We present a comprehensive study of the effect of hydrogen on the magnetic properties of Nd–Fe–B ... more We present a comprehensive study of the effect of hydrogen on the magnetic properties of Nd–Fe–B magnets. The research has been done on powder, bulk samples and plates of thickness 200–800μm. It includes the determination of the concentration of hydrogen by total combustion and by precision weight balance, X-ray studies, thermal desorption of hydrogen in high vacuum, insertion of hydrogen
An optical characterization system connected to an rf plasma reactor is described. This system is... more An optical characterization system connected to an rf plasma reactor is described. This system is based on two techniques, namely, polarization modulated ellipsometry (PME) and plasma optical emission spectroscopy (OES). The PME technique has two operative modes, the real time one and the spectroscopic one. The former provides the trajectories of the ellipsometric angles, (~, A), during the thin film growing process. The PME, in spectroscopic mode, allows us to determine the dielectric functions of the thin films in the uv-visible range . The OES technique indicates the relative intensity of the peaks corresponding to the de-excitation of species present in the plasma. The results obtained during the deposition of a-Si.'H thin films are presented to demonstrate the capabilities of the system.
The influence of the pressure of a sole water atmosphere during the pulsed laser deposition of hy... more The influence of the pressure of a sole water atmosphere during the pulsed laser deposition of hydroxyapatite thin films on Ti-6Al-4V substrates has been studied. The rest of the technological parameters involved in the process have been fixed near the conditions where the best crystalline coatings are obtained. The pressure of the water atmosphere has been varied between 0.15 and 1.5 mbar. The films properties have been analysed by means of XRD, SEM, FT-IR spectroscopy and SIMS. An optimal region, in order to Ž obtain thin films of highly crystalline hydroxyapatite, has been found near 0.5 mbar for the two excimer laser wavelengths 193 nm and . Ž . 248 nm used in this study. These films have a preferential orientation in the 100 direction. q 1998 Elsevier Science S.A.
The use of excimer lasers for treatment of dental hard tissues has considerable potential because... more The use of excimer lasers for treatment of dental hard tissues has considerable potential because the combined characteristics of low wavelength and short pulse result in limited heat diffusion and, therefore, tissue ablation without the problems of collateral damage. To date, there are relatively few published studies concerning the effects of excimer laser irradiation on dental hard tissues. Thus the present study was conducted to examine the morphological changes in tooth dentin subsequent to ArF excimer laser irradiation. The morphologic changes induced in normal, nondiseased human dentin following irradiation by an ArF excimer laser at fluences ranging from 1 to 4 J/cm2 and the number of laser pulses ranging from 50 to 1,000 were evaluated by scanning electron microscopy. Two modes of ablation, photochemical at low fluences and thermal at high fluences, were observed. A fluence of 1 J/ cm2 when combined with 50 or 100 pulses produced a uniform ablation of the dentin surface without signs of tissue melting. At fluences > 1.5 J/cm2, the thermal mode of ablation was more efficient at removing intertubular dentin than peritubular dentin. Further, when compared to the lower fluences, the higher settings produced a rougher ablation crater surface. Additionally, the higher fluences produced surface melting with each pulse and sealing of exposed dentinal tubules after irradiation with 100-300 laser pulses. The photochemical and thermal mechanisms of tooth dentin ablation were identified based on significant differences in tissue morphology following laser irradiation. The rates of tissue ablation and the observed morphologic changes indicate that the ArF excimer laser could be useful for caries removal and sealing of exposed dentinal tubules.
ABSTRACT A low pressure (2 mu bar) silane plasma has been obtained with a hot cathode DC glow dis... more ABSTRACT A low pressure (2 mu bar) silane plasma has been obtained with a hot cathode DC glow discharge and electrostatic confinement. The plasma parameters have been measured with a Langmuir probe and their dependence on confining potential for three different anode sizes have been obtained. The dependence of plasma parameters on discharge current has also been studied. It has been shown that the plasma density increases significantly with the confinement and this increase is attributed to the reflection of primary electrons at the confining electrode.
