Papers by Pagona Papakonstantinou
CRC Press eBooks, Dec 19, 2017
Applied Sciences (Web), 2020
Applied Surface Science, Sep 1, 2016
Substitution of hetero-atom doping is a promising route to modulate the outstanding material prop... more Substitution of hetero-atom doping is a promising route to modulate the outstanding material properties of carbon nanotubes and graphene for customized applications. Nitrogen-doping has been introduced to ensure tunable work-function, enhanced n-type carrier concentration, diminished surface energy, and manageable polarization. Along with the promising assessment of N-doping effects, research on the N-doped carbon based composite structures is emerging for the synergistic integration with various functional materials. Nitrogen undoped/doped graphene nano-flakes (GNFs/GNFs:N) and multiwall carbon nano-tubes (MWCNTs/MWCNTs:N) are used for comparative study of their electronic/bonding structure along with their defects state. X-ray absorption near edge structure (XANES) spectroscopy shows that the GNFs:N produce mainly pyridine like structure; whereas MWCNTs:N shows graphitic nitrogen atoms are attached with the carbon lattice. The I D /I G ratio obtained from Raman spectroscopy shows that the defects is higher in MWCNTs:N than GNFs:N. The electron field emission result shows that the turn on electric field is lower (higher electron emission current) in case of MWCNTs:N than GNFs:N and are good agreement with XANES and the results obtained from Raman spectra.
RSC Advances, 2016
The improvement of the plasma illumination (PI) properties of a microplasma device due to the app... more The improvement of the plasma illumination (PI) properties of a microplasma device due to the application of nanocrystalline diamond-decorated graphene nanoflakes (NCD-GNFs) as a cathode is investigated. The improved plasma illumination (PI) behavior is closely related to the enhanced field electron emission (FEE) properties of the NCD-GNFs. The NCD-GNFs possess better FEE characteristics with a low turn-on field of 9.36 V mm À1 to induce the field emission, a high FEE current density of 2.57 mA cm À2 and a large field enhancement factor of 2380. The plasma can be triggered at a low voltage of 380 V, attaining a large plasma current density of 3.8 mA cm À2 at an applied voltage of 570 V. In addition, the NCD-GNF cathode shows enhanced lifetime stability of more than 21 min at an applied voltage of 430 V without showing any sign of degradation, whereas the bare GNFs can last only 4 min. The superior FEE and PI properties of the NCD-GNFs are ascribed to the unique combination of diamond and graphene. Transmission electron microscopic studies reveal that the NCD-GNFs contain nano-sized diamond films evenly decorated on the GNFs. Nanographitic phases in the grain boundaries of the diamond grains form electron transport networks that lead to improvement in the FEE characteristics of the NCD-GNFs.
Journal of Applied Physics, Feb 15, 2006
Polarization dependent studies of near edge x-ray absorption fine structure ͑NEXAFS͒ show evidenc... more Polarization dependent studies of near edge x-ray absorption fine structure ͑NEXAFS͒ show evidence for the presence of aligned-bonded carbon structures and the formation of a nonplanar CN phase in tetrahedral amorphous nitrogenated carbon ͑ta-CN͒ films deposited at room temperature. Moreover, the analysis of NEXAFS data as a function of nitrogen concentration and annealing temperature leads to a comprehensive assignment of the local CN bonding configurations in these ta-CN films and suggests an unusual and almost thermally stable nitrogenated carbon structure.
Nanotechnology, Jan 24, 2011
7th Joint MMM-Intermag Conference. Abstracts (Cat. No.98CH36275), Aug 25, 2005
Meeting abstracts, Oct 9, 2022
The design of a laser scribed polyimide sensor for the measurement of pH within wound environment... more The design of a laser scribed polyimide sensor for the measurement of pH within wound environments is described. A number of probe formats have been characterized with both potentiometric and voltammetric methodologies shown to provide a robust means of determining pH. The versatility of the laser patterning on polyimide is shown to yield a mechanically flexible double sided probe that could be suitable for use in a wide variety of clinical applications
International Journal of Nanotechnology, 2017
The magnetic effects of chlorine and oxygen functionalised NCNTs have been studied. The diamagnet... more The magnetic effects of chlorine and oxygen functionalised NCNTs have been studied. The diamagnetic behaviour of non-functionalised NCNTs changes to paramagnetic behaviour on Cl-functionalisation; on O-functionalisation NCNTs become ferromagnetic. A prominent cusp-like behaviour is observed at around ≈45 K in M FC and M ZFC measurements, further confirming the ferromagnetic behaviour of O-functionalised NCNTs; but Cl-functionalised NCNTs do not shows any cusp-like behaviour indicating formation of paramagnetic behaviour. The change of magnetic behaviour occurs owing to formation of different bonding with carbon/nitrogen and/or Fe-catalyst atoms that is verified with theoretical calculation. The initial computational results show that the differential bonding patterns of the Cl-functionalised and the O-functionalised NCNTs are the main cause for the different magnetic behaviour in these systems.
