Silvia Milita - Academia.edu (original) (raw)
Papers by Silvia Milita
Crystal Growth & Design, Jul 15, 2023
Diamond and Related Materials, Aug 1, 1997
The relationship between the warpage of 4H-SiC CVD grown epi-wafers with crystal bending and subs... more The relationship between the warpage of 4H-SiC CVD grown epi-wafers with crystal bending and substrate properties is investigated. The wafer surface preparation before and after epitaxy is found to affect both long range properties such as the wafer flatness and to some extent local properties such as the epi-substrate interface. Structural characterisation is carried out using X-ray diffraction techniques and
Chemistry: A European Journal, Feb 3, 2023
Doped manganite perovskite (ultra)thin films (R1-xAxMnO3 - R = rare-earth, A = Ca, Sr, Ba and Pb)... more Doped manganite perovskite (ultra)thin films (R1-xAxMnO3 - R = rare-earth, A = Ca, Sr, Ba and Pb) show a very rich phase diagram and are considered as model system in fundamental solid state physics [1]. Moreover ferromagnetic metallic manganites are employed as prototypical spin injectors in several systems in order to reveal insights in a variety of spin related effects [2]. The La0.7Sr0.3MnO3 (LSMO) compound has stimulated an intense study since, in bulk form, it has one of the highest ferromagnetic transition temperature TC ~ 370 K. Understanding and controlling the morpho-structural and magnetic properties of LSMO films as a function of thickness is crucial for realizing applications that commonly demand for ultrathin layers. La0.7Sr0.3MnO3 thin films, with thickness t in the 4 - 16 nm range, were deposited on (001) oriented SrTiO3 substrates by means of channel spark ablation of a stoichiometric target in oxygen atmosphere [3]. The oxygen pressure in the chamber was 3.9·10-2 mbar, the substrate temperature was around 890 °C and the deposition rate was between 0.10 and 0.15 Å per pulse for a repetition rate of 6 Hz. After the deposition the films were cooled in vacuum (5.0·10-4 mbar) down to about 400 °C, where they were in situ conditioned by an annealing before removing them from the vacuum. The film thickness was estimated by XRR measurements, which also provided information on roughness and density. Both temperature (100 K £ T £ 300 K) and angular dependence of the magnetic properties were studied by a vector Vibrating Sample Magnetometer (vVSM). Ferromagnetism is observed down to 4nm (TC ~ 250 K), with TC increasing with the film thickness. For t = 16 nm, TC ~ 315 K and, at T = 100 K, the magnetization M ~ 490 emu/cm3, not far from the saturation value of bulk LSMO (560 emu/cm3). However, this gradual approach towards the ferromagnetic properties of bulk LSMO follows a non-monotonic trend. This suggests the existence of a strict correlation between the magnetic behaviour and the evolution of the microstructural and stoichiometric features during the growth process. Moreover, with increasing T from 200 K up to 300 K, a change of the magnetic anisotropy from a biaxial to an uniaxial symmetry has been clearly observed in all the films. Such behavior – probably related to a crossover from a low-temperature regime, where crystalline anisotropy dominates, to a high-temperature one, governed by magnetoelastic anisotropy – occurs progressively, with a substantial isotropic behaviour actually existing in a narrow temperature range. Magnetotransport properties have been carried out in four probes geometry, with the magnetic field in the film plane in order to complement and support the vVSM characterization. Most features are confirmed while open issues are related to the observed coercive field
Journal of materials chemistry. A, Materials for energy and sustainability, 2014
Meeting abstracts, 2009
not Available.
ECS transactions, Sep 25, 2009
Nanocrystalline semiconductors embedded in dielectric matrices are currently under investigation ... more Nanocrystalline semiconductors embedded in dielectric matrices are currently under investigation for use in Si-photonics and in memory devices. The aim of a joint research activity in the FP6-ANNA*) project (http://www.i3-anna.org) is to develop and improve metrologies for the measurement of nanocrystal properties.
Materials Science And Engineering: B, Jul 1, 1999
We describe an X-ray phase imaging technique able to detect micro and macrodefects on SiC. This t... more We describe an X-ray phase imaging technique able to detect micro and macrodefects on SiC. This technique enables investigation of thick samples, not accessible to light transmission microscopy and provides additional information on the defects.
