Search

Your search keyword '"Erni, Rolf"' showing total 716 results
Start Over Author "Erni, Rolf"
716 results on '"Erni, Rolf"'

204. Highly Mismatched, Dislocation-Free SiGe/Si Heterostructures

Author

Isa, Fabio, primary, Salvalaglio, Marco, additional, Dasilva, Yadira Arroyo Rojas, additional, Meduňa, Mojmír, additional, Barget, Michael, additional, Jung, Arik, additional, Kreiliger, Thomas, additional, Isella, Giovanni, additional, Erni, Rolf, additional, Pezzoli, Fabio, additional, Bonera, Emiliano, additional, Niedermann, Philippe, additional, Gröning, Pierangelo, additional, Montalenti, Francesco, additional, and von Känel, Hans, additional

Published
2015
Full Text
View/download PDF

206. Periodic Giant Polarization Gradients in Doped BiFeO3 Thin Films.

Author

Campanini, Marco, Erni, Rolf, Chan-Ho Yang, Ramesh, Ramamoorthy, and Rossell, Marta D.

Subjects
*POLARIZATION (Electricity), *THIN films, *ELECTRIC properties of multiferroic materials, *DOPING agents (Chemistry), *MAGNETIC properties
Abstract

The ultimate challenge for the development of new multiferroics with enhanced properties lies in achieving nanoscale control of the coupling between different ordering parameters. In oxide-based multiferroics, substitutional cation dopants offer the unparalleled possibility to modify both the electric and magnetic properties at a local scale. Herein it is demonstrated the formation of a dopant-controlled polar pattern in BiFeO3 leading to the spontaneous instauration of periodic polarization waves. In particular, nonpolar Ca-doped rich regions act as spacers between consecutive dopant-depleted regions displaying coupled ferroelectric states. This alternation of layers with different ferroelectric state creates a novel vertical polar structure exhibiting giant polarization gradients as large as 70 µC cm-2 across 30 Å thick domains. The drastic change in the polar state of the film is visualized using high-resolution differential phase-contrast imaging able to map changes in ferroelectric polarization at atomic scale. Furthermore, a periodic distortion in the Fe--O--Fe bonding angle suggests a local variation in the magnetic ordering. The findings provide a new insight into the role of doping and reveal hitherto unexplored means to tailor the functional properties of multiferroics by doping engineering. [ABSTRACT FROM AUTHOR]

Published
2018
Full Text
View/download PDF

208. Template-Assisted in SituSynthesis of Ag@Au Bimetallic Nanostructures Employing Liquid-Phase Transmission Electron Microscopy

Author

Ahmad, Nabeel, Bon, Marta, Passerone, Daniele, and Erni, Rolf

Abstract

Noble metal nanostructure synthesis viaseed-mediated route is a widely adopted strategy for a plethora of nanocrystal systems. Ag@Au core–shell nanostructures are radiolytically grown in real-time using in situliquid-cell (scanning) transmission electron microscopy. Here we employ a capping agent, dimethyl-amine (DMA) and a coordinating complex, potassium iodide (KI) in an organic solvent (methanol) in order to (1) slow down the reaction kinetics to observe mechanistic insights into the overgrowth process and (2) shift the growth regime from galvanic-replacement mode to direct synthesis mode resulting in the conventional synthesis of Ag@Au core–shell structures. A theoretical approach based on classical simulations complements our experiments, providing further insight on the growth modes. In particular, we focus on the shape evolution and chemical ordering, as currently there is an insufficient understanding regarding mixed composition phases at interfaces of alloys even with well-known miscibilities. Furthermore, the comparison of theoretical and experimental data reveals that the final morphology of these nanoalloys is not simply a function of crystallinity of the underlying seed structure but instead is readily modified by extrinsic parameters such as additives, capping agent, and modulation of surface energies of exposed crystal surfaces by the encapsulating solvent. The impact of these additional parameters is systematically investigated using an empirical approach in light of ab initiosimulations.

