Sn2+ instability is the critical bottleneck preventing the widespread implementation of lead-free tin-halide perovskites. While quasi-two-dimensional (Q2D) Dion-Jacobson (DJ) structures offer the leading stability solution, the field's reliance on empirical, application-independent trial-and-error for molecular selection has hampered progress. Herein, we progress beyond these limitations, presenting a high-throughput first-principles study of a set of chemically diverse diammonium spacers to establish a predictive design framework based on fundamental molecular characteristics. We unveil the following fundamental rules: nonpolar symmetry maximizes thermodynamic stability against decomposition; moderate steric bulk stabilizes polar spacers and promotes efficient packing; short spacers uniquely minimize out-of-plane hole effective masses by reducing electronic confinement; molecular polarity lifts electronic degeneracies near the CBM; aromatic cores could enhance electronic coupling near the band edges. These universally applicable principles provide the missing foundation for engineering stable, functional 2D DJ perovskites, accelerating their deployment in next-generation optoelectronics.

In sub-Saharan Africa (SSA), motorcycles play a major role in daily mobility and access to the city, as well as in the local economy. Walking remains the most common mode of daily travel but it does not provide city-wide mobility. Given the cost of the car and the marginal role of the bicycle, the motorcycle is the main alternative to conventional public transport. It weaves its way through congested roads and provides access to remote suburbs. In that context, the number of households owning a personal motorcycle is increasing, whereas motorcycle taxi services are developing fast. The aim of this paper is twofold. First, it presents an overview of the spread of motorbikes in SSA and their usage. Second, it discusses two major public health issues linked to this boom: the increase in road accidents and the contribution to growing air pollution. Data remain scarce on motorcycle equipment and use in SSA. In order to address this lack of statistical data, we used two datasets. We gathered Development and Health Survey results to provide information on the evolution of household motorcycle ownership rates across SSA. Then we analyzed microdata from a household mobility survey (Dakar, Senegal) and from a survey of transport users (Lomé, Togo) to characterize the uses of motorcycles and the daily mobility they allow. In Lomé, motorcycles are very common, whereas in Dakar, they are more marginal. The results highlight a strong variation in motorcycle ownership rates between SSA regions and between urban and rural areas. Personal use of motorcycles is often long-standing and may be combined with commercial use. Survey analyses show that personal motorcycle users are more male, younger and wealthier than public transport users, and more male and younger but less wealthy than car users. Motorcycle taxi users are more female and less wealthy than personal motorcycle users. The environmental and public health issues raised by the rapid growth in the personal and commercial uses of motorcycles call for real improvements in the public regulation. From this perspective, the lack of data on urban mobility and its impacts limits decision-making and the implementation of appropriate policies. A major challenge is to improve administrative and survey data in SSA cities.

The concept of residential cost has gradually emerged in the context of growing interestin taking into account the interactions between residential location, housing and mobility,and thus gaining a better grasp of the social and environmental issues involved interritorial dynamics. However, the existing statistical data, built up in thematic silos,do not allow this concept to be used to see whether it provides a relevant response tothese questions. This article assesses the experiment of a ‘residential cost’ module inthe latest local travel survey carried out in the greater Grenoble region over the period2019 and 2020 (a French EMC² certified by the public institution CEREMA). Onthe one hand, it shows the capacity of such a module, integrated into a local travelsurvey, to provide a robust estimate of the residential cost of the households surveyed.Secondly, it provides initial results on the residential cost of households as a function oftheir residential location and income, showing the value of such a concept for understandingthe economic constraints faced by the most modest households. The results ofthis experiment suggest that an optional ‘residential cost’ module could be developedas a back-up to the French EMC²s, to provide a clearer picture of the impact of localpolicies on the interaction between mobility and housing. La notion de coût résidentiel a progressivement émergé dans le contexted’un intérêt croissant pour prendre en compte les interactions entrelocalisation résidentielle, logement et mobilité, et ainsi mieux saisirles enjeux sociaux et environnementaux des dynamiques territoriales.Cependant, les données statistiques existantes, construites en silos thématiques,ne permettent pas d’outiller cette notion pour voir si ellerépond de manière pertinente à ces interrogations. L’article tire un bilande l’expérimentation d’un module ‘coût résidentiel’ au sein de la dernièreEnquête Mobilité Certifiée Cerema (EMC²) réalisée sur la granderégion de Grenoble sur la période 2019 et 2020. D’une part, il montre lacapacité d’un tel module, intégré à une enquête déplacements locale, àfournir une estimation robuste du coût résidentiel des ménages enquêtés.D’autre part, il fournit de premiers résultats sur le coût résidentieldes ménages en fonction de leur localisation résidentielle et leur revenu,montrant l’intérêt d’une telle notion pour comprendre les contrainteséconomiques que connaissent les ménages les plus modestes. Les résultatsde cette expérimentation permettent ainsi d’envisager le développementd’un module optionnel ‘coût résidentiel’ adossé aux EMC²françaises et permettant de mieux éclairer les politiques territorialeslocales sur leurs conséquences en matière d’interactions entre mobilitéet logement.

