The mechanical design of hybrid graphene/boron nitride nanotransistors: Geometry and interface effects

doi:10.1016/j.ssc.2017.12.001

Solid State Communications

Volume 270, February 2018, Pages 82-86

https://doi.org/10.1016/j.ssc.2017.12.001 Get rights and content

Highlights

•
Three likely types (hexagonal, octagonal and decagonal) were found for the interface of sheet after relaxation.
•
Considering both mechanical and electrical performances, CB bonds at the interface results in a more promising results.
•
In some configurations, the mechanical rupture began from BN sheets.
•
Graphene sheets started to rupture due to the instability of the octagonal and decagonal shape of the interface.
•
Nitrogen atoms are better choice for bonding to carbon at the interface of the hybrid.

Abstract

From electronic point of view, graphene resembles a metal or semi-metal and boron nitride is a dielectric material (band gap = 5.9 eV). Hybridization of these two materials opens band gap of the graphene which has expansive applications in field-effect graphene transistors. In this paper, the effect of the interface structure on the mechanical properties of a hybrid graphene/boron nitride was studied. Young's modulus, fracture strain and tensile strength of the models were simulated. Three likely types (hexagonal, octagonal and decagonal) were found for the interface of hybrid sheet after relaxation. Although C single bond B bonds at the interface were indicated to result in more promising electrical properties, nitrogen atoms are better choice for bonding to carbon for mechanical applications.

Introduction

Graphene has no band gap and it is considered semiconductor [1], while boron nitride is a dielectric material (band gap = 5.9 eV) [2]. Hybridization of these materials opens band gap of the graphene. Based on the literature, the value for the band gap energy is related to the concentration of boron nitride in the hybrid and this variable band gap helps the hybrid adjust its properties [3].

Because of broad applications of thin films mechanical, thermal, optical and vibration properties are the most interesting, among others. Sadeghzadeh [4], [5], [6] investigated the effects of geometry, the strain rate and temperature on the mechanical and thermal properties of single- and multilayer graphene used for designing diodes and transistors. The effects of temperature and grain size on the mechanical properties of polycrystalline boron nitride in the presence of crack were also checked [7]. Mortazavi and Rémond [8] showed that Young's modulus of boron nitride nanosheets varies between 800 and 850 GPa for the different chirality directions.

There exist two important challenges in the production of graphene-based field-effect transistors (GFETs) [9], [10]. The first is related to on/off switching of such devices which is managed by putting an insulator as a dielectric in the transistors. The other challenge is associated to the interface area between graphene and the dielectric material [11]. Since boron nitride structure is very similar to that of graphene and hence, bonding between these two materials is easier than other combinations, boron nitride may be the best choice as a dielectric material in such devices [12].

Recent experimental and theoretical studies focused on the thermal, elastic, electronic and thermoelectric properties of the graphene/h-BN interface [13], [14], [15]. Despite all the previous works, there has not been enough study on the simulation of graphene/BN hybrids and their linking, interfaces other than the simulation performed by Ding et al. based on the density functional theory (DFT) [16]. They studied mechanical properties of graphene/BN hybrid in the presence of vacancies in the zigzag and armchair linking interfaces. Their results showed that the formation energy of the defective graphene/BN interface increased with increasing inflection angles. However, Young's modulus for all graphene/BN systems studied decreased with an increase in inflection angles. The intrinsic strength of the hybrid graphene/BN sheets was shown to be affected by the inflection angles, the type of interface connection, and the type of defects. They calculated Young's modulus, fracture strength and fracture strain of graphene/BN to be 744 GPa, 95 GPa and 0.17, respectively [17].

In the present study, mechanical properties of graphene/BN hybrid were studied via the molecular dynamics simulation. At first, mechanical properties of pure graphene and pure boron nitride were explored. Then, by bonding graphene and boron nitride in a way that boron nitride sheet was placed between two single-layer graphene sheets, mechanical properties of the hybrid were investigated. The outcome of the present research may be significant for understanding the mechanism of graphene-BN interconnection and the development of corresponding devices such as graphene-based diodes and transistors.

