Some properties of As-doped silicene nanoribbons: A DFT study

Some properties of As-doped silicene nanoribbons: A DFT study used the Density functional method (DFT) and VASP software to investigate some properties of the structure of silicene nanoribbons after doping asen. There are six structures studied including top, valley, ortho, meta, para and 100% configurations. This work creates new materials for application in science and technology in the future.

Some properties of As-doped silicene nanoribbons: A DFT study

Phan Thi Thuy Linh 1* , Nguyen Phuc Nhan 1 , Luu Thuy Trang 1 ,

Vuong Ngoc Anh Dai 1 , Hoang Van Ngoc 1

1 Insitute of Applied Technology, Thu Dau Mot University, Binh Duong province, Vietnam

* Coressponding: 1824401020012@student.tdmu.edu.vn

ABSTRACT As the counterpart of graphene, silicene becomes a hot spot in low-dimension

material application after being recently grown on different metal-lic surfaces Silicene has a low bumpy hexagonal lattice structure with sp 2 /sp 3 mixed orbital hybridization in Si-Si bonds Limiting the quantum size of silicene is a simple and efficient method to extend the bandgap for silicene while keeping the low undulation honeycomb lattice The finite size limitation of 2D silicene can produce 1D silicene nanoribbons (SiNR) This study used the Density functional method (DFT) and VASP software to investigate some properties of the structure of silicene nanoribbons after doping asen There are six structures studied including top, valley, ortho, meta, para and 100% configurations This work creates new materials for application in science and technology in the future

KEYWORDS: Silicene nanoribbons, As-doped silicene, doped structure, doping configurations

1 Introduction

A new era of low-dimensional materials science has been ushered in since two-dimensional monolayer (2D) graphite structures were successfully synthesized by Greim and Novoselov by mechanical analysis in 2004 [1-3] This first 2D monolayer graphite system is widely known as graphene Graphene is made up of hybridized carbon (C) atoms on sp2 orbitals and arranged in a highly symmetric planar hexagonal lattice [4] The honeycomb lattice structure of graphene can

be extended to produce different C allotropes, where graphene can be stacked to form 3D graphite [5], curled to form nano carbon (1D) [6], was cut to form 1D nano carbon [7] and 3D bent to form a 0D fullerene bridge structure [8] The mechanism of orbital hybridization in graphene is that the C-(2s, 2px, and 2py) are hybridized to form stable bonds to form a planar 2D structure, and the C-2pz orbitals remain in the state freely form weak π bonds along the z-direction This demonstrates that the σ and π bonds in graphene are clearly separated, with the π orbitals mainly contributing to the Dirac cone structure in the low energy region near the Fermi level [9] π-conjugation in the wide energy range of graphene produces many new physical properties that have been of interest in many recent studies [10] To date, graphene has been used

in various high-performance applications However, the zero frequency band of graphene limits the application potential of graphene for nano-electronic applications To overcome the unfavorable properties of graphene, various methods have been used to widen the bandgap in graphene including surface functionalization [11], atomic doping [12], mechanical strain [13], layered configuration [14], finite-size limitation [15], defect generation [16], and applied external

electric field [17] After graphene, much research effort has been focused on graphene-like monoatomic 2D materials such as silicene [18], germanene [19], stanene [20], phosphorene [21], antimonide [22], Where silicene, a 2D graphene-like structure, is made up of silicon atoms arranged in a bumpy honeycomb lattice structure Silience possesses many new physical properties such as graphene [23]; however, silicene exhibits better compatibility in silicon element-based electronic devices than graphene, so silicene has attracted much research to deploy its potential for practical applications [24] Unlike graphene, silicene can only be synthesized through bottom-up epitaxial growing methods because silicon atoms do not have a 3D layered structure like graphite The most common method for synthesizing silicene monolayers is the deposition of silicon atoms on metal substrates [25-27] The successful experimental synthesis of silicene monolayers provided experimental evidence for the theoretical predictions of the existence of silicene in 1994 [28] To date, silicene has been deployed in many applications including room-temperature field-effect transistors (FETs) [29], gas sensors [30], and batteries [31]

