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In this study a seismic risk analysis of masonry buildings based on damage data of L’Aquila 2009 earthquake is presented. Typological loss curves and Expected Annualized Losses (EAL) values are pre...

We combine density functional theory and many body perturbation theory to investigate the electronic properties of Si(100) and Ge(100) surfaces terminated with halogen atoms (-I, -Br, -Cl, -F) and other chemical functionalizations (-H, -OH, -CH3) addressing the absolute values of their work function, electronic affinity and ionization potential. Our results point out that electronic properties of functionalized surfaces strongly depend on the chemisorbed species and much less on the surface crystal orientation. The presence of halogens at the surface always leads to an increment of the work function, ionization potential and electronic affinity with respect to fully hydrogenated surfaces. On the contrary, the presence of polar -OH and -CH3 groups at the surface leads to a reduction of the aforementioned quantities with respect to the H-terminated system. Starting from the work functions calculated for the Si and Ge passivated surfaces, we apply a simple model to estimate the properties of functionalized SiGe surfaces. The possibility of modulating the work function by changing the chemisorbed species and composition is predicted. The effects induced by different terminations on the band energy line-up profile of SiGe surfaces are then analyzed. Interestingly, our calculations predict a type-II band offset for the H-terminated systems and a type-I band offset for the other cases.

The article presents a preliminary assessment of seismic damage shown by 60 Mexican churches after the two earthquakes arisen in September 2017. The first earthquake occurred on September 7th and h...

The manufacturing of Portland cement is responsible for a big amount of energy and greenhouse gas (GHG) emission. Therefore, to date, it is imperative to find alternative materials to replace a major part of cement for sustainable concrete constructions. The present study forms a part of an on-going research project on the application of new cementitious matrices produced using different types of recycled materials. In particular, it focuses on the use of pulp and waste paper to partially replace Portland cement at varying percentages for producing a new lightweight mortar, frequently named papercrete. The development of this economical and eco-friendly material may permit of recycling a big amount of waste paper leading to lower housing costs with also ecological benefits. To this scope, an experimental campaign in the laboratory is carried out to characterize this new innovative material from a physical and mechanical point of view. The preliminary results of this on-going experimental campaign are illustrated and commented on in this paper. The obtained results confirm the possibility of applying this partially-recycled material as a possible alternative for strengthening existing panels of masonry.

Eight historical mosques of Kermanshah constructed in 18th or 19th century CE are investigated with ambient vibration tests on their sites and buildings. Conventional peak picking technique is used for determination of structures’ fundamental frequencies and spectral ratio of horizontal to vertical components along with ellipticity inversion of Rayleigh waves are considered to identify the natural frequency of ground and shear wave velocity profile to define the site conditions according to the national codes of Iran and Italy. The recorded motions on the buildings are used to calculate the fundamental frequencies of the structure. Afterward, buildings are modeled by macro-element method and material properties are tuned in the way that the fundamental frequencies from the modal analyses match with the measured values from AVTs. Finally, more modal analyses are performed by the calibrated models to present an empirical relation between the natural period of the mosques, the geometrical characteristics of the buildings, and the mechanical properties of the construction materials. The results show that the natural periods of the masonry buildings of the mosques are different from the values of empirical relations in the national codes. Meanwhile, the proposed empirical relation presents the natural periods of the buildings of this study reasonably well and can be used for other masonry buildings of similar architecture and materials.

Background: In this research a rapid vulnerability and risk assessment at a territorial level is performed. Methods: The methodology used, initially proposed for ancient masonry churches, is extended and applied to ten historic masonry mosques in Kermanshah city. The method could be considered as preliminary risk assessment approach of historic structures, refers to LV0 method, since the used methodology requires simple qualitative information. It involves the application of three distinct tools; the exposure, the seismic hazard, and the seismic vulnerability. Results: The comparisons among the obtained results, by considering also the damages suffered during the last earthquakes and war blasts, validate the methodology proposed, capable of providing a seismic risk scoring at a territorial level also for ancient masonry mosques. As known, through this kind of approach, important information is obtained in order to manage and to mitigate the seismic risk of a certain territorial asset. The results show that all ten mosques has medium earthquake vulnerability condition. Emad e Doleh mosque is the most vulnerable case with vulnerability of 34. Navab mosque is located on the most hazardous place. Furthermore, the seismic vulnerability map and seismic risk indices are presented for all the investigated mosques. Conclusion: The obtained results are useful for ranking the priorities and for preliminary defining an interventions plan to be examined in detail with additional quantitative investigations carried out with more refined approaches.