Solitary dopants or single impurities embedded in semiconductor matrix having unique magnetic and optical properties are emerging as a promising platform to realize novel quantum devices. The realization of such devices however requires an atomic level control over the growth of such quantum defects to establish reproducible and scalable defect creation strategies. Among the solitary dopants, transition metal doped in semiconductor quantum dots are particularly interesting due to the ease of optical spin addressability. In this article we have investigated the challenges associated with embedding magnetic impurities, considering the case of single Mn and Cr dopants in the CdTe lattice. Optical control of single spin of such magnetic impurities trapped in a CdTe quantum dot has already been reported. We show using the first principle based calculations that the interactions with CdTe intrinsic defects poses challenges to the growth of single Cr and Mn trapped in a CdTe nanostructure. We provide a detailed thermodynamic analysis establishing that control over the growth process to embed a single Mn in CdTe, can be achieved without significant challenge but remains elusive in the case of Cr. Interestingly, some of the defect complexes resulting from the interaction of the metal dopant and intrinsic defects present the possibility to control and manipulate the spin and oxidation state of the impurity in the complex configuration. These defect complexes opens up the possibility of tuning optical and magnetic properties of single TM dopants. Finally, we propose guidelines and defect engineering strategies to mitigate or on the contrary to select the creation of such complexes.

West African cities are undergoing rapid demographic growth and spatial expansion. The satisfaction of essential needs depends on everyday mobility and the conditions under which it is performed. The majority of the population relies on walking and public transport (PT) services, whether formal or informal. Based on a study conducted in Dakar, Senegal, this paper investigates the difficulties urban dwellers encounter when using PT and how they adapt their travel behavior to overcome these difficulties and fulfill their mobility needs. A mixed method is employed, utilizing a Household Travel Survey carried out in 2015 and 38 semi-structured interviews with Dakar residents conducted in 2022–23. In a context where all PT services have major shortcomings, these deficiencies in the PT system reinforce the difficulties urban dwellers face in their daily travels. They must adjust their trips in real-time by changing mode, time or even destination, or plan their trips in advance in order to have enough money to cover travel expenses or to limit financial and temporal costs. Otherwise, they might be staying at home, which impacts their economic and social integration. Modal choice is thus not determined by the formality or informality of PT modes but by what the modes offer in terms of practical solutions access to the city. These findings emphasize the necessity of considering mobility needs of urban residents into transport public policies.

In recent decades, the impacts of the rainy season have become more intense in many cities in West Africa, due to climate change and urban growth. This paper investigates the mobility resilience of urban residents to recurrent flooding in Dakar, Senegal. Based on semi-structured interviews conducted with Dakar residents and informal public transport operators in 2021–2023, along with analyses of the 2015 Dakar household travel survey and field observations, the results show that recurrent flooding exacerbates mobility challenges for urban residents, in particular the poor and those living in the peripheries. In order to maintain access to essential goods and services, residents, along with local communities, develop mobility and infrastructural adaptations to flooding. These results lead to a discussion about mobility resilience to climate change and the necessary adaptation of daily travel, public transport services and road infrastructure.

