# Infrared nanocrystals for space application: hardness to irradiations

Alexandre Neyret, Dario Mastrippolito, Bingbing Xia, Adrien Khalili, Maxime Lebreton, Giorgia Strobbia, Albin Colle, Marco Paye, Mariarosa Cavallo, Erwan Bossavit, et al.

► To cite this version:

Alexandre Neyret, Dario Mastrippolito, Bingbing Xia, Adrien Khalili, Maxime Lebreton, et al. Infrared nanocrystals for space application: hardness to irradiations. Advanced Functional Materials, 2026, pp.e24191. 10.1002/adfm.202524191. hal-05531263

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Submitted on 28 Feb 2026

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# Infrared nanocrystals for space application: hardness to irradiations

Alexandre Neyret¹⁻⁴, Dario Mastrippolito², Bingbing Xia², Adrien Khalili², Maxime Lebreton⁵, Giorgia Strobbia², Albin Colle², Marco Paye², Mariarosa Cavallo², Erwan Bossavit², Claire Abadie², Yoann Prado², Debora Pierucci², Victor Parahyba⁶, Francois Coursaget⁶, David Darson⁵, Emrick Briand², Ian Vickridge², Stephane Demiguel³, Sebastien Massenot¹, Jean-Marc Belloir⁴, Vincent Goiffon¹*, Emmanuel Lhuillier²*

¹ ISAE-SUPAERO, Université de Toulouse, 31055 Toulouse, France.

² Sorbonne Université, CNRS, Institut des NanoSciences de Paris, 4 place Jussieu, 75005 Paris, France.

³Thales Alenia Space, Allée des Gabians, Batiment V01 – 415, BP 99, 06156 Cannes la Bocca Cedex, France

⁴CNES, Centre Spatial de Toulouse, 18 Avenue Édouard Belin, 31400 Toulouse, France.

⁵ Laboratoire de Physique de l'Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, 75005 Paris, France.

⁶New Imaging Technologies SA, 1 impasse de la Noisette 91370 Verrières le Buisson, France.

**Abstract:** Colloidal nanomaterials are now a cost-effective strategy for the design of infrared imagers. Their increased maturity brings them to the point where the evaluation of their potential for space and astronomy applications becomes relevant. The first step is to test their robustness against irradiation, since this process is responsible for the performance degradation of most imagers. In this study, we explore the potential of HgTe nanocrystals for short-wave infrared sensing under X-ray and He⁺ ion irradiation. To first assess the degradation of the material itself, we test the evolution of a single-pixel photoconductive device upon irradiation and observe that only marginal degradation occurs for doses relevant to space applications, and degradation only occurs at a very high threshold, making this colloidal semiconductor quite promising to operate in harsh radiation environments. Complementary spectroscopic studies reveal very different degradation mechanisms upon X-ray (leading to oxidation) and He⁺ ion (sintering particles). We tested the potential of this material in a focal plane array and observed degradation, though not preventing imaging, in a range of doses where no effect was observed for the simple photoconductive device. This suggests that the CMOS readout circuit might be the bottleneck regarding operation under radiation.

**Keywords:** infrared detection, irradiation, nanocrystals, space.

*To whom correspondence should be sent: vincent.goiffon@isae-supaero.fr; el@insp.upmc.fr
INTRODUCTION

The infrared (IR) range is of utmost interest for astronomy and spatial applications since (i) it corresponds to the range of the blackbody emission for cold objects, and (ii) it matches the organic chemical fingerprint range, thus enabling chemical contrast imaging. Infrared imaging and spectroscopy are dominated by thin-film semiconductors made of PbS, Ge, and InGaAs in the short-wave infrared (SWIR), and by InSb, type II superlattices, and HgCdTe alloy for the mid-IR range.[1,2] Though highly performing (i.e., low dark current, quantum efficiency up to 90%), such photon detector suffer from a few limitations: their cost is high—though space is less sensitive to this issue— and more problematically, their performance decreases over time due to radiation exposure.[3]

This study focuses on dose related degradation. Energetic particles lose energy in matter via different interactions leading to various defects in electronic devices, causing malfunction and degradation.[4] The radiation dose represent this energy per unit mass deposited in a material by a particle and allows to quantify the amount of radiation a device has been exposed to. In the following of the article, the dose will be reported relative to the absorbing material using notation [material]. Two energy transfer mechanisms are studied: (i) Charged particles, X-rays and Gamma rays induce ionization, quantified by the Total Ionizing Dose (TID) and (ii) Massive particles can also induce atomic displacement in the semiconductor lattice, quantified by the Displacement Damage Dose (DDD). The dose scales linearly with particle fluence (DDD, TID $\propto \phi_{particle}$) and is given with respect to a material.

**Figure 1** illustrates the typical ionizing radiation dose for various applications, ranging from space and deep space under mild conditions to harsh conditions associated with nuclear reactors and particle physics research related environment. For the sake of illustration, a low earth orbit satellite over its 10-year lifetime receives about 100 Gy, or 10 krad [SiO$_2$], of ionizing dose.

