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Fatiha Kail

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Papers by Fatiha Kail

Interfacial Dzyaloshinskii-Moriya interaction in perpendicularly magnetizedPt/Co/AlOxultrathin films measured by Brillouin light spectroscopy

Physical Review B, 2015

Spin waves in perpendicularly magnetized Pt/Co/AlO x /Pt ultrathin films with varying Co thicknes... more Spin waves in perpendicularly magnetized Pt/Co/AlO x /Pt ultrathin films with varying Co thicknesses (0.6-1.2 nm) have been studied with Brillouin light spectroscopy in the Damon-Eshbach geometry. The measurements reveal a pronounced nonreciprocal propagation, which increases with decreasing Co thickness. This nonreciprocity, attributed to an interfacial Dzyaloshinskii-Moriya interaction (DMI), is significantly stronger than asymmetries resulting from surface anisotropies for such modes. Results are consistent with an interfacial DMI constant D s = -1.7 ± 0.11 pJ/m, which favors left-handed chiral spin structures. This suggests that such films below 1 nm in thickness should support chiral states such as skyrmions at room temperature.

Structural and magnetic study of nitrided Co74Fe8B12Si6 and Co74Fe4Mn4B12Si6 ribbons

Bulletin of Materials Science, 1999

The nitriding thermochemical treatment (NTT) is commonly used for steels. In this paper, the expe... more The nitriding thermochemical treatment (NTT) is commonly used for steels. In this paper, the experimental conditions required for NTT, and the influence of such treatments on the structure and hysteresis loops of Co74FesB12Si6 and C074Fe4Mn4B12Si6 ribbons are reported. The results have been compared with those obtained with ribbons treated according to conventional thermal treatment (CTT) as well.

Growth Study of Silicon Nanowires Synthesized Via Plasma-Assisted VLS Using Tin Catalysts

Modern Concepts in Material Science, 2020

5 sccm at a substrate temperature between 400 and 600 °C. SEMs showing that the Tin catalyzed SiN... more

Thermally Induced Structural Transformations on Polymorphous Silicon

Journal of Materials Research, Sep 1, 2005

is a nanostructured form of hydrogenated amorphous Si that contains a small fraction of Si nanocr... more is a nanostructured form of hydrogenated amorphous Si that contains a small fraction of Si nanocrystals or clusters. Its thermally induced transformations such as relaxation, dehydrogenation, and crystallization have been studied by calorimetry and evolved gas analysis as a complementary technique. The observed behavior has been compared to that of conventional hydrogenated amorphous Si and amorphous Si nanoparticles. In the temperature range of our experiments (650-700°C), crystallization takes place at almost the same temperature in polymorphous and in amorphous Si. In contrast, dehydrogenation processes reflect the presence of different hydrogen states. The calorimetry and evolved gas analysis thermograms clearly show that polymorphous Si shares hydrogen states of both amorphous Si and Si nanoparticles. Finally, the total energy of the main Si-H group present in polymorphous Si has been quantified.

Effect of substrate on hydrogen in and out diffusion from a-Si:H thin films

Journal of Materials Science: Materials in Electronics, Feb 13, 2007

We present a detailed study on the effect of the substrate on the structure and hydrogen evolutio... more We present a detailed study on the effect of the substrate on the structure and hydrogen evolution from p-type hydrogenated amorphous silicon thin films co-deposited on the grounded and RF electrodes of an asymmetric radio frequency glow discharge reactor, as well as the similar films exposed to an hydrogen plasma. We used spectroscopic ellipsometry and hydrogen evolution measurements to analyze the effects of the substrate, ion energy and hydrogen plasma on the films microstructure, thickness, hydrogen content, hydrogen binding and hydrogen evolution. The hydrogen evolution spectra show a strong substrate dependence. In particular on crystalline silicon substrate, we observe the formation of bubbles. For the various substrates, ion energy and hydrogen plasma treatment do not affect the hydrogen evolution spectra. These results indicate that the action of hydrogen in a-Si:H is modified by the nature of the substrate.

