Scientific project:
Solar cells made of III-V materials present the best efficiencies among currently available technologies, up to 46% under concentration. Nevertheless, their cost is significantly higher than mainstream silicon modules. The major part of this cost, about 80% to 90%, lies in the III-V substrates necessary for the growth of monocrystalline materials with sufficient quality.

We propose to explore a new strategy to reuse the substrate for several consecutive growths, in order to drastically reduce its cost contribution. The main goal is to modify the surface of the III-V substrate, so that the fabricated III-V layers can be easily detached, leaving a clean surface suitable for subsequent layer fabrication. A promising route for surface modification consists in depositing graphene layers on top of the substrate (see the attached file for figures).

The objectives of the thesis project are twofold: (i) To define and develop the technological stages of the method, which include the manufacture and transfer of graphene, as well as the epitaxy itself (by molecular beam epitaxy). (ii) Clarify the nature of the physical interactions between the fabricated layers, the graphene, and the substrate. Several mechanisms may be involved, including Van der Waals interactions across the graphene layer, but also nucleation phenomena localized at graphene openings. The contribution of these phenomena needs to be quantified so that they can be manipulated to produce III-V thin films of sufficient quality for the production of high-efficiency solar cells. This would constitute a new tool for the growth of III-V materials, opening up a wealth of applications, such as photovoltaics (targeted in this project), but also photonics on silicon or flexible devices...

This work will take place at the Center for Nanoscience and Nanotechnologies (C2N) in the SUNLIT team. It includes several methods of fabrication (III-V by MBE, clean room processing) and characterization (luminescence, SEM, TEM). Collaboration with high level scientists in specialized techniques are expected (XPS, STM). This environment gives the PhD candidate many opportunities to tackle this project challenge and gain experience.

The ideal candidate will have a master degree in physics, engineering, material sciences or related. Previous experience in clean-room is desirable but not essential. The candidate must show good organization skills to fabricate the target materials, using methods implying numerous parameters, in a clean room environment. A proactive approach is expected. Collaborative work being at the core of the program, communication skills are required for team working as well as regular presentation of work progress in internal meetings and conferences.

Website: https://sunlit-team.eu

(see attached .pdf file)

Centre de Nanosciences et Nanotechnologies

 UMR 9001 du CNRS – Université Paris-Saclay

10 bd Thomas Gobert – 91 120 Palaiseau – France      

PhD proposal

 All-Dielectric Metamaterials for Zero-Index-Photonic  : 

 

Negative Index and Near-Zero Index Materials at Terahertz

 Éric Akmansoy

Département Photonique

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Scientific framework 

Metamaterials have opened a new field in physics and engineering. Indeed, these artificial structured materials give rise to unnatural fascinating phenomena such as negative index, sub-wavelength focusing and cloaking. Metamaterials also exhibit near-zero refractive index. :[1, 2] These open a broad range of applications, from the microwave to the optical frequency domain. Metamaterials have now evolved towards the implementation of optical components. :[3]

We consider All-Dielectric Metamaterials (ADM), which are the promising alternative to metallic metamaterials, because they undergo no ohmic losses and consequently benefit of low energy dissipation, and because they are of simple geometry. :[4] They consist of high permittivity dielectric resonators involving Mie resonances. We have experimentally demonstrated negative effective permeability and/or permittivity by the means of all-dielectric metamaterials. :[5] Previously, we have also demonstrated a negative index all-dielectric metamaterial. :[6]

Metamaterials that exhibit Near-Zero Index metamaterials (NZI) have a large number of applications including wavefront engineering, directivity and gain enhancement of antennas, electromagnetic cloaking, phase matching for nonlinear applications, unidirectional transmission, defect waveguides, Zero-index Materials (ZIM) cavities. :[7]

The main feature of Zero Index Materials is that the phase distribution of the EM field is nearly constant, because of the decoupling of the electric and the magnetic fields, that results in the “decoupling of the “spatial” (wavelength) and the “temporal” (frequency)”. :[2] Zero Index Photonics has consequently fundamental and technological implications on different subfields of optics and nanophotonics. Optical components and antennas systems operating in the terahertz range are the targeted devices.

Recently, we have numerically demonstrated a metadevice, namely, a metalens that focuses an incident plane wave and is less than one and a half wavelength thick. Its focal length is only a few wavelengths and the spot in the focal plane is diffraction-limited. :[8] We have also addressed the role of the coupling of the modes of Mie resonances in an all-dielectric metamaterial so as to achieve negative index and Near-Zero Index at terahertz frequencies. :[9]

General framework and work Plan

This work takes place within the framework of the DisPoNT ANR ASTRID project. It gathers a group of scientists of different disciplines (chemists, material scientists and physicists). :[10] who deal with All-Dielectric Metamaterials design, hight dielectric material fabrication, structuration and characterization :[10, 11, 12] 

 

1. l’IRCER (INC – UMR 7315 – Limoges)  ; 

2. le CROMA (INSIS – UMR 5130 – Chambéry)  ; 

3. le laboratoire Albert Fert (INP – UMR 137 – Palaiseau)  ; 

4. le C2N (INSIS/INP – UMR 9001 – Palaiseau). 