<figure><img src="image_2.png" /><figcaption>**Figure 1** Typical Ionizing Dose (with respect to SiO$_2$) for different radiative environments and test radiation sources, and typical tolerance dose of image sensors. Adapted from [5].</figcaption></figure>

This is why emerging materials raise hope for more robust technologies. At the same time, the maturity requirements for space application being very high (i.e., need for long-term stability, reduced weight, electrical consumption, high operating temperature...), only a few mature
technologies reach the potential to be screened for space applications. Over the past four decades, colloidal nanocrystal (NC) materials have been pushed for optoelectronic applications. In the visible spectrum, they have reached a commercial status, being used as green and red light sources for displays and have had to demonstrate long-term stability of the order of 10 years. These inorganic semiconductor nanoparticles appear equally promising to address the IR spectral range.[6] Though efforts are slightly more recent, the colloidal nanocrystals (NCs) benefit from more than 20 years of experience that have shifted the material absorption from only the visible range to now cover the whole IR range, covering SWIR,[7] mid wave,[8,9] long wave[10,11] and even far IR[12–14] ranges. Beyond the capability to absorb IR, the integration of these semiconductor nanoparticles has been pushed toward the design of high-performing photodiodes and IR imagers.[15–21] However, their ability to withstand the space radiation environment remains mostly unexplored.[22,23] Conversely, the topic of NCs interacting with high-energy photons (X and gamma rays) is already explored in the context of scintillators.[23–25] There, the bright luminescence of NCs is used to detect photons with keV energies and beyond.

Though significant progress has been made to integrate III-V (InAs[26,27] and InSb[28]) or silver chalcogenides[29–32] NCs for SWIR sensing, those platforms remain at a material development stage. Conversely, two colloidal materials are nowadays mature enough to be integrated in advanced optoelectronic devices: PbS and HgTe.[33–35] Stability of PbS under X-ray irradiation has just been reported and shows encouraging results.[22] However, in the case of HgTe, its potential for space application and stability under radiation remains to be determined, even though this material has the benefit of covering the whole IR range thanks to the semimetal nature of the bulk material. Therefore, in this study, we investigate how HgTe NC films and detectors behave under two types of radiation: (i) hard X-ray photons from a tungsten target tube – with a broad energy spectrum up to 320 keV (see **Figure S1**) - that will mostly ionize samples and (ii) 500 keV He⁺ particles that can induce both ionization and displacements. Furthermore, the extreme flux of our He⁺ accelerator enables investigation in a fluence range that leads to accelerated degradation. While most studies focus only on changes in the electro-optical responses due to the irradiation, we provide insights into the irradiation effects through infrared and photoelectron spectroscopy measurements. We demonstrate that the active layer (i.e. the HgTe NC films) is very robust and requires very large irradiation doses to induce modification of the dark current and responsivity. We also bring evidence that damage mechanisms induced by X-ray and He⁺ irradiation are very different (oxidation vs sintering, respectively). Finally, we study how such HgTe NCs get damaged once integrated in an IR imager and exposed to the same two irradiation sources. In this case, damage is observed at a much lower dose threshold, suggesting that the degradation is due mostly to either the Complementary Metal-Oxide-Semiconductor (CMOS) readout circuit of the imager or its coupling with the NCs. Overall, our study shows that HgTe NCs appear only weakly sensitive to irradiation, making them quite promising for use in harsh operating conditions.

# DISCUSSION AND RESULTS

## Photoconductive device based on HgTe NCs as absorbing layer

To determine the impact of radiation on NC-based imagers, we followed a two-step process. We first address the case of a very basic photoconductive device based on HgTe NCs as a short-wave infrared absorbing layer. These devices rely on an intentionally basic geometry: a thin film of nanocrystals coupled to interdigitated electrodes deposited on a glass substrate, so that radiation effects can unambiguously be attributed to the active NCs layer. In a second step, we address the case of a complete focal plane array (FPA) in which the same HgTe NCs layer is coupled to a
readout integrated circuit (ROIC) to ensure IR detection. This process provides the ability to discern
the effect on the sensing material from the effects on the Focal plane array assembly.

To start, we synthesize HgTe NCs using the procedure developed by Keuleyan et al.[36] Through the choice of temperature and reaction duration, the particle size (Figure 2b) is adjusted to generate a band edge corresponding to 0.75 eV (≈1650 nm) in absorption, as shown in Figure 2a. By the end of the growth procedure, the NCs are capped with long insulating ligands (dodecanethiol with C₁₂ chains) that render the NCs electrically insulating. The native ligands are exchanged for shorter ones - HgCl₂ and mercaptoethanol (see Methods)- to generate a highly concentrated ink.[37,38] The latter is then spin-coated onto gold interdigitated electrodes fabricated by optical lithography on glass (see picture of the device as inset of Figure 2b).

<figure><img src="image_3.png" /><figcaption>**Figure 2** HgTe nanocrystals for SWIR sensing and imaging. a. Absorption and photoluminescence spectra for HgTe NCs capped with their long native ligands. b. Transmission electron microscopy image of HgTe NCs. The inset is an image of interdigitated gold electrodes on a glass substrate and coated with HgTe NCs (brownish film).</figcaption></figure>

The choice of a simple photoconductive device, such as an interdigitated electrode structure, is not arbitrary. Indeed, this device presents limited performances, only absorbing 10-20% and having a large dark current (typical film thickness is 250 nm). Though not optimized with respect to a full photodiode stack[39–41] the device's minimal configuration, composed of a reduced amount of materials, and interfaces, allows investigation of the radiation effects induced only on the absorbing material, the HgTe NCs.