Control and inspection of the conditions of elastomeric bearings used for seismic isolation purpose is a fundamental activity in ensuring and preserving the performance of a structure. The methods currently used, such as visual inspections, Operational Modal Analysis (OMA), release tests, very often present strong limitations due to their qualitative nature or else to the costs associated with their implementation and functioning. An innovative procedure based on the use of nanoindentation tests is proposed and validated through an experimental campaign. Its main benefits consist in the possibility of quantitatively estimating the current characteristics of elastomeric bearings, in conjunction with low implementation costs and influence on the isolating devices. The innovative procedure consists of coring a very small sample of rubber from a bearing and testing it with a nano-indenter in order to estimate the actual characteristics in terms of shear stress-strain relationships. The experimental tests showed good agreement between the properties calculated with the proposed method and the ones obtained directly through a traditional shear test, making such procedure a promising tool.

Nowadays, Sonic Pulse Velocity tests (SPV tests) are widely applied for detecting the morphology, hidden defects, and voids within structural elements. This technique, largely applied because non i...

Nowadays, safety assessment under seismic loading of historical masonry buildings, such as ancient churches, is an actual and important topic due to the potential human and economic losses ...

Semiconducting nanowires (NWs) offer the unprecedented opportunity to host different crystal phases in a nanostructure, which enables the formation of polytypic heterostructures where the material composition is unchanged. This characteristic boosts the potential of polytypic heterostructured NWs for optoelectronic and phononic applications. In this work, we investigate cubic Ge NWs where small (∼20 nm) hexagonal domains are formed due to a strain-induced phase transformation. By combining a nondestructive optical technique (Raman spectroscopy) with density-functional theory (DFT) calculations, we assess the phonon properties of hexagonal Ge, determine the crystal phase variations along the NW axis, and, quite remarkably, reconstruct the relative orientation of the two polytypes. Moreover, we provide information on the electronic band alignment of the heterostructure at points of the Brillouin zone different from the one (Γ) where the direct band gap recombination in hexagonal Ge takes place. We demonstrate the versatility of Raman spectroscopy and show that it can be used to determine the main crystalline, phononic, and electronic properties of the most challenging type of heterostructure (a polytypic, nanoscale heterostructure with constant material composition). The general procedure that we establish can be applied to several types of heterostructures., I.Z. acknowledges financial support from the Swiss National Science Foundation research grant (Project Grant No. 200021_165784). C.F. acknowledges financial support from Sapienza University scholarship “Borsa di Perfezionamento all’Estero 2017–2018”. R.R. acknowledges financial support by the Ministerio de Economia, Industria y Competitividad (MINECO) under grant FEDER-MAT2017-90024-P and the Severo Ochoa Centres of Excellence Program under Grant SEV-2015-0496 and by the Generalitat de Catalunya under grants no. 2017 SGR 1506. L.V. acknowledges financial support from the IDEX Paris-Saclay (ANR-11-IDEX-0003-02). This work was partly supported by the ANR HEXSIGE project (ANR-17-CE030-0014-01) of the French Agence Nationale de la Recherche. R.R. and M.A. thank Giacomo Giorgi and Thanayut Kaewmaraya for useful discussions.

Introduction: Existing old masonry arch bridges represent an architectural and cultural heritage of inestimable value because most of them were built in the last century and are still in service. They represent a very important part of roads and railways networks, having also an important strategic role. They are actually serving roads characterized by transit loads definitively heavier and more frequent than the ones of the past. Moreover, very often maintenance absence and material worn away, increased by the way by the environmental conditions, accelerate more and more the elements deterioration with a consequent loss of integrity and reduction of their carrying capacity. Methods: In this paper the seismic assessment of an old multi span masonry arch bridge still in service is evaluated. The bridge, located in Southern Italy, was built before the Second World War and crosses the “Cavone” River, from which it takes the name. Results and Conclusion: A series of numerical analyses are performed in order to evaluate its seismic performance and the model sensitivity with respect to the assumed masonry mechanical properties.

In this paper, an analytical model of confined concrete proposed for square sections is extended to the case of rectangular ones. The new and generalized formulation, based on the elasticity theory, is developed under the key assumption that the confinement arises in plane-strain conditions. The proposed model provides, through the analogy among the section core and internal cylinders, the confining pressure in polar coordinates to be applied for computing the actual concrete curve subjected to passive confinement. In this procedure, as for the square confined sections, any active confinement model derived from triaxial tests on cylindrical specimens may be involved. The extended model is also suitable for evaluating the confining pressure offered by additional external strengthenings in any material, such as for example FRP wraps and/or steel jackets. Comparisons among numerical simulations and experimental data demonstrate the accuracy of the new generalized analytical model in predicting the confined stress-strain relationship of concrete in the case of either newly designed or old existing concrete elements, also when multiple transverse reinforcements are applied.