However, the very small bandgap energy of silicene has shown many disadvantages to deploying silicene in electronic devices [32] Therefore, a lot of research has been done to extend the bandgap for silicene including chemical change [33], quantum limit [34], layered configuration [35], mechanical strains study [36], and apply to external schools [37] Among these methods, limiting the quantum size of silicene is a simple and effective method to extend the bandgap for silicene while keeping the low undulation honeycomb lattice The finite size limitation of 2D silicene can produce 1D silicene nano bands (SiNR) with the armchair edge (ASiNR) and zigzag (ZSiNR) forms [38] SiNR with enhanced bandgap energy can completely overcome the main obstacle of silicene for electronic devices [39] Experimentally, SiNR has been successfully synthesized from both top-down and bottom-up methods The top-down method is to cut 2D silicene sheets to form 1D nano silicene [40], while the bottom-up method is

to epitaxially grow 1D nano silicene on metal substrates or insulating thin films [41] SiNRs with their outstanding novel physical properties and their good compatibility in silicon-based electronic devices have attracted much interest in the scientific community recently [42] On the other hand, various applications require materials with more diverse physical properties such as large bandgap energies for semiconductors or optoelectronic applications

Therefore, diversifying the essential physical properties of 1D silicene nanoribbons to suit various applications is an important issue for science and technology Various methods have been used to diversify the essential physical properties of 1D silicene nanoribbons including chemical doping [43], passivation of edges [44], layered configurations [43], passivation [44], layered configuration [45], creating lattice defects [46], applying external fields [47] and forming heterostructures; Among these methods, the doping method is currently receiving a lot of attention from researchers both at home and abroad Therefore, we focus on studying some properties of Silence Nanoribbons when doped with As in the hope of creating new materials for application in science and engineering

2 Research Methods

In this work, we use density functional theory (DFT) to study and VASP software to simulate materials.Density functional theory (DFT) is a theory used to describe the properties of electron systems in atoms, molecules, solids, within the framework of quantum theory In this theory, the properties of the N-electron system are expressed as a function of the electron density of the entire system (which is a function of 3 spatial coordinate variables) instead of a wave function (which is a function of 3N spatial coordinate variables) Therefore, density function theory has a great advantage (and is currently the most used) in computing the physical properties for

particular systems from the very basic equations of quantum physics death

VASP (Vienna Ab Initio Simulation Packages): is a computer program for simulating materials

at atomic size First, VASP was developed by Mike Payne (MIT) The VASP was then brought

by Jurgen Hafner to the University of Vienna in Austria in 1989 The main program of VASP is written by Jurgen Furthmuller Jurgen Furthmuller and Georg Kresse joined Institut fur Materialphysik in 1993 Currently, VASP is being developed by Georg Kresse, recent additions include the development of methods commonly used in molecular quantum chemistry to periodic systems VASP has been used by more than 1400 research groups on the basis of a license agreement with the University of Vienna

3 Results and Discussions

3.1 Doped configurations

Fig 1a shows the pristine undoped configuration of a silicene nanoribbons unit cell; Fig 1b 1c in the order of top and valley structures with only 1 doped atom; Fig 1d 1e 1f in order the meta, ortho, and para structures all have 2 doped atoms; Fig 1g is a 100% configuration with 6 doped atoms

Table 1 The formation energy of the doping configurations Systems E0t(eV) E0p(eV) E0Si (eV) E0As(eV) ΔEf

Ortho -70.218542 -69.408218 -0.1353442

-0.09662854

-0.88775532

Meta -69.795159 -69.408218 -0.1353442

-0.09662854

-0.46437232

Para -69.991258 -69.408218 -0.1353442

-0.09662854

-0.66047132

100% -70.866743 -69.408218 -0.1353442

-0.09662854

-1.69081896

Top -69.866698 -69.408218 -0.1353442

-0.09662854

-0.49719566

Valley -69.783293 -69.408218 -0.1353442

-0.09662854

-0.41379066

The formation energy [48]: ΔEf = Et – Ep + n*ESi – n*EAs (1)

