The Fermi energy in acceptor doped SrTiO3 and BaTiO3

In order to evaluate the presence of space charge layers and the magnitude of band bending at electrode interfaces of mixed ionic-electronic conductors we have evaluated the Fermi energies in the bulk and at interfaces of acceptor-doped SrTiO3, BaTiO3 and (Ba,Sr)TiO3. While the interface Fermi energy can be directly obtained using photoelectron spectroscopy (XPS) if conducting electrode materials are deposited, the determination of the bulk Fermi energy is more challenging due to the high resistivity of the samples. One approach is to use XPS on thin films deposited on conducting samples. In general, we observed a good agreement between upper and lower limits of Fermi energies at thin films surfaces and at interfaces. Surprisingly, the Fermi energy is hardly observed below EF-EVB≈2eV (see Fig. 1), although defect chemistry calculations predict values as low as EF-EVB≈2eV for acceptor doped samples, such as Fe-doped SrTiO3 or Mn-doped BaTiO3.c,d Even at anode interfaces of ionically polarized Fe-doped SrTiO3 single crystals,e at which the oxygen vacancy concentration should be very low, we have not observed lower Fermi energies. Please click Additional Files below to see the full abstract

Charged defects in BaTiO₃ thin films

The work presented here focuses on the study of doped BaTiO₃ (BTO) thin films deposited by magnetron sputtering. Due to its ferroelectric properties and its high dielectric permittivity, BTO is used as a tunable capacitor or also in non-volatile memories (FeRAM). Nevertheless, these properties are strongly degraded when deposed as thin films as a results of the extrinsic interface effects. The strategy adopted in this study to improve these dielectric properties was to control the charged defects at the interface by multilayered doped BTO thin films (Mn, Nb and La). Studies on monodoped thin films and multilayers have shown that the carefully designed interfaces lead to increasing relative permittivity of BTO thin films, contradicting the common belief that interfaces behave like dead layers. The use of different techniques such as Electron Paramagnetic Resonance (EPR), dielectric impedance and in particular X-ray Photoelectron Spectroscopy (XPS) and Time-of-Fligh Secondary Ion Mass Spectroscopy (ToF-SIMS) have enabled us to relate the different physical and chemical aspects such as the Fermi level position and the defect chemistry at the interfaces of BTO multilayers. In addition, we have studied the particularities of the Fermi level position of Mn-doped layers. Charging phenomena or even surface photovoltage induce an artificial change in the Fermi level of the Mn-doped BTO when deposited on various substrates. Finally, we implemented a deposition technique using oxygen plasma which made it possible to lower the Fermi level position towards the valence band of Mn doped BTO

