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Projeto de investigação
Institute for Plasmas and Nuclear Fusion
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Publicações
Plasma-enabled growth of vertically oriented carbon nanostructures for AC line filtering capacitors
Publication . Bundaleska, N.; Felizardo, E.; Santhosh, N. M.; Upadhyay, K. K.; Bundaleski, N.; Teodoro, O. M. N. D.; Botelho do Rego, A. M.; Ferraria, A. M.; Zavašnik, J.; Cvelbar, U.; Abrashev, M.; Kissovski, J.; Mão de Ferro, A.; Gonçalves, B.; Alves, L. L.; Montemor, M. F.; Tatarova, E.; CeFITec – Centro de Física e Investigação Tecnológica; DF – Departamento de Física; North-Holland | Elsevier
Self-standing vertically oriented carbon nanostructures (VCNs) were synthesized using a large-scale microwave plasma under low-pressure conditions, employing methane as a carbon precursor. The influence of plasma operational and substrate conditions on nanostructure growth and morphology were systematically studied. Furthermore, post-synthesis N-doping of VCNs with nitrogen content of 2.4 at% N was achieved using an Ar-N2 microwave plasma. Plasma-enabled direct deposition of VCNs, both doped and un-doped, onto nickel foils has been accomplished. The assessment of the developed nanostructures as electrodes in high-frequency AC filtering capacitors, has demonstrated an overall capacitance of approximately 480 µF at 100 Hz, with a cut-off frequency of 4 kHz for a phase angle of −45°. The excellent electrochemical performance can be attributed to the appropriate structural and morphological properties peculiar for the directly deposited on nickel foil VCNs providing binder-free electrode fabrication, thus enhancing the electrode's conductivity and charge transfer kinetics. This plasma-enabled approach for electrode design on a large scale, coupled with excellent filtering performance, paves the way for many applications in high-frequency scenarios, offering an environmentally friendly alternative to conventional electrolytic capacitors.
Low temperature electrical transport in microwave plasma fabricated free-standing graphene and N-graphene sheets
Publication . Valcheva, E.; Kirilov, K.; Bundaleska, N.; Dias, A.; Felizardo, E.; Abrashev, M.; Bundaleski, N.; Teodoro, O. M. N. D.; Strunskus, Th; Kiss’ovski, Zh; Alves, L. L.; Tatarova, E.; CeFITec – Centro de Física e Investigação Tecnológica; DF – Departamento de Física; Institute of Physics Publishing
In this paper, the electrical transport in free-standing graphene and N-graphene sheets fabricated by a microwave plasma-based method is addressed. Temperature-dependent resistivity/conductivity measurements are performed on the graphene/N-graphene sheets compressed in pellets. Different measurement configurations reveal directional dependence of current flow—the room-temperature conductivity longitudinal to the pellet’s plane is an order of magnitude higher than the transversal one, due to the preferential orientation of graphene sheets in the pellets. SEM imaging confirms that the graphene sheets are mostly oriented parallel to the pellet’s plane and stacked in agglomerates. The high longitudinal electrical conductivity with values on the order of 103 S/m should be noted. Further, the current flow mechanism revealed from resistivity-temperature dependences from 300K down to 10K shows non-metallic behavior manifested with an increasing resistivity with decreasing the temperature d ρ / d T < 0 usually observed for insulating or localized systems. The observed charge transport shows variable range hopping at lower temperatures and thermally activated behaviour at higher temperatures. This allows us to attribute the charge transport mechanism to a partially disordered system in which single graphene sheets are placed predominantly parallel to each other and stacked together.
Measurement of 9Be(3He,pi )11B (i = 0, 1, ..., 9) nuclear reaction cross sections in the 1.0 MeV to 2.5 MeV energy range
Publication . Vítor, C. M.; Alves, E.; da Silva, R. C.; Mateus, R.; Cruz, J.; Catarino, N.; DF – Departamento de Física; LIBPhys-UNL; IOP Publishing
In fusion materials research using ion beam analysis techniques, the reactions 9Be(3He,pi )11B (i = 0, 1, 2…) are relevant to probe Be-related plasma-wall interactions. The cross sections for this reaction have been examined previously; nevertheless, there is a ∼40% difference in the studied energy interval between the two most relevant earlier studies. Therefore, a new data set for the differential cross sections 9Be(3He,pi )11B for the proton groups i = 0, 1, …, 9 is given. The measurements were performed using a thin beryllium film in the laboratory energy range from 1.0 MeV to 2.5 MeV in steps of 50 keV for lab angles from 115° to 165° to the incoming beam direction in steps of 10°. Additional measurements for intermediate angles were performed over the same energy range in steps of 250 keV. The results are in good agreement with one of the previous studies and a benchmarking measurement was performed against the yield of a beryllium thick target at 2.5 MeV for 135°.
Plasma-enabled multifunctional platform for gram-scale production of graphene and derivatives
Publication . Dias , Ana; Felizardo, Edgar; Bundaleska, Neli; Abrashev, Miroslav; Kissovski, Jivko; Ferraria, Ana M.; Rego, Ana M.; Strunskus, Thomas; Carvalho, Patrícia A.; Almeida, Amélia; Zavašnik, Janez; Kovacevic, Eva; Berndt, Johannes; Bundaleski, Nenad; Ammar, Mohammed Ramzi; Teodoro, Orlando M. N. D.; Cvelbar, Uroš; Alves, Luís L.; Gonçalves, Bruno; Tatarova, Elena; CeFITec – Centro de Física e Investigação Tecnológica; DF – Departamento de Física; Elsevier
Taking advantage of the high-energy-density microwave plasma environment as a unique 3D space for the self-assembly of free-standing nanostructures, a novel multifunctional platform for the continuous production of graphene and derivatives at the gram scale was developed. The platform is supported by a prototype plasma machine capable of performing a wide variety of industrially applicable processes within a single assembly environment. Free-standing graphene and nitrogen doped graphene, i.e., N-graphene nanosheets, and hybrid nanocomposites are assembled in a one-step process in seconds under atmospheric pressure conditions without the need of post-treatment. A single custom-designed machine enables the synthesis of an extensive array of hybrid nanomaterials featuring metal nanoparticles anchored in graphene. The method enables the conversion of a wide range of low-cost feedstock (e.g., ethanol, acetonitrile, etc.) into graphene and derivatives at a rate up to 30 mg/min. The resulting N-graphene sheets exhibit high quality, as evidenced by the highest reported presence of single atomic layers (45%), high ratio of 2D/G peak intensities in Raman spectra and N/O atomic ratio greater than one. The use of the obtained N-graphene in low secondary electron emission applications and in inkjet printing are explored. The presented plasma machine embodies significant potential to increase the effectiveness of plasma-driven process regarding productivity, costs and turnaround time.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
6817 - DCRRNI ID
Número da atribuição
UIDP/50010/2020