Luis Marques - Academia.edu (original) (raw)
Papers by Luis Marques
Research in Science & Technological Education, 1997
Abstract This study was initiated in an area of school science, earth science education, which ha... more Abstract This study was initiated in an area of school science, earth science education, which has been little explored. A sample of 493 Portuguese pupils aged 10‐11 and 14‐15 (at the beginning and end of secondary schooling) was involved. The study used ...
Chemistry of Materials, 1999
... LD Carlos,* † V. de Zea Bermudez, ‡ RA Sá Ferreira, † L. Marques, † and M. Assunção †. Depart... more ... LD Carlos,* † V. de Zea Bermudez, ‡ RA Sá Ferreira, † L. Marques, † and M. Assunção †. Departamento de Física, Universidade de Aveiro, 3810 Aveiro, Portugal, and Secção de Química, Universidade de Trás-os Montes e ...
High Temperature Material Processes, 2004
This paper presents a systematic characterization of hydrogen capacitively coupled very high freq... more This paper presents a systematic characterization of hydrogen capacitively coupled very high frequency discharges, produced within a parallel plate cylindrical setup, by comparing numerical simulations to experimental measurements for various plasma parameters. A good quantitative agreement is found between calculation and experiment for the coupled electrical power and the plasma potential, at various frequencies, pressures and applied voltages. However, the model generally underestimates the electron density and the self-bias potential with respect to measured values. Model predictions for the absolute density of H(n=1) atoms are compared to first diagnostic results, obtained by two-photon absorption laser-induced fluorescence diagnostics at various pressures and frequencies.
Plasma Sources Science & Technology, 2005
A two-dimensional (r, z) time-dependent fluid model was developed and used to describe a dc plana... more A two-dimensional (r, z) time-dependent fluid model was developed and used to describe a dc planar magnetron discharge with cylindrical symmetry. The transport description of the charged species uses the corresponding first three moments of the Boltzmann equation: continuity, momentum transfer and mean energy transfer (the last one only for electrons), coupled with the Poisson equation. An original method is proposed to treat the transport equations. Electron and ion momentum transport equations are reduced to the classical drift-diffusion expression for the fluxes since the presence of the magnetic field is introduced as an additional part in the electron flux, while for ions an effective electric field was considered. Thus, both continuity and mean energy transfer equations are solved in a classical manner. Numerical simulations were performed considering argon as a buffer gas, with a neutral pressure varying between 5 and 30 mTorr, for different voltages applied on the cathode. Results obtained for densities of the charged particle, fluxes and plasma potential are in good agreement with those obtained in previous studies.
Physical Review B, 1996
... The disorder, calculated from the peak width, is for the rhombohedral sample about half that ... more ... The disorder, calculated from the peak width, is for the rhombohedral sample about half that of ... essential both in obtaining the polymerized phases and in selecting the 1D or the 2D polymer. ... It is known that the molecular orientation favored under pressure is the one that has an ...
Physical Review B, 1997
We discuss the room-temperature infrared and Raman spectra for the pressure-induced rhombohedral,... more We discuss the room-temperature infrared and Raman spectra for the pressure-induced rhombohedral, tetragonal, orthorhombic C 60 polymers and the C 60 photopolymer. The interfullerene bonds are found to not only split the H ...
