# Contactless manufacturing of TERS-active AFM tips by bipolar electrodeposition

Yuhan Huang, David Talaga, Gerardo Salinas, Patrick Garrigue, Gary S Cooney, Stéphane Reculusa, Alexander Kuhn, Sébastien Bonhommeau, Laurent Bouffier

► To cite this version:

Yuhan Huang, David Talaga, Gerardo Salinas, Patrick Garrigue, Gary S Cooney, et al., Contactless manufacturing of TERS-active AFM tips by bipolar electrodeposition. Nanoscale, 2025, 17 (3), pp. 1411-1416. 10.1039/d4nr03068k. hal-04964368

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Distributed under a Creative Commons Attribution 4.0 International License
ARTICLE

Contactless manufacturing of TERS-active AFM tips by bipolar
electrodeposition

Received 00th January 20xx,
Accepted 00th January 20xx

DOI: 10.1039/x0xx00000x

Yuhan Huang,ª David Talaga,ª Gerardo Salinas,ª Patrick Garrigue,ª Gary S. Cooney,ª Stéphane Reculusa,ª Alexander Kuhn,ª Sébastien Bonhommeau*ª and Laurent Bouffier*ª

Tip-enhanced Raman spectroscopy (TERS) is a powerful technique for nanoscale chemical imaging. However, its worldwide expansion is still limited by the challenging fabrication of cheap, robust and efficient TERS tips as optical nanosources to amplify the Raman signal. An original method based on bipolar electrodeposition is described here to prepare gold-coated AFM cantilevers used as TERS tips. This wireless method is simple to implement, cost-effective, and allows for the parallel fabrication of several TERS tips with good reproducibility of the metal thickness and a relatively long lifetime. The TERS activity was confirmed by imaging graphene oxide flakes with high spatial resolution (below 10 nm). A promising yield of 64% was achieved for the fabrication of active TERS tips. Therefore, this method could pave the way for the development of new chemical routes for the preparation of TERS tips and other plasmonic nanostructures.

<table><tr><td>1</td><td>Introduction</td><td>28</td></tr><tr><td>2</td><td>Tip-enhanced Raman spectroscopy (TERS) has proved to be</td><td>29</td></tr><tr><td>3</td><td>powerful technique for nanoscale chemical and structural</td><td>30</td></tr><tr><td>4</td><td>imaging on various nanomaterials.<sup>1</sup> In TERS, a scanning probe</td><td>31</td></tr><tr><td>5</td><td>microscope (SPM), either an atomic force microscope (AFM)</td><td>32</td></tr><tr><td>6</td><td>a scanning tunnelling microscope (STM), is optically coupled</td><td>33</td></tr><tr><td>7</td><td>a Raman microscope. This cutting-edge system confers the</td><td>34</td></tr><tr><td>8</td><td>high spatial (lateral) resolution to the TERS technique by light</td><td>35</td></tr><tr><td>9</td><td>excitation of the localized surface plasmon resonance (LSPR)</td><td>36</td></tr><tr><td>10</td><td>the metal SPM probe. The global expansion of TERS as</td><td>37</td></tr><tr><td>11</td><td>common characterization technique is however facing the</td><td>38</td></tr><tr><td>12</td><td>major challenge of producing in a simple, cheap and reliable</td><td>39</td></tr><tr><td>13</td><td>way, TERS-active SPM probes (known as TERS tips). Many</td><td>40</td></tr><tr><td>14</td><td>fabrication methods have been proposed in the literature</td><td>41</td></tr><tr><td>15</td><td>fabricate TERS tips,<sup>2</sup> but there is no scientific consensus on the</td><td>42</td></tr><tr><td>16</td><td>ideal one so far. Micro- and nanofabrication methods are quite</td><td>43</td></tr><tr><td>17</td><td>efficient to manufacture them in a reproducible way, but they</td><td>44</td></tr><tr><td>18</td><td>are very expensive and require specific expertise. The</td><td>45</td></tr><tr><td>19</td><td>attachment or chemical coating of noble metal nanoparticles</td><td>46</td></tr><tr><td>20</td><td>on SPM probes is more cost-effective, but still requires</td><td>47</td></tr><tr><td>21</td><td>technical skills in colloidal chemistry to allow nanoparticles</td><td>48</td></tr><tr><td>22</td><td>be placed precisely at the probe tip apex. Physical vapor</td><td>49</td></tr><tr><td>23</td><td>deposition methods, such as thermal evaporation and</td><td>50</td></tr><tr><td>24</td><td>sputtering, are the most widespread techniques to fabricate</td><td>51</td></tr><tr><td>25</td><td>TERS tips by metallization of SPM probes. However, the</td><td>52</td></tr><tr><td>26</td><td>robustness and efficiency of the resulting probes can vary</td><td>53</td></tr><tr><td>27</td><td>greatly. Several companies also offer TERS tips, but the cost</td><td>54</td></tr><tr><td></td><td></td><td>55</td></tr><tr><td></td><td></td><td>56</td></tr><tr><td></td><td></td><td>57</td></tr><tr><td></td><td></td><td>58</td></tr><tr><td></td><td></td><td>59</td></tr><tr><td></td><td></td><td>60</td></tr></table>