Effect of X-ray irradiation on single pixel photoconductive devices

Prior to irradiation, the devices present ohmic IV curves both in the dark and under SWIR light
illumination, as shown in **Figure 3a**. Upon X-ray irradiation (see Figure S1 for the setup scheme),
limited conductivity changes are observed with the current variation remaining within the device-to-
device fluctuation, see **Figure 3c**. Only under large doses do the IV curves lose their ohmic character
(Figure S3) and become super linear and hysteretic, see **Figure 3b**. In practice, deviation from
linearity starts to appear at doses above 1 Grad, as depicted in **Figure 3d**. The photoresponse also
appears affected. Photocurrent ($J_{photo}$) tends to follow a power law with the incident illumination
power $J_{\text{photo}} = P^{\alpha}$, see **Figure 3e**. The value of the exponent drops as the dark current becomes nonlinear. Such a drop means that a higher light irradiance is required to generate the same increase in photocurrent and therefore reflect a drop of the responsivity and detectivity. It is the combination of the two effects that makes the response drops under such high irradiation dose (>1 Grad [HgTe]).

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

**Figure 3** Impact of 320 kVp X-ray irradiation on HgTe NCs photoconductive device. a. (resp. b.) IV curve in the dark and under illumination before (resp. after irradiation by X-ray, dose 4.2 Grad [HgTe]). c. Dark current as a function of the X-ray dose. d. Linear regression coefficient of determination of the IV curve. Value of 1 indicates an ohmic behavior, while a lower value translates to a superlinear and hysteretic behavior. Each color in graphs c and d corresponds to a given sample. e. Conductance as a function of the incident power illumination, ensured by a 1.55 µm laser diode. The dependence of the current is fitted with a power law, whose exponent is called α. f. Relative change of α (power law exponent from the current dependence as a function of incident light power) as a function of the X-ray dose.

The absorption spectrum appears unchanged (no shift, no broadening), see Figure S4, stressing that X-ray irradiation is not inducing particle sintering. X-ray photoemission spectroscopy (XPS) provides, on the other hand, interesting insights into the degradation mechanism induced by irradiation. The survey spectrum (**Figure 4a**) of the pristine material displays the expected features coming from Hg and Te, as well as C and S from the mercaptoethanol used as ligand. It is worth stressing that the O 1s state initially presents an extremely weak contribution, in spite of the air preparation of the sample and processing with non-anhydrous solvent. This contrasts with the spectrum post irradiation, where the O 1s peak intensity is drastically increased. Looking at the Hg 4f core level (**Figure 4b**), we observe a limited change of the spectrum, with just a broadening of
the spectrum on the high binding energy side. This suggests a limited surface oxidation. To confirm this hypothesis, we then conducted hard X-ray photoemission spectroscopy (HAXPES) using a Cr Kα source (5414.8 eV). Increasing the incident photon energy increases the photoelectron escape depth from 1 nm using conventional Al source (i.e., surface only of the NC) to 10-20 nm using a Cr source (i.e., larger than the NC size measured by TEM in Figure 2b). The HAXPES spectrum of Hg 4f is shown in Figure S6, showing that the peaks mostly overlap before and after X-ray irradiation. This confirms that for Hg the oxidation is just limited to the surface. In HgTe, Hg is coming under Hg⁺¹¹ form that is unlikely to be further oxidized and the weak shift that we observe is mostly due to the O incorporation within the NC, which higher electronegativity make Hg atoms more depleted. This situation contrasts with the one of Te that is reduced (Te⁻¹¹) in HgTe and thus likely to get oxidized. Indeed the X-ray effect appears far more dramatic in the case of the Te 4d state, see Figure 4c and S5. The non-irradiated Te 4d displays a doublet with a 40.2 eV for the Te 4d₅/₂,[⁴²,⁴³] while after irradiation, two extra contributions strongly shifted toward larger binding energy appears. Their binding energy for the Te 4d₅/₂ are respectively of 41.2 and 43.8 eV (Figure S5) consistent with metallic Te and TeO₂ species, respectively.[⁴⁴] The HAXPES spectrum (Figure S6) shows that this tendency to oxidation, though a bit reduced, also exists in the bulk of the nanocrystals.

Therefore, X-ray irradiation ionizes the nanocrystal and induces an oxidation of the tellurium, which is known to be the atom most prone to be oxidized out of the HgCdTe alloy.[⁴⁵] Metallic Te centers are likely to quench the formed exciton when absorbing light, while the wide band gap nature of TeO₂[⁴⁶,⁴⁷] likely reduces the light absorption. Both effects combined explain the reduced device IR responsivity after irradiation. Lack of oxygen in space operating conditions will probably reduce this degradation mechanism.

<figure><img src="image_5.png" /><figcaption>**Figure 4** *Photoemission spectra from X-ray irradiated sample.* a. Survey spectrum from the pristine and irradiated (320 kVp with a dose of 4.2 Grad [HgTe], curve is shifted for sake of clarity) HgTe NCs film. b. (resp c.) Core level relative to the Hg 4f state (resp Te 4d – decomposition in</figcaption></figure>
Figure S3) before and after X-ray irradiation. For all these curves, the source is an Al Kα (1486.6 eV), data acquired with Cr Kα (5414.8 eV) can be found in Figure S4.

Effect of He⁺ irradiation on single pixel photoconductive devices

Now that the X-ray effects have been revealed, we switch to irradiation with 500 keV He⁺, so as to introduce displacement damage in addition to ionization, see Figure S2. The He⁺ ions are generated by a Van de Graaff accelerator, which can provide high fluence while maintaining a small beam size, so that irradiation can be focused locally on the device.

Irradiating the same photoconductive single pixel device with such He⁺ source shows that conductivity maintains linearity even under large fluence (10¹⁵ cm⁻², corresponding to ≈7 Grad [HgTe] of ionization and 1.4x10⁹ TeV/g [HgTe] of displacement damage dose), see **Figure 5a-b**. It is only for very large fluence (>10¹⁶ cm⁻²) that a large increase of sample conductivity (**Figure 5c**) and a drop of the power law exponent is observed (**Figure 5d**). In this sense, HgTe NCs appear particularly robust toward an ionizing and displacement irradiation dose relevant for any space application.

