6 results on '"Marta D. Rossell"'
Search Results
2. Epitaxial Thin Films as a Model System for Li-Ion Conductivity in Li4Ti5O12
- Author
-
Michael Stiefel, Antonia Neels, Reto Pfenninger, Jordi Sastre-Pellicer, Arndt Remhof, Eduardo Cuervo Reyes, Marta D. Rossell, Max Döbeli, Jennifer L. M. Rupp, Corsin Battaglia, Rolf Erni, Evelyn Stilp, Zoltán Balogh-Michels, and Francesco Pagani
- Subjects
Materials science ,Analytical chemistry ,02 engineering and technology ,Atmospheric temperature range ,Conductivity ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Pulsed laser deposition ,Elastic recoil detection ,Transmission electron microscopy ,Ionic conductivity ,General Materials Science ,Crystallite ,Thin film ,0210 nano-technology - Abstract
Using an epitaxial thin-film model system deposited by pulsed laser deposition (PLD), we study the Li-ion conductivity in Li4Ti5O12, a common anode material for Li-ion batteries. Epitaxy, phase purity, and film composition across the film thickness are verified employing out-of-plane and in-plane X-ray diffraction, transmission electron microscopy, time-of-flight mass spectrometry, and elastic recoil detection analysis. We find that epitaxial Li4Ti5O12 behaves like an ideal ionic conductor that is well described by a parallel RC equivalent circuit, with an ionic conductivity of 2.5 × 10–5 S/cm at 230 °C and an activation energy of 0.79 eV in the measured temperature range of 205 to 350 °C. Differently, in a co-deposited polycrystalline Li4Ti5O12 thin film with an average in-plane grain size of
- Published
- 2018
3. Growth Assisted by Glancing Angle Deposition: A New Technique to Fabricate Highly Porous Anisotropic Thin Films
- Author
-
Marta D. Rossell, Rémi Longtin, Pierangelo Gröning, and Juan R. Sanchez-Valencia
- Subjects
010302 applied physics ,Glancing angle deposition ,GLAD ,Materials science ,Nanotechnology ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,Porous thin films ,0103 physical sciences ,Highly porous ,Perpendicular ,Anisotropy ,General Materials Science ,Hybrid materials ,Thin film ,Composite material ,0210 nano-technology ,Hybrid material ,GAGLAD - Abstract
We report a new methodology based on glancing angle deposition (GLAD) of an organic molecule in combination with perpendicular growth of a second inorganic material. The resulting thin films retain a very well-defined tilted columnar microstructure characteristic of GLAD with the inorganic material embedded inside the columns. We refer to this new methodology as growth assisted by glancing angle deposition or GAGLAD, since the material of interest (here, the inorganic) grows in the form of tilted columns, though it is deposited under a nonglancing configuration. As a >proof of concept>, we have used silver and zinc oxide as the perpendicularly deposited material since they usually form ill-defined columnar microstructures at room temperature by GLAD. By means of our GAGLAD methodology, the typical tilted columnar microstructure can be developed for materials that otherwise do not form ordered structures under conventional GLAD. This simple methodology broadens significantly the range of materials where control of the microstructure can be achieved by tuning the geometrical deposition parameters. The two examples presented here, Ag/Alq3 and ZnO/Alq3, have been deposited by physical vapor deposition (PVD) and plasma enhanced chemical vapor deposition (PECVD), respectively: two different vacuum techniques that illustrate the generality of the proposed technique. The two type of hybrid samples present very interesting properties that demonstrate the potentiality of GAGLAD. On one hand, the Ag/Alq3 samples present highly optical anisotropic properties when they are analyzed with linearly polarized light. To our knowledge, these Ag/Alq3 samples present the highest angular selectivity reported in the visible range. On the other hand, ZnO/Alq3 samples are used to develop highly porous ZnO thin films by using Alq3 as sacrificial material. In this way, antireflective ZnO samples with very low refractive index and extinction coefficient have been obtained.