rather prohibitive and their efficiency is quite variable too. With respect to the aforementioned preparation methods, electrochemistry is a promising alternative. It has several key advantages, such as the simplicity of the process, which does not require specific facilities such as the access to a clean room and/or expensive equipment. STM-TERS tips are often prepared by electrochemical etching of a silver or gold wire using a simple potential step or multiple pulses.<sup>3</sup> In contrast, AFM-TERS tips are manufactured by metallizing the AFM cantilever that is localized on a chip.<sup>4,5</sup> Experimentally, the electrochemical deposition of a thin metal layer can be performed inside a cost-effective homemade electrochemical cell comprising a set of electrodes that are connected to a power supply (i.e. typically a potentiostat or a galvanostat depending on whether the electrodeposition is enabled according to a potential step or with a controlled current). Unfortunately, these electrochemical approaches also have several drawbacks. In most cases, the electrodeposition at the nanoscale apex of an AFM probe has a poor reproducibility due the lack of control over key parameters, such as the immersion depth inside the electrolyte. Most importantly, although AFM probes are very fragile, the manufacturing of TERS tips requires a delicate handling of AFM cantilevers through a proper connection to the power supply, achieved by using a suitable holder, some copper tab or tin welding to an electrical wire. Irreversible damages to the tip can potentially occur at each step. In addition, the reproducibility of the electrodeposition process can be affected by tiny changes in the wetting proficiency inside the electrolyte, the exact positioning of the AFM chip with respect to the counter-electrode or the natural convection inside the electrochemical cell,<sup>5</sup> even though a reasonable reproducibility has been reported using pulsed electrodeposition.<sup>4</sup> Thus, there is still a

<footnote>ªUniv. Bordeaux, CNRS, Bordeaux INP, ISM, UMR 5255, F-33400 Talence, France.</footnote>

<footnote>E-mails: sebastien.bonhommeau@u-bordeaux.fr; laurent.bouffier@cnrs.fr.</footnote>

<footnote>Supplementary Information available: Experimental details, SEM characterization, EDX analysis, TERS spectra and TERS mapping. See DOI: 10.1039/x0xx00000x</footnote>
1 necessity to develop an affordable and reproducible method
2 accessible to a large number of users to fabricate TERS tips,
3 and especially AFM-TERS tips since AFM has broader areas of
4 application than STM.

5 Bipolar electrochemistry (BPE) is an unconventional
6 electrochemical approach offering the possibility to tackle such
7 a challenge. BPE takes place when a conducting or
8 semiconducting substrate is immersed inside an electrolyte
9 and subjected to an electric field.⁶ In this configuration, an
10 interfacial potential polarization is established along the
11 substrate enabling a driving force gradient with a maximum
12 polarization at both extremities. The anodic polarization is
13 obtained at the side facing the feeder cathode while a cathodic
14 pole is established at the edge in front of the driving anode.
15 (Figure 1a). The application of a sufficient electric field above
16 thermodynamic threshold value makes it possible to couple
17 Faradaic reactions across the substrate, which behaves like
18 so-called bipolar electrode. In other words, BPE is a contactless
19 method that allows wireless electrochemical processes to
20 performed. One key application of BPE is the fabrication of
21 dissymmetric particles,⁷ and surface gradients.⁸