Section snippets

Theory and model

Simulation was performed by Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) [18]. The interaction between carbon atoms in graphene was described by Tersoff potential parameters reported by Lindsay et al. [19]. The interaction between nitrogen and boron was described by Tersoff potential parameters developed by Matsunga et al. [20].

All simulations were conducted in the equilibrium state (EMD), and began at the constant temperature and constant pressure (NPT ensemble) with

Mechanical properties of graphene/BN hybrid

In the simulation of the hybrid, two general conditions can be considered. The first is a configuration in which the edge-to-edge linking of the graphene and boron nitride repeats successively and in the second one, the BN sheet can be placed between two graphene ribbons. The latest case was depicted in Fig. 1.

Various interface arrangements

Bonding energies of C single bond C, NB, CN and CB are 607, 389, 770 and 448 kcal/mol, respectively [24]. The arrangements depicted in Fig. 2 are the most probable ones out of 36 possible arrangements

Conclusion

Hybridization of graphene and BN has intrigued many researchers, as this combination converts graphene from a semiconductor with band-gap zero to a semiconductor with band-gap non-zero can have many applications in graphene-based transistors. It was observed that if carbon atoms bond to nitrogen atoms at the interface, higher mechanical properties would be obtained. On the other hand, if carbon bonds to boron at the interface, the band gap energy would be increased and semiconducting behavior

References (26)

S. Sadeghzadeh et al.
A study of thermal conductivity in graphene diodes and transistors with intrinsic defects and subjected to metal impurities
Superlattices Microstruct.
(2016)
R. Abadi et al.
Investigation of crack propagation and existing notch on the mechanical response of polycrystalline hexagonal boron-nitride nanosheets
Comput. Mater. Sci.
(2017)
B. Mortazavi et al.
Investigation of tensile response and thermal conductivity of boron-nitride nanosheets using molecular dynamics simulations
Phys. E Low-dimensional Syst. Nanostruct.
(2012)
Q. Wu et al.
In situ chemical vapor deposition of graphene and hexagonal boron nitride heterostructures
Curr. Appl. Phys.
(2016)
S. Plimpton
Fast parallel algorithms for short-range molecular dynamics
J. Comput. Phys.
(1995)
S. Plimpton
Fast parallel algorithms for short-range molecular dynamics
J. Comput. Phys.
(1995)
B. Mortazavi et al.
Molecular dynamics study on the thermal conductivity and mechanical properties of boron doped graphene
Solid State Commun.
(2012)
B. Mortazavi et al.
Nitrogen doping and vacancy effects on the mechanical properties of graphene: a molecular dynamics study
Phys. Lett. A
(2012)
A.C. Neto et al.
The electronic properties of graphene
Rev. Mod. Phys.
(2009)
K. Watanabe et al.
Direct-bandgap properties and evidence for ultraviolet lasing of hexagonal boron nitride single crystal
Nat. Mater.
(2004)

C.A. Pelotenia et al.

Structural and Electronic Properties of Silicene/hexagonal-Boron Nitride/Graphene Hetero-structure

(2015)

S. Sadeghzadeh et al.

The mechanical design of graphene nanodiodes and nanotransistors: geometry, temperature and strain effects

RSC Adv.

(2016)

S. Sadeghzadeh et al.

Thermal conductivity of porous graphene nanoribbon implemented in mass detection operations

Modares Mech. Eng.

(2016)

Cited by (31)

