Ripple-to-dome transition: the growth evolution of Ge on vicinal Si(1 1 10) surface

We present a detailed scanning tunnelling microscopy study which describes the morphological transition from ripple to dome islands during the growth of Ge on the vicinal Si(1 1 10) surface . Our experimental results show that the shape evolution of Ge islands on this surface is markedly different from that on the flat Si(001) substrate and is accomplished by agglomeration and coalescence of several ripples. By combining first principle calculations with continuum elasticity theory, we provide an accurate explanation of our experimental observations

Hug-like island growth of Ge on strained vicinal Si(111) surfaces

We examine the structure and the evolution of Ge islands epitaxially grown on vicinal Si(111) surfaces by scanning tunneling microscopy. Contrary to what is observed on the singular surface, three-dimensional Ge nanoislands form directly through the elastic relaxation of step-edge protrusions during the unstable step-flow growth. As the substrate misorientation is increased, the islands undergo a shape transformation which is driven by surface energy minimization and controlled by the miscut angle. Using finite element simulations, we show that the dynamics of islanding observed in the experiment results from the anisotropy of the strain relaxation.Comment: 4 figure

How kinetics drives the two- to three-dimensional transition in semiconductor strained heterostructures: the case of InAs/GaAs(001)

The two- to three-dimensional growth transition in the InAs/GaAs(001) heterostructure has been investigated by atomic force microscopy. The kinetics of the density of three dimensional quantum dots evidences two transition thresholds at 1.45 and 1.59 ML of InAs coverage, corresponding to two separate families, small and large. Based on the scaling analysis, such families are characterized by different mechanisms of aggregation, involving the change of the critical nucleus size. Remarkably, the small ones give rise to a wealth of "monomers" through the erosion of the step edges, favoring the explosive nucleation of the large ones.Comment: 10 pages, 3 figures. Submitted to Phys. Rev. Let

Electronic screening and correlated superconductivity in carbon nanotubes

A theoretical analysis of the superconductivity observed recently in Carbon nanotubes is proposed. We argue that ultra-small (diameter $\sim 0.4 nm$) single wall carbon nanotubes (with transition temperature $T_c\sim 15 ^{o}K$) and entirely end-bonded multi-walled ones ($T_c\sim 12 ^{o}K$) can superconduct by an electronic mechanism, basically the same in both cases. By a Luttinger liquid -like approach, one finds enhanced superconducting correlations due to the strong screening of the long-range part of the Coulomb repulsion. Based on this finding, we perform a detailed analysis on the resulting Hubbard-like model, and calculate transition temperatures of the same order of magnitude as the measured ones.Comment: 6 pages, 1 figure, PACS: 71.10.Pm,74.50.+r,71.20.Tx, to appear in Phys. Rev.

Step-step interaction on vicinal Si(001) surfaces studied by scanning tunneling microscopy

We report on measurements of step-step interaction on a flat Si(111)−(7×7) surface and on vicinal Si(001) surfaces with miscut angles ranging between 0.2° and 8°. Starting from scanning tunneling microscopy images of these surfaces and describing steps profile and interactions by the continuum step model, we measured the self-correlation function of single steps and the distribution of terrace widths. Empirical parameters, such as step stiffness and step-step interaction strength, were evaluated from the images. The present experiment allows to assess the dependence of the step-step repulsion on miscut angle, showing how parameters drawn from tunneling images can be used to interpolate between continuum mesoscopic models and atomistic calculations of vicinal surfaces

