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8. Investigation of Growth-Induced Strain in Monolayer MoS2 Grown by Chemical Vapor Deposition

Author

Luo, Siwei, Cullen, Conor P., Guo, Gencai, Zhong, Jianxin, and Duesberg, Georg S.

Subjects
Physics - Applied Physics, Condensed Matter - Materials Science
Abstract

Two-dimensional materials such as transitional metal dichalcogenides exhibit unique optical and electrical properties. Here we report on the varying optical properties of CVD grown MoS2 monolayer flakes with different shapes. In particular, it is observed that the perimeter and the central region of the flakes have non-uniform photoluminescence (PL) energy and intensity. We quantified these effects systematically and propose that thermally induced strain during growth is the origin. The strain relaxation after transfer of the MoS2 flakes supports this explanation. Detailed investigations of the spatial distribution of the PL energy reveal that depending on the shape of the MoS2 flakes, the width of the strain field is different. Thus, our results help to elucidate the fundamental mechanisms responsible for the differences in PL and Raman signals between the perimeter region and the center region of monolayer MoS2 and suggest that the induced strain plays an important role in the growth of monolayer materials.

Published
2019
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12. Building up a view and understanding of the multifunctional activity of black phosphorous nanosheet modified with the metal atom.

Author

Zhang, Hongyu, Xue, Xiong-Xiong, Guo, Gencai, Meng, Haiyu, Qi, Xiang, Zhong, Jianxin, and Huang, Zongyu

Subjects
ELECTROCATALYSIS, AB-initio calculations, GIBBS' free energy, ATOMS, OXYGEN evolution reactions, TRANSITION metals, HYDROGEN evolution reactions
Abstract

Constructing metal-semiconductor interfaces by loading metal atoms onto two-dimensional material to build atomically dispersed single-atom catalysts (SACs) has emerged as a new frontier for improving atom utilization and designing multifunctional electrocatalysts. Nowadays, studies on black phosphorus nanosheets in electrocatalysis have received much attention and the successful preparation of metal nanoparticle/black phosphorus (BP) hybrid electrocatalysts indicates BP nanosheets can serve as a potential support platform for SACs. Herein, by using large-scale ab initio calculations, we explored a large composition space of SACs with transition metal atoms supported on BP monolayer (M-BP) and built a comprehensive picture of activity trend, stability, and electronic origin towards oxygen reduction and evolution reaction (ORR and OER) and hydrogen evolution reaction (HER). The results show that the catalytic activity can be widely tuned by reasonable regulation of metal atoms. Ni-, Pd-, and Pt-BP could effectively balance the binding strength of the target intermediates, thus achieving efficient bifunctional activity for OER and ORR. Favorable bifunctional catalytic performance for OER and HER can be realized on Rh-BP. Especially, Pt-BP exhibits promising trifunctional activity towards OER, ORR, and HER. Multiple-level corrections among overpotential, Gibbs free energy, orbital population, and d-band center reveal that the trend and origin of catalytic activity are intrinsically determined by the d-band center of metal sites. The thermodynamic and dynamic stability simulations demonstrate that the active metal centers are firmly anchored on BP substrate with intact M-P bonds. These findings provide a theoretical basis for the rational design of BP-based SACs toward promising multifunctional activity. [ABSTRACT FROM AUTHOR]

Published
2023
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33. Cu- and Al-Decorated Monolayer TiSe2for Enhanced Gas Detection Sensitivity: A DFT Study

Author

Xiao, Landong, Guo, Gencai, Zhang, Mengyang, You, Manqi, Luo, Siwei, Guo, Gang, He, Chaoyu, Tang, Chao, and Zhong, Jianxin

Abstract

The rapid industrial development has contributed to worsening global pollution, necessitating the urgent development of highly sensitive, cost-effective, and portable gas sensors. In this work, the adsorption of CO, CO2, H2S, NH3, NO, NO2, O2, and SO2gas molecules on pristine and Cu- and Al-decorated monolayer TiSe2has been investigated based on first-principles calculations. First, the results of the phonon spectrum and ab initio molecular dynamics simulations demonstrated that TiSe2is dynamically stable. In addition, compared to pristine TiSe2(−0.029 to −0.154 eV), the adsorption energy of gas molecules (excluding CO2) significantly decreased after decorated with Cu or Al (−0.212 to −0.977 eV in Cu-decorated TiSe2, −0.438 to −2.896 eV in Al-decorated TiSe2). Among them, NH3and NO2have the lowest adsorption energies in Cu and Al-decorated TiSe2, respectively. Further research has shown that the decrease in adsorption energy of gas molecules is mainly due to orbital hybridization and charge transfer between decorated Cu and Al atoms and gas molecules. These findings suggest that TiSe2decorated with Cu and Al can effectively improve its sensitivity to NH3and NO2, respectively, making it promising in gas sensing applications.

Published
2023
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35. Rational design of a C3N/C3B p–n heterostructure as a promising anode material in Li-ion batteries.

Author

You, Manqi, Guo, Gencai, Luo, Siwei, and Zhong, Jianxin

Subjects
*LITHIUM-ion batteries, *ELECTRIC field effects, *BOND strengths, *ELECTRONIC structure, *ANODES
Abstract

It is urgent to develop high-performance anode materials for lithium-ion batteries. In this work, a C3N/C3B p–n heterostructure was systematically investigated by first-principles calculations. The bonding strength of Li in C3N is relatively low (−0.53 eV), whereas the C3N/C3B heterostructure (−1.64 eV to −2.84 eV) can greatly improve the bonding strength without compromising the Li migration capability. The good bonding strength and Li mobility in the C3N/C3B heterostructure are mainly caused by the synergy effect and internal electric field of the p–n heterostructure. Moreover, the electronic structures indicate that the C3N/C3B heterostructure has good conductivity with a tiny bandgap of 0.09 eV. Compared to pristine C3N, the stiffness of the C3N/C3B heterostructure improved significantly (549.35 N m−1). Besides, the C3N/C3B heterostructure presents a high lithium-ion storage capacity (986.61 mA h g−1). The ultrahigh stiffness, good conductivities of electrons and ions, high bonding strength of Li, and high capacity show that the C3N/C3B heterostructure is a prospective anode material for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

Published
2023
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38. Stack-dependent ion diffusion behavior in two-dimensional bilayer C3B.