22 In the past, BPE was already identified as a method of choice
23 for the preparation of surface-enhanced Raman spectroscopy
24 (SERS)-active substrates,⁹⁻¹¹ allowing for molecular sensing
25 provided that the LSPR of substrate metal nanoparticles
26 conveniently excited by laser light, like in TERS. An Ag-Au alloy
27 gradient was deposited on a stainless-steel substrate using BPE
28 prior to a post-modification by grafting a benzene thiol self-assembles
29 monolayer. Monitoring of the SERS response
30 alongside the bimetallic gradient allowed the determination of
31 the optimum alloy composition that maximized the signal
32 Moreover, by selecting another monolayer containing one
33 electroactive moiety such as quinone/hydroquinone redox
34 couple, SERS was also recorded under electrochemical control
35 along the bipolar electrode.¹¹ The use of electrochemical SERS
36 and BPE was found to be very appropriate for probing the local
37 potential distribution of solid-state nanopores.¹² The authors
38 demonstrated that the SERS signal from the redox-active NPs
39 Blue A dye was self-consistent with the variation of
40 polarizations on the gold nanopores. Finally, BPE fabrication
41 of a size gradient of truncated spherical Au nanovoids was
42 reported. The idea was to screen and identify the most
43 efficient SERS-active structure alongside the bipolar electrode
44 The highest enhancement was obtained for a particular
45 nanovoid dimension having a diameter of 260 nm.¹³ Once
46 again in this example, the key discovery was to use the
47 electrochemical driving force gradient alongside the bipolar
48 electrode in order to screen various electrodeposition
49 conditions.
50 Despite these previous reports on SERS applications, BPE has
51 never been employed for the electrochemical fabrication of
52 TERS tips. In this contribution, we will demonstrate the key
53 advantage of such a wireless approach to manufacture
54 multiple AFM-TERS tips with good reproducibility, not only
55 record TERS spectra but also to collect reliable TERS maps with
56 nanoscale spatial resolution.

<figure><img src="image_2.png" /></figure>

Experimental

**Pre-treatment of AFM chips.** Prior to metal deposition, n-doped

**Figure 1.** a) Diagram of a bipolar electrochemistry setup with the n-doped silicon AFM chip used as bipolar electrode (not to scale). The red and black electrodes are the driving cathode and anode, respectively. η<sub>a</sub> and η<sub>c</sub> indicate the anodic and cathodic overpotentials localized at the extremities of the bipolar electrode. SEM images recorded at various magnifications displaying a top view of the 3645 µm-long gold-coated chip (b), a tilted view of the end of a pristine cantilever (c), and the apex of the corresponding tip (d).

silicon AFM chips (ACCESS-FM, AppNano) were immersed for 2 min in 5% HF aqueous solution (prepared after dilution of a 48% v/v HF solution in water from Sigma-Aldrich, 99.99%). Subsequently, the chips were rinsed thoroughly with ultrapure (Milli-Q®) water and dried under a gentle N₂ gas flow.

**TERS tip preparation.** The freshly etched AFM chips were simply immersed in the plating electrolyte within the electrochemical cell, and placed parallel to each other but perpendicular to the two feeder electrodes, with the AFM cantilevers (and thus the AFM tips at their ends) facing the feeder anode. A 6.9 V/cm electric field was applied between the 2 feeder electrodes for 5 s to 15 s. Once the bipolar electrodeposition process was completed, the TERS tips were rinsed 3 times with Milli-Q® water and dried under a gentle N₂ gas flow. After preparation, the TERS tips were stored in Argon (99.9999% purity) until use for TERS experiments.