Urban Voids After the Pandemic. A New Chance for Greenway

Our proposal deals with the meaning of urban voids in the post-COVID-19 period to suggest new understandings of how urban green corridors can positively affect design for healthier and more sustainable cities. According to Secchi (1986), planning through the void involves a profound revision of the way we think about the city, reversing the points of interest, proposing as polarities the spaces that do not usually emerge. The void thus becomes an opportunity, a chance to improve the structure of our urban landscape (Lopez-Pineiro, 2020). A city is a powerful place, always in motion and transformation. It has an artificial spirit full of surprises and vague limits. It is the scene of remarkable transformations that in their wildness are partially ungovernable by the designers themselves. The desire to control them leaves a series of abandoned and unfinished spaces, “holes” that live from their discontinuity with the surroundings (Labriola, 2021). During a period of crisis, like the one that we are still living with COVID-19 (Fabris et al, 2020), it is common to re-think our cities to create better places for the community. After the long period of forced distance that we lived, an evolution of public space is recommended. During the pandemic, the emptiness of our cities permitted Nature to re-appropriate its spaces. Following this trend and thinking about a new kind of public space where Nature and its inside processes are the protagonists, it is possible to intervene in our cities. The porosity of the urban fabric in towns without humans, blocked at home by the never-ending lockdowns, became a new green corridor that revealed the presence of wildlife (both fauna and flora) as part of a forgotten urban layer that turned visible again. The preservation of this new asset should be possible. The spaces to allow this change can be the abandoned and empty areas present in the contemporary city’s sick body that we can finally heal. The so-called wastelands, voids, or terrain vague, have a significant value independent from the environment in which they are inserted, showing a relationship with the contemporary city extraneous to its rhythms. For this reason, they are the perfect place for experimentation in terms of greenways, a possible starting point to re-think how green can be part of the urban texture and how to conceive public and open spaces after the nowadays crisis. The paper considers the Metropolitan City of Milan as a remarkable case study to understand the pivotal role played by urban voids in the formation of greenways and their capacity of reshaping the environmental, aesthetic and healthy dimensions of urban landscapes

Journey to the Center of the Cookie Ecosystem: Unraveling Actors' Roles and Relationships

Web pages have been steadily increasing in complexity over time, including code snippets from several distinct origins and organizations. While this may be a known phenomenon, its implications on the panorama of cookie tracking received little attention until now. Our study focuses on filling this gap, through the analysis of crawl results that are both large-scale and fine-grained, encompassing the whole set of events that lead to the creation and sharing of around 138 million cookies from crawling more than 6 million webpages. Our analysis lets us paint a highly detailed picture of the cookie ecosystem, discovering an intricate network of connections between players that reciprocally exchange information and include each other's content in web pages whose owners may not even be aware. We discover that, in most webpages, tracking cookies are set and shared by organizations at the end of complex chains that involve several middlemen. We also study the impact of cookie ghostwriting, i.e., a common practice where an entity creates cookies in the name of another party, or the webpage. We attribute and define a set of roles in the cookie ecosystem, related to cookie creation and sharing. We see that organizations can and do follow different patterns, including behaviors that previous studies could not uncover: for example, many cookie ghostwriters send cookies they create to themselves, which makes them able to perform cross-site tracking even for users that deleted third-party cookies in their browsers. While some organizations concentrate the flow of information on themselves, others behave as dispatchers, allowing other organizations to perform tracking on the pages that include their content

Wastewater Treatment Using Alkali-Activated-Based Sorbents Produced from Blast Furnace Slag

Currently, slags from secondary steel production, foundries, and blast furnaces represent a major environmental problem since they end up mainly in landfills, and their valorization would bring undeniable advantages both to environment and economy. Moreover, the removal of heavy metal ions from mines wastewater is one of the challenges of the last decades, and adsorption has been proposed as one of the most promising techniques for this purpose. In this context, the use of alkali-activated slags as sorbent can be a good opportunity to develop low cost, environmentally friendly, and sustainable materials. Accordingly, wastewater decontamination by adsorption over a porous monolithic bed made of alkali-activated hydraulic binders is proposed. Alkali-activated materials were prepared using slags from the metallurgical industry and reacted with an alkaline component (high alumina calcium aluminate cement, CAC 80) at ambient conditions. The obtained monolithic foams were tested to evaluate the uptake efficiency towards metal capture. Solutions containing Cu(II), Fe(III), Ni(II), Mn(II), and simulating the metal concentrations of a real mine effluent were tested, both in single- and multi-ion solutions. Promising capture efficiency, values of 80–100% and of 98–100% in the case of the single ion and of the multi-ion solutions were obtained, respectively

WeDRAW: using multisensory serious games to explore concepts in primary mathematics

WeDRAW aims to mediate learning of primary school mathematical concepts, such as geometry and arithmetic, through the design, development and evaluation of multisensory serious games, using a combination of sensory interactive technologies. Working closely with schools, using participatory design techniques, the WeDRAW system will be embedded into the school curricula, and configurable by teachers. Besides application to typically developing children, a major goal is to examine this multisensory approach with visually impaired and dyslexic children