Physical Review Letters, 1995
We show in this Letter that heating under high pressure drives C60 to new distorted crystalline p... more We show in this Letter that heating under high pressure drives C60 to new distorted crystalline phases that are metastable at room temperature and pressure. We report three different distortions that are essentially characterized by two nearest neighbor distances, d'0~10 and d''0~9.2 Å. The excellent accord with theoretical calculations supports the view that these new carbon phases can be understood
Applied Physics A-materials Science & Processing, 1997
polymers. Pure and mixed phase polymeric samples were synthesized by simultaneously subjecting mi... more polymers. Pure and mixed phase polymeric samples were synthesized by simultaneously subjecting microcrystalline C60 powder or pellets to various pressures ( \valunit{1}{GPa} ) and temperatures ( \valunit{250}{\celsius} ). The optical spectra of the orthorhombic, tetragonal, and rhombohedral C60 polymer phases are observed to be quite distinct and rich. These spectra exhibit numerous lines and an overall downshift in frequency relative to C60 is observed, consistent with a loss of double bonds from the fullerene cage. The LDMS spectra of a sample synthesized at \valunit{2}{GPa} under hydrostatic conditions and \valunit{350}{\celsius} , exhibited a succession of \sim 12 clear peaks at mass numbers corresponding to (\chem{C_{60}})_{{N} = 1, 2\ldots 12} , similar to the LDMS data on the C60 photopolymer. This is taken as further evidence for interfullerene bonds in these high-pressure polymers. The XRD pattern of this sample indicates the presence of a strong texture in the sample.
Physical Review B, 2002
Synchrotron x-ray two-dimensional diffraction was used to study the evolution of C60 polymerizati... more Synchrotron x-ray two-dimensional diffraction was used to study the evolution of C60 polymerization in samples quenched from high pressure-high temperature. As for three-dimensional polymers, Debye-Scherrer ellipses are observed at low-pressure conditions, they are disrupted as polymerization progresses indicating an alignment of the growing polymer that finishes in fully textured samples. The anisotropic stress signature on C60 polymers gives a direct
Physical Review B, 1996
... The disorder, calculated from the peak width, is for the rhombohedral sample about half that ... more ... The disorder, calculated from the peak width, is for the rhombohedral sample about half that of ... essential both in obtaining the polymerized phases and in selecting the 1D or the 2D polymer. ... It is known that the molecular orientation favored under pressure is the one that has an ...
Physical Review B, 1997
We discuss the room-temperature infrared and Raman spectra for the pressure-induced rhombohedral,... more We discuss the room-temperature infrared and Raman spectra for the pressure-induced rhombohedral, tetragonal, orthorhombic C 60 polymers and the C 60 photopolymer. The interfullerene bonds are found to not only split the H ...
Physical Review Letters, 1995
We show in this Letter that heating under high pressure drives C60 to new distorted crystalline p... more We show in this Letter that heating under high pressure drives C60 to new distorted crystalline phases that are metastable at room temperature and pressure. We report three different distortions that are essentially characterized by two nearest neighbor distances, d'0~10 and d''0~9.2 Å. The excellent accord with theoretical calculations supports the view that these new carbon phases can be understood
Applied Physics A-materials Science & Processing, 1997
polymers. Pure and mixed phase polymeric samples were synthesized by simultaneously subjecting mi... more polymers. Pure and mixed phase polymeric samples were synthesized by simultaneously subjecting microcrystalline C60 powder or pellets to various pressures ( \valunit{1}{GPa} ) and temperatures ( \valunit{250}{\celsius} ). The optical spectra of the orthorhombic, tetragonal, and rhombohedral C60 polymer phases are observed to be quite distinct and rich. These spectra exhibit numerous lines and an overall downshift in frequency relative to C60 is observed, consistent with a loss of double bonds from the fullerene cage. The LDMS spectra of a sample synthesized at \valunit{2}{GPa} under hydrostatic conditions and \valunit{350}{\celsius} , exhibited a succession of \sim 12 clear peaks at mass numbers corresponding to (\chem{C_{60}})_{{N} = 1, 2\ldots 12} , similar to the LDMS data on the C60 photopolymer. This is taken as further evidence for interfullerene bonds in these high-pressure polymers. The XRD pattern of this sample indicates the presence of a strong texture in the sample.
Physical Review B, 2002
Synchrotron x-ray two-dimensional diffraction was used to study the evolution of C60 polymerizati... more Synchrotron x-ray two-dimensional diffraction was used to study the evolution of C60 polymerization in samples quenched from high pressure-high temperature. As for three-dimensional polymers, Debye-Scherrer ellipses are observed at low-pressure conditions, they are disrupted as polymerization progresses indicating an alignment of the growing polymer that finishes in fully textured samples. The anisotropic stress signature on C60 polymers gives a direct
Research in Science & Technological Education, 1997
Abstract This study was initiated in an area of school science, earth science education, which ha... more Abstract This study was initiated in an area of school science, earth science education, which has been little explored. A sample of 493 Portuguese pupils aged 10‐11 and 14‐15 (at the beginning and end of secondary schooling) was involved. The study used ...
