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Point defects in crystalline materials can behave as artificial atoms, with optical and spin properties that enable their exploitation in quantum sensing. Compared to bulk materials, where point defects are generally located far from the surface (which improves their stability and minimizes surface-induced charge and spin noises), in 2D materials point defects lie necessarily close to the surface. This allows to place the sensing probes as close as possible to the test object, without necessarily degrading neither their stability nor their sensing performance. Among the plethora of 2D materials, hBN occupies an outstanding place, given its ubiquitous presence in almost every 2D-based device and heterostructure. Interestingly, hBN hosts several types of spin-defects; among them, the negatively-charged boron vacancy (VB-) is the most studied one because, even though it shows a relatively poor luminescence intensity, it works at 300K and its spin can be initialized and read-out.
In this work we will introduce the use of VB- in hBN for quantum strain sensing [1]. The measurement of optically-detected magnetic resonance (ODMR) on VB- ensembles enables to achieve sub-micrometre spatial resolution that, combined with micro-Raman spectroscopy, can provide a spatially-resolved map of in-plane and out-of-plane strain distribution [1]. Subsequently, we will address the important issue of enhancing photon emission from VB- defects. To achieve such an enhancement, we will implement metallic (gold-based) nanotrenches in which the coupled effect of gap-plasmons and enhanced extraction efficiency results in a ~ 40-times emission enhancement with respect to a bare gold surface, while being compatible with ODMR measurements [2]. Finally, we will discuss the possibility of substituting the conventional optical detection by an electrical one, promoting thereby hBN as a practical real-field quantum sensor [3].
[1] X. Lyu et al., Nano Lett. 22 (2022) 6553
[2] H. Cai et al., Nano Lett. 23 (2023) 4991
[3] S. Ru et al., to be published

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