Marking of lines on clay brick pavers by vitrification with a Nd:YAG laser. [Journal of Laser App... more Marking of lines on clay brick pavers by vitrification with a Nd:YAG laser. [Journal of Laser Applications 18, 156 (2006)]. JW Restrepo, JM Fernández-Pradas, MA Gómez, P. Serra, JL Morenza. Abstract. Laser marking of architectural ...
... Phys. 3«, 168 (1965). 3L. L. Kazmerski, WB Berry, and G W. Allen, J. Appi. Phys. 43, 3515 (19... more ... Phys. 3«, 168 (1965). 3L. L. Kazmerski, WB Berry, and G W. Allen, J. Appi. Phys. 43, 3515 (1972). "JW Orton, BJ Goldsmith, JA Chapman, and MJ Powell, J. Appi. ... 'JYW Seto, J. Appi. Phys. 46, 5247 (1975). ,0G. Baccarini, B. Ricco, and G. Spadini, J. Appi. Phys. 49, 5585 (1978). ...
A hot-cathode silane dc discharge with electrostatic confinement devoted to the deposition of hyd... more A hot-cathode silane dc discharge with electrostatic confinement devoted to the deposition of hydrogenated amorphous silicon is analyzed by using a Langmuir probe. The electron energy distribution of the plasma shows the existence of two pseudo-Maxwellian populations with densities depending on the electrostatic confinement. The electron density of electrostatically confined plasma is higher than in the case of an unconfined
A dissolution test was performed with pulsed laser (Nd: YAG, 355 nm)-deposited calcium phosphate ... more A dissolution test was performed with pulsed laser (Nd: YAG, 355 nm)-deposited calcium phosphate coatings composed of hydroxyapatite (HA) and alpha-tricalcium phosphate (alpha-TCP) in different proportions, as a result of the use of different deposition rates. During immersion in a Ca2+-free Hank's solution, the dissolution kinetics were determined while other structural and compositional properties of the coatings were derived. It was possible to infer that the alpha-TCP is distributed uniformly and that the coating is of a non-columnar compact grain structure. The mass ratio of the phases for each coating was also determined and was related to the X-ray diffraction intensities. When incomplete, the hydroxylation level of the HA in the coatings is completed after immersion.
The formation of speci®c surface structures as a result of multi-pulse, high repetition rate Nd:Y... more The formation of speci®c surface structures as a result of multi-pulse, high repetition rate Nd:YAG (l 1:064 mm, t $ 300 ns, n 30 kHz) laser irradiation of Ti targets in vacuum is reported. The experiments are performed at laser intensity levels below the melting threshold of Ti for single laser pulse irradiation. An analysis of the early stage of surface transformation as well as of the further structure development by cumulative laser irradiation is done. A number of consecutive laser pulses are necessary to initiate the formation of the surface micro-structures. The process continues with the next laser pulses and the surface roughness increases. However, a change to a smooth, dendritic surface morphology takes place after a certain number of pulses. The irradiated areas are analysed by pro®lometry and scanning electron microscopy (SEM). The main physical phenomena implied in the laser induced surface microrelief development are discussed. #
ABSTRACT Depth calibration in sputter depth profiling may be seriously in error in the analysis o... more ABSTRACT Depth calibration in sputter depth profiling may be seriously in error in the analysis of inhomogeneous samples in which the erosion rate varies. In this work, we present a practical method to evaluate the sputter rate as a function of depth, requiring only routine instrumentation. Illustrative results in two inhomogeneous samples are presented.
