The SPACE PHOTONICS project addresses the need for optical metasurfaces and metamaterial engineering by implementing new nanolayers of Ag, Au, SiO2, ZnO, graphene oxide, deposited on special glasses, silicon and silicon oxide. Such a metamaterial has a negative refractive index independent of the angle (i.e. it has both negative permittivity and permeability), allowing it to act as a superlens and have reduced dimensions at the same time. The superlens (or flat lens), as a periodic structure of metal/dielectric nanolayers, represents an artificial component, capable of functioning as a lens tuned to optical frequencies. The new optical lens will be designed and developed by the project partners with the idea of obtaining new types of metasurfaces and photonic components. Using the dedicated technology (Radio Frequency Magnetron Sputtering and Lithography Processing) we propose a state-of-the-art technology up to TRL3.
General objectives:
"State of the art" of metamaterials and superlenses in space applications.
Analysis of ESA experiments for possible future developments in the use of metasurfaces for micro and nanosatellites.
Approaching appropriate coating techniques for obtaining thin nanometric layers with special design. With the help of the coating system we can produce, control and measure a very thin layer of Ag, Au in the range from 1 nm to 10nm. Studying surfaces and special design for practical metasurfaces.
Optimization of the deposition technique for obtaining ultrathin nanostructured films.
Chemical, structural and morphological analysis of components on different substrates for applications in space optics.
Structural and optical characterization: XRD, XPS, AFM, optical microscopy & profilometry, UV-Vis-NIR spectroscopy, ellipsometry, refractive index measurements of substrate materials and deposited components.
Experimental procedures regarding modification, nano-partitioning of surfaces through the lithography process. Careful design of the specific metamaterial for the experimental model.
Integrating the lithography process into the experimental model.
Design of materials with metamaterial properties, metasurfaces. Characterization of sample surfaces deposited and processed by lithography; concept technology.
RESULTS
Stage I
This stage included the 7 activities (A1.1 - A1.7) provided for in the Research Project Activity Plan. The study focused mainly on presenting the particularities of ultra-thin films that are to be used in the creation of structures with metamaterial behavior. The research project addresses the need to obtain optical metasurfaces and metamaterial engineering based on ultra-thin films (1-10 nm) deposited on different substrates (optical glass, quartz, silicon, SiO2/silicon). The constructive solutions of the technology concept - superlens, useful for space microsatellites, according to the current research stage were deepened in this stage together with the team of the first floor. The same was done for metamaterials, with possible applications in space microsatellites, obtained in recent years, emphasizing the beneficial role of the involvement of graphene in their structure. A whole study in our laboratories led us to optimize the materials used (e.g. Au, Ag) to be deposited on different types of substrates.
The solution for the experimental model of deposition of ultra-thin (1-10 nm) nanostructured films was proposed and described in detail, in order to prepare the future concept of technology - superlens, useful in space microsatellites (according to the specialized literature, a careful design of the specific metamaterial).
The technical study was carried out in partnership with the SME team. Under these conditions, the project partners (SME), took care of carrying out tests for technological transfer, obtaining controlled coatings through deposition techniques, with predetermined thicknesses. The functionality of the deposited nanostructures was emphasized, by performing structural analyses. Based on the depositions made, we were able to optimize the deposition parameters to obtain thin nanostructured films, useful in the creation of superlenses. We consider, within the framework of future activities, the design/simulation of the concept of technology - superlens. Algorithms for the structural, chemical and morphological characterization of ultra-thin films deposited by the radio frequency magnetron sputtering technique were performed. Finally, the study analyzes this research in order to establish a link with ESA experiments and to be in line with ESA programs for possible future developments, the use of metasurfaces, metamaterials for micro and nanosatellites. Possible programs for the design and 3D simulation of metamaterials. The foundations are laid for approaching a strategy for a higher TRL within ESA programs.
Result indicators:
research related to the concept of superlens technology in space microsatellites has been defined and identified at the current level
investigations have been carried out to select materials for the creation of metamaterialse
the necessary elements for metamaterials used in space applications were presented
deposition parameters for nanostructured films were proposed and selected
structural analysis techniques for deposited nanostructured films were prioritized and selected
technological transfer was achieved by optimizing the deposition conditions of ultrathin films and structural analysis techniques were selected for deposited nanostructured films
possible future developments in metamaterials research, in accordance with ESA programs, for applications in space optics, have been identified and established
Stage II
This stage included the 6 activities (AII.1 - AII.6) provided for in the Activity Plan of the research project. The scientific and technical study was carried out in a close collaboration agreement between the three teams. Within the research project, we focused at the beginning of this stage on the selection of algorithms for determining the optical properties of the deposited samples. Performing optical measurements in the UV-Vis-NIR range, ellipsometric measurements of the refractive index of the deposited materials. Within the second stage, nanostructures with good optical behavior were realized, investigated by models of the type: Swanepoel, Drude, Wemple DiDomenico. The optical, electrical and structural investigations of the nanostructures realized were carried out taking into account the type of substrate used (silicon, quartz, optical glass, borosilicate glass), the material used (noble metal, dielectric) and the thickness of the ultra-thin film (1-10 nm). Algorithms for optimizing the depositions for each sample, taking into account that with the increase in the thickness of the layers and the fundamental absorption edge moves towards longer wavelengths. From ellipsometric measurements, we were able to conclude that the dispersion of the refractive index for the investigated samples presents a normal dispersion, in the spectral range in which the measurements were made. Within the algorithms for determining the optical properties of the deposited surfaces, we used the Wemple-DiDomenico model determining the bandgap width for the analyzed samples. The dependence of the radiation absorption coefficient, α, on the wavelength for the deposited samples was calculated according to Swanepoel's method.