<figure><img src="image_6.png" /><figcaption>**Figure 5** Impact of 500 keV He⁺ irradiation on HgTe NCs photoconductive device. a. (resp b.) IV curve in the dark and under illumination, ensured by a 1.55 µm laser diode with various powers, for the pristine (resp. irradiated, with 10¹⁵ cm⁻² fluence) HgTe NCs photoconductive device. c. Relative change in the dark conductance as a function of the He⁺ fluence for the HgTe NCs photoconductive devices. d. Relative change of α (power law exponent from the current dependence as a function of incident light power) as a function of the He⁺ fluence. For all of these experiments, the He⁺ ions have 500 keV energy.</figcaption></figure>
The degradation mechanism under He⁺ irradiation appears quite different from the one induced by X-ray. Indeed, XPS measurements show only a limited change in the spectrum, see **Figure 6a-b**. Both Te 4d and Hg 4f states shows a 100 meV shift toward lower binding energy, suggesting a global rigid shift which will slightly reinforce the *p* character of the material, given the quasi intrinsic behavior of the pristine material[48] (i.e., Fermi level is close to the middle of the band gap). Alone, the increase of the majority carrier density cannot explain the observed increase of conductivity. Under large fluence (10¹⁵ cm⁻²), we observe a broadening and a shift of the reflectivity spectrum (**Figure 6c**) In HgTe NCs, due to the lack of bulk band gap, the band edge energy is due to quantum confinement. Such a shift suggests a loss of confinement, which is the signature of an increase in effective size, in other words particles experience a partial sintering - A behavior similar to the one observed for HgTe NCs upon thermal annealing.[49]

<figure><img src="image_7.png" /><figcaption>**Figure 6** Impact of 500 keV He⁺ irradiation on HgTe NCs material. a. (resp b.). Core level relative to the Hg 4f state (resp Te 4d – decomposition as Figure S5) before and after He⁺ irradiation. c. Absorption spectra within an irradiated area and away from an irradiated area. Here, top curve is shifted vertically to better highlight the spectral shift. For all these curves the source is an Al ka (1486.6 eV), the He⁺ fluence is 10¹⁵ cm⁻² and particle energy is 500 keV.</figcaption></figure>

## Effect of X-ray irradiation on FPA

Now that we have established the robustness of HgTe NCs for IR sensing under irradiation we examine the behaviour of a FPA into which they are integrated. We use a VGA format (640x512 pixels) ROIC with a 15 µm pitch. This ROIC enables a specific operation mode where two consecutive pixels are biased with different potentials. This functionality enables photoconductive operation of the FPA at the price of resolution reduced by a factor two. However, such strategy has a clear benefit since it enables the IR sensitization of the ROIC through a single step of NC deposition (i.e., no need for full diode stack where multilayer deposition is likely to reduce image homogeneity). The surface of the ROIC has been planarized so that surface texture is minimized. Regarding the NCs, we choose to deposit core shell NCs made of HgTe/CdS,[15] since the latter have proven to have a higher thermal stability, in particular toward the joule heat dissipation from the ROIC to the NCs film during operation. Similarly, to the single pixel device, the NCs are ligand-
exchanged to render them photoconductive and spin-coated directly at the surface of the pre-packaged ROIC.

The FPA is irradiated using hard X-ray energy over half of the ROIC (top part), while the other half is shielded by a large 60 mm steel shield absorbing 99% of Xray exposition (see Figure S1). On the image (Figure 7a) we clearly observe signal increase in the irradiated area. The linearity of the response is conserved, then the change can be corrected by a two-point correction (dark and gain) and the imaging capability is maintained, as shown by the corrected image in Figure 7b. This being said, the overall dark signal increases linearly under irradiation (Figure 7c), which comes with a drop of the signal-to-noise ratio (Figure 7d). Since we select the dose range (up to 4.4x10⁷ rad [HgTe] or 400 krad [air]) where the monopixel made of HgTe NCs only was previously shown to be mostly unaffected by irradiation, we conclude that the drop of performance of the imager mostly occurs within the CMOS ROIC or at its interface with the NC film.

<figure><img src="image_8.png" /><figcaption>**Figure 7** Effect of X-ray irradiation on HgTe NC-based imager. a. Raw image after X-ray irradiation (dose 44 Mrad [HgTe] at 320 kVp) of the top half of a photoconductive HgTe NCs-based imager. b. Same image after a two-point (dark and gain) correction. c. Dark signal in the irradiated area as a function of the X-ray ionizing dose. d. Ratio of the photoresponse over the dark current in the irradiated area of the imager as a function of the X-ray ionizing dose.</figcaption></figure>

