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Projeto de investigação
Plasma Enabled and Graphene Allowed Synthesis of Unique nano Structures
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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.
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.
Prospects for microwave plasma synthesized N-graphene in secondary electron emission mitigation applications
Publication . Bundaleska, Neli; Dias, Ana M.; Bundaleski, Nenad; Felizardo, E.; Henriques, J.; Tsyganov, D.; Abrashev, Miroslav V.; Valcheva, Evgenia P.; Kissovski, J.; Ferraria, A. M.; do Rego, A. M. Botelho; Almeida, A.; Zavašnik, Janez; Cvelbar, Uroš; Teodoro, Orlando M. N. D.; Strunskus, Thomas; Tatarova, Elena; DF – Departamento de Física; CeFITec – Centro de Física e Investigação Tecnológica; Nature Publishing Group
The ability to change the secondary electron emission properties of nitrogen-doped graphene (N-graphene) has been demonstrated. To this end, a novel microwave plasma-enabled scalable route for continuous and controllable fabrication of free-standing N-graphene sheets was developed. High-quality N-graphene with prescribed structural qualities was produced at a rate of 0.5 mg/min by tailoring the high energy density plasma environment. Up to 8% of nitrogen doping levels were achieved while keeping the oxygen content at residual amounts ( 1%). The synthesis is accomplished via a single step, at atmospheric conditions, using ethanol/methane and ammonia/methylamine as carbon and nitrogen precursors. The type and level of doping is affected by the position where the N-precursor is injected in the plasma environment and by the type of precursors used. Importantly, N atoms incorporated predominantly in pyridinic/pyrrolic functional groups alter the performance of the collective electronic oscillations, i.e. plasmons, of graphene. For the first time it has been demonstrated that the synergistic effect between the electronic structure changes and the reduction of graphene $-plasmons caused by N doping, along with the peculiar “crumpled” morphology, leads to sub-unitary (textless 1) secondary electron yields. N-graphene can be considered as a prospective low secondary electron emission and plasmonic material.
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Entidade financiadora
European Commission
Programa de financiamento
H2020
Número da atribuição
766894