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Il Tempo della Scienza

Seminari tecnici 2017

Sala Conferenze (Edificio M)
Strada delle Cacce 91, Torino

Data Relatore Titolo
14 marzo
ore 15
Alexander Weber-Bargioni
Molecular Foundry,
Lawrence Berkeley National Laboratory

The Blessing and Curse of Surface Defects in Novel Semiconductors

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Visualizing and understanding electronic and opto-electronic processes at their native length scale in hybrid or quantum confined material systems will enable unprecedented control over material functionality. This insight is specifically critical to identify the precise photo physical processes and loss mechanisms in light harvesting materials or to identify emerging functionality in quantum confined materials.
In the first part of my seminar I will report what we found when visualizing local opto-electronic processes critical for power conversion efficiency in lead halide perovskites. Photovoltaic devices based on hybrid perovskite materials have exceeded 22% efficiency within only 5 years of research and are assumed to operate homogeneous throughout the material. We visualized the photo­-current and photo voltage generation with 10 nm spatial resolution using photo current microscopy and find surprisingly an enormous inter and intra-grain heterogeneity. Moreover, we identify individual grains that carry in them the secret how to operate perovskite PV materials close to the theoretical limit.
In the second part I show how defects can evoke surprising functionality in 2-D semiconductors. 2-­D MoSe2 is a quantum confined transition metal dichalcogenide (TMD) with fascinating optical and electronic properties due to the confinement in z. Using Near Field Optical Microscopy, photo Scanning Tunneling Microscopy and non contact atomic force microscopy we set out to visualize and correlate in 2-D MoSe2 the morphology and electronic properties of defects with atomic resolution. We find how defects create spatially bound excitons to a charged defect site forming trions, how individual Se vacancies form atomically confined Type 1 hetero junctions for excitons, how one-atom wide 1-D defects create charge density waves in the midst of a direct band gap semiconductor, and how these 1-D defects, when laterally confined, allow charge density waves and particle in a box-­like states to coexist, forming soliton-like quasi particles.
In the last part of the seminar I will provide an outlook into a proposal for a new Center for Advanced Materials Exploration. We are at the brink of a new era for material science and solid state physics, where we discover new functionalities in hybrid materials, explore emerging quantum phenomena in low dimensional material systems, or assemble nanoscale building blocks into ever more complex architected materials. While offering extraordinary opportunities, this presents a significant challenge: virtually infinite possibilities to create novel materials. Driving the development of these new classes of materials is the ability to explore efficiently, potentially interesting parameter spaces. I propose to combine 21st century advancements in robotics, intelligent algorithms, and informatics, to automate state of the art synthesis, characterization and prediction techniques. I will discuss the basic motivation and possibilities of such a center, current developments towards this approach to exploration as well as the challenges that need to be overcome to create such an institute.

27 febbraio
ore 16:30
Matteo Galli
Università di Pavia, Dipartimento di Fisica
Photonics and Nanostructures Group

Enhancing the optical functionalities of silicon with photonic nanostructures

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Silicon has long been established as the material of choice for the microelectronics industry. This is not yet true in photonics, where the limited degrees of freedom in material design combined with the indirect bandgap are a major constraint. Recent developments, especially those enabled by nanoscale engineering of the photonic properties, are starting to change the picture, opening up new possibilities for the realization of Si-based photonic nanostructures with advanced optical functionalities. In this talk we will give an overview of the ongoing research in this active area. We will focus on resonant silicon nanostructures, in which the electromagnetic field may be confined to extremely small spatial regions, thus obtaining a dramatic improvement of both linear and nonlinear optical properties.

10 febbraio
ore 10:30
Marco Barbieri
Università degli Studi Roma Tre

Of fringes and fridges

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Information processing and thermodynamics share common methods and concepts, notably the one of entropy, and Landauer's principle has established how deep profound their link is. In this talk, we will discuss some experiments on which we seek to apply this philosophy to quantum photonic, by interpreting some quantum information tasks - entanglement detection, state discrimination, weak measurements - under the lens of thermodynamics.

26 gennaio
ore 14:30
Ed. 7
Gian Michele Ratto
Istituto di Nanoscienze del CNR e Scuola Normale Superiore di Pisa

A window with a view: two photon microscopy and the secret life of the brain

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Two photon microscopy has emerged as a powerful tool to image form and function in the brain in vivo: neurons and glia can be visualised by means of an ever expanding range of fluorescent probes and a wide variety of information can be collected in the intact brain. For example, transgenic mice expressing the Green Fluorescent Protein in selected neuronal population can be used to image the morphological development of neurons. Functional studies relies on genetically encoded or synthetic dyes to visualize cellular and network function with sub cellular resolution. At this time, two photon imaging is the only available tool that allows to peer into neuronal function in the intact brain at the cell population level. Indeed, intravital imaging has provided novel insights on brain structure and function with unprecedented temporal and spatial resolution. The availability of genetic and pharmacological models of brain pathologies, allow to investigate function and form in the normal and diseased cortex.

In this talk I will give an overview of what we can see in the brain when we put together two photon imaging with novel genetic sensor to image different aspects of brain cells.

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