Spatially Controlled Single Photon Emitters in hBN‐Capped WS₂ Domes

Abstract

Monolayers (MLs) of transition-metal dichalcogenides host efficient single-photon emitters (SPEs) usually associated to the presence of nanoscale mechanical deformations or strain. Large-scale spatial control of strain would enhance the scalability of such SPEs and allow for their incorporation into photonic structures. Here, the formation of regular arrays of strained hydrogen-filled one-layer-thick micro-domes obtained by H-ion irradiation and lithography-based approaches is reported. Typically, the H 2 liquefaction for temperatures T<32 K causes the disappearance of the domes preventing their use as potential SPEs. Here, it is shown that the dome deflation can be overcome by hBN heterostructuring, that is by depositing thin hBN flakes on the domes. This leads to the preservation of the dome structure at all temperatures, as found by micro-Raman and micro-photoluminescence (μ-PL) studies. Eventually, spatially controlled hBN-capped WS 2 domes show the appearance, at 5 K, of intense emission lines originating from localized excitons, which are shown to behave as quantum emitters here. The electronic properties of the emitters are addressed by time-resolved μ-PL yielding time decays of 1-10 ns, and by magneto-μ-PL measurements. The latter provide an exciton magnetic moment a factor of two larger than the value observed in planar strain-free MLs.

One (photon), two(-dimensional crystals), a lot (of potential): a quick snapshot of a rapidly evolving field

“…Indeed, the presence of emitters in nanobubbles formed during the deposition process of WSe 2 MLs due to the trapping of contaminants [77] seems to be in agreement with the identification-via near-field PL measurements performed at RT [78]-of localised, deeply bound excitons at the edge of WSe 2 nanobubbles, and with theoretical calculations suggesting the presence of points of high strain at the nanobubble periphery, due to atomic-scale wrinkling [79]. Moving to the micrometric scale, however, SPEs were also consistently observed on the edges of the hydrogen-filled bubbles that can be formed, in a controlled manner, on the surface of bulk TMDC crystals irradiated with low energy (∼20 eV) hydrogen ions (see figures 1(e) and (f)) [44]. This is partially at odds with the idea that a sharp, nm-scale strain gradient is required for the creation of QEs, given that microbubbles feature a gradual increase of the strain tensor moving from the bubble's edge towards its apex, where the highest strain is reached and where excitons would be expected to funnel [39].…”

“…QEs hosted by TMDCs emit, for the most part, in the visible range (620-780 nm), with the notable exception of MoTe 2 , which features emitters in the telecom range 1080-1550 nm [23]; hBN QEs, on the other hand, span the whole spectrum from UV to NIR. A plethora of methods have been employed to create defects in the crystalline structure of these materials, while their activation relies on annealing at high temperatures, in the case of hBN [20], and on the creation of strained configurations for W-based TMDCs, whether by deposition on etched substrates acting as stressors [33], by indentation with AFM tips [55], or by pressure-induced bulging of the crystal surface [44]. The strategies for the creation/activation of the emitters, as well as their main properties, have been the object of extensive discussions in sections 2 and 3.…”

“…The intimate link between the appearance of these emitters and strain appeared evident from the very beginning, since the SPEs were shown to form preferentially at the flakes' edges [41] or at the border of patterned micrometric holes etched in a silicon substrate [42]. In the following years, emissions from localised excitons were verified also for WS 2 [43,44], MoSe 2 [45][46][47], MoS 2 [48], for the WSSe alloy [49], and for MoTe 2 in the telecom wavelength range [23].…”

Solid‐State Single‐Photon Sources: Recent Advances for Novel Quantum Materials

“…[184] Another important strategy to deterministically induce local strain is the formation of nanobubbles under the topmost monolayer of WSe 2 bulk through hydrogen implantation. [185] The largest amount of strain is then found at the rim of the bubble, upon hBN capping these bubbles are also cryo-compatible.…”

Viscous fingering instabilities in spontaneously formed blisters of MoS2 multilayers

“…transition metal dichalcogenides -TMDCs) act as 'single photon emitters'. [18][19][20][21] In addition, the blisters show remarkable photo-detection capability as the excitons have a longer lifetime against recombination due to the funneling effect. 22 A blister test can be used to determine the intrinsic mechanical properties of a 2D material as well as its interfacial adhesion strength with a given substrate.…”