**TERS experiments.** TERS measurements were conducted using a side-illumination NanoRaman system (HR Evo Nano, HORIBA Scientific), which comprises an Omegascope atomic force microscope combined with a LabRAM HR Evolution Raman spectrometer. Linearly polarized laser light (633 nm, 170 µW) was used to irradiate the sample surface through a 100× objective (MITUTOYO, 0.7 NA). All TERS spectra were acquired using a 600 grooves/mm diffraction grating. All TERS maps were carried out in the hybrid contact mode developed by HORIBA (applied force ~1 nN). In this specific mode, the TERS tip is in contact with the sample surface only during the acquisition of the TERS signal. The sample probed by TERS was a test sample purchased from HORIBA which contained graphene oxide (GO) sheets and carbon nanotubes deposited on a gold-coated substrate. TERS spectra were slightly smoothened using the Savitzky-Golay algorithm and a baseline correction based on a 5th degree polynomial (LabSpec 6 software).
1 Scanning Electron Microscopy. A Tescan Vega 3 SEM equipped with a Bruker XFlash 630M energy dispersive X-ray (EDX) spectroscopy detector was used to perform SEM imaging at 58 mm working distance and 15 kV acceleration voltage, as well as the elemental analysis of AFM tip coatings. 60

6 7 Results and discussion 64

8 The principle of the developed BPE method is displayed in Figure 1a in the case of a single n-doped silicon AFM chip 65

9 9 Figure 1a in the case of a single n-doped silicon AFM chip 65 bipolar electrode, immersed inside the electrolyte and positioned in between two feeder electrodes. These later electrodes are commercially available platinum-coated glass slides separated by a 1.6 cm distance. The volume of the electrolyte is typically 2.5 mL. Notably, The AFM chip is directly immersed without any holder or fixation, a contactless setup that minimizes contamination risk from external supports during electrodeposition process. The AFM probe chip (length × width × thickness = 3400 µm × 1600 µm × 315 µm) carries 67 68 69 70 71 72 73 74

20 21 22 23 24 BPE. 74 During BPE, two electrochemical reactions are coupled and 75 take place at the two opposite sides of the bipolar electrode 76 under the influence of the applied electric field. Prior to BPE 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165

electric field of 6.9 V/cm (Figure 2b). These images clearly demonstrate that a thin gold layer was effectively deposited on the Si tip, as illustrated by the overlaid images displayed in Figure 2c. Interestingly, the value of the applied electric field is sufficient to coat with gold about 15% of the AFM chip, as shown in Figure 1b on which a ~ 500 µm-long metal deposit is clearly visible by optical contrast (shinny region on the right-hand side). Beyond this first proof-of-principle experiment, tuning the electric field strength should allow either the deposit to be concentrated at the extremity of the tip or, on the contrary, the zone of deposition to be extended over a

<figure><img src="image_3.png" /><figcaption>larger portion of the cantilever.</figcaption></figure>

<caption>Figure 2. SEM images of the Si tip apex (a) before gold electrodeposition, and (b) after gold electrodeposition (electric field: 6.9 V/cm; electrodeposition time:10 s), together with (c) their color-enhanced overlay.</caption>

A confirmation of the nature of the metal deposit was obtained by carrying out energy dispersive X-ray (EDX) analysis of two distinct zones at the two ends of an AFM chip (Figure S1a). In the absence of any visible deposit at the bottom of the AFM chip, only the signal assigned to Si was observed at 1.76 keV (Figure S1b). However, on the opposite side, the signal of gold pointing at 1.94 keV was clearly recorded on the tip cantilever, in addition to the Si contribution (Figure S1c).

The influence of the electrodeposition time was studied in order to demonstrate that the thickness of the gold layer can be readily controlled. Three AFM chips were coated with gold by applying an electric field of 6.9 V/cm for 5 s, 10 s and 15 s, respectively (Table S2). Their SEM characterization revealed that the amount of deposited gold is gradually increased with time. The thickness of the gold layer can be assessed from the apparent ROC of the TERS tip apex. The ROC measured for a 5 s deposition was estimated at 90 nm, and this value was found to double for a 15 s deposition (ROC ~ 180 nm). It is noteworthy that such large ROC values are compatible with TERS activity, and do not modify necessarily the TERS enhancement and the electromagnetic confinement at the origin of the high spatial resolution of TERS. In a non-gap-mode TERS configuration (for which the sample is placed on an insulating substrate and/or the tip-substrate distance is larger than 2-5 nm), the TERS enhancement and the resolution are expected to decrease with the size of the tip apex,¹⁶ but they also strongly depend on the presence of nanoscale protrusions at the very end of the tip.⁵,¹⁷ The fine control of the thickness of the gold deposit confirms that BPE is indeed a method of choice to fabricate TERS tips.