## Effect of He⁺ irradiation on FPA

A similar damage test has been conducted under He⁺ irradiation. Similarly, we select the fluence to be in a range (3x10¹¹ cm⁻²) where the photoconductive HgTe NCs are mostly unaffected. Upon He⁺ irradiation, image quality is directly impacted (see Figure 8a and b), with a local increase of the dark current by a factor ≈10, see Figure 8c. Conducting a series of experiments at various temperatures enables us to extract the dark current activation energy for each pixel by Arrhenius law fit, see Figure 8d. The activation energy maps as a function of the dark current magnitude display a bimodal distribution, where the non-irradiated pixels are associated with a lower dark current and a lower activation energy. This change of activation energy (75 ± 25 meV) can be connected to the energy shift induced by the irradiation (80-100 meV, in Figure 6c-d), which affects the charge transfer from the absorbing layer to the gold pad of the ROIC, though this might also reflect an increase of the leakage in the CMOS alone.
<figure><img src="image_9.png" /><figcaption>**Figure 8** Effect of He⁺ on HgTe NC-based imager. a. Image before irradiation. b Image after irradiation, where the irradiated area is highlighted by a red dashed circle. He⁺ fluence is 3x10¹¹ cm⁻² and ROIC integration time is 60 ms, the FPA is uncooled (i.e. not even thermally stabilized). c. Dark current map after irradiation, top inset is a profile of dark current along the red line depicted in the bottom map. d. Activation energy pixel density map as a function of the dark current magnitude displaying a bimodal distribution for the irradiated and non-irradiated area of the FPA. Dark signal (resp. Activation energy) distribution is plotted in log-scale on top (resp. right).</figcaption></figure>

CONCLUSION

To conclude, we have performed a systematic study of the irradiation damage induced by X-ray and He⁺ ions on HgTe NCs used as SWIR active detection layer. For the photoconductive single pixel device, we observe that large doses (1 Grad [HgTe] for X-ray and above 10¹⁵ cm⁻² for He⁺) are necessary to induce clear and irreversible damage, stressing the robustness of colloidal materials toward irradiation. The damage mechanism appears quite different in the two cases: X-ray irradiation leads to oxidation of the tellurium, which translates into a loss of linearity in the IV curve. Meanwhile, under He⁺ ions, no oxidation is observed but rather a sintering of the particles, which leads to an increase of the dark conductance. When integrated into a ROIC, damage occurs at a much lower threshold, suggesting that CMOS is the main bottleneck toward the integration of such a material for operation under irradiation. In both irradiation conditions, we have demonstrated tolerance to radiation up to multiple lifetimes of ionizing and displacement dose in space lifecycle scenario. The robustness to several orders of magnitude above this threshold opens up the prospect of harsh radiation environment application (e.g. nuclear disposal waste, particle physics research setups) for HgTe NCs based IR cameras.
**Chemicals:** Mercury chloride ($HgCl_2$, Alfa Aesar), mercury bromide ($HgBr_2$, Alfa Aesar), tellurium powder (Te, Alfa Aesar, 99.99%), Cadmium nitrate tetrahydrate ($Cd(NO_3)_2 \cdot 4H_2O$, Alfa Aesar, 99,9%), Cadmium chloride anhydrous ($CdCl_2$, Thermo Scientific, 99%), carbon disulfide ($CS_2$, Merck, >99,9%), trioctylphosphine (TOP, thermofisher scientific, 90%), oleylamine (OLA, Acros, 80-90%), octadecene (ODE, Acros Organics, 90%), dodecanethiol (DDT, Sigma-Aldrich, 98%), Oleic acid (99%, Alfa Aesar), ammonia solution 30% vol. ($NH_4OH$, Carlo Erba), Aniline (Merck, >99,5%), methanol (MeOH, Carlo Erba, 99.8%), acetone (VWR), absolute ethanol (EtOH, VWR), isopropanol (IPA, VWR), toluene (Carlo Erba, 99.3%), N,N dimethylformamide (DMF, VWR), 2-mercaptoethanol (MPOH, Merck, >99%), All chemicals are used as received, except oleylamine which is centrifuged before used. **Mercury compounds are highly toxic. Handle them with special care.**

**1 M TOP:Te precursor:** 6.35 g of Te powder was mixed in 50 mL of TOP in a three-neck flask. The flask was kept under vacuum at room temperature for 5 min and then the temperature was raised to 100 °C. Furthermore, degassing of the flask was conducted for the next 20 min. The atmosphere was switched to Ar and the temperature was raised to 275 °C. The solution was stirred until a clear orange coloration was obtained. The flask was cooled down to room temperature and the color switched to yellow. Finally, this solution was transferred to a nitrogen-filled glove box for storage.

**SWIR core $HgTe$ NCs:** In a 100 mL three neck flask, 540 mg of $HgCl_2$ (2 mmol) and 50 mL of oleylamine are degassed under vacuum at 110 °C for 30 min. Then, the atmosphere is switched to $N_2$, and the temperature stabilizes at 58 °C. Meanwhile, 2 mL of TOP:Te (1 M) is extracted from the glove box and mixed with 8 mL of oleylamine. Then, the TOP:Te solution is quickly injected. After 3 min, 10 mL of a mixture of 10% DDT in toluene is injected and a water bath is used to quickly decrease the temperature. The content of the flask is split over 3 centrifuge tubes. The solution is precipitated first with MeOH. After centrifugation, the formed pellets are redispersed in one centrifuge tube with toluene. The solution is precipitated a second time with absolute EtOH and sonicated for 3 min. Again, the formed pellet is redispersed in toluene. Then, the NCs are centrifuged in pure toluene to get rid of the lamellar phase. The solid phase is discarded.

**Gold interdigitated electrodes fabrication:** Glass substrates with a dimension of ≈1 cm x 1 cm were cut. The samples were rinsed with acetone, then isopropanol and dried with a $N_2$ gun. An adhesion promoter (Ti PRIME) was spin-coated onto the substrates and baked at 120 °C for 1 min. AZ5214E was spin-coated and baked at 110 °C for 1 min. The substrates were exposed to UV through a pattern mask for 1.5 s. The resist was then reversed by baking the samples at 110°C for 2 min. A flood exposure was then performed for 40 s. The resist was developed using AZMIF726 between 15 and 20 s and rinsed 30 s in water before being dried with $N_2$. The samples were cleaned with an $O_2$ plasma (30 W, 3 min), then 5 nm Ti + 80 nm Au were thermally evaporated. The resist was lifted off in 45°C acetone overnight.