The specific dome-shaped structures were grown by multi-pulse Nd:YAG (l ¼ 1:064 mm, t ¼$300 ns, a... more The specific dome-shaped structures were grown by multi-pulse Nd:YAG (l ¼ 1:064 mm, t ¼$300 ns, and n ¼ 30 kHz) laser irradiation of titanium targets in air at atmospheric pressure. The laser intensity values were chosen below the single-laser-pulse melting threshold of titanium. The chemical composition of the structures was studied as a function of laser pulse number as well as laser intensity, both at the outer surface layer and in depth. Micro-Raman spectroscopy, Auger electron spectroscopy (AES), and wavelength dispersive X-ray spectroscopy (WDX) were used as diagnostic techniques. Morphological investigations were performed by scanning electron microscopy. The obtained results revealed a lower oxygen concentration in the centre of the structures as compared to the borders and a lower concentration on the surface than in the depth. Moreover, it was found that the stoichiometry of the formed TiO 2Àx oxides increases from the structures centre towards the border and from the surface towards the depth. #
The growth mechanism of columns produced by excimer laser irradiation of a silicon target is inve... more The growth mechanism of columns produced by excimer laser irradiation of a silicon target is investigated. The micrometric columns are formed by a cumulative process with well-defined steps. The first steps lead to silicon hillocks, which evolve to columns through a little-understood mechanism. To investigate it, we irradiated a Si(100) single crystal in air with the necessary pulses of an
ABSTRACT Films of a-Si: H have been deposited by means of a dc hot cathode discharge of SiH4 with... more ABSTRACT Films of a-Si: H have been deposited by means of a dc hot cathode discharge of SiH4 with electrostatic confinement at a pressure as low as 0.4 Pa. The plasma used is quite quiescent as has been observed by means of reproducible Langmuir probe measurements. Substrates have been placed at different locations in between the electrodes, some of them facing the anode and the others facing the cathode.Films deposited on substrates facing the cathode present a granular, non-columnar, structure, an IR spectrum with only SiH absorption peaks, and a very low photoresponse. Films deposited on substrates facing the anode have a similar IR spectrum but are homogeneous, have lower hydrogen content, and present a high photoresponse. The optical absorption coefficient shows in all samples thenE=C(E–E0) x behaviour, but with exponentx=3 and notx=2 as is usually considered in a-SiH.
We present a comprehensive study of the effect of hydrogen on the magnetic properties of Nd–Fe–B ... more We present a comprehensive study of the effect of hydrogen on the magnetic properties of Nd–Fe–B magnets. The research has been done on powder, bulk samples and plates of thickness 200–800μm. It includes the determination of the concentration of hydrogen by total combustion and by precision weight balance, X-ray studies, thermal desorption of hydrogen in high vacuum, insertion of hydrogen
An optical characterization system connected to an rf plasma reactor is described. This system is... more An optical characterization system connected to an rf plasma reactor is described. This system is based on two techniques, namely, polarization modulated ellipsometry (PME) and plasma optical emission spectroscopy (OES). The PME technique has two operative modes, the real time one and the spectroscopic one. The former provides the trajectories of the ellipsometric angles, (~, A), during the thin film growing process. The PME, in spectroscopic mode, allows us to determine the dielectric functions of the thin films in the uv-visible range . The OES technique indicates the relative intensity of the peaks corresponding to the de-excitation of species present in the plasma. The results obtained during the deposition of a-Si.'H thin films are presented to demonstrate the capabilities of the system.
The influence of the pressure of a sole water atmosphere during the pulsed laser deposition of hy... more The influence of the pressure of a sole water atmosphere during the pulsed laser deposition of hydroxyapatite thin films on Ti-6Al-4V substrates has been studied. The rest of the technological parameters involved in the process have been fixed near the conditions where the best crystalline coatings are obtained. The pressure of the water atmosphere has been varied between 0.15 and 1.5 mbar. The films properties have been analysed by means of XRD, SEM, FT-IR spectroscopy and SIMS. An optimal region, in order to Ž obtain thin films of highly crystalline hydroxyapatite, has been found near 0.5 mbar for the two excimer laser wavelengths 193 nm and . Ž . 248 nm used in this study. These films have a preferential orientation in the 100 direction. q 1998 Elsevier Science S.A.