Electronic and ionic charged defects in doped BaTiO3 thin films

Les travaux ici présents portent sur l’étude des couches minces BaTiO3 (BTO) dopées et déposées par pulvérisation cathodique. Grâce à ses propriétés ferroélectriques et à sa forte permittivité diélectrique, leBTO est utilisé comme un condensateur accordable ou encore dans des mémoires non-volatiles (FeRAM). Néanmoins, ces propriétés sont fortement dégradées lors de sa déposition sous forme de couche mince àcause des effets extrinsèques d’interface. La stratégie adoptée dans cette étude pour améliorer ces propriétés diélectriques est de contrôler les défauts chargés à l’interface par des multicouches de couches minces de BTO dopé au Mn, Nb et La. Des études sur les couches mono dopées et les multicouches ont montré que les interfaces soigneusement conçues conduisent à augmenter la permittivité relative des couches minces de BTO, en contradiction avec la croyance commune selon laquelle les interfaces se comportent comme des couches mortes. L’utilisation des différentes techniques comme la Résonance Paramagnétique Électronique (RPE), l’impédance diélectrique et notamment la Spectrométrie de Photoélectrons X (XPS en anglais) et laSpectrométrie de Masse à Ions Secondaires à Temps de Vol (ToF-SIMS en anglais) nous a permis de relier les différents aspects physiques et chimiques comme le niveau de Fermi et la chimie de défauts aux interfaces des multicouches de BTO. De plus, nous avons étudié les particularités du niveau de Fermi des couches dopées au Mn. Des phénomènes de charge ou même du photovoltage de surface induisent un changement artificiel du niveau de Fermi du BTO dopé Mn déposé sur différents substrats. Enfin, nous avons mis en place une technique de dépôt à l’aide du plasma d’oxygène qui a permis de baisser le niveau de Fermi vers la bande de valence du BTO dopé Mn.The work presented here focuses on the study of doped BaTiO 3 (BTO) thin films deposited by magnetron sputtering. Due to its ferroelectric properties and its high dielectric permittivity, BTO is used asa tunable capacitor or also in non-volatile memories (FeRAM). Nevertheless, these properties are strongly degraded when deposed as thin films as a results of the extrinsic interface effects. The strategy adopted in this study to improve these dielectric properties was to control the charged defects at the interface by multilayered doped BTO thin films (Mn, Nb and La). Studies on monodoped thin films and multilayershave shown that the carefully designed interfaces lead to increasing relative permittivity of BTO thin films,contradicting the common belief that interfaces behave like dead layers. The use of different techniques suchas Electron Paramagnetic Resonance (EPR), dielectric impedance and in particular X-ray Photoelectron Spectroscopy (XPS) and Time-of-Fligh Secondary Ion Mass Spectroscopy (ToF-SIMS) have enabled us to relate the different physical and chemical aspects such as the Fermi level position and the defect chemistryat the interfaces of BTO multilayers. In addition, we have studied the particularities of the Fermi level position of Mn-doped layers. Charging phenomena or even surface photovoltage induce an artificial change in the Fermi level of the Mn-doped BTO when deposited on various substrates. Finally, we implemented a deposition technique using oxygen plasma which made it possible to lower the Fermi level position towards the valence band of Mn doped BTO

Electronic and ionic charged defects in doped BaTiO3 thin films

Les travaux ici présents portent sur l’étude des couches minces BaTiO3 (BTO) dopées et déposées par pulvérisation cathodique. Grâce à ses propriétés ferroélectriques et à sa forte permittivité diélectrique, leBTO est utilisé comme un condensateur accordable ou encore dans des mémoires non-volatiles (FeRAM). Néanmoins, ces propriétés sont fortement dégradées lors de sa déposition sous forme de couche mince àcause des effets extrinsèques d’interface. La stratégie adoptée dans cette étude pour améliorer ces propriétés diélectriques est de contrôler les défauts chargés à l’interface par des multicouches de couches minces de BTO dopé au Mn, Nb et La. Des études sur les couches mono dopées et les multicouches ont montré que les interfaces soigneusement conçues conduisent à augmenter la permittivité relative des couches minces de BTO, en contradiction avec la croyance commune selon laquelle les interfaces se comportent comme des couches mortes. L’utilisation des différentes techniques comme la Résonance Paramagnétique Électronique (RPE), l’impédance diélectrique et notamment la Spectrométrie de Photoélectrons X (XPS en anglais) et laSpectrométrie de Masse à Ions Secondaires à Temps de Vol (ToF-SIMS en anglais) nous a permis de relier les différents aspects physiques et chimiques comme le niveau de Fermi et la chimie de défauts aux interfaces des multicouches de BTO. De plus, nous avons étudié les particularités du niveau de Fermi des couches dopées au Mn. Des phénomènes de charge ou même du photovoltage de surface induisent un changement artificiel du niveau de Fermi du BTO dopé Mn déposé sur différents substrats. Enfin, nous avons mis en place une technique de dépôt à l’aide du plasma d’oxygène qui a permis de baisser le niveau de Fermi vers la bande de valence du BTO dopé Mn.The work presented here focuses on the study of doped BaTiO 3 (BTO) thin films deposited by magnetron sputtering. Due to its ferroelectric properties and its high dielectric permittivity, BTO is used asa tunable capacitor or also in non-volatile memories (FeRAM). Nevertheless, these properties are strongly degraded when deposed as thin films as a results of the extrinsic interface effects. The strategy adopted in this study to improve these dielectric properties was to control the charged defects at the interface by multilayered doped BTO thin films (Mn, Nb and La). Studies on monodoped thin films and multilayershave shown that the carefully designed interfaces lead to increasing relative permittivity of BTO thin films,contradicting the common belief that interfaces behave like dead layers. The use of different techniques suchas Electron Paramagnetic Resonance (EPR), dielectric impedance and in particular X-ray Photoelectron Spectroscopy (XPS) and Time-of-Fligh Secondary Ion Mass Spectroscopy (ToF-SIMS) have enabled us to relate the different physical and chemical aspects such as the Fermi level position and the defect chemistryat the interfaces of BTO multilayers. In addition, we have studied the particularities of the Fermi level position of Mn-doped layers. Charging phenomena or even surface photovoltage induce an artificial change in the Fermi level of the Mn-doped BTO when deposited on various substrates. Finally, we implemented a deposition technique using oxygen plasma which made it possible to lower the Fermi level position towards the valence band of Mn doped BTO

