Seminars and Events
Nanostructures, Surfaces, and Coatings and Molecular Astrophysics
Coordinator: Rául Gago
14 December 2018, 12:00 h. Sala de Seminarios, 182
Exploiting Graphene to stabilize Chromium compounds on Ni(111): from Cr carbide intercalation to high-quality ultrathin Cr oxide overlayers
Dipartimento di Fisica, Politecnico di Milano, Italy
During the last decade, graphene has been stabilized on many single crystal metallic substrates. For several transition metals, the hybridization between the d bands and the graphene π states strongly modifies the electronic structure of the latter. The intercalation of ultrathin layers at the graphene/metal interface is a possible strategy to influence such an hybridization. Metallic films have successfully been intercalated between graphene and the substrate in several cases. Conversely, the intercalation of compounds such as oxides, carbides or nitrates, is more challenging.
The presentation will be divided in two parts. In the first one, I show that it is possible to grow an ultra-thin Cr carbide film between graphene and Ni(111), by expoliting the segregation of C atoms from the bulk of the Ni substrate and the intercalation of evaporated metallic Cr at the same time.
In the second one, I will discuss how a reactive deposition of Cr in a oxygen atmosphere on the graphene/Ni(111) system leads instead to an ordered and layer-by-layer growth of a Cr2O3 ultrathin overlayer. Graphene, in this case, works as an ideal buffer layer for the growth of high-quality ultrathin oxide layers on a reactive metallic substrate, without oxidation/reduction reactions at the interface.
20 November 2018, 12:00 h. Sala de Seminarios, 182
Viscoelasticity of cells – implications for adhesion and motility
Institute of Physical Chemistry, University of Göttingen, Germany
A thin layer of cross-linked actin filaments located underneath the plasma membrane in eukaryotic cells drives pivotal aspects of cell mechanics and has far-reaching implications also for other biological processes. Myosin-driven contractility and actin-cytoskeleton membrane interactions are responsible for fundamental cellular processes such as cytokinesis, cell migration, cortical flows, and also contributes to the response to external deformation. How the interplay between the actin cytoskeleton, the membrane, and actin binding proteins drives these processes is far from being understood. To unravel general principles underlying actin cortex properties, a bottom-up in vitro system has been developed and compared with apical cell membranes derived from living cells.
By means of AFM indentation experiments and 2D microrheology employing video particle tracking we could show that essential features could be reproduced, while it is seemingly difficult to mimic the energy dissipation in real living systems upon deformation. We speculate that an intricate interplay between motor activity and dynamic cross-linking together with the presence of membrane reservoirs that buffer the tension in the cell membrane is responsible for this deviation between model systems and living cells.
Eventually, a continuum model based on tension stored in the cell membrane permits also to explain the critical force in adhesion and the prerequisite for cellular motility in Dictyostelium discoideum.
05 October 2018, 11:00 h. Sala de Seminarios, 182
Tracking a cell’s mass in real time: a new indicator of cell physiology
Eidgenössische Technische Hochschule (ETH) Zurich, Switzerland
Regulation of cell volume and mass is physiologically important for living organisms and dysregulation of these parameters is at the origin of many different diseases. Cell mass mainly comprises intracellular water, proteins, lipids, carbohydrates and nucleic acids and is tightly liked to metabolism, proliferation and gene expression. However, the mechanisms that regulate cell mass remain largely unknown.
Flow cytometers and Coulter devices are among the most commonly used technologies to characterize the volume of suspended cells. However, most mammalian cells are adherent and behave considerably different in the suspended and adherent state. Therefore, one should be able to determine the volume and/or mass in the adherent state. Over the recent years powerful technologies have emerged to track the mass of single suspended and adherent cells. However, it has not been possible to track individual adherent cells in physiological conditions at the mass and time resolution required to observe fast cellular dynamics.
I will introduce a picobalance that we have developed, which is based on an optically excited microresonator. It measures the mass of single or multiple adherent cells in culture conditions over days at millisecond time resolution and picogram (0.1% of cell mass) mass sensitivity. I will also present some results we have obtained using this technology, including the detection of fast and subtle mass fluctuations that seem to be universal to living mammalian cells. Our approach is easy to operate and compatible with state-of-the-art optical microscopies, therefore we anticipate it will contribute to the understanding of cell mass regulation.