E0t is the energy of the doping system; E0p is the energy of the pristine system; E0si is the energy of the free Si atom; E0As is the energy of the free As atom; ΔEf is the formation energy of the doping configurations The 100% configuration gives the smallest formation energy, so this

is the most stable and optimal configuration

Fig 1 Top view of the configurations of silicene nanoribbons when doped with asen

(a) pristine ; (b) top; (c) valley; (d) meta; (e) ortho; (f) para; (g) 100%

Fig 2 Side view of the configurations of silicene nanoribbons when doped with asen

(a) pristine ; (b) top; (c) valley; (d) meta; (e) ortho; (f) para; (g) 100%

Fig 2 shows side views of the pristine, top, valley, meta, ortho, para, and 100% configurations Looking at the image, we can see the warping of silicene nanoribbons before and after doping

3.2 Energy band structure and state density

Fig 3(a) show the original configuration of silicene nanoribbons has a band gap of 0.4eV and this is a semiconductor Fig 3(b) show after doping an As atom for silicene nanoribbons, the top configuration has no band gap because the fermium-level cutting energy bands go from the valence band to the conduction band, so this is a semi-metallic structure

Fig 4(a) show after doping an As atom for silicene nanoribbons, the valley configuration has

no bandgap because the fermium-level shear bands go from the valence band to the conduction band, so it is a semi-metallic structure And the meta configuration after doping two As atoms shows a bandgap of 0.44eV, so this is a semiconductor Compared with pristine configuration, the bandgap is wider than 0.04eV, so the meta configuration can be applied in semiconductor devices flexibly Fig 4(b) show after doping an As atom for silicene nanoribbons, the valley configuration has no band gap because the fermium-level shear bands go from the valence band

to the conduction band, so it is a semi-metallic structure And the meta configuration after doping two As atoms shows a bandgap of 0.44eV, so this is a semiconductor Compared with pristine configuration, the bandgap is wider than 0.04eV, so the meta configuration can be applied in semiconductor devices flexibly

Fig 3 Energy band structure (left), state density (right) of the pristine configuration (a)

and top configuration (b)

Fig 4 Energy band structure (left), state density (right) of the valley configuration (a)

and meta configuration (b)

Fig 5 Energy band structure (left), state density (right) of the ortho configuration (a)

and para configuration (b) Fig 5 show after doping two As atoms for silicene nanoribbons, the ortho and para configurations are both semiconductors when the ortho configuration has a bandgap of 0.34eV narrower than the pristine configuration of 0.07eV; The para configuration has a bandgap of 0.91eV and is wider than the pristine configuration of 0.51eV, so the para configuration can be applied very well in flexible semiconductor devices

Fig 6 Energy band structure (left), state density (right) of the 100% configuration (a) and the

contribution of Si(s), Si(p) partial states of the pristine configuration (b)

Fig 6(a) show after doping six As atoms for silicene nanoribbons, the 100% configuration has

a zero band gap, which is a semiconductor Around the Fermi level is the most concentrated states Fig 6(b) show the blue line is the Si(s) states of the silicon atom, and the red line corresponds to the Si(p) states of the silicon atom Si(s) is located at the bottom of the valence band and the top of the conduction band, while the Si(p) states are concentrated mainly at the top

of the valence band and the bottom of the conduction band (around the Fermi level) The peak of the highest state (p) of the pristine configuration corresponds to an energy level of ~ -1.8eV The peak of the highest Si(s) state of the pristine configuration corresponds to an energy level of ~-9eV

Fig 7 The contribution of Si(s), Si(p) partial states of the top configuration (a)

and valley configuration (b)

