Janus monolayer PtSSe under external electric field and strain: A first principles study on electronic structure and optical properties

doi:10.1016/j.spmi.2020.106683

Superlattices and Microstructures

Volume 147, November 2020, 106683

https://doi.org/10.1016/j.spmi.2020.106683 Get rights and content

Highlights

•
Spin-orbital coupling effect lowers PBE band gap of 1.547 eV–1.388 eV for equilibrium Janus monolayer PtSSe.
•
Under biaxial strains, band gap of PtSSe has the form of asymmetric concave down parabola with one maximum.
•
The ability of biaxial strains to tune PtSSe band gap to some values suitable for optoelectronic materials.
•
Good enhancement of absorption and reflectivity by biaxial strains and electric fields in the infrared and visible regions.

Abstract

The effect of biaxial strains $ε_{b}$ and electric field E on the electronic structure and optical properties of Janus monolayer PtSSe was studied by Density Functional Theory (DFT). A reasonable band gap of PtSSe was found to be 1.547 eV. In the infrared region, both biaxial strains and electric fields result in noticeable enhancement of the electronic structure as well as optical properties of PtSSe. Especially, under biaxial strains, the change of PtSSe band gap obeys the form of an asymmetric concave down parabola. This result confirms the existence of a maximum PtSSe band gap under biaxial strains $ε_{b}$ and the possibility of tuning PtSSe band gap to fit the requirement of the optoelectronic devices. The absorption rate in the visible light region of Janus monolayer PtSSe increases sharply and can be altered by strain engineering. Biaxial strain not only alters the absorption intensity but can also significantly shift the position of these absorption peaks. The present study provides additional information about the strain and electric field-induced electronic structure and optical properties of Janus monolayer PtSSe, which should be taken into account for better PtSSe-based devices.

Introduction

Renewable energy has long been subject to strong research, and nowadays it becomes an urgent demand due to the inevitable reduction of nuclear, and fossil energy sources. Solar energy is among the most promising resources. Silicon-based compounds are currently the best photovoltaic materials, whose efficiency is about 29% [1]. Many researches have been made in an effort to increase this efficiency where one of the key factors is to enhance the absorption rate of new photovoltaic materials like CdTe [2] or the development of photocatalyst materials, whose most popular representative is TiO₂ [3]. For all these materials, a tunable band gap is a key factor in improving efficiency [[4], [5], [6]]. Transition metal dichalcogenides (TMDs) are good candidates, as their in-plane asymmetry allows band gap tuning [[7], [8], [9], [10], [11]]. Moreover, the TMDCs also possess strong piezoelectricity, Rashba spin splitting effect [[12], [13], [14], [15]], and unique thermal properties [16], so they can be applied in sensors, thermoelectric, optoelectronics, spintronics, and quantum devices (see Table 1).

Recently, the Janus asymmetrical structures were discovered [17,18] and have attracted the attention of scientists [[19], [20], [21]]. The Janus monolayer PtSSe possesses advantageous properties of a promising photocatalyst such as the internal electrical field in its inversion asymmetric structure, active sites at Pt, and S atoms for inducing the reaction of hydrogen evolution [22]. Therefore, the PtSSe-based materials can be used in various applications, which also leads to many possible effects caused by surrounding conditions. For 2D materials, their electronic properties are very easy to be tuned by biaxial strains [19,[23], [24], [25], [26]]. However, to our knowledge, the band gap of PtSSe has not been measured experimentally, meanwhile, there is a big discrepancy between GGA and LDA band gap values which are 2.19 eV, and 0.64 eV, respectively [27]. It is worth mentioning that the PtSSe band gap must be some value between 1.20 and 1.60 eV, which are the experimental band gaps of PtS₂ and PtSe₂, respectively [28,29].

In this work, the effect of biaxial strains $ε_{b}$ and electric fields E on the electronic and optical properties of Janus monolayer PtSSe was theoretically studied by first-principles calculations. The respond of Janus monolayer PtSSe to the external electric fields E and strains $ε_{b}$ were studied by focusing on the change of electronic structure and optical properties. The achieved results were analyzed in detail to provide additional information about PtSSe as well as its possible applications.

Section snippets

Computational method

The Janus monolayer PtSSe was modeled as CdI₂ structure with space group $P 31 m$ , the vacuum space between layers was set to be 20 Å to avoid interaction due to the periodicity of the unit cell along the c-axis. The first-principles calculation was performed via the Quantum Espresso suite [30]. The current study is mainly focused on investigating the change of PtSSe properties under external strains, and electric fields. Therefore, the low computational cost GGA-PBE method [31,32] was chosen to

Results and discussion

The optimized octahedral atomic structure of monolayer PtSSe is shown in Fig. 1(a), and the dynamical stability is confirmed by the phonon dispersion curves, as depicted in Fig. 1(d), where there are no soft modes found among the nine vibration modes. The Pt atoms are sandwiched between S and Se layers. Similar to PtS₂, and PtSe₂ monolayers, the PtSSe belongs to CdI₂ structure, where each Pt atom is strongly bonded to six surrounding chalcogens making octahedral coordination [36]. In comparison

Conclusion

In summary, we systematically investigated the electronic and optical properties of Janus monolayer PtSSe under the effect of biaxial strains $ε_{b}$ and electric fields E. The calculated DOS shows $s p^{3} d^{2}$ hybridization of Pt, S, and Se orbitals confirming the octahedral coordination between these constituent atoms. The band gap of equilibrium PtSSe has a reasonable value of 1.547 eV, which lies between 1.20 eV and 1.60 eV of PtS₂ and PtSe₂, respectively. The electric fields E cause constantly and

Authors’ contributions

Dat D. Vo: Conceptualization, Software, Investigation, Validation. Tuan V. Vu: Conceptualization, Supervision, Investigation, Validation, Writing - original draft, Writing - review & editing. Samah Al-Qaisi: Investigation, Software, Validation. Hien D. Tong: Investigation, Software, Validation. T. S. Le: Conceptualization, Methodology, Investigation, Writing - original draft. Chuong V. Nguyen: Conceptualization, Investigation, Validation. Huynh V. Phuc: Conceptualization, Investigation,

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Janus monolayer PtSSe under external electric field and strain: A first principles study on electronic structure and optical properties

Highlights

Abstract

Introduction

Section snippets

Computational method

Results and discussion

Conclusion

Authors’ contributions

Declaration of competing interest

Chem. Phys.

Appl. Surf. Sci.

Appl. Surf. Sci.

Chem. Phys.

Comput. Phys. Commun.

Mater. Res. Bull.

Adv. Quant. Chem.

Fundamentals of Photovoltaic Materials

Nature

Nature Energy

Adv. Ener. Mater.

J. Phys. Chem. Lett.

Nat. Chem.

Angew. Chem. Int. Ed.

Nat. Commun.

Small

Phys. Rev. B

Phys. Rev. B

ACS Nano

Nature