Interband characterization and electronic transport control of nanoscaled GeTe/Sb2_2Te3_3 superlattices

The extraordinary electronic and optical properties of the crystal-to-amorphous transition in phase-change materials led to important developments in memory applications. A promising outlook is offered by nanoscaling such phase-change structures. Following this research line, we study the interband optical transmission spectra of nanoscaled GeTe/Sb$_2$Te$_3$ chalcogenide superlattice films. We determine, for films with varying stacking sequence and growth methods, the density and scattering time of the free electrons, and the characteristics of the valence-to-conduction transition. It is found that the free electron density decreases with increasing GeTe content, for sub-layer thickness below $\sim$3 nm. A simple band model analysis suggests that GeTe and Sb$_2$Te$_3$ layers mix, forming a standard GeSbTe alloy buffer layer. We show that it is possible to control the electronic transport properties of the films by properly choosing the deposition layer thickness and we derive a model for arbitrary film stacks

Casa della memoria

The House of Memory is a house, a collective house in which Milanese citizens hope to find protection for the memories they want to preserve. Nobody inhabits this house, and in this case the word house is understood as an envelope, a protected space, or a shelter that crystallizes memory within the flow of the metropolis. So the house becomes an object to be both protected and exhibited, a treasury to be surrounded with an envelope that both defends and exposes its content. Stefano Graziani’s photographs depict the construction of the building, while the texts by Howard Burns, Jean-Louis Cohen and Kersten Geers try to interpret its significance in the context of contemporary architecture. The book includes a complete set of drawings of the building. AUTHORS Howard Burns is a 1961 graduate of Ancient and Modern History from Cambridge University where he was a King’s College Fellow. He later taught art and architectural history at the Courtauld Institute in London and held the titles of Slade Professor of Fine Art at the University of Cambridge and Fellow at King’s College. He was the Robert C. and Marian K. Weinberg Professor of Architecture at Harvard University, Professor at the University IUAV in Venice, Visiting Professor at MIT and Senior Lecturer in the History of Architecture at Harvard University. Jean-Louis Cohen is Sheldon H. Solow Professor in the History of Architecture at the Institute of Fine Arts at New York University. From 1997 to 2003 he directed the Institut Français d’Architecture and the Musée des Monuments Français. He has been a curator for numerous exhibitions including The Lost Vanguard at the Museum of Modern Art in New York (2007) and Scenes of the World to Come and Architecture in Uniform at the Canadian Center for Architecture (1995 and 2011). In 2014, he was the curator of the French pavilion at the Venice Biennale of Architecture. Since 2014 he is a professor at the Collège de France. Kersten Geers is a founding partner of OFFICE KGDVS. He was professor at the University of Ghent, and visiting professor at Columbia University, NYC, and the Academy of Architecture in Mendrisio (CH), and is currently teaching at the EPFL, Lausanne (CH) and at the Harvard Graduate School of Design. Stefano Graziani is a photographer. He has worked and published di erent portfolios for Domus, A+U, Numero Press, Camera Austria, Log, Repubblica, Cross, FlashArt Italia, Abitare, Monopol Magazine, Marsilio. His work has been exhibited at Fondazione Ragghianti (2006), GC.AC Monfalcone (2006/2009), Festival della Filoso a, Modena (2006), Villa Manin Centro d’arte Contemporanea (2007), Manifesta 7, and at the XIII, XIV and XV Venice Biennale (2012, 2014, 2016)

Public Ambitions

Italy Under Construction Buildings, Landscapes, Positions in Contemporary Italian Architecture In a globalized yet fragmented world, how can architecture reevaluate its cultural and political role and enable practises of identification and belonging? What role does architecture occupy in shaping the relationship between regional cultures and international forces? Between the global hunger for the architectural icon and claims for the authenticity of regional craftsmanship, what is the architect’s agency within and against contemporary modes of architectural production? Italy Under Construction is a new programme of exhibitions and lectures on contemporary architecture in Italy. Presented by the Italian Cultural Institute in Toronto, the series investigates contemporary architectural practice and its interaction with culture, cities, and landscapes. The programme will bring together emerging and established voices from the architectural community, both from Italy and North America. With Toronto serving as a venue for transatlantic exchange, we hope to open a conversation on the relevance of new architecture in Italy within a broader discussion on architectural design challenges in a globalized world. Italy Under Construction will run for three years and host two exhibitions per year- the first will open in the fall of 2015 and the second in spring 2016. The fall series of exhibitions will focus on a pair of established architects, initiating a dialogue between different approaches to research, local context, and national processes. The spring exhibition is thematic in nature and will present new buildings from a selected group of architects organized around pressing contemporary issues such as the ambitions and opportunities of building public architecture, housing and urbanism, and the domestic landscapes of the private house