Estimating the saftey of an ancient masonry arch bridge is a legitimate, but very interesting, structural engineering challenge. This is due to the fact that most of these bridges are still in service and suffer from higher and more frequent cyclic loads, a problem not encountered in the past. Therefore, for these structures it is important to know the actual fatigue strength rather than the ultimate carrying capacity in order to provide useful indications on the remaining service life with also possible traffic load limitations.In this article, different models are applied according to the stress-life curve method for estimating the fatigue strength of a case study: an ancient multi-span masonry arch bridge still in service. The obtained results highlight that, unlike steel elements, current design codes do not provide any relevant indication as to the fatigue strength assessment of existing masonry membratures. Moreover, appropriate stress-life curves are needed for evaluating the actual capacit...

Recent advances in the fabrication of group IV homojunctions made by cubic-diamond (3C) and hexagonal-diamond (2H) phases call for a detailed understanding of the physics underlying their electronic structure. In this work, we employ hybrid density functional theory (hybrid-DFT) calculations to study the structural and electronic properties of Si and Ge polytype junctions. Starting from high-resolution transmission electron microscopy (HRTEM) micrographs of 2H/3C Si nanowires, we build a computational model that takes into account both crystal-phase effects and the length of the junction. We obtain accurate estimations of the magnitudes of the band offsets: In particular, we show that 2H/3C Si interfaces induce a type-II band alignment, whereas the Ge structures exhibit a type-I band offset. Furthermore, both Si and Ge homojunctions have direct gaps that are smaller than those of the bulk 3C phase. Finally, we demonstrate that, in all of the considered systems, varying the thickness of the hexagonal phase...

We report the observation of an intense anomalous peak at 1608 cm$^{-1}$ in the Raman spectrum of graphene associated to the presence of chromium nanoparticles in contact with graphene. Bombardment with an electron beam demonstrates that this peak is distinct from the well studied D$'$ peak appearing as defects are created in graphene; the new peak is found non dispersive. We argue that the bonding of chromium atoms with carbon atoms softens the out-of-plane optical (ZO) phonon mode, in such a way that the frequency of its overtone decreases to $2\omega_{\rm ZO}\sim\omega_{\rm G}$, where $\omega_{\rm G}$=1585~cm$^{-1}$ is the frequency of the Raman-active E$_{\rm 2g}$ mode. Thus, the observed new peak is attributed to the 2ZO mode which becomes Raman-active following a mechanism known as Fermi resonance. First-principles calculations on vibrational and anharmonic properties of the graphene/Cr interface support this scenario., Comment: 12 pages, 10 figures

Nowadays, seismic retrofit through isolation strategy represents a consolidated technique of protection against design earthquakes. This technique is also applied on existing structures extensively, due to the fact that it usually does not require any interruption of the building use and occupants evacuation. If applicable, it rapidly allows the seismically retrofitting of a building installed with seismic devices with low horizontal stiffness between the structure and the foundation decoupling, in fact, this allows the motion of the superstructure from the ground one. In this paper an application on an existing RC building of the seismic isolation is presented. The chosen building was built in the ‘90s only for vertical loads and realized without any detailing rule for structural ductility. The seismic retrofitting requirement stems from the fact that only recently, after the National seismic hazard maps update in 2003, the considered area has been upgraded to a medium-low seismic intensity zone, while at construction time no seismic classification was in existence by law. The case study peculiarity is that the seismic retrofitting has required an addition to seismic devices at the base, with related interventions such as the application of a bracing system consisting of two elastic steel frames. This intervention is required for stiffening the superstructure and, therefore, minimizing the higher vibration modes effects. The paper presents the main results obtained with a FEM model, implemented for simulating the initial and the design state when the interventions are considered. Finally, some results of non-linear dynamic time-history analyses are illustrated and commented for verifying superstructure elements and seismic devices.

Over the last few years, group IV hexagonal-diamond type crystals have acquired great attention in semiconductor physics thanks to the appearance of novel and very effective growth methods. However, many questions remain unaddressed on their extrinsic doping capability and on how it compares to those of diamond-like structures. This point is here investigated through numerical simulations conducted in the framework of the Density Functional Theory (DFT). The comparative analysis for group III and V dopant atoms shows that: i) in diamond-type crystals the bulk sites symmetry ($T_d$) is preserved by doping while in hexagonal crystals the impurity site moves towards a higher ($T_d$) or lower ($C_{3v}$) symmetry configuration dependently on the valence of the dopant atoms; ii) for Si and Ge, group III impurities can be more easily introduced in the hexagonal-diamond phase, whose local $C_{3v}$ symmetry better accommodates the three-fold coordination of the impurity, while n-type impurities do not reveal any marked phase preference; iii) for C, both n and p dopants are more stable in the hexagonal-diamond structure than in the the cubic one, but this tendency is much more pronounced for n-type impurities.