Journal of Applied Physics, Jun 1, 1996
The x-ray rocking curve analysis was used to investigate damage accumulation with increasing dose... more The x-ray rocking curve analysis was used to investigate damage accumulation with increasing dose in silicon implanted with 50 keV and 1 MeV 11B+ ions, and 50 keV, 180 keV, and 0.7 MeV 28Si+ ions. The damage buildup was studied by following the maximum value of lattice strain normal to the surface (ε⊥) and the depth integral of ε⊥. The ε⊥ profiles were obtained with a dynamical diffraction formalism by using automated best fits to experimental x-ray rocking curves. It is shown that, for doses below the amorphization limit, the damage increases sublinearly with dose and not very differently for B and Si ions. The sublinearity results from intercascade recombination of point defects produced under bombardment. The small differences, if real, in the sublinearities observed for the two ions could be explained by the different forms of aggregation to which the surviving defects evolve when the dose approaches the amorphization threshold. However, the study of damage growth must stop at the upper dose at which a continuous buried amorphous layer begins to form. In fact, starting from this dose, a simple semikinematical diffraction model shows that the determination of a unique peak value of ε⊥ depth profile, and hence of its integral, is not possible. This is the consequence of the fact that the sample behaves as an x-ray interferometer when an embedded amorphous layer is present. The analysis reported here is compared with similar studies recently published in the literature.
Materials Science Forum, Feb 1, 1996
![Research paper thumbnail of Erratum to: “Damage profiles in as-implanted 〈100〉 Si crystals: strain by X-ray diffractometry versus interstitials by RBS-channeling” [Nucl. Instr. and Meth. B 120 (1996) 64–67]](https://attachments.academia-assets.com/112305102/thumbnails/1.jpg)
](Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, Mar 1, 1997
Due to an error of the authors, the text of the last two sentences of Section 4 is incorrect. The... more Due to an error of the authors, the text of the last two sentences of Section 4 is incorrect. The correct text is as follows: In this case, the data relative to the damage produced by the light mass ions can be used to give an evaluation of the relative volume increase per interstitial in relaxed silicon. This value results to be about 1.2 x 10-2. ' PI1 of original article: SO168-583X(96)00480-6.
ACS Applied Electronic Materials, 2019
Materials Science Forum, 1998
Thin Solid Films, 2011
We propose to analyze ellipsometry data by using effective medium approximation (EMA) models. Tha... more We propose to analyze ellipsometry data by using effective medium approximation (EMA) models. Thanks to EMA, having nanocrystalline reference dielectric functions and generalized critical point (GCP) model the physical parameters of two series of samples containing silicon nanocrystals, i.e. silicon rich oxide (SRO) superlattices and porous silicon layers (PSL), have been determined. The superlattices, consisting of ten SRO/ SiO 2 layer pairs, have been prepared using plasma enhanced chemical vapor deposition. The porous silicon layers have been prepared using short monopulses of anodization current in the transition regime between porous silicon formation and electropolishing, in a mixture of hydrofluoric acid and ethanol. The optical modeling of both structures is similar. The effective dielectric function of the layer is calculated by EMA using nanocrystalline components (nc-Si and GCP) in a dielectric matrix (SRO) or voids (PSL). We discuss the two major problems occurring when modeling such structures: (1) the modeling of the vertically non-uniform layer structures (including the interface properties like nanoroughness at the layer boundaries) and (2) the parameterization of the dielectric function of nanocrystals. We used several techniques to reduce the large number of fit parameters of the GCP models. The obtained results are in good agreement with those obtained by X-ray diffraction and electron microscopy. We investigated the correlation of the broadening parameter and characteristic EMA components with the nanocrystal size and the sample preparation conditions, such as the annealing temperatures of the SRO superlattices and the anodization current density of the porous silicon samples. We found that the broadening parameter is a sensitive measure of the nanocrystallinity of the samples, even in cases, where the nanocrystals are too small to be visible for X-ray scattering. Major processes like sintering, phase separation, and intermixing have been revealed as a function of annealing of the SRO superlattices.
Synthetic Metals, 2012
In this paper we investigate the distribution of the electrically available states near the band-... more In this paper we investigate the distribution of the electrically available states near the band-edge in pentacene thin films of different thicknesses, aiming to the identification of the active thickness of pentacene layers in fully operational devices such as organic thin film transistors (OTFTs). The film structure has been studied by X-ray diffraction technique, while their relative electronic density of states distribution (DOS) around the band-edge has been investigated by photocurrent (PC) spectroscopy analyses. The effects of ion implantation on OTFTs have been investigated by PC analyses of OTFTs implanted with N + ions of different energy and doses. We show how PC spectroscopy has the remarkable ability to detect modifications of the DOS distribution in a non invasive way, thus allowing the direct study of the active semiconductor film in fully operational OTFTs.