Chemistry of Materials, 1999
... LD Carlos,* † V. de Zea Bermudez, ‡ RA Sá Ferreira, † L. Marques, † and M. Assunção †. Depart... more ... LD Carlos,* † V. de Zea Bermudez, ‡ RA Sá Ferreira, † L. Marques, † and M. Assunção †. Departamento de Física, Universidade de Aveiro, 3810 Aveiro, Portugal, and Secção de Química, Universidade de Trás-os Montes e ...
High Temperature Material Processes, 2004
This paper presents a systematic characterization of hydrogen capacitively coupled very high freq... more This paper presents a systematic characterization of hydrogen capacitively coupled very high frequency discharges, produced within a parallel plate cylindrical setup, by comparing numerical simulations to experimental measurements for various plasma parameters. A good quantitative agreement is found between calculation and experiment for the coupled electrical power and the plasma potential, at various frequencies, pressures and applied voltages. However, the model generally underestimates the electron density and the self-bias potential with respect to measured values. Model predictions for the absolute density of H(n=1) atoms are compared to first diagnostic results, obtained by two-photon absorption laser-induced fluorescence diagnostics at various pressures and frequencies.
Plasma Sources Science & Technology, 2005
A two-dimensional (r, z) time-dependent fluid model was developed and used to describe a dc plana... more A two-dimensional (r, z) time-dependent fluid model was developed and used to describe a dc planar magnetron discharge with cylindrical symmetry. The transport description of the charged species uses the corresponding first three moments of the Boltzmann equation: continuity, momentum transfer and mean energy transfer (the last one only for electrons), coupled with the Poisson equation. An original method is proposed to treat the transport equations. Electron and ion momentum transport equations are reduced to the classical drift-diffusion expression for the fluxes since the presence of the magnetic field is introduced as an additional part in the electron flux, while for ions an effective electric field was considered. Thus, both continuity and mean energy transfer equations are solved in a classical manner. Numerical simulations were performed considering argon as a buffer gas, with a neutral pressure varying between 5 and 30 mTorr, for different voltages applied on the cathode. Results obtained for densities of the charged particle, fluxes and plasma potential are in good agreement with those obtained in previous studies.
Physical Review B, 1996
... The disorder, calculated from the peak width, is for the rhombohedral sample about half that ... more ... The disorder, calculated from the peak width, is for the rhombohedral sample about half that of ... essential both in obtaining the polymerized phases and in selecting the 1D or the 2D polymer. ... It is known that the molecular orientation favored under pressure is the one that has an ...
Physical Review B, 1997
We discuss the room-temperature infrared and Raman spectra for the pressure-induced rhombohedral,... more We discuss the room-temperature infrared and Raman spectra for the pressure-induced rhombohedral, tetragonal, orthorhombic C 60 polymers and the C 60 photopolymer. The interfullerene bonds are found to not only split the H ...
Physical Review Letters, 1995
We show in this Letter that heating under high pressure drives C60 to new distorted crystalline p... more We show in this Letter that heating under high pressure drives C60 to new distorted crystalline phases that are metastable at room temperature and pressure. We report three different distortions that are essentially characterized by two nearest neighbor distances, d'0~10 and d''0~9.2 Å. The excellent accord with theoretical calculations supports the view that these new carbon phases can be understood
Applied Physics A-materials Science & Processing, 1997
polymers. Pure and mixed phase polymeric samples were synthesized by simultaneously subjecting mi... more polymers. Pure and mixed phase polymeric samples were synthesized by simultaneously subjecting microcrystalline C60 powder or pellets to various pressures ( \valunit{1}{GPa} ) and temperatures ( \valunit{250}{\celsius} ). The optical spectra of the orthorhombic, tetragonal, and rhombohedral C60 polymer phases are observed to be quite distinct and rich. These spectra exhibit numerous lines and an overall downshift in frequency relative to C60 is observed, consistent with a loss of double bonds from the fullerene cage. The LDMS spectra of a sample synthesized at \valunit{2}{GPa} under hydrostatic conditions and \valunit{350}{\celsius} , exhibited a succession of \sim 12 clear peaks at mass numbers corresponding to (\chem{C_{60}})_{{N} = 1, 2\ldots 12} , similar to the LDMS data on the C60 photopolymer. This is taken as further evidence for interfullerene bonds in these high-pressure polymers. The XRD pattern of this sample indicates the presence of a strong texture in the sample.