Author

Guo, Gencai, Peng, Yan, Luo, Siwei, Guo, Gang, Lai, Chen, You, Manqi, Xue, Xiongxiong, Huang, Zongyu, Wei, Xiaolin, Wang, Ruzhi, and Zhong, Jianxin

Subjects
*FAST ions, *BAND gaps, *IONS, *ION channels, *BOND strengths, *BILAYER lipid membranes
Abstract

In recent years, two-dimensional (2D) C-based materials have been intensively studied due to their excellent physicochemical properties. Meanwhile, extensive research has revealed that the electrical properties of layered materials can be tuned by changing the stacking pattern. However, the tuning of ion diffusion properties through stacking remains to be explored. In this work, bilayer C3B with different stackings as a lithium-ion battery anode material is systematically investigated by first-principles calculations. The calculated results show that bilayer C3B has better electronic properties (with a band gap of 0.44 eV to 0.54 eV) and enhanced bonding strength of Li (−2.82 to −3.27 eV) compared to monolayer C3B. Moreover, the intralayer migration barrier of Li can be regulated by stacking. Interestingly, the AB stacked configuration has the lowest migration barrier of 0.100 eV, which is significantly lower than those of other stacking configurations and monolayer C3B. Further studies revealed that the formation of fast ion diffusion channels in the AB stacked configuration is due to the combined effect of layer distance and in-plane charge transfer. These results offer a new strategy for the regulation of ion diffusion properties in 2D van der Waals materials. [ABSTRACT FROM AUTHOR]

Published
2022
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39. Inversion Symmetry and Exotic Interlayer Exciton Behavior in Twisted Trilayer MoS2Produced by Vapor Deposition

Author

Liu, Weiyang, Luo, Siwei, Qi, Xiang, Guo, Gencai, Li, Jun, Tang, Han, Li, Xu, Huang, Xixi, Tang, Zhiyuan, and Zhong, Jianxin

Abstract

Two-dimensional materials (2DMs) that are stacked vertically with a certain twist angle provide new degrees of freedom for designing novel physical properties. Twist-related properties of homogeneous bilayer and heterogeneous bilayer 2DMs, such as excitons and phonons, have been described in many pioneering works. However, twist-related properties of homogeneous trilayer 2DMs have been rarely reported. In this work, trilayer MoS2with the twisted angle of 12° by optimized vapor deposition rather than the conventional mechanical stacking method was successfully fabricated. The inversion symmetry of trilayer MoS2is changed by twist. Phonons and excitons produced by twist have an enormous influence on the interlayer interaction of trilayer MoS2, making trilayer MoS2appear to have exotic optical properties. Compared with monolayer MoS2, the phonon vibration and photoluminescence intensity of trilayer MoS2with one-interlayer-twisted are significantly improved, and the second harmonic generation response in the non-twist region of trilayer MoS2is ∼3 times that of monolayer MoS2. In addition, interlayer coupling, inversion symmetry, and exciton behavior of the twist region show regional differences. This work provides a new way for designing twist and exploring the influence of twist on the structures of 2DMs with few layers.

Published
2023
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46. Local spring effect in titanium-based layered oxides

Author

Su, Heng, primary, Guo, Gencai, additional, Ren, Yang, additional, Yu, Xiqian, additional, Zhang, Xu, additional, Ma, Tianyuan, additional, Lu, Yue, additional, Zhang, Zihe, additional, Ma, Hao, additional, Sui, Manling, additional, Li, Hong, additional, Sun, Chengjun, additional, Chen, Zonghai, additional, Xu, Guiliang, additional, Wang, Ruzhi, additional, Amine, Khalil, additional, and Yu, Haijun, additional

Published
2020
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49. 2D novel C5N2allotropes: High-performance anode materials for alkali metal ion battery

Author

You, Manqi, Guo, Gencai, Liao, Yujie, Luo, Siwei, He, Chaoyu, Tang, Chao, and Zhong, Jianxin

Abstract

Two-dimensional (2D) CN compounds have been extensively investigated for alkali metal ion batteries, and the known materials still manifest certain shortcomings when used as anode. Therefore, we predicted three novel 2D CN compounds, specifically C5N2allotropes, and explored their potential as anode materials for alkali metal ion batteries by first-principles calculations. The calculated results of phonon spectrum and ab-initio molecular dynamics revealed that all three C5N2allotropes are kinetic and thermodynamic stability. In addition, all the allotropes possess excellent mechanical properties (362.96–363.85 N m−1) and metallic properties, along with strong adsorption capabilities for Li, Na, and K. Crucially, they all exhibit good ion diffusion properties for Li, Na, and K, especially in C5N2-b and C5N2-c (the diffusion barrier of Li, Na, and K on C5N2are 0.242 eV on C5N2-b, 0.166 eV on C5N2-c, and 0.146 eV on C5N2-c, respectively). Besides, the C5N2allotropes show a high theoretical storage capacity (913.68 mAh g−1for Li/Na, 837.54 mAh g−1for K), along with a suitable voltage platform. These findings prove that the three novel C5N2allotropes have great potential to be used as high-performance LIBs/SIBs/PIBs anode material and provide new insights into predicting new 2D materials.

Published
2024
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