ACS Omega
Poor thermal conductivity in the through-thickness direction is a critical limitation in the perf... more Poor thermal conductivity in the through-thickness direction is a critical limitation in the performance of carbon fiberreinforced polymer (CFRP) composites over a broad range of applications in the aviation industry, where heat dissipation is required (e.g., battery packs, electronic housing, and heat spreaders). In this work, it is demonstrated for the first time that a hierarchical network of vertically oriented graphene nanoflakes (GNFs), with nanoconfined silicon carbide (SiC) nanocrystals, self-assembled on carbon fibers (CFs) can provide significant improvement to the thermal conductivity (TC) of CFRPs in the through-thickness direction. The vertically aligned SiC/GNF heterostructures were grown directly on CFs for the first time by single-step plasmaenhanced chemical vapor deposition (PECVD) employing tetramethylsilane (TMS) and methane (CH 4) gases at temperatures of 800 and 950°C. At the deposition temperature of 950°C, the controlled introduction of SiC/GNF heterostructures induced a 56% improvement in through-thickness TC over the bare CFRP counterparts while simultaneously preserving the tensile strength. The increase in thermal conductivity is accomplished by SiC nanocrystals, which serve as linkage thermal conducting paths between the vertical graphene layers, further enhancing the smooth transmission of phonons in the vertical direction. The work demonstrates for the first time the unique potential of novel SiC/GNF heterostructures for attaining strong and thermally conductive multifunctional CFRPs.
2020 7th International Conference on Signal Processing and Integrated Networks (SPIN)
The design of a laser scribed polyimide sensor for the measurement of pH within wound environment... more The design of a laser scribed polyimide sensor for the measurement of pH within wound environments is described. A number of probe formats have been characterized with both potentiometric and voltammetric methodologies shown to provide a robust means of determining pH. The versatility of the laser patterning on polyimide is shown to yield a mechanically flexible double sided probe that could be suitable for use in a wide variety of clinical applications
Superconductor Science and Technology, 2020
The effect of 600 keV He + ion irradiation on the temperature and magnetic field dependence of th... more The effect of 600 keV He + ion irradiation on the temperature and magnetic field dependence of the critical current density J C in high quality BaFe 1.84 Co 0.16 As 2 (Co-doped Ba122 type) thin films is investigated. The films are prepared by pulsed-laser-deposition (PLD) on CaF 2 (00) substrates. The irradiation dosages are varied in between 110 13 to 110 16 cm-2. Upon irradiation, the superconducting transition temperature T C drops slightly from 23 K for the unirradiated sample to about 20 K for the sample with the highest irradiation level. The J C values of the thin film samples are calculated by using the Bean critical state model. The results showed that J C could be enhanced substantially. The maximum J C value at 4.5 K temperature is enhanced up to 2.4 MAcm-2 under 1 T field. The analysis of pinning force dependence on magnetic field shows that the pinning behavior is not changed in the irradiated samples, suggesting more pinning centers of similar nature to those of presented in the unirradiated samples are introduced by the irradiation process. The results indicate that the irradiation of light element ions He + with relatively low energy could increase the critical current density in iron based superconductors.
Journal of Physics: Conference Series, 2010
The first successful preparation of EuH 2 films by pulsed laser ablation of Eu in a hydrogen atmo... more The first successful preparation of EuH 2 films by pulsed laser ablation of Eu in a hydrogen atmosphere is reported. The films are reddish and order ferromagnetically at T C = 18 K with a saturation moment of 7 μ B per Eu ion. The complex dielectric function and the polar Kerr rotation have been measured and are compared with results of a LDA + U calculation.
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Papers by Pagona Papakonstantinou