Journal of The Electrochemical Society, 2001
ABSTRACT
Journal of Applied Physics, 2012
We report on the structural and optical characterization of two-dimensional arrays of silicon nan... more We report on the structural and optical characterization of two-dimensional arrays of silicon nanocrystals (SiNCs) suitable for photovoltaic applications. Single and multiple SiNC layers were grown on quartz by low pressure chemical vapor deposition of Si and subsequent thermal oxidation steps. The single SiNC layers consisted of one SiNC layer embedded in two silicon dioxide (SiO2) layers, whereas the multi-layered structure consisted of five SiNC layers of equal thickness separated by SiO2 layers. SiNC layers with thicknesses ranging from 2 to 25 nm were investigated. A thorough structural characterization of the films was carried out by combining grazing incidence x-ray diffraction, x-ray reflectivity, and transmission electron microscopy (TEM). Both XRD and TEM measurements revealed that the SiNC layers were polycrystalline in nature and composed of SiNCs, separated by grain boundaries, with their vertical size equal to the SiNC layer and their lateral size characterized by a na...
Advances in Physics, 2005
This article presents a review of the structural and magnetic properties of ultrathin epitaxial F... more This article presents a review of the structural and magnetic properties of ultrathin epitaxial Fe films on GaAs(001) and related semiconductor substrates. Interest in these systems and Fe/GaAs(001) in particular has increased significantly over the last two decades, largely due to the emergence of the field of magnetoelectronics. Since then numerous studies of molecular beam epitaxy of Fe on GaAs(001) have been carried out, making it by far the best researched Fe/semiconductor(001) system. Issues such as magnetic anisotropy in the ultrathin regime, however, remain controversial with contradictory reports in the literature giving rise to considerable controversy within the field. By carefully scrutinizing the enormous amount of literature published on Fe/GaAs(001) so far and analysing these results within the wider context of Fe/semiconductor(001) systems, this article tries to settle some of these controversial issues, hence providing a long overdue ‘common denominator' for research in this area.
Crystal Growth & Design, Jul 15, 2023
Diamond and Related Materials, Aug 1, 1997
The relationship between the warpage of 4H-SiC CVD grown epi-wafers with crystal bending and subs... more The relationship between the warpage of 4H-SiC CVD grown epi-wafers with crystal bending and substrate properties is investigated. The wafer surface preparation before and after epitaxy is found to affect both long range properties such as the wafer flatness and to some extent local properties such as the epi-substrate interface. Structural characterisation is carried out using X-ray diffraction techniques and
Chemistry: A European Journal, Feb 3, 2023
Doped manganite perovskite (ultra)thin films (R1-xAxMnO3 - R = rare-earth, A = Ca, Sr, Ba and Pb)... more Doped manganite perovskite (ultra)thin films (R1-xAxMnO3 - R = rare-earth, A = Ca, Sr, Ba and Pb) show a very rich phase diagram and are considered as model system in fundamental solid state physics [1]. Moreover ferromagnetic metallic manganites are employed as prototypical spin injectors in several systems in order to reveal insights in a variety of spin related effects [2]. The La0.7Sr0.3MnO3 (LSMO) compound has stimulated an intense study since, in bulk form, it has one of the highest ferromagnetic transition temperature TC ~ 370 K. Understanding and controlling the morpho-structural and magnetic properties of LSMO films as a function of thickness is crucial for realizing applications that commonly demand for ultrathin layers. La0.7Sr0.3MnO3 thin films, with thickness t in the 4 - 16 nm range, were deposited on (001) oriented SrTiO3 substrates by means of channel spark ablation of a stoichiometric target in oxygen atmosphere [3]. The oxygen pressure in the chamber was 3.9·10-2 mbar, the substrate temperature was around 890 °C and the deposition rate was between 0.10 and 0.15 Å per pulse for a repetition rate of 6 Hz. After the deposition the films were cooled in vacuum (5.0·10-4 mbar) down to about 400 °C, where they were in situ conditioned by an annealing before removing them from the vacuum. The film thickness was estimated by XRR measurements, which also provided information on roughness and density. Both temperature (100 K £ T £ 300 K) and angular dependence