The configurational energy gap between amorphous and crystalline silicon

Physica Status Solidi (rrl), Sep 19, 2011

Hydrogen diffusion and induced-crystallization in intrinsic and doped hydrogenated amorphous silicon films

Thin Solid Films, Sep 1, 2005

We have studied the evolution of the structure of intrinsic and doped hydrogenated amorphous sili... more We have studied the evolution of the structure of intrinsic and doped hydrogenated amorphous silicon films exposed to a hydrogen plasma. For this purpose, we combine in situ spectroscopic ellipsometry and secondary ion mass spectrometry measurements. We show that hydrogen diffuses faster in boron-doped hydrogenated amorphous silicon than in intrinsic samples, leading to a thicker subsurface layer from the early

Hydrogen-plasma etching of hydrogenated amorphous silicon: a study by a combination of spectroscopic ellipsometry and trap-limited diffusion model

Philosophical Magazine, 2004

The kinetics of etching hydrogenated amorphous silicon by a hydrogen plasma has been studied by i... more The kinetics of etching hydrogenated amorphous silicon by a hydrogen plasma has been studied by in-situ spectroscopic ellipsometry measurements. The formation of a hydrogen-rich sublayer is clearly emphasized. Its thickness increases from 7 to 27 nm when the temperature during the hydrogen-plasma treatment is raised from 100 to 250 C. This effect is interpreted by solving the differential equation for trap-limited hydrogen diffusion through a mobile surface. By assigning the thickness of this sublayer to the mean diffusion distance of hydrogen we determined values of the effective diffusion coefficient of hydrogen higher than 10 À14 cm 2 s À1 with an activation energy of 0.22 eV. The density of hydrogen traps is found to decrease from 7.3 Â 10 18 to 4.5 Â 10 17 cm À3 as the temperature of the hydrogen treatment increases from 100 to 250 C with an activation energy of 0.43 eV. This effect is interpreted by a thermal equilibrium involving hydrogen transitions between shallow states and hydrogen-trapping sites.

Can the crystallization rate be independent from the crystallization enthalpy? The case of amorphous silicon

Journal of Physics: Condensed Matter, 2012

The crystallization enthalpy measured in a large series of amorphous silicon (a-Si) materials var... more The crystallization enthalpy measured in a large series of amorphous silicon (a-Si) materials varies within a factor of 2 from sample to sample (Kail et al 2011 Phys. Status Solidi RRL 5 361). According to the classical theory of nucleation, this variation should produce large differences in the crystallization kinetics leading to crystallization temperatures and activation energies exceeding 550 • C and 1.7 eV, respectively, the 'standard' values measured for a-Si obtained by self-implantation. In contrast, the observed crystallization kinetics is very similar for all the samples studied and has no correlation with the crystallization enthalpy. This discrepancy has led us to propose that crystallization in a-Si begins in microscopic domains that are almost identical in all samples, independently of their crystallization enthalpy. Probably the existence of microscopic inhomogeneities also plays a crucial role in the crystallization kinetics of other amorphous materials and glasses.

Experimental evidence for extended hydrogen diffusion in silicon thin films during light-soaking

Journal of Non-Crystalline Solids, 2006

We have used mass spectrometry to detect hydrogen effusing from silicon thin films exposed to lig... more We have used mass spectrometry to detect hydrogen effusing from silicon thin films exposed to light. Our results indicate a long range diffusion of hydrogen through the whole film, which ends with its release into the vacuum system. The changes in the film properties are characterized by dark and photoconductivity and hydrogen exodiffusion measurements. From the evolution of dark conductivity measurements after turning off the light, we show that this long range motion of hydrogen is not due to the heating of the sample. A comparison of hydrogen exodiffusion spectra of as-deposited and light-soaked samples shows that the weakly-bonded hydrogen content decreases by 30% for a-Si:H films and that the tightly-bonded hydrogen migrates to grain boundaries of crystalline regions in the case of pm-Si:H films. These results clearly demonstrate the long range motion of hydrogen during light soaking.

