Project/scholarship details
- Project/scholarship ID
41574
- Reference
POCTI/CTM/41574/2001
- FundRef URI
- Funder
FCT - Fundação para a Ciência e a Tecnologia, I.P.
- Funder's country
Portugal
- Funding program
POCI
- Funding amount
125,000.00 €
- Start date
2003-09-15
- End date
2006-09-14
Documents
Mesoscopic modelling of bipolar charge Evolution in CN-PPV LEDs
Ramos, Marta M. D.; Correia, Helena M. G.; Ribeiro, R. M.Since various chances are possible in the molecular structure of the repeat unit, substituted poly(para-phenylenevinylene) (PPV) has ben used as active component in light-emitting diodes (LEDs) to obtain light emission in a wide range of colours. A major aspect determining device performance is the competition between current flow, trapping and recombination within the polymer layer. By suitable Monte Carlo cal...
Effect of molecular properties on the performance of polymer light-emitting diodes
Ramos, Marta M. D.; Almeida, A. M.; Correia, Helena M. G.; Ribeiro, R. M.; Stoneham, A. M.The performance of a single layer polymer light-emitting diode depends on several interdependent factors, although recombination between electrons and holes within the polymer layer is believed to play an important role. Our aim is to carry out computer experiments in which bipolar charge carriers are injected in polymer networks made of poly(p-phenylene vinylene) chains randomly oriented. In these simulations,...
Polarization behavior in systems with competing ferroelectric and antiferroelec...
Milhazes, J.; Lanceros-Méndez, S.; Cadilhe, A. M.The dielectric hysteresis loop constitutes the main feature indicative of the properties of a ferroelectric material, but in complex systems with ferro- and antiferroelectric interactions, the hysteresis loops are often multiple. In the present work, we introduce a model based on the coexistence of ferro- and antiferroelectric regions, which can describe the aforementioned multiple loops. Based on our model, si...
Intra-molecular properties of DMeOPPV studied by quantum molecular dynamics
Correia, Helena M. G.; Ramos, Marta M. D.Introducing methoxy electron donor groups into a poly(para-phenylene vinylene) (PPV) chain will lead to the appearance of unique electronic properties at the molecular scale which should affect the overall properties of light-emitting diodes based on these polymers. Self-consistent quantum molecular dynamics calculations have been used to provide information on intra-molecular properties of poly(2,5-dimethoxy-p...
Computer simulation of electron transfer in molecular electronic devices
Correia, Helena M. G.; Ramos, Marta M. D.The study of electron transfer through individual molecules bound to metal electrodes has become important due to the potential application in molecular electronic devices. Since the electronic and atomic motions in these molecules influence each other they need to be treated self-consistently. We have used self-consistent quantum chemistry molecular dynamics calculations to discuss some of the issues related t...
Quantum modelling of poly(vinylidene fluoride)
Correia, Helena M. G.; Ramos, Marta M. D.Although extensive studies have been conducted on poly(vinylidene fluoride) (PVDF) because of its ferroelectric, pyroelectric and piezoelectric properties, the effects of inverted monomer units, on the molecular scale properties of this polymer are not fully understood. Therefore, we have used a method combining molecular dynamics with a self-consistent semi-empirical quantum mechanical method to study the effe...
Atomistic modelling of processes involved in poling of PVDF
Ramos, Marta M. D.; Correia, Helena M. G.; Lanceros-Méndez, S.Poling processes play an important role in the design and preparation of many ferroelectric materials for practical uses in the field of sensors and actuators. Particularly, the processing of piezoelectric beta-poly(vinylidene fluoride) (PPVDF) involves mechanical stretching in order to transform the extruded a-phase into the P-phase and poling of this later material in order to optimize the piezoelectric respo...
Effects of electric field and charge distribution on nanoelectronic processes i...
Ramos, Marta M. D.; Correia, Helena M. G.The injection of charge carriers in conducting polymer layers gives rise to local electric fields which should have serious implications on the charge transport through the polymer layer. The charge distribution and the related electric field inside the ensemble of polymer molecules, with different molecular arrangements at nanoscale, determine whether or not intra-molecular charge transport takes place and the...
Modelling molecular transformations in ferroelectric polymers induced by mechan...
Correia, Helena M. G.; Ramos, Marta M. D.We describe a new approach to model the dynamical structural modifications of ferroelectric polymer molecules induced by uniaxial stretching and by the application of electric fields of various strengths and orientations. Our approach combines a self-consistent quantum mechanical method with molecular dynamics, removing the need to use inter-atomic potentials in the dynamic calculations. Here we present results...
What can we learn from vibrational analysis calculations of defective polymer c...
Correia, Helena M. G.; Ramos, Marta M. D.The possibility of using infrared (IR) spectroscopy to determine the concentration of inversion monomer defects in polymers depends on the knowledge of the relationship between the spectral properties and the polymer microstructure. This can easily be achieved by performing vibrational analysis. In order to investigate the changes in IR spectra of poly(vinylidene fluoride) resulting from the presence of monomer...
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