In As atmosphere, we analyzed the crystallization dynamics during post-growth annealing of Ga droplets residing at the top of self-assisted GaAs nanowires grown by molecular beam epitaxy. The final ...crystallization steps, fundamental to determining the top facet nanowire morphology, proceeded via a balance of Ga crystallization via vapor-liquid-solid and layer-by-layer growth around the droplet, promoted by Ga diffusion out of the droplet perimeter, As desorption, and diffusion dynamics. By controlling As flux and substrate temperature the transformation of Ga droplets into nanowire segments with a top surface flat and parallel to the substrate was achieved, thus opening the possibility to realize atomically sharp vertical heterostructures in III-As self-assisted nanowires through group III exchange.
In 2018 a collaborative project between Politecnico di Milano (PoliMI) and Regione Lombardia (RL) was launched to join forces and expertise toward the improvement of the regional transport ...infrastructures maintenance management. One of the project goals was the development of regional guidelines aimed to support the design and implementation of monitoring systems for bridges. The focus of this paper is on the illustration of the Monitoring Regional (MoRe) guidelines and of their implementation on nine pilot monitoring systems designed and deployed within the project. The (MoRe) guidelines tackle the entire monitoring process from the analyses of the monitoring goals and the preliminary investigations needed to the identification of the phenomena and relevant indicators to monitor, up to the selection of monitoring devices and the presentation of results. A short illustration of the permanent monitoring systems installed on nine exemplary bridges in the Lombardia region concludes the paper.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
In III-V nanowires the energetic barriers for nucleation in the zinc blende or wurtzite arrangement are typically of a similar order of magnitude. As a result, both arrangements can occur in a single ...wire. Here, we investigate the evolution of this polytypism in self-catalyzed GaAs nanowires on Si(111) grown by molecular beam epitaxy with time-resolved in situ x-ray diffraction. We interpret our data in the framework of a height dependent Markov model for the stacking in the nanowires. In this way, we extract the mean sizes of faultless wurtzite and zinc blende segments-a key parameter of polytypic nanowires-and their temporal evolution during growth. Thereby, we infer quantitative information on the differences of the nucleation barriers including their evolution without requiring a model of the nucleus.
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•We study 2 critical issues (interface abruptness and strain release) in InAs/GaAs NWs.•Structural and chemical interface sharpness ≤1.5nm, better than in previous ...reports.•Simultaneous elastic and plastic relaxation is shown that agrees with FEM simulations.•Structural, chemical and strain release investigations were performed by STEM.•New MBE self-seeded method whereby InAs is grown by splitting In and As depositions.
The structure, interface abruptness and strain relaxation in InAs/GaAs nanowires grown by molecular beam epitaxy in the Ga self-catalysed mode on (111) Si have been investigated by transmission electron microscopy. The nanowires had the zincblende phase. The InAs/GaAs interface was atomically and chemically sharp with a width around 1.5nm, i.e. significantly smaller than previously reported values. This was achieved by the consumption of the Ga droplet and formation of a flat top facet of the GaAs followed by the growth of InAs by splitting the depositions of In and As. Both elastic and plastic strain relaxation took place simultaneously. Experimental TEM results about strain relaxation very well agree with linear elasticity theory calculations by the finite element methods.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
DEVELOPMENT OF A NEW URBAN LINE WITH INNOVATIVE TRAMS BORGHETT, FABIO; Colombo, Cristian Giovanni; Longo, Michela ...
WIT Transactions on the Built Environment,
01/2021, Volume:
204
Journal Article, Conference Proceeding
Open access
The trend of the population increase combined with the global climate change and the rising energy prices make sustainable mobility a big issue for urban communities. Since in urban areas it is in ...act a process of infrastructure development, the modernization of Light Rail Vehicle (LRV), whose final purpose is to intensify the urban transport network in an environmentally friendly way (reduction of visual and noise pollution), will be chased too. This paper is focused on a study developed in the North of Italy (Brescia) and its target is to plan a new tramline without catenary to reduce the urban and architectural impact of infrastructure. In this way, it is possible to reduce the environmental impact especially in specific areas of an urban centre. The work analyses the use of the batteries and the main parameters to size the storage system technology in order to supply the tram correctly whenever it crosses the catenary free section.
A systematic optical study, including micro, ensemble and time resolved photoluminescence of GaAs/AlGaAs triple concentric quantum rings, self-assembled via droplet epitaxy, is presented. Clear ...emission from localized states belonging to the ring structures is reported. The triple rings show a fast decay dynamics, around 40 ps, which is expected to be useful for ultrafast optical switching applications.
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