of the magnetic properties were studied by a vector Vibrating Sample Magnetometer (vVSM). Ferromagnetism is observed down to 4nm (TC ~ 250 K), with TC increasing with the film thickness. For t = 16 nm, TC ~ 315 K and, at T = 100 K, the magnetization M ~ 490 emu/cm3, not far from the saturation value of bulk LSMO (560 emu/cm3). However, this gradual approach towards the ferromagnetic properties of bulk LSMO follows a non-monotonic trend. This suggests the existence of a strict correlation between the magnetic behaviour and the evolution of the microstructural and stoichiometric features during the growth process. Moreover, with increasing T from 200 K up to 300 K, a change of the magnetic anisotropy from a biaxial to an uniaxial symmetry has been clearly observed in all the films. Such behavior – probably related to a crossover from a low-temperature regime, where crystalline anisotropy dominates, to a high-temperature one, governed by magnetoelastic anisotropy – occurs progressively, with a substantial isotropic behaviour actually existing in a narrow temperature range. Magnetotransport properties have been carried out in four probes geometry, with the magnetic field in the film plane in order to complement and support the vVSM characterization. Most features are confirmed while open issues are related to the observed coercive field
Journal of materials chemistry. A, Materials for energy and sustainability, 2014
Meeting abstracts, 2009
not Available.
ECS transactions, Sep 25, 2009
Nanocrystalline semiconductors embedded in dielectric matrices are currently under investigation ... more Nanocrystalline semiconductors embedded in dielectric matrices are currently under investigation for use in Si-photonics and in memory devices. The aim of a joint research activity in the FP6-ANNA*) project (http://www.i3-anna.org) is to develop and improve metrologies for the measurement of nanocrystal properties.
Materials Science And Engineering: B, Jul 1, 1999
We describe an X-ray phase imaging technique able to detect micro and macrodefects on SiC. This t... more We describe an X-ray phase imaging technique able to detect micro and macrodefects on SiC. This technique enables investigation of thick samples, not accessible to light transmission microscopy and provides additional information on the defects.
Journal of Applied Physics, Jun 1, 1996
The x-ray rocking curve analysis was used to investigate damage accumulation with increasing dose... more The x-ray rocking curve analysis was used to investigate damage accumulation with increasing dose in silicon implanted with 50 keV and 1 MeV 11B+ ions, and 50 keV, 180 keV, and 0.7 MeV 28Si+ ions. The damage buildup was studied by following the maximum value of lattice strain normal to the surface (ε⊥) and the depth integral of ε⊥. The ε⊥ profiles were obtained with a dynamical diffraction formalism by using automated best fits to experimental x-ray rocking curves. It is shown that, for doses below the amorphization limit, the damage increases sublinearly with dose and not very differently for B and Si ions. The sublinearity results from intercascade recombination of point defects produced under bombardment. The small differences, if real, in the sublinearities observed for the two ions could be explained by the different forms of aggregation to which the surviving defects evolve when the dose approaches the amorphization threshold. However, the study of damage growth must stop at the upper dose at which a continuous buried amorphous layer begins to form. In fact, starting from this dose, a simple semikinematical diffraction model shows that the determination of a unique peak value of ε⊥ depth profile, and hence of its integral, is not possible. This is the consequence of the fact that the sample behaves as an x-ray interferometer when an embedded amorphous layer is present. The analysis reported here is compared with similar studies recently published in the literature.
Materials Science Forum, Feb 1, 1996
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, Mar 1, 1997
Due to an error of the authors, the text of the last two sentences of Section 4 is incorrect. The... more Due to an error of the authors, the text of the last two sentences of Section 4 is incorrect. The correct text is as follows: In this case, the data relative to the damage produced by the light mass ions can be used to give an evaluation of the relative volume increase per interstitial in relaxed silicon. This value results to be about 1.2 x 10-2. ' PI1 of original article: SO168-583X(96)00480-6.