Fig 7(a), the peak of the highest Si(p) state of the top configuration corresponds to an energy level of ~-2.6eV, shifting 0.8eV in the negative direction relative to the pristine configuration The peak of the highest Si(s) state of the top configuration corresponds to an energy level of

~-10eV, shifting 1eV in the negative direction compared to the pristine configuration For Fig 7(b) the peak of the highest Si(p) state of the valley corresponds to an energy of ~-2.5eV, shifting 0.7eV in the negative direction relative to the pristine configuration The peak of the highest Si(s) state of the valley corresponds to an energy level of ~-9.6eV, shifting 0.6eV in the negative direction relative to the pristine configuration

The contribution of the Si(p) state of the valley configuration in the formation of the energy band structure is the largest compared to the remaining configurations

Fig 8 The contribution of Si(s), Si(p) partial states of the meta configuration (a)

and ortho configuration (b)

For Fig 8(a), the peak of the highest Si(p) state of the meta configuration corresponds to an energy level of ~ -2.3eV, shifting 0.5eV in the negative direction compared to the pristine configuration The peak of the highest Si(s) state of the meta configuration corresponds to an energy level of ~-9.8eV, shifting 0.8eV in the negative direction compared to the pristine configuration For fig 8(b), the peak of the highest Si(p) state of the ortho configuration corresponds to an energy level of ~-2.3eV, shifting 0.5eV in the negative direction relative to the pristine configuration The peak of the highest Si(s) state of the ortho configuration corresponds

to an energy level of ~-9.1eV, shifting 0.1eV in the negative direction compared to the pristine configuration

Fig 9 The contribution of Si(s), Si(p) partial states of the para configuration (a)

and 100% configuration (b) For Fig 9(a), the peak of the highest Si(p) state of the para configuration corresponds to an energy level of ~-2.8eV, shifting 1eV in the negative direction relative to the pristine configuration The peak of the highest Si(s) state of the para configuration corresponds to an energy level of ~-9eV, which is unchanged from the pristine configuration For Fig 9(b), the peak of the highest Si(p) state of the 100% configuration corresponds to an energy level of ~ -2.6eV, shifting 0.8eV in the negative direction relative to the pristine configuration The peak of the highest Si(s) state of the 100% configuration corresponds to an energy level of ~ -8.9eV, shifting 0.1eV towards the positive direction compared to the pristine configuration

The contribution of the Si(s) state of the para configuration in the formation of the energy band structure is the largest compared to the remaining configurations

Fig 10 The contribution of As(s), As(p) partial states of the top configuration (a)

and valley configuration (b) For Fig 10(a), the peak of the highest As(p) state of the top configuration corresponds to an energy level of ~ -3.5eV The peak of the highest As(s) state of the top configuration corresponds

to an energy level of ~-7.7eV For Fig 10(b), the peak of the highest As(p) state of the valley

configuration corresponds to an energy level of ~-3eV The peak of the highest Si(s) state of the valley configuration corresponds to an energy level of ~-7.8eV

Fig 11 The contribution of As(s), As(p) partial states of the meta configuration (a)

and ortho configuration (b) For Fig 11(a), the peak of the As(p) state is the highest of the meta-configuration with an energy level of ~-2.3eV The peak of the highest As(s) state of the meta-configuration corresponding to the energy level is ~-9.9eV For Fig 11(b), the peak of the highest As(p) state

of the ortho configuration corresponds to an energy level of ~-4.3eV The peak of the highest Si(s) state of the ortho configuration corresponds to an energy level of ~-8.8eV

For Fig 12(a) the peak of the highest As(p) state of the para configuration corresponds to an energy level of ~ -3.4eV The peak of the highest As(s) state of the para configuration corresponds to an energy level of ~-8.2eV For Fig 12(b) the peak of the highest As(p) state of the 100% configuration corresponds to an energy level of ~ -2.5eV The peak of the highest Si(s) state of the 100% configuration corresponds to an energy level of ~-5.2eV

The contribution of the As(p) state of the 100% configuration in the formation of the energy band structure is the largest compared to the remaining configurations