It has also been supported by the MITI  of the CNRS. Therefore, the PhD student will collaborate with the all consortium partners.

During this research project, All-Dielectric Metamaterials and Metarsurfaces, and Metadevices :[3] will be numerically designed ; Negative Index and Near-Zero Index will be addressed. The All-Dielectric Metamaterials will also be characterized in the THz frequency range. In the first instance, our aim is to demonstrate near-zero index and negative index. Then, we will consider and realize a graded index lens based on a metasurface (2D metamaterial) for applications to biology, medicine, atmospheric gaz sensing. 

 

Fig. 1: (left) Negative index from an ADM (shaded area)[9], (center) Mode coupling : frequency of the first two modes of Mie resonances as a function of the distance  between the two resonators ; frequency degeneracy is observed :[9] ; (right) PMMA mould fabricated by the LIGA process (Lab. Albert Fert) 

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Bibliography

 

[1]  Iñigo Liberal and Nader Engheta, "Zero-Index Platforms : Where Light Defies Geometry", https://www.optica-opn.org/home/articles/volume_27/july_august_2016/features/zero-index_platforms_where_light_defies_geometry/

[2]  I. Liberal and N. Engheta, “Near-zero refractive index photonics,” Nature Photonics, vol. 11, pp. 149 EP –, 03 2017.

[3]  N. I. Zheludev and Y. S. Kivshar, “From metamaterials to metadevices,” Nat Mater, vol. 11, pp. 917–924, 11 2012.

[4]  S. Jahani and Z. Jacob, “All-dielectric metamaterials,” Nature Nanotechnology, vol. 11, pp. 23 EP –, 01 2016.

[5]  T. Lepetit, E. Akmansoy, and J.-P. Ganne, “Experimental evidence of resonant effective permittivity in a dielectric metamaterial,” Journal of Applied Physics, vol. 109, no. 2, p. 023115, 2011.

[6]  T. Lepetit, É. Akmansoy, and J.-P. Ganne, “Experimental measurement of negative index in an all-dielectric metamaterial,” Applied Physics Letters, vol. 95, no. 12, p. 121101, 2009.

[7]  N. Shankhwar, Y. Kalra, Q. Li, and R. K. Sinha, “Zero-index metamaterial based all-dielectric nanoantenna,” AIP Advances, vol. 9, no. 3, p. 035115, 2019.

[8]  F. Gaufillet, S. Marcellin, and E. Akmansoy, “Dielectric metamaterial-based gradient index lens in the terahertz frequency range,” IEEE J Sel Top Quant, vol. 10. 1109/JSTQE. 2016. 2633825, 2017.

[9]  Akmansoy, Eric and Marcellin, Simon, “Negative index and mode coupling in all-dielectric metamaterials at terahertz frequencies,” EPJ Appl. Metamat., vol. 5, p. 10, 2018.

[10]  C. Dupas, S. Guillemet-Fritsch, P.-M. Geffroy, T. Chartier, M. Baillergeau, J. Mangeney, J.-F. Roux, J.-P. Ganne, S. Marcellin, A. Degiron, and É. Akmansoy, “High permittivity processed SrTiO3 for metamaterials applications at terahertz frequencies,” Scientific Reports, vol. 8, no. 1, p. 15275, 2018

[11] Djemmah, Djihad Amina and Geffroy, Pierre-Marie and Chartier, Thierry and Roux, Jean-François and Bouamrane, Fayçal and Akmansoy, Éric. "Processing High Permittivity TiO2 for All-Dielectric Metamaterials Applications at Terahertz Frequencies" , Proceedings of the Sixth International Symposium on Dielectric Materials and Applications (ISyDMA’6), pp. 177–183, 2022

[12] Djihad Amina Djemmah, Delphine Gourdonnaud, Pierre-Marie Geffroy, JeanFrançois Roux, Fayçal Bouamrane, Éric Akmansoy, "From bulk toward micro-structured TiO2 ceramics for All-Dielectric Metamaterials at terahertz frequencies", 18th European Conference on Antennas and Propagation (EUCAP2024), 17-22 March 2024 Glasgow, Scotland  

 

poursuite en thèse envisageable