Physical Review B, 2002
Synchrotron x-ray two-dimensional diffraction was used to study the evolution of C60 polymerizati... more Synchrotron x-ray two-dimensional diffraction was used to study the evolution of C60 polymerization in samples quenched from high pressure-high temperature. As for three-dimensional polymers, Debye-Scherrer ellipses are observed at low-pressure conditions, they are disrupted as polymerization progresses indicating an alignment of the growing polymer that finishes in fully textured samples. The anisotropic stress signature on C60 polymers gives a direct
Physical Review B, 1996
... The disorder, calculated from the peak width, is for the rhombohedral sample about half that ... more ... The disorder, calculated from the peak width, is for the rhombohedral sample about half that of ... essential both in obtaining the polymerized phases and in selecting the 1D or the 2D polymer. ... It is known that the molecular orientation favored under pressure is the one that has an ...
Physical Review B, 1997
We discuss the room-temperature infrared and Raman spectra for the pressure-induced rhombohedral,... more We discuss the room-temperature infrared and Raman spectra for the pressure-induced rhombohedral, tetragonal, orthorhombic C 60 polymers and the C 60 photopolymer. The interfullerene bonds are found to not only split the H ...
Physical Review Letters, 1995
We show in this Letter that heating under high pressure drives C60 to new distorted crystalline p... more We show in this Letter that heating under high pressure drives C60 to new distorted crystalline phases that are metastable at room temperature and pressure. We report three different distortions that are essentially characterized by two nearest neighbor distances, d'0~10 and d''0~9.2 Å. The excellent accord with theoretical calculations supports the view that these new carbon phases can be understood
Applied Physics A-materials Science & Processing, 1997
polymers. Pure and mixed phase polymeric samples were synthesized by simultaneously subjecting mi... more polymers. Pure and mixed phase polymeric samples were synthesized by simultaneously subjecting microcrystalline C60 powder or pellets to various pressures ( \valunit{1}{GPa} ) and temperatures ( \valunit{250}{\celsius} ). The optical spectra of the orthorhombic, tetragonal, and rhombohedral C60 polymer phases are observed to be quite distinct and rich. These spectra exhibit numerous lines and an overall downshift in frequency relative to C60 is observed, consistent with a loss of double bonds from the fullerene cage. The LDMS spectra of a sample synthesized at \valunit{2}{GPa} under hydrostatic conditions and \valunit{350}{\celsius} , exhibited a succession of \sim 12 clear peaks at mass numbers corresponding to (\chem{C_{60}})_{{N} = 1, 2\ldots 12} , similar to the LDMS data on the C60 photopolymer. This is taken as further evidence for interfullerene bonds in these high-pressure polymers. The XRD pattern of this sample indicates the presence of a strong texture in the sample.
Physical Review B, 2002
Synchrotron x-ray two-dimensional diffraction was used to study the evolution of C60 polymerizati... more Synchrotron x-ray two-dimensional diffraction was used to study the evolution of C60 polymerization in samples quenched from high pressure-high temperature. As for three-dimensional polymers, Debye-Scherrer ellipses are observed at low-pressure conditions, they are disrupted as polymerization progresses indicating an alignment of the growing polymer that finishes in fully textured samples. The anisotropic stress signature on C60 polymers gives a direct