The optical response of the deposited materials is described by the Drude model, by fitting the experimental dependencies for ε' and ε". The integration of graphene oxide into nanostructures was achieved by centrifuging a graphene oxide (GO) dispersion.
Functional modeling/simulation procedures of the structures were performed with the finite difference method. A GO/Ag/SiO2/Ag/Si sample was tested and evaluated, deposited on a silicon substrate and the metamaterial effect was observed, with a negative refractive index. It was observed that for red radiation, the intensity is proportional to the angle, and for blue radiation it is inversely proportional. Using masks obtained by photolithography, the lithography process was allowed to be integrated into the experimental model, consisting of irradiating the PMMA/printing the structures on supports, with electron beam lithography (EBL).The highlighting of the metamaterial structures was done by SEM images, a linear structure based on metamaterial with a width of ~ 100 nm separated by 250 nm. Based on the depositions made, we were able to create a recipe for obtaining nanostructured multilayers, useful in the creation of superlenses. Under specific conditions, created by performing similar depositions, the technological transfer was carried out to our partner IMM, to obtain nanostructures with refractive index values that tend towards negative values. Through the studies and optimizations carried out within the framework of this project, important steps were taken towards the creation of metasurfaces for the development of new types of lenses that would help in future space missions. Under these conditions, the ISS partners took care of the involvement in the ESA programs, for possible future developments, of the use of metasurfaces, metamaterials, superlenses for micro and nanosatellites. Based on the design and 3D simulation of metamaterials/metasurfaces, respectively of the concept of technology – superlens, the basis for approaching a strategy for a higher TRL within ESA programs.
Result indicators:
research related to the concept of superlens technology in space microsatellites has been defined and identified at the current level
investigations have been carried out to select materials for the creation of metamaterials
the necessary elements for metamaterials used in space applications were presented
au fost propuşi şi selectaţi parametrii de depunere pentru filme nanostructurate obţinute
deposition parameters for nanostructured films obtained were proposed and selected
a fost atins transferul tehnologic, prin realizarea optimizării condiţiilor de depunere a filmelor ultrasubţiri şi au fost selectate tehnici de analiză structurală pentru filme nanostructurate depuse
technological transfer was achieved by optimizing the deposition conditions of ultrathin films and structural analysis techniques were selected for deposited nanostructured films
The functional modeling and simulation of the structures was performed using the Finite Difference Method (MDF). The selection of the constituents for metamaterials/metasurfaces was made based on how operable the materials are in the spectral range of interest, and which do not passivate under natural working conditions. For these reasons, we chose gold and silver, and SiO2 and ZnO as dielectric materials. Different types of substrates (silicon, quartz, borosilicate glass and optical glass) with transmissions of 90% and 97%, respectively, in the spectral range 0.8-1.2 μm, which are appropriate for the proposed research, will be used.
To create a metasurface, one starts with a flat plate on which structures of the order of microns or even nanometers are then deposited (or lithographed from). These modify the phase of the incident light, creating a new wavefront. For example, a metasurface with a hyperbolic phase profile (see Fig. 1) acts as a lens without spherical aberration. In this situation, the two-dimensional metasurface must function as a conventional spherical lens, i.e., the waves emerging from the metasurface must interfere constructively in the focal plane. According to Fermat's principle, the radiation transmitted through the metalens at different positions (x, y) should satisfy the phase relation:
Fig.1 - Theoretical phase simulation for lenses with various focal lengths: a) 10, b) 25, c) 37, d) 50, e) 75 and f) 100 mm.
For a classical lens the angle of refraction and, therefore, the focal length depend on the curvature of the lens surface and the material used to construct it. For metalenses there is no theoretical formula that correlates the refractive index to the focal length or numerical aperture. Therefore, the electromagnetic field resulting from the propagation of radiation through various structures can be defined by solving the boundary conditions of Maxwell's equations within some calculation methods, such as the Finite Difference Method (FDM) (Fig. 2).
Fig.2 - Simulation of the electric field passing through a plano-convex lens with a focal length of 25 mm, using FDM.