The use of excimer lasers for treatment of dental hard tissues has considerable potential because... more The use of excimer lasers for treatment of dental hard tissues has considerable potential because the combined characteristics of low wavelength and short pulse result in limited heat diffusion and, therefore, tissue ablation without the problems of collateral damage. To date, there are relatively few published studies concerning the effects of excimer laser irradiation on dental hard tissues. Thus the present study was conducted to examine the morphological changes in tooth dentin subsequent to ArF excimer laser irradiation. The morphologic changes induced in normal, nondiseased human dentin following irradiation by an ArF excimer laser at fluences ranging from 1 to 4 J/cm2 and the number of laser pulses ranging from 50 to 1,000 were evaluated by scanning electron microscopy. Two modes of ablation, photochemical at low fluences and thermal at high fluences, were observed. A fluence of 1 J/ cm2 when combined with 50 or 100 pulses produced a uniform ablation of the dentin surface without signs of tissue melting. At fluences > 1.5 J/cm2, the thermal mode of ablation was more efficient at removing intertubular dentin than peritubular dentin. Further, when compared to the lower fluences, the higher settings produced a rougher ablation crater surface. Additionally, the higher fluences produced surface melting with each pulse and sealing of exposed dentinal tubules after irradiation with 100-300 laser pulses. The photochemical and thermal mechanisms of tooth dentin ablation were identified based on significant differences in tissue morphology following laser irradiation. The rates of tissue ablation and the observed morphologic changes indicate that the ArF excimer laser could be useful for caries removal and sealing of exposed dentinal tubules.
ABSTRACT A low pressure (2 mu bar) silane plasma has been obtained with a hot cathode DC glow dis... more ABSTRACT A low pressure (2 mu bar) silane plasma has been obtained with a hot cathode DC glow discharge and electrostatic confinement. The plasma parameters have been measured with a Langmuir probe and their dependence on confining potential for three different anode sizes have been obtained. The dependence of plasma parameters on discharge current has also been studied. It has been shown that the plasma density increases significantly with the confinement and this increase is attributed to the reflection of primary electrons at the confining electrode.
Marking of lines on clay brick pavers by vitrification with a Nd:YAG laser. [Journal of Laser App... more Marking of lines on clay brick pavers by vitrification with a Nd:YAG laser. [Journal of Laser Applications 18, 156 (2006)]. JW Restrepo, JM Fernández-Pradas, MA Gómez, P. Serra, JL Morenza. Abstract. Laser marking of architectural ...
... Phys. 3«, 168 (1965). 3L. L. Kazmerski, WB Berry, and G W. Allen, J. Appi. Phys. 43, 3515 (19... more ... Phys. 3«, 168 (1965). 3L. L. Kazmerski, WB Berry, and G W. Allen, J. Appi. Phys. 43, 3515 (1972). "JW Orton, BJ Goldsmith, JA Chapman, and MJ Powell, J. Appi. ... 'JYW Seto, J. Appi. Phys. 46, 5247 (1975). ,0G. Baccarini, B. Ricco, and G. Spadini, J. Appi. Phys. 49, 5585 (1978). ...
A hot-cathode silane dc discharge with electrostatic confinement devoted to the deposition of hyd... more A hot-cathode silane dc discharge with electrostatic confinement devoted to the deposition of hydrogenated amorphous silicon is analyzed by using a Langmuir probe. The electron energy distribution of the plasma shows the existence of two pseudo-Maxwellian populations with densities depending on the electrostatic confinement. The electron density of electrostatically confined plasma is higher than in the case of an unconfined
A dissolution test was performed with pulsed laser (Nd: YAG, 355 nm)-deposited calcium phosphate ... more A dissolution test was performed with pulsed laser (Nd: YAG, 355 nm)-deposited calcium phosphate coatings composed of hydroxyapatite (HA) and alpha-tricalcium phosphate (alpha-TCP) in different proportions, as a result of the use of different deposition rates. During immersion in a Ca2+-free Hank's solution, the dissolution kinetics were determined while other structural and compositional properties of the coatings were derived. It was possible to infer that the alpha-TCP is distributed uniformly and that the coating is of a non-columnar compact grain structure. The mass ratio of the phases for each coating was also determined and was related to the X-ray diffraction intensities. When incomplete, the hydroxylation level of the HA in the coatings is completed after immersion.