Dakar is an emblematic case of the modernization of urban transport in West Africa. Yet, informal transport services, particularly collective taxis, continue to develop. The aim of this article is to highlight, beyond the attractiveness of the profession for unemployed men, the internal factors within the profession and the organization of collective taxis that contribute to the dynamism of the activity. Based on surveys conducted with clandestine collective taxi drivers at taxi stands, we show that drivers entering the profession perceive the activity as attractive and drivers currently in operation are generally satisfied. However, the latter agree on the strenuous nature of the activity. Challenges are numerous: fluctuating demand, risk of breakdowns, and petty corruption, making working conditions difficult. Through their spatial, social, and economic organization, taxi stands allow drivers, at least in part, to collectively cope with these challenges, ensuring the continuity of the activity and its visibility in public space.

Ce chapitre s'intéresse aux liens entre pauvreté et déplacements quotidiens. A partir des résultats d'une enquête ménage mobilité menée à Dakar, il montre que des déplacements quotidiens pénibles freinent les initiatives visant à sortir des situations de pauvreté. C’est en améliorant les conditions de marche à pied et l’accès aux transports collectifs que les politiques de mobilité peuvent prendre en compte les besoins des citadins pauvres.

In Dakar, the capital of Senegal, the urban transport policy aims to restructure and modernize the supply of public transport. The implementation of this policy since the years 2000 has led to the creation of the public bus company Dakar Dem Dikk and the replacement and reorganization of a number of minibuses owned by informal operators, which locally go under the name of Tata. However, this new supply still coexists with older, more or less informal, transport modes, mainly “Car Rapides” and “Ndiaga Ndiaye” minibuses, collective clandestine taxis, and “yellow and black” taxis. The question then arises as to the impact of the new public transport supply on the mobility practices of the city’s residents. Data from two household mobility surveys, undertaken respectively in 2000 and 2015, in the Region of Dakar is used to conduct a diachronic analysis of mobility behavior. The results highlight the extent to which changes in public transport supply have modified flows and mode use for different categories of urban residents, in a context where daily mobility is highly dependent on public transport.

Through systematic study of the passivation of the CH 3 NH 3 PbI 3 surface with different ammonium molecules, we introduce the concept of the Supramolecular Virtual Crystal (SVC) and propose a novel method to design the molecular passivation of the HOIP surface.

The interfacial interaction of 2D materials with the substrate leads to striking surface faceting affecting its electronic properties. Here, we quantitatively study the orientation-dependent facet topographies observed on the catalyst under graphene using electron backscatter diffraction and atomic force microscopy. The original flat catalyst surface transforms into two facets: a low-energy low-index surface, e.g. (111), and a vicinal (high-index) surface. The critical role of graphene strain, besides anisotropic interfacial energy, in forming the observed topographies is revealed by molecular simulations. These insights are applicable to other 2D/3D heterostructures.

We observe helical dislocation network in twisted bilayer graphene (tBLG), which is accompanied by large out-of-plane deformation. By atomistic calculations, we demonstrate two distinct out-of-plane deformation modes, breathing mode with small out-of-plane deformation and bending mode with one order larger corrugation magnitude compared to the breathing mode. The out-of-plane deformation is caused by inhomogeneous interlayer coupling resulting from the periodic stacking order of the tBLG moiré superlattice. Instead of commonly observed screw dislocation in tBLG, we demonstrate a slip-induced helical dislocation network in the bending mode tBLG. We show that bending mode deformation is more stable at low twist angles, as the energy savings due to interface energy exceeds the energy penalty due to the strain energy caused by the large out-of-plane deformation. Our work provides a detailed picture of a new helical dislocation structure in tBLG and establishes a direct connection between the dislocation and deformation. Therefore, understanding the dislocation mechanics of tBLG may open up the possibility to control the corrugation, and reveal an opportunity to tune the intriguing physical properties of twisted bilayer graphene.