**NC ink preparation:** Before deposition, the NCs are prepared into a concentrated ink. A volume of 0.65/OD of the prepared $HgTe$ solution, 0.2 mL of DMF and 0.8 mL of exchange solution (30 mg $HgCl_2$ and 2 mL of MPOH in 18 mL of DMF) were added to a centrifuge tube and agitated thoroughly with vortex mixing and sonication. 5 mL of hexane was added to wash the solution, agitated thoroughly without sonication, then discarded after phase separation. The NCs were then precipitated by adding 4 mL of toluene and centrifugating at 6000 rpm for 3 min. The remaining
pellet was dried for 60 s under vacuum then redispersed in 250 µL of DMF by agitating and sonicating.

**NC film preparation:** The NCs are then deposited on the various substrates prepared before. A few drops of filtered DMF were deposited on the substrate and left for 30 s, then dried by spincoating at 4000 rpm for 30 s. Then, 15 µL of previously prepared ink were deposited on the substrate and spincoated at 1250 rpm for 180 s then 6000 rpm for 60 s. The contact pads were then cleaned using a cotton swab with ethanol.

**DC Photoresponse measurements:** The DC photoresponse measurements were collected using a Keithley 2634b as both a source of bias and an amperemeter. A 1550 nm laser diode was used as the light source. To vary the intensity of the laser, the total incident power was first measured for different input currents using a PM100A Thorlabs power-meter and a Ge detector. The photocurrent was then calculated as the difference between dark current and current under illumination.

**Infrared absorption and luminescence:** Absorption spectra have been acquired using FTIR (Nicolet IS50 FTIR) with an integrated total attenuated reflexion setup. The acquisition used a white light (equivalent to a blackbody with maximum of emission at around 2 µm), a CaF₂ beamsplitter and a DTGS (Deuterated Triglycine Sulfate) detector. The spectra are typically obtained in continuous scan mode with 4 cm⁻¹ resolution and averaged at least 32 times. For photoluminescence, a NC layer is coated on a glass slide and setup in front of the external input of the same FTIR. The glass slide is illuminated with a blue flashlight. The luminescence signal is collected through the interferometer (CaF₂ beamsplitter) on InGaAs detector. The spectra are typically obtained in continuous scan mode with 4 cm⁻¹ resolution and averaged at least 64 times.

**Photocurrent spectra measurements:** The spectral dependence of the photoresponse is measured with a Fisher IS50 FTIR (CaF₂ beamsplitter, white light illumination) while the sample is biased with a Femto DLPCA 200 amplifier, which is also used for amplifying the photocurrent signal before sending the signal back into the FTIR for spectral analysis. The spectra are typically obtained in continuous scan mode with 4 cm⁻¹ resolution and averaged at least 32 times.

**Micro-FTIR measurements:** Infrared reflectance maps are collected using a Nicolet RaptIR+ infrared microscope from Thermo Fisher Scientific. The sample is placed on a motorized XYZ stage. The sample is illuminated using the infrared source from a Nicolet IS50R FTIR, which has passed through the interferometer (KBr beamsplitter). The light is focused on the sample using a 15x IR Cassegrain objective and collected in the same way to measure reflectance. The collected interferogram is then measured by a MCT detector with an optical velocity of 1.8988 cm/sec and a gain of 1. Maps are performed by moving the stage point by point in X and Y directions and collecting an IR spectrum for each point, with 150 µm x 150 µm aperture for data collection. The data are collected with 16 cm⁻¹ resolution and 8 sample scans for average.

**X-ray photoemission spectroscopy:** Photoemission spectroscopy measurements were performed using a PHI GENESIS setup. The samples were introduced into the load-lock chamber and degassed until a vacuum of 2·10⁻⁷ mbar was reached. They were then transferred to the analysis chamber (base pressure 2·10⁻⁹ mbar). The spectra were recorded using a monochromatic Al Kα X-ray source (hv=1486.6 eV) for XPS and Cr Kα X-ray source (hv=5414.8 eV) for HAXPES. Both sources have a spot size of 100 µm in a normal emission configuration at room temperature. No charge compensation was applied.
Core-level spectra (Hg 4f and Te 4d) were acquired with a pass energy (PE) of 27 eV for XPS and PE 140 for HAXPES. The zero-binding energy (BE) reference, corresponding to the Fermi level, was calibrated using the leading edge of a clean Ag foil.

Hg 4f and Te 4d core-level spectra were fitted using Gaussian-Lorentzian line shapes and linear background subtraction.

**He⁺ 500 keV irradiation procedure:** Irradiation was performed on the SAFIR Platform at Sorbonne University. The 500 keV ⁴He⁺ beam, produced by a HVEE AN2500 Van de Graaff accelerator, was collimated to a 2 mm diameter spot. Beam current was tuned in the 2 nA to 500 nA range. For the sake of illustration, 50 nA corresponds to 1.6 µA/cm²; 0.8W/cm²; 10¹³ particles/s, a flux chosen to allow reasonable irradiation times whilst limiting sample heating. In these conditions, the required fluxes were obtained in periods ranging from a few seconds to a few minutes. Fluence was accurately determined by using the entire irradiation chamber, insulated from earth, as a Faraday cup, and integrating the current with a Brookhaven model 1000 current integrator.

