Abstract:By investigating the optoelectronic properties of prototypical graphene/hexagonal boron nitride (h-BN) heterostructures, we demonstrate how a nanostructured combination of these materials can lead to a dramatic enhancement of light-matter interaction and give rise to unique excitations. In the framework of ab initio many-body perturbation theory, we show that such heterostructures absorb light over a broad frequency range, from the near-infrared to the ultraviolet (UV), and that each spectral region is charact… Show more
“…In fact, the heterostructures consisting of single layer silicene and graphene sandwiched between h-BN bilayers also show a band gap opening and high carrier mobility while the silicene and graphene layer remain nearly unaffected by h-BN 54 , 55 . In addition, the periodic heterostructures with a graphene sheet sandwiched between four h-BN layers also show similar phenomenon 56 . Figure 6 Density of states for structure III of the stanene/h-BN heterobilayer.…”
The structural and electronic properties of stanene/hexagonal boron nitride (Sn/h-BN) heterobilayer with different stacking patterns are studied using first principle calculations within the framework of density functional theory. The electronic band structure of different stacking patterns shows a direct band gap of ~30 meV at Dirac point and at the Fermi energy level with a Fermi velocity of ~0.53 × 106 ms−1. Linear Dirac dispersion relation is nearly preserved and the calculated small effective mass in the order of 0.05mo suggests high carrier mobility. Density of states and space charge distribution of the considered heterobilayer structure near the conduction and the valence bands show unsaturated π orbitals of stanene. This indicates that electronic carriers are expected to transport only through the stanene layer, thereby leaving the h-BN layer to be a good choice as a substrate for the heterostructure. We have also explored the modulation of the obtained band gap by changing the interlayer spacing between h-BN and Sn layer and by applying tensile biaxial strain to the heterostructure. A small increase in the band gap is observed with the increasing percentage of strain. Our results suggest that, Sn/h-BN heterostructure can be a potential candidate for Sn-based nanoelectronics and spintronic applications.
“…In fact, the heterostructures consisting of single layer silicene and graphene sandwiched between h-BN bilayers also show a band gap opening and high carrier mobility while the silicene and graphene layer remain nearly unaffected by h-BN 54 , 55 . In addition, the periodic heterostructures with a graphene sheet sandwiched between four h-BN layers also show similar phenomenon 56 . Figure 6 Density of states for structure III of the stanene/h-BN heterobilayer.…”
The structural and electronic properties of stanene/hexagonal boron nitride (Sn/h-BN) heterobilayer with different stacking patterns are studied using first principle calculations within the framework of density functional theory. The electronic band structure of different stacking patterns shows a direct band gap of ~30 meV at Dirac point and at the Fermi energy level with a Fermi velocity of ~0.53 × 106 ms−1. Linear Dirac dispersion relation is nearly preserved and the calculated small effective mass in the order of 0.05mo suggests high carrier mobility. Density of states and space charge distribution of the considered heterobilayer structure near the conduction and the valence bands show unsaturated π orbitals of stanene. This indicates that electronic carriers are expected to transport only through the stanene layer, thereby leaving the h-BN layer to be a good choice as a substrate for the heterostructure. We have also explored the modulation of the obtained band gap by changing the interlayer spacing between h-BN and Sn layer and by applying tensile biaxial strain to the heterostructure. A small increase in the band gap is observed with the increasing percentage of strain. Our results suggest that, Sn/h-BN heterostructure can be a potential candidate for Sn-based nanoelectronics and spintronic applications.
