ROCAM 2024

INVITED LECTURE S2-IL11

Novel nanostructured nanocomposites with tunable conductivity for electromagnetic shielding and potential uses in electronics and optoelectronics applications

Emmanouil KOUDOUMAS1,2

1. National Institute for Research and Development in Microtechnologies, 077190 Voluntari, Romania
2. Center of Materials Technology and Photonics, School of Engineering, Hellenic Mediterranean University, 71410 Heraklion, Crete, Greece

Contact: koudoumas@imt.ro;koudoumas@hmu.gr

Electromagnetic interference (EMI) can disrupt the operation of electronic devices, equipment and systems, as well as can affect life. With the new generation of communications at 5G technology, EMI shielding becomes quite important, since, as frequency increase, so interference does. As a result, without proper shielding, our brand-new phones or other electronic equipment might not work in the right way. The present work concerns the design, synthesis, and characterization of novel rare earth elements doped metal oxide-graphene nanocomposites materials with tunable conductivity suitable for the shielding of electromagnetic radiation in the >5GHz spectral range. The ZnO:RE/Graphene (RE: Er, La, Sm) nanocomposite materials were obtained using a two stages method: electrospinning of precursor solutions followed by calcination at 600 °C (for 2 hours in N2 medium). All materials show a granular structure formed by nanocrystallites agglomerations randomly distributed in a lace-like and flakes-like matrix. Materials nanostructuring was found to be strongly affected by the nature of the dopant. Er dopant was found to lead to “aeration” of the nanomaterial promoting the formation of the lace-like matrix that suspends nanosized granular nanoparticles, while, in the case of La doping, the respective nanoparticles were smaller and the matrix was more compact. Sm doping resulted in smaller size nanoparticulates embedded in a porous 3D lace-like foamy matrix. The materials were found to exhibit a quite interesting conductivity variation as a function of frequency, since, this was presenting a considerable increasing for higher frequencies and temperatures. Simulations were performed to explain the unusual behavior of these materials. According to the theoretical and experimental observations, it seems that ZnO:RE/Graphene (RE: Er, La, Sm) nanocomposite materials may be excellent candidates to be used as tunable bandgap semiconductors in electromagnetic shielding applications.

Acknowledgments: This research was supported by project PNRR CF23/ 14 11 2022 financed by the Ministry of Research, Innovation and Digitalization in I8. Development of a program to attract highly specialized human resources from abroad in research, development, and innovation activities within the – PNRR-III-C9-2022 -I8 PNRR/2022/Component 9/investment 8.

INVITED LECTURE S2-IL12

Complex 3D nanostructured surfaces in WO3 thin films made by spray deposition

Mirela Petruta SUCHEA1,2

1. National Institute for Research and Development in Microtechnologies, 077190 Voluntari, Romania
2. Center of Materials Technology and Photonics, School of Engineering, Hellenic Mediterranean University, 71410 Heraklion, Crete, Greece

Contact: mira.suchea@imt.ro;mirasuchea@hmu.gr

The talk will present our recent studies regarding the evolution of a unique 3D structured surface of tungsten oxide (WO3) thin films made by spray deposition, not yet studied in detail, consisting of a complex combination of nano-balls and walls-like features. Since the surface morphology and structure play a crucial role in most optoelectronic applications, and WO3 is one of the most important metal oxide semiconductors in a huge variety of these applications, a detailed study of these, recently observed and reported, unique 3D complex architecture of WO3 films is of great importance for further development of films and devices. In this context, series of WO3 films with different thicknesses and made with different tungsten peroxide precursor concentrations were fabricated by spray pyrolysis. The samples were thoroughly characterized by field emission scanning electron microscopy (FE-SEM), X-raydiffraction and Raman spectroscopy. Results suggest that, for the employed fabrication parameters, the main differences in the structure affect mostly the surface morphology and slightly the surface texturing. These observations prove the viability of the fabrication by the spray pyrolysis of coatings with such surface morphology and open new perspectives for better sensors, electrochromic and photochromic devices, etc.

Acknowledgments: IMT’s contribution was partially supported by the Romanian Ministry of Research, Innovation and Digitalisation through the “μNanoEl,” Cod: 23 07 core Programme and project PNRR CF23/ 14 11 2022 financed by the Ministry of Research, Innovation and Digitalization in I8. Development of a program to attract highly specialized human resources from abroad in research, development, and innovation activities within the – PNRR-III-C9-2022 – I8 PNRR/2022/Component 9/investment 8. HMU contribution to this work was partially supported by NATO Science for Peace and Security Programme, grant G5868.

ORAL PRESENTATION S3-OP1

Strain analysis in vanadium oxide thin films by Rietveld refinement

 Cosmin ROMANITAN1,* , Ioan Valentin TUDOSE2 , Jose Manuel CAICEDO1,3, Iuliana MIHALACHE1 , Nikolay DJOURELOV4 , Oana BRINCOVEANU1 , Raluca GAVRILA1 , Cristina PACHIU1 , Andreea POPESCU1 , Mirela Petruta SUCHEA1,2,* , Emmanuel KOUDOUMAS1,2 , Jose SANTISO1

1. National Institute for Research and Development in Microtechnologies, 077190 Voluntari, Romania
2. Center of Materials Technology and Photonics and School of Engineering, Hellenic Mediterranean University, 71410 Heraklion, Crete, Greece
3. Catalan Institute of Nanoscience and Nanotechnology, ICN2, CSIC and The Barcelona Institute of Science and Technology (BIST), 08193 Bellaterra, Barcelona. Spain
4. Extreme Light Infrastructure-Nuclear Physics (ELI-NP), “Horia Hulubei” National R&D Institute for Physics and Nuclear Engineering (IFIN-HH), 077125 Magurele, Romania Contact: cosmin.romanitan@imt.ro; mirasuchea@hmu.gr