**X-ray irradiation procedure:** Irradiation was performed on an Xplorer 320 platform from Actemium. X-ray photons are produced by a COMET MXR-321 irradiation tube. Electrons generated by thermoionic emission of a filament are accelerated by an electric field toward a tungsten target (30° angle). Consequently, photons are emitted by the target from characteristic x-ray emission lines and bremsstrahlung in the material. This results in a broad soft to hard x-ray spectrum tunable by (i) the tension of the electric field defining the shape of the spectrum (ii) the filament current that linearly scales the flux of photons (iii) high pass energy filters to remove the low energy photons that are quickly stopped in the stack under study. The flux in given condition is monitored by a PTW 23342 probe measuring the dose rate in mGy/s. Devices were irradiated with 320 kVp tube voltage, 12.5 mA and 3 mm Be, 2 mm Al, yielding up to several kGy/h with respect to air. Devices are irradiated in air at room temperature, unbiased.

**Dose computation:** (i) X-ray induced ionizing dose and are computed from mass attenuation and mass energy-transfer coefficient from NIST XCOM Xraycross section database. X-ray spectra are computed using SpekPy v3.0. In the X-ray irradiation condition the conversion factor from dose relative to air kerma (measurement by probe) are the following: x110.1 for HgTe and x3.15 for SiO₂ (ii) He⁺ induced ionizing dose and displacement damage dose are computed based on Stopping and Range of Ions in Matter (SRIM) electronic and nuclear energy loss coefficient in the matter.

**Ammonium phenyldithiocarbamate synthesis (NH₄PDTC)[⁵⁰,⁵¹]:** In a 3-neck 100 mL flask under nitrogen bubbling at room temperature, equipped with a trap of NaClO, 25 mL of NH₄OH, 25 mL acetone and aniline (10 mL, 0.11 mol) were introduced and cooled down with an ice bath. Then, CS₂ (10 mL, 0.16 mol) was added dropwise with vigorous stirring. The solution turned red after 5 minutes, and a pale-yellow crystalline product slowly precipitated over the following 90 minutes. The product was collected by vacuum filtration and washed with 4 times CHCl₃. The NH₄PDTC was dried under vacuum and stored in a freezer to prevent decomposition.

**Cadmium bis(phenyldithiocarbamate) synthesis [Cd(PDTC)₂]⁵⁰:** In an Erlenmeyer flask, NH₄PDTC (600 mg, 3.2 mmol) was dissolved in 50 mL water. The solution was clear yellow. Then, Cd(NO₃)₂·4H₂O (493 mg, 1.6 mmol) was dissolved in 40 mL water and added dropwise to the flask over 5 minutes, leading to immediate precipitation of Cd(PDTC)₂ as a pale yellow powder. The product was collected by centrifugation, and washed with 25 mL of absolute ethanol. The precipitate was ground with a mortar and pestle, dried under a Schlenk line and stored in a desiccator. Yield: (Mw=449 g.mol⁻¹)
**HgTe core for core shell material:** In a 100 mL three-neck flask, 36 mL of oleylamine was degassed under vacuum at 110°C for 1 h. Then the atmosphere was switched to N₂ and the temperature was set at 90°C. Meanwhile, in a 20 mL vial, 194 mg (0.5 mmol) of HgBr₂ with 256 µL of oleic acid (0.8 mmol) was dissolved in 3.6 mL of oleylamine under sonication and degassed at 110°C for 30 min. Then, the solution in the vial was cooled down to room temperature and switched to N₂ atmosphere. 0.4 mL of TOP:Te (1 M) was injected into the vial. The solution turned orange quickly and was injected into the hot oleylamine in flask through a syringe. After 30 s, the reaction was quenched with 2 mL of a solution of DDT in toluene (10% v/v) and ice bath. The content of the flask was transferred to a falcon and precipitated by adding MeOH. The pellet was redispersed in toluene. The nanocrystals were precipitated a second time with absolute EtOH and redispersed in toluene. The toluene solution was centrifugated to remove the unstable phase and then filtered with 0.2 µm PTFE filter. This material is the one used for the detection side.

**CdS shell growth:** 36 mg CdCl₂ was added to 36 mL of a 50% (v/v) oleylamine-octadecene solution in a flask and was degassed at 110°C for 30 min. The mixture was then cooled down to 40°C and switched to N₂ atmosphere. 7 mL of HgTe core solution (0.45 OD at 400 nm after a 500x dilution) was introduced to the flask, and 3 cycles of vacuum/N₂ cycles were conducted. Cd(PDTC)₂ (100 mg, 2 mmol) in 2.6 mL of a 25% (v/v) oleylamine-octadecene mixture was then injected at 40°C quickly, and the flask was heated up to 80°C for 2 min. Then, degassing was done to remove CS₂. The reaction was quenched by injecting 2 mL of a 10% (v/v) DDT/OA-toluene solution and cooling down to room temperature. The content in the flask was transferred to a centrifuge tube and precipitated with EtOH. The pellet was redispersed in toluene and then precipitated again with IPA. After redispersion, the toluene solution was centrifugated to remove the unstable phase (the supernatant was kept).

**Nanocrystal coupling to readout integrated circuit:** readout circuits are provided by New Imaging Technologies. The circuit is a NIT1601 quantumC, with VGA format (640x512 pixels, 15 µm pitch). It enables the application of in-plane electric field, allowing for photoconductive operation of the ROIC. The ROIC surface is planarized to minimize texture of the NC film and packaged before NC deposition. Prior to NC deposition, the surface of the ROIC is plasma cleaned using O₂ plasma to enhance its surface wettability. NC ink is spin-coated so that a 200 nm thick film is formed. Then the detector is dried under vacuum for 2h. Following that, the film is annealed at 100°C for 5 min in air. The chip is then integrated into a home-built camera, which includes a Peltier stage to control the chip temperature down to -40°C and control driving bias and clocks.