Published
2019
Full Text
View/download PDF

209. ALD-ZnxTiyO as Window Layer in Cu(In,Ga)Se2Solar Cells

Author

Löckinger, Johannes, Nishiwaki, Shiro, Andres, Christian, Erni, Rolf, Rossell, Marta D., Romanyuk, Yaroslav E., Buecheler, Stephan, and Tiwari, Ayodhya N.

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.

Published
2018
Full Text
View/download PDF

210. Off-axis and in-line electron holography studies on CuInGaSe2

Author

Keller Debora, Buecheler Stephan, Reinhard Patrick, Pianezzi Fabian, Snoeck Etienne, Gatel Christophe, Rossell Marta D., Erni Rolf, and Tiwari Ayodhya N.

Abstract

Electron holography is employed to study variations of the electrostatic crystal potential in Cu(InGa)Se2 (CIGS) thin film solar cells at different length scales: Long range potential variations across the layer structure of the solar cell as well as inhomogeneities within the layers are analyzed by off axis holography. In line holography is applied to examine the local potential variation across a CIGS grain boundary. The phase reconstruction from a focal series is performed by a modified transport of intensity equation (TIE) which is optimized to reduce common artifacts. For comparison three different microscopes of different optical configurations were used for in line holography. Based on the results the impact of the used microscope as well as further acquisition parameters on the in line holography measurement is assessed. The measured potential variations are discussed considering the effect of different possible sources that may cause potential fluctuations. It is found that most of the variations are best explained by mean inner potential fluctuations rather than by inhomogeneities of the electronic properties. Finally the present resolution limit of both methods is discussed regarding the feasibility of future electronic characterization of CIGS by holography.

Published
2016

212. Integration of GaN Crystals on Micropatterned Si(0 0 1) Substrates by Plasma-Assisted Molecular Beam Epitaxy

Author

Isa, Fabio, primary, Chèze, Caroline, additional, Siekacz, Marcin, additional, Hauswald, Christian, additional, Lähnemann, Jonas, additional, Fernández-Garrido, Sergio, additional, Kreiliger, Thomas, additional, Ramsteiner, Manfred, additional, Dasilva, Yadira Arroyo Rojas, additional, Brandt, Oliver, additional, Isella, Giovanni, additional, Erni, Rolf, additional, Calarco, Raffaella, additional, Riechert, Henning, additional, and Miglio, Leo, additional

Published
2015
Full Text
View/download PDF

227. Local indium segregation and band structure in high efficiency green light emitting InGaN/GaN diodes

Author

Jinschek, Joerg R., Erni, Rolf, Gardner, Nathan F., Kim, Andrew Y., and Kisielowski, Christian

Subjects
InGaN Electron Microscopy LED, Materials Sciences
Abstract

GaN/InGaN light emitting diodes (LEDs) are commercialized for lighting applications because of the cost efficient way that they produce light of high brightness1,2. Nevertheless, there is significant room for improving their external emission efficiency3 from typical values below 10 percent4 to more than 50 percent5, which are obtainable by use of other materials systems that, however, do not cover the visible spectrum. In particular, green-light emitting diodes fall short in this respect1-3, which is troublesome since the human eye is most sensitive in this spectral range. In this letter advanced electron microscopy is used to characterize indium segregation in InGaN quantum wells of high-brightness, green LEDs (with external quantum efficiency as high as 15 percent at 75 A/cm2). Our investigations reveal the presence of 1-3 nm wide indium rich clusters in these devices with indium concentrations as large as 0.30-0.40 that narrow the band gap locally to energies as small as 2.65 eV.

