Cathodoluminescence monitoring of quantum emitter activation in hexagonal boron nitride Sébastien Roux12 Clarisse Fournier1 Kenji Watanabe3 Takashi Taniguchi4 Jean-Pierre Hermier1 Julien

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Cathodoluminescence monitoring of quantum emitter activation in

hexagonal boron nitride

Sébastien Roux1,2,∗, Clarisse Fournier1,∗, Kenji Watanabe3, Takashi Taniguchi4, Jean-Pierre Hermier1, Julien

Barjon1, Aymeric Delteil1,†

1Université Paris-Saclay, UVSQ, CNRS, GEMaC, 78000, Versailles, France.

2Université Paris-Saclay, ONERA, CNRS, Laboratoire d’étude des microstructures, 92322, Châtillon,

France.

3Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044,

Japan

4International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044,

Japan

∗These two authors contributed equally.

†aymeric.delteil@uvsq.fr

(Dated: 18 October 2022)

The ability to locally activate or generate quantum emitters in two-dimensional materials is of major interest for the

realization of integrated quantum photonic devices. In particular, hexagonal boron nitride (hBN) has recently been

shown to allow a variety of techniques for obtaining quantum emitters at desired locations. Here, we use cathodolumi-

nescence (CL) to monitor in situ the local activation of color centers by an electron beam in hBN. We observe that the

CL signal saturates at a given surface dose, independently of the electron current density. Based on photoluminescence

and photon correlations, we show that the number of photoactive color centers is proportional to the CL signal, and

we estimate the maximum density of quantum emitters that can be generated by our technique. Our results provide

insights about the activation mechanism and could help to optimize the controlled generation of single photon sources

in hexagonal boron nitride.

The recent discovery of quantum emitters in two-

dimensional materials1–6 has unveiled new roads towards in-

tegrated quantum photonics. Among the most promising 2D

platforms, hBN has been shown to host a broad diversity

of high-quality color centers, emitting in various wavelength

ranges, from ultraviolet to near infrared6–10. A large frac-

tion of the current research effort is devoted towards control

of the position and wavelength of these single-photon emit-

ters (SPEs) for integration into photonic structures11–13. In

this context, we have previously demonstrated the possibil-

ity to locally activate a recently discovered family of quantum

emitters using an electron beam14. These blue-emitting color

centers – abbreviated B-centers in the following – have a re-

producible emission in the blue range, with very attractive op-

tical properties, such as a high stability and a remarkably low

inhomogeneous broadening of the SPE ensembles14–16. How-

ever, their microscopic structure, as well as the mechanisms at

the origin of their generation, remains to be understood. The

current understanding is that they stem from the modiﬁcation

of a complex that preexists in the as-grown hBN crystal15,16.

We therefore refer to the generation process as an activation.

Here, we demonstrate the possibility to measure the cathodo-

luminescence (CL) of the B-centers in-situ during the irradi-

ation process. We subsequently characterize the sample in

photoluminescence (PL) to estimate the number of optically

stable SPEs generated by our technique and therefore to infer

the efﬁciency of the method. We expect this work to provide

insights on the color center activation mechanism.

We exfoliated a hBN ﬂake grown using the high-pressure

high-temperature technique17 on a SiO2/Si substrate. Fig-

ure 1b shows a scanning electron microscope (SEM) image

of the ﬂake. Its thickness has been measured by atomic force

microscopy to be 160 nm. CL is measured by collecting the

sample emission by an aluminium parabolic mirror, with a

hole to accommodate for the electron beam (ﬁgure 1a). The

bare CL spectrum of the ﬂake is shown on ﬁgure 1b, where

the free exciton can be observed at 215 nm, as well as three

peaks around 305 nm often attributed to emission from car-

bon defects18. The presence of this sub-bandgap emission has

recently been identiﬁed as a prerequisite for the generation of

B-centers in hBN15. No PL emission from B-centers is ob-

served prior to the irradiation process.

We have then irradiated the hBN crystal using a defocused

electron beam of 1 µm diameter in a SEM. The irradiation

conditions are kept constant during the whole process, with

a voltage of 15 kV and a current of 9 nA. We continuously

recorded the CL spectra during the irradiation, using a long-

pass ﬁlter to eliminate the second order diffraction of the ex-

citon luminescence. Figure 2a shows the CL spectra taken

at time intervals of 3 s. The emergence of the typical B-

center emission peaks can be clearly observed. Their room-

temperature spectra are composed of a zero-phonon-line at

440 nm and a red-shifted optical phonon replica ∼160 meV

away. Figure 2b shows the integrated intensity as a function

of time. After a stark linear increase, the emission rapidly

reaches a plateau, which we attribute to saturation of the SPE

activation.

We repeated the experiment at various positions on the crys-

tal while varying the beam diameter between 170 nm and

7.5 µm. The voltage and current are kept identical – there-

fore the current density varies by more than three orders of

magnitude. Figure 2c shows the CL intensity as a function of

the dose per unit area for four irradiation spots. Despite some

slight variations between the different irradiations, it can be

seen that the CL signal follows the same general trend, with a

linear increase for surface doses smaller than ∼1013 e·µm−2

arXiv:2210.05028v1 [physics.app-ph] 10 Oct 2022

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CathodoluminescencemonitoringofquantumemitteractivationinhexagonalboronnitrideSébastienRoux1;2;,ClarisseFournier1;,KenjiWatanabe3,TakashiTaniguchi4,Jean-PierreHermier1,JulienBarjon1,AymericDelteil1;1UniversitéParis-Saclay,UVSQ,CNRS,GEMaC,78000,Versailles,France.2UniversitéParis-Saclay,ONERA,CNRS,...

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Cathodoluminescence monitoring of quantum emitter activation in hexagonal boron nitride Sébastien Roux12 Clarisse Fournier1 Kenji Watanabe3 Takashi Taniguchi4 Jean-Pierre Hermier1 Julien

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