped samples may host interesting electron–electron interaction effects. Full article

(This article belongs to the Special Issue 2D Semiconductor Nanomaterials and Heterostructures)

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12 pages, 3108 KiB

Open AccessArticle

Phase-Controllable Chemical Vapor Deposition Synthesis of Atomically Thin MoTe₂

by Tao Xu, Aolin Li, Shanshan Wang, Yinlong Tan and Xiang’ai Cheng

Nanomaterials 2022, 12(23), 4133; https://doi.org/10.3390/nano12234133 - 23 Nov 2022

Cited by 2 | Viewed by 1782

Abstract

Two-dimensional (2D) molybdenum telluride (MoTe₂) is attracting increasing attention for its potential applications in electronic, optoelectronic, photonic and catalytic fields, owing to the unique band structures of both stable 2H phase and 1T′ phase. However, the direct growth of high-quality atomically thin MoTe₂ with the controllable proportion of 2H and 1T′ phase seems hard due to easy phase transformation since the potential barrier between the two phases is extremely small. Herein, we report a strategy of the phase-controllable chemical vapor deposition (CVD) synthesis for few-layer (<3 layer) MoTe₂. Besides, a new understanding of the phase-controllable growth mechanism is presented based on a combination of experimental results and DFT calculations. The lattice distortion caused by Te vacancies or structural strain might make 1T′-MoTe₂ more stable. The conditions for 2H to 1T′ phase conversion are determined to be the following: Te monovacancies exceeding 4% or Te divacancies exceeding 8%, or lattice strain beyond 6%. In contrast, sufficient Te supply and appropriate tellurization velocity are essential to obtaining the prevailing 2H-MoTe₂. Our work provides a novel perspective on the preparation of 2D transition metal chalcogenides (TMDs) with the controllable proportion of 2H and 1T′ phase and paves the way to their subsequent potential application of these hybrid phases. Full article

(This article belongs to the Special Issue 2D Semiconductor Nanomaterials and Heterostructures)

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11 pages, 2522 KiB

Open AccessArticle

Efficient Optical Modulation of Exciton State Population in Monolayer MoS₂ at Room Temperature

by Zeqian Ren, Qiwei Zhang, Xiu Li, Lixia Guo, Jizhou Wu, Yuqing Li, Wenliang Liu, Peng Li, Yongming Fu and Jie Ma

Nanomaterials 2022, 12(18), 3133; https://doi.org/10.3390/nano12183133 - 9 Sep 2022

Viewed by 1876

Abstract

The modulation of exciton energy and state density of layer-structured transition metal dichalcogenides (TMDs) is required for diverse optoelectronic device applications. Here, the spontaneous inversion of exciton state population in monolayer MoS₂ is observed by turning the pump light power. The excitons prefer to exist in low energy state under low pump power, but reverse under high pump power. To discuss the mechanism in depth, we propose a semiclassical model by combining the rate equation and photo−exciton interaction. Considering the modifying of exciton−exciton annihilation, the spontaneous inversion of exciton state population is phenomenologically described. Full article

(This article belongs to the Special Issue 2D Semiconductor Nanomaterials and Heterostructures)

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