## DATA AVAILABILITY

The data that support the findings of this study are available from the corresponding author upon request.

## ACKNOWLEDGMENTS

The authors acknowledge as well CNES and Thales Alenia Space for co-funding this research work within the space scope. We acknowledge support from the EMIR&A French network (FR CNRS 3618) on the platform SAFIR. The project is supported by ERC grant AQDtive (grant n°101086358) and from French National Research Agency (ANR) through the grants MixDferro (ANR-21-CE09-0029), Quicktera (ANR-22-CE09-0018), Operatwist (ANR-22-CE09-0037-01), E-map (ANR-23-CE50-0025), DIRAC (ANR-24-ASM1-0001), camIR (ANR-24-CE42-2757) and Piquant (ANR-24-
CE09-0786). We acknowledge the use of clean-room facilities from the "Centrale de Proximité Paris-Centre" and support from Renatech+ for micro and nanofabrication. This project has also received financial support from the CNRS through the MITI interdisciplinary programs (project WITHIN) and Region Ile de France through Sesame project INSIDE.

## COMPETING INTEREST

The authors declare no competing interests.

## Supporting Information

Supporting Information includes (i) description of the irradiation step, (ii) extra photoemission analysis of the sample including spectra decomposition and HAXPES data.

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Supporting information

Infrared nanocrystals for space application: hardness to irradiations

Alexandre Neyret¹⁻⁴, Dario Mastrippolito², Bingbing Xia², Adrien Khalili², Maxime Lebreton⁵, Giorgia Strobbia², Albin Colle², Marco Paye², Mariarosa Cavallo², Erwan Bossavit², Claire Abadie², Yoann Prado², Debora Pierucci², Victor Parahyba⁶, Francois Coursaget⁶, David Darson⁵, Emrick Briand², Ian Vickridge², Stephane Demiguel³, Sebastien Massenot¹, Jean-Marc Belloir⁴, Vincent Goiffon¹*, Emmanuel Lhuillier²*

¹ ISAE-SUPAERO, Université de Toulouse, 31055 Toulouse, France.

² Sorbonne Université, CNRS, Institut des NanoSciences de Paris, 4 place Jussieu, 75005 Paris, France.

³Thales Alenia Space, Allée des Gabians, Batiment V01 – 415, BP 99, 06156 Cannes la Bocca Cedex, France

⁴CNES, Centre Spatial de Toulouse, 18 Avenue Édouard Belin, 31400 Toulouse, France.

⁵ Laboratoire de Physique de l'Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, 75005 Paris, France.

⁶New Imaging Technologies SA, 1 impasse de la Noisette 91370 Verrières le Buisson, France.

*To whom correspondence should be sent: vincent.goiffon@isae-supao.fr; el@insp.upmc.fr

Table of content

<table><tr><td>1. Irradiation sources</td><td>2</td></tr><tr><td>2. Analysis of the X-ray irradiated sample</td><td>4</td></tr><tr><td>3. Photoemission analysis of the He<sup>+</sup> irradiated sample</td><td>6</td></tr></table>
1. Irradiation sources

<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /></figure>

**Figure S 1 X-ray irradiation.** a. Image of the sample with the X-ray irradiator. Partial shadowing of the sample by introducing a steel block on the optical path. b. Spectrum of the source operated under 320 kVp with 3 mm Be inherent filtering and additional 2 mm Al to cut low energy X-ray c. is a schematic of the scene from part a. d. is a top schematic of the irradiated sample.
<figure><img src="image_14.png" /></figure>

**Figure S 2 He⁺ source.** a. Image of the Safir Van de Graaff accelerator from Sorbonne Université. The instrument is used to generate positively charged helium ions with a 500 keV acceleration. b. Mean energy deposition profile resulting from one 500 keV Helium ion. The major contribution comes from ionization (black) and recoil (red) for a sample made of an HgTe layer deposited on a glass substrate. Both ionization and recoils energy deposition are constant in the detection layer.
## 2. Analysis of the X-ray irradiated sample

<figure><img src="image_15.png" /><figcaption>**Figure S 3 Evolution of the IV under various dose of X-ray radiation.**</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>**Figure S 4 Normalized absorption spectra before and after X-ray (4.2 Grad[HgTe]) irradiation.**</figcaption></figure>
<figure><img src="image_17.png" /><figcaption>**Figure S 5 XPS spectra decomposition for the X-ray irradiated sample.** a. (resp b.) Core level relative to Te 4d) before (resp. after) X-ray irradiation. For all these curves the source is an Al ka (1486.6 eV).</figcaption></figure>

<figure><img src="image_18.png" /><figcaption>**Figure S 6 HAXPES spectrum from HgTe NCs after He⁺ irradiation.** a. HAXPES spectrum for Hg 4f for the pristine film and irradiated film. b. Same for the Te 4d state.</figcaption></figure>
3. Photoemission analysis of the He⁺ irradiated sample

<figure><img src="image_19.png" /></figure>

**Figure S 7 XPS spectra decomposition for the He⁺ irradiated sample.** a. (resp b.) Core level relative to Te 4d) before (resp. after) He⁺ irradiation. For all these curves the source is an Al ka (1486.6 eV).