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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.
Vacuum ultraviolet spectroscopy of pyrimidine derivatives
Publication . Kossoski, Fábris; Mendes, Mónica; Lozano, Ana I.; Rodrigues, Rodrigo; Jones, Nykola C.; Hoffmann, Søren V.; da Silva, Filipe Ferreira; CeFITec – Centro de Física e Investigação Tecnológica; DF – Departamento de Física; Faculdade de Ciências e Tecnologia (FCT); RSC - Royal Society of Chemistry
As a prototypical molecule in the important class of halopyrimidines, 2-chloropyrimidine has been the subject of numerous spectroscopic studies. However, its absorption spectrum under vacuum ultraviolet (VUV) radiation has not yet been reported. Here, we close this gap by presenting high-resolution VUV photoabsorption cross-sections in the 3.7-10.8 eV range. Based on time-dependent density functional theory (TDDFT) calculations performed within the nuclear ensemble approach, we are able to characterize the main features of the measured spectrum. By comparing the present results for 2-chloropyrimidine with those of 2-bromopyrimidine and pyrimidine, we find that the effect of the halogen atom increases remarkably with the photon energy. The two lowest-lying absorption bands are overall similar for the three molecules, apart from some differences in the vibrational progressions in band I (3.7-4.6 eV) and minor energy shifts in band II (4.6-5.7 eV). Larger shifts appear in band III (5.7-6.7 eV), especially when comparing pyrimidine with the two halogenated species. The three molecules absorb more strongly in the region of band IV (6.7-8.2 eV), where the bands look qualitatively different because the mixing of excited configurations is strongly dependent on the species. At higher energies (8.2-10.8 eV) the three spectra no longer resemble each other. An important finding of this study is the very satisfactory comparison between experiment and theory, as the combination of TDDFT calculations with the nuclear ensemble approach yields cross-sections much closer to experiments than the simpler vertical approximation, in shape and magnitude, and across the whole spectral range surveyed here.
Valence and Rydberg excitations of 4-fluorotoluene in the 4.3-10.8 eV photoabsorption energy region
Publication . Dalagnol, LVS; Kumar, S; Lozano, AI; Bettega, MHF; Jones, NC; Hoffmann, SV; Barbosa, AS; Limao-Vieira, P; CeFITec – Centro de Física e Investigação Tecnológica; DF – Departamento de Física; PERGAMON-ELSEVIER SCIENCE LTD
This work reports on the first measurements of the lowest-lying singlet states as studied by photon spectroscopy for para-fluorotoluene, 4-C7H7F. Here we present the high-resolution vacuum ultraviolet photoabsorption spectrum in the 4.3–10.8 eV energy-range, with assignments supported by ab initio calculations (vertical excitation energies and oscillator strengths) at two different levels of theory, equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) and time-dependent density functional theory (TD-DFT). The electronic state spectroscopy of 4-C7H7F reveals the main character of the transitions to be valence, mixed valence-Rydberg and Rydberg, with the associated vibronic series. The absolute cross-section measurements were obtained and used to estimate the photolysis lifetime of 4-fluorotoluene from the sea level up to limit of the stratopause (50 km) in the Earth's atmosphere.
The electronic spectra of trifluoroacetic acid and chlorodifluoroacetic acid in the 4.5 – 10.8 eV photon energy region
Publication . Puppi, P. S.; Barbosa, A. Souza; Jones, N. C.; Hoffmann, S. V.; Akther, U. S.; Mason, N. J.; Limão-Vieira, P.; CeFITec – Centro de Física e Investigação Tecnológica; DF – Departamento de Física; Faculdade de Ciências e Tecnologia (FCT); PERGAMON-ELSEVIER SCIENCE LTD
Synchrotron radiation has been used to record for the first time absolute vacuum ultraviolet photoabsorption cross-sections of trifluoroacetic acid (TFA) and chlorodifluoroacetic acid (CDFA) in the 4.5–10.8 eV energy range. In order to further our knowledge of the major electronic transitions and thus help interpret the photoabsorption data, theoretical calculations using time-dependent density functional theory (TD-DFT) level have been performed. These calculations have provided important information on the nature of the excited electronic states which have been assigned to valence, mixed valence-Rydberg and Rydberg transitions. Due to the lack of any information about CDFA ionic states, we also provide Equation-of-Motion Coupled-Cluster Single and Doubles (EOM-CCSD) vertical ionisation energies. Photolysis lifetimes in the Earth's atmosphere for both chemical compounds have also been estimated from the absolute photoabsorption cross-section data.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
Concurso de avaliação no âmbito do Programa Plurianual de Financiamento de Unidades de I&D (2017/2018) - Financiamento Programático
Número da atribuição
UIDP/00068/2020