Silicon nanocrystals and nanowires have been extensively studied because of their novel properties and their applications in electronic, optoelectronic, photovoltaic, thermoelectric and biological devices. Here we discuss results from ab initio calculations for undoped and doped Si nanocrystals and nanowires, showing how theory can aid and improve comprehension of the structural, electronic and optical properties of these systems., S. O. acknowledges support/funding from University of Modena and Reggio Emilia under project “FAR2017INTERDISC”. S. O. and I. M. thank the Super-Computing Interuniversity Consortium CINECA for support and high-performance computing resources under the Italian Super-Computing Resource Allocation (ISCRA) initiative, PRACE for awarding us access to the resource MARCONI HPC cluster based in Italy at CINECA. I. M. acknowledges support/funding from European Union H2020-EINFRA-2015-1 and H2020-INFRAEDI-2018-1 programs under grant agreement No. 676598 and No. 824143, project MaX-MAterials at the eXascale. M. A. greatly acknowledges the Transnational Access Programme of the HPC-EUROPA3 (project HPC17PB9IZ). Some of the high-performance computing (HPC) resources for this project were granted by the Institut du development et des ressources en informatique scientifique (IDRIS) under the allocation A0040910089 via GENCI (Grand Equipment National de Calcul Intensif). This work was supported by the ANR HEXSIGE project (ANR-17-CE030-0014-01) of the French Agence Nationale de la Recherche. M. P. acknowledges INFN for financial support through the National project Nemesys. We also acknowledge financial support by the Ministerio de Economía, Industria y Competitividad (MINECO) and MICIU (Ministerio de Ciencia y Universidades) under Grants FEDER-MAT2017-90024-P, FIS2015-64886-C5-4-P and PGC2018-096955-B-C44-P, the Severo Ochoa Centres of Excellence Program under Grant SEV-2015-0496 and the Generalitat de Catalunya under Grant 2017 SGR 1506.

The formation energies of n- and p-type dopants in III–V arsenide and phosphide semiconductors (GaAs, GaP, and InP) are calculated within a first-principles total energy approach. Our findings indicate that—for all the considered systems—both the solubility and the shallowness of the dopant level depend on the crystal phase of the host material (wurtzite or zincblende) and are the result of a complex equilibrium between local structural distortion and electronic charge reorganization. In particular, in the case of acceptors, we demonstrate that impurities are always more stable in the wurtzite lattice with an associated transition energy smaller with respect to the zincblende case. Roughly speaking, this means that it is easier to p-type dope a wurtzite crystal and the charge carrier concentration at a given temperature and doping dose is larger in the wurtzite as well. As for donors, we show that neutral chalcogen impurities have no clear preference for a specific crystal phase, while charged chalcogen impurities favor substitution in the zincblende structure with a transition energy that is smaller when compared to the wurtzite case (thus, charge carriers are more easily thermally excited to the conduction band in the zincblende phase)., We acknowledge financial support by the Ministerio de Economía, Industria y Competitividad (MINECO) under grants FEDER-MAT2017-90024-P and PGC2018-096955-B-C44, the Severo Ochoa Centres of Excellence Program under grant SEV-2015-0496, and the Generalitat de Catalunya under grants no. 2017 SGR 1506. We thank the Centro de Supercomputación de Galicia (CESGA) for the use of their computational resources. M.A. acknowledges the ANR HEXSIGE project (ANR-17-CE030-0014-01) of the French Agence Nationale de la Recherche. Part of the high-performance computing resources for this project were granted by the Institut du développement et des ressources en informatique scientifique (IDRIS) under the allocation A0040910089 via GENCI (Grand Equipement National de Calcul Intensif). S.O. acknowledges support/funding from the University of Modena and Reggio Emilia under project “FAR2017INTERDISC” G.G. acknowledges PRACE for awarding the access to the Marconi system based in Italy at CINECA and the Italian ISCRA program.We acknowledge financial support by the Ministerio de Economía, Industria y Competitividad (MINECO) under grants FEDER-MAT2017-90024-P and PGC2018-096955-B-C44, the Severo Ochoa Centres of Excellence Program under grant SEV-2015-0496, and the Generalitat de Catalunya under grants no. 2017 SGR 1506. We thank the Centro de Supercomputación de Galicia (CESGA) for the use of their computational resources. M.A. acknowledges the ANR HEXSIGE project (ANR-17-CE030-0014-01) of the French Agence Nationale de la Recherche. Part of the high-performance computing resources for this project were granted by the Institut du développement et des ressources en informatique scientifique (IDRIS) under the allocation A0040910089 via GENCI (Grand Equipement National de Calcul Intensif). S.O. acknowledges support/funding from the University of Modena and Reggio Emilia under project “FAR2017INTERDISC” G.G. acknowledges PRACE for awarding the access to the Marconi system based in Italy at CINECA and the Italian ISCRA program.