Controllable toughness enhancement in graphene hybrid materials via planar twist-angle of carbon nanotubes
2024, Computational Materials Science
A controllable toughness enhancement in graphene hybrid materials via twist-angle of CNTs was first investigated. The mechanical properties, such as out-of-plane deformation, stress–strain curves, strain energy and interlayer loading transfer of Gr Hybrid model coupled by twist-angle CNTs were investigated by molecular dynamics simulations and nonlinear fracture mechanics theory. We find that these mechanical properties are sensitive to the existence of twist-angle CNTs in the Gr hybrid model. The crosslinking sites can be considered as structural defects. In addition, the CNTs exert a strengthening influence on the out-of-plane deformation, interlayer loading transfer as well as bond strain energies, thereby deflecting the crack paths of Gr Hybrid model under axial tension. Nevertheless, the existence of CNTs also triggers a reduction in the in-plane stress and the associated strain due to sp² + sp³ hybrid state. We find that this abnormal improvement in toughness derives from the localization of the stress fields arising from their out-of-plane displacements at the interface, resulting in the stress fields being localized only at the crosslinking sites. These interfacial toughening strategies can redistribute crack tip stress in a wider range, avoid stress concentration, and at the same time realize a lot of energy dissipation by promoting crack deflection, thus achieving overall high toughness.
Carbon nanotubes at the Graphene/hBN interface abnormally enhance its fracture toughness
2024, Diamond and Related Materials
Different from Van der Waals heterojunction, defects often appear at the interface of the planar heterostructures due to the low-dimensional structure characteristics. These defects lead to complex mechanical problems, and seriously affect application of planar heterostructures in flexible electronics devices. The most commonly used method to improve the toughness is to reduce/eliminate the interfacial structural defects. Using a defective Graphene/hBN interface, we show surprisingly that Carbon Nanotubes (CNTs) are able to enhance the toughness at the interface. It is found that interlayer stress transfer, bonding strain energies and energy release rate of the defective Graphene/hBN interface with CNTs are higher than those of free-defect Graphene/hBN interface, which is in strong contrast to the general view that interfacial defects reduce toughness. By combining the analysis of atomic mechanics and fracture mechanics theory, we find that the abnormal enhancement in interfacial toughness comes from the stress field localization arising from sp² + sp³ hybrid state and out-of-plane deformation at the interface. In addition, the stress field at the distal end of the simulated models gradually decays with the CNTs height, resulting in the stress fields to be controlled at the interface. This abnormal mechanism provides a new dimension for enhancing toughness in two-dimensional heterostructures.
Effect of the interface on mechanical and fracture properties of lateral graphene/hexagonal boron-nitride heterostructure: A molecular dynamics study
2023, Diamond and Related Materials
Graphene (Gr) and hexagonal boron-nitride (hBN) based heterostructures are a unique class of materials with unique mechanical and electronic properties. In the first of its kind, the present article employs the Tersoff potential-based molecular dynamics simulations to investigate the effect of interface on the mechanical and fracture properties of three different interface systems, namely hexagonal (6|6), pentagon-heptagon (5|7) and heart-shaped (HS). The results from this study indicate that the interface deteriorates the mechanical properties of Gr and hBN nanosheets, and the heterostructures have slightly reduced failure stress and strain as compared to pristine Gr or hBN nanosheets. However, fracture properties of interface systems exhibit monotonic decrease/increase or considerable improvement in their values depending upon the interface type and distance of crack from the interface. This deterioration or improvement in fracture properties may be attributed to the altered distribution of atomic stress per atom and the misalignment angle, which reduces the strain-induced change in critical bond length. Finally, these establish the mechanical robustness of these heterostructures, which may be very useful in designing Gr/hBN-based tailored nanocomposites.
Role of grain boundary and nanoholes in geometrical deformation and bonding energies of graphene/hexagonal boron nitride
2022, Diamond and Related Materials