- Published
- 2016
4. Origin of the Critical Thickness in Improper Ferroelectric Thin Films
- Author
-
Alexander Vogel, Alicia Ruiz Caridad, Johanna Nordlander, Martin F. Sarott, Quintin N. Meier, Rolf Erni, Nicola A. Spaldin, Morgan Trassin, and Marta D. Rossell
- Subjects
Critical thickness ,Oxygen vacancies ,Interfaces ,Improper ferroelectricity ,General Materials Science ,Electron energy loss spectroscopy ,YMnO3 ,Transmission electron microscopy - Abstract
Improper ferroelectrics are expected to be more robust than conventional ferroelectrics against depolarizing field effects and to exhibit a much-desired absence of critical thickness. Recent studies, however, revealed the loss of ferroelectric response in epitaxial improper ferroelectric thin films. Here, we investigate improper ferroelectric hexagonal YMnO3 thin films and find that the polarization suppression, and hence functionality, in the thinner films is due to oxygen off-stoichiometry. We demonstrate that oxygen vacancies form on the film surfaces to provide the necessary charge to screen the large internal electric field resulting from the positively charged YMnO3 surface layers. Additionally, we show that by modifying the oxygen concentration of the films, the phase transition temperatures can be substantially tuned. We anticipate that our findings are also valid for other ferroelectric oxide films and emphasize the importance of controlling the oxygen content and cation oxidation states in ferroelectrics for their successful integration in nanoscale applications., ACS Applied Materials & Interfaces, 15 (14), ISSN:1944-8244, ISSN:1944-8252
- Full Text
- View/download PDF
5. Dopant-Induced Modifications of Ga x In (1– x ) P Nanowire-Based p–n Junctions Monolithically Integrated on Si(111)
- Author
-
Heike Riel, Marta D. Rossell, Heinz Schmid, Rolf Erni, Luca Francaviglia, Anna Fontcuberta i Morral, Nicolas Bologna, Vasileios Theofylaktopoulos, Kirsten E. Moselund, Marco Campanini, and Stephan Wirths
- Subjects
010302 applied physics ,Materials science ,Silicon ,Dopant ,business.industry ,Doping ,Nanowire ,chemistry.chemical_element ,Heterojunction ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Epitaxy ,7. Clean energy ,01 natural sciences ,law.invention ,Semiconductor ,chemistry ,law ,0103 physical sciences ,Solar cell ,Optoelectronics ,General Materials Science ,0210 nano-technology ,business - Abstract
Today, silicon is the most used material in photovoltaics, with the maximum conversion efficiency getting very close to the Shockley–Queisser limit for single-junction devices. Integrating silicon with higher band-gap ternary III–V absorbers is the path to increase the conversion efficiency. Here, we report on the first monolithic integration of GaxIn(1–x)P vertical nanowires, and the associated p–n junctions, on silicon by the Au-free template-assisted selective epitaxy (TASE) method. We demonstrate that TASE allows for a high chemical homogeneity of ternary alloys through the nanowires. We then show the influence of doping on the chemical composition and crystal phase, the latter previously attributed to the role of the contact angle in the liquid phase in the vapor–liquid–solid technique. Finally, the emission of the p–n junction is investigated, revealing a shift in the energy of the intraband levels due to the incorporation of dopants. These results clarify some open questions on the effects of dopin...
- Full Text
- View/download PDF
6. ALD-Zn x Ti y O as Window Layer in Cu(In,Ga)Se 2 Solar Cells
- Author
-
Shiro Nishiwaki, Johannes Löckinger, Christian Andres, Ayodhya N. Tiwari, Stephan Buecheler, Rolf Erni, Marta D. Rossell, and Yaroslav E. Romanyuk
- Subjects
Materials science ,Band gap ,02 engineering and technology ,01 natural sciences ,7. Clean energy ,Atomic layer deposition ,Sputtering ,0103 physical sciences ,zinc titanium oxide ,General Materials Science ,Thin film ,Absorption (electromagnetic radiation) ,010302 applied physics ,Photocurrent ,business.industry ,buffer/window layer ,CIGS ,021001 nanoscience & nanotechnology ,Copper indium gallium selenide solar cells ,Cu(InGa)Se2 solar cell ,ALD ,Optoelectronics ,0210 nano-technology ,business ,Layer (electronics) ,Research Article - Abstract
We report on the application of ZnxTiyO deposited by atomic layer deposition (ALD) as buffer layer in thin film Cu(In,Ga)Se2 (CIGS) solar cells to improve the photovoltaic device performance. State-of-the-art CIGS devices employ a CdS/ZnO layer stack sandwiched between the absorber layer and the front contact. Replacing the sputter deposited ZnO with ALD-ZnxTiyO allowed a reduction of the CdS layer thickness without adversely affecting open-circuit voltage (VOC). This leads to an increased photocurrent density with a device efficiency of up to 20.8% by minimizing the parasitic absorption losses commonly observed for CdS. ALD was chosen as method to deposit homogeneous layers of ZnxTiyO with varying Ti content with a [Ti]/([Ti] + [Zn]) atomic fraction up to ∼0.35 at a relatively low temperature of 373 K. The Ti content influenced the absorption behavior of the ZnxTiyO layer by increasing the optical bandgap >3.5 eV in the investigated range. Temperature-dependent current–voltage (I–V) measurements of solar cells were performed to investigate the photocurrent blocking behavior observed for high Ti content. Possible conduction band discontinuities introduced by ZnxTiyO are discussed based on X-ray photoelectron spectroscopy (XPS) measurements.
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.