Italian historical buildings do not respect often standard requirements established by National regulations, so that they need of an energy requalification. In addition, commonly the adopted provisions do not belong to an integral design approach in which different aspects, such as architectonic, energetic, and structural should be together considered for obtaining a total building rehabilitation. This work mainly addresses to the application of non-invasive methods for energy retrofitting of historical buildings in Italy. In particular, an energy audit protocol is studied and applied to a case study, consisting on an ancient masonry building located within the historical center of “Sassi of Matera,” recognized as UNESCO site since 1993. In the paper some energy efficiency measures are considered, by examining also alternative interventions with respect to the classical ones, by applying innovative and sustainable materials, fashionable as well from a structural point of view. This proposal, to be investigated more in detail in future, responds to the criteria of non-invasiveness for preserving the cultural heritage identity, and simultaneously improving the energy and the structural response.

In this paper, seismic vulnerability and risk assessment of two samples of churches, located in Teramo and Ischia island (Naples gulf), both affected by the most recent earthquakes that occurred in Italy, are presented. To this aim, we applied a simplified method particularly suitable for seismic evaluations at a territorial scale, providing a global resulting score to be compared among the cases analyzed. The data obtained allowed us to provide vulnerability maps and a seismic risk index for all the considered churches. In addition, the calculated indexes permit a preliminary health state evaluation of the inspected churches, for ranking the priorities and planning additional in-depth evaluations.

The protection of cultural heritage from seismic risk is an open issue due to the difficulties in finding technical solutions allowing a balance between their effectiveness and invasiveness. Among the available protection techniques, seismic isolation is one of the most suitable obtaining a significant performance improvement by acting on a limited portion of the structure. In this paper, it is shown an application of such technique on a reinforced concrete frame building catalogued as of historical interest by Italian Ministry of Cultural Heritage. It was realized in 30’s representing the “Modern Style” of Italian Architecture, also known as Italian Rationalism, and designed only for vertical loads without any specific regulation for lateral loads. Geometry, material properties and reinforcements characteristics have been derived from an extensive investigation campaign. By the means of a FEM 3D model they are simulated among them the seismic responses of both existing and retrofitted building through a seismic isolation system composed by elastomeric and sliding isolators. Furthermore, a new methodology for estimating the seismic capacity exhibited by the structure in the past is presented and applied.

This paper proposes simplified formulations for estimating the main frequencies of ancient masonry churches. The formulations are derived starting from the results of numerical analyses with finite elements models, whose geometric parameters are assigned in accordance with specific relationships established on a set of 50 existing churches. The so-obtained formulations are also compared with the results of a series of experimental dynamic identification tests chosen from literature. Finally, starting from these experimental results, through numerical regressions, formulas for predicting the main frequencies of ancient masonry churches are proposed, too., The research activity carried out by SL has been supported by the ELARCH scholarship and mobility, a project funded under the Erasmus Mundus Action 2 Partnership (EMA2) by the European Commission, and coordinated by the University of Basilicata (www.elarch.org). ELARCH project: Reference number 552129-EM-1-2014-1-IT-ERA MUNDUS-EMA21 funded with support of the European Commission. This document reflects the view only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

This paper aims to propose numerical models for seismic assessment of old existing RC beam-column sub-assemblages. In particular, two modeling approaches are described: for internal (usually named “C joints”) and for external (named “T joints”) beam-column sub-assemblages, both designed only for vertical loads without reinforcing details rules (such as inadequate bars lap splice, absence of hoops within the joint panel). They were developed starting from the failure mechanisms observed during an experimental campaign carried out on specimens reproducing old existing RC sub-assemblages cast in full and reduced scale, as well as reinforced with smooth longitudinal bars. The proposed models are not time-consuming with respect to both modeling and computational efforts, and do not require any calibration procedure from an experimental data set. They may be easily implemented in a general-purpose finite element program since merely based on geometrical and mechanical properties of RC elements. The numerical predictions show a good agreement with the experimental ones demonstrating that the proposed models are able of reproducing the lateral response of the two considered sub-assemblages typologies, in terms of both failure mechanism and hysteretic dissipative capacity.