Electronic and ionic charged defects in doped BaTiO3 thin films

Les travaux ici présents portent sur l’étude des couches minces BaTiO3 (BTO) dopées et déposées par pulvérisation cathodique. Grâce à ses propriétés ferroélectriques et à sa forte permittivité diélectrique, leBTO est utilisé comme un condensateur accordable ou encore dans des mémoires non-volatiles (FeRAM). Néanmoins, ces propriétés sont fortement dégradées lors de sa déposition sous forme de couche mince àcause des effets extrinsèques d’interface. La stratégie adoptée dans cette étude pour améliorer ces propriétés diélectriques est de contrôler les défauts chargés à l’interface par des multicouches de couches minces de BTO dopé au Mn, Nb et La. Des études sur les couches mono dopées et les multicouches ont montré que les interfaces soigneusement conçues conduisent à augmenter la permittivité relative des couches minces de BTO, en contradiction avec la croyance commune selon laquelle les interfaces se comportent comme des couches mortes. L’utilisation des différentes techniques comme la Résonance Paramagnétique Électronique (RPE), l’impédance diélectrique et notamment la Spectrométrie de Photoélectrons X (XPS en anglais) et laSpectrométrie de Masse à Ions Secondaires à Temps de Vol (ToF-SIMS en anglais) nous a permis de relier les différents aspects physiques et chimiques comme le niveau de Fermi et la chimie de défauts aux interfaces des multicouches de BTO. De plus, nous avons étudié les particularités du niveau de Fermi des couches dopées au Mn. Des phénomènes de charge ou même du photovoltage de surface induisent un changement artificiel du niveau de Fermi du BTO dopé Mn déposé sur différents substrats. Enfin, nous avons mis en place une technique de dépôt à l’aide du plasma d’oxygène qui a permis de baisser le niveau de Fermi vers la bande de valence du BTO dopé Mn.The work presented here focuses on the study of doped BaTiO 3 (BTO) thin films deposited by magnetron sputtering. Due to its ferroelectric properties and its high dielectric permittivity, BTO is used asa tunable capacitor or also in non-volatile memories (FeRAM). Nevertheless, these properties are strongly degraded when deposed as thin films as a results of the extrinsic interface effects. The strategy adopted in this study to improve these dielectric properties was to control the charged defects at the interface by multilayered doped BTO thin films (Mn, Nb and La). Studies on monodoped thin films and multilayershave shown that the carefully designed interfaces lead to increasing relative permittivity of BTO thin films,contradicting the common belief that interfaces behave like dead layers. The use of different techniques suchas Electron Paramagnetic Resonance (EPR), dielectric impedance and in particular X-ray Photoelectron Spectroscopy (XPS) and Time-of-Fligh Secondary Ion Mass Spectroscopy (ToF-SIMS) have enabled us to relate the different physical and chemical aspects such as the Fermi level position and the defect chemistryat the interfaces of BTO multilayers. In addition, we have studied the particularities of the Fermi level position of Mn-doped layers. Charging phenomena or even surface photovoltage induce an artificial change in the Fermi level of the Mn-doped BTO when deposited on various substrates. Finally, we implemented a deposition technique using oxygen plasma which made it possible to lower the Fermi level position towards the valence band of Mn doped BTO