The formation of speci®c surface structures as a result of multi-pulse, high repetition rate Nd:Y... more The formation of speci®c surface structures as a result of multi-pulse, high repetition rate Nd:YAG (l 1:064 mm, t $ 300 ns, n 30 kHz) laser irradiation of Ti targets in vacuum is reported. The experiments are performed at laser intensity levels below the melting threshold of Ti for single laser pulse irradiation. An analysis of the early stage of surface transformation as well as of the further structure development by cumulative laser irradiation is done. A number of consecutive laser pulses are necessary to initiate the formation of the surface micro-structures. The process continues with the next laser pulses and the surface roughness increases. However, a change to a smooth, dendritic surface morphology takes place after a certain number of pulses. The irradiated areas are analysed by pro®lometry and scanning electron microscopy (SEM). The main physical phenomena implied in the laser induced surface microrelief development are discussed. #
ABSTRACT Depth calibration in sputter depth profiling may be seriously in error in the analysis o... more ABSTRACT Depth calibration in sputter depth profiling may be seriously in error in the analysis of inhomogeneous samples in which the erosion rate varies. In this work, we present a practical method to evaluate the sputter rate as a function of depth, requiring only routine instrumentation. Illustrative results in two inhomogeneous samples are presented.
The specific dome-shaped structures were grown by multi-pulse Nd:YAG (l ¼ 1:064 mm, t ¼$300 ns, a... more The specific dome-shaped structures were grown by multi-pulse Nd:YAG (l ¼ 1:064 mm, t ¼$300 ns, and n ¼ 30 kHz) laser irradiation of titanium targets in air at atmospheric pressure. The laser intensity values were chosen below the single-laser-pulse melting threshold of titanium. The chemical composition of the structures was studied as a function of laser pulse number as well as laser intensity, both at the outer surface layer and in depth. Micro-Raman spectroscopy, Auger electron spectroscopy (AES), and wavelength dispersive X-ray spectroscopy (WDX) were used as diagnostic techniques. Morphological investigations were performed by scanning electron microscopy. The obtained results revealed a lower oxygen concentration in the centre of the structures as compared to the borders and a lower concentration on the surface than in the depth. Moreover, it was found that the stoichiometry of the formed TiO 2Àx oxides increases from the structures centre towards the border and from the surface towards the depth. #
The growth mechanism of columns produced by excimer laser irradiation of a silicon target is inve... more The growth mechanism of columns produced by excimer laser irradiation of a silicon target is investigated. The micrometric columns are formed by a cumulative process with well-defined steps. The first steps lead to silicon hillocks, which evolve to columns through a little-understood mechanism. To investigate it, we irradiated a Si(100) single crystal in air with the necessary pulses of an
ABSTRACT Films of a-Si: H have been deposited by means of a dc hot cathode discharge of SiH4 with... more ABSTRACT Films of a-Si: H have been deposited by means of a dc hot cathode discharge of SiH4 with electrostatic confinement at a pressure as low as 0.4 Pa. The plasma used is quite quiescent as has been observed by means of reproducible Langmuir probe measurements. Substrates have been placed at different locations in between the electrodes, some of them facing the anode and the others facing the cathode.Films deposited on substrates facing the cathode present a granular, non-columnar, structure, an IR spectrum with only SiH absorption peaks, and a very low photoresponse. Films deposited on substrates facing the anode have a similar IR spectrum but are homogeneous, have lower hydrogen content, and present a high photoresponse. The optical absorption coefficient shows in all samples thenE=C(E–E0) x behaviour, but with exponentx=3 and notx=2 as is usually considered in a-SiH.
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Papers by J.L. Morenza