We studied the physics of common p- and ntype dopants in hexagonal-diamond Si, a Si polymorph that can be synthesized in nanowire geometry without the need of extreme pressure conditions, by means of first-principles electronic structure calculations and compared our results with those for the well-known case of cubic-diamond nanowires. We showed that (i) as observed in recent experiments, at larger diameters (beyond the quantum confinement regime) p-type dopants prefer the hexagonaldiamond phase with respect to the cubic one as a consequence of the stronger degree of three-fold coordination of the former, while n-type dopants are at a first approximation indifferent to the polytype of the host lattice; (ii) in ultrathin nanowires, because of the lower symmetry with respect to bulk systems and the greater freedom of structural relaxation, the order is reversed and both types of dopant slightly favor substitution at cubic lattice sites; (iii) the difference in formation energies leads, particularly in thicker nanowires, to larger concentration differences in different polytypes, which can be relevant for cubic-hexagonal homojunctions; (iv) ultrasmall diameters exhibit, regardless of the crystal phase, a pronounced surface segregation tendency for p-type dopants. Overall these findings shed light on the role of crystal phase in the doping mechanism at the nanoscale and could have a great potential in view of the recent experimental works on group IV nanowires polytypes., M.A. greatly acknowledges the Transnational Access Programme of the HPC-EUROPA3 (project HPC17PB9IZ). Part of the high-performance computing (HPC) resources for this project were granted by the Institut du developpement et des ressources en informatique scientifique (IDRIS) under the allocation A0040910089 via GENCI (Grand Equipement National de Calcul Intensif). This work was supported by the ANR HEXSIGE project (ANR-17-CE030-0014-01) of the French Agence Nationale de la Recherche. We also acknowledge financial support by the Ministerio de Economía, Industria y Competitividad (MINECO) under Grants FEDER-MAT2017-90024-P and FIS2015-64886-C5-4-P, the Severo Ochoa Centres of Excellence Program under Grant SEV-2015-0496, the Generalitat de Catalunya under Grants 2017 SGR 1506. S.O. acknowledges support/funding from University of Modena and Reggio Emilia under project ”FAR2017INTERDISC”.

This paper presents the seismic assessment of the Cathedral of Matera, in southern Italy, to determine the capacity of the structure when subjected to earthquakes. This church dates back to the 13th century and is one of the most representative monuments of the Apulian Romanesque architecture. Within the context of the evaluation of the seismic response of the cathedral, modal identification tests were performed in order identify and characterize the main dynamic properties of the structure. The results of these tests were used to develop a representative finite element model, which is able to provide the response to seismic actions. A pushover analysis was performed to characterize the seismic behavior of the structure. The results of the seismic analyses on the cathedral show that its vulnerability is high, being the transversal direction the less stiff and resistant. Elements as the nave and the façade, along with the bell tower, might be the most vulnerable to seismic actions. Additionally, it was observed that components as the trusses of the central nave strongly modify the seismic response and capacity of the structure. Apparently, the structure might not be able to withstand a strong earthquake from the region or might present several damage after one. Hence, it is recommendable to perform further studies about the seismic behavior, especially of the most vulnerable elements., The authors would like to acknowledge the University of Minho for supporting the experimental campaign. Thanks is also extended to Dr. Nuno Mendes, University of Minho, for his guidance and help for performing the in-situ tests on the cathedral. The authors would also like to thank to the ELARCH project number 552129-EM-1-2014-1-IT-ERASMUS MUNDUS-EMA 21 for funding the graduate studies of the first author.

We discuss results of ab initio calculations for Si, Ge, and Si/Ge nanowires and nanocrystals showing that theory can improve the comprehension of the properties of these systems. First, we consider doped and undoped freestanding hydrogenated nanowires and we explore their properties as a function of the size, geometry, and composition. Secondly, we focus the discussion on the electronic properties of matrix embedded Si, Ge, and Si/Ge nanocrystals by pointing out the role played by composition, quantum confinement, and strain. The discussed results show that, for Si/Ge nanowires, the interface between Si and Ge region plays an important role determining, in some case, the formation of a type II band offset, which is essential for photovoltaic applications. Moreover, for Si/Ge core-shell nanowires, it is shown that: i) selective doping results in the formation of hole or electron accumulation, with interesting consequences for the use of these materials in thermoelectrics and ii) through compensated doping, it is possible to tune the optical properties of these systems. For the embedded nanocrystals, the outcomes suggest that Ge nanocrystals can be suitable as optical absorption centers and that Si/Ge nanocrystals, owing to the localization of the band edge states, are interesting for photovoltaic cells.

International audience; Selective oxidation of the silicon element of silicon germanium (SiGe) alloys during thermal oxidation is a very important and technologically relevant mechanism used to fabricate a variety of microelectronic devices. We develop here a simple integrative approach involving vapor−liquid−solid (VLS) growth followed by selective oxidation steps to the construction of core−shell nanowires and higher-level ordered systems with scalable configurations. We examine the selective oxidation/ 16 condensation process under nonequilibrium conditions that gives rise to spontaneous formation of core−shell structures by germanium condensation. We contrast this strategy that uses reaction-diffusion-segregation mechanisms to produce coherently strained structures with highly configurable geometry and abrupt interfaces with growth-based processes which lead to low strained systems with nonuniform composition, three-dimensional morphology, and broad core−shell interface. We specially focus on SiGe core−shell nanowires and demonstrate that they can have up to 70% Ge-rich shell and 2% homogeneous strain with core diameter as small as 14 nm. Key elements of the building process associated with this approach are identified with regard to existing theoretical models. Moreover, starting from results of ab initio calculations, we discuss the electronic structure 23 of these novel nanostructures as well as their wide potential for advanced device applications.