Published
2004

230. Monodisperse Colloidal Gallium Nanoparticles: Synthesis, Low Temperature Crystallization, Surface Plasmon Resonance and Li-Ion Storage

Author

Yarema, Maksym, primary, Wörle, Michael, additional, Rossell, Marta D., additional, Erni, Rolf, additional, Caputo, Riccarda, additional, Protesescu, Loredana, additional, Kravchyk, Kostiantyn V., additional, Dirin, Dmitry N., additional, Lienau, Karla, additional, von Rohr, Fabian, additional, Schilling, Andreas, additional, Nachtegaal, Maarten, additional, and Kovalenko, Maksym V., additional

Published
2014
Full Text
View/download PDF

239. A general approach to fabricate fe3O4 nanoparticles decorated with Pd, Au, and Rh: Magnetically recoverable and reusable catalysts for Suzuki C-C cross-coupling reactions, hydrogenation, and sequential reactions

Author

Universitat Politècnica de Catalunya. Institut de Tècniques Energètiques, Universitat Politècnica de Catalunya. GREENER - Grup de recerca d'estudis energètics i de les radiacions, Gonzàlez de Rivera, Ferran, Angurell Purroy, Inmaculada, Rossell Abrodos, Marta-Dacil, Erni, Rolf P., Llorca Piqué, Jordi, Jiménez Divins, Nuria, Müller Jevenois, Guillermo, Seco García, Miquel Angel, Rossell Alfonso, Josep Oriol, Universitat Politècnica de Catalunya. Institut de Tècniques Energètiques, Universitat Politècnica de Catalunya. GREENER - Grup de recerca d'estudis energètics i de les radiacions, Gonzàlez de Rivera, Ferran, Angurell Purroy, Inmaculada, Rossell Abrodos, Marta-Dacil, Erni, Rolf P., Llorca Piqué, Jordi, Jiménez Divins, Nuria, Müller Jevenois, Guillermo, Seco García, Miquel Angel, and Rossell Alfonso, Josep Oriol

Abstract

A facile strategy has been explored for loading noble metals onto the surface of ferrite nanoparticles with the assistance of phosphine-functionalized linkers. Palladium loading is shown to occur with participation of both the phosphine function and the surface hydroxyl groups. Hybrid nanoparticles containing simultaneously Pd and Au (or Rh) are obtained by successive loading of metals. Similarly, ferrite nanoparticles decorated with Pd, Au, and Rh have also been formed by using the same strategy. The catalytic properties of the new nanoparticles are evidenced in processes such as reduction of 4-nitrophenol or hydrogenation of styrene. Besides, the sequential process involving a cross-coupling reaction followed by reduction of 1-nitrobiphenyl has been successfully achieved by employing Pd/Au decorated nanoferrite particles. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., Postprint (published version)

Published
2013

240. Potassium-induced surface modification of Cu(In,Ga)Se2 thin films for high-efficiency solar cells

Author

Chirilă, Adrian, primary, Reinhard, Patrick, additional, Pianezzi, Fabian, additional, Bloesch, Patrick, additional, Uhl, Alexander R., additional, Fella, Carolin, additional, Kranz, Lukas, additional, Keller, Debora, additional, Gretener, Christina, additional, Hagendorfer, Harald, additional, Jaeger, Dominik, additional, Erni, Rolf, additional, Nishiwaki, Shiro, additional, Buecheler, Stephan, additional, and Tiwari, Ayodhya N., additional

Published
2013
Full Text
View/download PDF

242. A General Approach To Fabricate Fe3O4 Nanoparticles Decorated with Pd, Au, and Rh: Magnetically Recoverable and Reusable Catalysts for Suzuki CC Cross‐Coupling Reactions, Hydrogenation, and Sequential Reactions

Author

Gonzàlez de Rivera, Ferran, primary, Angurell, Inmaculada, additional, Rossell, Marta D., additional, Erni, Rolf, additional, Llorca, Jordi, additional, Divins, Núria J., additional, Muller, Guillermo, additional, Seco, Miquel, additional, and Rossell, Oriol, additional

Published
2013
Full Text
View/download PDF

249. Sorption enhanced CO2 methanation

Author

Borgschulte, Andreas, primary, Gallandat, Noris, additional, Probst, Benjamin, additional, Suter, Riccardo, additional, Callini, Elsa, additional, Ferri, Davide, additional, Arroyo, Yadira, additional, Erni, Rolf, additional, Geerlings, Hans, additional, and Züttel, Andreas, additional

Published
2013
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results