Based on mixed survey data collected on the territory of the Lyon metropolitan area, this article attempts to describe and analyze the differentiations in terms of access and conditions of practice of teleworking in the context of the health crisis. Analysis resulting from the crossing of quantitative data, factor analysis and qualitative interviews allows us to present, on the one hand, the differences in access to teleworking after the strict confinement of spring 2020 and on the other hand the differentiated conditions at practice of teleworking from home. Our results highlight significant differentiations both from the point of view of access and the conditions of practice according to professional characteristics, gender and residence among working people, referring to and reinforcing some aspects of inequalities already present in society.

Dossier : Les mobilités post-Covid : un monde d'après plus écologique ?La Covid-19 a-t-elle signé le grand retour de la voiture en ville du fait des craintes de contamination dans les transports publics ?À partir d'une enquête dans la métropole lyonnaise, les auteur•es relativisent cette idée mais pointent une refonte des usages de la voiture avec le télétravail.Au début de la crise sanitaire de la Covid-19, au moment du confinement strict décrété le 17 mars 2020 en France, l'usage de la voiture comme celui des autres modes de déplacements s'est effondré (figure 1).Pourtant, les flux de voitures ont chuté moins fortement et ont connu une reprise plus rapide en sortie de confinement, surtout en comparaison des transports en commun.Ce constat interroge quant à la pérennité de la tendance à la réduction de la place de la voiture dans les mobilités du quotidien.Plus largement, quels sont les effets de la crise Covid sur l'usage de la voiture à court et plus long terme ?Le projet Covimob a pour objectif d'analyser les évolutions de mobilité et d'usage des modes de transport en lien avec les bouleversements liés à la crise sanitaire dans la métropole de Lyon 1 .Il apporte donc des réponses à cette question, notamment à travers trois types de données mobilisées dans cet article : des données de comptages routiers s'étendant de janvier 2019 à août 2023 2 , des données quantitatives issues de deux enquêtes web 3 , et une enquête qualitative réalisée à la sortie du confinement strict, entre juin et début octobre 2020 4 .Les évolutions dans l'usage de la voiture résultent de transferts modaux multiples (changements de modes de déplacements utilisés) et d'une demande de déplacements fortement affectée par la crise sanitaire et ses conséquences (figure 1). 1 Le projet Covimob a été financé par le CNRS, la métropole de Lyon, le Sytral (autorité organisatrice de la mobilité urbaine) et l'IDEX Lyon -Saint-Étienne, et mené par le LAET, en collaboration avec Transae, Arcadis et Mobil'homme.Voir en ligne : https://web.msh-lse.fr/covimob/.2 Comptages du PC routier CRITER de la métropole de Lyon : https://geo.data.gouv.fr/fr/datasets/f9325b6ac863c149c1597c7f51b6640049986e26 .3 La première a été réalisée en juin 2020 auprès d'habitants de la métropole de Lyon et du département du Rhône (2 298 individus).La seconde, de type panel, a été diffusée en avril 2021 auprès des répondant•es de la première enquête ayant accepté d'être recontacté•es (513 individus).Plusieurs modes de diffusion ont été utilisés pour la première enquête : Facebook (54 % des réponses), fils d'information du Sytral et de l'application OnlyMoov (https:// www.onlymoov.com/) et, pour les communes situées hors métropole de Lyon, mairies (ces trois canaux ayant apporté 37 % des réponses), la part restante (9 %) provenant d'autres canaux professionnels (CCI) ou associatifs.4 Parmi les enquété•es, vingt habitent dans la métropole de Lyon, neuf habitent Lyon-Villeurbanne et les onze autres dans des communes périphériques du territoire métropolitain.Les cinq autres sont domiciliés dans le département du Rhône (hors métropole). 2 Janv.