First-principles calculations of work function tuning induced by different chemical terminations on Si(100) surface are presented and discussed. We find that the presence of halogen atoms (I, Br, Cl, and F) leads to an increase of the work function if compared to the fully hydrogenated surface. This is a quite general effect and is directly linked to the chemisorbed atoms electronegativity as well as to the charge redistribution at the interface. All these results are examined with respect to previous theoretical works and experimental data obtained for the (100) as well as other Si surface orientations. Based on this analysis, we argue that the changes in the electronic properties caused by variations of the interfacial chemistry strongly depend on the chemisorbed species and much less on the surface crystal orientation.

Semiconducting nanowires (NWs) are firm candidates for novel nanoelectronic devices and a fruitful playground for fundamental physics. Ultra-thin nanowires, with diameters below 10 nm, present exotic quantum effects due to the confinement of the wave functions, e.g. widening of the electronic band-gap, deepening of the dopant states. However, although several reports of sub-10 nm wires exist to date, the most common NWs have diameters that range from 20 to 200 nm, where these quantum effects are absent or play a very minor role. Yet, the research activity on this field is very intense and these materials still promise to provide an important paradigm shift for the design of emerging electronic devices and different kinds of applications. A legitimate question is then: what makes a nanowire different from bulk systems? The answer is certainly the large surface-to-volume ratio. In this article we discuss the most salient features of surface physics and chemistry in group-IV semiconducting nanowires, focusing mostly on Si NWs. First we review the state-of-the-art of NW growth to achieve a smooth and controlled surface morphology. Next we discuss the importance of a proper surface passivation and its role on the NW electronic properties. Finally, stressing the importance of a large surface-to-volume ratio and emphasizing the fact that in a NW the surface is where most of the action takes place, we discuss molecular sensing and molecular doping., We acknowledge support under contracts Nos. FEDER-MAT2013–40581-P of the Ministerio de Economía y Competitividad (MINECO), Grant 2014 SGR 301 of the Generalitat de Catalunya. and the Nanodesign project “Nanoharvesting” funded by the IDEX Paris-Saclay (ANR-11-IDEX-0003-02). Support from Ψk and European Science Foundation (ESF) is also greatly acknowledged.

Recent experimental investigations have confirmed the possibility to synthesize and exploit polytypism in group IV nanowires. Driven by this promising evidence, we use first-principles methods based on density functional theory and many-body perturbation theory to investigate the electronic and optical properties of hexagonal–diamond and cubic–diamond Si NWs as well as their homojunctions. We show that hexagonal–diamond NWs are characterized by a more pronounced quantum confinement effect than cubic–diamond NWs. Furthermore, they absorb more light in the visible region with respect to cubic–diamond ones and, for most of the studied diameters, they are direct band gap materials. The study of the homojunctions reveals that the diameter has a crucial effect on the band alignment at the interface. In particular, at small diameters the band-offset is type-I whereas at experimentally relevant sizes the offset turns up to be of type-II. These findings highlight intriguing possibilities to modulate electron and hole separations as well as electronic and optical properties by simply modifying the crystal phase and the size of the junction., We thank L. Vincent for fruitful discussions. We acknowledge financial support by the Ministerio de Economía y Competitividad (MINECO) under grant FEDER-MAT2013-40581-P and the Severo Ochoa Centres of Excellence Program under Grant SEV-2015-0496 and by the Generalitat de Catalunya under grants no. 2014 SGR 301. M.A. and T.K. acknowledge support from the Nanodesign project "Nanoharvesting" funded by the IDEX Paris-Saclay (ANR-11-IDEX-0003-02). Part of this work was made possible thanks to the HPC resources of IDRIS under the allocation i2015097422 and i2016097531 made available by GENCI (Grand Equipement National de Calcul Intensif) and the computer resources, technical expertise, and assistance provided by the Red Española de Supercomputación. M.P. acknowledges the EC for the RISE Project No. CoExAN GA644076 and CINECA for ISCRA-B Project No.HP10B0LUWN, for computational resources.

International audience; The strong excitonic emission of hexagonal boron nitride (h-BN) makes this material one of the most promising candidate for light emitting devices in the far ultraviolet (UV). However, single excitons occur only in perfect monocrystals that are extremely hard to synthesize, while regular h-BN samples present a complex emission spectrum with several additional peaks. The microscopic origin of these additional emissions has not yet been understood. In this work we address this problem using an experimental and theoretical approach that combines nanometric resolved cathodoluminescence, high resolution transmission electron microscopy and state of the art theoretical spectroscopy methods. We demonstrate that emission spectra are strongly inhomogeneus within individual few layer flakes and that additional excitons occur at structural deformations, such as faceted plane folds, that lead to local changes of the h-BN layers stacking order.

