Uncovering the morphological effects of high-energy Ga+ focused ion beam milling on hBN single-photon emitter fabrication

Abstract

Many techniques to fabricate complex nanostructures and quantum emitting defects in low dimensional materials for quantum information technologies rely on the patterning capabilities of focused ion beam (FIB) systems. In particular, the ability to pattern arrays of bright and stable room temperature single-photon emitters (SPEs) in 2D wide-bandgap insulator hexagonal boron nitride (hBN) via high-energy heavy-ion FIB allows for direct placement of SPEs without structured substrates or polymer-reliant lithography steps. However, the process parameters needed to create hBN SPEs with this technique are dependent on the growth method of the material chosen. Moreover, morphological damage induced by high-energy heavy-ion exposure may further influence the successful creation of SPEs. In this work, we perform atomic force microscopy to characterize the surface morphology of hBN regions patterned by Ga+ FIB to create SPEs at a range of ion doses and find that material swelling, and not milling as expected, is most strongly and positively correlated with the onset of non-zero SPE yields. Furthermore, we simulate vacancy concentration profiles at each of the tested doses and propose a qualitative model to elucidate how Ga+ FIB patterning creates isolated SPEs that is consistent with observed optical and morphological characteristics and is dependent on the consideration of void nucleation and growth from vacancy clusters. Our results provide novel insight into the formation of hBN SPEs created by high-energy heavy-ion milling that can be leveraged for monolithic hBN photonic devices and could be applied to a wide range of low-dimensional solid-state SPE hosts.

Quantum Emitters in Hexagonal Boron Nitride

“…Xu et al produced SPE arrays by nano-indentationan AFM tip was used to fabricate arrays of holes in hBN (Figure c) . Ultrashort laser pulses (Figure d) have been used to fabricate visible SPEs ,− and ensembles of V B – centers, as have focused ion beams (Figure e,f). − The image in Figure e shows four 7×7 spot arrays fabricated in a flake of hBN by a Ga + beam . Here, the ion dose was high and ion beam sputtering produced a hole at each irradiation site.…”

“…The image shows four 7×7 spot arrays fabricated in a flake of hBN by a Ga + beam (scale bar = 5 μm). Reprinted with permission from ref . Copyright 2022 AIP.…”

“…29−31 The image in Figure 1e shows four 7×7 spot arrays fabricated in a flake of hBN by a Ga + beam. 30 Here, the ion dose was high and ion 23 (c) Nano-indentation using an AFM tip. 24 (d) Material breakdown using ultrashort laser pulses.…”

Selective Generation of Luminescent Defects in Hexagonal Boron Nitride

“…At the same time, optical and AFM images (Section S5, Supporting Information) clearly show that Ga implanted flakes were more damaged, consequence also of the concurrent sputtering during implantation. [54] Further discussion about the induced defects' nature is supported by Raman spectroscopy, which is an often-neglected tool for studying the optical properties of hBN defects, [55] as the main target in previous works was to check the emission wavelength and the single photon purity of hBN emitters. From the Raman spectra in Figure 1d-f, we can see that next to the intrinsic hBN phonon line at 1357 cm −1 , [56] all the implanted flakes showed a second broader peak centered at 1290 cm −1 (marked by the dashed line in Figure 1e-g), not present in our pristine material (Figure 1d).…”

Substrate-Induced Modulation of Quantum Emitter Properties in 2D Hexagonal Boron Nitride: Implications for Defect-Based Single Photon Sources in 2D Layers

“…In large part, this challenge arises because a significant number of intrinsic and extrinsic defects in hBN are deep level defects, resulting in a large and complex chemical phase space for defect-based QEs in hBN. Although some advances have been made in narrowing down candidate defects, ,,− their exact chemical nature is still debated. The difficulties in identifying the precise defects responsible for quantum emission are compounded by large variations in the defect properties, even if the defects are assumed to be the same species. , The observed variations in different properties, such as the brightness and emission frequencies, are often attributed to differing local strains at the defect sites.…”