ACS Applied Electronic Materials, 2019
Materials Science Forum, 1998
Thin Solid Films, 2011
We propose to analyze ellipsometry data by using effective medium approximation (EMA) models. Tha... more We propose to analyze ellipsometry data by using effective medium approximation (EMA) models. Thanks to EMA, having nanocrystalline reference dielectric functions and generalized critical point (GCP) model the physical parameters of two series of samples containing silicon nanocrystals, i.e. silicon rich oxide (SRO) superlattices and porous silicon layers (PSL), have been determined. The superlattices, consisting of ten SRO/ SiO 2 layer pairs, have been prepared using plasma enhanced chemical vapor deposition. The porous silicon layers have been prepared using short monopulses of anodization current in the transition regime between porous silicon formation and electropolishing, in a mixture of hydrofluoric acid and ethanol. The optical modeling of both structures is similar. The effective dielectric function of the layer is calculated by EMA using nanocrystalline components (nc-Si and GCP) in a dielectric matrix (SRO) or voids (PSL). We discuss the two major problems occurring when modeling such structures: (1) the modeling of the vertically non-uniform layer structures (including the interface properties like nanoroughness at the layer boundaries) and (2) the parameterization of the dielectric function of nanocrystals. We used several techniques to reduce the large number of fit parameters of the GCP models. The obtained results are in good agreement with those obtained by X-ray diffraction and electron microscopy. We investigated the correlation of the broadening parameter and characteristic EMA components with the nanocrystal size and the sample preparation conditions, such as the annealing temperatures of the SRO superlattices and the anodization current density of the porous silicon samples. We found that the broadening parameter is a sensitive measure of the nanocrystallinity of the samples, even in cases, where the nanocrystals are too small to be visible for X-ray scattering. Major processes like sintering, phase separation, and intermixing have been revealed as a function of annealing of the SRO superlattices.
Synthetic Metals, 2012
In this paper we investigate the distribution of the electrically available states near the band-... more In this paper we investigate the distribution of the electrically available states near the band-edge in pentacene thin films of different thicknesses, aiming to the identification of the active thickness of pentacene layers in fully operational devices such as organic thin film transistors (OTFTs). The film structure has been studied by X-ray diffraction technique, while their relative electronic density of states distribution (DOS) around the band-edge has been investigated by photocurrent (PC) spectroscopy analyses. The effects of ion implantation on OTFTs have been investigated by PC analyses of OTFTs implanted with N + ions of different energy and doses. We show how PC spectroscopy has the remarkable ability to detect modifications of the DOS distribution in a non invasive way, thus allowing the direct study of the active semiconductor film in fully operational OTFTs.
Journal of The Electrochemical Society, 2001
ABSTRACT
Journal of Applied Physics, 2012
We report on the structural and optical characterization of two-dimensional arrays of silicon nan... more We report on the structural and optical characterization of two-dimensional arrays of silicon nanocrystals (SiNCs) suitable for photovoltaic applications. Single and multiple SiNC layers were grown on quartz by low pressure chemical vapor deposition of Si and subsequent thermal oxidation steps. The single SiNC layers consisted of one SiNC layer embedded in two silicon dioxide (SiO2) layers, whereas the multi-layered structure consisted of five SiNC layers of equal thickness separated by SiO2 layers. SiNC layers with thicknesses ranging from 2 to 25 nm were investigated. A thorough structural characterization of the films was carried out by combining grazing incidence x-ray diffraction, x-ray reflectivity, and transmission electron microscopy (TEM). Both XRD and TEM measurements revealed that the SiNC layers were polycrystalline in nature and composed of SiNCs, separated by grain boundaries, with their vertical size equal to the SiNC layer and their lateral size characterized by a na...
Advances in Physics, 2005
This article presents a review of the structural and magnetic properties of ultrathin epitaxial F... more This article presents a review of the structural and magnetic properties of ultrathin epitaxial Fe films on GaAs(001) and related semiconductor substrates. Interest in these systems and Fe/GaAs(001) in particular has increased significantly over the last two decades, largely due to the emergence of the field of magnetoelectronics. Since then numerous studies of molecular beam epitaxy of Fe on GaAs(001) have been carried out, making it by far the best researched Fe/semiconductor(001) system. Issues such as magnetic anisotropy in the ultrathin regime, however, remain controversial with contradictory reports in the literature giving rise to considerable controversy within the field. By carefully scrutinizing the enormous amount of literature published on Fe/GaAs(001) so far and analysing these results within the wider context of Fe/semiconductor(001) systems, this article tries to settle some of these controversial issues, hence providing a long overdue ‘common denominator' for research in this area.