Vanadium oxides (VOx) compounds have unique properties that can be further exploited for a wide range of applications, such as charge storage, photodetectors, sensors, smart windows, thermochromic coatings or photocatalysis [1]. For example, vanadium dioxide (VO2) reveals a significant change in the resistance (for microbolometers) or in the transmission spectrum (for thermochromic coatings) with changing temperature. On the other hand, the layered crystal structure of vanadium pentoxide (V2O5) leads to the reversible lithium-ion insertion/extraction processes, becoming suitable for electrochromic coatings and charge storage devices. It was showed that crystallite size and defects are strongly linked with the characteristics of the MIT (metal-insulator transition) in VO2 [2], while higher texture coefficients on (001) in V2O5 could enhance the coloration efficiency in the range of -1 to +1 V, as well as the Li-diffusion in charge storage devices [3,4]. It is clear that a deep understanding of the crystal structure of the VOxmaterials is required for developing new applications with enhanced physicochemical properties. In this presentation, thin films of VO2 and V2O5were obtained by pulsed laser deposition (PLD) and spray pyrolysis technique (SPT) in different conditions. The microstructure of the prepared films was assessed non-destructively using X-ray diffraction in the framework of Rietveld refinement, which enables the calculation of the unit cellparameters, mean crystallite size and lattice strain. Other investigation tools, such as diffuse reflectance spectroscopy (DRS) or Raman spectroscopy support the Rietveld data. According to the experimental findings, the dislocations formed at the grain boundaries are further responsible for the transition from insulator to metallic phase, as well as for the electrochromic and charge storage ability of the material.

Acknowledgments: The financial support of the Core Program code 2307/29.12.2022 is gratefully acknowledged. MPS and EK acknowledge the partial support of PNRR/2022/C9/MCID/I8 CF23-14 11 2022 contract 760101/23.05.2023 financed by the Ministry of Research, Innovation and Digitalization in “Development of a program to attract highly specialized human resources from abroad in research, development, and innovation activities” within the –PNRR-IIIC9-2022 -I8 PNRR/2022/Component 9/investment 8. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 101007417 having benefitted from the access provided by ICN2 in Bellaterra, Barcelona within the framework of the NFFA-Europe Pilot Transnational Access Activity, proposal ID282.

POSTER PRESENTATION S2-PP15

Dependence of La-doped ZnO nanocomposite properties of dopant concentration for semiconductor materials fabricated by electrospinning calcination method

Cosmin ROMANITAN1 , Petronela PASCARIU1,2,3, Cristina PACHIU1 , Oana BRINCOVEANU1 , Iuliana MIHALACHE1 , Dumitru MANICA1 , Marina MANICA1,4, Florian PISTRITU1 , Andreea POPESCU1 , Oana NEDELCU1 , Octavian Narcis IONESCU1 , Mirela SUCHEA1,2*, Emmanouel KOUDOUMAS1,2*

1. National Institute for Research and Development in Microtechnologies, 077190 Voluntari, Romania
2. Center of Materials Technology and Photonics, School of Engineering, Hellenic Mediterranean University, 71410 Heraklion, Crete, Greece
3. “Petru Poni”Institute of Macromolecular Chemistry, 700487, Iaşi, Romania
4. Faculty of Physics, University of Bucharest, 077125 Magurele, Romania.
5. School of Engineering, Department of Electrical and Computer Engineering, Hellenic Mediterranean University, 71410 Heraklion, Crete, Greece

Contact: *mira.suchea@imt.ro; mirasuchea@hmu.gr; koudoumas@imt.ro; koudoumas@hmu.gr

Zinc oxide is one of the most important types of metal oxides that have been studied thus far, due to its excellent properties such as high transparency, high exciton binding energy (60 meV) and low toxicity. It has been employed in various applications, such as gas sensors, photovoltaic cells, fuel cells and even transistor fabrications. However, zinc oxide suffers from two main obstacles that limit its use. First, its high energy gap, which limits its absorption of visible light, limiting its uses in solar energy applications. Second its low electrical conductivity, which limits its uses in areas such as electronics and supercapacitors. One of the successful strategies for solving these two impasses is the doping process. Therefore, the effect of various metal dopants on the physical properties of zinc oxide was extensively explored. La-doped ZnO nanofibers were successfully synthesized by electrospinning, followed by calcination at 700 °C in air varying the dopant concentration from 0 to 5%. The microstructure and morphology of the La-doped ZnO nanocomposite semiconductors were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. The characterization shows that the resulting La-doped ZnO semiconductors have a nanostructured tridimensional microstructure that is strongly affected by La dopant content. XRD characterization shows the presence of some La2ZnOx phase at higher concentration (e.g., 1%). SEM studies shows that increase of La concentration leads to an increase of nanocrystallites size (while XRD analysis shows that almost constant) and a radical change of shape and assembling of agglomerations into the 3D microstructures. The present results analysis lead reveal that by electrospinning-calcination used technique one can still obtain novel and interesting ZnO based nanocomposite semiconductors with unique properties.

Acknowledgements: This research was supported by project PNRR CF23/ 14 11 2022 financed by the Ministry of Research, Innovation and Digitalization in I8. Development of a program to attract highly specialized human resources from abroad in research, development, and innovation activities within the – PNRR-III-C9-2022 -I8 PNRR/2022/Component 9/investment 8.