Défauts chargés dans les couches minces dopées de BaTiO3

The work presented here focuses on the study of doped BaTiO 3 (BTO) thin films deposited by magnetron sputtering. Due to its ferroelectric properties and its high dielectric permittivity, BTO is used asa tunable capacitor or also in non-volatile memories (FeRAM). Nevertheless, these properties are strongly degraded when deposed as thin films as a results of the extrinsic interface effects. The strategy adopted in this study to improve these dielectric properties was to control the charged defects at the interface by multilayered doped BTO thin films (Mn, Nb and La). Studies on monodoped thin films and multilayershave shown that the carefully designed interfaces lead to increasing relative permittivity of BTO thin films,contradicting the common belief that interfaces behave like dead layers. The use of different techniques suchas Electron Paramagnetic Resonance (EPR), dielectric impedance and in particular X-ray Photoelectron Spectroscopy (XPS) and Time-of-Fligh Secondary Ion Mass Spectroscopy (ToF-SIMS) have enabled us to relate the different physical and chemical aspects such as the Fermi level position and the defect chemistryat the interfaces of BTO multilayers. In addition, we have studied the particularities of the Fermi level position of Mn-doped layers. Charging phenomena or even surface photovoltage induce an artificial change in the Fermi level of the Mn-doped BTO when deposited on various substrates. Finally, we implemented a deposition technique using oxygen plasma which made it possible to lower the Fermi level position towards the valence band of Mn doped BTO.Les travaux ici présents portent sur l’étude des couches minces BaTiO3 (BTO) dopées et déposées par pulvérisation cathodique. Grâce à ses propriétés ferroélectriques et à sa forte permittivité diélectrique, leBTO est utilisé comme un condensateur accordable ou encore dans des mémoires non-volatiles (FeRAM). Néanmoins, ces propriétés sont fortement dégradées lors de sa déposition sous forme de couche mince àcause des effets extrinsèques d’interface. La stratégie adoptée dans cette étude pour améliorer ces propriétés diélectriques est de contrôler les défauts chargés à l’interface par des multicouches de couches minces de BTO dopé au Mn, Nb et La. Des études sur les couches mono dopées et les multicouches ont montré que les interfaces soigneusement conçues conduisent à augmenter la permittivité relative des couches minces de BTO, en contradiction avec la croyance commune selon laquelle les interfaces se comportent comme des couches mortes. L’utilisation des différentes techniques comme la Résonance Paramagnétique Électronique (RPE), l’impédance diélectrique et notamment la Spectrométrie de Photoélectrons X (XPS en anglais) et laSpectrométrie de Masse à Ions Secondaires à Temps de Vol (ToF-SIMS en anglais) nous a permis de relier les différents aspects physiques et chimiques comme le niveau de Fermi et la chimie de défauts aux interfaces des multicouches de BTO. De plus, nous avons étudié les particularités du niveau de Fermi des couches dopées au Mn. Des phénomènes de charge ou même du photovoltage de surface induisent un changement artificiel du niveau de Fermi du BTO dopé Mn déposé sur différents substrats. Enfin, nous avons mis en place une technique de dépôt à l’aide du plasma d’oxygène qui a permis de baisser le niveau de Fermi vers la bande de valence du BTO dopé Mn