Helium versus hydrogen dilution in the optimization of polymorphous silicon solar cells

Journal of Non-Crystalline Solids, 2004

We have studied how the increase of pressure in the deposition of polymorphous silicon can reduce... more We have studied how the increase of pressure in the deposition of polymorphous silicon can reduce the ion energy and the damage of the player in p-in solar cells. By increasing the pressure during the deposition of the i-layer to 3 Torr, we have been able to increase the fill factor and the solar cell efficiency up to 8.4%. In an attempt to reduce the optical gap and increase further the deposition rate we have studied the use of He dilution. Changing the dilution from hydrogen to He leads to a higher deposition rate at lower rf power while keeping similar transport properties. Moreover, the lower hydrogen content of He diluted films results in a smaller band gap and a higher short circuit current in solar cells. Thus, silane-He mixtures allow to reduce the ion energy for a constant deposition rate and to minimize the damage at the player and p/i interface. The cells show a fill factor of 0.69, V oc of 0.91 V, an initial efficiency of 9.3% on textured SnO 2 .

Hydrogen Diffusion in Boron-Doped Hydrogenated Amorphous Silicon Films: Crystallization and Induced Structural Changes

MRS Proceedings, 2005

We have studied the evolution of the structure of boron-doped hydrogenated amorphous silicon film... more We have studied the evolution of the structure of boron-doped hydrogenated amorphous silicon films exposed to a hydrogen plasma. From the early stages of exposure, hydrogen diffuses and forms a thick H-rich subsurface. At longer times, hydrogen plasma leads to the formation of a microcrystalline layer via chemical transport without crystallization of the initial layer. We observe that the hydrogen content increases in the films during a plasma exposure and once the microcrystalline layer is formed hydrogen diffuses out of the sample accompanied with a decrease in the boron content. This effect can be attributed to the electric field developed within the heterojunction a-Si:H/μc-Si:H that drives the positively charged hydrogen atoms in the boron-doped layer towards the μc-Si:H layer.

Tin versus indium catalyst in the growth of silicon nanowires by plasma enhanced chemical vapor deposition on different substrates

Thin Solid Films

Aberrometry from Astronomy to Vision Science

Medical Technologies Journal, 2019

Aberrometry is a branch of optical metrology and more specifically of astronomy. This branch is a... more Aberrometry is a branch of optical metrology and more specifically of astronomy. This branch is applied to the science of vision. It allows dramatic improvements in human vision research, such as refining the visual capabilities of healthy and diseased subjects beyond physiological limits. Aberrometry relies on the ocular wave front collection with the help of an aberrometer, which allows establishing the precise and quantitative record of the various optical aberrations of the human eye, whether low or high degree. In this work, we draw our approach to apply these concepts to refractive surgery and adaptation in order to relate the changes in Higher-Order Aberrations (HOAs) following wavefront-guided femtosecond laser-assisted (WFG FS-LASIK), and to explore the correlations between preoperative spherical equivalence (SE) and mechanisms of HOAs affecting the visual quality.

Thermally induced structural transformations on polymorphous

is a nanostructured form of hydrogenated amorphous Si that contains a small fraction of Si nanocr... more is a nanostructured form of hydrogenated amorphous Si that contains a small fraction of Si nanocrystals or clusters. Its thermally induced transformations such as relaxation, dehydrogenation, and crystallization have been studied by calorimetry and evolved gas analysis as a complementary technique. The observed behavior has been compared to that of conventional hydrogenated amorphous Si and amorphous Si nanoparticles. In the temperature range of our experiments (650-700°C), crystallization takes place at almost the same temperature in polymorphous and in amorphous Si. In contrast, dehydrogenation processes reflect the presence of different hydrogen states. The calorimetry and evolved gas analysis thermograms clearly show that polymorphous Si shares hydrogen states of both amorphous Si and Si nanoparticles. Finally, the total energy of the main Si-H group present in polymorphous Si has been quantified.