A systematic theoretical study of the work function behavior for Si1-xGex heterostructures over the whole composition range, from Si (x = 0) to Ge (x = 1), is presented. Our results, obtained through Density Functional Theory calculations and in good agreement with experimental evidences, show that increasing the Ge content lowers the work function value. We find that in order to exactly reproduce this behaviour in relation to the work function of pure Ge and Si systems and their concentrations, a deviation from the linear Vegard's rule is necessary. However, the calculated bowing parameter is very small, thus making the simple linear interpolation a valid approximation to obtain the work function of complex SiGe alloys. (C) 2016 AIP Publishing LLC.

One of the main challenges for Silicon-Germanium nanowires (SiGe NWs) electronics is the possibility to modulate and engine their electronic properties in an easy way, in order to obtain a material with the desired electronic features. Diameter and composition constitute two crucial ways for the modification of the band gap and of the band structure of SiGe NWs. Within the framework of density functional theory we present results of ab initio calculations regarding the band structure dependence of SiGe NWs on diameter and composition. We point out the main differences with respect to the case of pure Si and Ge wires and we discuss the particular features of SiGe NWs that are useful for future technological applications.

First-principles calculations on the structural, electronic, and optical properties of B-P codoped SiGe core-shell nanowires are discussed. We show that the simultaneous addition of B and P impurities into the wire can be energetically favored with respect to the single-doping. We demonstrate that impurities energetic levels in the band gap are dependent by the Si/Ge band offset, as well as by their location in the wire (i.e., core or shell region). This electronic tunability results in a significant optical modulation, as demonstrated by the red-shift of the first optical peak when B and P locations are switched in the wire. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4768475]

Dopant deactivation in pure Si and pure Ge nanowires (NWs) can compromise the efficiency of the doping process at nanoscale. Quantum confinement, surface segregation and dielectric mismatch, in different ways, strongly reduce the carrier generation induced by intentional addition of dopants. This issue seems to be critical for the fabrication of high-quality electrical devices for various future applications, such as photovoltaics and nanoelectronics. By means of Density Functional Theory simulations, we show how this limit can be rode out in core-shell silicon-germanium NWs (SiGe NWs), playing on the particular energy band alignment that comes out at the Si/Ge interface. We demonstrate how, by choosing the appropriate doping configurations, it is possible to obtain a 1-D electron or hole gas, which has not to be thermally activated and which can furnish carriers also at very low temperatures. Our findings suggest core-shell NWs as possible building blocks for high-speed electronic device and new generation solar cells.

Impurity doping of semiconducting nanowires has been predicted to become increasingly inefficient as the wire diameter is reduced, because impurity states get deeper due to quantum and dielectric confinement. We show that efficient n- and p-type doping can be achieved in SiGe core-shell nanowires as thin as 2 nm, taking advantage of the band offset at the Si/Ge interface. A one-dimensional electron (hole) gas is created at the band-edge and the carrier density is uniquely controlled by the impurity concentration with no need of thermal activation. Additionally, SiGe core-shell nanowires provide naturally the separation between the different types of carriers, electron and holes, and are ideally suited for photovoltaic applications. © 2010 American Chemical Society.

Results of first-principles DFT simulations provide strong evidence that, at zero temperature, for [110] oriented SiGe nanowires (NWs), the segregated structure is favoured with respect to the mixed ones; for this observation two different schemes of calculations are presented and discussed. Moreover the segregation strongly influences the NWs electronic properties, inducing a reduced quantum confined effect (RQCE). We show here that it depends on the effect of strain in the plane normal to the direction of growth and not on the choice of lattice parameter in the direction of growth. A qualitative evaluation of the band offset between Si and Ge for SiGe NWs is also presented.

Actually, most of the electric energy is being produced by fossil fuels and great is the search for viable alternatives. The most appealing and promising technology is photovoltaics. It will become truly mainstream when its cost will be comparable to other energy sources. One way is to significantly enhance device efficiencies, for example by increasing the number of band gaps in multijunction solar cells or by favoring charge separation in the devices. This can be done by using cells based on nanostructured semiconductors. In this paper, we will present ab-initio results of the structural, electronic and optical properties of (1) silicon and germanium nanoparticles embedded in wide band gap materials and (2) mixed silicon-germanium nanowires. We show that theory can help in understanding the microscopic processes important for devices performances. In particular, we calculated for embedded Si and Ge nanoparticles the dependence of the absorption threshold on size and oxidation, the role of crystallinity and, in some cases, the recombination rates, and we demonstrated that in the case of mixed nanowires, those with a clear interface between Si and Ge show not only a reduced quantum confinement effect but display also a natural geometrical separation between electron and hole.

International audience; The scope of this Minireview is to provide an overview of the recent progress on carbon nanotube electrodes applied to organic thin film transistors. After an introduction on the general aspects of the charge injection processes at various electrode-semiconductor interfaces, we discuss the great potential of carbon nanotube electrodes for organic thin film transistors and the recent achievements in the field.