# Comparison of 2 processes based on NIL and lift-off for the fabrication of thick nano antennas for solar PV-TE applications

Jean Baptiste Doucet, Franck Carcenac, Léopold Boudier, Inès Revol

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Jean Baptiste Doucet, Franck Carcenac, Léopold Boudier, Inès Revol. Comparison of 2 processes based on NIL and lift-off for the fabrication of thick nano antennas for solar PV-TE applications. 51st International Micro and Nano Engineering Conference, Conference Organising Chair: Zahid Durrani, Imperial College London, UK; Co-organising and Program Chair: Harold Chong University of Southampton, UK, Sep 2025, Southampton, United Kingdom. hal-05508882

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Submitted on 13 Feb 2026

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Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
Comparison of 2 processes based on NIL and lift-off for the fabrication of thick
nano antennas for solar PV-TE applications

Jean-Baptiste Doucet<sup>a</sup>, Franck Carcenac<sup>a</sup>, Leopold Boudier<sup>a</sup>, Inès Revol<sup>a</sup>

a LAAS-CNRS, Université de Toulouse, Toulouse, 31400, France
e-mail : jbdoucet@laas.fr

Since conventional solar cells do not absorb the near-infrared and infrared solar spectrum, improving efficiency by combining a photovoltaic cell with a thermoelectric generator in a hybrid energy device is a promising approach. A propitious method to enhance the conversion efficiency of this device involves implementing a nanostructured photothermal interface between the solar cell and the thermoelectric generator. In this respect, diabolo-shaped nickel nano antennas are a good candidate for such interfaces, and they can be created using electron-beam lithography and lift-off techniques [1]. However, we require a faster and more cost-effective lithography method to address the demands of large surface areas at reduced costs.

Although nanoimprint lithography has proven to be an efficient method to combine with lift-off for metal deposition as early as 1995[2], it was only suitable for very thin layers at that time. Bilayer or trilayer lift-off processes have been investigated subsequently to achieve thicker depositions, and commercial solutions are proposed, but the targeted metal deposition thickness is only 40 nm[3].

For efficient photothermal conversion, a metal thickness of at least 150 nm is required, while the neck of a
typical diabolo structure needs to be as narrow as 50 nm.

We present here both bilayer and trilayer lift-off processes that we developed, along with the results we
obtained using these processes for depositing metals with thicknesses of 150 nm and above.

Both processes rely on soft nanoimprint lithography [4] combining thermal imprinting in a polymer foil with a UV nanoimprint step, based on a simple methacrylate homemade photoresist, with the secondary polymer mold. For the lift-off, we investigated several hard layer/sacrificial underlayer combinations.

Although the bilayer process does not meet the needs for high aspect ratios and sub-100 nm definition, it is simpler and involves a wet etching step instead of a dry etching one, and might be of interest for larger structures. When we use our trilayer nanoimprint and lift off process on silicon or fused silica, it shows that thicknesses above 150 nm and even 200 nm can be achieved. The definition of the diabolo antennas is similar to what is obtained with electron beam lithography, including the 50 nm large neck (see Figs 1, 2 and 3).

This work was supported by the LAAS-CNRS micro and nanotechnologies platform, a member of the French RENATECH network, and the French Agence Nationale de la Recherche (ANR), under grant ANR-21-CE50-0003 (project HYDRES).

<footnote>[1] Hanauer et al., Photothermal Conversion of Solar Infrared Radiation by Plasmonic Nanoantennas for Photovoltaic-Thermoelectric Hybrid Devices ACS Applied Energy Materials 2023, 6, 2128.</footnote>

<footnote>[2] S. Chou, et al., Imprint of sub-25 nm vias and trenches in polymers, Appl. Phys. Lett. 67 (21) (1995)</footnote>

<footnote>[3] T. Handte, et al., Manufacturing of nanostructures with high aspect ratios using soft UV-nanoimprint lithography with bi-and trilayer resist systems, Micro Nano Eng., 14 (2022)</footnote>

<footnote>[4] S. Pelloquin, et al., Soft mold NanoImprint Lithography: a versatile tool for sub-wavelength grating applications, Microsyst. Technol. 1–8 (2018).</footnote>
<figure><img src="image_2.png" /><figcaption>**Figure 1.** SEM images of Ni structures made by NIL and our trilayer lift-off process on silicon. Tilted view of various shapes (left), vertical view of diabolo (right)</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>**Figure 2.** AFM image of Ni antennas made by NIL and our trilayer lift-off process on fused silica showing that a thickness of more than 200 nm can be reached</figcaption></figure>

<figure><img src="image_4.png" /><figcaption>**Figure 3.** AFM images of various antennas obtained by > 200 nm Ni deposit after NIL and our trilayer lift-off process on fused silica</figcaption></figure>