Infrared evidence of a Slater metal-insulator transition in NaOsO3

The magnetically driven metal-insulator transition (MIT) was predicted by Slater in the fifties. Here a long-range antiferromagnetic (AF) order can open up a gap at the Brillouin electronic band boundary regardless of the Coulomb repulsion magnitude. However, while many low-dimensional organic conductors display evidence for an AF driven MIT, in three-dimensional (3D) systems the Slater MIT still remains elusive. We employ terahertz and infrared spectroscopy to investigate the MIT in the NaOsO3 3D antiferromagnet. From the optical conductivity analysis we find evidence for a continuous opening of the energy gap, whose temperature dependence can be well described in terms of a second order phase transition. The comparison between the experimental Drude spectral weight and the one calculated through Local Density Approximation (LDA) shows that electronic correlations play a limited role in the MIT. All the experimental evidence demonstrates that NaOsO3 is the first known 3D Slater insulator.Comment: 4 figure

Intense terahertz pulses from SPARC-LAB coherent radiation source

The linac-based Terahertz source at the SPARC_LAB test facility is able to gene rate highly intense Terahertz broadband pulses via coherent transition radiation (CTR) from high brightness electron beams. The THz pulse duration is typically down to 100 fs RMS and can be tuned through the electron bunch duration and shaping. The measured stored energy in a single THz pulse has reached 40 μ J, which corresponds to a peak electric field of 1.6 MV/cm at the THz focus. Here we present the main features, in particular spatial and sp ectral distributions and energy characterizations of the SPARC_LAB THz source, which is very competitive for investigations in Condensed Matter, as well as a valid tool for electron beam longitudinal diagnostics

Transmittance and reflectance measurements at terahertz frequencies on a superconducting BaFe_{1.84}Co_{0.16}As_2 ultrathin film: an analysis of the optical gaps in the Co-doped BaFe_2As_2 pnictide

Here we report an optical investigation in the terahertz region of a 40 nm ultrathin BaFe$_{1.84}$Co$_{0.16}$As$_2$ superconducting film with superconducting transition temperature T$_c$ = 17.5 K. A detailed analysis of the combined reflectance and transmittance measurements showed that the optical properties of the superconducting system can be described in terms of a two-band, two-gap model. The zero temperature value of the large gap $\Delta_B$, which seems to follow a BCS-like behavior, results to be $\Delta_B$(0) = 17 cm$^{-1}$. For the small gap, for which $\Delta_A$(0) = 8 cm$^{-1}$, the temperature dependence cannot be clearly established. These gap values and those reported in the literature for the BaFe$_{2-x}$Co$_{x}$As$_2$ system by using infrared spectroscopy, when put together as a function of T$_c$, show a tendency to cluster along two main curves, providing a unified perspective of the measured optical gaps. Below a temperature around 20 K, the gap-sizes as a function of T$_c$ seem to have a BCS-like linear behavior, but with different slopes. Above this temperature, both gaps show different supra-linear behaviors

