Finally, we demonstrate an approach to tune the bubble geometry and optical properties by utilizing decomposition of the trapped material via electron beam irradiation. We observe a strong phonon-coupled luminescence from the hBN bubble regions and discuss its origin and spatial variation.
These results provide insights into the bubble geometry as well as the thickness-dependent bending rigidity of vdW multilayers, an important parameter for strain engineering.
Moreover, single photon emitters attributed to structural defects have been observed in hBN multilayers in a wide spectral range 23, 24.īy combining experimental measurements and theoretical modeling, we show that bubbles formed by bending of vdW multilayers exhibit radius- and thickness-dependent geometry and strain across the bubble, unlike the constant values seen in the case of monolayers. The optical emission of hBN can be further enhanced and systematically tuned by the twist angle between two stacked multilayers as a result of moiré superlattice effects 15. Importantly for applications, hBN emits strong near-band edge emission with large excitonic binding energy 19, 21 its intensity increases with hBN thickness, in contrast to TMDs that are luminescent only in the monolayer limit 22. We focus on hBN as a promising material for optoelectronic and quantum optics applications because it exhibits rich optical properties in the ultraviolet region at room temperature 15, 19 with a large band gap of approximately 6 eV 20. Here, we study the mechanical behavior of bubbles between stacked multilayers of hexagonal boron nitride (hBN) that we find show a strong localized optical emission. Strain engineering of vdW multilayers should present new opportunities in optoelectronics since multilayers of vdW materials exhibit robust optical performance 15, 16, 17, their bending is different from that seen in a monolayer or in classical plate theory 18, and multilayers circumvent issues related to exfoliation and manipulation of monolayers. However, the use of bubbles and induced strain to modify optical properties has so far been limited to monolayers. For optoelectronics and photonics, bubbles in monolayer transition metal dichalcogenides (TMDs) can serve as strain-induced local emitters 13 and optical cavities 14. Furthermore, bubbles between non-permeable graphene membranes have been used to trap material for liquid cell electron microscopy applications 12. For example, the ability to trap materials under extremely high pressure inside bubbles leads to unusual phenomena such as nano-confined hydrophobic ice 7 or chemical reactions that would not occur under ambient conditions 11. Potential applications of bubbles in vdW heterostructures have been recently reported due to their unique structure, the resulting strain, and the pressure in the bubble (vdW pressure) 9, 10. During the stacking process, vdW forces squeeze out and trap a material, such as hydrocarbons 3, 4, 5, air 6, or water 7, 8, adsorbed on the surface resulting in formation of bubbles at the interface between the stacked layers. A unique approach to understand the role of mechanical deformation on optoelectronic properties of vdW materials is to take advantage of the bubbles that are formed during the fabrication of vertical vdW heterostructures. Van der Waals (vdW) layered materials and their heterostructures exhibit extraordinary physical properties while readily allowing out-of-plane deformation, which is of great interest for flexible and conformal electronics 1, 2. Our results open a route to design and modulate microscopic-scale optical cavities via strain engineering in vdW materials, which we suggest will be relevant to both fundamental mechanical studies and optoelectronic applications. We then utilize the polymeric material confined within the bubbles to modify the bubble geometry under electron beam irradiation, resulting in strong luminescence and formation of optical standing waves. We use this behavior to elucidate radius- and thickness-dependent bubble geometry and the resulting strain across the bubble, from which we establish the thickness-dependent bending rigidity of hBN multilayers. Compared to bubbles in stacked monolayers, bubbles formed by stacking vdW multilayers show distinct mechanical behavior.
Here, we demonstrate strong and localized luminescence in the ultraviolet region from interface bubbles between stacked multilayers of hexagonal boron nitride (hBN). Extraordinary optoelectronic properties of van der Waals (vdW) heterostructures can be tuned via strain caused by mechanical deformation.
0 kommentar(er)