Besides the electrodeposition time, the parallel fabrication of TERS tips constitutes a critical aspect to make BPE more appealing for the TERS community. Standard potentiostatic electrodeposition necessitates manufacturing these tips once
1 at a time. Such a limitation can be circumvented since BPE is 43

2 contactless method. The parallel electrodeposition of three 44

3 AFM chips was performed by immersing them side by side 45

4 the same electrochemical cell filled with gold plating solution 46

5 Within our small electrochemical cell (3.4 cm in diameter) 47

6 AFM chips were spaced by a few millimetres (~ 5 mm), and 48

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>

7 the same homogeneous electric field distribution, resulting in 69

8 similar gold thicknesses at their surface (Table S3). 70

9 Simultaneous gold bipolar electrodeposition on five tips have 71

10 been also performed occasionally, with similar quality of the 72

11 metal layer. The scale-up of the electrochemical cell should 73

12 quite straightforward (with appropriate dimensions of the 74

13 electrochemical cell to maintain a homogeneous electric field 75

14 distribution), and allow the parallel fabrication of many more 76

15 TERS tips. 77

16 78

17 **Figure 3.** a) Left: Tapping-mode topographical AFM image of a part of GO flake scanned by a TERS tip. Scale bar: 100 nm. Right: Two TERS maps corresponding to the white dotted boxes in the AFM image. The red dotted lines indicate the edge of a GO flake within a multilayer structure. Spectral range for intensity integration: cyan D band: 1220-1420 cm⁻¹; green G band: 1520-1660 cm⁻¹; scanning step size: 10 nm; acquisition time: (1) 3 s, (2) 5 s. b) Black spectra (obtained on day 1): TERS spectra a-d measured at the positions marked with red a-d labels in TERS maps 1 and 2. The tip-out spectrum illustrates the TERS spectrum obtained when the tip is retracted from the sample surface. Red spectrum: TERS spectrum e recorded using the same TERS tip two weeks after (day 15) fabrication (storage under Ar) when the tip is engaged on the sample surface. 79

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experimental electrodeposition parameters, 64% of the TERS tips (7 out of 11 tips) produced by BPE showed a TERS efficiency sufficient to collect TERS spectra. This constitutes an improvement compared to the 53% fabrication yield reported for some potentiostatic methods,⁵ and the ~60% yield of metal sputtering.²⁰ This 64% yield is a reasonable value considering the cost-effectiveness and simplicity of the bipolar electrodeposition method, and offers a practical alternative to expensive micro- and nano-fabrication techniques with higher fabrication yield.²,²¹

**Figure 3a** shows an AFM image alongside four TERS maps, acquired using a single TERS tip (TERS measurements with additional tips are provided in **Figures S3, S4** and **S5**). The region imaged in **Figure 3a** is only a small portion of a larger graphene oxide (GO) flake (**Figure S6**). The cyan and green TERS images were obtained through integration of the intensity within the 1220-1420 cm⁻¹ and 1520-1660 cm⁻¹ range, respectively, which encompass the characteristic marker bands of GO, namely the D band, situated around 1350 cm⁻¹, and the G band, at approximately 1580 cm⁻¹ (**Figure 3b**). The TERS signal exhibits relatively homogeneous intensity across the GO flake regions, rather than being more intense at the GO edges and steps, as already reported for graphene¹⁸,²² and GO.¹⁸,¹⁹ This is seemingly due to the presence of folds and wrinkles (**Figure S6**). Unlike flat GO sheets, these disordered structures introduce defects that can enhance the TERS signal, resulting in a more uniform distribution within the dotted-line region. This increased TERS signal should arise from the better alignment of the axially polarized near-field component with the Raman polarizability tensor components involved in GO vibrations, in regions where the GO lattice is somewhat disrupted.¹⁹ The AFM topographical images in **Figure 3a** and **4a** suggest the GO to be multi-layered and much thicker than 1-5 nm, which implies a limited gap-mode enhancement, or a weak effect of the gold-coated substrate on the TERS enhancement.¹,²³ The observed TERS enhancement seems to be largely due to the tip itself.
<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /><figcaption>**Figure 4.** (a) Left: Tapping-mode topographic AFM image of a part of GO flake scanned by a TERS tip. Scale bar: 100 nm. Right: TERS map bounded by the white dotted square box in the AFM image. The red dotted lines indicate the edge of a GO flake within a multilayer structure. Spectral range for intensity integration: 1200-1670 cm⁻¹; scanning step size: 5 nm, acquisition time: 5 s. (b) Three TERS intensity profiles along the arrows drawn in Figure 4a, with their corresponding full width at half maximum. Band for intensity integration: 1350 cm⁻¹.</figcaption></figure>

