Luis Miguel Encastin Santos - Academia.edu (original) (raw)

Papers by Luis Miguel Encastin Santos

Procedia Technology, 2014

We have studied the optimal deposition conditions for the production of low-oxygen-content Zinc n... more We have studied the optimal deposition conditions for the production of low-oxygen-content Zinc nitride films (ZnON) by Pulsed Laser Deposition (PLD). In particular, substrate temperature has been varied between 100 and 500 ºC. The film properties, particularly its morphology, showed a strong dependence on substrate temperature. Substrate temperatures beyond 350ºC led to highly crystalline and smooth films with a band gap of 3.32 eV and with resistivities ranging from 10-2 to 100 Ωcm. Film quality and surface oxygen content changed rapidly with exposure to air as evidenced by XPS analysis.

Proceedings of 2012 21st IEEE Int. Symp. on Applications of Ferroelectrics held jointly with 11th IEEE European Conference on the Applications of Polar Dielectrics and IEEE PFM, ISAF/ECAPD/PFM 2012, 2012

ABSTRACT We use optical transmission spectroscopy and spectral ellipsometry (SE) to determine the... more ABSTRACT We use optical transmission spectroscopy and spectral ellipsometry (SE) to determine the real and imaginary part of the complex dielectric function in both ceramic samples and thin films of lead-free NaxK1-xNbO3 (NKN). Thin films of NKN were prepared by pulsed laser deposition (PLD) from ceramic NKN targets. The optical band gap from transmission measurements in thin films yield an optical band gap of 3.94 or 3.55 eV, depending on whether direct or indirect transitions, respectively, are assumed. The fit procedure of SE results, based on the Tauc-Lorentz model, resulted in a band gap for films of 3.66 eV, whereas the band gap of the thick ceramic samples was 3.79 eV. Examples of amorphous and highly polycrystalline thin films, deposited at 450 and 600 °C, respectively, are discussed.

physica status solidi c, 2010

Polycrystalline Zn3N2 films were prepared on sapphire and quartz substrates by reactive pulsed la... more Polycrystalline Zn3N2 films were prepared on sapphire and quartz substrates by reactive pulsed laser ablation of a metallic zinc target in a nitrogen plasma atmosphere using a frequency‐doubled Nd:YAG laser, assisted by a 13.56 MHz radio‐frequency (RF) plasma. The morphological, structural and optical properties are studied by Scanning Electron Microscopy, X‐ray diffraction, transmittance and ellipsometric spectroscopy. SEM revealed a very smooth and crack‐free film surface. X‐ray diffraction indicates that the Zn3N2 films deposited at 400 °C substrate temperature are cubic in structure with no preferred orientation. The lattice constant has been estimated to be a = 0.97 nm. The absorption coefficient is deduced from the transmission spectra, and its dependence on photon energy is examined to determine the optical band gap. Refractive index and film thickness are deduced from spectroscopic ellipsometry measurements. Zn3N2 is determined to be a n‐type semiconductor with a direct band...

Ferroelectrics, 2013

ABSTRACT Thin films of lead-free NaxK1-xNbO3 (NKN) were prepared by pulsed laser deposition (PLD)... more ABSTRACT Thin films of lead-free NaxK1-xNbO3 (NKN) were prepared by pulsed laser deposition (PLD) from ceramic targets of stoichiometric NKN or doped with 6% of lithium niobate (LN). At a deposition temperature of 600°C a strong dependence of film morphology on laser fluence is revealed by SEM microscopy. Optical properties like band gap and index of refraction were obtained through transmission measurements and analysis based on the Tauc model. The results were compared to spectral ellipsometry using a fit to the Tauc-Lorentz model, and slightly smaller band gap values were obtained. C-V characteristics of sandwich structures yielded high permittivity of 380 in pure NKN films and tunability at 1 kHz of 3.2% at 1.5 MV/m applied electric field.

Procedia Technology, 2014

We have studied the optimal deposition conditions for the production of low-oxygen-content Zinc n... more We have studied the optimal deposition conditions for the production of low-oxygen-content Zinc nitride films (ZnON) by Pulsed Laser Deposition (PLD). In particular, substrate temperature has been varied between 100 and 500 ºC. The film properties, particularly its morphology, showed a strong dependence on substrate temperature. Substrate temperatures beyond 350ºC led to highly crystalline and smooth films with a band gap of 3.32 eV and with resistivities ranging from 10-2 to 100 Ωcm. Film quality and surface oxygen content changed rapidly with exposure to air as evidenced by XPS analysis.

Proceedings of 2012 21st IEEE Int. Symp. on Applications of Ferroelectrics held jointly with 11th IEEE European Conference on the Applications of Polar Dielectrics and IEEE PFM, ISAF/ECAPD/PFM 2012, 2012

ABSTRACT We use optical transmission spectroscopy and spectral ellipsometry (SE) to determine the... more ABSTRACT We use optical transmission spectroscopy and spectral ellipsometry (SE) to determine the real and imaginary part of the complex dielectric function in both ceramic samples and thin films of lead-free NaxK1-xNbO3 (NKN). Thin films of NKN were prepared by pulsed laser deposition (PLD) from ceramic NKN targets. The optical band gap from transmission measurements in thin films yield an optical band gap of 3.94 or 3.55 eV, depending on whether direct or indirect transitions, respectively, are assumed. The fit procedure of SE results, based on the Tauc-Lorentz model, resulted in a band gap for films of 3.66 eV, whereas the band gap of the thick ceramic samples was 3.79 eV. Examples of amorphous and highly polycrystalline thin films, deposited at 450 and 600 °C, respectively, are discussed.

physica status solidi c, 2010

Polycrystalline Zn3N2 films were prepared on sapphire and quartz substrates by reactive pulsed la... more Polycrystalline Zn3N2 films were prepared on sapphire and quartz substrates by reactive pulsed laser ablation of a metallic zinc target in a nitrogen plasma atmosphere using a frequency‐doubled Nd:YAG laser, assisted by a 13.56 MHz radio‐frequency (RF) plasma. The morphological, structural and optical properties are studied by Scanning Electron Microscopy, X‐ray diffraction, transmittance and ellipsometric spectroscopy. SEM revealed a very smooth and crack‐free film surface. X‐ray diffraction indicates that the Zn3N2 films deposited at 400 °C substrate temperature are cubic in structure with no preferred orientation. The lattice constant has been estimated to be a = 0.97 nm. The absorption coefficient is deduced from the transmission spectra, and its dependence on photon energy is examined to determine the optical band gap. Refractive index and film thickness are deduced from spectroscopic ellipsometry measurements. Zn3N2 is determined to be a n‐type semiconductor with a direct band...

Ferroelectrics, 2013

ABSTRACT Thin films of lead-free NaxK1-xNbO3 (NKN) were prepared by pulsed laser deposition (PLD)... more ABSTRACT Thin films of lead-free NaxK1-xNbO3 (NKN) were prepared by pulsed laser deposition (PLD) from ceramic targets of stoichiometric NKN or doped with 6% of lithium niobate (LN). At a deposition temperature of 600°C a strong dependence of film morphology on laser fluence is revealed by SEM microscopy. Optical properties like band gap and index of refraction were obtained through transmission measurements and analysis based on the Tauc model. The results were compared to spectral ellipsometry using a fit to the Tauc-Lorentz model, and slightly smaller band gap values were obtained. C-V characteristics of sandwich structures yielded high permittivity of 380 in pure NKN films and tunability at 1 kHz of 3.2% at 1.5 MV/m applied electric field.