The first step in making a metalens is its design, taking into account the intended focal length and the wavelength(s) of the incident radiation for which it must be made. In Fig. 3a, b and c, half of the phase profile for such a metalens with a diameter of 400λ is shown. This first step in the design of a metalens is necessary to achieve the discretization of the phase depending on the size of the lens. In general, an incremental division into zones of π/4 is sufficient. Thus, we will have eight constant phase zones that will reconstruct the entire 2π domain. For technological and computational power reasons (in MDF simulations) we will select a smaller size for the metalens, considering a radius of 50λ. This approximation is sufficient to achieve a metalens with the desired properties.
Fig.3 - Phase profile for a metalens with focal length of 30 mm. A metalens with diameter of 400λ is simulated.
The next step is to find the spatial coordinates of the metalens corresponding to the constant phase zones. Table 1 presents the eight constant phase zones along with the radial spatial coordinates of the metalens, necessary to reconstruct the hyperbolic phase profile.
Table 1 - The 8 constant phase zones and the spatial coordinate domains along the radius of the metalens, corresponding to them.
phase [rad]
2π
7π/4
3π/2
5π/4
π
3π/4
π/2
π/4
r [mm]
0-0.5 2.8-3 4.1-4.2 5-5.2
0.5-1.2 3-3.2 4.2-4.4 5.2-5.3
1.2-1.6 3.2-3.4 4.4-4.5 5.3-5.4
1.6-1.9 3.4-3.5 4.5-4.6 5.4-5.5
1.9-2.2 3.5-3.7 4.6-4.7 5.5-5.6
2.2-2.4 3.7-3.8 4.7-4.8 5.6-5.7
2.4-2.6 3.8-4 4.8-4.9 5.7-5.8
2.6-2.8 4-4.1 4.9-5 5.8-5.9
Next, the elements that can induce the phase thresholds described above, without too much attenuation of the transmission, must be found. After several attempts, it was decided to adopt a unit cell in the form of a crossed Si dipole deposited on a SiO2 substrate. The dimensions of such a resonator together with the eight elements, corresponding to the phase thresholds multiple of π/4, are shown in Fig. 4.
Fig.4 - The unit cell of the metalens and the eight resonators of different sizes, used for phase control.
Thus, the metalens (Fig. 5) will be composed of a periodic array of identical elements in the form of crossed and precisely positioned dipoles. It can be seen that the only variable is the size L of the resonator (dipole). The unit cell has the size of 80 µm X 80 µm, W = 12 µm, H = 20 µm and the thickness of the SiO2 substrate is 0.5 µm.
Garoi Florin; Udrea Cristian; Damian Cristian; Prepelita Petronela, Coltuc Daniela IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY Volume: 9 Issue: 2 Pages: 200-208 Published: MAR 2019 [ DOI: 10.1109/TTHZ.2019.2890971 ]
F. Garoi, "Profilometry by polarizing phase-shifting interferometry", ROM J PHYS; acceptat spre publicare (2018) [ in press]
P. Prepelita, I. Stavarache, F. Garoi, C. Negrila, V.Craciun, M. Udrea, N. Becherescu, A. Nistorescu,
"Deposition of the ultra-thin layers to be integrated in the micro and nanosatellites", APPL SURF SCI –
urmeaza sa fie trimis (2019)
Conferences
Petronela Prepelita, V. Craciun, N. Becherescu, A. Nistorescu, Influence of deposition process on the
structural properties of gold and silver ultra-thin films, - ICPAM 12 Conference 2018
Petronela Prepelita, I. Stavarache, F. Garoi, C. Negrila, B. Sbarcea, V.Craciun, N.Becherescu, A.Nistorescu, Role of annealing treatment in oxide thin films deposited by rfMS technique - ICPAM 12 Conference 2018
Petronela Prepelita, I. Stavarache, D. Craciun, F. Garoi, C. Negrila, V. Craciun, Comparative analysis of asdeposited and rapid thermal annealed ITO thin films, EMRS FALL Conference 2017
Petronela Prepelita, Doina Craciun, Florin Garoi, Implementation of new nano-films of Ag, Au, SiO2, ZnO for metamaterial engineering, IBWAP Conference 2018
Petronela Prepelita, Influence of deposition process on the structural properties of Au ultra thin films, IBWAP Conference 2018
F. Garoi, Petronela Prepelita, I. Iordache, M. Bojan, Fractal dimension of speckle images for roughness
assessment of thin films, ISCP-INDLAS Conference 2018.
Petronela Prepelita, Valentin Craciun, Florin Garoi, Mihaela Filipescu, Deposition of the nanostructured multilayers using rfMS technique EMRS FALL Conference 2018
Petronela Prepelita, I. Stavarache, D. Craciun, F. Garoi, C. Negrila, B. Sbarcea, V. Craciun Optical properties of as-deposited and rapid thermal annealed ITO thin films, TCM Conference 2018
Workshop
Workshop withing Vasile Alecsandri University from Bacău, promoting the project STAR 178
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