Fermi level engineering for large permittivity in BaTiO3-based multilayers

Multilayered doped BaTiO3 thin films have been fabricated by physical vapor deposition (PVD) on low-cost polycrystalline substrates with the aim to improve dielectric properties by controlling point charge defects at the interfaces. We show that carefully designed interfaces lead to increasing the relative permittivity of the BaTiO3 thin films, in contradiction with the common belief that interfaces behave as dead layers. High relative permittivity up to 1030 and tanδ = 4% at 100 kHz and room temperature were obtained on BaTiO3 multilayered films deposited on Si/Pt substrates by PVD. The large permittivity is suspected to be an extrinsic contribution due to band bending at the interfaces, as inferred by in-situ X-ray photoelectron spectroscopy. A 20-nm depletion layer was found to be associated with an interdiffusion of dopants, as measured by depth profiling with time-of-flight secondary ion mass spectrometry. The films exhibit high permittivity and low dielectric losses stable between 200 and 400 K, which meet the requirement of electronic application

Simple synthesis and characterization of vertically aligned Ba0.7Sr0.3TiO3 –CoFe2O4 multiferroic nanocomposites from CoFe2 nanopillar arrays

A new strategy to elaborate (1-3) type multiferroic nanocomposites with controlled dimensions and vertical alignment is presented. The process involves a supported nanoporous alumina layer as a template for growth of free-standing and vertically aligned CoFe2 nanopillars using a room temperature pulsed electrodeposition process. Ba0.70Sr0.30TiO3–CoFe2O4 multiferroic nanocomposites were grown through direct deposition of Ba0.7Sr0.3TiO3 films by radio-frequency sputtering on the top surface of the pillar structure, with in situ simultaneous oxidation of CoFe2 nanopillars. The vertically aligned multiferroic nanocomposites were characterized using various techniques for their structural and physical properties. The large interfacial area between the ferrimagnetic and ferroelectric phases leads to a magnetoelectric voltage coefficient as large as ~320 mV cm−1 Oe−1 at room temperature, reaching the highest values reported so far for vertically architectured nanocomposite systems. This simple method has great potential for large-scale synthesis of many other hybrid vertically aligned multiferroic heterostructures

Evolution over Time of Ventilatory Management and Outcome of Patients with Neurologic Disease∗

OBJECTIVES: To describe the changes in ventilator management over time in patients with neurologic disease at ICU admission and to estimate factors associated with 28-day hospital mortality. DESIGN: Secondary analysis of three prospective, observational, multicenter studies. SETTING: Cohort studies conducted in 2004, 2010, and 2016. PATIENTS: Adult patients who received mechanical ventilation for more than 12 hours. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Among the 20,929 patients enrolled, we included 4,152 (20%) mechanically ventilated patients due to different neurologic diseases. Hemorrhagic stroke and brain trauma were the most common pathologies associated with the need for mechanical ventilation. Although volume-cycled ventilation remained the preferred ventilation mode, there was a significant (p < 0.001) increment in the use of pressure support ventilation. The proportion of patients receiving a protective lung ventilation strategy was increased over time: 47% in 2004, 63% in 2010, and 65% in 2016 (p < 0.001), as well as the duration of protective ventilation strategies: 406 days per 1,000 mechanical ventilation days in 2004, 523 days per 1,000 mechanical ventilation days in 2010, and 585 days per 1,000 mechanical ventilation days in 2016 (p < 0.001). There were no differences in the length of stay in the ICU, mortality in the ICU, and mortality in hospital from 2004 to 2016. Independent risk factors for 28-day mortality were age greater than 75 years, Simplified Acute Physiology Score II greater than 50, the occurrence of organ dysfunction within first 48 hours after brain injury, and specific neurologic diseases such as hemorrhagic stroke, ischemic stroke, and brain trauma. CONCLUSIONS: More lung-protective ventilatory strategies have been implemented over years in neurologic patients with no effect on pulmonary complications or on survival. We found several prognostic factors on mortality such as advanced age, the severity of the disease, organ dysfunctions, and the etiology of neurologic disease