24 September 2018, 12:00 h. Salón de Actos
Topological defect engineering in ferroelectrics: from domain wall memory to emergent functionalities
Prof. Nagarajan VALANOOR
School of Materials Science & Engineering, University of New South Wales (UNSW)
The word ‘defect’ conjures up images of classical point and line defects to a typical materials scientist. However a concept that is even more pervasive is the phenomenon of a topological defect. Particularly in ferroic materials topological defects are inherent. Due to degeneracy in possible orientations of the order parameter upon cooling below the ferroic phase transition temperature, ferroic phases tend towards the formation of discrete domain structures. Adjacent domains are separated by naturally occurring planar topological defects called domain walls.
The first part of talk will focus on “ferroelectric domain wall memory device”, an emerging technology in which the wall through its conductivity (rather than the domain) stores information. We demonstrated1 recently a prototype non-volatile ferroelectric domain wall memory, scalable to below 100 nm, which exhibits relatively high OFF-ON ratios (~103) with excellent endurance and retention. Our work thus constitutes an important step toward integrated nanoscale ferroelectric domain wall memory devices.
In the second part, nanoscale bubble domains in ultrathin ferroelectric films will be introduced. We detected this singular type of ferroelectric domains in ultrathin epitaxial PZT/SrTiO3/PZT sandwich structures by piezoresponse force microscopy and aberration-corrected TEM. The dimensions, polar topology and structure of these domains are disclosed.
These two examples highlight the richness of polar topologies that may develop in ultrathin ferroelectric structures and bring forward the prospect of emergent electronic functionalities due to topological transitions.
02 February 2018, 12:00 h. Sala de Seminarios, 182
Alta-Integración en la Red Eléctrica de las Energías Renovables Intermitentes (eólica, solar-FV y solar CSP)
José Manuel Martínez-Duart
Presidente del GE-Energía de la RSEF, Senador de la E-MRS
En Europa el sector industrial que produce un mayor porcentaje de emisiones de CO2 es el sector de generación de electricidad con cerca del 25% del total. La hoja de ruta para el año 2050 de la Unión Europea (UE) tiene como objetivo que dicha proporción se acerque a cero. Para ello se propone la instalación de un gran porcentaje de solar (FV y CSP) y de eólica que representen entre ellas, en el caso de España, hasta un 70% de la demanda anual total. Debido a la variabilidad e intermitencia características de este tipo de renovables (VRES) implicaría que en ciertos períodos podría sobrar electricidad mientras que en otros faltaría. Aunque esto se podría solucionar, respectivamente, con técnicas de almacenamiento de electricidad (storage) y con plantas de generación de respaldo (backup), sin embargo, las técnicas de almacenamiento son todavía muy caras y las de respaldo necesitan utilizar combustibles fósiles por lo que ambas deben minimizarse. En esta presentación se expone un método de Optimización por Programación Lineal que da la mejor proporción de VRES, que simultáneamente minimiza los surpluses y los respaldos. A partir de estos resultados se proponen algunas recomendaciones sobre varios aspectos de la hoja de ruta de la futura transición energética en España.
16 January 2018, 12:00 h. Sala de Seminarios, 182
Characterization of organic self-assembled monolayers using bimodal
Atomic Force Microscopy
École Polytechnique Fédérale de Lausanne, Switzerland
Self-assembled monolayers (SAMs) are one of the most attractive methods of surface modification, as they are highly versatile and their manufacturing approach is easy to scale up. One of their key features is molecular ordering, which, however, is difficult to determine experimentally.
Bimodal AFM was used as a novel approach for the characterization of SAMs’ ordering, via its correlation to surface elasticity.
Alkanethiol SAMs on Au (111) were used as a model system. Surface elasticity has been reliably determined and found to be ligand-length dependent. A similar investigation has been extended to the characterization of octadecylphosphonic acid SAMs on Al2O3. Monolayer formation and ordering as a function of formation time were determined via surface elasticity.
The characterization method was then extended to provide localization of the chemical
species present in thiolated binary SAMs. Within the systems tested phase separation down to ~10 nm domains could be observed both in the topography and in the elasticity channel, allowing, for the first time, the chemical identification of the domains.