**Figure 4** presents another TERS map from the same sample area as in **Figure 3a**, that was obtained by integrating the TERS signal over the same spectral range. Three TERS profiles obtained by intensity integration of the D band at 1350 cm⁻¹ along arrows indicated in the TERS map are also provided. They show full widths at half maximum between 66 and 12 nm, which suggests that TERS imaging was performed with a spatial resolution better than 10 nm. This value is much smaller than the radius of curvature of the tip apex (~100 nm in this case), and is consistent with the electron confinement of a nanoscale gold protrusion at the extremity of the tip apex.¹⁷

Moreover, this is in line with the resolution achieved in similar samples using gold-coated tips.¹⁹

The lifetime of TERS tips is also an important criterion to consider them reliable for characterization by TERS. It is crucial to vary from hours to months depending on the robustness of the metal coating, TERS imaging parameters, as well as environmental conditions.²³,²⁴

TERS spectra at marked positions a-d in TERS maps 1 and 2. A large enhancement of the GO D and G bands is observed when the tip is engaged on the GO surface, but no signal can be discerned when the tip is retracted 18 µm above the GO surface (tip-out spectrum). Two weeks later, a TERS spectrum can still be discerned using the very same tip (red spectrum).¹⁷ provided that it was stored under Ar atmosphere until use.¹⁸ This tip thus remained TERS-active during measurements.

day 1 and day 15, after a TERS mapping time of nearly 7 hours, which is sufficient for most TERS imaging experiments. This suggests that tips prepared by bipolar electrodeposition are quite stable in time due to the inertness of gold, and robust enough to withstand day-long TERS imaging periods.

## Conclusions

An original wireless BPE method was used for the parallel preparation of gold-coated AFM-TERS tips with good reproducibility of the metal thickness and a satisfying fabrication yield (64%). Since the approach is contactless, it significantly prevents possible mechanical damage due to the wiring step necessary when employing more conventional electrodeposition approaches. This fast, inexpensive and easy fabrication method led to good TERS activities and relatively long lifetimes of the TERS probes, which proved to be quite robust. These AFM chips were not only TERS-active but were also successfully used to perform TERS mapping. It turned out that they were appropriate to perform TERS imaging in air with high spatial resolution (below 10 nm). This original method is easy to implement anticipating the rapid opening of new perspectives for the design of optical nanosources for TERS and beyond.

## Author contributions

Yuhan Huang: Methodology, Investigation, Formal analysis, Validation, Visualization, Writing - original draft; David Talaga: Investigation; Gerardo Salinas: Investigation; Patrick Garrigue: Investigation; Gary S. Cooney: Investigation; Alexander Kuhn: Funding acquisition, Methodology; Sébastien Bonhommeau: Conceptualization, Funding acquisition, Methodology, Project administration, Supervision, Writing - original draft; Laurent Bouffier: Conceptualization, Methodology, Supervision, Writing - original draft.

## Conflicts of interest

"There are no conflicts to declare".

## Data availability

Data for this article, including SEM images, TERS spectra and TERS mapping are available at https://mycore.core-cloud.net/

## Acknowledgements

The PhD scholarship of YH was funded by the Agence Nationale de la Recherche under contract N° ANR-20-CE29-0004 (AQUATERS). The PhD scholarship of GSC was funded by the University of Bordeaux. AK and GS acknowledge financial support by the European Research Council (ERC, Advanced Grant ELECTRA) under the European Union's Horizon 2020 research and innovation program (grant agreement N° 741251). TERS measurements were performed at the platform
1 SIV (Spectroscopie et Imagerie Vibrationnelle) funded by 66

2 European Union (FEDER), the Région Nouvelle Aquitaine and 67

3 the University of Bordeaux. 68

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