“…These complications hold for arbitrary van der Waals heterostructures, which present growing interest due to their adjustable electronic properties [26][27][28][29][30] and potential applications [31][32][33][34]. In order to predict their dielectric properties, much work has been dedicated to rigorous and accurate calculations using time-dependent density-functional theory (TDDFT) and many-body perturbation theory (see Refs.…”
High-energy electronic excitations of graphene and MoS 2 heterostructures are investigated by momentumresolved electron energy-loss spectroscopy in the range of 1 to 35 eV. The interplay of excitations on different sheets is understood in terms of long-range Coulomb interactions and is simulated using a combination of ab initio and dielectric model calculations. In particular, the layered electron-gas model is extended to thick layers by including the spatial dependence of the dielectric response in the direction perpendicular to the sheets. We apply this model to the case of graphene/MoS 2 /graphene heterostructures and discuss the possibility of extracting the dielectric properties of an encapsulated monolayer from measurements of the entire stack.
“…Combining different 2D systems, quantum confinement effects allow for tailoring their opto-electronic properties [16][17][18]. This not only concerns level alignment at the interface [19][20][21][22][23][24][25][26] but also the way the system interacts with light, i.e., quantum efficiency, as well as the character and spatial distribution of electron-hole (e-h) pairs [14,15,[27][28][29][30][31][32].In this Rapid Communication, we show that the nature and dimensionality of excitons can also be governed in a single vdW-bound bulk material, taking h-BN as an example. This seems surprising at a first glance as e-h pairs in this material have been found to exhibit basically the same character and extension in bulk [6][7][8], monolayers [10], as well as in interfaces with graphene [14].…”
With the example of hexagonal boron nitride, we demonstrate how the character of electron-hole (e-h) pairs in van der Waals bound low-dimensional systems is driven by layer stacking. Four types of excitons appear, with either a two-or three-dimensional spatial extension. Electron and hole distributions are either overlapping or exhibit a charge-transfer nature. We discuss under which structural and symmetry conditions they appear and they are either dark or bright. This analysis provides the key elements to identify, predict, and possibly tailor the character of e-h pairs in van der Waals materials.Two-dimensional (2D) systems and layered weaklybound structures thereof are considered the materials of the 21st century. Their wealth of intriguing properties is widely explored from a fundamental scientific point of view but also in view of a plethora of possible applications [1,2]. Hexagonal boron nitride (h-BN) is one of these materials, consisting of covalently bound sheets that are held together by van der Waals (vdW) forces [3]. h-BN is a wide-gap semiconductor, exhibiting pronounced excitonic effects in its optical excitations that are present irrespective of the material's dimensionality [4][5][6][7][8][9][10][11]. Owing to the flat geometry of its in-plane hexagonal lattice, h-BN is often chosen as a building block in vdW heterostructures [12][13][14][15]. Combining different 2D systems, quantum confinement effects allow for tailoring their opto-electronic properties [16][17][18]. This not only concerns level alignment at the interface [19][20][21][22][23][24][25][26] but also the way the system interacts with light, i.e., quantum efficiency, as well as the character and spatial distribution of electron-hole (e-h) pairs [14,15,[27][28][29][30][31][32].In this Rapid Communication, we show that the nature and dimensionality of excitons can also be governed in a single vdW-bound bulk material, taking h-BN as an example. This seems surprising at a first glance as e-h pairs in this material have been found to exhibit basically the same character and extension in bulk [6][7][8], monolayers [10], as well as in interfaces with graphene [14]. Here we demonstrate how strongly stacking impacts the optical excitations of a vdW crystal at the absorption onset and beyond. By varying the arrangement of individual h-BN layers, we find in total four types of electron-hole pairs, of a two-dimensional, three-dimensional (3D), and charge-transfer character, and discuss their appearance by symmetry considerations. We focus on the five structures that are obtained by including four inequivalent atoms in the unit cell, allowing only a rigid translation by one bond length and/or exchanged positions between the two atomic species. We employ density-functional theory [33-37] and many-body perturbation theory (MBPT, including G 0 W 0 [38,39] and the Bethe-Salpeter equation [40][41][42][43]), implemented in the all-electron framework of the exciting code [44][45][46].Prototypes of the four kinds of excitations that can appear in h-BN ar...
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