This study examines the daily mobility practices of urban residents in major African cities focusing on the case study of Dakar, Senegal. With population growth, urban sprawl, inadequate public transportation options, and limited motorized means among households, everyday travel proves to be both costly and difficult for many sub-Saharan African city residents. This article investigates the difficulties encountered by individuals in achieving their daily mobility needs and explores the adaptations they implement to meet their essential needs. To accomplish this, it draws upon a collection of 38 semi-structured interviews conducted with Dakar residents in 2022 and 2023, focusing on their daily mobility, as well as secondary analyses of a household mobility survey from 2015. It demonstrates how difficulties associated with the urban context and limitations in public transportation reinforce and exacerbate individual challenges in terms of physical strain, time loss, and financial pressure on household budgets. Urban dwellers, in response to these systemic transportation difficulties, employ various strategies as adjusting their current journeys by changing modes, routes, or destinations based on their requirements; pre-planning their trips and seeking financial or practical support; or accepting and resigning to the difficulties by internalizing them. The case of Dakar highlights the pervasive economic constraints in daily mobility and urban lifestyles in sub-Saharan Africa.

By means of a precise folding–tearing process, screw dislocations with helical cores — appearing in pairs and taking on a DNA-like double-helix structure — are engineered to control the growth of twisted bilayer graphene.

Isolated atomic planes can be assembled into a multilayer van der Waals (vdW) heterostructure in a precisely chosen sequence. These heterostructures feature moiré patterns if the constituent 2D material layers are stacked in an incommensurable way, due to a lattice mismatch or twist. This design-by-stacking has opened up the promising area of moiré engineering, a term that can be understood in two different perspectives, namely, (i) structural—engineering a moiré pattern by introducing twist, relative strain, or defects that affect the commensurability of the layers and (ii) functional—exploiting a moiré pattern to find and tune resulting physical properties of a vdW heterostructure. The latter meaning, referring to the application of a moiré pattern, is seen in the literature in the specific context of the observation of correlated electronic states and unconventional superconductivity in twisted bilayer graphene. The former meaning, referring to the design of the moiré pattern itself, is present in the literature but less commonly discussed or less understood. The underlying link between these two perspectives lies in the deformation field of the moiré superlattice. In this Perspective, we describe a path from designing a moiré pattern to employing the moiré pattern to tune physical properties of a vdW heterostructure. We also discuss the concept of moiré engineering in the context of twistronics, strain engineering, and defect engineering in vdW heterostructures. Although twistronics is always associated with moiré superlattices, strain and defect engineering are often not. Here, we demonstrate how strain and defect engineering can be understood within the context of moiré engineering. Adopting this perspective, we note that moiré engineering creates a compelling opportunity to design and develop multiscale electronic devices.

Controlling the microstructure of hybrid halide perovskite thin films is essential for optimizing their performance in optoelectronic devices. It is well established that the strain state of the perovskite layer affects its stability. Likewise, the orientation of the perovskite lattice is a determining parameter as these materials have shown pronounced anisotropies in their physical and mechanical properties. In this work, the authors focus on the understanding of the mechanisms that govern the strain and texture observed in MAPbI 3 thin films deposited on various oxide substrates. A thorough study of the evolution of the strain of the perovskite layer upon cooling down to room temperature from the crystallization temperature (100 °C) shows an essentially relaxed behavior of the perovskite layers. This result contradicts the commonly accepted hypothesis according to which MAPbI 3 layers synthesized above ambient temperature are strained due to the large mismatch in the thermal expansion coefficients of the perovskite and its substrate. The texture in MAPbI 3 layers is investigated by means of synchrotron full‐field diffraction X‐ray microscopy. This technique allows the direct observation of the [hh0] and [00l]‐oriented domains at the origin of the observed textures, demonstrating both their twin and ferroelastic nature. The stability of the different domain orientations is investigated by DFT calculations, illustrating the determining role of the chemical environment at the film‐substrate interface. PbI 2 ‐ terminated surfaces are found to favor the [hh0] orientations while for MAI‐terminated ones, both [hh0] and [00l] domains are equally stabilized. The different results constitute an important step of clarification and understanding from the perspective of controlling the microstructure of perovskite layers.