Design or Extinction

L’ultimo capitolo di Vers une architecture s’intitola Architecture ou Révolution. Per Le Corbusier, nel 1923, le cose sono chiare: c’è una possibile rivoluzione e una architettura che potrebbe evitarla. La narrazione è una, il processo è uno, e i suoi possibili sviluppi sono due: una ottusa resistenza che provocherà una catastrofe, oppure una consapevole adesione. È lo stesso paradigma che definisce la storia europea dal 1789 al 1989: la reazione allo spirito del tempo distingue progressisti e conservatori, chi abbraccia le trasformazioni della modernità contro chi tenta di resistervi. L’urgenza delle scelte è tutta basata sul tempo: qualcosa di nuovo s’a accia sulla scena, e a questa novità bisogna reagire. La soluzione corretta si riduce a una sola mossa, un solo progetto, sempre nettamente opposto a un’alternativa in tut- to contraria.The last chapter of “Vers une architecture” is titled “Architecture ou Révolution”. For Le Corbusier, in 1923, matters were clear : there was a possible revolution and an architecture that could avert it. There was one narration, one process, with two possible developments: an obtuse resist- ance that would cause a catastrophe, or a conscious acceptance. It was the same paradigm that defines European history from 1789 to 1989: the reaction to the spirit of the times distinguished progressives from conservatives, those who embraced the trans- formations of modernity, and those who attempted to resist them. The urgency of these choices was all based on time: something new that would appear on the scene, a novelty calling for a reaction. The correct solution boiled down to one move and one design only, always sharply opposed to a totally contrary alternative

The perspectives of Giuseppe Lombardo-Radice and of the idealist intellectuals on Maria Montessori

The Italian historiographical tradition on the reception of Maria Montessori has highlighted the widespread misunderstanding that she faced in Italy, often accompanied by prejudicial devaluation, if not by actual personal attacks. Within this critical panorama, stronger resistance was exhibited by Catholics and Neo-Kantians than by Idealists, and in particular Gentile and Lombardo-Radice showed deep appreciation for Montessori, offering her remarks that were rather interesting from a pedagogical standpoint – and are still to be considered thoroughly if we wish to approach her method critically. Furthermore, Lombardo-Radice also brought into the Italian debate a series of international criticisms that had the same tone and content as those addressed to her by the intellectuals involved in the new school movement, as evidenced by an analysis of the articles that Ferrière published in the magazine Pour l’Ère Nouvelleduring the 1920s. By doing so Lombardo-Radice confirmed his divergence from Gentile and his proximity to the progressive school movement

Influence of the long-range ordering of gold-coated Si nanowires on SERS

Controlling the location and the distribution of hot spots is a crucial aspect in the fabrication of surface-enhanced Raman spectroscopy (SERS) substrates for bio-analytical applications. The choice of a suitable method to tailor the dimensions and the position of plasmonic nanostructures becomes fundamental to provide SERS substrates with significant signal enhancement, homogeneity and reproducibility. In the present work, we studied the influence of the long-range ordering of different flexible gold-coated Si nanowires arrays on the SERS activity. The substrates are made by nanosphere lithography and metal-assisted chemical etching. The degree of order is quantitatively evaluated through the correlation length (ξ) as a function of the nanosphere spin-coating speed. Our findings showed a linear increase of the SERS signal for increasing values of ξ, coherently with a more ordered and dense distribution of hot spots on the surface. The substrate with the largest ξ of 1100 nm showed an enhancement factor of 2.6 · 103 and remarkable homogeneity over square-millimetres area. The variability of the signal across the substrate was also investigated by means of a 2D chemical imaging approach and a standard methodology for its practical calculation is proposed for a coherent comparison among the data reported in literature

State and evolution of the African rainforests between 1990 and 2010

This paper presents a 2005 map of Africa’s rainforests with new levels of spatial and thematic detail, being derived from 250m resolution MODIS data, and having an overall accuracy of 84%. A systematic sample of Landsat images (with supplemental data from equivalent platforms to fill sample gaps) is used to produce a consistent assessment of deforestation between 1990, 2000 and 2010 for West Africa, Central Africa and Madagascar. Net deforestation is estimated at 0.28% yr-1 for the period 1990-2000 and 0.14% yr-1 for the period 2000-2010. West Africa and Madagascar exhibit a much higher deforestation rate than the Congo Basin. Based on a simple analysis of the variance over the Congo Basin, we show that expanding agriculture and increasing fuelwood demands are key drivers of deforestation while well-controlled timber exploitation programmes have little or no direct influence on forest-cover reduction at present. Rural and urban population concentrations and fluxes are identified as strong underlying causes of deforestation in this study.JRC.H.5 - Land Resources Managemen