Hydrogen evolution in hydrogenated microcrystalline silicon carbide thin films

Journal of Vacuum Science & Technology B, 2019

Evolved gas analysis (EGA), infrared attenuated reflection (ATR), and Raman spectroscopy experime... more Evolved gas analysis (EGA), infrared attenuated reflection (ATR), and Raman spectroscopy experiments are used to study hydrogen evolution in hydrogenated microcrystalline silicon carbide (μc-Si1−xCx:H) films prepared by plasma-enhanced chemical vapor deposition. The results are compared with microcrystalline silicon (μc-Si:H). The effused hydrogen and carbon-hydride groups (CH, CH2, and CH3) are measured up to 800 °C. Their EGA curves have a peak at 410 °C, attributed to the methyl groups incorporated in the amorphous matrix during the deposition process. Moreover, hydrogen evolution curves show narrow and sharp peaks centered at 425 and 520 °C, corresponding to hydrogen desorbing from silicon hydrides at grain boundaries. While its content is more important than hydrogen bonded to silicon in the amorphous and denser crystalline regions of μc-Si1−xCx:H, but remains lower than in the μc-Si:H film. Raman and ATR data indicate that the μc-Si1−xCx:H film is composed of small size silicon crystallites embedded in a hydrogenated amorphous silicon carbide matrix and confirmed that carbon is incorporated in the amorphous matrix as methyl groups (CH3), inducing a decrease in SiHx groups compared to the μc-Si:H film.Evolved gas analysis (EGA), infrared attenuated reflection (ATR), and Raman spectroscopy experiments are used to study hydrogen evolution in hydrogenated microcrystalline silicon carbide (μc-Si1−xCx:H) films prepared by plasma-enhanced chemical vapor deposition. The results are compared with microcrystalline silicon (μc-Si:H). The effused hydrogen and carbon-hydride groups (CH, CH2, and CH3) are measured up to 800 °C. Their EGA curves have a peak at 410 °C, attributed to the methyl groups incorporated in the amorphous matrix during the deposition process. Moreover, hydrogen evolution curves show narrow and sharp peaks centered at 425 and 520 °C, corresponding to hydrogen desorbing from silicon hydrides at grain boundaries. While its content is more important than hydrogen bonded to silicon in the amorphous and denser crystalline regions of μc-Si1−xCx:H, but remains lower than in the μc-Si:H film. Raman and ATR data indicate that the μc-Si1−xCx:H film is composed of small size silicon crystallites embedded...

Optimization of the Solar Cell Structure for the Industrial Implementation in Very Large Area a-Si:H PV Modules

This paper reports on work performed in the FP7 European project HELATHIS. It presents the develo... more This paper reports on work performed in the FP7 European project HELATHIS. It presents the development of a TCO-glass combining a low iron-content substrate with a SnO 2 -layer with enhanced carrier mobility and therefore higher optical transmission, achieving in average 7.4% single junction module efficiency in T-Solar standard production. First results of the further optimization of the fabrication process with this TCO glass indicate an increase of the single junction module efficiency in the future to nearly 8% in the stabilized state. Lightsoaking experiments of modules present very similar stabilized efficiency in the investigated i-layer thickness range between 140 to 260 nm, therefore, decreasing the i-layer thickness permits to increase the factory production capacity from about 55 up to about 75 MW/year. Investigation of the deposition of Al-doped ZnO layers by rf-sputtering from rotatable targets for the back reflector indicates improvement in the I sc and V oc . Implementation of such targets allows to expand the target life time and to reduce the maintenance time in comparison to standard planar targets. Ga-doped ZnO layers, when implemented in the back reflector, present similar cell performance compared with Al-doped ZnO.

Molecular hydrogen-induced nucleation of hydrogenated silicon nanocrystals at low temperature

Surface and Interface Analysis, 2019

Molecular hydrogen diffusion in nanostructured amorphous silicon thin films

Physical Review B, 2009

We study hydrogen stability and its evolution during thermal annealing in nanostructured amorphou... more We study hydrogen stability and its evolution during thermal annealing in nanostructured amorphous silicon thin films. From the simultaneous measurement of heat and hydrogen desorption, we obtain the experimental evidence of molecular diffusion in these materials. In addition, we introduce a simple diffusion model which shows good agreement with the experimental data.

Relaxation and derelaxation of pure and hydrogenated amorphous silicon during thermal annealing experiments

Applied Physics Letters, 2010