The geometric deformation, bonding energies and mechanical properties of graphene-h-BN heterostructures (Gr-h-BN) under the coupling of external field (strain rate and temperature) and internal field (grain boundary (GBs) and nanoholes) were studied by using molecular dynamics and nonlinear mechanics. The results show that GBs and nanoholes will cause the Gr-BN-GBs configuration to deviate from the plane configuration, and produce a saddle shape with positive curvature and negative curvature, and its displacement field diverges with distance. In addition, the presence of GBs and nanoholes leads to a reduction in failure stress, Young's modulus and Von-mises stress. However, the presence of GBs and nanoholes also improves the bending rigidities of two dimensional (2D) materials. The adverse and strengthening effects induced by GBs and nanoholes are strongly dependent on temperature and strain rate. A full study of the built-in distorted stress field generated by the interaction of defects in 2D materials will help us to understand the physical mechanism of the relationship between structure and properties in low dimensions, and even design new applications.
Tailoring the effects of interface physics on the free vibration of graphene-boron nitride heterostructure
2022, Diamond and Related Materials
Citation Excerpt :
In this regard, the deformation of the nanostructure in decagonal interface geometry is more than the other two interfaces modes, which causes a significant deformation in the vibrational mode shapes of nanostructures with a decagonal interface, as was shown in Fig. 7(e), (g) and (h). The geometry of the octagonal interface is also approximately stable [5]; therefore, the effect of this instability is evident in the form of modes shown in Fig. 7(b) and (c). On the other hand, the bond energy (CN or CB bond) affects the mode shapes of nano-structure [5].
In electronics, inductive capacitors are made by two conductive plates, which are filled with non-conductive material between them. In this study, the graphene nano-sheet is utilized as capacitor plates and boron-nitride nano-sheet as its filler, and the effect of interface type of that of nanostructures on the vibrational properties of nanocapacitor has been studied using Molecular Dynamics (MD) approach. For this purpose, different interface types of graphene and boron-nitride nano-sheets are studied, including; CB66NC, CB68BC, CB88BC, CB108BC, CB1010NC, CN88NC, CN108NC, and CN1010NC. For the MD simulation, the LAMMPS software is implemented. The obtained results showed that CB66NC has the highest natural frequency and this is the most comfortable interface type to fabricate nano-capacitors, from a vibrational perspective. Furthermore, the CB66NC has the most stable because the hexagonal connection interface is more stable than the octagonal and decagonal, and the Carbon-Nitrogen bond energy which is used in the CB66NC interface type is higher than the Carbon-Boron bond energy.
Effect of Grain Boundaries’ Doping on the Mechanical Properties of Nitrogen-Doped Bicrystalline Graphene
2022, Diamond and Related Materials
Grain boundaries and doping play an important role in influencing the mechanical behaviour of materials. In this article, Tersoff potential based molecular dynamics simulations were employed to comprehensively investigate the effect of random N doping on the mechanical behaviour of pristine and bicrystalline graphene nanosheets. For bicrystalline nanosheets, three types of grain boundaries with high, transition and low tilt angles, were considered here. Each grain boundary model was doped as a whole nanosheet, only grain boundary area, and/or non-grain boundary area. Our results show that the configurations with doping of grain boundary area showed more deterioration in failure stress and failure strain values than the configurations with doping of the non-grain boundary area. Also, N doped pristine nanosheets and the configurations with non-grain boundary area doping showed a monotonic increase in Young's modulus while a monotonic decreasing-increasing trend was predicted for the rest of the configurations. These results show that the doping of the grain boundary area is more detrimental to the mechanical properties than the doping of the non-grain boundary area. Moreover, even after N doping, the high angle grain boundaries show higher strength as compared to the low angle grain boundaries.

View all citing articles on Scopus

View full text

CommunicationThe mechanical design of hybrid graphene/boron nitride nanotransistors: Geometry and interface effects

Highlights

Abstract

Introduction

Section snippets

Theory and model

Mechanical properties of graphene/BN hybrid

Various interface arrangements

Conclusion

Superlattices Microstruct.

Comput. Mater. Sci.

Phys. E Low-dimensional Syst. Nanostruct.

Curr. Appl. Phys.

J. Comput. Phys.

J. Comput. Phys.

Solid State Commun.

Phys. Lett. A

The electronic properties of graphene

Rev. Mod. Phys.

Direct-bandgap properties and evidence for ultraviolet lasing of hexagonal boron nitride single crystal

Nat. Mater.

Structural and Electronic Properties of Silicene/hexagonal-Boron Nitride/Graphene Hetero-structure

The mechanical design of graphene nanodiodes and nanotransistors: geometry, temperature and strain effects

RSC Adv.

Thermal conductivity of porous graphene nanoribbon implemented in mass detection operations

Modares Mech. Eng.

Communication
The mechanical design of hybrid graphene/boron nitride nanotransistors: Geometry and interface effects